Please email Karl your questions by clicking "Contact Us". Please label your email "Karl: Question".

Some questions and answers will be posted in this section.

Page 6: Questions 169-192, click on links or browse page.
Q169 G-62 exhaust for Mustang ? Q181 12 cylinder radial torque ?
Q170 Sachs 4.2 ignition ? Q182 1/4 scale R-2800 ?
Q171 Adjusting dual carbs ? Q183 Four stroke inline for Mig 3 ?
Q172 3 blade for Enya 120 ? Q184 Power to weight ratio ?
Q173 Engine for Hangar Nine Corsair ARF ? Q185 Radial comparisons ?
Q174 Robart radial engine for glow ? Q186 Gloster Gladiator engine ?
Q175 Correct radial power for Top Flite Corsair ? Q187 Top Flite P-51 power ?
Q176 Engine for Yellow Aircraft Zero ? Q188 Velocity stack ?
Q177 Mick Reeves Spitfire engine ? Q189 P&W R2800 counterweights ?
Q178 Saito 91 flexible muffler ? Q190 Engines for a Ziroli B-25 ?
Q179 Zenoah 38 for a 1/5 Top Flight Mustang ? Q191 Engines for a Ziroli Hellcat ?
Q180 Brown Saito ? Q192 Prop drives ?

Question 169: " Hello Karl, I was hoping you could help me out with my P-51. I recently purchased a Zenoah G-62 for my Top Flite Giant scale Mustang and I am not sure which exhaust to order to ensure minimal cutting of the cowl. Also, this is my first giant scale bird and I am not quite sure why others are putting a engine extension on theirs and some are not? Perhaps you have a few tips for me to continue my project. Hopefully I am not overpowering this plane with a 62 cc engine but many others say it is a good combo. Thanks for any help you may have. Mike G."

Karl: "Hi Mike and thanks for the question(s). Most of the input you have received about this combo is correct. The G62 is a good choice. As to the engine extension, there are two approaches that I am aware of 1) the extension of the engine away from the firewall soas to get the engine closer to cooling air, and make more room for a muffler that is mounted rearward, especially if the engine is inverted. I have seen several versions where the cylinder head is slightly protruding from the lower cowling just under and aft of the spinner. This keeps the head directly in the cool air. 2) A PSRU (Propellor Speed Reduction Unit) extension on the front to lower the prop tip speed, soas not to blow up the prop and engine by over-revving the engine. This would necessitate mounting the engine directly to, or at least a shorter distance from, the firewall, as compared to the aforementioned method. As far as the exhaust goes, here also are several methods. One of the cheapest and fastest ways is to buy tight flex tubing and build an adapter from the cylinder to the pipe, and with the aide of a few fabricated brackets you can run it back to where the muffler sits, hopefully cozy behind the engine. There is also a muffler line known as Slimline, and they might be able to help you with a narrow-cowl muffler. We in this field are awaiting Saito's realization that they need to build a larger version of the 200Ti in-line shallow-vee twin, designed just for these types of aircraft. The one they have is really suited only for 1/6 scale, maybe even 1/7, but nowhere near 1/5 for power and displacement. An engine of that configuration would help legions of builders and fliers alike. 4-stroke engines are usually less troublesome, in the long-run I've found. They may take some tweaking initially, but they are less sensitive to changes in things like oil/fuel mix, temp, and attitude. All engine makers are making great strides, however. Electronic ignition is here to stay, thankfully. Hope this helps, Mike. Karl"

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Question 170: "I have the classic Glass F4F Wildcat with a sachs 4.2. I lost the key for the prop mount on the shaft. where could I get another one? Also , I need to know how to set up up theengine on ignition. I dhave never run an engine on ignition before so setting up the magnet and pick up and settiin the timing is a mystery to me. Here are a coupla pics of the prop and crank without the missing keyway. Thanks in advanceThanks in advance"

Karl: "Thanks for the questions, Tony, the F4F looks great. I believe you can find a key for that type of shaft at a shop which has parts for small gas engines such as a lawn-mower shop, lawn care equipment shop, etc. Don't go to Sears, I doubt very much they would carry anything like that. You could also try an industrial equipment supply store. Usually they have so many of these types of gadgets just for the really odd-type jobs people are doing.
As far as the ignition, it is real simple since this is a 2-stroke engine. Normally these engines which aren't used in RC, use the magnet imbedded in the flywheel to pass under the coil which is in turn mounted to the cylinder assembly in some fashion. In the case of RC, the prop provides the weight for overturning when the piston is not under the power stroke so some kind of counterweight isn't always needed. In this case, I think the Sachs engine needs the weight. In a 2-stroke there is the compression stroke, which brings the piston to TDC (Top Dead Center) then ignites. This brings the power stroke where the rotational power comes from (Torque). Yet, at this same time the piston is travelling to BDC (Bottom Dead Center) and during its travel opens the ports in the cylinder and by an occurence we call cylinder scavenging, the spent exhaust is whooshed out of the cylinder by the incoming new charge of air/fuel. Then, when the piston is headed to TDC it starts all over. That's why these engines don't have valves like we know them. Set the ignition to TDC, this likely will align with the keyway on the crank that you use for the prop hub, according to your pictures. In some engines there is a rotary valve or a reed valve that controls the air/fuel charge amount. This is important to align as well so the spark plug isn't firing in a dead hole, which is to say, a cylinder with no fuel. If you are using a computerized ignition system, then the computer will take over the timing as far as load is concerned. Otherwise, you do alot of bench-testing to find the optimum idle and power band based on where you adjust the coil. Look at the engine from the output end, where the flywheel and coil are. Locate the coil straight-up first and run it. Then loosen the coil bolts and shift it slightly clockwise keeping no more than .020" away from the flywheel. Retighten the bolts and rerun the engine. Rotating the coil this way will effectively manually advance the ignition timing. If you get it right, the engine should idle real smooth---for a 2-stroke---not smoke alot, and have a smooth transition off-idle well into the power band. Hope this helps, Tony, and welcome to our site. Hope you like it. Karl "

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Question 171: "Hi, I sent you a post a long time ago about doing a gear reduction for a fuji 80 twin. Well, after the big swap meet at Perry this weekend I ended up buying a used twin. The guy had "Sachs 4.2 Twin" listed on the engine and I bought it for $200 (not too unreasonable since it had no mufflers or ignition system ($250 from CH ignitions). Anyway, after talking to a few people, I think it has twin sachs HEADS and someone made the crankcase. There is decent compression and the crank seems straight.

Now for the quesitons....
I dont have a clue how to adjust dual carbs... (someone said to get a heat detector gun and measure the head temp while adjusting it) -I will try that, but what about for low end? Can I mount the engine with the carbs pointed down? What if the spark advance is off? How can I tell?? (the spark advance horn is a little loose and it moved slightly.) I guess I am just worried about this engine now that I bought it.
Thanks, If you need a few pics let me know and I will take them."

Karl: "Nice to hear from you, Pat, thanks. Adjusting carbs really isn't all that tough, it just takes a little time is all. Yes, you can mount the carbs inverted for updraft configuration. Perhaps the easiest way is to turn the idle (low end) screws all the way in at first to get a base line for the number of turns out. This is not 100% accurate since the screw taper, spring compression and so on may make it uneven. After turning the screws in fully, start by backing both screws out the same number of turns until you have a steady idle. Try then to transition to off-idle response through the part-throttle settings and just listen for what seems like engine miss, stalling or loading up (exhaust will be bluish-black). Adjust until it goes away. The heat sensing gun is an excellent way to measure evenness of the idle fuel settings. I believe the temp should be less than or near 200 degrees at idle with slightly more after running through different throttle positions, as though flying. The smoke tells alot about how you are doing here. If there is almost no smoke, too lean. Too much smoke, too rich. If there is consistent smoke that can be seen but appears to dissipate soon, you are on the right track. Always bench-test first whenever possible. Always making sure you are clear of the spinning prop, while the engine is running, make the finer adjustments and check with the temp gun. The change you make in the screws won't affect the temp right away, so be patient. Adjust, wait for maybe a minute then check again. Too lean and you will burn a hole in the piston or sieze it all together. That's bad. Too rich and you foul the plugs and it will still quit on you. The 2-strokers are real picky about fuel settings. With regards to the spark advance, set it at straight up (zero degrees advance) first and see how the horn fairs. If it stays tight, that is good. If not, then you have to remedy that right away since the performance of everything else depends on that. Make it tight. If you have a operation manual for the engine, refer to that about making the timing adjustments. Some allow none since capacitors usually take up the duties of timed charge release so it's like a "set-it-and-forget-it" deal. Still, some do allow adjustment soas to maximize the engine's power. Hope you find this helpful, Pat. Happy flying. Karl"

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Question 172: "I want to put a three blade prop on my enya 120 I do not need extra power I have it abundance, What I need is ground clearance What 3 blade would work best on the enya 120, Do I have to adjust my carb when I change the prop Does this effect the idle will it be faster-slower Thanks Lawrence "

Karl: "Hi Lawrence. Master Airscrew I think has a prop that will work great. The last time I looked at their stuff they had up to 13" diameter props in their small prop line, and up to 16" in the large line of 3-blades. They look great, too. I would recommend these for smaller-scale birds. Ground clearance of course, relies much on the type of plane, landing gear and so on so without knowing any of that, I cannot really address that issue here and do it justice. Keep in mind that the more pitch you have in the prop, the more bite it will have in the air, which does equate to load on the engine so you might have to do a little tweaking of the carb. Bench-test first. If you have a real aggressive prop pitch of, say 14 or more, you likely will have to make adjustments. Use your best judgement as to what to do, or how much to adjust. Hope this helps, Lawrence. Karl"

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Question 173: "Karl, I'm workng on a 60 size Hangar 9 Corsiar ARF. I'm just about finished with it and am debating on what kind of engine/muffler set up to put in it. Cost is a big concern, but I want to go 4 stroke (I know you like the $aito). I've never had a 4 stroke, but have been reading up on them. Right now, I'm thinking about going with the Thunder Tiger 91FS. What is your opinion of this engine and what other engines do you think I should consider? Thanks, Tommy- Eglin AFB, FL"

Karl: "Thanks for the question, Tommy but please allow me to first thank you and your commrades for serving this most blessed and sovereign country in our U.S. Military. I come from a family of which at least one of us went into the service and let me tell you, there is no greater cause for this country than to be one of the chosen to protect it. It takes special people to be there for us in that capacity. For the record, most of us here in the US DO appreciate what our military does here and abroad. Don't listen at all to the mainstream press, they are so off base you can't even believe it. Thank you. Onward.
Of course I like the Saito line, especially the radials. They have a 3-cylinder 1.7 cid unit that would work real well here for you. Of course they also have some of the best big-bore singles around so you have alot to choose from in this particular line. Here's what I have to say about the Thunder Tigers. Some I have talked to say the carb's can be somewhat finicky about adjustments, which is to say that you have to revisit your adjustments alot to maintain them. Some say the engine is at least as good as any O.S. or similar plant. Only a few really don't use it because they don't like the way it looks. Big deal. It ain't what's on the outside that matters anyway, right? I would say the Thunder Tiger is an ok choice, but if it were me, I would look at reliability as a first. At the risk of overstating the obvious, if you have engine trouble in flight, well, bad things happen. Go for a proven and reliable engine regardless of whether you have a few hundred dollars invested or a few thousand. The muffler that the engine comes with is, theoretically, the best choice for the plane/engine. Do some asking around once you get it flightworthy and do some tweaking to maximize the performance. Hope this helps you. Karl"

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Question 174: "Hi Karl, What a great web site you have. My question is why does Robert offer their radial engine in glow fuel while some of the other radials use gas/oil mix? Does one have a advantage over the other or what. Thank You, Wayne in Spain"

Karl: "Thanks, Wayne in Spain. How's the rain? Hahaha, just a feeble attempt at humor there, buddy, nothing personal. I was hinting at the 60's movie "My Fair Lady". Nevermind. Onwards. Recently I asked Bob over at Robart the same question, why don't you build the 780 as a gasser, and he said to retool the process to accomodate gear drives for magnetos, fuel pump, oil system, etc., was prohibitively expensive. Given the present cost of arguably the hobby's best radial engine, I took that as a good thing. He's thinking of us little guys, I like to think. Besides, they have lots of research to support their decision to stay with the glow engine.

As far as comparing to some of the other offerings on fuel type, here's what I can tell you so I hope this helps. Gas is cleaner to the airframe than glow fuel. Glow fuel leaves an oily and somewhat corrosive residue that plagues certain finishes. It is difficult to remove from your plane's finish sometimes due to this. Most glow engines use the lubricant in the fuel to lube the bottom end while the engine's running, so it serves a dual purpose. To my knowledge there are no 2-stroke gasser radials widely offered and these 2-strokers use a gas/oil mix much the same as glow fuel. They work differently with different metal components internally in the engine. Now, of the 4-stroke gasser radials out there, and there are a few, to my knowledge, they utilize a dry-sump oiling system which is separate from the fuel system for the one reason, that you can't mix them and dillute the oil, thus killing the oil's protective intent to the inside of the engine. Those engines are designed to run on the fuel alone, not a mix. Taking RC Showcase's 215cc radial, for example, and mixing the gas and oil will spell certain death for that baby.

The real difference is cost. Gas units usually need some kind of ignition system since the compression alone will not light the mix---that would be a diesel then. Ignition systems cost more to build in to the engine. So, by designing a glow engine, there is no need for a dedicated ignition system other than glow plugs for starting cold then letting the compression heat keep it running. To me, it is a wash since you get a better, cleaner running engine with gas, but more cost. With glow, you have a lower cost intially, but lots of fuel-related mess to clean after flying. Hope this helps you, pal, and it's good to hear from our friends in Spain now and again, thank you! Karl"

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Question 175: "Hi Karl, I have read several post regarding the radials, but I don't feel comfortable with the answers. I'm not getting a definitive "yes" this will work for this aircraft. It is still unbuilt/in the box and the estimated weight from the manufacturer when completed with electronics will be 20-26 lbs. However, I suspect it may hit 30 with the working cowl flaps and functional gear doors. The Cowl diamter is 10 inches. First off, these are my choices for radial engines. The SAITO FA-325R5D the O.S. FR5-300 5 CYLINDER SIRIUS and the TECHNOPOWER 9 Cylinder "C" Naturally I'd like to go with one of the fist two choices I've noted because of cost. www.top-flite.com suggest the SuperTigre G4500 or the U.S. Engines 41cc. At first glance either one of these engines should have plenty of power to pull this aircraft nicely. However, in the Tech-Notes for the Giant Scale Corsair it has a link
http://www.gpmd.com/cgi-bin/wgpinf100p?&I=TOPA0410, which specifically reads in the engine section ("do not recommend 5 cyl radial") without explanation. Care to give me your evaluation on the subject. Also, the instructions for this aircraft informs me to only use the gear doors for static purposes. What gives? Any thoughts... I want to do this aircraft right in scale and have all the bells and whistles. The Technopower 9 cylinder C is about as high as I would like to go. Thanks in advance for your help, Michael"

Karl: "Excellent questions, Michael. I see you have been doing your homework, as I had to do a few years ago when I first began doing research for my project, a 1/5 scale F4U. There is alot to this answer, but I'll try to hit the highlights. 1) The OS radial is the most powerful of the 5-cylinder glow offerings at 4.0 hp. The Saito is only slightly less----splittin' hairs, really. I love the look and the idea of putting a 9-cylinder radial (one half of the P & W R2800!!! ) in the front of a Corsair model, but according to Marc Linville at TechnoPower, the 9 doesn't have enough power for a 25-plus pound model. In my research, Michael, I went all over and found that there are some great gassers out there but are too big for the cowl and I would have to cut---very bad for scale appearance. Too small of engines won't allow safe and good flying. Solo Props actually has a very good answer to lower-powered engines with a ground-adjustable-pitch (GAP) prop, but the pitch needed to compensate for lack of power, may actually work backwards since then the pitch likely would be too aggressive for the torque capabilities. One engine you didn't mention is the Saito FR 450 3-cylinder radial. It is less than the TechnoPower unit, I believe, and has more than 4 hp. This one, coupled with a Solo Prop, may get the best scale performance of all of them. The last engine to consider is the Robart R780----got 4-grand? That is the perfect one, believe it or not. But it is pricey. Regardless, the Robart one is proven, they regularly modify design for best cost/reliability. I believe that airplane mfr's spec a 2-stroke glow or gas for cost, abundance, yet ignore the builder's desire to successfully compete on "the circuit" of airshows and collect points. Radials which are correctly matched to the airframe, along with the prop, gain big points, Michael.

2) As far as why Top Flite does not recommend a 5-cylinder radial I believe has to do with a pilots' skills of even the limits of the airframe itself. The full-sized planes had a nasty torque roll on take off that required full right rudder to keep from crashing. These larger scale ones, with radial power, do the same thing. It takes lots of concentration to get 'er airborne safely. If you are a novice or have taken a long hiatus from the sport and are getting back to it with new technology, you may be lacking. I apologize if you are not a novice, Michael. I am also answering this soas to possibly help others who might be, so don't take it personal, thanks.

3) Gear doors are a must if you are building scale. Why in the world would someone say to install gear doors for static, when you are also scored on scale flight? The gear doors are a big part of the scale flight score since many planes with "sequenced" gear doors have to have them operate correctly if you want to garner as many points as possible. That's a wierd one to me, too.

Anyway, I hope this helps you decide, Michael. The F4U is my personal favorite warbird. I also personally think it was a better plane than most fighter/attack/bomber-role planes. It's hard to argue with a P-51, really, but one bullet in the right spot will kill a P-51 or any other liquid-cooled plane. These air-cooled radials could really take a beating in combat. I'd rather get back to base with a gimpy plane than not at all. Keep us posted on your choice and progress. Karl"

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Question 176: " Attention Karl or engine expert. I have a yellow aircraft zero, and I want a gas engine in it. Will a Zenoah G-45 work without cutting up the cowl? I want a gas engine, reliable, with the right power ( not overpowered) that will fit in the cowl without modification other than maybe a muffler exit. I do not like how some engines carbs and full mufflers stick out of a beautiful scale airplane. Thanks for your time. -Danny"

Karl: "Thanks for the question, Danny. Here's what some friends say, as well as some other pointers you might be willing to look at. First, with a wingspan of 80" I think your cowl will fit the G45 nicely. However, let's look at the engine recommendations. It appears to me that they don't recommend an engine much larger than around 2.2 cid. the G45 is more. Yes, it should fit, but you were also concerned with overpowering the bird. Evolution has some great gas engines that should work well--the 35GT for example. A G38 will also be great for fit and power. Think with me outside the box for a moment, will you? Consider the Saito FA 200Ti, it comes in at 3 hp, has a shallow-vee design with compact carb and exhaust outlets. I only mention this one because it will work for sure without cutting the cowl. I know it's not a gasser, but you have several parameters to meet here, and trying to get the proverbial cake and eat it too is, well, difficult to say the least. Based on advise, experience and knowledge, if you are hard-set on a gasser, then go with the G38 for size and power. Then go visit www.soloprops.com and see their selection of ground-adjustable-pitch props to match it. You likely will never have to buy another prop. If you are willing to consider non-gassers then look at Saito and OS for radials. Cool stuff there as well. Hope this helps you make a decision. That's what we're here for. Karl"

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Question 177: "Karl,im building a Mick Reeves spitfire(1/4scale)was thinking of installing a 5.8 brison single cylinder power plant,my question is since its a large single cylinder 95cc engine,will i have bad vibration problems?also how does this engine run in your opionion?Have you seen other warbirds with this engine?"

Karl: "Thanks for the question, Mike. Since I rarely get the opportunity to pitch this engine, I will do so inspite of what seems obvious to me. All of the major British fighters, the Hurricane, Spit, Fury had water cooled v-12's. Go to this site: www.quarterscalemerlin.com and see the 1/4 scale beauty they have. Just to whet the appetite, it is water cooled and can have a supercharger installed--right from the scale drawings. You simply have to see it to believe it.

As for the Brison, 'tis true many modelers use it, but IN MY OPINION, one that large would likely be a vibration nightmare in that size. You can opt for an opposed twin by 3W or DA, these will make for smoother operation simply because of the design. The Brisons do run well, make no mistake, but let me share an observation here. I am seeing an increase in the people who want to build more true-to-scale, which includes many more details in flight controls, demarcation, what have you. This translates into sharper attention to details such as better airframe integrity, better control of vibrations, etc. and bottom line is, this means a greater investment monetarily. Build your plane so you can have fun, period. Are you going to compete with it? If so, that raises the bar for durability and accuracy at least. Do you want to have dozens or hundreds of flights on an airframe and years of enjoyment? Most of us do, so design and build it accordingly, and yes, this can mean different things to different people in this sport. Chances are if you skimp in one area, it will bite you later. Look at that Merlin project for fun or....., and look into the ones offered by 3W, Desert Aircraft, ZDZ, Quadra, to name a few. You have a lot of choices between price range you want, type of engine, etc. Hope this help you. Karl"

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Question 178: "I am mounting a Saito FA91S in a Folk Wulfe cowl and the stock muffler is not my choice. I purchased a flexible muffler from an RC supply store but, even with call them, it is the wrong size. Does one of the Saito flexible mufflers fit the FA91S? My conclusion at that point is that the flexible mufflers were designed for multi-cylinder engines. Ron in Houston"

Karl: "Good question, Ron, thank you. To my understanding, Saito does in fact have flexible tubing for their engines, albeit for the radials, but I think since the exhaust outlets are similar and should be able to be adapted to the 91. Just keep working on it, usually a solution presents itself in due time. Hope this helps. Karl"

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Question 179: " Hi Karl I am in the process of building the Top Flite Giant 1/5 P51 Mustang. I have a Zenoah 38 which I plan to use in this model. Will this engine have the power to fly scale manoeuvres. The model will probably weigh in at around 20lbs. Thank you for your advise Glenn"

Karl: "Thank you for the question, Glenn. I think the G-38 will suit you well here. It has a little over 3 hp with their tuned pipe, and can swing up to a 22"
diameter prop. Next, check out this outfit: www.warbirdpropdrives.com as they have some sweet goodies you may well find useful on your project in the
way of a prop reduction drive to save rpm and improve performance, to a constant-speed prop for the 1/5 scale P51. Good luck with the build. Karl "

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Question 180: "Karl, I have a Saito 120 that I bought new about 10 years ago. It still runs great however it has a buildup of bownish something around the exterior of the head. It looks like a burnt film that might have been created by excessive heat. Is there something I can use to clean that off with?

Also, that engine has always needed the needle valve to be open much more than any of my other engines. Right now I have it open 4 1/2 turns for the best running. It that odd to have the needle open so far? Thanks, Chris"

Karl: "Hello, Chris and thanks for the questions. First, about the Saito. If the engine had not been run very long before it was boxed ten years ago, then it likely would not have gotten very hot. One possible reason for the discoloration is from what machinists and engine guys call Cosmoline. Cosmoline is a heavy preservative that is sprayed onto newly machined parts be them cast iron, aluminum, titanium or whatever. Usually these metals will corrode when exposed for some length to the atmosphere. Another word is Oxidize. Since the atmosphere is impure, usually these cooties will wreak havoc on metal surfaces if left unabated. Over time the cosmoline will yellow and discolor and leave a real ugly finish. It smells bad too when it is burned off. It cleans off with a petroluem-based solvent such as a brake cleaner, cleaning solvent, etc. Do what you can to remove the worst of it, then when the engine is running, the residue that is left will burn off. If that does not get rid of it, then try using a brass or steel wire brush around the head areas that are affected---the small variety used when cleaning brake parts or other smallish kinds of things. They look like a crude, wood-handled tooth-brush. There are also more "ergonomic" versions with formed plastic handles.

The second issue may actually have alot to do with the length of time this engine sat boxed. Since fuel and oil is petroleum, when certain elements of the fuel evaporate, it leaves behind heavier ones that feel sticky or gummy. This we call "varnish" Now, from what I have ever read and learned from observation with these, 4 1/2 turns does seem extreme so let's try this. You will likely have to have a gasket and seal kit to install once you disassemble the unit, so don't do it until you have the kit. My opinion here is to disassemble the engine and carb, clean every part carefully and inspect. If no abnormal wear is present, then reassemble the unit installing the new kit parts. Having to back the needle valve off so much usually indicates improper metering of fuel and/or air elsewhere in the engine. This translates into what we call a "vacuum leak" or "fuel bypass" . One allows too much air to enter, the other fuel, resulting in the conditions you describe. According to my information, turning the screw out 1 1/2 to 3 turns is usually enough. Remember this thing---whether it is a gas engine or a glow fuel engine, it is still an internal combustion unit and most of the principles apply whether you are working on a ship engine or an RC engine. I really hate to use the cliche, but in these cases, size doesn't matter---just stick with the basics. Hope this helps, Chris. Karl "

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Question 181: "hi there Karl, i am trying to find some information on radial engines, precisely how much Torque the produce. i am interested in a 12 cylinder engine, but would be happy with any torque info you can give me. i've read that radial engines rev at very low speeds, is there any way that the engine speeds can be increased. many thanks for your help Michael"

Karl: "Thanks for the question, Michael, I like the radial questions. I am sad to have to tell you that no 12-cylinder radials have ever been produced, either in full-scale or RC form. The simple reason is that due to the physics of things like torque, firing order, etc, what has to happen is that the cylinder firing must be out of phase (which, in this explanation, will mean, NOT 180 degrees across from the next firing cylinder) in order to produce rotation, torque, etc. The closest you will get is a 9 cylinder radial in both full scale and RC. All radials have to have an odd number of cylinders in order to operate period. The only even-numbered cylinder count of radials would be 18 and 28, but these were multi-row engines.

That said, the engines in RC that you can obtain in radials are from Saito, O.S. Engines, TechnoPower, RCS, Robart, and I believe even 3W or Desert Aircraft has another 5-cylinder gas radial that is nothing short of awesome.

To answer the torque question is a little more difficult since after all the information and research I have done over the last 3 years, I have never found torque spec' for any of these. It doesn't mean that the builders don't have the information, it just means they haven't deemed that spec important enough to publish with the rest of the engine spec's. The amount of applied torque is always affected by the weight of the plane and the prop size you select. As a general rule, gas radials make much better torque at a lower rpm than the glow engine radials. There are certain limits to everything, of course, so even though the glow engines can handle higher rpm's doesn't necessarily mean they are what you want. If you are building a large-scale plane and using a radial, look at the gas versions, then the glow versions. I have mentioned before in one of these other posts that you can approach your build starting with scale first, or engine and build the plane around it, or simply a certain type of plane, how much scale reproduction you want, you can use pretty much any criteria you want to start with. Be prepared to be flexible!! I had to go through 2 or 3 different engine choices for my project before I found one that would work like I wanted to. Hope this helps you, sorry I couldn't just spit out the spec's for you, Michael. Happy flying. Karl"

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Question 182: "Hi Karl; WOW! A true 1/4 scale R2800 you say? Any way I could see a picture of one of these engines? Also would like to see a true R985 in 1/4 scale if there is such an animal. Thanks for any help. Bill"

Karl: "Hi Bill, Yes, it is a true 1/4 scale beauty. I have personally seen one of these, as well as several in various stages of production. I have seen the shop and it is clean and professional. You can visit the company's site this way www.Napco-ltd.com and it will have links to show some cool pictures, as well as the company's mission/goal statements, etc. The owner is Paul Knapp and the engine is his pet project. Ask him if he would send you some pic's electronically.
As for the smaller radial, I don't know anywhere you can get a model version. It is true that these smaller engines, including but not limited to the Jacobs engine, were used in smaller planes like trainers, barnstormers, mail planes, other types of aerial transport. I just heard about a guy in Kansas that took 9 Saito 120 cylinders and designed and built a crankcase for them, and built his own 9-cylinder 4-stroke glow fuel radial engine with twin carbs. Way cool! I love America, the things you can do here!!! Anyway, hope you can have your curiosity satisfied, Bill. Happy flying. Karl"

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Question 183: "hi karl i`m from austria and my english isn`t so well so i´ll try i`m looking for a 4-stroke inline twin motor like saito 100 ti inline V-motor for a mig-3 1:4 scale but 18ccm(europe) are not enough so maybe you can help me find a motor. best regards herbi"

Karl: "Guten Tag, Herrprofessordoktor Doppler, Wie Geht's?
Wilkomen aus Amerika!

To my knowledge, the Saito 200 ti may be what you are looking for. It basically is the same as the 100 ti but twice as big. The web page that has this information on Saito engines doesn't go into much detail about what size plane it will fly. The only hint is a 1.20-sized airplane. It doesn't even say what the power rating is. Since this is important information, you would think that they would include it. I haven't seen the MiG kit you are building, so I have to admit that it is hard to do better at matching the engine and plane together. I am a big believer in matching as close to possible. If you need a larger engine, you will likely have to use something from Zenoah, ZDZ, Quadra, or some others. Even with all the phenomenal advances in RC technology, we still have limitations, pal. So, there are some cases where we just can't have all that we want in this sport. Hope this helps and good luck with the build. Tchuss! Karl"

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Question 184: "Hello Karl,I would like you clarified to the importance of the relation between the weight and the power. The truth is that I do not understand anything, how is possible that TechnoPower Engine 9c weighs 22 lbs and only of 2,5 HP? for example, the saito FA-325R5D weighs 5.3 lbs and gives 4Hp. In an aero-engine I believe that the relation is fundamental weight/power, but do not know if there is to consider some factor more. Thank you. Best regards, Enrique "

Karl: "Como estas, Enrique? Thank you for the question. I will do my best to answer this, and some of my background will be evident so bear with me, please. Power-to-weight ratios ( PTW's)are very important when ever the engineering for a self-propelled vehicle is necessary. Let me try to illustrate one part of this in hopes you will get the idea, and I will address the specific engine issue after that. If you have a vehicle that weighs 2,000 lbs, an engine that weighs 500 lbs and makes 90 horsepower, this vehicle is severely underpowered at over 27 lbs per horsepower ( that's a ratio of 27.7:1). It will take all the engine rpm's it can make to get the vehicle going, let alone sustain steady speed or even climb a hill. Trying to get a 2,500 lb car moving with less than 100 hp is time-consuming. To get the engine rpm up into the power band, we call it, where the theoretically best power production is, uses up any remaining rpm needed for any driving maneuvers. In Nascar racing, all the cars weigh 3,200 lbs and have 800 horsepower engines, so the PTW is much more desireable at 4:1, which is 4 lbs per horsepower. This close of a ratio means that it makes lots of power and doesn't need all of it to get moving or do what it was designed to do. Now, when it comes to RC airplanes, things don't change much, we still want a low PTW. You try to build the airplane light since you want it to fly well, and we don't have the luxury of being able to bolt on any high-horsepower engine we want. The more power you need, the bigger the engine will be. The bigger the engine, the heavier it makes the overall plane package you follow me so far? Now, when it comes to the TechnoPower radial, it actually weighs 4.5 lbs. I was looking at TechnoPower's website and they don't show the power spec's but if 2.5 hp is true, then they have a 1.8:1 power The 9-cylinder
"C" class only displaces 4.0 c.i.d. Finally, in RC, PTW is ultimately important because of balance and Center-of-Gravity (CG). These are not dragsters we are building, where we can have a very low vehicle weight and very high engine power numbers. For airplanes to operate well, they have to be balanced. During the building process is when you check and recheck the balance so you can make changes as you build. Once finished, if the plane still isn't level but it's close, then you adjust trim when you set up the first flight. Enrique, I hope this helps you understand power-to-weight ratios and their importance in RC. If you still need clarification, please let me know and I'll be glad to help. Adios, Amigo. Karl"

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Question 185: "Karl; Is there any good website(or as substitute, book or magazine article) that will show pictures and give specs, as well as prices, on all the currently available Model Radials? Thanks again, Bill"

Karl: "Thanks again for the radial questions, Bill. In the July 2003 issue of Model Airplane News magazine, on page 74 there is just such an article about radials. Gassers and glow engines are covered. Information, pictures, I found them rather helpful myself. Go to www.modelairplanenews.com and search archives of past issues for that article by Gerry Yarrish. Hope this helps, pal. Karl"

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Question 186: "Hi Karl, I plan to build a 25% Gloster Gladiator and want a smooth running twin cylinder gas engine to fit inside the 11.125 inch radial cowling. After searching the internet and all things considered,(dollars,type of plane, flying style etc.) I have decided on the Zenoah GT-80. But I am unable to determine if this engine will fit center of the cowling without hiting the spark plugs with the caps on. My question is "will this engine fit and if not what engine would you recomend for this warbird. Thank you for your help. dan. PS. love your website."

Karl: "Hi Dan, I can't say that I am familiar with the Gloster Gladiator, but 1/4 scale radials are in, for sure. First let me suggest tilting the twin slightly in the cowling, in the hopes that it is not perfectly concentric and will have enough room elsewhere on its circumference to accomodate the plugs. The carb does not have to be level, flat, vertical or whatever to work properly. When you install the engine/carb setup, then fly the bird, it will go through all possible angles and attitudes. Second, look at the Saito FR450 R3 radial. This is a glow engine, but is their largest and would even fit the cowl. Again, in the hopes that the cowl measurements are off, and maybe this manufacturer's numbers as well, only slightly, look at the RCS 215 cc radial. This one is gas, has 13 hp, electronic ignition, you name it. The Saito one is 3 cylinders and the RCS one is 5. Cool stuff. Take a look at those and let us know what you think.

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Question 187: "Hi. I am building the 1/5 top flite P-51 and was wondering about engine size. I have a US 41 and a zdz 40 laying around and was planning on using one of them, preferably the zdz. I have heard reports of the us 41 be marginal power for this plane. Do you think the zdz would have more performance or am I waisting my time? Any info would be greatly appreciated as I don't have much experience with gasoline engines. Also what prop sizes would you recommend for the zdz 40? Thank you very much! Daniel"

Karl: "Hi Dan, You might look into the G-45 or ZDZ equivalent for power. There are so many cool things for these planes now--we have inline twins up to 100 cc, I know about a fully-functional constant-speed prop with P-51 blades that is now being developed and is close to going on the market. There is even belt-driven gear reductions for high-rpm engines in narrow cowled planes like any British unit, and certain Allied units such as the P-51. Perhaps the best thing of all is, these things are not just items to make your plane look good and garner more points at shows, but they actually are functional and allow you to really maximize the engine/airframe combination for speed, scale flight and reliability. Here are some sites you could visit just for kicks and giggles: www.soloprops.com and www.warbirdpropdrives.com Both of these places have done really great things for our sport. Hope this helps. Karl"

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Question 188: "G'day Karl, I have made my own velocity stack for my DA100, at the moment mine is square on the end while the baught items all have a bevel cut on the ends, is this important or just cosmetic? If it needs to be cut at an angle should it face to the front or to the back of the aircraft. I would also like it to stick just outside of the engine cowl, will the air rushing past it cause a vacuum inside the stack and actually decrease performance instead of enhancing it? Your ideas will be greatly appreciated. Regards, Wazza"

Karl: "G'day, Pimjunta, from the USA. The velocity stack is a cool idea. Keep in mind, though, that any assistence you give to the air entering the engine has to be met with sufficient fuel to maintain the stoichiometry of the air/fuel. What that means is, if you add air, it leans out the mixture and can cause--well, you know. So adding the fuel to keep it running well is paramount, sir. So when you add the stack, make sure you tweak the fuel metering system in order to keep catastrophy at bay. As far as the location of the stack, it is true that if you have a flat top, reaching just the outer surface of the cowl, you will have a siphon-type result which will suck air out, and it'll fail once you get enough airspeed over the stack. If possible, it is my opinion that you should aim the intake of the stack to the front, slightly protruding from the cowl so it will get air, but not function like a ram-air and fuel-starve the engine.
Hope this helps. Good question. Karl"

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Question 189: "Hi Karl, My name is George and I am dealing with P&W R2800 engines at Hellenic Aerospace Industry (HAI) in Greece. During overhaul of R2800 engines we have to weigh both forward and rear counterweights (without bolts and nuts) before installing them on engine. We have found lots of counterweights with a weight 0,3 - 0,4 lb less than the minimum required (22,75 lb is the minimum for the forward and 19,20 lb for the rear counterweight). My question is: Can we use them as they are? What would be the effect of a lighter counterweight in the torque or generally speaking in the performance of the engine? Thank you very much in advance."

Karl: "George, thank you not only for the question but also for your patience whilst I did some research. Based on what I found, here is what I can tell you, and I will refer you to some people at perhaps the best radial engine builder in the continental U.S. First, the lighter weights would not pose an overwhelming problem. We are only talking less than a pound between the two. Two scenarios present themselves here. ONE, it is likely you have an engine that has had the counterweights machined true from an earlier overhaul or TWO is that the engine in question was prepped as a racer by lightening the counterweights much the same way a hotrodder lightens the flywheel or uses a lighter one. The lighter counterweights result in higher rpm's or at least faster throttle response. Now, in your situtation, you obviously need to balance the whole assembly, that is a given. In theory anyway, the net result would be a loss of torque because of less weight means less mass, which translates into less inertia, although in my opinion this loss would be negligible. George, thanks again for being so patient and I hope I answered your question. Keep me posted on this progress. Thanks, Karl"

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Question 190: "i karl wat kind of engine should i use for a 118" b-25 from ziroli i estimate it would be around 35 - 45 pounds when the warbirds is completly finish and i to get the b-25 off the ground in about 60 feet ,billy "

Karl: "Hi Billy, since I am a round-engine guy I'll tell you some choices in radials first. You have Saito's FR 450R3, their largest glow radial; then you have Robart with their splendid work in the R780 glow radial; for much less money you can choose from either TechnoPower's 9-cyilnder glow radials or RC Showcase's R215 5 cylinder gas radial. If you want real scale points, with totally unique sound and appearance, these will fill the bill. On the lighter money side we have a variety of gas one-lungers from ZDZ, Quadra, Zenoah, Cactus Aviation. You will likely need something in the G-62 range, possibly more due to weight, being a multi-engine plane, and not worry about using up all the engine's rpm's just to fly. Solo Props has scale flying ground-adjustable-pitch props to choose from, and Warbird Propdrives has belt-driven gear reduction drives as well as functional constant-speed props they are nearly through developing. I like the general rule that if the manufacturer of an airframe recommends an engine specifically or an engine range, go to just slightly more than the range, not to spite the manufacturer, but to be on the safe side to ensure you have the power on hand to be fun, reliable and safe. Hope this helps, feel free to reply again if anything is unclear or you just want to update us. Thanks, Karl. "

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Question 191: "Karl I am starting a Ziroli Hellcat soon and would like your opinion on type and size of engine. Ziroli recommends a 3.7 to 5.8 C.I. engine. I have a ZDZ80 single now and was considering it but the Zenoah GT80 twin looks good (it would be a smoother running engine) but seems down on horse power is there anything one can do to increase the power of the GT80, or is there any other engines that would do the job. Thanks Tom"

Karl: "Thanks, Tom. There are several engines to choose from in RC for the various kits. They range in price from 2-stroke gassers that meet the kit-makers' recommendations, to authentic, fully functional gas and glow radial engines. The Ziroli Hellcat is an awesome bird Tom, I have been to a local airfield in my town and seen several. In my opinion, you should consider radial power. There is much less vibration, they look and sound way more cool, and with the options now on the market for propellors and prop drive systems, we no longer have the excuses we used to for a lack of performance or poor appearance (..read, "non-scale"...). In my humble opinion, the best engine for a 95" w/s warbird is the Robart radial. It is 7.8 cid, has ten hp, will fit the above-mentioned props and drive systems, is reliable as all heck and the best part is you won't wear out the engine because it won't be working that hard to fly the plane. Lower work load means lower rpm, less fuel, etc. You get the picture. Thanks for the question I hope I helped you. Karl"

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Question 192: "Hi Karl, why is it that very few people use a prop drive on their models? These systems are available, I was just reading about one on www.warbirdpropdrives.com with the DA- 50 Eng and www.soloprop.com these are new, then there is the Byro Reduction Drive with Q-42 Eng,this may be old, but I see so many bombers and fighters in rcwarbirds.com with tooth pick props. Is using direct drive better than using a realistic looking prop with a reduction system? There is Jeff at the bottom picture of fighters with a mustang name Sizzlin Liz claimed to have tried two different reduction systems, they both probably sucked and he had to go back to direct drive.Is it the cost, extra weight or they just don't know?the prop drive is $300 the controlable pitch prop is $390 the blade itself is $100 and the prop hub you adjust on the ground is $ 110.Could you tell me if these products are so great, why are so few people using them,thank you. "

Karl: "Thanks, Carl. Man, if I had the answers to those questions, I would have written a book and been able to retire years ago! hahaha!
I don't even know where to start here. I have been dialoging with the folks at Solo Props and Warbird Propdrives for a year now, trying to stay abreast of their latest developments and offerings because I have asked them if I could then tell all the folks who write in to me and ask, if I can tell them something as long as it doesn't divulge secrets or simply wrong information. My quest started when so many people told me that you can't have a scale-sized flying prop on a warbird (1/6 scale or larger...) due to physics limitations of the prop at certain rpm's. The two company's you mentioned have all but beat that myth by not only designing, but also producing functional, adjustable scale flying props that are true to the scale appearance, even. The systems are relatively affordable for sure, I totally agree with you. Toothpick props look, well, stupid to me. I'm sure those who still use them have reasons so just for the record, I am not passing judgement on anyone who swears by them, I'm just stating what I think. I think that "back in the day" the Byron part was useful. I have seen ads from the '80's when they were sold and it is difficult to tell why they weren't more popular. It could simply be folks were afraid because it was new and different and misunderstood.

I don't have the proverbial crystal ball so I can't really know why more people aren't on the bandwagon for these latest offerings, Carl. This much I CAN say with all certainty that the people at both SoloProps and Warbird Propdrives have safety as their utmost concern. No one wants a constant speed hub to come apart at 5,000 rpm, or prop blades to come out during a low, high speed flyby where spectators can easily be skewered with one. So, they aren't going to market them heavily until the AMA and all other appropriate governing bodies for this sport.hobby are satisfied that no failures will occur due to manufacturing or design defect.

There is also the rule issue. Some airfields have rules limiting the prop diameter, but more for sure is the fact that no one really knows yet what kind of rules we should have regarding multi-piece props. I think there used to be rules against them, but with high-tech design programs, machinery, higher technical skills and computer-controlled machine operations, I think it is time to allow multi-piece props across the board. According to the powers-that-be at Warbird Propdrives, they haven't had a single prop failure due to poor quality of any phase or component. If they had a failure, it was likely to push the envelope of the system ( like what some will do once they buy these goods...) to ensure its absolute safety.

Carl, if you believe in these products as I do, get to know the people who run the operations---at least via e-mails---and you will find that at the heart of all of this is the good-ol' entrepreneurial spirit that has driven these United States for centuries. They saw a need, came up with an idea and filled it. And filled it well they have, between these two companies. Once you know something about what makes them tick, buy one or both of the systems and try them. Nothing is more effective than word-of-mouth adveritising so if you like the product, it works well for you, then tell people about it fast. Don't rush them, though, we want them to have the best product out there they can. It affects all of us.

Hope this answers your questions, Carl. Thanks for visiting our site. Let us know if you have seen one of these systems in operation and send me a note, okay? Thanks, Karl"

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