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 8: Questions 217-239, click on links or browse page.
Q217 Liquid cooled inline ? Q229 Overheating 4 cycle ?
Q218 Large props for large electric P-38 ? Q230 Radial engine for Ziroli AT 6 ?
Q219 Geared OS .61 ? Q231 Crankshaft straightened ?
Q220 3 blade props for RCV 90 ? Q232 Belt drive ?
Q221 Super Tigre 90 in cowl muffler ? Q233 4 blade for 60 powered Mustang ?
Q222 4 stroke engine noise ? Q234 3 blade prop for OS 46 ?
Q223 Saito 220 mount ? Q235 3 blade prop for Saito 150 on P-40 ?
Q224 OS 120 fuel problem ? Q236 Robart R 780 radial for Corsair ?
Q225 Prop for B-17 ? Q237 Forest Edward radial plans ?
Q226 Custom exhaust ? Q238 Compression testing ?
Q227 EVO 26 ? Q239 Engine mount for G62 on Nosen P-51?
Q238 4 blade on H9 P-51 ?  

Question 217: "Dear Karl, I have been out of RC flying for some time, being involved with real aeroplanes (and Spitfires, but at scale 70%) But as usual the high cost drags me back to the models. A long time ago, I started an interest to built a scale Seafire at 1:5 or maybe a little bigger, depending on the engine. BUT, I wanted, and still want to built it only with a full liquid cooled engine. I feel it very strange that all engines have been copied in model, except the liquidcooled one for aircraft flying. With so many Spitfires, Hurricanes, Mustangs and P-38 around there must be a demand! I would like to do it right, like the jets, finally fly with the Proper engine. One day I was adviced by a modeler who built a real working Merlin copied V-12 of 56 cc,– but air cooled, And he told me that making the liquid cooled engine was ofcourse possible, but I had to prevent the engine for OVER cooling! Ever since I was looking for the liquid cooled inline, V or what ever engine to use in a big scale RC model. Can you tell me: is there any development that way??? What can you tell me about liquid cooling?? I’m more as highly interested to your reply. Best wishes, from Holland in Europe, Harry"

Karl: "Greetings, and thanks for visiting our site. Hope you enjoy seeing the different warbirds, projects, etc. I was very happy to receive your question, as I do have some information to tell you about that may just help you. In my opinion, sir, you should build a 1/4 scale Spit and have someone who has experience in airframe design help you, since the engine I will tell you about will need an extra measure of strength, for obvious reasons. There is an outfit in California (USA) that has designed and built a 1/4 scale Merlin V-12, and they have the supercharger, water cooling system and fuel controls as well. They can be found at this web site: www.quarterscalemerlin.com, and you simply have to see it to believe it. I don't remember what the projected weight of the engine is, but you obviously will have some design and construction challenges ahead of you. DO IT RIGHT from start to finish so it is the most safe, most reliable and most enjoyable airplane you have ever built. You won't need a gear reduction unit on the front since this one has it built in, a la full-scale. The water cooling system will add significant weight as well, which is obvious, but with the power, correctly chosen servos and radio as well as the overall flight controls, that shouldn't be THAT much of an issue. There is a crew in England that have built several large (emphasis on LARGE) scale true-jet-powered transport planes. One was a B-52, the other a C-130 and they flew well. I apologize for not having their contact info here, but surf around and you should find them with connections to anything large-scale RC. In short about the Merlin, it has everything you stated that you were looking for-liquid cooling, supercharger, gear-reduction for the prop, and runs on glow-fuel. Harry, hope this helps and please keep us posted here on your progress. I am very interested to see someone actually install this engine in a correct-scale plane that can handle it, and see how it goes. Thanks again, Karl"

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Question 218: "I'm Don from San Diego!. We're constructing a 13 ft, wingspan model of a P-38G to be electric powered. We are trying to locate a source for large propellers, 26-28 inches dia, and around 10-12 pitch, 3 blade. I thought you might know of a source. Would appreciate any info you can provide. Thanks, Don"

Karl: "Glad to attempt to be of help, Don, thanks for asking. There is an outfit in Canadia that has designed and built some fabulous examples of large-scale props. Their web-address is: www.soloprops.com. I know they carry props of the diameter you need, and perhaps if you ask them nicely---(just kidding, they really are great with tech questions...) you may be able to help them with designs for electrics. To be totally honest, I don't have blade weight spec's to access soas to inform you of whether or not the blades are light-enough for electric. They are CNC machined, finished by hand and weighed for static balance, and dynamic balanced as well. This is a top-shelf operation, Don. The props are what's called Ground-Adjustable-Pitch, which means even though you don't have to bring ten or twelve different props to the field to test, you still have to make the pitch change on the ground, fly it to see the results and that can be somewhat time consuming, but you have state-of-the-art technology to be sure. They are the only place I know of that makes a prop the size you need, period. I can't seem to find bigger ones from Master Airscrew, Menz, Bolly, noone. Hope this helps, Don. Karl"

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Question 219: "Karl, I recently picked up an old OS .61 with a factory installed 2:1 gear reduction unit. I am assuming that this approach was taken to reduce rpm and turn larger diameter props before 4-strokes were readily available, but this is only a guess. I remember seeing the Byron marketed reduction gear system, but the particular engine/system I picked up seems to be factory direct. I have been unable to find or receive any information from OS and was hoping that you could provide some historical insight and maybe even some technical specs/information along with recommended prop sizes. I've tach'd it out with a 16X5 prop at around 8,500 rpm peak and this seems about right. I don't have a dynamometer or any other "fancy" system to measure torque or bhp. I've included some photos for your reference. Thanks for any help you can provide. Sincerely, Chad"

Karl: "Hi Chad, thanks for the question. It is true that two stroke engines always turn higher rpm's to get into the power band than do 4-stroke engines. For alot of RC'ers the lower rpm's are preferred to higher rpm's for a few reasons. The lower rpm extends engine life due to the fact there is less wear and tear on the internals. Reducing the prop speed can allow you to still use the engines' power band rpm of 10,000 rpm or more but still swing a 3 or 4- blade prop scale speed. Having a prop speed exceed the speed of sound (supersonic) is a bad thing. For one, you can buy 4-stroke engines that can handle larger props to get the speed and performance you want. For two, you can use a prop speed reduction unit (commonly referred to as a PSRU). Byron had a nifty unit in the 80's that utilized belt driven gears at a 2:1 ratio. I don't know if Byron is producing that one anymore but an outfit called Warbird Propdrives has not only a much-improved design, but also a fully-functional constant speed prop set up to go with their design. This is a work of art indeed. Based on the information you provided, it appears technologically that this could well have been something offered about the same time as Byron's stuff. Having a factory gear reduction for these is a rare thing, I believe, so keep it in good condition. Keep the gearcase lubed and check things like prop shaft end-play, lateral movement, fluid leaks,etc. On this size engine, you MIGHT, read MIGHT be able to handle up to an 18" prop, with the reduction, but don't hold me to that. You'll have to buy some and bench-test to see what happens. If the engine lugs, smokes alot when you add more throttle, doesn't seem to run smooth in the cruise rpm ranges, you probably have it over-propped. Make adjustments to prop diameter, blade count, and pitch to find the optimum for your plane/engine combo. Hope this helps, visit us again anytime. Karl"

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Question 220: "Ok Karl I have am cgoing to purchase the RCV 90sp engine and the manfgr. recommends for 3 blade prop size a 15.75x10 or a 15x13.5. My question is; can you provide me with a list of prop manfrgs. who make these sizes. I like the solo brand but that is a little pricey for me. I have tried Master Airscrew, Zinger, and Graupner, but none have the correct size. APC offers said needed size but I am looking for one a little more scale and realistic. By the way the engine is going into a VQ Models Macchi MC 205 Veltro. Thanks for the input and answers. Gaylan"

Karl: "Hello, Mr. Clark, thanks for visiting our site. Here's what I can tell you, although it seems you have done some of your own research already so I
apologize in advance if this seems redundant. Master Airscrew has 16x10 and 16x8 3-blades for just under 15 bucks. Bolly has 16- and 16 1/2" 3 blades for 52 bucks. You can get those through Cactus Aviation in Tuscon, AZ. Through Desert Aircraft you can get these ones-Air Models has a 16x12 for 74 bucks, Mejzlik has a 16x11 for 59 bucks, Menz and MSC have no 3-blade offerings, according to the site links. The size in the 3-blade does seem smallish to me, and in my opinion the RCV engine should be able to swing a 16" prop with no problem. Just be careful about how much pitch you
have. Hopefully this will help you in your quest for the right prop. Karl"

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Question 221: "Hi Karl, I inherited a Top Flite P-40 Warhawk with a Supretigre G-90 engine installed. The engine has both the Top Flite in-cowl header and muffler installed. It is my understanding that the header will work fine on that size of engine, but the muffler (made for a .60-.75 engine) is too restrictive which will cause overheating problems with the larger .90 size engine. The airplane is very scale-looking and I would like to keep it that way, so is there anything I can do to either modify the Top Flite .60-.75 size in-cowl muffler to work, or is there another in-cowl muffler which will work as a substitute? Because the engine is mounted inverted, a different muffler would either need to work with the header I have or a different compatable header will be needed. Any advice you may have will be very helpful. Scott"

Karl: "Thanks for the question, Scott. You might actually consider looking into mufflers for similar-sized engines that are used on RC cars or boats. Internal combustion engines need to breathe well to make good, reliable, consistent power. So it stands to reason that if you have an engine that has been designed and engineered as a .90, you should match all related components to maximize its potential. In short, I agree that you need to look into all mufflers for that engine size, then narrow it down to the one(s) that fit the cowling to keep the exterior clean. Good plan, stick with it. Hope this helps. Karl"

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Question 222: "Hello Karl, I have purchased a Pica Spitfire which is powered by an OS .91 Surpass II that I am told it has around 20 flight on it. When I cracked the engine, it cranked easily but makes a weird sound. I would explain the sound as metallic sounding similar to a diesel engine. It sounds as if something is rattling in the engine and is speed sensitive. All the while the engine runs great and exhibit’s excellent power and acceleration. This is my first 4 stoke engine and I am wondering is this normal or if not, what you suggest. I have taxied the Spit but am waiting to fly until I know more about this engine/sound. I appreciate your taking the time to answer my question. Mike "

Karl: "Hi Mike, thanks for the question. There may be two things happening here. Of those, it likely is the first moreso, so I'll start with that one. It could be that the valve-to-rocker arm clearance is excessive. Once it warms up or speeds up, it likely won't have too much of an effect on power. However, if the valve clearance is excessive, it WILL be rpm-related, which is to say that it will have a noticeable "tick-tick-tick" sound at idle that occurs approximately twice a second or slightly more. When you apply power it will make the ticking noise faster, hence rpm-related. What you need to do is go to the specifications for that engine and remove the rocker covers and adjust the valves according to procedure. If you find the clearance excessive and readjust the valves, you have found and fixed the problem.

The other item could be deeper in the engine, with the crank bearings or rod bearings. The crankshafts on these types of engines these days, at least many but not all, are supported by three roller/ball bearings-one each at the ends, and a center support of some design. If it appears that the fasteners for the bottom end have been tampered with, it is possible someone else was inside the case, possibly did not install all the parts upon reassembly, or installed them incorrectly. If you find it necessary to break open the bottom case, purchase first a set of seals and gaskets as appropriate for the engine and install these new parts when you reassemble. While you are disassembling and inspecting, be sure to take time, visually be sure of what you are observing, like witness marks for wear, contact of components where there should be none. Look for signs around the counterweight areas in the case, abnormal burnished wear marks on the crank ends, etc. These could point to problems with crank straightness or bearing integrity. If any are present, fix them because they are signs of impending engine failure. Anyhow, this is alot, so take it in slowly! hahaha! Hope this helps. Karl"

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Question 223: "Hello Karl, first- sorry about my bad English. Now my Question.I fly an Fokker D VII with a Wingspan 2005mm = 80". His Weight 8,5 kg, that means 17 or 18lbs, my engine is an Laser 180. I think the Model is realy Scaleflying, but I want to have a little more Power for Loops and Rolls.So I buy a Saito 220 and installed him. Two weeks ago on our Field I did Break-in the Engine.But there is a lot of shaking by this engine and the silencer screws and other things will be turn off.I take the original Glow Plug and a glasfiber engine mount -not flexibel.Also a wooden Prop 22x6. Do you know about this Problem, must I have an metal engine mount? Thanks for your listening. regards Klaus.

Karl: "Gruss Gott, Klaus, und danke fur diese frage! Ich habe sehr viel meine Deutsche vergessen! Hah! First, make sure that the crankshaft is straight. If it is bent, it will cause this concern. If it is bent, replace it. That will be a part you can only get from Saito. Saito should also have rubber engine mounts or neoprene mounts that absorb the vibrations. These engines will always have vibrations inherent since they are a byproduct of physics. Then, make sure that the propellor is balanced dynamically. You can static-balance the prop, but these things are in motion when working, so they need to be balanced dynamically moreso. If, after fixing all of these that need fixing it still vibrates badly, then perhaps you should replace the engine assembly or at least the internal parts. Other than that, there shouldn't be too much to cause this concern. Hope this helps Klaus! Auf Wiedersehen! Karl"

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Question 224: "G'day Karl Listen I have the new os 120 ax with the Bisson inverted muffler and a perry pump to go with it. My problem is with the tuning of it. The bottom end is running fairly lean with the pump and it is running to fast!!!! My next problem is that the mid range is too rich but the high end is only 300 rpm off peak and the low end is lean as. The pump pressure is screwed way out to release pressure but it is still richening up. Have you got any suggestions mate?"

Karl: "Hi Oscar, how's life down-under? Good to hear from you Aussies once in a while. Let's us know how far-reaching our help is. Pretty cool. About this running rich/lean thing. It is not common for a new engine (OS or other..) to have these types of problems. Basically there is a fuel-metereing problem for sure. Since the engine design could be considered "static", which is to say, the internal routing of the air/fuel follows the same path, has the same restrictions, etc., at all rpms. That said, what seems to be happening is that the fuel supply is inconsistent with the requirements--not enough fuel when needed, too much when not. Try using a Kline-style or similar pulse/pressure pump. Based on what I've learned, when the rpm is higher, indicating high demand, the exhaust pulses are high, keeping the pressure in the tank consistent. At least in theory. This may be a good place to start for rectifying this problem. ALWAYS BENCH-TEST the engine before you fly. You don't want to spend valuable time building a great plane and have it crash on its maiden flight due to an engine glitch that should have been found and dealt with before flying. Try this and let us know how the progress goes. Thanks, Karl"

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Question 225: " I just ordered the wingspan models B-17c kit and was wondering what you would recommend as the best prop for this plane. I need something that will look nice but hold up well at the same time with a decent price. Also do you mind giving a link as to where i can find it. Thank you in advanced for the help."

Karl: "Hi Brandon, thanks for visiting us. In my opinion, the prop that will look the best and likely perform the best is from Solo Props. You can find them at this web address: www.soloprops.com. They have, what could be considered the best performing props for warbirds short of functional Constant-Speed props. Check them out and see what you think. Thanks, Karl." Editor note: You can also try Graupner, I used those on my B-17 with good results, Paul.

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Question 226: "I've recently gotten back into the hobby ,and boy the idle mind is the most devilish playground,after going thru many forums and threads it seems that the one point most everyone is trying to make is realism. My question to you professor is.......it possible to create a wrap around muffler for 2-4 stroke motors to exit out of 2 multi-ported exhaust stacks?like say as in a P-51 exhaust configuration?considering back-pressure and heat deflection issues,(plus a dirty plane) I think it would be a pretty cool sight.......do ihave too much time on my hands or what?????"

Karl: "Welcome to our great site, Mr. Martinez. You are observant when you assess that the main thrust these days is, in fact, obtaining a more realistic-looking and functioning warbird. For a long time now we in this hobby have been forced to accept the simple things such as cheesy (in my opinion..) single side or bottom exhaust outlets for planes. Now, see, even the planes with radial engines on the full-sized units modelled had to have holes cut in the cowlings to make a route for the exhausts. Planes with narrow cowls such as the Spit, Mustang, P-40 and others, have suffered the same malady.Behold, at this place, (web address...) www.Keleo-Creations.com they have absolutely invented for us, the antedote. If you are looking for a reasonably-priced custom exhaust for any type of engine, any number of cylinders, I think this is your solution. Go visit their site and enjoy. Thanks for visiting. Karl"

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Question 227: "Hi Karl! I flew my American Eagle AD-1 for the first time this weekend...made flying my P-51 seem like hard work! Now I really want a 1.20 size to build and hang an Evo 26 on. Any ideas where I can get one? 4Pi used to make an ARC but have discontinued it. Thanks. Bob Hicks, ASE Master."

Karl: "Thanks for the question, Bob. If you are asking about where to find an EVO 26, look no further than Horizon Hobby, they have several of the
Evolution engines for sale. If you are asking about where to find a 1.20 sized Skyraider, I would like to defer to a couple of my fellow advisors who may have the answer- Jack Devine or Jeff Quesneberry. Both of these guys have their proverbial fingers on the pulse of the kit world than I. Even ask our ARF advisor. Try him first if you are looking for an ARF. Hope this helps. Karl"

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Question 228: " I would like to swing a 4-blade prop with this bird (H9 P-51), any info on airframe integrity issues,prop size,etc. will be helpfull.This is my first project in 15 yrs. and there is just too many options out there,the reason for this engine choice is power to wieght ratio,plus i can get it for under 200.00$,good deal?-good choice?( overkill )?I'm guesstimating flying weight to be 15-17lbs with this engine,plus all the bells and whistles.........I imagine this bird will fly like a raped ape,if i dont peel the wings off of her....flying will be done at sea level also.........thanks mopartybob"

Karl: "Hi, Mr. Martinez and thanks for visiting our site. You sound like I did a few years ago when I started getting back into the hobby---so many new gadgets, so little dollars, hahahaha! If you are into the latest stuff, go see this outfit: www.warbirdpropdrives.com and look at the functional constant-speed prop-reduction unit they have. Via the links on their site you can even contact the guy who built their functional scale exhaust system for a two-stroke gas one-lunger. Prop speed is an issue. The way engines these days are getting larger, more powerful, etc, the prop speeds are also beingaffected. That's one reason the folks at Warbird Propdrives has developed the reduction system and CS hub. You might also look into Saito's 200ti Twin. It has a shallow vee design just for narrow-cowled planes like yours. Hope this helps, let us know how it's going. Karl"

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Question 229: " Hi Karl! First of all, great site, a terriffic source of information regarding any type of rc-aircraft really. I'm having problems with an ASP 61FS that keeps overheating inside the cowl of a La7. And I've got suggestions to build a "baffle plate" in front of the engine and a duct to lead the air across the engine. The construction itself has a well placed exithole for the air so I don't really see why this is happening...Anyways! That wasn't really my question :) Here it comes... At the field some heli-guy told me that they always break in their engine mounted and installed in their helis. And this is why I get this problem. I ran this engine in a bench before installing it in the plane.What this guy is getting at, I guess, is that the engine during the break in get accustumed to the temperatures around it. Is this correct? Should I bother struggling with the baffle or should I just buy a new ring for the engine and repeat the break in precedure while mounted in the plane? Thanks in advanceCheers, Jocke"

Karl: "Thanks for visiting us, and this is a good question. Heat has this type of effect-when cooling airflow is limited the engine will heat up faster for sure. The strange implication to me here is that the engine has some sort of "memory" for operating temperature. This seems unlikely to me since when you are flying the air temp is changing with altitude, speed, direction, etc. This much is true, however, that when you bench-test the engine (as I recommend to all pilots/builders) it will reach a certain temp that the engine metal can tolerate. I have an all-aluminum engine test sled and what I notice is that this metal acts as a heat-sink for the engine, thus allowing higher temp before it shows adverse reaction to the heat. Removing heat from the engine is the whole purpose of the fins-it has more surface area to take the heat away from crucial parts. When it is in the open air circulates around it from all angles, and it is in the prop wash as well, so this keeps it cool. Installed in the plane, airflow is restricted for obvious reasons when it's cowled, so heat rises, affecting fuel management and overall performance. It behouves you to make sure the baffle is located to maximize the airflow through the cowling. The exit for the air should be able to handle at least the same volume of air, probabaly a little less, to keep the velocity inside the cowling effective enough to carry the heated air outside the cowling. In my opinion, it is worthwhile to pay good attention to installing a well-designed and placed baffle. Keep in mind that hot air rises, so the tendency is for the lower parts of the engine to be slightly cooler than the upper parts-theoretically anyway. That can be debated based on several factors which I won't expound on here. So, if it helps, study the configuration of the installed engine and its relationship to the cowling cooling area, how hot air will act, the shape of the inside surface of the cowling, and see if you can determine how to shape and place the baffle to get maximum cooling, to keep the engine from grenading due to heat. Hope this helps, Joachim. Karl"

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Question 230: "Hi Karl. Like you I love the sound of a radial engine. I see that a few people have asked about engines for the Ziroli AT-6. What is your personal recommendation / choice. I'd rather not go glow as the Harvards never had methanol engines. Also what smoke system would you pick?
Cheers from New Zealand, Terry "

Karl: "Thanks for the note, Terry and welcome to you in NZ from all of us here at RC Warbirds. There are many radials to choose from, Terry. You didn't specify the scale your Texan is, but if it's 1/5 scale or larger you are in good shape for engine choices if you are installing a radial. I know you aren't interested in glow, as per your question, but Saito has a great large 3-cylinder that should haul that plane around with ease if its weight is around 22 lbs or less. You can select a prop to match from Menz, SoloProps, Bolly, maybe even Maejlik. If your Texan is larger, you can look into the awesome gas radial at www.rcshowcase.com, they have a 215cc 5-cylinder unit that is, well, artistry. As to the smoke, I claim alot of ignorance there, pal. You might find this simple-minded, but whenever a plane smokes, to me that's bad. Especially under normal circumstances. That said, when the smoke is used in air shows, etc, that's not exactly normal when you are defining normal from the perspective of why the plane was originally built and the type of service it saw in the late '30's through the '40's. I realize, however, that many rc'ers like to have smoke onboard for the rc airshows. I just never got into that side of it I guess. Terry, hope this helps you, and happy flying. Karl"

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Question 231: " Need some help to get a bent crankshaft straightened. The engine is a BME twin, 2.8 cu.in. I cannot seem to get to the manufacturer and do not know where else to try. Do you have a recommendation? Thanks, Larry Wilson"

Karl: "Thanks for the question, Larry. As a matter of fact, since this is simply a small engine, try looking up what small engine shops there are that do major overhauls. Crank balancing equipment is specific and usually can only be found at a shop that rebuilds engines. Hope this helps. Karl"

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Question 232: " Hi Karl, i am from Germany and like big Warbirds. Just had maiden flight with a fiber classic spitfire (2,58meter) with a self- built- 124 cc inline row engine ( using zenoah s cylinder / piston). Runs very smooth, turning Props 28 x 14 3-blade up to 5200 revs. next Project is a P40 (2,85 meter span), same engine (built two of them), but new concept: i d like to try a gear reduction with a ratio between 1:1,75 and 1:2. Should turn a Prop in the range of 32 x 16 or maybe 34 x 16. Should look great on the big P40. So now my Question: can you say something about using which type of belt? V-Belt (or belts?) or toothed type? As the inline-engine runs very smoth indeed, I thought that toothed belts should last ( i wouldnt use one on a single cylinder engine), and they dont need so much tension?! Best wishes Detlef"

Karl: "Hello, Detlef and thanks for the question. Sounds like you have a great project in the works with the P40. There are two ways for
belt-driven reduction drives to be employed. One is by a v-belt. Smoothe-running and quiet but prone to slippage, which will reduce the prop's effectiveness. Thinking of the application in a high-speed pass or simulating a diving run, the prop may not keep up, causing drag, or
it may windmill faster than the drive gear on the crank shaft. Both of these scenarios are unwelcome, which really goes without saying. In my opinion, I would use a ribbed belt such as those used for timing belts in automotive applications. Of course, you will have to find the right diameter, and you likely will have to put up with some noise, but the action is much more positive. When the engine speeds up, so will the prop; when you throttle back, so will the prop. I think that's the better way to go. Hope this helps, Detlef, thanks for being patient for the answer. Karl"

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Question 233: "Hi! Andre Otto from South Africa. I would like to try a 4 blader on my P51 (Blackhorse P-51 Mustang .60 powered by an asp/magnum 1.20fs). I currently use a 16*8 wooden prop. What 4 blade prop would you suggest I try? Thanx, Andre"

Karl: "Hello, Andre and welcome to our site. It's a long way to where you are, that's for sure. It's good to know how far-reaching our impact is. For starters, try this place-www.warbirdpropdrives.com and see what they are using for the prop on their big Mustang. They are using a different airplane for the testing of their reduction drive system, but not only is the reduction drive aimed at the Mustang/Spitfire combo, they are using P-51-style blades for testing. Those are wood, but they are also working on some carbon-fiber units as well. I haven't visited their site in a while so maybe they have updated information now. Another place to look is here-www.soloprops.com. They are in Canada, North America and have some great equipment as well. I
can also think of possibly APC propellors, or Menz. You'll likely have to fish around the web to find them as I have had no luck whatsoever in finding a website per se that represents Menz specifically. Usually have to go to say, Horizon Hobby or RC Universe online to find them. Hope this helps, Andre and thanks for your patience."

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Question 234: "Karl, thank you for takeing all these questions. First I don't have a warbird yet but im working my way there. I have a cessna 182 skylane that weighs about 6.5 lbs. Currently useing an O.S. .46AX and an 11x6 prop. I would like to move to a 3 blade prop for scale and maby a little extra drag to slow this baby down on landing. None the less what 3-blade would you suggest for this set up? thank you nick"

Karl: "Thanks for the question, Nick. In my opinion you should look into Master Airscrew stuff. They have some neat-looking 3-blades that would work well in that scale. Besides, the 182 does come with a 3-blade standard, especially on the turbo version. I'm pretty sure the non-turbo does as well, but it makes more sense on the turbo version. APC is another one that has some cool carbon-fiber props. Try those and see what you come up with. Thanks for visiting our site. Karl"

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Question 235:"I'm delving into a larger bird than what I'm used to...I bought a .140 sized P40 from Nitro Models, (CMP), and a 150 Saito for a power-plant. Can you provide any insight as to what 3 bladed props would work on this combo...I'll probably buy a couple of 2 bladed ones also but I live in Key West and there aren't very many of us to draw upon each other's experiences with this sized airplane. I'll also be looking for a spinner/nose cone to match...any insight would be appreciated! JW"

Karl: "Thanks for the question, JW. Sorry for the late reply. Has been very hectic at my house lately. Master Airscrew makes some really neat looking three-bladers for 1/6 scale and smaller aircraft, as well as Bolly. Do a search say, from RCWarbirds's site, or Horizon Hobby, RC Universe to get more info. The Bolly prop, as well as Mezjlik (sp) are foreign units and not yet widely sold here, but are pretty affordable nonetheless. You can also try the links to different prop company's through this site: www.desertaircraft.com. They have a few links that may help as well since they deal in a wide variety of applications. Hope this helps. Karl "

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Question 236: "Karl, I have a 100" composite F4U Corsair, I want to use a Robart R 780 Radial engine on it. The plane weighs about 24 lbs without the engine and prop. The total weight is expected to be around 43 lbs. Do you think the R 780 Radial engine will fly this plane? The R 780 Radial and the Quadra 100M (which the plane manufacture recommends) have the same specifications, with the R 780 turning a slightly larger diameter prop. The Robart engine has the HP, the weight and cubic in required. Will it fly the plane thanks? Ed"

Karl: "Thanks, Leslie, for the question. I love these kinds. Based on over two years' research I have done for just this kind of combination I
believe, yes, the R780 will do just fine. It has 10hp advertised, likely will run smoother than a non-radial, then you can use a scale-sized flying prop from Solo Props and have a plane that, in my humble opinion, will be the envy at every field at which you fly. There are, of course, other props available that are of what I call the toothpick variety--two-blade wood props. Considering the potential investment in different props of a whole range of diameters, pitches, and blade counts, you could easily be spending several hundred dollars. Now, that said, you still have to haul all those props to the field, induce more wear and tear on the crucial blade-hub and prop nut components switching from one prop to the other. Using a Solo Prop, you can make the adjustments to pitch on the ground between flights, anywhere from 6- or 8-pitch up to 24. In my opinion, spend 2- to
3-bills on a Solo unit and save time, wear and tear, and have a ball just looking at it, even! Hope this helps. Karl"

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Question 237: " Hi Karl I have a set of Forest Edwards plans to build a 5 cylinder radial engine,however.i've had them for so long now and when i recieved them they were not in great shape to begin with and was missing information. I would like to know if you could tell me where i could find a set of new plans for this engine. Aswell i would like to know if you know anybody who has one of these engines,i would like to do a bit of research before i tackle on a build like this. Thanks Jean-Guy"

Karl: "Good question, Guy, I think I know a good source for your needs. This guy I know, and have toured his manufacturing facility, has a hobby
that deals almost exclusively in collecting, designing and building RC scale radial engines. He's been around for a while, so all you can do
is ask. I can't guarentee since I don't know what he knows, but it's the only solid chance I know of. Hope this helps. www.napco-ltd.com. The guy you want to ask for is Paul. Thanks for visiting our site. Karl"

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Question 238: " Hello, I have been reading your website and have a question. I recently picked up a compression tester. How many PSI should an engine have? Is it the same for 2 and 4 strokes? How about gas engines? What is the proper way to test? I have always tested by feel but I think it would be a nice to have some accuracy. I got the tester at a swapmeet and there are no instructions. Web searches have come up empty, only revealed where to buy one. Hope you can help. Regards, Tom "

Karl: "Hi Tom, thanks for visiting our site. Pretty cool, huh? Sorry for the delay. Compression in an internal combustion engine is important. In a gas engine, the compression of the air/fuel mix in the cylinder helps determine the power output. If the air is compressed to only, say, 10 psi, when the air/fuel mix lights off it will compress the air further before the expansion of the gasses acts upon the piston and pushes it down. This causes a loss of power. When the piston is pushed down it makes torque. The speed of this action, and how the cylinder "recharges" for another burn is measured in horsepower. Ideally, you want as much of the air in the cylinder compressed as possible, so when the above-mentioned activity occurs, the only place for the piston to go is down, making power.

In a gas engine, the air/fuel mix is lit with a spark plug so compression doesn't need to be very high. In an automotive engine typical compression is anywhere between 150 psi and 190 psi, depending on several factors.

In a glow engine, as in our hobby, there is no spark plug so the engine is designed to have high compression to light the mixture. Since the fuel used is methanol/nitro-methane, it will only ignite under high compression. Most of us use a tactile method of checking compression. With a prop on the engine, glow plug installed and some lube inside the crankcase, try spinning the prop steadily with a finger. Don't try starting it yet. If the resistance of the compression causes the prop to suddenly stop with your finger slipping off, and the prop kicking backwards, the compression is sufficient to run it. I have heard in certain circles that compression for these should be around 40 psi. Don't quote me because some engines have two rings, some have one; some engines are four-stroke, some are two, which also plays a role. Besides, we are still talking only about small RC engines, so we can't expect them to have the same numbers as a full-sized car engine. Here's one method you can try. If you have a .91-sized engine, it will fly a 1/6 scale plane. You have the higher compression glow engine, not a gas engine for your plane. So, if a full-sized engine in a car (say a v-6) has 190 psi compression, divide this number by 6 and you have 31.6 psi. This seems pretty accurate but keep in mind that a gas engine has lower compression than glow, so allow for a number higher than the mathematical result. Again, this isn't rock-solid, it's based on conversations, listening, experience with engines. I have not personally had to check compression on a glow engine, so I'm sorry if that deludes you. It's not intentional.

As far as method, connect your compression gauge to the engine and make sure it is seated in the plug hole well, and not leaking. don't allow fuel ingestion and open the throttle fully. Opening the throttle allows easy air flow into the cylinder and there for will give you max results. "

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Question 239: Hi Karl, What is the best option for mounting a G62 in a Nosen P-51. Hard or soft?? If soft mounting, what brand of soft mount??

Karl: Mr. Stricker, thanks for the question. Through most of my time being around this hobby I have not seen very many soft-mounted 2-strokes on a 1/6 scale or larger airframe. Or even smaller ones for that matter. Perhaps long ago before I was into the hobby there were some and likely out of necessity. There have been many improvements over the last decade or so with regards to engine bal-ancing--internal, external, etc. Of course, the extent to which one needs to balance a power plant, and the method, depends of course, on how sound the initial design is and the attention given to the detail of exact weight of reciprocating parts.

Radial engines, for example, by design tend to emit fewer vibrations since they are arranged in a circular pattern and can therefore distribute thrust loads more evenly. A single-cylinder or even a flat-opposed layout tends to be prone to more vibration since the loads are dispersed linearly.

That said, based on personal observations, discussions and seeing hundreds of photos, I believe it would be best to mount this via the "hardmount" method. As I said, due to advancements in engine design and machining, the vibration issue has been greatly reduced for these types of RC engines so I hope this helps. Thanks again and visit any time. Karl

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