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 5: Questions 145-168, click on links or browse page.
Q145 G-62 for Top Flite Corsair ? Q157 Top Flite P-47 engine ?
Q146 ZDZ 80 prop ? Q158 World Models P-51 engine size for four stroke ?
Q147 FE-120 full expansion engine ? Q159 Engine for enlarged 120" Corsair ?
Q148 Twin Technopower 7 cylinder type plane ? Q160 Saito or OS radial for Jungman ?
Q149 3M five cylinder radial ? Q161 Gas alcohol mix for model engines ?
Q150 DO335 engines overheating ? Q162 Engines for Ziroli B-25 at high altitude ?
Q151 Saito 91 runs poorly with muffler pressure ? Q163 What engine for 1/6 scale Mustang ?
Q152 Moki RCS radial questions ? Q164 Vailly FW 190 engine ?
Q153 Cam timing for Saito 450 radial ? Q165 Electric flight question ?
Q154 3 W 256 radial warbird choices ? Q166 Warbirds for a Saito 450 radial ?
Q155 18 cylinger radial uses ? Q167 Smaller muffler for two stroke gas ?
Q156 G 26 carb fix ? Q168 In cowl muffler for Super Tigre 90 ?

Question 145: "Hello Karl, I have searched the internet looking to see if a Zenoah G-62 will pull the top flite giant scale corsair with authority? The instructions in the kit say that this model is built for the G-62. Yet, from the internet I get mixed impressions; some say that the G-62 is absolutely impressive while others say it is a poor choice and at least a 70cc gas engine should be used (top of the range). I expect that the wt. will come-in at about 24lbs. Any help would be appreciated here. And thanks. I really enjoy reading your column. I have learned much. John"

Karl: ''Thanks for visiting us, John, and we here are glad we are providing a site that does truly help you learn. The G-62 is a great power plant, indeed. You might also look at some of the Saito smaller radials, and some from an outfit in California Techno Power Engines. Their site is www.TechnoPower.com They have 5,7, and 9-cylinder radials to offer. Some are for 1/6 scale and some for 1/5 scale. Then go to www.soloprops.com and find the prop you need. Between these suggestions, you should get the just right power combination for the Corsair. Great fighter plane, too. The first to exceed 400 mph! Hope this helps. Karl "

Back To List

Question 146: "Hi Kark could you tell me what prop would be best for my ZDZ 80? I am putting it in a 37lb. 1/4 scale Fb 109G. I sell MSC props and would like to use one of them if I could."

Karl: ''Hello, Tom, glad you asked. You might try the 28 or 30 inch prop, this should assist in getting the bird off the ground. Allow me to take a tangent for a moment into territory which you may or may not have been, at this point in your endeavor. Go to this site: www.quarterscalemerlin.com and see what a beautiful work of art they have there as a powerplant choice. Then go to this one: www.soloprops.com and take a look at their offerings. Now, it sounds like the all-composite BF109 G is an awesome plane, and it deserves just as awesome of a powerplant. As you know, the real 109's had 3-blade props on them, so that is why I suggested the prop outfit. We all know that when it comes to RC stuff, especially with warbirds, we can simply build one as cheap as possible so we can fly soon after we build or buy, or we can go all out for scale realism in all areas. Obviously I don't know which end of the spectrum you're at, but maybe my suggestions will inspire you and challenge you. As to your question, the ZDZ 80 is a great one, to be sure. You can try a larger (27-32-inch) prop in a 2-blade, or a smaller (23-26-inch) in a 3 blade and play with pitch until you get good flights. Hopefully you will know soon if one works better than the other since if it doesn't move enough air, it will take high rpm's and lots of runway to get airborne, so you throttle back and taxi to your station to try a different prop. Solo Props have ground-adjustable pitch props in a variety of diameters, so you should not have a problem finding one that works. You can use the scale diameter and play with pitch only, with one prop, not having to invest in a dozen props and wear out the prop shaft threads removing and installing props. Anyway, I think I answered your question, and the plane looks great. 1/4 scale is cool. Karl "

Back To List

Question 147: "Karl, I have a question about FE-120(200),full expansion, glow engine. Their size and shape look nice to install in the nose cowling. And they seems to have enough power as long as their advertisement say. I don't know why most people don't use them in spite of MMC's advantage. Is there any defect or weak point of them, durability, noise, heat problem or so? I'm interested in those engines, but I wonder why almost none of modeler do use those. Regards. Tsutomu "

Karl: ''Mr. Mabuchi, it is good to get a question from you. I don't know why more modelers aren't using these engines. The only theory I have is that they simply look strange, the technology is unfamiliar and their history to my knowledge is very foggy, so RC'ers won't know about getting technical help, spare parts, etc. and these are all big concerns for fliers. If there are any fliers out there, reading this site and have flown them, please get in touch with me via RC Warbirds and share the info. This hobby is incredible in the technological changes that it experiences on a yearly basis. Things are constantly in the works, so new stuff is interesting, for sure.
After studying the technical drawings and explanations of these engines, they sound like a cross between a rotary and a diesel. In a diesel, the use of the heat to convert to operational energy is what makes them so far superior to gas engines as far as thermal efficiency. But the basic design is such that there are few moving parts to rob energy, cause friction related wear, and so on. I don't know why the 200 is nearly $1600 dollars US and the 120 is less than $500. You are correct in your observations that they will fit well in a cowling for a round engine, but, being a fanatic for all things radial, I am sort of biased. I would say try it and see. The principles of operation are sound, so it looks pretty good to me. Hope this helps. Karl "

Back To List

Question 148: "Karl, I currently have (2) TechnoPower 7 cyl. "B" series radials. (1) is NIB and the other is unrun after a factory O/H where the crank was replaced with a H/D version. My question is this, what is a good plane for these engines? I had the first engine on a 60" WACO. This plane looked and sounded GREAT, my concern now is the power output of this engine. The plane flew somewhat scale, i.e. sluggish. I tried a number of props and finally settled on was a 15-10 for best performance. I am thinking about a 16" SOLO prop for the next one. I have purchased a Mid West 1/6 Super Stearman 65" kit for one of these engines. My concern is weight. Will this engine pull it around. I would like to do this one up scale ++, oleo struts and such. I know that battery technology has improved since this engine was last flown 6 years ago. I am in hopes that significant reductions in weight can be made in this area. The old 5 "D" Cell glow driver weighed a ton. These engines are just too beautiful to remain in the box or an the shelf. Can you offer some suggestions as to other kits that are suitable for these engines? Best regards, John "

Karl: ''Great question, John. Radial engines are my favorite mode of aircraft propulsion. Jets are cool, loud, and all that, but when you stand on the tarmac listening to an R1830 or an R2800 roll over at idle,.....what can I say, but, pure music, pal. The TechnoPower engines are real good. The fact they have sizes to fit even smaller scale planes is a real plus since no one else who is selling a radial has any that will fit a 1/6 scale or even 1/7 scale that has more than 3 cylinders. Saito is close, they have 4 radials, I think, ranging from 90-size to 450. Their R 450 is larger displacement than the 325 5-cylinder. I believe you have a few choices of planes, if you'll bear with me. How about a PBY, or a B24? A Ford tri-motor? C 47? If bombers interest you, how about a B 17? The neat thing is, too, that you can custom fit the plane to the engine if you really find a combination you like, but think the scale is not quite right. There's also several monoplanes from the 20's and 30's to consider: Beech Staggerwing, DeHavilland Beaver, etc.

Lastly, I believe the Solo Prop is the way to go too. Just this past weekend I attended a fly-in for a local flying club, over 100 planes were there, from WW I bipes and "tripes" to even a couple of 3 D planes. In attendance was a guy who built this fabulous PT 19 or 23, tandem trainer from WW II. He had never heard of Solo Props and his plane had a Robart R780 on it! If you want a great prop to go with a great engine, then find a plane that will work, stick the radial on it and the Solo prop. Boom done, baby. Hope this helps, John. Karl "

Back To List

Question 149: "Hi Karl, Ken Lawson here again. I am the Aussie who wrote to you some months ago re interference and the big five cylinder Moki 215cc petrol fourstoke. I re built my ten foot Skyraider and the machine has been flying very well. First up powered by a DA 100, and more recently with the Moki. I have had no further episodes to suggest that this engine is a nest of problems from the radio noise side of things. We even ran a spectrum analysis on the engine and all was well. So, what caused the crash is still a mystery. The engine has had several flights in the second Skyraider airframe and has performed flawlessly. I use a 32x14 wood prop and get 7400 rpm which I think is very good. It does not lack in the power department even hauling 54lbs of airplane ! I just thought that I would give you some feed back so as to put minds at rest ! Have you any experience of the new 250cc petrol five cylinder radial put out by 3M ? I, like you am a radial nut ! All the best. Ken Launceston Tasmania Australia"

Karl: ''Thanks for the follow-up, Dr. Lawson. The Skyraider you built is a beaut! She looks stunning in the air, my friend, great job on the build and engine choice (See pictures here). I always appreciate the pictures (if possible to include...) and the updates on projects. It lets me know there is still a connection between us here at RC Warbirds, and you fellow rc'ers.

As to the 3W gas radial, I have not heard a thing about it yet, other than to see it on their website. They don't provide alot of specifics about it. Give me a couple of weeks and maybe I can come up with something.

You really need a scale, flying ground adjustable pitch prop on that baby, Doc. Go to this site www.soloprops.com and look into them. As far as I am concerned, they have set the bar on propellors for large-scale planes. We all know the reasons behind why there are so many 2-stroke gassers that run 2-blade props, these guys figured out the problems and fixed them. Pretty much quiets the nay-sayers against scale props. Do me a favor, check them out and get back to me again. They are scheduling the release of a 4-blade hub, also ground adjustable pitch, due out later this year. No solid date for it though. Hope it works for you. Karl "

Back To List

Question 150: "I have a question that I hope you can help me with, I have the Al Masters DO335 with a os 160 front and a 60 on the rear. The problem I am having as you can gues is it appears that the engines are overheating or leaning out about 6 min into the flight. The plane just seems to loose power and I am still at full throttle. Could this be the fuel I am using or isit a cooling issue? I am not sure if I am even asking the right question but hopefully you will get the jist of the question. Thanks"

Karl: "Thanks for the question, Tony. The DO335 was a tandem-twin engined plane and I'm sure that engine cooling was a priority on the full-sized units as well. The OS engines are good choices. First, run the engines in the fuse on the ground at roughly the throttle setting and duration you would flying. Note the smoke amounts, the smell, see if the engines run rougher, and use a laser temp gun to pinpoint head temp of each engine. This may take some time since you don't want to open up the fuse for easier access, since you don't fly it that way. You want to replicate as accurately as possible, the conditions on the ground as are in the air, to test the problem. It is only when you thoroughly understand the problem that you can come up with an effective solution. In 2-stroke glow engines, as with anything else, heat kills. In general, the more fuel you put to an engine, the cooler it runs. The less fuel, the hotter, and so on. If you find that your fuel delivery is the same--which is to say, fuel line length and inside diameter, from the source---then you need to assess the cooling potential of the engine's location in the fuse. It may be necessary to install NACA style ducts along the fuse to allow more air to circulate, and have the proper exit size. When the air exits to the rear, the plane's slip-stream will carry the gasses out, but you have to have sort of a venturi effect in the fuse in order to have the velocity sufficient to cool properly. Just be patient, do as much testing on the ground as possible before you go airborne soas to minimize losses. Whether it is a high-dollar scale warbird, or an ARF, it is still a tough loss to bear when they go down due to physics, eh? Hope this helps, and be patient. Karl "

Back To List

Question 151: "Hi Karl: My Saito 91 quits running when I advance the throttle more than 1/2 open -- UNLESS I disengage the fuel line connected to the muffler nipple. In other words, without the muffler pressure -- the engine runs great -- really great. But when I connect the pressure line the engine quits above 1/2 throttle. Can you provide my with any suggestions? Many thanks, Paul "

Karl: "Thanks for the question, Paul. There are a couple of things you should look at here. First, make some adjustments to the needle for "cruise" adjustment. There should be an idle needle and something like a "high" needle. Because of the nature of carburetors, one of two things are happening 1) the engine is pushed beyond the rich limit it can tolerate and it is flooding out. If you are getting inordinate amounts of smoke from the exhaust in the minutes or seconds before it dies, this may be your problem. 2) the added pressure in the carb is affecting the diaphragm and it is basically shutting off the fuel. The pulses of the engine and crankcase cause the diaphragm to pulse, metering the fuel under different operating conditions. What can happen with too much pressure is the diaphragm sticks shut, causing just what you are experiencing. It's sort of like blowing up a balloon and blowing too hard---the neck pinches off and no air goes in. Similar thing going on. You can also look at it this way, that if you take a car engine and do some mild things to make it run smoother, more reliably, etc. and then you add a blower that is say, 10% over driven, you are never going to get enough fuel into that engine unless you change some other things in the engine design to accommodate the added engine pressure. So, all that to say, try a different diameter tube for tank pressurization even change the length, tweak or at least check your carb settings for proper fuel delivery at that throttle setting and see just how effective bench testing will change it. This is not the kind of problem you can always fly the plane to see what changed---you could lose the plane, pal. Whenever possible, always bench-test the power plant to ensure proper operation. Hope this helps you and happy flying. Karl "

Back To List

Question 152: "Hi Karl More questions for the master technician !
Question #1 With the Moki Modelli Radial the instructions state that "the valve clearance is set at 0.05-0.08 mm (5 - 8 thou)" . I do not see that the metric gap give is equivalent to the imperial gap give. Therefore which to use ? I naturally contacted the Americans (RCS) who were adamant that the 5 to 8 thou was the correct gapping. The Europeans (Stuart Mackay/ Moki Modelli) stated that there was a misprint in the instructions and that one should use the metric gap of 0.05 - 0.08 mm.
Meanwhile it struck me that the imperial gap made more sense and that is what I have been using. What would you suggest is the correct gapping on such an engine ?

Question #2 The instructions state that the glad nuts X5 (holding the exhaust stubs to the collector ring) should be tightened before each session. Sure enough they are always loose. Will these nuts ever bed in and settle, or is it that because of the difference in metals (aluminum/steel) and their different coefficients of expansion that they will never settle and always need attention ? What happens in the real radial engine world ? Thank you, Karl. Regards Ken"

Karl: "Hello again, Doc. The Stearman looks awesome! And the perfect choice of powerplants, I might add. Good job. As for the valve clearance, since I know nothing of imperial measure---that is, unless we are simply talking metric---I can't really advise on imperial if it is in fact different. However, since the valve-train is exposed to the air, this is good to keep things cool, but also allows you to go with a smaller gap since the metals will have less tendency to expand very much. Bear in mind that on a full-sized engine, the clatter you hear when it idles is part of what we have fallen in love with--(well, some of us perhaps!) when it comes to vintage airplanes. That clatter can also ruin pricey parts, so in my opinion, let the engine run till it's hot, then set the gap, unless something else is specified in the manuals that came with the engine, so you don't run the risk of over-adjusting and possibly burning valves or having some other failure. You want a slight clatter of noise, not immediately noticeable.
Now, as for the exhaust, your foresight is keen where the problems created by dissimilar metals is concerned, so this is why on old engine stuff "back in the day" we periodically say here, always had re-torquing spec's due to these differences. Of course, we are talking back in the days of early metallurgy and casting methods, so there was alot to be desired. On a full-sized radial, the exhaust pipes were secured by a method that is still used today in different areas, but the real ones are sort of on steroids, due to the size, vibrations etc. Basically, the pipes were secured in place by a type of flare-nut or compression fitting (ferrule fittings). One part of the joint was secured in the head hard and fast, as sort of the go-between from the aluminum head to the steel tubes for the exhaust. After that, the pipe has the "nut" on it that is actually tightened, and this is fed into the first part of the joint and tightened securely. This ring, essentially, typically had up to eight notches in its circumference to allow for a torquing tool to be inserted into the notch, then turned to the proper setting. Consider the pipe's diameter was around 4 inches, perhaps less, it depended upon the displacement and cylinder count, whether or not the engine was supercharged. So, enough for context, now for the answer, haha.

When comes to your engine, perhaps try removing some of the paint from the part of the tube that connects to the collector ring. Part of what may be occurring is improper torque is attained due to the paint, and it works loose easier. If you are brave enough, try removing the paint and giving a little more turn to the glad nut when tightening. Go flying, let it cool and see what happens. That's all I have to say about that. Thanks, Ken. Karl Allen "

Back To List

Question 153: "Hello Karl, I have a Saito's FA-450R3D Triple that for some reason I disassembled it about 8 years ago and could not assemble it back because I didn't know how to set the timing for the cams until a couple of weeks ago looking at an Instruction Manual for Saito Singles on page 8 they describe how to set the cam for the right timing so I assembled each of the cams on my Saito 450 following this instructions but I forgot that in this case we have to consider the firing order of the cylinders as well, so looking at the Supplemental Instructions for the 450 I figured out that the firing order 1,3,2 meant that every piston fires in sequence one right after another, not every other piston like for instance in a 7 cylinder radial. So I tested my engine and its sound was not as I recalled from 8 years ago and the maximum RPM with a 22x10 prop was around 6,000-6,100. Then I changed the timing on #2 cylinder (looking at the engine from the front, the top cylinder I named it #1 and the next cylinder, counterclockwise is #2 and then #3) so that the firing order would be 1,3,2 and tested the engine now with a more pleasant sound and 300 additional RPM. Question: Which is the right way? I must tell you do to the fact that I live in Mexico, it is very difficult to send the engine back to the service center and then to bring it back. I will appreciate your feedback. Thank you,, Patricio"

Karl: "Muchas Gracias, Amigo Patricio! Como estas? Bien, bien. You are correct in learning that in a radial engine, the number one cylinder is at the top, and firing order is set through the engine's rotational direction. So, in short, if Saito says the firing order is 1-3-2 and that is how you now have the engine set up, then you have it right. Good job. Make sure you now pay close attention to the overall running condition of the engine--how smooth it idles, when you apply more throttle does it want to hesitate, stumble or does it have a miss related to timing? Monitor fuel use and glow-plug condition as well. When you are satisfied with the results of the pre-flight checks, then try to take it up in your bird and see how she does. Good luck and happy flying. Adios. Karl"

Back To List

Question 154: "Karl, Robert here from Dayton. I am wondering if you have researched what war bird plane kits will fit the new 3W-256 radial engine that will turn a 36"x10" prop? I Think this would be a fantastic engine in an F6F Hellcat! Maybee 3W will come out with a few of their own warbird kits and accessories that would fit this big radial? What kits do they have in Germany that will fit this engine. I would love to here back from you or if you have any other contacts in Europe that might help, please send me their e-mail. Thanks, Robert"

Karl: "Gruus Gott, Herr Haman, wie geht's? I have done some research into this engine and have found that the diameter (over 11") is too large for many closed-cowl planes such as a Hellcat, Jug, what have you. Even a 1/5 F4U Corsair is too small. Most of those kits have the cowl around 10-11 inches. I Think that is why the kits that 3W recommends are open-cowled units such as biplanes or trainers such as the PT19. Obviously, with the open cowl, size doesn't matter----to a point. Why would you spend lots of money on a nice kit that won't fit that engine? My suggestions would be to enlarge the plans of an existing plane, so the formers and cowling are large enough to enclose the engine, find a different engine,.... The 3W radial is a beaut to be sure. Sounds real cool. Looks cool, and is alot cleaner than a glow engine. I don't have any contacts in Europe as yet so I can't help you there, sorry. I would pressure 3W to offer a kit or two just to whet the appetites of us enthusiasts, that will fit the engine. That would be smart business, indeed. Hope this helps, Robert. Karl "

Back To List

Question 155: "I visited the rc warbirds site and saw a question that I would like to investigate further with you. The question was in regards to an 18 cylinder radial engine and it's possible uses in rc.Particularly its low 2500 rpm speed. The company providing these plans is ageless engines , they have plans for several sizes from including 5 ,7 , 9, double row 14 and 18 cylinder engines. The owner of the company believes the high torque produced would be very difficult to overcome in rc plane use ( IE rolling the plane) Would you be willing to give an opinion on this as well as elaborating on the possible ways to deal with the low rpm. thanks alot
charlie fasano"

Karl: "Thanks for the inquiry, Charlie. I would be glad to elaborate some here, if it helps you and possibly others. The heads at Ageless Engines are correct when they say the torque generated by these engines would easily overpower the airframe. The best version of the P & W R2800 radial produced so much torque in the F4 Corsair, for example, the pilot had to stomp on full right rudder to stay somewhat straight on the flight deck or off of the land-based runway. The cool thing is, that if you build a larger warbird (1/5 scale or bigger) you have to do much the same, to keep the plane straight on take-off. Especially if you are using radial power, such as the Robart unit. If my memory serves me ( I have spoken with the folks at Ageless about this very subject, over 2 years ago...) the people at Ageless did not recommend using any of their powerplants for actual RC use, they were really interested in the collector and accomplished machinist/builder. These museum-quality pieces usually take several months to over a year to complete, and most use them for bragging rights, for lack of a better term. A friend of mine in near where I live has a company that manufactures one of the only truly 1/4 scale replicas of the P&W R2800 radial--complete with pressurized ignition system, dual magnetos, dry sump oiling, the works. It's even painted the same grey color. I am a very accomplished builder and good with most things mechanical, and this thing would possibly see me retiring by the time it was started. These engines do produce alot of torque for scale powerplants, and the airframe has to be stout enough to handle it. If you had the money to buy one of these engines (which could run you at least $8,000.00,...) you could even have a gear-reduction housing in the front case, rather than direct-drive, and lower the prop speed. However, if the rpm range's max is less than 3,000, you should be safe. Controlling the torque roll is difficult even on a real full-sized plane, let alone an RC one. If it were large enough, in my opinion you probably could build an airframe with suitable controls to handle this problem. Another way to deal with this problem is with an adjustable pitch prop. No one that I have found as yet builds a solid prop of a sufficient scale diameter (32" or more.....) to harness the power. The only outfit I feel strongly about recommending is Solo Props from Canadia. They have a variety of Ground-Adjustable-Pitch (GAP) props with 2 blades, 3 blades and soon 4 blades, with round or square tips. You don't have to have 10 different props to do the job that one can, all you have to do is adjust the pitch according to the changing flight conditions. This is a great product, let me tell you. I have heard from a couple folks who are flying with them and swear by them. My personal opinion over all, Charlie, is if you want a world-class, once-in-a-while flown RC plane, you can build an airframe to handle the power and torque of one of those engines. You must realize that you would likely be setting trends in design for things such as servos, air systems for retracts, fuel, and you would most likely have to design some sort of alternator or generator to handle additional electric loads. The sky's the limit---pardon the phrase---of how you might want to do such a project. Great amounts of research and design needs to take place as the foundation first, because the whole project's success rests on what you know will and will not work. If you are going to do something like this, do it right and don't cut corners. A 1/4 scale project has interested me for some time now, showing the compatibility of different systems, designs, raising the bar for RC ideas and so on, and utilizing a fully-functional gas-burning radial like the ones produced by Ageless or others. My friends' operation only builds gas-burning engines, no glow. Lastly, let's be real honest about this. The owner of Ageless rightly states a recommendation for display use, not for use in RC. You have to know there are people out there who are just stupid enough to spend the money for one of these projects, screw it up because of lack of information or something else important, and try to make Ageless responsible. So naturally they need to issue that caveat. You and I both know, though, there will be those big thinkers out there who will dare to try. More power to 'em, just take time to do it right, please. Hope this answers your questions, Charlie, and thanks again. Karl"

Back To List

Question 156: "I have a g-26 and it hasen't been running as good as it normally has in the past lately, I pulled the plug and determined that it was fouled. Someone in our club was telling me that he had to rout a tube from the diaphragm cap on the carb. to the air intake stack(velocity stack), have you heard of this being done and what does it do? Thanks Shawn"

Karl: "Thanks, Shawn. I haven't heard of this very much, but I believe I can help with some insight as to what might be causing this problem. Likely the age and number of flights you have on this engine has caused some wear, and the cylinder or the crankcase is allowing too much fuel to get into the chamber and fouling the plug. Check compression, try to find out from Zenoah what the compression pressure is supposed to be, then use a regular compression testing tool to verify. Next, disassemble the engine, all the while inspecting the internal components as you do so, to check for wear, excess play or clearances. Dirt that is aspirated into the engine will cause sealing problems. The tube your flying buddy speaks about is likely an attempt to balance the air/fuel ratio so it will at least stay running. Check the diaphragm for integrity and replace if necessary. 2-strokers mix the fuel and lube in the crankcase prior to induction into the cylinder for burning. The more wear and clearance that is between the case and the crank, the worse it runs. Try these checks and/or repairs and see what happens. Preventative maintenance goes along way, my friend. Good question.

Back To List

Question 157: "Karl, I have a TF p-47 Gold Edition kit that I will be starting work on soon. I have a choice of two engines; OS 91FX, or the OS 90 Surpass II. I prefer 4-strokes for the sound, but I'm wondering if the Surpass has adequate power for this plane. What is your view on this? Thanks. Dave"

Karl: "Thanks Dave, for visiting our site, I hope it has what info you need. I know for myself right now I'll do my best to answer your question. You might look into the Saito 90cc single which has just a tad more power (1.7 hp as opposed to 1.6 for the FS Surpass...) But the best choice might just be Saito's FR170R3 radial. I think it is just a little more on power and is even a radial, which is what all the Jug's came with. FYI--the P-47 had the same engine in it as the F4U Corsair did, the P&W R2800 radial. The Jug is one tough plane, Dave. Once I read an article written by a P-47 pilot whose bomb armed but did not jettison during his squadron's sortie. He came all the way back to the base in England and once the plane touched the ground, the bomb came off and exploded. The explosion basically broke the plane in half just behind the cockpit. He survived, obviously, and was sworn to fly only the Jug from then on. If a bomb could break it in two and still protect the pilot, he was sold. Pretty cool, huh? Happy flying, and I hope this helps. Karl"

Back To List

Question 158: "Hi Karl, I just bought a World Models P51 it’s the new 60 size and I would like to ask your opinion. I was planning to install an OS 91 Surpass with a factory pump. But I had really wanted to put motor and a new Slimline inverted pitts muffler in my Original NIB EZ Dago Red my favorite P51. So I figured if I need to buy another engine it should be a 120 four stroke for my new P51 I just am not sure which one I do like OS’s I was thinking a 120 Surpass III Pumper? Any help you can give would be appreciated. Thank You, Joe Elston"

Karl: "Great question, Joe, and Merry Chirstmas. I truly think that the Saito 200 Ti would fill the bill nicely. This is available in 1.20 size, which is what you are looking for, and it is a shallow-vee twin four-stroker. It is designed just for planes like yours. Among the benefits are twin cylinders for plenty of power, cool sound, and it really looks impressive. It is a shallow vee so the exhausts and heads will stay inside the cowlings of these narrow-cowled planes. You can't hardly go wrong with Saito's either, man, they are perhaps the best offering for so many sizes of planes in 4-stroke power. When the flying season was full-stride here, where I live, you could find Saito's on just about every type of warbird, and lots of the trainers, pylon racers. Hope this helps you in your decision. Karl"

Back To List

Question 159: "Karl, I took a set of zeroli plans and blew them up 33%, thus a 120" corsair. My question is will a sach's 5.8 carry this bird? I think this is about 95cc or 9.5hp. Thanks for your help."

Karl: "Hi Russ and Merry Christmas, pal. Here's what I sincerely think you should do. Choose between either the RCS 215 gas radial, or the other one offered by 3W aviation. The Corsair came with a radial, they run smoother, and since they are 4-strokers, you don't have the mess from mixed oil and fuel running all over the outside of the plane from the exhausts. The RCS www.rcshowcase.com) unit has at least 13 hp and will swing at least a 32" prop. Then look at this company www.soloprops.com for the coolest in propellors. It is possible that the Sachs unit will be enough at 9.5 hp, but you have greatly increased the size and weight of the bird, and you don't really want to be flying a warbird at the outer limits ( or nearly ) of the power capabilities of the engine, it makes it more difficult to control. Give the radials a look, really. If you decide to use one, you will not regret it, I can assure you. Hope this helps. Karl"

Back To List

Question 160: "Karl, I’m considering either a SAITO 5 cylinder or the OS 5 cylinder for a 33% Bucker Jungmeister that I’m building from Gary Alan plans (as seen in Model Airplane News a couple of years ago). The model should come in at around 25 lbs. The full size aircraft weighed 1,290 lbs fully loaded, and the engine produced 160 hp. Based on a power to weight ratio, these engines will be just slightly more powerful in the model than the full size Siemens 7 cylinder was in the actual aircraft. Do you have any comments on the OS engine vs. the SAITO. They’re both about the same cubes, but OS offers either a rear exhaust ring or a front mount exhaust ring. I don’t see the same option for the Saito. Technopower also makes a 9 cylinder, but is way more powerful at 4.2 ci. I don’t think my airframe could handle that much engine. Prior to ownership changeover, Technopower produced a 7 cylinder 3.2 ci engine. I wrote to the current owner who replied that in all the time that engine was being offered, only 7 units were sold, so that model was discontinued. Do you know of any SAITO or aftermarket sources for an exhaust ring for the SAITO? Would you recommend a glow driver setup for either of the above engines (i.e. Mac Daniels)? Any one of the above engines will just fit inside my cowl. Do you know of any source for a 7 cylinder, 3.2 ci engine? I’m leaning toward the OS engine, mainly because of the exhaust ring. I look forward to your comments."

Karl: "Welcome to our site, Dr. Kranc, I hope you find it informative. I just realized, and please, I truly do not mean any measure of disrespect, but I spent 4 years studying German and your name literally means "Dr. Sick" in that language, with likely a simple letter change at the end from a "k" to a "c". That's one of those things in life that make you chuckle once in a while. Anyway, onward.

Here's what I can say about this issue. The O.S. offering is slightly more cubes than the Saito, true. If my memory serves me, from some pictures I've seen in the past of Axis WW II fighters and trainers, I think the Bucker did have an exhaust ring in the front. Here's how it plays out, sir; if you want as much scale appearance as possible, then go with the O.S. due to the ring thing. If you mean to compete with this plane, then it will help you garner points. If you are staying conservative on the power, then use the Saito, but without the ring, unless you want to build one yourself. Of the people I have talked to that have a radial in their plane, they all use a glowdriver to start, so the fuel burns evenly when cold, and to prevent the lower cylinders from loading up at idle. The way they do it is to use a switch on the throttle lever to the carb that stays closed at idle and just off idle and maintains power to the glowplugs under these conditions, then opens and shuts off for take-off, flying, etc, and any situation that requires part-throttle position. This is a great assist when you are taxiing or in staging getting the engine warm. I do not know of a source for the 3.2 cid radial right now. You might try this guy, his name is Paul Knapp and owns an outfit called Napco, Ltd. I believe the website is www.napcoltd.com They specialize in the design and manufacture of radials, all gas. Paul is an excellent source of information on TechnoPower, among others. Again I'm sure that is Paul's site, if not, please e-mail me back here to let me know and I'll see if I can't get it for you. Thanks for your questions, Doctor. Hope we can be of more help to you in the future. Karl"

Back To List

Question 161: " Greetings from Brazil Karl;Here goes two questions concerning fuel;First:Our gasoline here in Brazil have a mix of alcohol, in a proportion between 22-to-25% of alcohol(not the metanol kind) to reduce polution emissions, problem is that this alcohol is corrosive for engine parts(cars have especial treatments on engine parts),of course we have millions of small gas engines running with this gasoline, but what about our model engines?What is your opinion about aviation gasoline on model engines?thats here this fuel is not blended with alcohol,I know full size aircraft engine has different combustion chambers and lower compression ratios,but an opinion from an expert will be more conclusive. I guess this question could be especially interested for you U.S. modellers as both federal and local(Californian)U.S. Govt. authorities was here studying this mix to introduce in the U.S. The second question is about glow fuels,What is your opinion about blend our own glow fuels? I would like to do some gallons to use especially on training seasons, big glow engines are "big mouth"you know and fuel cost here is sky height. In advance Karl, I would like to thank- you and this great website for your generosity with these questions, I have already learning a lot from your answers. Fabio."

Karl: "Thanks for the question, Fabio, they are good ones. I could scarcely believe it when you said how high the alcohol content is in your gasoline!! Alcohol is usually good because it burns cooler and cleaner, so generally it is a good thing. Since it has a higher volatility, controlling the burn is tricky sometimes. To try to answer your first question, try using castor oil or mineral oil to the "pump" gas in increments. For example, secure up to 5 single gallon cans of this gas, and keep track of how much oil you add to
each, and run some of each in a test engine to measure things like cylinder head temp, power output, evaluate idle quality, off-idle response, etc. For one gallon, add, say, 2 tablespoons of oil, then in another, 3 or 4 tablespoons, and so on. Run some from each can one turn at a time and record what you find. Adding some oil to the fuel supply may well serve to protect the internal engine parts from the corrosive effects of the alcohol. Try it and see.
Mixing your own fuel can be fun, if you can find ample quantities of nitro methane to start with. Playing with fuels can kill you, so be careful. Nitro doesn't just burn, it explodes, and nitro is the base fuel for glow engines. If I were you, I would do alot of research first, before I ventured into this type of chemistry. Hope these helped. Karl"

Back To List

Question 162: "Question on engines for Ziroli 101" B-25: I'm building the 101" Z B-25 and am to the point of purchasing engines. I was thinking of Zenoah G-38's, but a couple of responders on RC Universe suggested G-26's instead. My problem is that I fly at 3500 feet, so I have some loss of power in the summer (density/altitude). I don't mind the extra power, as I can always throttle back. I was also thinking about Brison 2.4's. What do you suggest? Thanks, Lee"

Karl: "Thanks for the question, Lee, and I apologize for the long delay in answering. First I would like to recommend the Saito 170-3 radial for this plane. It is slightly larger--1.70 cid vs. 1.60 cid-- than the G26 and can swing up to 16 inch props. The radials usually run smoother, less vibration to the airframe which translates into less stress on the frame. You can buy flex exhaust tubing for the engine which will allow you to custom-fit the tubes to the cowls and save the cutting of the cowls for engine fit. The carb's are in the back of the engine so you don't have one sticking out the side or the bottom. Since radial powered planes (in kit form) have the cowl flaps open, utilizing this for air flow across the radial is a natural. One of the coolest parts to this whole deal is, you can buy a ground-adjustable propellor as small as 16" diameter, that can be fit to the Saito prop shaft. Since prop tip speed is a big deal, getting an engine to operate within the rpm limitations of some props is a real problem. There are not yet feasible built-in propellor speed reduction units for the front engine cases for any model radial, so we fudge with smaller props, many props we bring to the field, etc, just to get the right combo. By using a "GAP" prop, you can change the prop pitch to control airspeed and engine speed. Here is the site you should check out: www.soloprops.com This is awesome! Next we need to look at this altitude issue you have. The best thing (in a perfect world) would be to have a sensor in the manifold that worked like say, the MAP sensor on a car; when the fuel demand is up, it automatically sends a signal to turn up the fuel pressure to meet that demand. When you are starting out at 3500 feet, it doesn't give you much of a ceiling before weird things start happening to the fuel delivery. As to the fuel, about all I can say is use a good clunk in the tank and a good tank pressurization system to ensure adequate fuel is getting to where it needs to be. Planes flying at high altitude is exactly why turbos were invented. The turbo and later turbo-superchargers used on P51's and even the radial planes of that day used them extensively to increase reliability at altitude. Consider fabricating some ducting or something that will feed more air to the carb, or at least get it directed to the opening, to have more air for the engine to get at. This, in turn, should let you fatten the fuel mix and alleviate this lack of power thing. Hopefully this can help you. Karl"

Back To List

Question 163: "Hey Karl Firstly I would like to thank you for all the great work you do. I am in the process (too late to turn back now) of building a 1/6, 74" span Mustang which should (he said optimistically) come in at around 15 lbs. What would be a nice 4 stroker to power her around. Also I would like to run a 4 blade prop so what would you suggest. Thanks in advance Glenn, Townsville Australia"

Karl: "G'Day, Mate and thank you for visiting our site. Glenn, have I got the engine for you!! Take a look at Saito's 200 Ti twin. It is a shallow vee design for narrow cowls, runs 3 hp and looks and sounds real cool!
Bolly might have the prop you need, since they make alot of 3 and 4 bladers. If you don't have any luck with them, try this place www.soloprops.com and ask if they have anything that will fit that crank. They are slated to have a new 4-blade ground-adjustable-pitch ( GAP ) prop out by February, so check in with them. They are definitely the "go-to" people for props of that type. Your plane, at 15 or so pounds, should fly pretty well with a diameter ranging 16-20 inches, and pitch range 8-12 ( assuming you want a more scale look to the prop..). A GAP prop would fit so many flying conditions, yet with any other you would have to buy several different props and remove and install them until you found the best combination, and by that time the conditions changed yet again so all of that goes out the window, mate. One caveat here, Glenn. Solo Props is in Canada and you are in Australia, so be up front with Solo if you contact them, so you don't have any shipping headaches, savvy? Anyway, hope this helps, pal, and happy flying. Karl "

Back To List

Question 164: "Hi Karl, can you advise on best engine/prop set -up for the vailly fw190; and the reason for your choice?
Many thanks Keith"

Karl: "Thanks for the question, Keith and apologies all over for taking so long to answer your question. I think the perfect engine for such a fine airplane is the Saito 450 R3D radial. It'll swing a 22" prop, has plenty of power for scale flight and is well suited for any 1/5 scale plane with a round cowl. You can visit www.keleo-creations.com to see what they have in flex exhaust tubing or exhaust ring for this engine. Then try www.soloprops.com and see what they have in propellors for the same. You will not be disappointed, my friend. It might even work to adapt the scale FW 190 prop fan to aid in the cooling of the radial, should you choose to install that one. A long time to wait for such a short answer, sorry pal. Happy flying and I hope this helps. Karl "

Back To List

Question 165: "hi Karl, is electric flight included in your specialty? I would really like to know if there is some trick to match the best prop with the right engine. Could you help me out? happy landings, J-W"

Karl: "Thanks for the question, Jan. Is that Dutch, by chance? My family ancestry on my mother's side is Dutch, so some things sound familiar. Electric's really don't float my boat so I haven't spent much time at all researching them. This much I do know, and that is electric technology has grown leaps and bounds the last 10 years or so, and through some subscriptions to a couple of RC magazines I can catch some of the latest. One thing that is a big deal regardless of how much amp-hours your motor is capable of, is the parasitic loss of charge above normal use, caused by a prop that is too aggressive for the motor. Many of the same principles apply for electric's as gassers or glow engines. Start with a target weight for the plane, then what type of power you're going to use. What kind of flying, and these will likely point you to an appropriate prop for the airplane. Too low of a pitch and you'll have great acceleration and higher rpm, but no top end; too steep of a pitch and you'll have the opposite. Then add diameter, blade count, etc. Another thing that is similar is the power-to-weight ratio of engines. If you want more power, it will inevitably result in a heavier engine. In electric's, this is accomplished by windings of copper wires, stepped or series.mounted capacitors, larger heat sinks, armatures and so on. Copper wire is metal and gets heavy fast. At least in a fuel-burning engine you have the possibility of making more power without adding weight---to a point. Jan, I hope this helps at least a little. Like I said, electric powered models just aren't what I am very interested in in terms of building and flying. I peruse the articles once in a while just to stay informed as a modeler. Thanks again for the question and happy flying. Karl"

Back To List

Question 166: "Karl, I am considering getting a Saito 450R3-D, 3 cylinder engine. It is 75cc, 5.5hp weight 2950g. Overall length 200mm, Diameter 250mm. Can you recommend any radial warbirds that this will fit in? Ideally the aircraft should weight under 40lbs 'wet' otherwise due to CAA and UK reg's the aircraft has to have an inspection and certificate of airworthiness. It's a bit involved and I don't want to get into that. If that is too big for under 40lbs models what about the Saito 5cylinder radial Dia:220mm, weight 2400g, 3.8hp, 53cc, length:170mm. I really like the thought of a radial, but obviously don't want to choose the wrong engine, or aircraft, especially if I end up chewing the cowl, to fit the engine. thanks, (sorry for all those stats) Chris"

Karl: "Hi Chris and welcome to our site. There are plenty of birds to choose from for the awesome 450 R3 radial. It will fit most 1/5 scale birds such as my favorite, the F4U Corsair, and these--P47 Thunderbolt, F8F Bearcat, F6F Hellcat, Douglas Skyraider, SBD Dauntless, Helldivers, A-T6 Texans, T-28 Trojans. On the axis power side you have a variety of Japanese planes, the Kate, the Zero, and I think the Betty bomber was radial powered. I'm pretty sure the German FW190 was also. Most of the German planes used water-cooled V-12's, the plans and castings for which they obtained from a then-too-willing-to-pacify Great Britian in the early '30's under the guise of "international commerce" and friendship. Yeah, right. Anyway, once you study warbirds for a while, both axis and allied, you will find a veritable plethra of planes to choose from. Maybe I mentioned one here that you want to build, but you may still choose one that hardly anyone else has ever built. That's part of the beauty of this hobby, pal. The 5-cylinder radial from Saito is real cool for it's looks and sound. You should go to this site and ask about a suitable propellor for these engines, you won't be disappointed--www.soloprops.com . Hope this helps, Karl. "

Back To List

Question 167: "Hi, I plan to mount a 3W 75i in a Vailly Tempest. When I had purchased the engine I also took the suggested 3W muffler and manifold for the 75i, which are ~12inch.. and ~5inch. in length respectively. In order to fit the plane the muffler has to be run through the firewall and into the forward area of the fuselage. I inquired about a smaller muffler and was basically told "Bad idea, the engine won't run properly." Could you explain to me how true is this? Also, if I may, If the 3W muffler is installed. In regards to heat, would you suggest closing-off and insulating the forward area of the fuselage occupied by the muffler, from the rest of the internal fuselage area? Thanks very much for any help, John, Switzerland"

Karl: "Welcome to our site, John, and all the way from Switzerland, no less! Cool ! The folks at 3W, or whoever gave you the input about mufflers are correct. A 2-stroke gasser engine relies heavily on backpressure for proper operation. This is accomplished by changing the lengths, diameters of the pipes and baffling inside the muffler itself. In circles other than RC planes, the muffler portion is called an expansion chamber. When the exhaust gasses leave the engine they are hot and moving fast. The chamber allows the gasses to cool somewhat and the baffles control the pressure that pulses back to the engine. The diameter of the chamber, the length make all the difference. As an example, a good friend of mine races high-performance go-karts with high-tech 2-strokers on them, and if he changes the length or other size of the expansion chamber too much, it can mean the difference between 1st place and last place. In RC planes, this pressure in a properly designed chamber will help maintain a steady idle, smoother transition to part-throttle and better top-end. If you change too much or if the engine already is designed with too narrow of a window of acceptibility of mufflers, you will kill the performance. Remember, what ever changes you do make, bench test the combination first so you don't loose planes.

Now, as far as the heat deal, I would recommend insulating the formers which the muffler passes through, and build in some way to draw cooling air back into that part of the engine compartment soas to keep the muffler from causing a bon-fire of sorts, with your airplane. Hope this helps, John. Thanks, Karl. "

Back To List

Question 168: "Hi Karl, I'm building a top flite 1/7 scale spitfire and I'm planning on using a super tigre G90 for power. What in cowl muffler do you think I can use?? Thanks, Roberto"

Karl: "Thanks for the question, Roberto. One thing you might try is simply add some pipe to the length, and use a Pitts-style muffler since it would have bottom exits and could fit nice and compactly. One other option would be to buy a Saito 200Ti inline twin and that would fit inside the cowl nicely, plus have an exhaust system for it already. Hope this helps, pal. Karl. "

Back To List

Notice: Questions or statements regarding product quality and/or usage are solely the opinion of the writer and not necessarily the opinion or recommendation of rcwarbirds.com or rcwarbirds.com owner/webmaster. By asking a question you are giving rcwarbirds.com or rcwarbirds.com owner/webmaster the right to post your question and name on this page. Not all questions are answered or posted. All questions and answers are copyright rcwarbirds.com


Join Our Email List

Become an RCWarbrids site supporter by making a donation.


The Web