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 4: Questions 121-144, click on links or browse page.
Q121 Engine for Meister P-47 ? Q133 Too much carb pressure on G-38's ?
Q122 3 blade props for VQ P-38/Saito 72? Q134 TF P-51 4 blade and scale exhaust ?
Q123 Straight pipes for a Saito ? Q135 G-62 carb replacement parts ?
Q124 Ziroli B-25 engine choice ? Q136 Four blade prop on Top Flite P-51 ?
Q125 1.20 for 7th scale Spite ? Q137 LA .46 vibration ?
Q126 G-23 hard to restart ? Q138 Engine for Top Flite Corsair ?
Q127 Coleman fuel for gassers ? Q139 Variable pitch props ?
Q128 Carb relocation ? Q140 Saito four strokes ?
Q129 Modified exhaust and overheating ? Q141 Large four blade props ?
Q130 Moki 1.8 prop extension ? Q142 4 strokes for three engine bomber ?
Q131 US 41 gear drive ? Q143 Motor quits in vertical ?
Q132 Engine for a 78" Antonov ? Q144 GSP FW 190 engine ?

Question 121: "KARL, im building a meister scale p-47 razorback with a custom built glass fuse, wing will also be glassed, approx ready to fly wieght of high 40's, would like to overpower it incase i get into a situation, was thinking on a quadra 100 gas with electrinic ingition, whats your thoughts?"

Karl: ''Thanks for the question, Mr. Williamson, I think I have some good suggestions. When researching for the answer to your question, I learned that the plane you are building is targeted for 35-40 lbs. and is 102" w/s. Now, to achieve what you want in power, there are many choices, and the engine from Quadra is a good choice, however, I feel compelled to encourage you to think outside the proverbial box and look into some awesome engines that not only are well-proven and make better power, but are overlooked by many rc'ers. One is the 5-cylinder gas radial from 3W (Cactus Aviation). I don't know the cost, but it has electronic ignition, makes a little more than 13 hp, and measures 12.79" across. The other engine is the RCS 215 gas radial, also 5 cylinders, also electronic ignition, it does have an advertised horsepower of 13, measures 11.7" in diameter and costs just less than $2,500.00. The other engine is a glow engine, 7 cylinders, 10 hp and costs $4,000.00 from Robart. Now, you have lots of potential with props here with all these engines since they are larger and can swing a larger prop. More diameters and pitches to play with. For scale operation and appearance, all of these will fill the bill. The limiting factor will be the diameter of the cowling, as to whether or not they will fit and of course the depth of your pockets. If none of these prize-winning scale features interest you, then, yes, the Q-100 is ok, but may seem anti-climactic, in my opinion. The sight of a round engine and prop pointing towards the sky is as right as rain, my friend. Hope this helps. Karl."

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Question 122: "Karl I have recently come across a VQ P-38. I purchased new 2 Saito 72s..What sz 3 bladed propwould you recommend for this engine/plane combo..Thanks , Mike"

Karl: ''Thanks for the question, Mike. After looking at the size of the plane, the engine choice and projected weight, (which is usually subject to change during construction....) I think a prop that is scale diameter would be the first choice, then deal with pitch. I don't know about you, but even in a P-38 model, when you see a 3-blade of scale diameter swinging around, it just gives you that warm feeling all over that all is right in the world, savvy? I know this plane comes with a 3-blade spinner, so that's what to shoot for. As for the pitch, this engine--unless the info is a typo---handles a bigger prop than the FA 80 does. Go figure. Try to not overload the engine with prop load. Larger prop means lower rpm, which is good since it saves the engine, but I will state here again some of the basics---larger diameter, lower rpm, more blades, less pitch. It can be confusing because one thing affects another here, we are talking about surface area of the prop blade that is available to move air. A propellor basically is like the plane's wing, but vertical and spinning. That is why you see so many larger planes with small 2-blades because they are using engines that spin over 10,000 rpm to make power. Your choice of the 72 4-stroker is a good one, and the best prop to use may actually turn out to be more than one prop, so look at props in the range of 13x12, 13x10, 14x8. Hope this helps. Karl. "

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Question 123: "Hi Karl, I was wondering if you could help me with this, I just got on the list with KMP for one of there new B-25s and im looking ahead to motors. I like the new saito 82s and think they would be a good combo, but my question is the exhaust pipe on saito comes straight out the side with a muffler pointing straight back witch would look ugly. Can you run a 4 stroke on a straight pipe (5 or 6 inches don't know yet) and have enough back pressure to feed it? This way I could keep the exhaust inside and it should sound even better. Sure hope you can help. Thanks Karl, James"

Karl: ''Good question, James, thank you. First, when looking at Saito's stuff online, I didn't see the '82' to which you were referring, so I looked at the next posted size up, the .91. This engine should be quite adequate for the plane, provided it isn't more than say, 20 lbs or so. As for the exhaust, it shouldn't be hard to bend some pipe around to fit the cowl---you can use hand-held tubing benders for this, and get it to go where you want, and even have the exit in the scale location between the cowl and firewall. I can't say with absolute certainty about this as it pertains to this RC engine, but from a physics and engine pressure perspective, if you run open pipes, what you lose in pressure from a muffler, you can recover with length of pipe, savvy? With any engine made, if you make the exhaust pipes long enough, eventually you will have low, low pressure at the exit--if it's even measurable. Of course, these would be pipes of unreasonable length. So simply changing the pipe length will affect the performance to be sure. I recommend looking into using the head-end of the pipe to attach to the engine, and seeing if bending one around to fit the space works, then braze the bent tube to the section coming out of the head. Can be done. Hope this helps. Karl."

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Question 124: "Karl, I plan on using RCS 1.40 engines in a Ziroli 101" B-25. My choice is based on the fact that the engines just fit within the cowl and this will help maintain scale appearance. Thrust calculations with 18/10 3 blade props come out to near 19lbs thrust at 8000 RPM. The aircraft with these engines will come in at about 30 - 32 lbs. Am I making a mistake with these engines? Iran"

Karl: ''Thanks for the question, Iran. Here is my opinion about this. I think the RCS 140 will be just under what you are going to need. It isn't rated for an 18" prop and you will need the extra rpm room on occasion, and this size limits your prop choices. After looking at the 180, I think that would be a better choice, as you DO have more rpm room, you can play with props better ( blade count, diameter, pitch, etc...) and perhaps one of the most overlooked benefits is the lower rpm required to get the plane in the air doesn't cause so much wear and tear on the internals. Hope this helps, Karl."

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Question 125: "Hi Karl Another question from across the pond. I mailed you a couple months back about an engine choice for a 1/7th scale top flite gold edition spit (Page 5 question 99). I went with your advice and got hold of a Saito 1.20. What a beautiful piece of engineering this is. My question is.... with this fitted the planes all up weight is 12lbs....... am I going to get of the ground with this weight. I'm a little worried about the high wing loading and the high flying speed I'm have to maintain to stay in the air. This is my first warbird and I'm a little worried about going home with the plane in a refuse bag after my first flight. Thanks in advance Dave"

Karl: ''Again, good to hear from you, Dave. The 1.20 should be fitted with a prop that is close to the maximum diameter soas to get the most efficiency out of the engine/prop combination. Looking at your projected all-up weight, the engine and all, I can see how the wing loading is a concern since the spit's had broad chords for the wings. I could not get a power estimate from Saito about the 1.20 but it classifies as a big single, and with a 14-16 " prop, getting off the ground should work fine. When you dial in the engine, always bench-test first, work out as many of the bugs here as possible. Many users of these engines state that very little time needs to be spent on valve-adjustment, carb tuning, etc. , that they can just set it and forget it unless you are changing nitro content in the fuel. Go with a 3-blade, really. Not only were 3-blades on the production planes, you can easily find a 1/7 scale prop for the spit that should add to scale realism as well. Hope this helps, Karl."

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Question 126: "Hi Karl, I,m new to gas engines and I'm having starting problems with a G 23 It will pop and crack a little and even run for a small amount of time, but it is very hard to restart. help! thank Robert Cline"

Karl: ''Thanks for checking us out, Bob. Gas engines are pretty simple but can be a little frustrating at times. In this case, check the spark plug for gas fouling. You'll know this when you remove it from the head and it smells strongly of fuel, has a shiny sheen to it and looks black or dark brown. Try to ensure you have adequate compression by removing the plug and installing a compression gauge (standard automotive spark plug thread should work here...) and crank several times while observing the gauge. Should be around 100 or a little more. If the plug is gas fouled, change the plug, recheck your carb settings and start out a little lean, but richen somewhat quickly after it starts so you don't burn a hole in the piston. The optimum setting will let the engine idle in the spec' range for several minutes. Recheck at say, half throttle and make a few rapid and a few slow transitions in the throttle position to see how response is. Smoke will be plentiful but shouldn't be as a large dense cloud. There should be no hesitation, bogging or shutdown during any of these tests. Last, if you want, check at wide-open throttle briefly to see what rpm you have. Correct tuning of the carb and fuel equates to higher rpm's, especially in a 2-stroker. Also check continuity and connection of the plug wire. Obviously if there is a poor connection you won't get all the juice to the plug where it needs to be. Hope this helps, Karl"

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Question 127: "Hi Karl, What is your opinion on using Colman camp fuel in our two stroke gassers? I know your are going to ask "why use it". One is the odor of gas in the car/house and two is how clean it burns. I looked at a friends G26 with 15+ gallons through it and it looked like new with minimal carbon build up on the piston/exhaust port area. Perhaps running Amsoil at 64~80:1 may have an influence. Best regards, Jim"

Karl: ''Hello, Jim. There are a couple of benefits to using Coleman fuel. The best ones are what you mentioned. Coleman fuel is still a hydrocarbon-based fuel so it will be fine in the 2-strokers. I have heard of several rc'ers that fly their gassers on it and rave about it. The fuel is plentiful, it doesn't require as much lube, though, if I'm not mistaken. Plus, it burns cooler so there would be less risk to your plane's finish via the exhaust heat. Happy flying. Karl "

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Question 128: "Karl, I have a Sachs 4.2 that I am putting in a ¼ scale P-51. My problem is the carb will stick out the side of the cowl…which is not acceptable. Do you know of a retro fit to move the carb to the rear or…is there another recommendation for an engine with rear carb? Jeff"

Karl: ''Thanks for the question Jeff. What will likely work real well is to buy some bulk aluminum tubing that is slightly less diameter than the carb outlet below the throttle plate ( probably no more than .030" smaller on a side, for an overall reduction of .060"). What the reduction will help do is maintain some of the velocity of the air going into the engine. The velocity is crucial and when you lengthen the path for the air/fuel, you lose some of that unless you compensate elsewhere. It is very easy to use a dremel tool to gently round the edge where the tube adapter plate meets the carb. So what you will need is about a 1/8" thick aluminum plate to match the carb base. Make the tube of sufficient length and configuration to relocate the carb, say, more to the rear, or lower towards the intake under the cowl if the engine is inverted. Then it will be possible to cut and adapt the new tube section to the flange where it mates to the engine. Weld these components together with a tack weld so it is easier to cut them if you have to tweak any angles. Give it some thought before you start, so you will minimize the cutting of metal, reduce downtime and cost. Hope this helps, pal. Karl "

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Question 129: "Hi Karl, I'm curious as to whether or not, a mod I made to a Qaudra 75 exhaust will create any problems such as overheating? It is in a Meister P-47, and has a stock muffler with 2 stacks. I didn't want to cut the bottom of the cowl for the exhaust to exit, so I cut the stacks down to about 1" in length, ran flexible copper tubing out the P-47 dummy exhaust and connected them to the muffler stacks with blue heat resistant tubing (used on tuned pipes). Basically all I did was in essense, extend the exhaust stacks about 8 1/2" each. I haven't run up the engine as yet, but hope to this weekend. Do you think this will create a problem with cooling??? Thanks,
Rob Bailey"

Karl: ''Thanks for the question, Rob. The only thing that I would watch for is how the wavy or corrugated interior walls of the copper tubing might cause a baffling effect and slow the exhaust flow, which in turn could cause over heating or loading in the engine. Always check engine temp as you test, if it is safe to do so, put a hand or something else to monitor the exhaust flow at the exit while the engine is run up. If it seems to really push away what ever you have in front of it and some effort is required to keep the test material close to the exit hole, then I'd say the beast is flowing pretty well, savvy? Other than that, I can't foresee any problems. Karl."

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Question 130: "Dear Karl, I am building a 1/5 scale Mark V Spitfire using a Moki 1.80. I wonder if you know any source for a 1 inch prop extension. I want the extension so I can have room for a hinged air inlet door to preserve the scale appearance on the ground. Without the extension the door would block the carb. Also, I am using a J-tec inverted muffler, but I have heard rumors that without plugging one outlet I might not get enough pressure to the tank. Can you confirm or deny this or suggest a better choice? Thanks, Barry"

Karl: ''Thanks for the question, Barry. I received your question the same day the movers disconnected my computer since we relocated to another state and just this week got my computer back up and running so I apologize for the delay. Based on what you told me, I think some internal threaded stock would work as the extension. There are a couple of ways to do this 1) you use a 2-piece system where you install an internally-threaded sleeve over the existing prop shaft and then install another piece of threaded stock into the other end after attaching it to the prop shaft. Use threadlock on each end. The trick would be to relocate the prop hub adapter's rear section so it still maintains the clamping force necessary to hold the prop on the shaft. 2) you use again a piece of internally-threaded stock so it will attach to the prop shaft. Install a spacer behind this that is sufficient to fit over the sleeve and the shaft so it contacts the existing flange on the prop shaft at the engine so you have the clamping capabilities. Once you have these pieces installed, try to weld them together to make a one-piece adapter that screws on to the Moki and when you need to change engines you won't damage anything. If at first you don't think these ideas will work, all you have to do is inquire of other pilots or the local hobby shops and see what they say. Necessity is the mother of invention, savvy? I don't know about the muffler issue, though, sorry. All I can say is that if there is low internal pressure in the muffler, then, yes you could well suffer from fuel starvation, but mufflers are all different so I can't advise on that particlular one, sorry. Hope this helps. Karl "

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Question 131: "Hi Karl, my son and i are building a B. N. P51 102" WING, we are useing a us41 engine, don't care about speed.My son wants to keep every thing in side the plane.Is there a Co.that makes a Elect Start & Gear drive that will work on a 41? We also want to try and use a 4 blade prop.Thank you, Bill "

Karl: ''Thanks for the patience and the question, Bill. I spend alot of time reading through the RC magazines and the only trick thing I have seen along these lines electrically is an alternator to install on the back of some engines to keep the batt's charged and so on. I have not seen nor heard of an electric start for that size engine and when you say gear drive I have to assume that you are referring to a prop speed reducer. That said, in my research over the years I found that Byron made a P.S.R.U. (propellor speed reduction unit) in the late '80's that was killer and fit most 1/5 scale and larger planes, but I haven't been able to find who makes it now or if there is a new one on the market. As far as the 4-blade prop, there are some foreign companies such as Fuchs that might, but they are expensive for a scale size 3 or 4 blade if you are in the 1/5 scale and larger realms. There is a great company in Canadia that makes an awesome propellor for large-scale planes ( a 32" 3-blade with ground-adjustable-pitch was quoted for my plane as only $189 and some change...). They tell me they are working on a 4-blade system but it might not be available till close to the end of the year. Hope this helps. Karl "

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Question 132: "Hi i have a very important question i just finished a 78" in wingspan Antonov-2 its pretty much scale the whole weight of the model is 5 to 6 pounds but the problem is that i dont know what should i use to power it what engine size what prop can you point me in the right direction. Thanks Tommy"

Karl: ''Hi Tommy. Obviously, the trick is to find the engine that is right in the middle of the power needs. Too small and the engine works too hard to do its job. Too large and the plane is nose-heavy and, believe it or not, works too little. Since the plane is light and has a 6-ft-plus span, you might look into the Saito FA 56 or 72. You might want the smaller one since the prop sizes are more reasonable. But props are a whole 'nother ball game, pal. You will have to play with prop blade count, pitch and diameter to find the
perfect prop for this plane. Hope this helps, Karl."

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Question 133: "Karl, I have a twin with 2 G-38's. The engines are tightly cowled and only the volostiy stacks of the carbs stick out. Bith engines run well on the ground. When The plane leaves the ground both engines go really rich and sould terrible. I have flown the plane 3 time like this and will loose it if I don't get this fixed. I have been told that the Daiphram is getting to much pressure and is making the the diaphram press in causing it to go rich??? What does it sound like to you....I am planning on venting the daiphram back in the nacelle to get away from the pressure in the cowl...Is this right ??? Ty"

Karl: ''My opinion here, is, Ty, that you relocate the carb behind the engine via a fabricated manifold that adapts from the carb to the side of the cylinder. It sounds like what is happening is the air pressure at flight speed is too much for the carb. If the diaphragm is atmospherically adjusted, this would present the problem. By putting the carb intake out of the direct airstream around the cowl, this stabilizes the carb's internal fuel metering capabilities and should remedy this problem. I'm glad you have been lucky so far and haven't lost the plane. The next thing is to take extra time to readjust the carb at as many rpm levels as it might see during flight. Make sure it doesn't fatten up or lean out. Both of these are bad, savvy? Hope this helps. Karl. "

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Question 134: "hey karl, i plan on useing a 4 blade prop with a reduction drive and working manifolds for my top flight p-51 1/5 scale but im not sure what engine i should use..i want it as scale as possible and i want it to fit totally in the cowl..and where can i find a reduction drive for a scale 4 blade prop.thanks Alan"

Karl: ''Whoa, Alan you sure know how to pick the questions, pal! Not to worry, it's not a bad thing. One option you have is to bump up the scale of the P 51 to 1/4 scale and go to this website: www.quarterscalemerlin.com and prepare to be so amazed it might make you cry. The "merlin" in the site name does in fact imply it is a 1/4 scale merlin V-12, pushrod, gear reduction for the prop, water pump, supercharger, the works. Since they sell it in rough casting form, this would set you back several months or years to build, but alas, you would get what is commonly known as a PSRU (Propeller Speed Reduction Unit) because this engine is THAT scale. You can buy all the castings and plans and have a mcahine shop do all the machine work. Then you have to ask, is it worth it? At least look at the site FYI.

Another option is to ask Byron (Iron Bay Models) if they have any left-over or unsold psru's. This would help alot since there aren't very many in-line twins or larger 4-strokes to do this job. If you know how to do any mechanical drafting, you could design your own set of gears, brackets, chain or belt drive, engine mount, etc. Necessity is the mother of invention, they say. These answers may not be what you like, because if you are like me, once you start a project, you want to see it through to completion not dawdle along the way with changes or other delays, savvy? I am trying to put myself in your shoes and ask myself what options I would have in a similar situation, Alan.
In the engine department, the weight of the plane will determine alot of the engine choices. Saito has a beautiful in-line twin that was specifically designed for narrow-cowl applications. But alas, it is too small at only 3 HP. Doesn't swing a scale-sized prop. I looked into ZDZ, Zenoah, O.S. and Cactus Aviation and after all this, I think probably your best bet on an engine is either a G38 or a G45. Again, the weight of your plane will be the determining factor here--this includes the weight of any and all scale items you build into it.

As far as a scale 4-blade, I didn't have any luck. One company to look into is the Fuchs outfit. I used to have their contact info but since I moved I haven't been able to find it. They are a Hungarian company if my memory serves me, and they simply have an outlet here through some other company. Fuchs makes large-scale props. You will be swinging a prop at least 20" across and none of the engines I found can handle that, except for maybe the G45. Again, the ability of the engine to swing a prop depends on the power band you are looking to operate the engine in most of the time, and how aggressive the prop is. One outfit to look at is one called SoloProps and they are in Canadia. My friend Jack turned me on to them and even though they only have scale 2 and 3-blade props available, I know they are working on a 4-blade set-up. This IS a company you should check out---I won't spoil it for you, just go there,

Anyway, the answer was long, but I hope it gave you some needed info. When you are selecting a prop, engine and so on, things can get confusing with all the details to consider, amen? I'm glad you came to us and asked this question, Alan so thank you. We have many excellent advisors here at RC Warbirds and if we can keep on helping you in this endeavor, just keep asking. Thanks, Karl. "

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Question 135: "Hi Karl, The Carb throttle plate came loose somehow in my G-62 Carb. Now its all boogered up, and must be replaced. The Carb is a Walbro HDA-48D. I can't find anyone who sells the little carb parts, just an entire replacement, any ideas who might? Thanks"

Karl: ''Thanks Lee. You and some others might scoff at this, but let me explain something first. The engine is a G-62, a 2-stroke gasser. The carb is a Walbro, which is very common on many other 2-stroker applications. I can tell you from fact that you can find carb rebuild kits from many lawn-mower and other gas-powered lawn care apparatus outlets. There is a place near my former home that sells John Deer tractors, Homelite saws, line trimmers, etc. Even 2-stroke lawn mowers. This shop also sells overhaul kits for nearly every engine that powers the lineup of products at this store. I have seen Walbro overhaul kits go across their counters a couple of times. What I am saying is that instead of limiting your search to model stores, try a regular lawn and garden equipment store. I had a Macollough(spelling) weed-eater and it had a Walbro. Same for its replacement, a Homelite. Give it a shot, Lee. Hope this helps. Karl "

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Question 136: "I have a giant size (83" wingspan) Top Flight P-51 with a Zenoah G-62 engine. I want to put a 4 blade prop on it. Can you tell me what pitch and size I should use? Also, where can I purchase the prop and spinner. I have not been able to find anything at master air screw or iron bay models. I have seen several P-51's that have a Mentz prop or a Bryon prop on them but I am unable to locate these companies. Any suggestions will be appreciated , Frank"

Karl: ''Thanks Frank, you can find the Menz props through Cactus Aviation or Desert Aircraft. They are really good props, and should do you well. I don't have a clue on the Byron, though, sorry. you might want to look at an outfit in Canada called Solo Props They have a 4-blade ground adjustable pitch prop abd hub system that is second-to-none so if you want the scale size and blade count, check with them. Hope this helps. Karl"

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Question 137: "Hi Karl, I'm preparing my C-130 for the "first flight" and noticed that the engines seem to vibrate a bit much. I'm using O.S. L.A. .46's (non-ball bearing). I have balanced the props, so I'm confident that this is not an issue. I do detect some "flex" in the engine mounts, which consist of 7/16" thick aircraft plywood, vertically situated with the engines in a side mount configuration. I'm going to reduce the "flex" in the engine mounts to minimize the vibration.
I have two questions:
Q - Is the "flex" in the engine mounts a "cause" or "symptom" of the vibration?
Q - If I used "Ball Bearing" type engines, could I expect substantially reduced vibration?
Thanks, Joe "

Karl: ''Thanks, Joe. There are a couple of things going on here. First, balance is balance. Regardless of roller bearing shafts or babbit bushing style, if the assembly is balanced, it should vibrate little. The second is the prop. Static balancing is good, but you don't fly the plane with the props at a stand-still, savvy? The prop is spinning at least 5,000 rpm and this is where the dynamic balancing has to be right on. I believe it should be done on all planes 1/6 scale and larger. After all, they do it on real planes, why not RC? Under the physics loads the prop endures when taking off, flying, etc, it takes on a whole new set of problems to overcome. Blade flex, tip speed. The reason you see so many large or multi-engine birds with small 2-blade props is because the engine can't swing a scale-sized prop and fly the plane, the engine spins too fast. You can't always put a larger engine on the thing, wrong size, too much money, whatever. So they use high-revving engines and a little more pitch to rely on the rpm's to fly it. Since in the manufacture of the props the utmost effort is made to ensure accurate mold conformity/uniformity, what have you, the makers are still at the mercy of the physical properties of the plastic or carbon. This is reflected in the mass of each blade. Now, you can static balance the prop, and this is a good start, but the prop has to spin, and if the mass is different between the blades, you will have a vibration. That's why with full-sized steel props they magna-flux and x-ray every blade before it gets used on a prop, and with wood props they cure and dry the wood in batches to match, so the density is consistent, get it? So you still could have a prop problem, so see what recourse you have there.

As for the engine mounts, this is difficult to a point. If the mount is loose from the get-go, the engine will move around on it and eventually fall off if not addressed. But if it starts off solid and gets looser, then you have an engine problem. You might even try different engines---a different O.S. offering, or go with a Saito or Magnum. Lots of engine options that are very good. The other thing to consider is the attitude of the engines in relationship to the fuse. Do they follow the chord parallel or do they have a slightly nose-up attitude. Reason I mention this is maybe the engines are working against the airframe too much and it is showing up at the mounts. Look at the plane from the side, as if in level flight, and see how the engines are situated. If one appears to want to point up, another is to the left or appears to be pointing more downward, then fix this first. You don't want the engines working against eachother. Hope this helps, good questions, Joe. Karl"

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Question 138: "Hi Karl, I am in the early planning stages of a Top Flight Giant Scale Corsair build. I am trying to determine what engine to use in this bird. This is going to be my first large scale plane and I have no gas experience. I thought about sticking with a familiar glow engine and using the Super Tigre G4500, however, maybe I should just take the plunge now and get into gas. This plane is a bit over 1/5 scale and will weigh around ~26# +/-. Can you recommend the perfect engine for this bird? Thanks! Regards, Steve"

Karl: ''Yes, Steve, I can recommend the perfect engine for this bird, but you won't like the price. First, let me share a bit from my own experience. Over 2 years ago I started researching RC planes since so much has changed since I did some as a kid over 25 years ago. I decided on my plane, then power, then details, demarcation, and so on. I went through several engine choices. I had decided that mine would have radial power and I was not budging on that. One choice was a 4 hp glow radial and I was told it would not be nearly enough to get my 1/5 Corsair off the ground. I looked into the gas radials from RC Showcase, Desert Aircraft and some others and they were too big for the cowl. It would have to be flown with out it or cut up. The only place that had the right engine, the right size and the right power was Robart. Their engine is a masterpiece, pal and it sounds awesome! This, of course, only applies if you had decided on radial power as have I. In the gasser category, you have so many options. Zenoah makes perhaps the most reliable gasser 2-stroke around. They all have electronic ignition now, I think, so misfires and stalls are hardly a problem, as far as ignitions go. I have seen both in operation and I think the G-series would be a good place to start. There are many features that make one engine more desireable over another, so you will have to do some shopping as well. As for me, my "thing" is if a plane was built with a round engine, put one in it, if possible, in RC. When I was a kid, if you had a 36" ws plane, you had a big plane. Now we have fully functional jet engines with afterburners, a full-detail 1/4 scale Merlin V-12 with water cooling and supercharger! Times have changed indeed. Hope this helps you, you picked a good one to build, good luck. Karl"

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Question 139: "Karl, I am looking for the variable pitch product that Gerard enterprises used to import. Do you know of any similar product on the market? Regards, Arturo Z."

Karl: ''Hello, Arturo, and thanks for visiting RC Warbirds. As a matter of fact I do know of an outfit that could likely fulfill your needs very well. My friend Jack Devine turned me on to this company when I was looking for a prop for my own project. The website is www.soloprops.com and they have props from 16" to 32" diameter, all ground-adjustable pitch, wood blades and all balanced. I am not familiar with Gerard Enterprises so to that I cannot comment. Solo props should be able to fix you up real well, so give them a look. Hope this helps you. Karl "

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Question 140: "Karl, What would you consider the most reliable and economic four stroke on the market today? I am looking at starting a new project (Don Smith B-24) this year and need some advise on which engines would be best. Thanks for you time. James"

Karl: ''Thanks, Jim. Saito, Magnum, Evolution and O.S. all make great four-strokers. I recently watched a guy fly a bipe at one of the fields near my house and the sound is quite unique, to be sure. For many reasons I would recommend any suitable size engine from the Saito line. They aren't known as "The Four Stroke People" for nothing, y' know. Their design has improved air flow around the head, for cooling, the valve train is easy to access should you even have to. I spoke with another guy from a hobby shop by where I live and he said he has used a Saito for years and never had to adjust the valves, even. That sounds pretty reliable to me, pal. Just remember, when you are looking at selecting the engine for any given plane, I like the rule of thumb that what ever the max recommended engine size is, go just one size bigger. The reason I try to go by is that you will have more reserve power when needed, there is less wear and tear on the engines since you can handle bigger props or more aggressive pitches. The less the engine has to work to get the bird in the air, the better and happier they will be, whether you have a single engine or multi's. Hope you find this helpful, and good luck with the B-17. Karl"

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Question 141: "Hello gentlemen I am waiting for some plans to build a giant scale p-51 mustang but am getting some parts together now and need some advice..I am building a plane with a 102" wing span the plane will weigh approx. 15 to 25 Lbs. i am using a built 31cc homelite engine and need to know what size prop to use. I would like to use a 4 blade maybe a 20x10x4 or a 22x10x4 which would you use i would like to stick to a 4 blade for realizm, also where can i buy these props... Thanks....Chuckie.... "

Karl: ''Hi Chuckie. This question of scale sized props for warbirds has become a popular one lately. Again, I am pleased to promote a company in Canadia by the name of SoloProps. Their site is www.soloprops.com As of now they only have 2 and 3 blade versions, but one of their engineers told me this summer that by late fall they should have a 4 blade hub and blade unit for sale. The whole principle is based on having a scale-sized prop that you can also fly with. Over a year ago when I was researching this same topic I was told it couldn't be done simply because the prop tip speed is supersonic when a scale-sized prop is used on a 1/6 scale or larger warbird, and when that happens, it basically comes apart very fast. Bad thing. The whole deal is to have a prop that you can change blade count and pitch in order to compensate for prop speed and engine combinations. For my project I am using radial power so this was crucial with out a speed reduction unit. Solo Props has what are called Ground Adjustable Pitch (GAP) props and are state of the art, balanced, CNC machined and made super-easy by making all blades adjust simultaneously with one adjustment provision. I don't own mine yet so I have not been able to investigate its operation. I suspect that by the time you will actually need the prop, their 4-blade should be out on the market. Give them a look and let me know if they can serve your needs. Hope this helps. Karl"

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Question 142: "Hi, I am building a Cant Z1007bis, which was an Italian WWII Bomber with three engines. The manufacturer of the kit used three 40-sized 2-strokes with 12x4 props (2-bladed). I would like to go with 4-strokes. My question is: At a weight of 16-18 pounds, can I go with three O.S. 40FS (9x7 props, 3-bladed), or would I need three O.S. 52FS? Thank you for your input! Alex"

Karl: ''Hi Alex. In my humble opine I would go with the 52's for a couple o reasons. 1) you can handle more prop, which might mean closer to scale size, and you will have plenty of power on hand. 2) The rpm's will always be lower than on a comparable 2-stroker so there is alot more wear of the internals. You don't need to wrap the engines tight on take-off, so a more controllable rpm engine is a good idea. I have never heard of that plane before, so how 'bout you send some pictures when you're done, eh? Hope this helps. Karl"

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Question 143: "Hey Karl, Great site and I'd be grounded without you guys! I've got a peculiar problem... I'm running a G-62, 1/8" tubing, no binding, no leaks... When my Yellow P-47 goes vertical for a wing over, the motor quits and it's dead stick home. I've checked to make sure my fuel lines aren't clinched, my clunk is aft, and all seems to be well. I'm considering programming a switch for higher idle for flight and maneuvers if that will solve the problem. I understand there could be a myriad of problems that would cause such a condition, but, beat's me, I can't find it. Any suggestions? Thanks! ... Dave "

Karl: ''Thanks Dave, good question. First, let's look at the diameter of the fuel line. At 1/8" I.D. it still could be insufficient. Since you are running a G-62 there may be more of a fuel requirement than you think, under those circumstances. See, what you want is velocity to get the fuel from the pressurized tank to the carb. Think about a cylinder head for a car. When you look at the intake ports, they are sort of smallish looking, and when further inspection is done, you begin to understand that the air inside that port is flat gettin' with it as far as speed. The faster the air moves into the cylinder, the faster it fills up. If you take a high-performance head with intake ports that flow as much as 200% more air than a stock head, you see that installing the head on a production engine is foolish because you can't run the engine fast enough on the street to make the head work well. So here is what I would recommend, revisit your choice of muffler system to make sure the pressure tap for the tank has enough pressure there to supply fuel while vertical or inverted. You can install a pressure gauge and run the thing up whilst observing the pressure reading to verify. Second, check for leaks in the tank cap and related fittings. If there is a leak, no way will it hold pressure to feed the carb. Third, experiment with fuel line diameters, keeping in mind what I said about air/fuel velocity getting into the engine. Hope this helps, Dave, and thanks again. Karl "

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Question 144: "Hi Karl, I just bought one of these planes and I have to engine choices and want to know your opinion; the first is the Saito 120 and the second is the Zenoah G-26, the latter one has way more power but it would be my first gas engine, so out of the two which one is the right one and what are the pro’s and con’s of each engine? What would be your choice for this aircraft? Regards from southern Mexico. Mauricio "

Karl: ''Hola, Mauricio, Como estas? Es bueno oir de usted de Mexico, Mauricio, bienvenido a nuestro sitio, yo espero lo sirve bien.
I cheated and used an online translator, sorry. Just an attempt to help you feel attended to, Mauricio. To begin with, the Saito 120 is an excellent choice, and you can use a little more prop with that one, since you don't have to worry about the rpm so much. The Zenoah line is, well, what can I say, fantastic. They are tried and true, proven, and very reliable. If you want to look at something else, try the Saito small radials, or say a five-or seven-cylinder radial from TechnoPower engines in California. If you don't want to try them, then I would install the G-26 simply for weight and compactness. Hope this helps ya, pal. Karl "

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