just unpacked my e-bay seafury to give it an official weigh in , total unassembled weight -dry
8.51 pounds . based on unassembled weight , plus 8 servos , 1500 amh pack , CJ retracts , gluw , wheels do you think a 91 4 stroke would fly this plane .
Wings =4 pounds 66" span , Fuse 2 pounds fiberglass .the rest is the small parts

I fly a 10.5 # P-40 on an OS .91 Surpass II
and a 10.5# F4U on the same engine, there is plenty of power (see my Gallery)
so you should be OK

Thanks US , I have to add my other componant parts , I just want to make sure I am not exceeding 12 pounds all said and done .

The general rule of thunb for 4 strokes is .1 cubic inch per pound. If you are going to end up with a 12 pound plane, a 120 would be a better choice. Remember that you will need to run an 8 pitch prop for the airplane to go fast enough to fly right. If it was me, I would get the plane basically assembled and do a CG check. If you are tail heavy as probably you will be, a big heavy motor works better than adding weight.

I know after looking at what has to be added in the way of glass reinforcements ect , I think I am better off with a 120 4 stroke .
I need some major surgery on the wing to add retracts so that alone is going to add some weight , thanks I guess a 120 is in order

Checkout the YS110, Central hobbies for about $325

I have stayed away from Y/S engines , i know they are at the top for quality and performance but fellow Rcs say you really need a hand in the engine knowledge for these motors and that is not me . I want to break it in , oil it and forget it .

Gotta say that I totally agree with the 'general' rule of .1 cu. in. per lb (except with Y.S., as they have MUCH more power per cu. in.).
That is why the Saito .82 is a good choice for current Top Flite Corsair project, which I anticipate weighing about 8.5 lbs.

I don't agree with the 8" pitch tho: I prefer bigger props with less pitch, some down to 6" (pitch), and I can assure you, mine fly right

I never thought about it that way, but yes .1 cu in per lb for a conventional 4-stroke is a good rule of thumb for adequate flying power. But I would make this a minimum for a warbird that needs to go fast to fly "scale". Since the full-scale Seafury topped out at over 450 MPH I would say that your model counts as one of these!

A 6 pitch prop is fine for a 40-size warbird, especially with a 2-stroke engine. But I've found that as the models get bigger and the engine RPM for the larger engines is lower (especially with a 4-stroke) more pitch is needed to get adequate flight speed. An 8 pitch on a 4-stroke sounds about right for your plane, I think that you would find that with a 6 pitch prop the 'Fury will look like it is just cruising along even when at full throttle.

Yes, there is lots of controversy on YS engines here on RCU. While I wouldn't recommend one as a first 4-stroke, if you have some experience and $$ is not a huge factor then they are ideal for warbirds. They put out tons of power for their size and have exceptionally reliable idles (and deadsticks on planes with retracts can be a very bad thing for obvious reasons). A 110FZ on a 12 lb warbird would be a great combo. But if you really just don't want to go there then the new Saito 125 would be my second choice.

Walt

Thanks for the advice , I did not know that Saito has a 125 , I will have to look into this . I am baseing some of my data on the Top Flight seafury , planes are close in size 64" span vs 66" , but this plane is certainly not scale , I have to split the flaps , mod the elelavtor- I dont know why in gods name they build the elevator the way the did unless it was overly sensitive , rudder needs a counter balance and I have to make compensation for retracts .
Outside of that lol , its not a bad ARF for the money . Foberglass fuse is really nice and it actually has real monocote . If your interested look under e-bay in NewYork Grace , dont "buy now ' he will put everything up for bid at one time or another

Obviously, some interpret scale flying differently than others. Altho a full scale Sea Fury may have been capable of 450 mph, I doubt that it was anywhere near sea level at the speed. Most '400 mph' planes (except for race planes) top out at closer to 300 mph, maybe 350 at sea level.

But the real point I want to make is: the models we are talking about here are typically 1/8 ~ 1/7 scale, so a scale speed would be those fractions multiplied by what the full scale flies at. In the case of a 400 full scale, a 1/8 scale would then be a 50 mph model.

My previous Top Flite Corsair used Master Airscrew 3 blade 12 x 6 props, and flew quite well and at scale speeds, while putting along at 2/3 throttle. I could even enter loops at the setting, throttling up as I entered it, and backing off on the down side.

I could make very slow passes at just above idle, with the gear and flaps up.

Scale flying is a subject of it's own, and subject to debate. Some think fast, VERY fast, while others think differently. I think what is really unfortunate is that some warbird events (such as Terre Haute, IN Warbird Day) judge best flight as the one in which a warbird has a higher power to weight ratio than all the others, is able to take off and fly straight up, and ideally even hover. In my opinion, "Best Flight" at a warbird event should go to the most realistic looking flight. Just my opinion.

I base my pitch selection on engine speed and wing loading and find that most 1/7, 1/8 warbirds perform best with an 8 pitch prop on a 4 stroke. This allows them to run in that 80 mph range where they seem to like to fly. This selection has nothing to do with scale performance or scale speeds but just getting the maximum performance out of the combination. I have no experience on flying warbirds in a scale manner. I'm just a sport flyer who likes warbirds. I do try to get an optimized package so I can run smaller motors which saves money. My 7 lb 4 oz, 1/8 scale Wildcat performs extremely well on a Saito .65 and when I get around to it, it will loose a 1/2 pound with the mods I'm working on. An airplane needs to be designed as a total package for the end use it will see, along with the ability of the pilot to fly it and the budget it must be built under. Thats why there are so many different opinions on how to do this. You can build two totally different airplanes from the same kit depending on what your planning on doing with it when your done. I build my planes as light as I can, power them with motors that will fly them so they are not overpowered or underpowered, keep them fairly simple for cost and maintenance reasons and then I fly the h*ll out of them.

Corsair J,

I went thru the calcs and you are right, with a span of 66" this would make the plane 1:7 scale, and a 6 pitch might be OK. But I still think that an 8 pitch would be better. And if the plane weighs in around 12 lbs it will take some power to run an 8 pitch and still get reasonable thrust.

I learned my lesson on propping bigger warbirds when I maidened my first 77" H9 Mustang (1:5.7 scale) with a 6 pitch prop. After a scary flight I went home and did the math- with the big 4-stroke turning 8900 RPM the theoretical airspeed was only 50 MPH. And since "scale" top speed for the plane was more like 75 MPH it was no wonder I had to keep the throttle wide open to feel comfortable flying it! With an 8 pitch prop it flew much better, and with a 10 pitch it flew very scale. The bigger pitch meant less thrust and so the plane was nowhere near unlimited, but the higher airspeed attainable was well worth it.

I see a lot of folks moving to larger warbirds making the same mistake that I did, hence my advice.

Of course my latest 77" Mustang is sporting a big YS and a 12 pitch prop. OK so it does not exactly fly scale without holding back on the throttle, but it sure is fun!

Walt

Nope, but I like to have a little extra power.

ya I kinda got that idea a little earlier , I think a 120 is in order lol

Hi!
If you choose a .90 four stroke you should use either a 14x6 or 13x8 APC ...most likely a 14x6 APC is best.
For a 1.20 fourstroke a 15x8 or a 16x6 APC.

Regards!
Jan K
Sweden

Does anyone have a good rule of thumb for 2 stroke engine displacement and plane weight. I know for 46 size engine 6lbs is about max and for .61 10lbs is about max. My question is what about the larger displacements?

A good rule of thumb for any size single engine fighter type model is to have one Horse Power for every 5 to 8 pounds of aircraft. This is true all the way from a .40 size model up to the real thing. This is of course a guidline for power-loading and cases outside of the paremeters above can be found but in general if you are within these parameters, you will have a model with the correct power.

The power, not displacement should be considered when choosing a powerplant, in this way you have a target HP first and can choose an engine of the desired type such as: Gas, Glow, 2 or 4 stroke secondly. Also, even though manufacturers (sometimes) overinflate their products performance figures the range I show takes this into account. For instance, a typical .40 size warbird weighing about six pounds flies good on a .46 which in many cases has an average rated power of 1.2 HP. This puts the model at about a five pounds to one horsepower range and the performance shows it while a smaller .40 will fly it more scale like with a loading of maybe 6.5 to 7 pounds per HP.

The problem with horse power ratings is that they are based on an ideal RPM, and especially in the case of 2 strokes, this translates to a smaller prop than the one which you will want to use for a warbird. In other words, the rated horsepower can only be achieved with a small prop.

I agree but here again, use the figures as stated by manufacturers and prop the engine correctly and get the ratio between 5 and 8 pounds per "rated" HP and you will have good power. If you like a little more power, aim for only five pounds per HP. Look at examples of models from .40 size up to those 1/3rd scale jobs in Europe and I think you will find most models when correctly powered will fall within 5 to 8 pounds per HP. Again I am talking single engine fighter types. From a full scale P-51 down to a Tower Hobbies AFR 51 - all will fall within the range.

That .1 cu in per Pound is just a rule of thumb and works well with your average four stroke. Throw a YS motor in there and a rethink maybe needed except that most guys running YS motor seenm to overpower everything anyway. I think .75 cu. in. per pound would be fair when it comes to 2 strokes based on my experience for what thats worth. .45 for a 6 pound plane and a .61 for a 8 pond plane etc.

Low@slow,

I get what your saying, I think, and perhaps that works for a class of model sizes such as .40 to 1.0 size models but, engine displacement is not always constant to output. I can show you a class of glow motors that are getting nearly 5 Horse Power for each cubic inch of displacement while, some others are getting less than 1 HP per cubic inch. Gas and four stokes have different outputs from two stroke glow, so it is a engine’s output that is the one constant that can be applied to other constants such as an aircraft’s weight to indicate what to expect.

Where talking average sport motors here, not quicky 500 motors. The stuff 90% of the people at the flying field use which of course you would need to adjust per application etc. Just a place to start. I would say that most OS, Saito, Magnum etc would fit into this catagory. Although getting 3.5 hp out of a .40 at 25000 rpm is wild.