Engine Comparisons and a/c size

[jim gilmore]

I/m wondering if anybody has ever charted the comparative strength of engines. I do not just mean from the same size but it would be nice to have a comparative chart of where a babe bee is from a norvell ,049 to a fox .15 to .35 and .60's and even ro-jets on 1 chart to be able to compare the actual airplane size and weight in general.

[john e. holliday]

I don't think anyone on this forum has that kind of cash to do such a test or even the time.  Have fun,  DOC Holliday

[Alan Hahn]

I/m wondering if anybody has ever charted the comparative strength of engines. I do not just mean from the same size but it would be nice to have a comparative chart of where a babe bee is from a norvell ,049 to a fox .15 to .35 and .60's and even ro-jets on 1 chart to be able to compare the actual airplane size and weight in general.

Jim,
I am guessing that such a question doesn't have a sensible answer.

Let me give you three examples--look at 1/2a stunt, the bigger planes, and ~35 size planes.

In 1/2a, it seems the object is to fly the biggest plane with the smallest engine (even if 1/2a has crept up to 1cc engines!). Here we go to high nitro fuels and small props to let the engine rev and haul the plane around. It's lots of fun.

But if you look at the big stuff (~40 size and above it seems), there the object seems to be to cram the biggest most detuned displacement engine (usually running a large slow turning prop) into a small airframe. Well heck, it seems to get the job done---to motor thru our typical "contest" weather.

And in the middle (~35 size planes) we are using smaller engines (like 25's) running in high rpm-low pitch mode.

Now if you set up an engine test, how would you arrange the parameters? High, low nitro fuel, venturi sizes (or in the case of 1/2a do you drill out the venturi), max power, stunt power, .....

And this leaves out the electrics!

And as Doc says, who has the cash for it all!

I think the best is to look around, search the forums on particular designs and see what people are using, or simply post what you want to build and see what people say--and I am sure you will get plenty of alternatives--probably too many  .

[jim gilmore]

Ok, well I guess doing it is a bit costly from a point of view. Just that well a 1/2A pathfinder seems to be as large as a sig akromaster. So I'm trying to get a handle on where the engine sizes are not, just in numbers but in actual performance.
Yes, there does seem to be a leaning in the larger engines to make them run very consistantly at reduced capacity. I'm guessingbthat this does make them do what they do as a constant. same rpm/torque and leave the ability go add if needed due to conditions.
After all it's nice to have more if you needed it than to need it and not have it.
 As far as electrics go I'd say that it is a bit like apples to oranges. But the only thing that I can consider a constant isn't engine size but wingarea and weight.So maybe if we were to find a way to calculate somethink like wingspan/weight and prop size and pitch come up with some formula  ? 
As a kid I flew the 144 sq topflite models with a golden bee.
(cosmicwind/hawkerhurricana nd p51b)

[George]

Jim,

You need to look at how an aircraft is constructed in addition to its size. You may notice that for a given size, a sport plane that may be able to withstand some rough handling will have a heavier structure than say, an all-out stunt plane. Different purposes, different structure.

A plane built to be bullet-proof usually will be too heavy to fly well.

George

[phil c]

You can get most of the info you want from the engine tests that were published in Model Airplane News before they went RC/up.  That covers most engines up to the early 80's.  There were additional tests in RC Sport Flyer for quite a long time.  To cover the stunt specific engines we'll need someone like Frank Williams or someone else with a computerized engine test stand to get the data in a reasonable amount of time.  You can do it yourself with a fairly simple test stand that pivots with the torque of the engine, a tach, and about 8 test props.  At 15 min/prop it only takes half an hour to get a reasonable torque curve.

Kavan sold a series of calibrated test props in the 70's.  Just measure the rpm and look on the chart for the torque and horsepower.

[rustler]

Not sure if my comment which follows is relevant here, but here goes......

Back when Mike Billinton published a test on the FP40, he did a small sub-test running the motor at typical 4-stroke stunt revs, for interest. He got an amazingly low figure around 0.3bhp. I figured power is what it's all about, so if that's all the power that is needed for a 35 size stunter, then any motor which produces 0.3bhp should do. I did sketch out a 35 size design for a TD15, figuring that if it was run aproaching peak revs, e.g. 8x4? or particularly 9x3? it should give around 0.35bhp and do the job. Shame I never built it! My point is I was reckoning power is what counts, not capacity.

[Mark Scarborough]

I really think that torque is a more relevant number than HP is IMHO

[jim gilmore]

while there may be stats for the older engines It's the new engines I am trying to find a comparison for.
0S max  la       .09
OS max  la       .15
Thunder tiger   .09
Thunder tiger   .15
magnum          .15
enya                .09
AP hornet         .09
AP                    .15

[rustler]

I really think that torque is a more relevant number than HP is IMHO

I have NEVER been able to understand this concept. I suspect it is a folk myth. Surely you can have the greatest torque in the world, but if the end result is 0.1bhp you aint goin' anywhere? Sure torque comes into the bhp calc, but that's where it's headed, - bhp. Witness the geared 60's we see, (Webra, O.S.), - here we can get a direct comparison. Looking at PROP rpm and output shaft, the geared motor produces (say) twice the torque, but at (say) half the revs. But the engine revs and bhp are the same!