Zenoah 186 Triple with reduction drive

[rob ellis]

I have shelved this project for now because all calculations for the static power show that it will be well over powered for the 1/3 Spitfire, so I will be going with the Twin Zenoah with the reduction drive, air cooled which should be better suited with a more realistic power to weight ratio. Turning a 36 X 16 prop at 3850 rpm will give around 70 lb of static thrust with a projected weight of 88 lb for the model.

Dear dave,,,,overpowerd,,,,you can never have enough power,,,,just fly it on lower throttle,,,,id rather more grunt than not enough..plus rather than add dead weigh in the front,,wouldnt that weight be better as power from a third jug,,,,
rob,

[Steve Rickett 2333]

I have shelved this project for now because all calculations for the static power show that it will be well over powered for the 1/3 Spitfire, so I will be going with the Twin Zenoah with the reduction drive, air cooled which should be better suited with a more realistic power to weight ratio. Turning a 36 X 16 prop at 3850 rpm will give around 70 lb of static thrust with a projected weight of 88 lb for the model.

Hi Dave,

Sorry, but I would tend to agree with Tinus. 70lb static thrust is great but have you thought that a 16" pitch prop rotating 3860 times a minute cannot pull the model forward any faster than 58 mph. (if you have a 100% efficient propeller) You'll probably achieve about 85% efficiency which is only 49mph, you still need to take into account other percentages which are well above my head, so that number may come down further.

A 1/3rd Spitfire will probably want to fly up to 100 mph, so just taking the assumptions above you'll need about 30-31" of pitch if your propellor is 85% efficient at those low revs.

80 mph would be approx 25" pitch at 3850rpm.

I bet the triple would be just about right......

[Phil Clark]

Agree 100% with the above........at these low rpm's, you'll be needing 25" of pitch as a minimum to achieve the flying speed a 1/3 scale Spit will need. The big 400+ radials are all running 24-25" minimum and also operating around the same rpm's. I think you'll be very disappointed with the 124 twin......I'd stick to the triple.

Phil

[rob ellis]

water cooled tripple,,,,what ever its weight comes out at i guess you will need that in thrust,,maybe more to fly it like it a spitfire,,,

[Karl mander]

Dave

I to must agree, the spitfire is going to be a big plane and is going to need the triple unless you want to float it around.
You've seen the tempest fly enough times with the twin, scale but could do with more power , I know my magneto engine isn't as powerful as yours but in a 1/3 spit it would be lost.
My triple pulls the 41kg firefly around again in a scale manner but I would love more power to do the big loops etc.
I would lose the water cooling, my triple has shown no signs of overheating in over an hour of flying.
Plus if you don't do the triple my shedology engine will be the only one flying.
My triple is turning a 36x12 prop statically at 4700 rpm.

[Tinus Nielsen]

Karl: Have you tried a prop with more pitch than the 12"?
Theoretically you should be able to spin a 32x20x2 at the same rpm which would provide a lot more speed, and possibly the inertia to perform bigger maneuvers, even though the static thrust would be a little less.
A compromise prop could be a 34x18x2, which might be easier to find, and this would still provide a little more speed at slightly lower rpm.

No matter how you spin it 15 hp, or thereabout, is 15 hp, and when bolted to a 30-40 kg model the power to weight ratio makes it necessary to use the momentum to perform "warbird" maneuvers.

[Karl mander]

It flew previously on a 37 x14 prop and was woefully over propped, at least with the 36 x 12 the engine is hitting the right revs.
As you state you can dress it up how you want but 15hp on a 41kg model isn't going to set the world alight.
Karl