Partially powered rotors from PRA magazine

[phantom]

J C , I built a helicopter with a 503 and by those numbers it looks like it should have been a great performing machine but that was not the case it would fly but only at wide open throttle and with the tuned pipe from a snowmobile it was close to 60 hp, what am I doing wrong?
Norm.

 

[Smack]

There are some efficiency estimations and assumptions, Norm.
They may have been too optimistic.

Pictures ??? :yo:

Brian

 

[Jean Claude]

The power I have indicated is very realistic, Norm. But, as I said, it corresponds to:
1) Rotor 24 'x 7" Smaller requires increase the power
2) Forward speed of 60 mph. Slower requires increase induced power.
3) Rotor is alone. Add the power of tail rotor
4) Add the parasitic drag of airframe
5) Add the power for rise
6) Rotax said his engine 503 two bicarburators produces only 50 Hp with tuned exhaust system

 

[phantom]

A 503 is 50 hp with the aircraft exhaust system that is not much tuned, the snowmobile system makes more power, you have to use larger jets with it and with a little port work it's not hard to get 60 hp and you can ger about 50 hp with a 447 but it builds more heat, we use to think we were doing great with a 60 hp 503 but now I see 300 cc engines doing that so engines keep getting smaller and lighter but I have to wonder what their longevity will be like, I once converted a 503 to a diesel , it ran great for a few minutes, when I did a full power run up the cylinders came off.
Norm.

 

[Jean Claude]

Norm, Do you know what power could produce a 503 without tuned exhaust system, just a muffler ?

 

[phantom]

They will do around 44 hp with just a muffler, the old alpine snowmobile ran that way, just a can type muffler , there were two different 503s used in snowmobiles one had low exhaust ports and only put out about 42 hp and then the higher hp which has the same cylinder as the aircraft 503 but has a different crank, the snowmobile crank is not cut away near the rod pin like the an aircraft engine , this makes it smoother and stuffs the case a bit more. The engine on my airboat has a snowmobile crank to get that smoothness and power.
Norm.

 

[Jean Claude]

Good to know.
Thank you, Norm
So, Rotax 503 gearbox B without exhaust system (42 hp, 84.2 lbs) seems better that Rotax 447 because integration and fairing is much more easy.
But what becomes of fuel consumption?

 

[phantom]

Fuel burn will depend on what kind of muffler you use, when I built my first power unit using 3 503s driving a single prop I found that I could change things by changing the length of outlet pipe on the can type muffler, so you get a little tuning effect with any kind of muffler.
Norm.