How much power

[Erfolg]

1. How do you decide on the power required for a autogyro.
2. How do you decide on the Kv required
3. What is a typical pitch used on the propeller.

Go on, gives us a clue!

[Richard Harris]

Erfolg,

Power requirements for me have never been calculated, it has always been trial and error, you can have one machine that flies just fine but put a different set of blades on and there may be more drag and it struggles to fly.

As a rough guide I would say 120-150 watts per pound in weight of the model, always better to have more as we can throttle back.

An Autogyros flight envelope is very varied, but mostly they are flown at lower speeds. Because of this I try to use large diameter low pitched props, this gives the power just where I need it. I dont think I have ever used a motor with a KV rating higher than 1300 rpm per volt, infact the lower the kv the better for me.

For instance: my Fire Fly is spinning a 12 x 4 prop on a 830 kv outrunner pulling around 100 watts, all the pull is where I want it at lower airspeeds. The model can weigh between 1- 1 1/2 lbs and still fly fine.

There are however problems when you try and scale down a full size pusher, my Nel would look odd with a 12" prop, so this is a higher pitch cut down prop. With this I have to think a little in advance as there is a bit of lag as power is applied, but I can live with that most of the time

Rich

[Erfolg]

How does the Firefly compare to a 3/4 Panther?

Perhaps more pertinently, was sized prop does the Panther use? I have looked through the Panther thread, to date I have not found a reference to prop size or motor description.

The fine pitch certainly does make sense.

I had supposed that there was a relationship to rotor dia, and weight, with respect to motor power, I suspect the challenge is obtaining some values for current drawn, in actual flight, to determine a empirical value.

One other thing which has started to trouble me is how to stop the rotating rotor. I have dealt with small errant helicopters, which would not shut down and apparently intent on self destruction. I am more hesitant with a +900mm rotor.

[Malcolm - coolwind.co.uk]

Erfolg,

Helicopters and Autogyros are very different types of rotor. A Helicopter rotor is often made of Carbon fibre and are quite heavy, and they are driven by the motor, so an errant Helicopter is a dangerous thing. An autogyro has much lighter blades and are not driven, they just freewheel, as they dont have much momentum they can easily be stopped with the palm of the hand on the centre spindle,

Malcolm

[Richard Harris]

Another thing to consider Erflolg is the advantages of the DC head, not only does it give you the ability to be in full control at all speed ranges (even backwards) it is handy on the ground. As soon as an autogyro touches down then the rotor disc can be pushed forwards which slows down the rotors. The wind is no longer going up through them but biased towards the top of the blades.

Like wise it comes in handy to pre spin the rotors by pulling them back whilst slowly taxiing.

Rich