Pre-Rotator RPM Questions
 

Are there any 2 place gyros out there that pre-rotate to flight RPM? I've noticed most do not, is this the case because of too much stress to the system? What are the other concerns involved with such a setup?

Wouldn't the take off distance be reduced quite a bit if the rotor was ready @ flight rpm? Sure would be nice on no wind days.

Jeff

Jeff,

The Butterfly "Golden" and "Turbo Golden" models are both 2 place machines that are available with the Metro Launch Pre-rotator that takes the rotors all the way up to full flight speed before any rollout starts. Larry designed this system so the Golden (which was originally designed to be a tandem trainer) could be used more like a utility aircraft (with bigger payloads) and get in and out of short unimproved airports in other countries. The goal was to be able to take off from a typical soccer field and it will do just that.

Thanks Doug, I wonder why more companies don't offer a setup like that?

The Butterfly "Golden" and "Turbo Golden" models are both 2 place machines that are available with the Metro Launch Pre-rotator that takes the rotors all the way up to full flight speed before any rollout starts.
I didnt know the 'golden' hada tail rotor????

Jeff, unless you have somthn like a tail rotor on your gyro, theres no point in buildn a prespinner capable of flight rrpm, coz youd start rotating on the spot before you got there.
A prespinner that will get them to 90% is plenty, but you still need sum room to get the rest of the machine from 0 AS to min AS before you lift off.

Unless you do jump takeoffs, there is little difference in take-off distance between pre-rotating to flight rrpm or even just to half flight rrpm because you still need to have forward airspeed to maintain rrpm.

The biggest advantage of faster pre-rotating is that you can go to full throttle quickly and avoid rotor flap and this of course means you get to takeoff airspeed quicker.

The blades however spin up very quickly so even when taking off with half rrpm needed for takeoff the blades spin up to flight rrpm in a short period of time and only adds 10's m of metres to your take-off distance.


Most of the modern European gyros all pre-rotate to over 200 rrpm, but when you start the ground run you loose some rrpm anyway until you have enough airspeed to maintain the rrpm and then as your airspeed increases the rrpm starts to increase.

Jump take off require prerotating to many rrpms greater than flight rrpm so that by the time you have enough forward airspeed to maintain flight rrpm the rotors are still spinning fast enough.

cool, thanks for the responses guys!

I was looking for some videos of Trikes doing short takeoffs, I didn't find many good ones. The guy I used to hangar with, had a Toucan with a 503...he could just about do a jump takeoff. With 2 onboard it was almost as impressive !

Gyos just don't takeoff as fast. But look at this plane ....

Short field Take Off, Turbo Zenith 801 - YouTube

Birdy, there is another way to prerotate to full flying speed without a tail rotor. Settting the collective pitch to 0 during prerotation.

And Jal, if you prerotate your rotor to more rpm than the required for flying speed, you could do the take off with flat rotor, build up air speed very quickly and take off very short..., just pulling the stick, like in a plane.

Ferran

cool plane, I've seen a few of those. Doesn't do it for me though like an autogyro :)

That still torques the airframe does it not?

Our M912 and the SCII both get close to flight RRPM (280-300max), but still need a short run to lift off.

McCulloch J-2s prerotate to well over flight speed, but you still need a ground run to attain the necessary airspeed for flight. same goes with any prerotator, except the jump takeoff, overspeed type, but then you have a lot more complexity for very little gain.

Jon,

You are right there is a lot of torque to the airframe to spin the rotors up to full flight speed, however with the wheels sitting on the ground it isn't going to move the machine at all (unless you were facing into a strong headwind). There has to be 20 to 30 mph worth of air going through the rotors before you are going to have lift and once the lift starts to take the weight off the wheels you could have a torque problem to deal with if you were still putting power into the pre-rotator.

All of the Butterfly models (with the metro Launch System) still need about 100 ft of forward motion to build up airspeed on a calm day, before they can take off. Of course if you have a bit of a head wind it can shorten that to a pretty impressive short takeoff.

Doug,
I was eluding to the fact that you don't need a tail rotor nor zero collective.
We studied this a bit when we were testing the machine with floats. When you prerotate the frame would spin a bit so we added a large enough water rudder to counter the effect....and it works :)

You’re right, I’ve not seen ANY good STOL trike videos on Youtube. In my opinion…here’s’ why.

They don’t make STOL trikes any more. The market trend is for faster/smaller wings 100-160 sq/ft compared to 240-320 sq/ft of yesteryear (twice as large).

My best STOL videos are 25-30 years old. I’ve been meaning to post them. Truly amazing! Beats the Alaskan STOL comp vids.

I have, (as far as I know) the largest trike wing in the world. It has amazing STOL capabilities. It was purpose built before Part 103 (circa 1980) to set a world hang gliding record for the most number of pilots at the same time. It was built to fly 8 pilots. I believe the standing record is around six. I have photos somewhere.

I've approached several manufactures to make me a big wing (or replacement sail) but there’s no market. Sailmakers typically won't copy sails without patterns due to stretch…frustrating. Still in the market. Thought about getting my own sewing machine.

Here's an Atlas 240 sq/ft clip. Note the 320 sq/ft performs even better.