CVT for use on gyrocopter prerotator. Is it possible?

[shroomer1966]

Hello all.

Am in the process of building an autogyro, like this one

http://www.rotorflightdynamicsinc.co...ea81dom001.jpg

The main rotor is not driven, unlike a helicopter. it freespins. The propulsion is from the rear prop.
To takeoff, there is a system called a pre-rotator which is engaged and which then spins the rotor head up to about 250+ rpm.
It is then disengaged, and the machine runs down the runway like a plane until the rotor rpm is high enough to take off.

I want to build a mechanical pre-rotator system. essentially there is a cog just behind the rear (driven) prop onto which a belt is tensioned. It spins a shaft, and the shaft
then transfers this power to the main rotor via some universal joints and another set of cogs (which also engage and disengage).

My reasoning for putting a CVT in the line. Initially it will give a soft start, allow for a smooth transfer of power to the rotor head, and will hopefully allow for a maximum transfer of power at the higher end.

My query is this.

The engine is a rotax 582. Engine specs are

http://www.rotaxservice.com/documents/582perf.pdf

The gearbox reduction is 2.58:1

I would like to engage the pre rotator from idle up to 5000 rpm, so the shaft from the engine (to apply to CVT) would be running at approx 390 rpm to 1950 rpm. This could be geared up or down dependant on cog size I choose, so I can choose what rpm to send to the CVT primary input drive. The output can also be geared, depending on the cog ratio I apply to the rotor head.

My query is this.

Would a CVT be suitable for this task. I only need to apply perhaps 5 hp to the rotor head to get it to spin to speed, I am aiming for 300 rpm.
Given that the engine output is approximately 45 hp at 5000 rpm, if this was applied (gently, to spin the rotor up slowly) to a small CVT capable of transferring 5+ hp, would the CVT be capable of handling the power without damage.

If suitable, what CVT would be best. I am looking for the lightest most compact unit that would do the job.

[bigoilbob]

The CVT might actually be less "gentle", because of torque multiplication starting up. Remember, that unless the shaft was designed for rotation/prerotation, it's torque carrying capability is just an extra benefit. Tortional stress also reduces the pull strength of a shaft, and I wouldn't want you dodging a very expensive, lethal, whirlygig during your take off roll. But as is obvious, I actually know little about this. I know that gyrocopter prerotating systems have been around for a long time, but are CVT's used in them? If not, I would find out why not. Not much new under the sun, and why reinvent gyrocopter prerotation technology needlessly? Especially because you might be messing with your health and wealth.

[shroomer1966]

Thanks for that. I realize that a CVT has never been used on a pre-rotator before, but then again small light CVT's have not been around for long either,
so that may be part of the reason. People are putting electric pre-rotation systems on gyro's now as well, only because light, high power lipo batteries have become available.
They were not there years ago either.
New tools become available, and people try to adapt them. It may be possible, and it may not, that is what I am trying to find out.

The pre-rotator system will both engage and disengage from the engine before flight, and indeed even before the take off roll. The CVT in line
has no bearing on that fact, so it should have no safety implications during flight at all. The CVT may introduce additional forces on the drive shaft spinning the main rotor,
but I would have thought not. There will only be tortional, not pull stresses involved.

Any pre-rotation system will be thoroughly tested before it is used.

Is it possible to adapt a small CVT to use inline on a mechanical drive system of this type? It is only turning a rotor blade instead of a wheel. To my mind, theoretically it should work, and that is what I am trying to find out
from someone who knows CVT's better than I do.

[bigoilbob]

I'm out. You obviously know much more than me on the subject, But I hope you do lots of due diligence and keep safe. I'm a paramotor pilot, but just totally safety crazy........

[shroomer1966]

I fly ultralight trikes as well, am the same way about safety. I did a couple of para-glider courses, but did not have the nerve for it!

[Skyliner70cc]

Not a fan of CVTs, they don't engage gently. Why overcomplicate the pre-rotator. Just engage it with a manual clutch with engine at idle and slowly bring the rotor rpm up to desired RRPM.

A small snowmobile or ATV CVT should easily handle any horsepower you throw at it.


I'm curious, what does a gyro such as that cost to build? I intend to get one eventually as being in a constant state of auto-rotation is kinda neat, ya think?

[Skyliner70cc]

Not a fan of CVTs, they don't engage gently. Why overcomplicate the pre-rotator. Just engage it with a manual clutch with engine at idle and slowly bring the rotor rpm up to desired RRPM.

[shroomer1966]

The engine idles at around 1000 rpm, so any initial slippage for the rotor head to catch up to the engine rpm would have to be done by a belt.
With a reduction ratio of 2.58, the speed of the pulley from the prop (to engage the drive shaft) would be around 400 rpm. I was hoping that a CVT might be able to absorb these initial
rpm without engaging the output drive, thereby saving slippage on the belt, and make for a smoother process.
Those were my thoughts. The original mechanical system as you described just used belt slippage as a clutch of sorts.

The CVT's used on a lot of small scooters (125cc 4 stroke) generally absorb lower rpms, and then gently engage as you increase the engine speed. I was hoping to do a similar thing with
the CVT on the gyro.

Cost of gyro's? Depends very much on how you approach it. I am building it (or getting it built) off plans. Main costs are rotor head, rotor and engine. First 2 will be new I assume, then the rest is up to you how you go about it. Probably figure somewhere in the 10 -15K USD range if you do a lot of the work yourself. Some of the earlier Bensons or similar could probably be built a lot cheaper.