Gyro Prerotation Speed

[Gyronaut]

Perhaps some of you techincal Guru's can advise me.

I prerotate to about 140rpm on my Gyro before starting my takeoff roll, the first 30 meters or so is to get the rotor RPM up to 250+ then the nose wheel gets light. at about 300rpm (+40mph the machine gets light and its airborn in about 50 meters (depending on weight). My logic tells me that if I was able to pre-rotate to + 300rpm I would be airborn 30 to 50 meters earlier.

Now here is the question:

My prerotator system works off a jockey wheel pulled down onto a hub at the prop. This drives a flexible shaft which runs up to the rotor main-gear with a bendix gear. If I were able to put a gearbox in-line that I could engage at 120rpm reducing the ratio I would get far more RPM on the main gear thereby increasing my rotor RPM pre-takeof and thus reducing my takeoff roll significantly. This would make it a true STOL aircraft.

Any clever engineers out there with some ideas?

As it is I am able to land with almost zero roll-on under most circumstances but the takeoff roll is extended simply to build up rotor RPM. [When the South Easter blows here in Cape Town, zero-roll landings are normal and you have to take care not to reverse back down the runway]

If anyone has any experience with H202 (Hydrogen Peroxide) tip rockets or innovative methods to drive a rotor I would also be keen to hear from you. Simply put, if you are able to pre-rotate a gyro rotor to 300rpm or more and you introduced a small pitch change then logic tells me vertical takeoff and landing is possible. Anyone had any experience?

As far as I am concerned, we South Africans are not behind the rest of the world in any way when it comes to Gyro technology. The Groen Brothers are making a name for themselves internationally and in my experience the Sycamore is a solid, tough, good looking and effecient machine for the price so why not improve? I sure would like to have true STOL abilities!

I look forward to hearing from anyone that has experience in this field.

Len

[t-bird]

I don’t think that you will be able to take off with 300 RPM.

I usually prerotate to about 185 RPM in the magni.

With a higher RPM , more drag on the disk, you would take longer to accelerate. The difference between the airflow generated by your forward speed and the speed of the disk is also bigger. This will reduce the speed of the rotor until the rotor and airflow generated by the forward speed are more in balance.

Some one told me that he had preroted his Magni to 300 RPM , all of that was lost within 15 second after the take off roll to about 195 RPM

I have taken mine up to 220 RPM and was sitting at 190 RPM after the take off roll. At 185 RPM it drops to about 175 – 180 RPM.

The Sycamore RPM will also be lower than the Magni because the blades are longer.

Have you check the pitch on the prop ?

If you have a 914 turbo – Climb at 60 mph turbo with full power and turbo engage. The engine RPM should be at 5 800 rpm. If lower adjust the prop. This will make a huge difference.
The turbo does not engage properly if RPM is too low.

Cater concept gyro do a vertical take off and the Russian ones. The problem is that you have a collective like a helicopter, this complicate the rotor head design and take off becomes quite difficult. http://www.cartercopters.com/ http://www.oskbes.ru/index.htm

[Gyronaut]

I guess that makes a lot of sense T-bird! you might also find yourself in the air way behind the power curve very easily. hmm.

Prop pitch is correct, did a static test and adjusted pitch till we got around 5 700rpm at full throttle on the ground. Gets to almost exactly 5 800 in the air.

I am very happy with my takeoff roll distance as is with 31ft rotors at sea level but was thinking that it would be even shorter at higher prerotated speed. What you say makes perfect sense to me though. The way my prerotator is designed I can't get more than 140rpm out of the rotor without increasing the engine RPM to over 2000. Winds up to 250 very quickly and from there its a doddle. With max all-up weight at sea level my rotor runs at about 325rpm @ 70mph. I get quite good speed with the longer rotor too. Although VNE is 95 I have reached 100 in a descent but it does start to shake and then I get nervous so pull back and bleed off some speed quickly. Angle of attack is small then so PPO becomes a reality although the large horizontal stabilizers on our machines make it hardly possible I believe. My machine is happiest at about 85 - 90 mph straight and level then running at about 5 300 (just before the turbo kicks in)

Suppose the designers did know what they were doing so best to leave well enough alone then.

Thanks for your input, much appreciated

Len

[t-bird]

I was flying at 115 mph over Harties a week ago.

It is fast and the Magni is very stable at that speed.

I unusually fly at 80 – 85 mph it becomes uncomfortable for the passengers if you go above that because of the wind.

Your fuel consumption becomes ridiculous over 90 mph.

If you want to fly fast buy a samba. A gyro is not built for speed and that is part of the fun.

I will be very happy with a machine that cruises along at 80 mph.

A lot of marketing goes into this Gyro cruise @ 105 mph and the other @ 95 mph. In reality you would cruise @ 80- 85 mph.

[diver]

Quote "Although VNE is 95 I have reached 100 in a descent but it does start to shake and then I get nervous so pull back and bleed off some speed quickly"
VNE = NEVER exceed speed - so why do it? Just a thought.

[t-bird]

Hi Diver

VNE in a Gyro is an indicated speed that can differ with rotor speed.

Gyro blades turn anti-clock wise.
The wing to your right will be in the wind – no problem here
On your left hand side it will be with the wind – Could be a problem.
Near VNE the wind will start overtaking your left wing. The wing will actually start to stall.
Because the right wing is giving lift and left is stalling you would get huge amounts of stick shake.

This stalling of the wing is dependant on the rotor speed and the forward airspeed.

You can take off with a low rotor speed and reach VNE at 40 MPH.
If you apply full power with low rotor RPM you will roll over – Dynamic roll over.
The correct procedure would be to reduce power and gently apply it when the shake is gone.

At the coast your VNE would be lower – lower rotor RPM due to thicker air.
You can by mistake apply a bit of negative G’s that will reduce Rotor RPM and VNE.

Magni’s VNE 130 MPH very near to MAX cruising speed of 125 MPH
MT-03’s VNE 101 MPH which is very low and not true VNE which should be nearer to the Magni’s 130 MPH

Reaching true VNE is much more dangerous than in a fixed wing. Your rotor blade will stop turning.
A gyro will give you warning that you are starting to reach VNE with a stick shake.

I am not saying that it is correct to fly over VNE only that you can reach VNE at much lower speeds in a gyro if you want to.