One more modified RAF -

[twistair]

- first such bird assembled in Russia. RAF2000 kit and stability augmentation kit were purchased by an individual who built this aircraft himself with a little help of local fellows. It is his first experience so some things aren't excellent but - it flies. Definetely it flies not that good as SH does due to 68'' prop and carburated engine (cruise at 4400 rpm solo at 95-100 kmh). One thing which surprised me in this aircraft is that the owner/builder replaced standerd prerotator with hydraulic one a-la Dominator. I believe he didn't know that Parker pump/motor used in Dominators aren't enough for 30' rotor. As a result - moderate 140-150 rrpm on prerotation.

[route66]

Alex, I am Back! I had to relook this system and something came to mind you might be able to explain. The machine above could only develop 140-150 RPM in prerotation, is that a bad thing? How much should it produce to be functional? While I don't have many hours flying gyros I have always been taught my prerotator would get me to 100-120 and then added power to work on speed and air assist to get the rotors to 180 and at this point release the prerotator and let the airspeed and flow bring my rotor to flight. As I explained, I am as new as they come and this is not a challenge, just an information quest. I am only asking why is it important to have a prerotator that has capabilities to do more than you will use. As far as the hydraulic system which I think would work well I did change mine back to the stock as the added 13 pounds did not make sense to me. I think we all would like 300rpm prerotations and verticle takeoff, but then we would all have heli's. (that would be cool though, yet expensive, thats why we chose gyros). You have more experience and I hope you can let me know your opinion on what is the best prerotator speed. I am sure I am missing something here and can't wait to learn. Thanks, Brandon

[ScottTinnesand]

Brandon,

The short answer is that you'll simply need more runway for takeoff if your prerotator only achieves 100-200. Not necessarily bad, just not as good as it could be.

In experimentation with the AAI Modified RAF and Sparrowhawk, I have released the prerotator as low as 80-90 to see exactly how long it would take to achieve take-off rotor RPM. The most important thing is to know the aircraft well and not rush it! Low-speed blade flap is just waiting to manifest during prerotations like this.

The most optimal prerotation speed would be 180-200 via the prerotator. This would allow for use of much shorter take-off distances and not restrict you to airports or landing areas that have long landing and take-off surfaces.

Scott

[KenSandyEggo]

Even achieving 200 rrpm does not allow you to go to immediate full power. You still have to nurse it along until you reach some ground speed. Otherwise you'll just balloon up into the air with no forward speed to fly and you'll just wallow and mush around way behind the power curve and maybe even descend back down to the runway.

[twistair]

Brandon, I'm not so experienced at all :) I'm just experienced enough to be sure that I still need to know much more :)

As for prerotator RPM: since we here in Russia have very few airstrips available for general aviation we're very interested in shortest take-offs. One of main things here for me sounds like every 20 rrpm on start shortens your take-off roll aprroximately twice. Numbers are not exact but they are principal. I had never tried a gyro without prerotator but I've seen once how a big gyro (The Hunter, 30' SportCopter rotor) tried to take-off after it's prerotator was broken... It was loooooooong :)
ScottTinnesand told it already so I can only second this: main thing which is given us by prerotator is significantly shortened take-off roll. Another critical thing is that if you can prerotate to some rrpm which make flapping less possible - your flying will be more pleasant and safe.
I can tell that there is a lot of difference (for us, short strips runners) to have, say, 160 or 180 rrpm on a SparrowHawk. There is still big differenece between 180 and 200, 200 and 220. No difference further - you also need to reach minimum take-off speed. Probably more than 210-220 is even bad for a SparrowHawk since it will try to jump into the air before you reach good take-off airspeed. This gyro doesn't like such tricks (say, well powered Dominator likes them - if a pilot correlates).
I believe that me personally don't like to fly a gyro with poor prerotator - but, again, we're flying from short and rough airstrips - or just from rough terrains. In case your airstrip is long enough and you plan to fly this airstrip only - the main thing which a prerotator gives is flapping-free rrpm edge.

[Envy]

(sorry for bad english)
OK, there is some more explanations... for this case. I'm the builder/owner of the gyro shown there. (First of all, note to many folks who makes photo of my gyro: BEFORE you place any of it photo in any www resource ASK ME FIRST. I'm sure to have some talk with Alex "twistair"...)
In everyday normal operations, i'm fly solo which is gives me normal uniterrupted takeoff at 275 rotor RPM at 40 mph, while std rotor RPM is about 305 at 60 mph normal fly speed. There is remain plenty of power...
I'm like my bird, so i'm not torture prerotator clutch. At 2600 RPM engine, the rotor blades is prerotated to 110 RPM (no wind conditions). Then i'm start takeoff roll, and after about 350 meters go into air. That is enough for me and for prerotator clutch. Also, i'm apply full power (5200 engine RPM) at 200 rotor RPM. The trying to fly up begins at 240 rotor RPM...
So, the potential effectiveness of hydraulic prerotator lies above 150 RPM... But i'm prefer to reserve it not for normal operation.

[lanichol]

Even achieving 200 rrpm does not allow you to go to immediate full power. You still have to nurse it along until you reach some ground speed. Otherwise you'll just balloon up into the air with no forward speed to fly and you'll just wallow and mush around way behind the power curve and maybe even descend back down to the runway.

Ken is exacly right! I flew in 3 different gyros and a Cessna 150 in one week.

Ken's can bring up the blades quick due to his hydrolic clutch & modified tower(which every cabled prerotator gyro should go to in my opinion) and has a tendancy to want to jump off the runway before the necessary ground speed is achieved. And with Ken's design, the Airflow FI in combination with the IVO prop, you feel the horses behind you. This was on a hot 100+ day. Ken may remember the rate of climb, but I still remember seeing the airspeed on the climb out..it was way past what I expected.

A conventional modified AAI gyro that I flew in Buckeye needed the help of the forward speed to get the rotor RPM up to 170. Ken's could start out at 200!

The Sparrow Hawk was very similar to the standard AAI mod.

As for the 150 Cessna. I was back home for a class reunion and flew with my instructor from many years ago. It climbed out slowww. I was being tossed around in thermals. And the cross wind landing was a pain. wait-wait, get blow sideways, wait-wait, pull-pull, wait, finally touch down.

But I took off and landed!

I felt much more comfortable in the gyro! The landings in a gyro are very similar to a square parachute. glide, flair, tippy toe touchdown, stop.

I almost feel like I get cheated out of 10 seconds of gliding above the runway waiting to loose airspeed.