rrpms of dragon wings

[scottessex]

How fast rpm's wise do dragon wings need to be spinning before they won't flap? I know they take longer to spin up, but at what rpm do they go through that "zone" or is it just a trial and error thing to figure out.
I know I will not be able to accelerate as fast as with my old rotorhawks.

[Brent_Brown]

Whats up no prerotator?

[scottessex]

No I have a prerotator, but I have a rotor tach too. just wondering cuz on this rough runway, the idea is to get off the ground as soon as possible. With the rotor hawks i could spin up as fast as I could and then accelerate at a good rate and get into ground effect and build speed. When I flew John's dragon wings on the old gyro I started out the same way and got into small flap, scared me! so I know I have to accelerate slower and let the blades come up to speed more carefully. Just didn't know if there is a magic number I should look for on the rotor tach.

[gyropilot]

Scott,

When moving on the ground, I'm very careful to watch for flap in my DW's anytime the rrpm is below 100. I consider 70 rrpm or below to be entering the danger zone and flap is very easy to get into depending on taxi speed, winds, etc.

I usually don't begin my takeoff run until the rrpm is at least 150. If I happen to be looking at the rrpm during the takeoff roll (which is unlikely due to the position of my rotor tach down by my throttle hand), I don't go to full power until I see 250 rrpm.

On the other hand, the Rotordyne blades I used to fly were extremely forgiving with regards to blade flap. The flapping danger zone was closer to 50 rrpm and I could easily roll out onto the runway with 70 rrpm and start from there with no flapping if I didn't push it too hard. It seemed like blade flap never started with those blades no matter how sloppy or rushed my takeoffs got. They were great blades for a beginner gyro pilot.

When I "graduated" to DW's, I learned quickly I had to pay a lot more attention to rrpm management. One time I rolled onto the runway with the DW's spinning less than 100 rrpm (and the prerotator not engaged) for a rushed takeoff due to congested landing traffic. I basically tried the same technique I had always gotten away with on the Rotordynes. However, not long after I started the rushed takeoff roll with the DW's, I knew something didn't feel right... then I began to feel the tell tale light pounding in the cyclic! I immediately cut the power, leveled the rotor disk, applied the brakes, and turned off the runway. I made a quick radio call that I was aborting takeoff (not seconds after starting) due to "mechanical problems." No damage was done and I wound up getting back in line for takeoff again. That close call sure taught me a lesson that the DW's weren't going to tolerate me being sloppy.

I've since adopted the practice of applying the prerotator again to "freshen-up" the rrpm as I roll out onto the runway for takeoff. I keep the prerotator applied several seconds into my takeoff roll until I'm sure the blades are accelerating well. Haven't had a problem since then... even when I need to get airborne fast.

Regards,

John Landry

[scottessex]

Thanks John, That's the kind of info I need to know. Thanks.

[Aussie_Paul]

.....when you say, "I've since adopted the practice of applying the prerotator again to "freshen-up" the rrpm as I roll out onto the runway for takeoff. I keep the prerotator applied several seconds into my takeoff roll until I'm sure the blades are accelerating well. Haven't had a problem since then... even when I need to get airborne fast."

I had never flown DW until a few months ago and it has been a new learning curve with rotor management for me!!!!! LOL

Scott, if your are operating out of a rougher field that has marginal length for some conditions, :eek: I cannot see how you can operate DWs with out a pre rotator.

Aussie Paul. :)

[RHerron]

Scott,

Spin up to at least 100 and don't "cob" it until you see 200 rpm. You will find that the DW's will spin up quickly from 200.
200 is the "sweet-spot".

Having operated for years with the DW's and an electric prerotator, the technique has been verified.

John's technique is right on. Keep them nursed up with the prerotator anytime they drop much below 100.

Ron H

[steveb]

I look for 180rpm on my DWs before accelerating, I don't usually go to full power until I've got at least 200rpm. I've never tried lower rpms so I don't know what the limits are but those numbers have always worked for me.

I fly off a short strip (200 yards) - normally pre-rotate to 180rpm then let off the brakes and keep the pre-rotator on until I see the blades start to accelerate - then the pre-rotator comes off and the power goes in. I find that if I let the pre-rotator go before I let the brakes off then I lose 20 to 30 rpm before the blades start to accelerate again.

[Brent_Brown]

Scott what RRPM can you get out of your pre-ro?

[scottessex]

I don't know yet as I have not put the blades on and tried it, I will try it and see what rpm the prop over comes the brakes and use that as my pre rotation rpm limit and see what the rotor speed is.

[Thumpernator]

Scott,

I don't want to scare you, but there is NO magic number where the rotor is not capeable of flapping.

I once asked that same question to Ernie a few years ago. Until you get airborne, with the rotor fully supporting the machine, you can still flap the blades. Now, I'm not saying that you can't flap them in flight, because you can. But your concern was referring only to the takeoff, so I won't get into the flight part.

Do not rely on your rotor tach to tell you what the blades are doing during takeoff. It's the combination of several things that will tell you when the rotor is ready to accept more air.

Not an all inclusive list of these things, but you need to feel what the cyclic is telling you, the attitude of the machine (when it rocks back, for instance), the blur of the rotor, etc.

You're already a gyroplane pilot, so you know what I mean. Forget the numbers and feel the machine.

[cgmg]

Scott,

I agree with Thumpernator regarding not watching rotor rpm. Our instructor teaches, and flies, without a rotor tach.

We were taught to slowly accelerate from pre-rotation until the blades blur, and the nose comes off the ground. Use a count of three to accelerate to full throttle. Position the stick properly, and the machine lifts off when it's ready to fly. The only time we have both gotten in trouble was when we didn't wait for the blades to blur.

It takes patience and practice, but what I did, after getting comfortable with our Dragon Wings, is to try to shorten my takeoff distance by about 50-75' with each successive takeoff. I now can get off in 800' in all but the hottest days if I really have to. Since we have the luxury of both a 2000' and 2400' airstrip, it's not necessary to force things.

Be patient and practice with your Dragon Wings, and you'll probably be amazed at how much you can eventually shorten your takeoff distance.

[GyroRon]

Pre rotate to 200 and you can nail the throttle on the Hirth. If the pre rotator won't do 200 with the gyro sitting still, then hold in the pre rotator as you begin your takeoff roll and keep it in till you get to 200, then release and nail it. You should not have flapping above 200 RRPM with the little Hirth. You would need to worry if you have a bigger more powerful engine. I know your goal is to get airborne as soon as possible since your strip is kinda bumpy.