The effectiveness of advanced short field take-off technique

ckurz7000

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Just a quick disclaimer: the following statements and procedures were tested in an ArrowCopter. I expect they will also apply to MTOs, Calidus, Cavalon, Xenon, ELA, etc. They definitely don't apply to gyros like Magnis, which can leave the prerotator engaged during the take-off roll. I don't recommend you try them unless you have already done them before. Go and get an instructor to teach you first, because there is the real danger that you will flap the blades and bang up your beautiful gyro.

Usually when people want to do a short-field take-off they prerotate as high as possible and do a more or less normal take-off procedure.

I already posted in an earlier thread that anything above about 190 rrpm on the prerotator is not going to get you off any quicker. So there really is no point to strain your gear and prerotate to 240 or even more. You will not clear the imaginary 50 ft tree any sooner.

There is, however, one thing you CAN do which may get you into biiiig trouble if you don't do it properly. That's why I put the word "advanced" in the procedure's name. If you haven't donw it before, don't try it on your own. Get an instructor to show you first.

If you really need to get off the ground and over the 50 ft tree in the shortest possible distance, here is what you can do:

1) Prerotate as high as possible. And this time I really do mean it and it does make a difference.

2) Keep the stick at the FORWARD stop and go to full throttle. You will be accelerating much more quickly than with the stick held back. However, your rotor rpm will also decline. If it falls below 200 rrpm you have to abort the take-off!

3) About 10-15 km/h before reaching Vx pull the stick back (my Vx is at 85 km/h, so I pull the stick back at about 65-70 km/h). Don't yank it back but bring it back snugly over the course of about 1-2 seconds.

4) You will lift off immediately, therefore watch out to maintain a suitable pitch attitude to continue climbing at Vx.

The other day I was curious as to how much this technique is shortening the ground roll and the distance over a 50 ft obstacle. I did 9 standard take-offs and 5 advanced take-offs. The upshot is that the advanced technique shortens ground roll by about 12% and total take-off distance by about 7%. So it doubles as an advanced soft/rough field take-off technique as well.

Thought you might be interested in that.

-- Chris.
 
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Chris, I would be telling people how to do this unless your 100% sure it will work every time.
 
So Chris what is your shortest take off roll?? in feet or yards. no wind
 
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I have found that if you want a gyro to be able to take off short you need not only a prerotator that can get to three hundred rpm but a prop with a diameter at least twenty five percent of your rotor diameter, more is better but I'm sure there is a point where there would be no improvement but I haven't found it yet and an eight foot prop with a twenty three foot rotor is almost a helicopter, it can break ground in about thirty feet and climb with the rotor full back at a very low speed, if the engine were to quit while in this condition you get to build a new gyro and should get twenty five dollars for the old one as scrap metal.
Norm
 
Hi Chris, this method may work - but I also suspect that this technique allows absolutely no wriggle room for error and the risk of incurring a high speed blade flap is unacceptably high. In fact, I'd go as far to say that other than for a very skilled and experienced pilot it would be a case of "not if but when" someone would likely end up bending their gyro by trying to take off using this procedure on an unsafe, marginal runway.
 
If I may add that finding oneself having to attempt such a marginal take-off in the first place is the wrong place to be in... and I'll share a very very close call I had in such a situation.

About ten years ago 2 friends and I flew our gyros on a 1,500 nautical mile round-trip adventure safari to the remote Wild Coast of South Africa. We landed (uneventfully) on an old "bush strip" runway in the Dwesa Forest Nature Reserve where we had arranged a fuel drop. What we failed to notice from the air (nor from our Google Earth pre trip planning) was that the long-unused hillside runway surrounded by forest had subsided to such an extent that the gyros would have insufficient counter-steer to maintain a straight take-off roll along the badly sloped camber of the runway. Choosing the flattest section of useable runway (barely 150ft) we macheted back vegetation to provide clearance for the rotors where we would attempt our take off again. During my take-off attempt I pre-rotated to approx 250rpm, stood on the left rudder to try and anticipate and counteract the side-slope to the right - and upon releasing the brakes and commencing a fast roll on the uneven surface I immediately realised I could not counteract the slope sufficiently as the gyro veered downhill off the side of the narrow runway. Aborting would not have stopped the gyro ploughing headlong into the bush and small trees at the bottom of the hillside slope - and instead I opted to bang open the throttle, engage full turbo, hold the stick forward, and literally race the gyro directly at the approaching dense foliage - where, with mili-seconds to spare, I hauled back hard on the stick and managed to yank the gyro into the air and over the tree line. It was darn darn close - as evidenced by the leaves snagged in the tail-wheel. I have often questioned my decision. Perhaps simply ploughing into the bush would have been the safer option? It was a spur of the moment decision to try and fly out of the trouble ahead instead - and I got lucky.

I don't need to point out where the lessons to be learned are. During my military days we used the Six P's principle: Piss Poor Planning results in Piss Poor Performance and our planning had been just that - Piss Poor! The bush strip was actually unusable - and relying on Google Earth (and also the opinion of a non-pilot local resident) to determine its suitability beforehand had been a major mistake. We were forced to land there to overnight for a few days and to refuel. Proper planning would have averted having to try such a marginal short field takeoff in the first place - and my seriously lucky narrow escape from disaster.
 
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I really really don't recommend this in an AutoGyro

I really really don't recommend this in an AutoGyro

I accidentally did it this way once.

I thought I was a goner.
 
I think I have seen video of this method but it looked like everything ended up in the dumpster.
 
High density altitude and gross weight will make a huge difference.
Several smaller things could also make a difference.
I wouldn't try it with less than 125 hours in type.
 
Setn up your prespinner properly shortns your roll by 75%, with 0 risk of blade flap and a near virtical climd out.
One day you blokes will catch up. ;)
 
Chris, you have just one day ahead.
Yesterday, by simulating accurately the takeoff distance, I find your result which we should not run with the stick back immediately after the pre-launch. It is more efficient to start the run with the stick at the FORWARD stop.
Three reasons for this:
One is that the static thrust of the rotor reduces acceleration of the run.
Second is that the rrpm can not increase, as the flow is pumped by the rotor inertia from its upper side.
Third is that during this time, the rate of loss of rrpm is stronger, because of the rotor thrust.


The forward speed when the stick must be pulled on the back stop is one to which the flow can pass through in the auto-rotating direction.
It depends on the rrpm, and the disc angle on the rear stop.

Remenber I had already raised this issue here, saying "VRS", i.e transition between flow from upper side, to flow from underside.
 
7% less roll distance is poor reward for running the risk. The results nevertheless are interesting. What would be the optimum disc angle(s) to accelerate the rotor during ground roll?

Dino
 
Just to be absolutely clear about it: I don't recommend this procedure. I am merely persuing this as a kind of research and to satisfy my curiosity. It contributes to our understanding of the take-off procedure in general. I have performed this procedure maybe 50 times so far. There is a way to do it safely, but I wouldn't recomment it as part of the standard training or normal toolset of a gyro pilot.

-- Chris.
 
This technique is too advanced for me Chris.

I have found short fields with surrounding trees to have some peculiar turbulence that may inhibit climb out.

I have a low fear threshold and find fear diminishes my joy.

Thank you for the testing Chris. It is always interesting to quantify things.
 
Hi Chris:
Curious if you have tried finding the distance to takeoff and clear 50 foot obstacle by disconnecting your pre-rotator safety switch so you could continue to pre-rotate as you start your ground roll. For example, something like
1) Pre-rotate to 15 RRPM while stationary
2) Apply more power and start ground roll and smoothly pull the stick back to neutral cruise
3) Keep applying more power and keep pre-rotator engaged
4) At Vx the stick should be almost all the way back and you should already be at full power
5) the gyro leaves the ground and you adjust the stick to maintain attitude and Vx and keep full power

In the AR-1 the pre-rotator is actuated by a handle squeeze mechanically. So there is no pre-rotator kill switch. The pilot has to be trained to know how to manage rotors
 
In my opinion, there is no danger in keep the stick on the forward stop before 25 mph during the accéleration. The rate of slower of rotor is the same as the flow is still "helicopter"

Take off procedure of Cierva 30:

 
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