Effect of prerotation on takeoff distance

Vance

Gyroplane CFI
Staff member
Joined
Oct 30, 2003
Messages
17,229
Location
Nipomo,California
Aircraft
Givens Predator
Total Flight Time
2400+ in rotorcraft
I have stayed out of this thread because it seems there is an almost religious fever around what the rotor is doing backed up with what I feel is a poor interpretation of how an airfoil works.

In my opinion an airfoil stalls when the critical angle of attack is exceeded and stall is unrelated to airspeed.

In my opinion it is best to follow the Pilot’s Operating Handbook procedure for takeoff.

If the POH doesn’t have guidance for a short field takeoff then optimize each part of the takeoff like the Rotorcraft Flying Handbook says or find a better place to takeoff.

In my experience flying at an unfamiliar airport my takeoff performance may be very different from what it is at my home airport for a number of reasons.

Even at my home airport the takeoff and climb out performance may vary from takeoff to takeoff.

I was just watching the video of my maintenance flight of three patterns at SMX my climb out varied between four hundred and eight hundred feet per minute at fifty knots.

In my experience if you have a 50 foot obstacle to climb over in windy conditions there will be sink on the lee side further degrading climb out performance.

The only time I do a maximum performance takeoff (short field) is when I am giving instruction because that is one of the practical test standards.

In my opinion the reason short field takeoff procedures are taught is to show people a gyroplane in no wind conditions is not a short takeoff aircraft.
 

Tyger

Super Member
Joined
Nov 25, 2017
Messages
1,936
Location
Clermont, NY
Aircraft
Magni M16
Total Flight Time
470
You mean the nosewheel on the ground...? Or skimming the ground...?
ON the ground. I am not saying that this is my standard takeoff technique, but for short-field it works very well for me. It might be very different with a side-by-side.
 

Heron

Platinum Member
Joined
Oct 30, 2003
Messages
7,559
Location
Bauru - Sao Paulo - Brasil
Aircraft
Golden Butterfly
Total Flight Time
7.5 h.
There is a video somewhere that shows a gyro in heavy winds, taking off and flying backwards and repeting it, you should watch it.
The rotor needs only rpm to drag the gyro back, the gyro needs some wind over the controls surfaces to be maneuverable, you can prerotate until the wheels loose grip, no more!
The gliders tied to a rope with enough wind will fly, from where it sits.
So what was your question? You loose acceleration? Hell yes remember Uncle Ken Brock, they are draggy . . .
Does enough prerotation will shorten your take off roll? Yes if you have power enough!
If, lets say, a Magni is ahead of a Golden, both prerotate equaly and take off, the Golden will be atop of the Magni so it can't go up! Thats power, not prerotation!
Balance of power and disc load is a good thing!
 

WaspAir

Supreme Allied Gyro CFI
Joined
Oct 21, 2006
Messages
5,437
Location
Colorado front range
Aircraft
Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
Total Flight Time
stopped caring at 1000
That's not possible with our fixed-pitch gyros...
It's not possible with the A&S18A either. You can have either a gyro that lets you tilt the disc aft, or one that lets you increase blade pitch, but there's no gyro out there that would let you do both separately. On jump gyros, you will LOSE rpm with the rotor drive disengaged while airspeed increases, because you still have flat pitch in the blades. This paragraph is utter garbage that the FAA included in the handbook that doesn't apply to any aircraft ever put into manufacture, and was obviously written by some clueless soul who never flew a jump gyro or read the manuals for them.

If the prerotator is capable of spinning the rotor in
excess of normal flight r.p.m., the stored energy may be
used to enhance short-field performance. Once maximum
rotor r.p.m. is attained, disengage the rotor drive,
release the brakes, and apply power. As airspeed and
rotor r.p.m. increase, apply additional power until full
power is achieved. While remaining on the ground,
accelerate the gyroplane to a speed just prior to VX. At
that point, tilt the disk aft and increase the blade pitch
to the normal in-flight setting. The climb should be at a
speed just under VX until rotor r.p.m. has dropped to
normal flight r.p.m. or the obstruction has been cleared.
When the obstruction is no longer a factor, increase the
airspeed to VY.
 
Top