question about prerotation

blw2

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I'm a fixed wing guy only just interested in gyros
A few weeks ago I listened to a webinar through the FAA Wings program that was about working in uncontrolled airport patterns with gyros.
The guy showed a video to give fixed wing pilots an understanding of what sort of delay to expect when the take the runway...lineup and wait...for prerotation. I knew you guys did that already, so nothing new
& I think I at least on a basic level understand why you wouldn't prerotate in the runup area prior to taking the runway
but the thing I'm wondering about
is with typical GA airport you'll have a runway roughly 3,000 ft long at least.
Why not prerotate just long enough to get very minimal RPM...even just blade movement.... then roll and let the relative wind generate the required rotation speed before liftoff?
Seems to me that it would help to 'fit' into the traffic flow better and would actually be safer.
 

Vance

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That is a good and reasonable question Brad.

Not all gyroplane pilots pre-rotate the same way.

For a low time pilot the takeoff procedure is very task intensive and anything they do to reduce the work load is a good thing.

Stopping on the runway is one way to do this.

To give you an idea of what is involved I have copied the procedure from a Cavalon Pilot’s Operating Handbook.

“4.8 Take-off Procedure

Check relative wind

Maintain control stick in forward position with right hand

Switch pneumatic mode selector to FLIGHT and return to brake with left hand

Hold wheel brake without having locking pawl engaged

While holding wheel brake adjust throttle to give 2000 RPM (1600 RPM red overdr.)

Activate and hold pre-rotator.

To reduce lateral stick force during prerotation, adjust the forward stick position by pulling it slightly aft and to the right

Let pneumatic clutch fully engage (stabilization at about 110 rotor RPM).

If necessary release pre-rotator button momentarily and press again to maintain engine RPM within green arc, respectively prevent engine from stalling!

Carefully increase throttle (~ 20 R-RPM/sec) to 200 R-RPM – max. 220 R-RPM

When the minimum required rotor rpm is reached, release pre-rotator button

Gently – but smartly - move control stick fully aft (stick travel ~ 1 sec.). In a strong headwind be prepared to stop movement before nose wheel rises!

Release wheel brake with throttle unchanged

Monitor rotor speed and progressively increase throttle to take-off power.”

Trying to accomplish this on the roll while monitoring everything is a challenge for a low time pilot requiring multitasking and elevating the risk.

Takeoff mishaps account for about a third of gyroplane accidents in the USA.

Too much forward speed for rotor rpm and you lose control of the blades often striking the empennage or the propeller. Worst case the gyroplane rolls over. This is often referred to as flapping the blades.

Trying to rotate before the blades are up to speed is a common way to destroy a gyroplane.

Some experienced gyroplane pilots began their pre-rotation behind the hold short line.

It increases the workload, requires multitasking and elevates the risk.

The takeoff procedure is what it is to reduce the risk of a mishap.

A low time pilot may take a little longer on the runway.

It is my observation that for an experienced gyroplane pilot stopping on the runway to pre-rotate takes no longer than a typical piston twin.

As a gyroplane pilot I would be embarrassed to shut down the airport by destroying my gyroplane on takeoff because I wanted to fit in.
 

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WaspAir

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Why not prerotate just long enough to get very minimal RPM...even just blade movement.... then roll and let the relative wind generate the required rotation speed before liftoff?
Seems to me that it would help to 'fit' into the traffic flow better and would actually be safer.
What you suggest is what simple gyros without prerotators do after gettting the blades moving by hand, and it isn't faster overall. You must roll very slowly at first, gaining rotor rpm before you get much forward speed, or you induce the "flap" that Vance mentioned. Initial rotor rpm is gained much faster sitting still on the runway with a strong prerotator than creeping along as rpm builds from airflow alone, and the net time is improved.

You really don't want other traffic trying to land behind or crowd the takeoff of a slow moving gyro on the first third of the runway, so you haven't improved the traffic flow until you're actually up and away.
 
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Tyger

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From my experience, most gyros do start to prerorate before crossing the hold-short line (I certainly do), but it's best to build up to takeoff rpms when facing into the wind, and you usually need to be on the runway to do that.
 
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jm-urbani

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in france we pre-rotate after alignement, I have never seen anyone here starting the process at the holding point of before
 
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loftus

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Not flying gyros presently but I would routinely begin prerotation at the same as I began the taxi from the hold short line. So that RRPM was usually close to minimum RRPM by the time I was aligned on the runway for takeoff, thus allowing the stick to be brought back and throttle applied for takeoff without pausing on the runway. I never found it to be task intensive as I would not leave the holdshort line till I'd established that the runway was clear and/or I'd been cleared for takeoff. This certainly shortens the time from leaving the holdshort line till liftoff which is helpful to all at a busy airport.
 

PW_Plack

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Even once a small gyro is airborne, its speed in flight may be below the stall speed of the next landing aircraft in sequence. I'm not sure there's any way to dramatically speed up the process without encouraging the gyro pilot to sidestep the runway immediately after the wheels lift, which brings its own risks, both to the gyro pilot and other aircraft in the vicinity.
 

Jazzenjohn

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I start the blades rotating when I taxi and virtually always taxi with my blades turning at about 65 RRPM. When i'm nearing the cross taxi and I've scanned for planes, I begin to spin them up to full speed as I make the call and turn on the cross taxi. I go into position and hold while it fully spins up and go when everything is ready. I'm at a non towered airport and that is just the way I've gravitated to be as unobtrusive as I can be.
 

jm-urbani

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Not flying gyros presently but I would routinely begin prerotation at the same as I began the taxi from the hold short line. So that RRPM was usually close to minimum RRPM by the time I was aligned on the runway for takeoff, thus allowing the stick to be brought back and throttle applied for takeoff without pausing on the runway. I never found it to be task intensive as I would not leave the holdshort line till I'd established that the runway was clear and/or I'd been cleared for takeoff. This certainly shortens the time from leaving the holdshort line till liftoff which is helpful to all at a busy airport.
on the magni, the DTA's and also on my amateur monoseater the pre-rotator is linked to the propeller, I don't know what is your system but I am wondering how you can manage both the rrpm and the taxiing speed ?

an other thing on those gyros it is not wise to re-engage the pre rotator when the rotor is already turning ( you risk breaking the bendix and the thooth ring).

so if I initiate the pre-rotation at the holding point , i won't be able to re-engage the prerotator one aligned .. and againt on short runways we need to get full pre-spinn rrpm to take off .

your style of pre-spinning is ok for long runways and not for short ones .. personally even if the runway is 3 km long , the soon I get airborne the better because the part of the runway behind me is useless

all of this is one of the reasons why I am attempting to build a brushless pre-rotator to reduce my 2 minutes pre-rotation time to 30 seconds
 

Doug Riley

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If the runway layout allows, I "hold short" with the gyro pointing partly into the wind (about 45 deg. off the takeoff heading). That way, I can prerotate more or less facing the wind, but still see the final approach path. Once the approach is clear and RRPM is up to 180 or more, I let up the brakes but don't disengage the prespin. I begin my takeoff roll with the prespin still engaged, and continue increasing throttle until the wind takes over accelerating the rotor and the Bendix drops out on its own.

This is still not an instantaneous process, but it consumes as little active-runway time as is possible with a gyro.

This technique requires a fairly powerful prerotator and the ability to see the approach path over your shoulder.

If I'm in the middle of this process and a fixed-wing craft taxis up behind me, I'll often wave it ahead of me, space permitting.
 

loftus

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on the magni, the DTA's and also on my amateur monoseater the pre-rotator is linked to the propeller, I don't know what is your system but I am wondering how you can manage both the rrpm and the taxiing speed ?

an other thing on those gyros it is not wise to re-engage the pre rotator when the rotor is already turning ( you risk breaking the bendix and the thooth ring).

so if I initiate the pre-rotation at the holding point , i won't be able to re-engage the prerotator one aligned .. and againt on short runways we need to get full pre-spinn rrpm to take off .

your style of pre-spinning is ok for long runways and not for short ones .. personally even if the runway is 3 km long , the soon I get airborne the better because the part of the runway behind me is useless

all of this is one of the reasons why I am attempting to build a brushless pre-rotator to reduce my 2 minutes pre-rotation time to 30 seconds
Not sure if I am describing it that well, and not advocating it as a short field takeoff technique. But just never found it difficult to begin prerotation at the hold short line when cleared for takeoff. Begin to taxi forward with the brake still controlling forward speed as I turn onto the runway into position still with stick forward and allowing RRPM to continue to accelerate as I taxi into position and by which time RRPM was at 160, allowing stick back, complete release of the brake, and advancement to full power. Never needing to reengage the prerotator which cannot be done anyway in an MTO when the stick is pulled back because of a microswitch that automatically disengages the prerotator when the stick is pulled back. This technique was taught to me by my CFI to help facilitate a shorter time from being cleared by the tower till liftoff when I did some of my training with him at his base which was a towered airport in Houston. Simply saves a few seconds when taxiing in position can be used to build some RRPM rather than starting from zero RRPM when in position. I'm not promoting it as a technique to shorten the takeoff roll, rather a technique to shorten the time from tower clearance to takeoff, or time holding up other aircraft behind me at a busy airport as KDED my base often is. Also not saying it's an essential technique if one is not comfortable with it, I just never had a problem with it. In contrast my hangarmate in his Calidus prefers the traditional way for all his takeoffs.
 
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Vance

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on the magni, the DTA's and also on my amateur monoseater the pre-rotator is linked to the propeller, I don't know what is your system but I am wondering how you can manage both the rrpm and the taxiing speed ?

an other thing on those gyros it is not wise to re-engage the pre rotator when the rotor is already turning ( you risk breaking the bendix and the thooth ring).

so if I initiate the pre-rotation at the holding point , i won't be able to re-engage the prerotator one aligned .. and againt on short runways we need to get full pre-spinn rrpm to take off .

your style of pre-spinning is ok for long runways and not for short ones .. personally even if the runway is 3 km long , the soon I get airborne the better because the part of the runway behind me is useless

all of this is one of the reasons why I am attempting to build a brushless pre-rotator to reduce my 2 minutes pre-rotation time to 30 seconds
I have not found it difficult to manage taxi speed even with a pre-rotator connected to the engine.

On a short runway I have all the more reason to pre-rotate behind the hold short line so my blades are spinning up as I approach the centerline adding distance to the runway.

I teach by the POH of the aircraft I am training in and if the POH says stop on the runway that is what I teach.

In The Predator I began my pre-rotation before I cross the hold short line and typically get the blades to 100 rpm by the time I reach the centerline so I can bring the cyclic half back and begin to use the wind to get the blades up to speed.

In my opinion automobile starter would not survive if I had it engaged more than 20 seconds. I am on starter number four at 2000 hours and 2,500 pre-rotations.

At my home airport I tell the tower if I have a low time primary student so they can better judge the time for takeoff.

They do not want to have an airliner need to go around if I am dawdling on the runway.

At a not towered airport I announce delay on runway for spool up so the other pilots know not to crowd me.

When I am doing stop and goes I typically do not use the pre-rotator.

I feel aviation should not be hurried and pre-rotation should not be rushed trying to fit in.

Because of my maneuverability at low speeds (I can side step if the tower requests it) and accurate landings I suspect I spend less time on the runway than a typical fixed wing.

I spend a lot less time on the runway than a typical low time fixed wing pilot.
 

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jm-urbani

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Not sure if I am describing it that well, and not advocating it as a short field takeoff technique. But just never found it difficult to begin prerotation at the hold short line when cleared for takeoff. Begin to taxi forward with the brake still controlling forward speed as I turn onto the runway into position still with stick forward and allowing RRPM to continue to accelerate as I taxi into position and by which time RRPM was at 160, allowing stick back, complete release of the brake, and advancement to full power. Never needing to reengage the prerotator which cannot be done anyway in an MTO when the stick is pulled back because of a microswitch that automatically disengages the prerotator when the stick is pulled back. This technique was taught to me by my CFI to help facilitate a shorter time from being cleared by the tower till liftoff when I did some of my training with him at his base which was a towered airport in Houston. Simply saves a few seconds when taxiing in position can be used to build some RRPM rather than starting from zero RRPM when in position. I'm not promoting it as a technique to shorten the takeoff roll, rather a technique to shorten the time from tower clearance to takeoff, or time holding up other aircraft behind me at a busy airport as KDED my base often is. Also not saying it's an essential technique if one is not comfortable with it, I just never had a problem with it. In contrast my hangarmate in his Calidus prefers the traditional way for all his takeoffs.
all of this shows that we need effective reliable and quick brushless pre-rotators that are able of pre-spinning up to 200 rpm in 25 seconds
 

Tyger

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on the magni, the DTA's and also on my amateur monoseater the pre-rotator is linked to the propeller, I don't know what is your system but I am wondering how you can manage both the rrpm and the taxiing speed ?
an other thing on those gyros it is not wise to re-engage the pre rotator when the rotor is already turning ( you risk breaking the bendix and the tooth ring).
so if I initiate the pre-rotation at the holding point , i won't be able to re-engage the prerotator one aligned .. and againt on short runways we need to get full pre-spinn rrpm to take off .
I have a Magni. I manage taxi speed with the brakes, as a matter of course. Even at engine idle I would usually be going too quickly down a hard taxiway with no brake.
I prerotate up to 100 rpm, with stick forward, at or near the hold short line, at which rpm it becomes safe to pull the stick all the way back and move onto the runway, taking advantage of the wind to help spin the rotor to takeoff rpm before beginning the takeoff roll.
I am not clear why I would need to "re-engage the prerotator once aligned" – it's normally engaged the entire time.
It's rare that I have ever had to disengage the prerotator after starting to spin up, but on the times that I have it's never been a problem re-engaging it with the rotor spinning, with no damage to the bendix or ring gear. The Magni rep assures me that it's not a problem.
 

jm-urbani

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it would not be possible to taxi idle on a grass surface, we have to push the throttle to make the giro leace the holding point. hence we would have to pull back the throttle and it is really dangerous for the shaft to force the rotor to decelerate ( shafts are mande to turn in only one sense )

in those conditions the only possibility would be to disengage and re-engage the prespiner which is perfectly harmful for the system too

what you are doing is maybe possible on your kind of surface but not on the ground

that's just my experience
 

Tyger

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I'm afraid I don't really understand what you are trying to explain in your first sentences, jm. What shaft are you talking about?
Magni prerotators allow for controllable slip between the propeller and the bendix, and the flex cable allows them to stay engaged in all stick positions. My home field is grass/turf, and I have never had to disengage my pre-rotator there despite, as you say, often having to push the throttle a bit to get moving on the turf.
 

coyotekyk

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I think the shaft jm-urbani means is the flex cable.
It is true that they are designed to exert torque in just one direction.
 

Vance

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it would not be possible to taxi idle on a grass surface, we have to push the throttle to make the giro leace the holding point. hence we would have to pull back the throttle and it is really dangerous for the shaft to force the rotor to decelerate ( shafts are mande to turn in only one sense )

in those conditions the only possibility would be to disengage and re-engage the prespiner which is perfectly harmful for the system too

what you are doing is maybe possible on your kind of surface but not on the ground

that's just my experience
Every gyroplane I have flown had some sort of one way clutch and the pre-rotator could not slow the rotor down.

My clients often press and release the pre-rotator and in over 2,000 hours I have worn out one ring gear.

In my opinion it takes more skill to pre-rotate on the move and that adds to the risk.
 

Sv.grainne

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I'm not a pilot yet but after reading this forum I timed the pre-rotation sequence when I went out with a friend in his Tango yesterday. We were flying off of a grass strip but after taxing out and stopping he engaged the pre-rotator at engine idle then brought RRPM up to about 200rpm and we started takeoff roll. Pre-rotation period was 15 seconds. This does not seem like an issue to me!
 

WaspAir

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I've flown out of busy towered airports at which it would be hard to know when to start a spin-up before clearance onto the runway and if you mis-judged it a re-engagement could certainly be necessary (preferred over several minutes of continuous engagement). Sometimes you just don't know when it will be your turn.

Much of this stuff is model dependent.

In the 18A there is no one-way clutch and reducing throttle will slow the rotor.

I always ask the tower (or advise traffic) that I'll be in postion for a minute for rotor spin-up before departure, and it does take about that long with an 18A or J-2. Towers usually modify their sequence to fit me in better and often give me a "line up and wait" to provide time to get the rotor going, sometimes adding "advise when ready".
 
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