Effect of prerotation on takeoff distance

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,955
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
From a standing stop to unstick in about 10 seconds, suggests a stronger headwind. But, accepting your figures, wouldn't the take-off have been even shorter beginning with 300 RRPM? Rhetorically asked, can the U-jointed AR-1 be power-prerotated to 300 RRPM with significant back stick, and, if so would such reduce the service life of the prerotator components (the U-joint in particular)?

MTO Sport 2017 and new Cavalon still use U joints and they pre-rotate to 300+ RRPM but they do not recommend pulling the stick back to do it but forward, actually technically just forward of neutral not completely forward
Yes the upper U joint deteriorate faster if the pre-rotation is done with stick back and they should be changed out faster if that is being done. However, let me ask how many people and how many times do they have to do this "short" takeoff roll where it is really needed. The only ones they need this done continuously and spend $100 every 2-3 months to replace the U joint constantly would be those who takeoff constantly from a very short strip or very bad soft field. Otherwise this technique would be used only when necessary

We prefer the flexshaft prerotator for reasons already stated, and we've the brakes to hold engine thrust for 300 RRPM. Other firms choose the U-jointed driveshafts. To each their own.

That's great. Flexshafts are available off the shelf. Tom Milton's old company offers them. If you can show that compared to pre-rotation to X RRPM with stick forward versus pre-rotation to the same X RRPM with stick back makes a significant difference in nil wind on the same gyro to clear 50 foot obstacle (the standard definition of takeoff distance), that would be a good thing to see and consider.


fara, in this thread I've read of no "promoting" these company test pilot steep climbs (yours included) as "official ways of takeoff procedure." For the typical owner, it is safest to stay in ground effect after take-off until at least Vx or Vy has been achieved. This completely avoids the H/V danger zone.

Good to hear your proper recommendation to build speed to Vx before starting climbout. That is where the real short field takeoff distance is measured at gross weight with zero wind at sea level 59 degrees F. All standards of compliance ask for that or rather ask for a speed from which you can recover after an abrupt engine out from any height during initial takeoff
 
Last edited:

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,955
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
Eric Changer's takeoff is irrelevant, because it is only possible by very low load and exceptionally high thrust-to-weight ratio (0.7).
In these exceptional conditions, takeoff at high rpm (330) becomes possible because the gyro can take a lot of support on the tail wheel and lift the main wheels until giving the disc an A.o.A of 30 degrees.
The vertical component of the propulsion then lightens the rotor load to the point that 25 mph and 300 rpm are enough to take off.
No mystery. Spectacular demonstration, not recommended for novices.

In other words if you want that performance, you have it in your own hands. Fly one up and lose 60 pounds and carry half tank or less into headwind and accept responsibly the higher risk that comes with it
 

Philbennett

Junior Member
Joined
Aug 17, 2014
Messages
506
Location
London
What is the definition of successful here?
It sounds like the definition of successful is Magni not having as many rotor strikes than say AutoGyro in takeoff phase?
If that is the criteria, the blame falls squarely on the pilot and more than likely the instructor and instruction given. Magni's can have a fairly long takeoff run on the ground because of straight keel. In a soft field that's a significant disadvantage. Their design philosophy is to protect against over-rotation from bad pilot technique but they pay for it in longer unstick (from the ground time). No free lunch.

The point of the blade flapping / sailing events where pilots set off with the stick fully forward isnt instructor/ instruction related because I know of no instructor who suggests doing that. This problem is pure pilot lapse/error.

Why does it happen well as I have explained to guys like Vance the more complex a process and the less time you spend doing it you can get snagged. He loved to argue all day long, until he got snagged. Not because he didn’t know but because he over looked the fundamentals.

Same here - if the stick come so back as part of the pre-rotation process rather than after it you’re obviously less likely to get snagged.

I hear you on the other dynamics but that wasn’t the point I was making.

As for higher pre-rotative rrpm and shorter take off distance. If you don’t bring the stick fully rearward (so you minimise drag) then it makes a difference in AutoGyro sport. With a 915 motor you can be +50ft solo within around 100ft.
 

Resasi

Gold Supporter
Joined
Jul 2, 2007
Messages
8,256
Location
London/ Kilifi Kenya
Aircraft
Gyrs, RAF 2000/Mgni/Bnsn/Hrnet/Mrlin/Crckt/MT-03/Lyzlle AV18-A/Prdtor. Pax ArrowCopter
Total Flight Time
100+ gyro, 16,000+ other
If you don’t bring the stick fully rearward (so you minimise drag)...
If you bring the stick full back, ie disc tilted back to the max angle of attack, then surely you will introduce a component of lift acting forward, and therefor you have created drag?

Understood that this is taught as a safe procedure to learn. Bring it all the way back, then, from there, ease it forward from that reference you have mentioned elsewhere, to neutralise that component?
 

anthom

Member
Joined
Mar 20, 2011
Messages
1,104
Location
Texas
Aircraft
AR1, Aviomania Genesis Sport
Total Flight Time
3500
I was re-reading this thread from the beginning.

It is great to have a gyroplane to be able to take off in as short a distance as possible and then accelerate to Vx or Vy. It seems that the studies show that using a technique like the Cierva gyros used will reduce the take off distance. However, my concern is still the flapping of the teetering rotors resulting in a possible crash. Take this technique as described in post #33:

And lastly, the shortest takeoff can be achieved by the known short-field technique: prespin as high as possible, accelerate to Vx with the stick forward (and, hence, a flat rotor disk with no drag penalty) and then bring the stick back to rotate and lift off. BEWARE, however, to try this yourself if you have never done it before. You will probably flap the blades and flip the gyro over -- a rendition of the classic Flap-'n-Flip ;). So don't try this unless you know exactly what you're doing.

The problem with the above technique is that the above method is quite different from the FAA manual for a short field take off, which basically is a normal take off with emphasis on pre-rotation. There is no question of accelerating on the ground with the stick forward, and is not advocated anywhere. The above procedure quoted seems to be a Cierva gyro take off technique.

While there are some very good pilots out there, what do the instructors teach the students? Most gyros can prerotate to 200 RRPM. That seems adequate for a normal take off. The endeavor it seems, is to shorten that distance more. The recent videos show that it can be done. Personally, I teach as per the FAA manual.

It seems that a new set of videos by SportCopter may shed more light on this.
 

Philbennett

Junior Member
Joined
Aug 17, 2014
Messages
506
Location
London
Hey Leigh - no sorry I was talking in that post about pre-rotation to 300-320rrpm with the newer AutoGyro models - here you just bring the stick back pretty much to the stick position point of regular flight actually.

Tony - vis the blade flapping point I think with the tip speed ratios required for flapping then it requires some effort (or a total failure to monitor ) to get yourself in trouble. Pre-rotate to 220rrpmand in my opinion you need to see around 50-55mph airspeed before you get into trouble - that is a relative long time.
 

Resasi

Gold Supporter
Joined
Jul 2, 2007
Messages
8,256
Location
London/ Kilifi Kenya
Aircraft
Gyrs, RAF 2000/Mgni/Bnsn/Hrnet/Mrlin/Crckt/MT-03/Lyzlle AV18-A/Prdtor. Pax ArrowCopter
Total Flight Time
100+ gyro, 16,000+ other
With ref to the two posts above.

Phil, understood. Actually it was what I thought you were trying to say, but to be specific, if I understand correctly, in the newer gyro models, the stick is bought back to normal flight attitude...it would in fact have further back stick available if you pulled it right back.
Yes 220 RRPM and 50-55mph does give at least give a margin to play with

Thomas. In full agreement with you. The idea of accelerating forward with the disc flat is as Chris has said is a pretty risky thing to do, as he in fact pointed out, and I do not think any Instructor to my knowledge would ever teach that.

I experienced with Rotor Hawkes, which are pretty benign blades, a very instructive experience on one high wind day. Without a preotator on the Bensen had decided to go and have some fun, I love windy days. I suppose it was probably around 20-25 with much stronger gusts, had patted up the blades with the stick forward and disc flat then, without even moving forward began to ease the stick back, and almost immediately experience a very rapid onset of blade sail.

It was violent and the side to side stick forces very strong. Stick forward cured that, and my immediate appetite for ‘fun’. The idea of accelerating down a runway with the disc flat does not appeal to me in the slightest no matter how fast its RRPM.

Very obviously the RRPM obtained when hand patting is very low, when compared with the speeds obtained by even a mediocre pre-rotator, but it was one of the moments that very indelibly drives home a useful lesson not easily forgotten.
 
Last edited:

XXavier

Member
Joined
Nov 13, 2006
Messages
1,352
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
694 gyro (Apr. 2021)
In the tests I've been doing recently with my ELA (now fitted with Averso Stella aluminum blades), when performing the take-off run after a normal (to 220 rrpm) launch, it seems to me that I'm no longer feeling the strong braking action typical of the old, original composite blades from ELA, and also that my present alu-blades lose less revs, and need a shorter time in order to recover the lost revs.

Perhaps the reason is that the ELA blades, being more elastic, twisted strongly under load, the AoA rose, and the switch from antirotation- to autorotation state took longer...

But these are all 'subjective measurements', and I 'll welcome any comments...
 

Jean Claude

Junior Member
Joined
Jan 2, 2009
Messages
2,259
Location
Centre FRANCE
Aircraft
I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
Total Flight Time
About 500 h (FW + ultra light)
Perhaps the reason is that the ELA blades, being more elastic, twisted strongly under load, the AoA rose, and the switch from antirotation- to autorotation state took longer...
In my opinion, under load, ELA blades twist less than Averso blades, because the ELA chord is balanced nearly 0.25 c
"now fitted with Averso Stella" Of the Same diameter?
 
Last edited:

anthom

Member
Joined
Mar 20, 2011
Messages
1,104
Location
Texas
Aircraft
AR1, Aviomania Genesis Sport
Total Flight Time
3500
Tony - vis the blade flapping point I think with the tip speed ratios required for flapping then it requires some effort (or a total failure to monitor ) to get yourself in trouble. Pre-rotate to 220rrpmand in my opinion you need to see around 50-55mph airspeed before you get into trouble - that is a relative long time.
That may be so, Phil. However, the take off technique described in the referenced post recommends accelerating with stick forward to Vx, which in most cases is probably 50 to 60 in most gyros. While this can be done without incident by some very skilled pilots, I do not see any advantage in trying this. Certainly not something I would teach anyone.

The point that I am again making is that the technique as described is not how it is per the FAA Gyroplane manual, which is what I follow. To call Chris' technique a "short field take off" is IMHO incorrect because stick forward is not described in the manual. If there is another reference to a "short field take off" for teetering rotor systems with forward stick, then I am unaware of it.

I have experienced blade flap and know that it is not something I would try and play "Russian Roulette" with.
 

XXavier

Member
Joined
Nov 13, 2006
Messages
1,352
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
694 gyro (Apr. 2021)
In my opinion, under load, ELA blades twist less than Averso blades, because the ELA chord is balanced nearly 0.25 c
"now fitted with Averso Stella" Of the Same diameter?
The new blades are, each one, ca. 5cm longer. Chord is the same...
 

Philbennett

Junior Member
Joined
Aug 17, 2014
Messages
506
Location
London
Yes Leigh you’re right the issue will bringing stick fully aft is that at launch - especially with a 915 motor - you will need to be quick in that forward movement as the motor can over come the drag and then you just get dumped on the tail.
 

Tyger

Super Member
Joined
Nov 25, 2017
Messages
1,249
Location
Germantown, NY
Aircraft
Magni M16
Total Flight Time
420
The point that I am again making is that the technique as described is not how it is per the FAA Gyroplane manual, which is what I follow. To call Chris' technique a "short field take off" is IMHO incorrect because stick forward is not described in the manual. If there is another reference to a "short field take off" for teetering rotor systems with forward stick, then I am unaware of it.

This is the technique I was taught for short-field takeoff (from the FAA Handbook):
"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."
It's not accelerating with the stick forward ab initio, but pushing it forward, just enough to stay on the ground, once takeoff rpm (but not yet Vx) has been achieved. When I do this on my gyro, it feels just like when the turbo kicks in on my car – I reach Vx and then climb very quickly.
 

fara

AR-1 gyro manufacturer
Joined
Oct 31, 2011
Messages
3,955
Location
Tampa, FL
Aircraft
AR-1
Total Flight Time
4000+ 380 gyroplanes. Sport CFI Gyro and Trikes
In the tests I've been doing recently with my ELA (now fitted with Averso Stella aluminum blades), when performing the take-off run after a normal (to 220 rrpm) launch, it seems to me that I'm no longer feeling the strong braking action typical of the old, original composite blades from ELA, and also that my present alu-blades lose less revs, and need a shorter time in order to recover the lost revs.

Perhaps the reason is that the ELA blades, being more elastic, twisted strongly under load, the AoA rose, and the switch from antirotation- to autorotation state took longer...

But these are all 'subjective measurements', and I 'll welcome any comments...

I have time in ELA with composite blades (25 hours or so), AutoGyro (MTO Sport and MTO 2017 Aluminum blades) and of course in AR-1 with Averso Stella Aluminum extrusion blades. Stella's do not decay as much. However at least with the straight hub bar they take longer to get to 200 RPM than AutoGyro or ELA
 

anthom

Member
Joined
Mar 20, 2011
Messages
1,104
Location
Texas
Aircraft
AR1, Aviomania Genesis Sport
Total Flight Time
3500
This is the technique I was taught for short-field takeoff (from the FAA Handbook):
"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."
It's not accelerating with the stick forward ab initio, but pushing it forward, just enough to stay on the ground, once takeoff rpm (but not yet Vx) has been achieved. When I do this on my gyro, it feels just like when the turbo kicks in on my car – I reach Vx and then climb very quickly.
Not sure about what you were taught. I'm afraid you have mentioned the latter portion of the technique which calls for being able to initially pre-rotate higher than flight RPM and then followed by what you have quoted. You seem to have omitted that part in your quote from the manual. That level of pre-rotation is not possible in most modern gyros, except for the jump take off ones. Also the part where the "blade pitch to be increased to normal in-flight setting" is dubious. In an earlier thread, started by JC a few months ago, the portion you mentioned had been de-bunked.

The first portion of the short field technique is what I advocate according to the FAA manual if you cannot prerotate higher than say 200 to 220, namely, "The technique is identical to the normal takeoff, with performance being optimized during each phase. Using the help from wind and propwash, the maximum rotor r.p.m. should be attained from the prerotator and full power applied as soon as appreciable lift is felt. VX climb speed should be maintained until the obstruction is cleared. Familiarity with the rotor acceleration characteristics and proper technique are essential for optimum short-field performance."
 
Last edited:

XXavier

Member
Joined
Nov 13, 2006
Messages
1,352
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
694 gyro (Apr. 2021)
This is the technique I was taught for short-field takeoff (from the FAA Handbook):
"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."
It's not accelerating with the stick forward ab initio, but pushing it forward, just enough to stay on the ground, once takeoff rpm (but not yet Vx) has been achieved. When I do this on my gyro, it feels just like when the turbo kicks in on my car – I reach Vx and then climb very quickly.

That's not possible with our fixed-pitch gyros...
 

XXavier

Member
Joined
Nov 13, 2006
Messages
1,352
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
694 gyro (Apr. 2021)
I have time in ELA with composite blades (25 hours or so), AutoGyro (MTO Sport and MTO 2017 Aluminum blades) and of course in AR-1 with Averso Stella Aluminum extrusion blades. Stella's do not decay as much. However at least with the straight hub bar they take longer to get to 200 RPM than AutoGyro or ELA

The moment of inertia is probably very different. I have no data of the m. o. i. of the Stella rotor, but I suspect that it has to be bigger than that of the ELA rotor, for the same diameter, because the ELA blades are much lighter...

Another thing that I noticed after I changed to the Stella blades is that more forward trim was needed, as if the new blades caused a larger flapping angle that had to be compensated by pushing the stick... If my interpretation is not wrong, what happens is that the Stella blades have a larger nose-up moment than the ELA composite blades (or perhaps it's that the ELA blades have a larger nose-down pitching moment than the Stella blades...).
 

Tyger

Super Member
Joined
Nov 25, 2017
Messages
1,249
Location
Germantown, NY
Aircraft
Magni M16
Total Flight Time
420
That's not possible with our fixed-pitch gyros...
Yes, obviously. Just ignore the bit about blade pitch... it is always at the "normal in-flight setting". Everything else applies.
 
Last edited:

Tyger

Super Member
Joined
Nov 25, 2017
Messages
1,249
Location
Germantown, NY
Aircraft
Magni M16
Total Flight Time
420
Not sure about what you were taught. I'm afraid you have mentioned the latter portion of the technique which calls for being able to initially pre-rotate higher than flight RPM and then followed by what you have quoted. You seem to have omitted that part in your quote from the manual. That level of pre-rotation is not possible in most modern gyros, except for the jump take off ones. Also the part where the "blade pitch to be increased to normal in-flight setting" is dubious. In an earlier thread, started by JC a few months ago, the portion you mentioned had been de-bunked.

The first portion of the short field technique is what I advocate according to the FAA manual if you cannot prerotate higher than say 200 to 220, namely, "The technique is identical to the normal takeoff, with performance being optimized during each phase. Using the help from wind and propwash, the maximum rotor r.p.m. should be attained from the prerotator and full power applied as soon as appreciable lift is felt. VX climb speed should be maintained until the obstruction is cleared. Familiarity with the rotor acceleration characteristics and proper technique are essential for optimum short-field performance."
I only pre-spin it to about 220, at which point I know I won't get any blade flap with the stick back, even at full power. Once I get to flight rpm (during the roll), it wants to lift off, but I keep it on the ground with some forward stick and then I am at Vx in a matter of maybe two seconds. The salient point from the manual is that of keeping it on the ground (nosewheel included) until Vx is attained, which happens very quickly.
I do not attempt this from a soft surface, for obvious reasons. As my instructor once said, "You don't ever want to combine soft-field with short-field takeoffs"
 

XXavier

Member
Joined
Nov 13, 2006
Messages
1,352
Location
Madrid, Spain
Aircraft
ELA R-100 and Magni M24 autogyros
Total Flight Time
694 gyro (Apr. 2021)
You mean the nosewheel on the ground...? Or skimming the ground...?
With the M24 (that can't be much different from the M16 in takeoff technique), I launch the rotor to 220 too, and then open the throttle partially, keeping the front wheel rolling until I've enough airspeed to have rudder authority. At that moment I pull the stick in order to unstick the front wheel, but I don't pull too much lest the tailwheel contacts the ground. I then open the throttle to the max, and the gyro takes off... The revs recover only during the last stage of the run...

It's much easier with the ELA...
 
Top