Rotax 915 is not for new pilots

rdalcanto

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A year ago when I had the opportunity to fly several different gyros, including the AR1, Magni M24, Cavalon, Tercel, and Taurus, I noticed that I had more trouble keeping the Tercel and Taurus on the centerline on takeoff when flying solo (not a problem with the weight of two people). At the time, I attributed it to the dual rudders being outside the prop wash on the Trendak gyros. It turns out that the issue was actually the power increase and p-factor increase from the more powerful Trendak engines. I was able to fly a 914 equipped M24 for several months while I waited for mine to arrive from Italy (and then have the SBs that were out on the 915 engine). When flying solo, keeping the 915 powered M24 on the centerline can be a real challenge compared to the 914 powered version (otherwise identical gyros). Gyros are light weight, and the p-factor when you go to full throttle early in the T.O. run pulls the gyro very hard to the left. It is completely controllable with a lot of right rudder, but that also means the nose wheel is turned a lot should it touch back down while trying to balance on the mains. This is less of an issue in a gyro like the Magni that has a castering nose wheel, but it is still an issue. I would strongly recommend, based on my experience, to not put low time gyro pilots in a gyro with that much power. Having a lot of power is great for fast climbs and is safer when we talk about not getting behind the power curve, and everyone wants the latest and greatest engine. However, getting safely off the ground is priority number one. That being said, if there is plenty of runway, the engine torque with the 915 is less of an issue if you slowly add the power as you accelerate down the runway, as opposed to applying it quickly while just starting the take off run.
 

Philbennett

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How about focus on two things - tale off technique and aircraft rigging. You already alluded to part of the first - why firewall the throttles before you are ready? But also ensure you are actually aligned well in the first place - many people causually line up actually pointing with nose wheel 20-30degs off. Pre-rotate accurately so you are not spending longer building RRPM in a ground roll that the pre rotator should. Then what aboit crosswind and where i the disc ??

Regards rigging rudder straight, nose wheel straight isnt going to work well for you in the take off phase because of your need to use rudders (aerodynamic divices) verse nose wheel (contact with the road) the origjnal MT03/spprt was rigged with quite a lot of offset.

Finally if you still cant get on then getting the nose wheel off earlier will inceease "comfort".
 

Tyger

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Perhaps you should rig the rudder a bit right with the nose wheel straight. That's now mine is rigged, and I only have a 912.
 

GyrOZprey

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On my most recent Flight Review ...my CFI & I worked out that it was really not advantageous to go full turbo on the 914 powered gyro..until we had lifted off ...then it was easy & much safer to counter the P-factor torque-roll in the air rather than on the surface! I have modified my standard take-offs now in higher-powered machines to reserve that extra power for the climb-out rather than the TO roll!
 

Tyger

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But is it really p-factor when you begin your takeoff roll? Your prop should still be at a low angle of attack then. I would think "p" only starts to become a factor once your nose wheel is off the ground.
 

fara

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I remember you coming to visit us kindly and taking a flight in an AR-1
I actually recently trained in a Trendak for 2 hours. Actually having rudders on the outside should be an advantage. I started to get used to the Trendak rudder and stick feel. I would have to fly it a few more hours with an instructor to really feel comfortable. One up I have no idea what it will be like but they do use ballast one up. I did not care for the Trendak engine as much. I do believe that 915iS is a better choice for that gyroplane.
I did not notice getting off the center line as much as you mention. With a higher power and torque engine, it does require more care. We noticed that in trikes going from Rotax 582 powered machines to 912ULS or 914 machines and trikes have no rudder so you are forced to engineer other things to make this manageable. We did it with thrust line offset. Airplane manufacturers also use some thrust line offset partially for the same reason. It lessons the flat turn tendency since your distance to vertical tail and rudder is set in stone. You can use rudder rigging to a certain degree also but it starts to become a bit much beyond a certain point and a thrust offset is a better option.

One thing I emphasize to myself and people working with me is that powered aircraft are designed against an intended engine set. Like 912 to 914 series. Changing engine to a much higher power or lower power should not be taken casually in design. An AR-1 with 915 frame or for a XO-360 will not exactly match an AR-1 for 912 or 914 frame. Other designers have different philosophy
 
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rdalcanto

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Perhaps you should rig the rudder a bit right with the nose wheel straight. That's now mine is rigged, and I only have a 912.
There is. It is fine for cruising flight. You can't imagine the p-factor difference between the 912 with a tiny 3 blade prop, and the 915 with the huge 5 bladed prop that I have. It is an issue when the front wheel comes off the ground. At that point, with a lot of throttle, you have to basically stand on the right pedal to hold it straight if you are solo. With two people, both the Magni with the 915, and the Tercel with the modified engine, are MUCH easier to keep straight. I had my Sport rating and was working toward my Private when I was flying the Tercel. The first flights were with an instructor, and I had no issues. When I went to fly it solo is when I suddenly found myself heading toward the runway lights on the left. I did a lot of flights in the Tercel, and the p-factor when solo was always a concern for me. With more experience, it has become a non-issue, but I predict there will be a lot of accidents with new pilots flying new gyros with the more powerful engines. Today I was rolling the throttle on much more slowly, and it helped, but you use more runway. It is good to have the skill to be able to do a short field takeoff as well by going to full throttle quickly.prop.jpeg
 
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Tyger

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But why should there be more p-factor with one person than with two? Is it because you significantly increase your angle of attack when solo?
 

Vance

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In my experience engines come with a throttle that controls horsepower.

More horsepower just means more is available.

The throttle allows people to use as much as they are comfortable with.

The Predator has 160 horsepower and often the person controlling the power has very little experience flying a gyroplane. I have yet to have a takeoff go badly because of too much power. Some have gone badly from too little power and I have had to add power to straighten things out.

These people I see that rapidly open the throttle as soon as they hit their target rotor rpm are not following the pilots operating handbook for takeoff procedure.

If I was concerned with a client using too much power in their gyroplane I could always rig the throttle to where it did not open all the way.

I recommend aborting a takeoff that is not on the centerline as part of the process of learning to control the aircraft. It is usually a combination of too much throttle too soon and not enough rudder.

The rudder doesn’t work well at low speeds and its effectiveness goes up by the square of the increase in the speed.

Waiting till you have 20kts of forward speed before going to full throttle may have value in your gyroplane and it won’t increase the takeoff roll by much.
 

Vance

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But why should there be more p-factor with one person than with two? Is it because you significantly increase your angle of attack when solo?

In my experience everything happens quicker solo so challenges become magnified.
 

XXavier

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I can't see any reason for the 'P-effect' at take off in the M24/915 to be more severe than in a 'normal' M24/914. Of course, the Rotax 915 is more powerful than the 914, but that's maximum power. I'm now flying a M24/914, and when taking-off in that gyro, specially when starting the run, I don't open the throttle to the max, but increase the power slowly, while keeping the gyro centered with right pedal and left stick... If my gyro were fitted with a more powerful engine, I would take off with the same power, with a bit less throttle...

There's a difference when taking-off solo, but that's due to the backward displacement of the c.g., so that the front wheel rises easily too much too soon...
 

NJpilot

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Seems to me the progressive power application of the take off technique that avoids premature lift off and wheel balance may be a 915's best friend.

John

 

ventana7

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Short takeoffs are impressive, but since 99% of gyro flying in the US is from airports with long runways what is the difference if you use 50’ or 200’ or 500’ of a 3,000+ foot runway.

I have 140+ HP in my Xenon and add power slowly. For me this usually makes me pop off the ground closer to flying speed and reduces the immediate need for a quick lowering of the nose to accelerate in ground effect.

Rob
 

NJpilot

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Short takeoffs are impressive, but since 99% of gyro flying in the US is from airports with long runways what is the difference if you use 50’ or 200’ or 500’ of a 3,000+ foot runway.

I'm not sure if this is a comment is about the technique the video describes. It certainly is not a short take off technique. In other videos by the same instructor he laments that gyros are considered STOL aircraft by so many.

I have 140+ HP in my Xenon and add power slowly. For me this usually makes me pop off the ground closer to flying speed and reduces the immediate need for a quick lowering of the nose to accelerate in ground effect.

Rob
Now this is very close to what the instructor in the video professes. He also reduces full back stick "one fist" once rotor rpm is seen increasing.
Most videos I see show the pilot stabbing full throttle the instant pre rotor rpm is reached. This provides full p-factor when the gyro has least rudder authority.
 

Vance

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I recommend a takeoff technique that involves balancing on the mains and letting the gyroplane fly when she is ready.

I teach that cyclic control is about pressure rather than position.

In most of the gyroplanes I have flown if balancing on the mains is done correctly with a correctly set up gyroplane; she will lift off very close to Vy.

This is the technique recommended in the AutoGyro pilots operating handbooks.

I feel condemning balancing on the mains because many people have not learned to do it well is not the best choice.
 

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Philbennett

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Hello everyone, happy im that instructor who made the video cited so you can have a view from the horses mouth so as to speak.

Firstly someone introduced the term p-factor and it has been incorrectly applied to everything since!

This thread is about the 915 in a Cavalon not being suitable for a novice and questions/statements as to why.

The reason it has caught the original posters attention is nothing more complex than more air is being moved. Aero engines can produce all the BHP they like but it means very little until that power is transmitted represented as thrust via the prop. Hence why the 915 powered gyroplanes (well all the ones available in the UK) have props that have the ability to move more air typically an additional blade to the same diameter prop.

That creates more propeller slipstream which interacts with the tailplane which is what you feel. At this point we have a consistent AoA and thus no change in p-factor.

Take offs in gyroplanes are very simple and merely require a good process to be followed consistently. I have a view, others have theres. I wont seek to sell a view but ill say this.

If a pilot can not take off consistently then frankly he shouldnt hold a licence. It is pitiful to see all these take off accidents in fully functioning aircraft. It demonstrates that people simply do not understand the basic principles of what they are trying to achieve.

The ability and desire to be able to acquire and maintain directional stability in the take off roll is a given. If we have to start the learning point earlier than this goodness knows what the students understanding is!

However once we accept this ill leave you with this point. Every single take off accident i have read in a UK AAIB report usually contains a reference to RRPM. Typically this:-
"The pilot pre-rotated to 200RRPM and started the take off roll.... the pilot considered he had let the RRPM decay too much...".

So wheel balance or not you MUST monitor RRPM because if you dont how can you ever know if its decaying or not?? If you have directional stability in the ground roll, increasing RRPMs then get on with it. 100% power and take off. You need 100% power to take off (anything less increases danger) and by the time that is appropriate 100% power is coming after you are already at what? 80-85%? So its not a huge change.
 

Jean Claude

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Not to mention the yaw control, the minimum pre-launch rpm must be linked to the acceleration ability of the gyroplane.
Without this, the divergence of flapping can be reached.
So, 130 hp with only one pilot requires more prelaunch rrpm that 100 hp with 2 passengers.
I wonder if the manufacturers tested the new margin available
 
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Tyger

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Firstly someone introduced the term p-factor and it has been incorrectly applied to everything since!

...more propeller slipstream which interacts with the tailplane which is what you feel. At this point we have a consistent AoA and thus no change in p-factor.

That was my sense too, Phil. In fact, if the prop is turning counter-clockwise (viewed from the rear), my understanding was that any p-factor that obtains from increasing its angle of attack would yaw the aircraft to the right, since the descending blades are on the left, no?
 

Jean Claude

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If the prop is turning counter-clockwise (viewed from the rear)
P factor makes yaw to the right (Nothing at zero forward speed)
Twisted flow on the low rudder makes yaw to the left (Dominant at low forward speed )
Sans titre.png
 
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WaspAir

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You could also get a little bit of precession with a pitch change.
 
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