RAF 2000 Stabilator vs HS

[enewbold]

I just received a note from Greg Gremminger regarding HS and Stabilator issues with the RAF 2000 machines and was wondering if anyone would care to comment and/or amplify on his comments. I'm asking this for INFORMATIONAL purposes only, NOT to start any flame wars, as I am seriously considering purchasing an RAF 2000 within 30 days.

Thanks, Ed Newbold.

Ed, I'm not really up to speed on HS's available for RAFs. You are right, though, I don't believe you should fly a standard RAF without a HS. Even with a good HS, there has been an RAF buntover-type accident! I'd still be very careful and not fly either fast or in much turbulence! I have heard one report of an RAF with both a good HS and the RAF "stabilator". We don't know if this combination would avoid the possibility of a buntover, but the reports suggest it "feels" very stable and I suspect it would be very difficult to PIO. This does not mean it might not still be susceptible to a "buntover.

To avoid a buntover, the gyro must test to have positive static G-Load stability. This is an easy test, but nobody has reported having done it yet! I have a couple of articles coming up in the next several issues of the PRA Rotorcraft magazine explaining how to test for the three static stability criteria. I would be interested in knowing how the RAF with different combinations of HS and "stabilator" perform to the static stability tests.

Regarding the machine you're interested in, I would probably take the risk with it and put both a good HS and the RAF "stabilator" on it - then I'd be careful and conduct the static tests to see if there are any flight conditions where you would still have to worry about buntovers!

One more point - even though the addition of a HS is, at least in my opinion, a very necessary thing for an RAF, it does further exacerbate the efficiency issue with RAFs. The down slope of the large windscreen is both destabilizing and a performance issue - at high airspeed the down load on the sloping windscreen creates a nose-down destabilizing pitch reaction AND puts more load on the rotor. With a very large HS, the destabilizing effects of the sloping windscreen can be somewhat offset - but to completely balance this download effect requires a very large HS and another large download on the rotor - performance efficiency!

These are just my thoughts from other people's inputs, but I think they are consistent with other's testing, with engineering analysis, and with reports from others who have investigated some of these issues. Perhaps a good benchmark of this performance efficiency "hit" is that RAFs require higher HP engines than some tandem designs without the extra down-load of a large sloping windscreen and the large HS required to balance it!

Anyhow, if you could make it to Shelbyville on Saturday, we would look forward to seeing you. If you want to come on Sunday, call my cell to see if I will be staying into Sunday afternoon.

Greg Gremminger

[Doug Riley]

Ed: I think Greg about covers what's known right there. The "stabilator" is a form of aerodynamic trim spring that feeds pressures into your control system. It tends to keep the rotor's angle of attack constant.

As it happens, the offset gimbal head already does that. The stabilator overlaps the gimbal head's function, but it does so without the large static trim-spring pressures that a non-stabilator system has. Provided that you use a light touch on the stick, the stabilator will help to isolate the rotor from the unstable behavior of the airframe.

What the stabilator CAN'T do is stop a a PPO once it gets going. Part of the lethal nature of a PPO is that it disables the rotor as a control device by exaggerating and prolonging zero G. In zero G, there is no rotor thrust. The stabilator works by manipulating the rotor -- if there's no rotor thrust, manipulating the rotor doesn't help.

For PPO prevention, you need pitch stability in the airframe itself. A HS of sufficient power can supply such stability, even with a large engine thrustline offset. However, the "numbers" tell us that it's nearly impossible to provide full PPO protection with the stock RAF layout using a HS. The thrustline offset is just too big. The crashes Greg alludes to tend to bear this out.

The RAF HS installations to date have been strictly eyeball engineering. To my knowledge, no one has bothered to do the numbers, then size, position and set the incidence of the HS so as actually to neutralize the PPO moment created by the engine. This would require quite a lot of negative incidence (sufficient to create a down-load of over 100 lb.). This is the performance effect that Greg alludes to.

Without such detailed setup, the HS is strictly a shot-in-the-dark "patch" of unknown effectiveness. We have only anecdotes to tell us that it helps.

Bottom line: the HS and stabilator both are helpful in reducing the dangers of the high thrustline, but neither one appears to be a complete fix at this stage of development.

[quadrirotor]

The stab-elevator! scroll down this page.

http://autogire.nuxit.net/Galerie_ph...otos_irkut.htm

[enewbold]

Originally Posted by Doug Riley

Bottom line: the HS and stabilator both are helpful in reducing the dangers of the high thrustline, but neither one appears to be a complete fix at this stage of development.

Thanks for the input, Doug. I appreciate the explanations. The machine I'm considering is a very low-time RAF 2000, but it has neither the HS nor the Stabilator, so I would have to add both items prior to flying the thing. I am not an inherent gambler! <smile>

Do you (or anyone else reading this thread) have info about where to purchase these add-ons and an approximate price for them?

[Gyropilot007]

Ed:

I can only offer my opinion based on my, to date, very limited experience. I own a RAF and currently I have both the stabilator and a large HS installed. This is my opinion.

I have never flown an RAF without a stabilator. My instructor was Duane Hunn and he has a stabilator installed. I have over thirty hours in his machine and I never exprienced any instability. Neither a tendency to PIO or bunt over. We flew in many varying wind conditions.

When I first started flying my gyro solo, I only had the stabilator installed just like Duane's. I few it for a few hours like that and then I installed the stabilizer. What a difference!!! The pilot workload has greatly decreased. The amouint of pitch corrections required has been dramatically reduced. Flying is much more enjoyable and, to be honest, I feel safer.

I will say that I think the stabilizer has had an effect on the performance. the climb rate has slightly decreased and the rpms need to be a bit higher for cruise. In my opinion the trade-off is well worth it.

I currently have the 2.2 liter Subaru engine but I've purchased the 2.5 and will be installing it soon. I'm a big guy and I need the extra horses.

Well, I hope I've been of some help.

Best regards to you all,

Bob McGuire

[Chuck_Ellsworth]

"and then I installed the stabilizer. What a difference!!! The pilot workload has greatly decreased. "

It never ceases to amaze me to read some of these comments, a horizontal stabilizer is used on almost all things that fly. For instance how many birds have you seen flying around without one?

What exactly do these guys that are RAF approved so called instructors teach you about basic aerodynamics?

Nothing?

That is what I thought.

Chuck E.

[Gyropilot007]

Chuck:

I have a background in engineering, not aeronautical but electrical. Nevertheless, I do have a basic understanding of aerodynamics. Of course I expected the workload to decrease when I installed the stabilator. I was happy with the results, but I will add the the aircraft was perfectly flyable without it.

Regarding Duane Hunn, he NEVER discouraged the use of a stabilizer. He left the decision up to me. Although I perfer the handling characteristics of my machine with the stabilizer I would not hesitate to fly in an RAF without one installed.

Best regards,

Bob McGuire

[Chuck_Ellsworth]

I note your remarks...

" Although I perfer the handling characteristics of my machine with the stabilizer I would not hesitate to fly in an RAF without one installed. "

And my expertise is flying and advanced flying training, many years ago I was involved for a short period of time with RAF with the intention of setting up a flight training program for them.

Until I actually started flying one of their RAF 2000's and found it to be unacceptably unstable in pitch.

They would not improve their product so I severed my relationship with them.

You of course are entiteled to your own opinion and your own choice of what you fly.

I however value my life more than to fly a standard RAF 2000, because of my understanding of how things fly. By the way I do own one that has sat in my hangar since I built it in 1992, and never flew it once I realized what a risky endeavour that would be.

But enjoy and good luck....

Chuck E.

[Chuck_Ellsworth]

" Regarding Duane Hunn, he NEVER discouraged the use of a stabilizer. He left the decision up to me. "

A professional flight instructor with integrity leads and teaches by example.

Hunn , Logan and what ever remanants of RAF's Ask First Group are left demean professionalisim in flight instruction by refusing to lead by example and correct the design faults that RAf have been selling to an ignorant public for over 15 years.

In my opinion of course.

Chuck E.

[Alan Coats]

When Duane Hunn had his operation set up in Oklahoma I took an introductory gyro flight with him. There were two new RAFs in the hangar that Duane was putting a horizontal stabilizer on, or at least the owners were putting them on in his hangar.

I was REALLY new to gyros at the time, so didn't know enough to ask him about who made them or why they were being installed on RAFs.

Alan

[Gyropilot007]

Chuck:

There is no doubt that you have more experience flyiing gyroplanes than I. Therefore I pose this question to you. Would you fly an RAF if it had the stabilator and a stabilizer? If you answer yes or no please explain your reasoning.

Best regards,

Bob McGuire

[Chuck_Ellsworth]

That is a fair question, so I shall answer it this way.

First off I have no experience with their "Stabilator " however knowing Don LaFleur and Pete and their thinking that a horizontal stabilizer is a "Gadget " my hunch is the stabilator would fit into the same catagory.

I own an RAF 2000 and before I will fly it I plan on rebuilding it and correcting the high thrustline off set.

Or to be even more clear no I would not bother flying any aircraft with the ability to suddenly depart controlled flight should a sudden upset be encountered.

There are far to many properly designed flying machines avaliable to risk my life on something designed by people with no understanding of the subject.

I hope that is a satisfactory answer?

Chuck E.

[Udi]

Originally Posted by Chuck_Ellsworth

...Or to be even more clear no I would not bother flying any aircraft with the ability to suddenly depart controlled flight should a sudden upset be encountered.

There are far to many properly designed flying machines avaliable to risk my life on something designed by people with no understanding of the subject...

This reply is so simple and clear that I can't understand why there are still people out there who don't get it? I wouldn't say there are "many" well designed gyros, but they are available. Why buy a poorly designed gyro, slap not one, but TWO, band aids on it, and HOPE to end up with a safe flying machine?

The only explanation is that people like to experiment, and are willing to take risks while doing so. There is nothing wrong in buying and improving the RAF, but you have to remember that you will always be a test pilot. The RAF with the two stabilizers on it may be a fun flying machine, but NOBODY can tell you under what circumstances this aircraft will depart controlled flight. Too many people have learned that the hard way (or at least their families did).

Udi

[Gyropilot007]

Chuck:

Ok, then I post another question to you. What modifications, in your opinion, would make the RAF a safe machine?

Best regards,

Bob McGuire

[GyroRon]

Bob, I wouldn't be scared to fly your ship. I would still fly it knowing it could buntover if allowed so needless to say I would be paying attention to it as I flew it. Your ship comparied to a stock RAF is night and day. A stock RAF would have me on full alert if I were flying one and quite frankly I would be Scared the whole time.

In my opinion the safest mod you could do to a RAF is to go for the AAI mod kit. Or to make your own mods to result in the same overall result. But.... I would most likely not do that to yours if it were mine. One easy and cheap mod I would do is to extend the rear keel at least 2 feet longer to move the stab further back. The Rudder would have to stay about where it is now so the blades don't hit it, but you could put the stab WAY further back if you wanted. Doing that would allow the stab to be far more effective and powerful on stabilizing the gyro.