NCLT Dichotomy

gyroplanes

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(I meant to put a question mark after "Dichotomy")
I copied this here from another thread. Please help me with this.
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Quote:
Originally Posted by Screw
Screw-In

1. The Bensen, as designed, was a very close to CLT machine with a Mac or VW direct drive engine.
Screw-Out


This and other statements cause me great concern.

Chuck Beaty has recently been touting the "safety" of the old Bensens and our old method of learning to fly one.

I have to agree with Chuck about "Self training" I haven't seen a decline in fatalities since dual came along. I don't condone self-training any more. That's a subject for another thread.

Our chapter did the old double hang test vertical C of G determination on a member's VW Bensen. This old Bensen (with a very short mast by today's standards) came in real close to CLT. I expected it would.

What causes my heartburn???

I remember the old days. Gyro carnage didn't start with Dennis Fetters Air Commands.

Don't get me wrong. I believe in the benefits of CLT. I just can't understand how these NCLT early Bensens still managed to PIO / PPO as often as they did..

Our beloved gyroplanes didn't earn their horrid reputation with the advent of the Air Commands, it was very well established before then.

When I was a student at the FAA academy in Oklahoma City, OK. thirty years ago, I spent my spare time in their library sifting through all of the gyro accident records. There was a staggering number of accidents, virtually all of the fatal accidents displayed the tell tale signs of PIO / PPO.

The FAA library did not have a copy machine, so I hand copied each and every accident for my records.

When I was the PRA Safety Editor we published these reports in the PRA magazine. I still have them and maybe after the Chistmas confusion I could dig them out.
 
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scottessex

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See what you did Screw! If you would have come out to the house today, you would not have had time to stir the pot here on the forum!!!!:eek:
I think everyone has thier undies in a twist (see more Screw posts) because summer is over and they can't fly as much!:mad: :cool:
 

GyroRon

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Tom, my guess is that the old Bensens were close but not quite CLT. They were still a few inches off of being CLT, and with no horizontal stabs they were easy to over control in pitch resulting in PIO and possibly PPO.

The double hangtests and other ways of testing for VCG on a old type Bensen these days would more than likely show better CG alignment than the real early machines due to the early machines using the boat type fuel tanks mounted down low and most machines now having switched out to seattanks which places the fuel up higher.

I think alot of the earlier accidents could be explained by the lack of proper training, the key word being PROPER. Properly self training may not have been bad, but I think alot of people rushed it. If you rushed the self training you probably didn't learn all you needed to.
 

C. Beaty

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Bensens did tumble out of the sky in the old days, Tom. In every single case where I have personal knowledge, it was someone that had skipped the Bensen training program. As president of the Sunstate Rotor Club for 10 or 15 years during the late 60s and through the 70s and early 80s, I tracked all accidents in Florida closely. I have yet to find a fatality that I’m aware of that is not listed on the NTSB site.

A stock Bensen, because it did not have a horizontal stabilizer, was poorly damped in pitch. The lag and overshoot inherent in such a configuration inevitably leads to PIO for most individuals without training.

The time spent on a towline was a start toward developing the reflexes that enabled the pilot to stay ahead of the machine. The remainder was acquired during the early hours spent balancing on the main wheels and then wallowing down the runway at a few feet of altitude.

The people who killed themselves in a Bensen were generally loners and as often not fixed wing pilots who thought the procedures outlined in the Bensen training manual silly. Any club member was dissuaded from simply strapping in and flying.

Even so, most of the fixed wing pilots who killed themselves more than likely would have survived had their Bensen been equipped with a Ron Herron “T” tail or similar.

I have seen both Bensens and AirComands tumble out of the sky. The Bensens would go through 3 or 4 cycles of porpoising before tumbling. AirComands would simply bunt with no obvious porpoising beforehand, reflecting the difference between CLT and a large offset of the propeller thrust line.

Individuals who have never flown a CLT machine with proper tail surfaces simply can’t comprehend how crisp the response and how easily such a machine flies.

Furthermore, most gyros being sold today are Bensens in everything but name; seesaw rotor, pusher engine, same gimbal rotorhead with the same bearing Bensen used, same 2 x 2 aluminum tubes rearranged slightly and generally, even the same mast angle. Some got it right, some didn’t.
 
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Screw

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Screw-In

As it's my understanding, the old Bensens and Ken Brock KB-2s when equipted with a Mac or Vw engine was very close to CLT. I think the thrustline was only 2 inches above the CG.

If I'm wrong, please tell me.

Of course, the use of a Horizontal is a must!

Sorry Scott. I don't mean no harm.

Screw-Out
 

Timchick

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John,
How many hours did you fly your KB-2? Did you ever feel like you were starting into porpoising?
 

Hognose

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The original Bensen B-8M plans (if you haven't got a set, you can see a set in the museum in Mentone) show the CG located precisely on the thrust line.

I am told by guys from the Bensen Era that that depicted more of a wish than a reality.

By the way, a friend of mine decided to teach himself to fly a Bensen he bought at a yard sale. He rolled it up in a tight little ball (it sounds from the description like he tried to take off with too little RRPM and flapped the blades badly). He survived the accident, and now thinks he was not only lucky to survive, but lucky to have crashed.

"Or I'd have kept trying to fly it..."

He is a highly experienced FW pilot and was a PPC pioneer as well.

cheers

-=K=-
 

Screw

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Screw-In

I flew it over 40 hours and no. I had a "T" Tail. She flew very stable.

Tim, I think there is a misunderstanding between what is HTL. I think the misunderstanding is that alot of folks think that all Bensens or KB-2s are HLT machines when in fact they are not.

Over the years of course people wanted bigger props and 2 stroke engines with more power. As a result, Air Command, Ken Brock Mfg (KB-3) and others truly made HTL Machines by simply raising the engine and mast to swing a larger prop.

I don't know who first came up with the idea of dropping the keel and CLT, but it's been a winner so far. If you look at what the most popular gyros out there, most incoorperate some type of drop keel, powerful 2 stroke engines, large props, and Horizontals.

To further answer your question Tim, I think it would have porpoised had I not had the horizontal, and I also think any gyro would without a horizontal.

Screw-Out

Screw-Out
 

mceagle

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The early Air Commands had the ability to reach higher speeds, where they became nose down to the extent of running out of back stick. A low center of pressure combined with a high thrust line and no back stick meant that a bunt over was mandatory, limited only by airspeed and pilot experience. New chums often had the lethal combination of too much of one and not enough of the other.
I dare the same could be said of the standard RAF, although I do not know whether they got close to full back stick or not. They were certainly well nose down.
 

Hognose

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C. Beaty said:
Furthermore, most gyros being sold today are Bensens in everything but name; seesaw rotor, pusher engine, same gimbal rotorhead with the same bearing Bensen used, same 2 x 2 aluminum tubes rearranged slightly and generally, even the same mast angle. Some got it right, some didn’t.

You know, not having built a gyroplane, it was only when I went to Mentone in 2003 and saw my first RAF 1000 did the Bensen heritage of the lead sleds strike me. OK, so I'm dumb as a keg of nails.

I just reread Jean Fourcade's paper and the abstracts of Stewart Houston's studies. I notice that the physics of many of the problems we have been discussing so heatedly are explained by theory in Fourcade's work, and the theory is validated by experimentation in Houston's.

Much of the argument concerns whether the mishaps we are seeing are instantiations of the class of mishaps predicted by this research, or something else.

Science is a wonderful thing. I wish more of my countrymen had more education in it.

Here is what I take away from all that stuff -- no, never mind. Here are things for people to read them themselves.

Jean Fourcade, engineer, theorist:
http://www.asra.org.au/L_Stability.htm

Stewart Houston & Douglas G. Thomson, professors of engineering, experimenters:
http://www.aero.gla.ac.uk/Research/Fd/Project5.htm

[I think the actual papers are these:
Houston, S.S., "Longitudinal Stability of Gyroplanes". The Aeronautical Journal Vol. 100 No. 991, pp. 1-6 (1996)

Houston, S.S., "Identification of Autogyro Longitudinal Stability and Control Characteristics". AIAA Journal of Guidance, Control and Dynamics Vol. 21 No. 3, pp. 391-399 (1998)

Houston, S.S., "Identification of Gyroplane Lateral/Directional Stability and Control Characteristics from Flight Test". Proc. Inst. Mech. Engrs, Part G, Vol. 212 No. G4, pp. 271-285 (1998)

Houston, S.S, Thomson, D.G., Spathopoulos, V.M., "Experiments in Autogyro Airworthiness for Improved Handling Qualities", Presented at the American Helicopter Society 57th Annual Forum, May 2001.

Houston, S.S., Thomson, D.G., "Identification of Gyroplane Stability and Control Characteristics", NATO RTO, RTO Meeting Proceedings 11: RTO-MP-11, AC/323(SCI)TP/7 ëSystem Identification for Integrated Aircraft Development and Flight Testingí, March 1999, ISBN 92-837-0006-6

Spathopoulis, V.M., Thomson, D.G., Houston, S.S., "Flight Dynamics Issues Relating to Autogyro Airworthiness and Flight Safety", Paper No., Proceedings of the 54th American Helicopter Society Annual Forum, Washington, May 1998

Houston, S.S., Thomson, D.G., "Flight Investigation of Gyroplane Longitudinal Flight Dynamics", Paper 108, Proceedings of the 23rd European Rotorcraft Forum, Dreseden, Germany, September 1997.

Houston, S.S., Thomson, D.G., "A Study of Gyroplane Flight Dynamics", Paper No. VII-6, 21st European Rotorcraft Forum, St Petersburg, Russia, August 1995.]

I note that although Houston reaches a very firm conclusion w/r/t thrustline, the CAA (which funded him to the tune of half a million quid) has not actually acted on his research, and instead (thru PFA) not only permits, but requires, high thrustline gyros to be flown without even a stabilizer.

Sometimes it's a relief to see that bureaucracy isn't just local to the country I happen to be in and battling with at any given moment.

cheers

-=K=-
 

GyroRon

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Screws KB-2 would fly nose down at high speeds and not sure if the 2 inch or so HTL accounted for that or possibly the large horizontal stab being at the wrong angle and causing the nose lowering at high speeds.
 

Aussie_Paul

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Ron......

Ron......

GyroRon said:
Screws KB-2 would fly nose down at high speeds and not sure if the 2 inch or so HTL accounted for that or possibly the large horizontal stab being at the wrong angle and causing the nose lowering at high speeds.
..... I believe that it would be the parasitic, or as it is sometimes called these days, form drag, would be responsible for that increasing nosedown attitude as you got faster.

Aussie Paul. :)
 

scandtours

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Just from my experience.
My first gyro was a Bensen with 70 Hp McCulloch and 50 in prop. Stick
rudder and stab were replaced later from Ken Brock. With some modifications I moved KB stone guard stab which is semisymmetric to the aft and with the flat surface on top ( upside down). The gyro behaved completely different
and become much more stable. I could not believe it myself.
George K
 

C. Beaty

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A fixed wing aircraft flies more and more nose down with increasing airspeed. As forward speed increases, more forward stick is required to reduce the wing’s angle of attack and to keep it from climbing.

A CLT gyro controlled with an elevator would behave in exactly the same way as a FW.

A CLT gyro controlled by cyclic pitch is prevented from assuming as great a nosedown fuselage attitude by the fixed horizontal stabilizer.

With increasing airspeed, the rotor disc flies flatter which moves its thrust line rearward with respect to the CG since the fuselage attitude tends to be held level by the stab. This increases static stability* about the pitch axis and gives an increasingly solid feel with increasing speed. *Static stability depends upon the strength of the restoring force following a disturbance.
 

Hognose

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Interesting. It appears that the UK CAA issued a directive -- a Mandatory Permit Directive, which is like an AD for non-TC'd aircraft that in Britain get a "Permit to Fly," rather than a special C of A as in the USA -- in August requiring all UK single-seat gyros to be limited, those with pods more so than those now, in:
- Never Exceed airspeed (Vne 61kt)
- Permissible Weather Conditions (max surf wind 15; VNe 55kt in turb)
- Pilot Experience (PPL-G and 50 post PPL solo hours to fly pod)

And the limitations can be lifted if you can demonstrate to the PFA that you are within 2 inches of CLT.

In addition, all single-seat gyros must add an "acceptable horizon reference" and open-frame gyros are restricted to a minimum speed of no less than 26kt, except in the landing flare. These requirements in the new directive are not waiverable.

Have we had a discussion here of CAA MPD 2005/008 here? If so, can someone point me to the discussion?

I don't remember talking about this. Some parts of it are clear to me
- separating podded from open machines
- pilot experience requirements
- airspeed limitations on non-CLT gyros
- max wind limits on non-CLT gyros (there are gust delta limits too)
- horizon reference

I'm not sure I "get" why the minimum speed limits on the open-frame gyros.

cheers

-=K=-
 

Aussie_Paul

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Hognose said:
Interesting. It appears that the UK CAA issued a directive -- a Mandatory Permit Directive, which is like an AD for non-TC'd aircraft that in Britain get a "Permit to Fly," rather than a special C of A as in the USA -- in August requiring all UK single-seat gyros to be limited, those with pods more so than those now, in:
- Never Exceed airspeed (Vne 61kt)
- Permissible Weather Conditions (max surf wind 15; VNe 55kt in turb)
- Pilot Experience (PPL-G and 50 post PPL solo hours to fly pod)

And the limitations can be lifted if you can demonstrate to the PFA that you are within 2 inches of CLT.

In addition, all single-seat gyros must add an "acceptable horizon reference" and open-frame gyros are restricted to a minimum speed of no less than 26kt, except in the landing flare. These requirements in the new directive are not waiverable.

Have we had a discussion here of CAA MPD 2005/008 here? If so, can someone point me to the discussion?

I don't remember talking about this. Some parts of it are clear to me
- separating podded from open machines
- pilot experience requirements
- airspeed limitations on non-CLT gyros
- max wind limits on non-CLT gyros (there are gust delta limits too)
- horizon reference

I'm not sure I "get" why the minimum speed limits on the open-frame gyros.

cheers

-=K=-

Hi Kevin, boy the UK officiates conduct all sorts of knee jerk reactions over there!!!. If they had said that, "And the limitations can be lifted if you can demonstrate to the PFA (PopulayFlying Assn which is all aircarft types) that the craft meets the US ATSM pitch stabnility standards". That would have been a sensible way to handle the situation.

Scenario. A person could have the CoM to thrust line offset at 2" and have a very poorly designed inefficient stab with no moment arm, or even no stab at all, and they will lift they limits!!!

Aussie Paul. :)
 
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Harry_S.

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Rotor Control

Rotor Control

It is my opinion...there is no other method, nor less expensive method, nor safer method, nor idiot proof method, to learn all there is to know about basic rotor control, than with dual instruction in a two seater towed Bensen Glider.

I wonder how many of the young gyronaut aces, have even been in a towed glider. Land or water??


Cheers :)
 

gyroplanes

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Devil's advocate

Devil's advocate

I have to play the Devil's Advocate now and again. I grew up in a time when we were taught to question everything. I glad no one misconstrued my post as questioning the need for NCLT or H Stabs.

Chuck Beaty and I have very similar recollections regarding the past.

I too have witnessed several fatal gyro flights. The Old Bensen style gyros did mimic a divergent, roller coaster path before the fatal outside loop. Air Command and the Marchetti fatals I saw bobbled very little before the fatal plunge.

A loveable fellow from Wisconsin, vice president of our chapter and good friend, learned to fly an enclosed Air Command low rider 532 with factory stock H Stabs. He flew it home from Oshkosh and flew it at several air shows around the midwest. Dave was in love with our sport and converted a step van to haul his ship around the country in.

Dave wanted to get another Air Command for his son. He bought another 532 without enclosure and stabilizers. I watched him test fly it. It was a gusty, windy day and he bobbled around the sky quite a bit.
After he landed, he commented that this machine didn't fly anything like his. He said he was going to go through the engine and convert it to CLT over the winter. By spring, all he had accomplished was the engine work.

He and a fellow club member went to the airport in the spring to install the engine. They decide to hear it run, then he decided to taxi it. The next thing the other guy saw was him taking off (hey, it was a warm spring day) he flew it like a man possessed according to witnesses. He made a fast pass, waived to some people in an airplane taxiing out and plunged to the ground.

I would have done the conversion for him had I known.
 
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Doug Riley

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I'm afraid that some of what has been said here (and elsewhere by fairly respectable gyro people) will lead to needless confusion. Here are two things that are FALSE:

1. PIO causes PPO. If a gyro PIO's, it's always in danger of PPO.

2. There is something inherent in all gyroplanes that makes them subject to a mysterious malady called "buntover." IOW, gyros would rather be upside down, if we would only let them.

Pilot-induced oscillation -- PIO -- happens when pilot and machine, taken together, lack damping. They bob up and down at their natural frequency. All types of aircraft (and, in fact all kinds of machinery operated by humans) can and do PIO. PIO does not necessarily lead to a PPO or any other kind of crash; the system may settle down after awhile, especially if it has at least a LITTLE damping and the operator has the sense to hold the controls still. PIO occurs when the pilot-machine system lacks dynamic stability and has a lag in its response.

(Even a non-laggy machine like car steering can PIO if the driver is drunk. It's the familiar "weave," caused by lag in the driver, not in the car. You have to look at the total system, machine plus operator.)

OTOH, PPO is an example of STATIC instability. A force on the airframe pushes or pulls the whole craft over. No oscillation is involved in PPO, and no oscillation necessarily precedes it.

NO tendency to push over is present in any properly designed gyro rotor. There is NO force generated by the rotor itself that is continually trying to flip the rotor over. Even if the rotor is dipped low enough in the front that the air hits the "disk" on its upper side, the rotor will not "dig in" and continue flipping like a coin. Instead, the rotor will simply generate lift in a downward direction. This may actually push the gyro's tail down and restore positive angle of attack.

To borrow an old campaign phrase, "it's the airframe, stupid." PPO happens if, and ONLY if, the (1) prop thrust line is above the CG AND (2) there is no other force that counters the nose-down torque created by the high thrust line.*

Pilot skill can often completely compensate for poor dynamic stability -- remember, PIO is a lack of damping in the man-machine SYSTEM. If the pilot has plenty of "training, training, training," than the pilot can sometimes do the damping job with no help from the machine. It's a lot of work, but you can learn to do it automatically with enough practice. All pilots of tailless gyros -- old Bensens included -- develop this skill, if they survive the learning process.

The seeming link between PIO and PPO is this:

Teeter-rotor, cyclic-controlled gyros, PPC's, trikes and weight-shift hang gliders have as their primary control a device that points the lifting surface in various directions to carry out the pilot's wishes. This setup makes the aircraft simpler. It does, however, deprive the pilot of control during moments of zero "G."

HTL machines would all be un-flyable unless something countered the nose-down effect of the prop thrust. Since HTL machines do fly, something does counter the prop thrust. If the "something" is rotor thrust, however, watch out. Rotor thrust is interrupted by zero G events. The "PIO connection" is simply that PIO will produce a zero G event if it persists through a few cycles. The PIO lets the PPO genie out of the bottle. Without a built-in tendency to PPO, PIO will not lead to PPO.

OTOH, if a gyro experiences a PPO after PIO-ing, then that gyro was susceptible to PPO all along. This means the gyro became statically unstable at low G -- a frame-layout defect that could have been corrected in the design.

*(There is one other kind of pitchover that I know of besides PPO -- the drag-over. If the frame layout is such that the pod, wheels, radiator or what-not tend to pull the nose down, then they can act in a way that mimics HTL, even if there is no HTL. This is most likely to happen at high airspeeds, especially if the nose tends to get lower at such speeds. Note, however, that the airframe, not the rotor, is again the culprit. The vague term "bunt" suggests that there are any number of other varieties of pitchover. I know of no others besides these two.)
 
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gyroplanes

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Nicely put Doug.
The thrust line and Center of gravity mis-match is often represented as a torque arm. Your explanation above also describes a torque arm below the gyro acting in the SAME direction as a high thrust line would. Drag below the center of gravity compounds the high thrustline problem.

Now we have both nozzles of Chuck Beaty's lawn sprinkler.


I saw, what I believe was a very graphic example of something similar to this, an "anti-horizontal stabilizer".

I knew a guy who flew Bensens for years. He built a Marchetti Avenger (H stabless) he added an Air Command two place SxS pod enclosure.
Flying it solo, he said it "acted strange in gusts" and that "it was the closest to PIO as he ever came".
He took Duane Hunn flying with him one day and said that with the extra weight "it flew great".

He added some lead shot to the nose and went out and enjoyed himself. He flew it around and had a great time.

The next day a far more experienced pilot went with him for a "ride" to check it out. Several club member ta twere present aske if they were going to remove the shot ballast. The experienced guy said it wasn't necessary.

The take-off looked normal. Things soon became "hairy" as I observed the gyro bobbling around a bit during climbout. It just didn't look right. They levelled off on downwind, gained speed and there was a slight pitch up followed by a nose over "bunt". Both were killed.
 
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