History of the Gyroplane - part 16 pilot induced oscillation PIO

[@cameronlapworth2284]

This is an excellent series and I agree with much of this but I have some quibbles 1) in Australia around the time the air command accidents that lead to their banning Horizontal Stabs were mandated. Since there has been no appreciable reduction in fatalities,. But all gyros are fitted with stabilisers. Many large. Remember the mangoose stealth looking gyro? What happened there? 2) Speed. Remember if the rotor is tilted sufficiently forward the angle is more vertical. If the disk drops below zero what matters. My STEM kids make gyro gliders in class you know how I get them to stop. By unloading the rotor. If the rotor has no lift you have zero control. What happens in the 1/2 second between unload and fly through rotor or tail comes up through rotor is IMO mute. Your dead anyway. 3) Glasgow unis summary on stabs for us was they aren't very effective until very high speeds at those speeds gyros become dangerous. Thus they are insufficient. 3). The key factor here is speed for both high cg vs thrust line and by the way thanks for acknowledinging downthrust. 4). Can we not ever get to the conversation about rotor wing loading, speed and how that impacts on VNE? Thus seems the thing no one sufficiently brings up. The air command at 30mph is stable. As at that speed the rotor is tilted back at 9 degrees. It's more of a problem at say 80mph because with say 23ft 8inch N8H12 section rotors it's going to have a more shallow disk angle than say a Bensen (and perhaps I'm jumping the gun on you). There's a some experiment that anyone claiming thrust line/HS will stop the deaths can do and I'd suggest they try first in RC gyros (as large as possible). Put any configuration you like on fly up to high speed and punch the stick forward hard as you can. That no one has ever attempted this tells me we are playing at the margins. The Wallis crash happened at what speed? 90+knots wasn't it? A guy I knew flying a tall tail high cg machine boasted to us he was going to crack 100mph in his machine. Several of us warned him but he claimed he'd be fine because he had a stabiliser and high cg to thrust line. The bunt over in his case happened at 94knots. His 27ft rotors cut his tail off just above the stabiliser and his body was found some 50m in front of the airframe. His harness ripped and his leg left in the cockpit caught under the instrument panel as he was flung through the windscreen. Does high cg vs thrust line or downthrust help. Yes I suspect it does. Will it stop you fatally unloading your rotor. NO IT WILL NOT. It feels like this debate is centred around what to do in the last half second of you machine flying when in reality we should be concentrating on when you exceeded you VNE. Simply don't fly that fast. As for PIO. I saw it only once. When a student of mine got caught with a stretchy rope on the gyro glider. My fault I brought the dam rope. I backed off the power to the car so he sank to the ground which got him out of it. I've never read an eyewitness describe ossilations. If they are happening it's not many perhaps only one but the evidence I read in 16 years of fatalities didn't show one clear case. For all we know it was a steady push forward on the stick until the machine unloaded, perhaps at that point due to thrust line. Bolt a group to the ground in a strong wind and simply pushing the stick forward far enough will unload the rotor. That stick force is the maximum benefit a stabiliser can provide. So after landing how much force does it take? If stability is what we want the the bensen design manual provided an answer. Overbalanced rotors chordwise. You need to be careful too much and they get into weave. However I have flown wooden rotors in which the builder accidentally overbalanced them to 30% not 25% they were rock solid boring in fact. But our sport is no longer one that encourages real experimentation or takes responsibility for proper training. You sir are an exception to this I applaud this series even when I may have quibbles. Well done.

[@gyrocopterflyingclub6148]

Hey - thanks for the kind comments. On your points a lot to chew over and I might try and cover some of this is a later film as you raise some interesting points. I too have always been slightly sceptical of stabs on gyros not in the fact that a properly designed and integrated one might not be helpful but I just can't see how some of these things (that frankly look like a piece of 5-10mm ply board) lashed at a random point and seemingly with no regard to the prop wash really work! If I was an aerodynamics student it would make a very nice project actually. As you say Glasgow weren't that convinced. Your point of large R/C models is interesting and I think what the Glasgow study also highlights to me is the fact that it is a multi 100 page report with some complex maths, authored by some knowledgable people and yet within 5 mins you have quite a few people dismiss it. Which surprises me - I don't think it was helped by the UK authority also contradicting some of its content (I'm thinking RAF stabs). It probably could do with a revisit in parts to confirm or deny. I agree your point re: will it stop you unloading the rotor - no. Although I think the Wallis accident was air display / low time / poor prep and like many of these accidents there are in many cases too many variables. One element that I think is a huge impact are the physical controls and their function. I will cover that at some point. We had floor mounted sticks, pump action sticks, hanging sticks .. Interesting on the rotor balance and 30% v 25% I have a paper from Peter Lovegrove who found 25% provided poor stability. It is in his Gyroplane miscellavia vol.6 If you don't have it I'll try and scan and email it.

[@cameronlapworth2284]

@@gyrocopterflyingclub6148 thanks. I've tested quite a few wooden rotors over the years in our club me and another bloke built a number of sets and we used the gyro glider to test. As I said before that another student built a set intended for the glider as we were borrowing a club members metal blades. He stuffed up and balanced them at 30% instead of 25%. They were so stable we sent a whole bunch of student solo that weekend. With one student we hit a massive thermal the hall guague topped off it was massive we should have ended up at the top of the rope probably gained a few few. I'd smacked the students hand off the stick. Impressive. My wooden rotors are at 25% as bensen recommended. I was disappointed that the Glasgow report didnt model for the effects of chord width flexibility I personally have found that flexible blades or. Wood significantly more stable. The Wallis accident I agree was low hours on type. Possibly too unaware of the degree of danger he was in at the high speeds. But they analysed the film to find he was going too fast. I note that Wallis speed records were set with 19ft rotors and he had a small pitch trim to flatten the nose. My instructor when he put his pod on his machine added an upside down aerofoil to keep the nose more level at speed. Ciervas had similar but one side was upsidedown and the other an upright aerofoil to counter tourque from the large prop to they also had ground adjustable. But the mistake I think in the confidence of all stabilisers is in trying to stabilise the wrong thing. The airframe hangs on a universal joint. This means if I over control the stick wants to move in the correcting direction if I'm letting it fly itself. I agree with you video that good gyro glider training helps this. Particularly as it allows for solo flight with less weight than any powered machine. One guy I knew killed himself in an air command in front of my brother. The month before he rejected coming down to train with a club and qualified instructor because he didn't want to drive 4hours every month for training. I hadn't visited the club as at that time I was a beginner but he'd smashed his nose wheel.when he punched the nose forward after an unexpected take off. I watched a friend of mine plead with him to get training and warned that doing this would result in neg g. But he didn't listen. So we've had a lot of blame for the machine over the years. In part this is because it's a small sport and no one wants to do the responsible thing and question the skills of the stubborn or aggressive pilot or question the xomparitive skills of the instructor. I suspect some protectionism happening. I know I was extremely lucky to get a great instructor and in the time I was gyro glider instructor he never had a single student under his instruction bend a set of blades let alone a fatality or neg g type death. He did have people go off and do their own thing and smash upmaches he had stubborn and disobent students go their own way. And yet I had students in the glider that had had 30+ in two seat machine and couldn't fly the glider! It's complicated. I agree that trustline helps but even here I unload my rotors after each landing. It's not hard to do even if the airframe is flat which it probably won't be at high speeds. And establishing a real VNE for each machine would be difficult unless you set a new hang test for each rotor diameter,. Pitch a d fuel level. I note most machines have massive long rotors. Why does no one suggest I wonder that rotors be kept shorter? Wallis held speed and for a long time altitude records with short rotors. Shorter rotors and for any airspeed you will have a higher angle which even if you have poor cg vs thrust line provided you don't fly fast your disk vector will try to pull the nose up. The dominators have this ugly approach because they use zero downthrust. Anyway I've rabbited on long enough. But I'll leave you with a prediction. Fix cg thrust line and stabiliser issues and people will still keep doing this until they slow down, and we get a better class of instructor s in general (I can only speak for down here) and students listen to them. Again this is an excellent series.

[@czesaw8751]

You present very interesting information about gyroplanes. Thanks to such enthusiasts as you, such an interesting topic may interest those who did not know anything about gyroplanes before. Great channel.

[@gyrocopterflyingclub6148]

Glad you enjoyed it!

[@czesaw8751]

@@gyrocopterflyingclub6148 (⁠•⁠‿⁠•⁠) Maybe someday I'll build a BENSEN gyrocopter - 35 years ago I bought working drawings of this tiny gyrocopter, but life got in such a way that I had to abandon these intentions. Regards

[@tanyano9]

Excellent, moving more towards the dynamics of single seaters, thought provoking stuff ...

[@gyrocopterflyingclub6148]

tanyano9 What is very interesting is that there was a great deal of knowledge in period and it’s surprising that not more was done authoritatively to help the situation that effectively killed all uk makers from 1970 and then finally in the 90s and it’s kept us effectively stuck with just 2 makers in the UK space since. AV18 exempted. Even if guys were ambivalent to the safety case why didn’t they protect their business interests????!

[@tanyano9]

@@gyrocopterflyingclub6148 sadly that would only been done by enthusiasts who would be passionate about the topic, as the authorities won't care and it's much easier for them to just ban something rather than making the effort to educate themselves.....?

[@gyrocopterflyingclub6148]

tanyano9 maybe but you might think the enthusiasts of the time would have lobbied harder or highlighted the issue more?? Maybe they did?

[@tanyano9]

@@gyrocopterflyingclub6148 I would like to think so but being British and so laidback we just let the authorities ban or heavily regulate....Only when it's gone or banned do we miss it.....Such a shame and many missed oppitunities...

[@brianpearson6000]

Computer modelling by Glasgow showed a 2 inch high thrust line on a VPM M16. Everything followed from that. They were about 8 inches out as has been proven by real world double hang tests. They pretty much discounted the effect of the HS. Newer gyros prove that high thrust line gyros can be stable. Many think the Wallis crash was a torque over when the rotor thrust was lost. This is just as fatal as a push over as was seen at the world air games. All that being said...most aircraft have the thrust line going through the centre of mass. But gyros built like this don't look sexy. ...and sex sells. The Aviomania is an exception and also addresses the torque issue. Nice videos.

[@silverlightaviation]

It is amazing to me how Glasgow university was so far off on something as fundamental as calculating or determining vertical CG of an aircraft they had on hand.

[@ZeroGMVideos]

And,one more...hehe. Im looking for an AirCommand (Classic) (HLT).. is it "SAFE TO FLY" just with horizontal Stabilizer? i mean.. is it so much diference between CLT and HLT? Apreciate for your comments! Regards

[@gyrocopterflyingclub6148]

Hi - thank you for the kind comments. Its not an aircraft that is legal to fly in the UK anymore and initially this aircraft was not sold with any stabilizer. In terms of "safe to fly" the real answer is that you can fly it safely you just need to be aware and consider the aircraft characteristics.

[@ZeroGMVideos]

Excellent videos! (im suscribed!) I have a question: PIO is reducted by horizontal stabilizer.. ok.. but CLT is said as "needed" in gyros...but, gyros like ELA, or MAGNIGYRO.. are not CLT modified.. So, are they dangerous anyway? Thnaks for your answer!

[@gyrocopterflyingclub6148]

Hi the short answer is that no they are not needed, as a pilot you just need to be aware of the limitations and fly accordingly.

[@stationmanager2567]

I think the first thing would be a pilot of an aircraft is to developed a good working knowledge of the weather. So many times one can go out flying on what appears to be a good day and run into clear air wind gradients mechanical turbulence on a perfectly clear day. Even, in fact, fixed-wing aircraft, wind gradients can strip your airspeed in seconds. Also, the huge G force on any aircraft can be massive. Wind gradients can load an aircraft in a split second to 3 G with no trouble. So in rotary-wing aircraft including helicopters, there is a major problem.95% of fixed-wing aircraft are placarded. That helpful, but doesn't solve the problem. A great deal of experience is needed in any aircraft with wind gradients, and clear air mechanical turbulence, especially below 500ft. I haven't flown a gyroplane, but have done a lot of time in helicopters, and the big concern all the time is wind gradients.

[@hadleymanmusic]

Wonder if theres a desire for pre built tail planes?

[@shimy333]

why don't they use a ducted propeller? wouldn't that force direct air over the rudders all the time?

[@gyrocopterflyingclub6148]

shimy333 hi yes I see where you are coming from but really the prop wash over the rudder is usually not an issue. As far as the propwash over the horizontal element is concerned that interaction has much to do with how that surface is placed relative to the prop. A duct would do that with consistency but the structure would be quite (in light gyroplane terms) complex / heavy and expensive (just from the make up of a duct - remember prop size is circa 60in and the duct bigger than that) additionally you would need to also make specific prop blades to ensure efficient propeller interaction with the duct and the design of the duct would need to be pretty clever to allow for its interaction with the airflow over the fuselage. If you look at part 8 of this series the aircraft that did employ a duct was designed by ex-AVRO Canada guys who one assumes used information from a bigger project for their gyroplane - and even that wasn’t really for the sport market. So in summary I think there is a lot of work/cost/ weight and complexity for a solution that (in my view) can be done with a regular tailplane. The issues Gyroplanes have had over the decades is down to multiple issues that had been left unaddressed and in an environment where the regulator wasn’t really focused upon them. So training, prop thrustline, tailplane and don’t ignore the controls themselves - for years you have hanging sticks, floor mounted, throttles on a twist grip, quadrant- it’s all fundemental to the safe operation and all in an environment where there was no differences training and even TODAY there is NO revalidation of those differences- so you fly an aircraft today, get competent, then leave it for 30 years and still be legal to fly that aircraft when you return. Idiocy.

[@shimy333]

@@gyrocopterflyingclub6148 I think more tractor style gyros need to be designed....would solve this problem according to everything i've read about gyros...it's just the Benson design is so easy for the home builder to make..

[@murraybarker7618]

Tractor gyros are no safer than pushers. A high thrustline tractor gyro is no different than a high thrustline pusher. The thrust is acting in the same way above , thru, or below the centre of gravity.

[@rbnhood39]

A ducted prop would also help prevent a rotor and propeller contact.

[@codehound8033]

@@gyrocopterflyingclub6148 -- Has anyone tried replacing the one 60 inch prop with two 42 inch props rotating in opposite directions of each other and driven by belt or chain from the lower mounted engine?

[@Allan_aka_RocKITEman]

SECOND! 🤭