Pilot induced oscillation on a trike

[Big-D]

As per a previous post, and at Wargames' request a quick discussion about Pilot Induced Oscillation

I have only ever really experienced PIO on an Airborne trike and let me tell you this is quite scary and you could quite easily loose control completely

When I did my conversion onto Airborne the instructor (Larry Eschner) told me to build up some speed and put the plane into a steepish bank, not a radical manouvre at all, just a medium fast turn - What resulted was that the plane started veering quite violently from side to side Now I can almost bench press the weight of an empty trike but I did not have the strength to bring the wing under control and things were getting completely out of hand

The oscilating just became worse the more I tried to control it untill the instructor told me to let go of the wing completely - As I let go of the wing it recovered almost immediately.

The name says it all, it is PILOT INDUCED - Before flying the Airborne I had approxamatly 200 hours experience on Aquila, Safari, Mainair Gemini, Air Creation - I flew the Airborne trike the same way I would fly the others, on the Airborne I tended to over compensate which causes the oscilating I guess

This is a common occurence for people flying the Airborne for the first time and for this very reason Larry Eschner warned me under no uncertain terms to not even consider trying to fly my Airborne without a Airborne rated instructor the first time.

As for the physics behind it - I am not sure, could be my imagination but I think an Airborne's wing is "higher" - Meaning further away from the undercarridge. It looks that way - I could be completely wrong

Anyhow, anyone reading this - I am not saying anything bad about Airborne, just stating that the PIO is not to be messed with without the knowledge of how to recover: - "just letting the wing go when it starts oscilating" - As bizarre as that sounds, it works

After a few hours on AIrborne it never oscilated with me again, telling me that is just flies differently to other trikes and once I mastered the wing I had no problems.


D

[nicow]

It sounds like a stall to me...

[Biggles]

Some questions:
What were you doing when it started ocillating? Just turning or maintaining a steady rate turn with left and right inputs?

Does the trike in question have wheel spats with winglets? I am highly suspicious of these winglets because if the undercarriage is not dead into the airflow they will aerodynamically effect the handling. Especially as you can change the "heading" of the undercarriage independent of the wing by twisting the bar (yaw). So imagine you are in a fast turn and the pilot is twisting the wing the winglets might not be dead onto the airflow. The winglets will cause a fishtailing type effect with the undercarriage winging, with johnny pilot making it worse by twisting the undercarriage as he tries to settle the whole thing down. Releasing the wing will mean that the whole shebang will settle down again.

[Biggles]

Was the wing in the neutral position in the turn? And releasing the wing allowed to to move to the neutral position?

[Wargames]

Big D,

Thanks for the explanation. I will go and think about it for a while. Interesting situation though.

Dirk

[John Boucher]

I'm no boffin at this and I am sure the men with the big hats on this forum like Ducky etc. will give their input.

My logic says it's like a motorcycle getting a speed wobble or a serious tank slap and the more you as rider tries to rectify the situation the worse it gets (thus some models of bikes came out with a steering damper. The rake angle of the front fork obviously the reason. The Suzuki TL1000R had one and I know because I owned one and experienced the bitch first hand powering out of a turn to hard) I think your reaction time to the problem is just that fraction too slow and then applied too much too late. The result is you stand up, take your hands off and change the COG and voila...

But a trike is hardly a motorcycle....

[Blue Max]

Sorry gents. I am try-ing hard to understand this one.
Can some-one plse explain this to me in Afrikaans..
I try to praat your Thaal.!!!

[Mc Guyver]

[quote="Big D"]As per a previous post, and at Wargames' request a quick discussion about Pilot Induced Oscillation

I have only ever really experienced PIO on an Airborne trike and let me tell you this is quite scary and you could quite easily loose control completely

When I did my conversion onto Airborne the instructor (Larry Eschner) told me to build up some speed and put the plane into a steepish bank, not a radical manouvre at all, just a medium fast turn - What resulted was that the plane started veering quite violently from side to side Now I can almost bench press the weight of an empty trike but I did not have the strength to bring the wing under control and things were getting completely out of hand

The oscilating just became worse the more I tried to control it untill the instructor told me to let go of the wing completely - As I let go of the wing it recovered almost immediately.

The name says it all, it is PILOT INDUCED - Before flying the Airborne I had approxamatly 200 hours experience on Aquila, Safari, Mainair Gemini, Air Creation - I flew the Airborne trike the same way I would fly the others, on the Airborne I tended to over compensate which causes the oscilating I guess

This is a common occurence for people flying the Airborne for the first time and for this very reason Larry Eschner warned me under no uncertain terms to not even consider trying to fly my Airborne without a Airborne rated instructor the first time.

As for the physics behind it - I am not sure, could be my imagination but I think an Airborne's wing is "higher" - Meaning further away from the undercarridge. It looks that way - I could be completely wrong

Anyhow, anyone reading this - I am not saying anything bad about Airborne, just stating that the PIO is not to be messed with without the knowledge of how to recover: - "just letting the wing go when it starts oscilating" - As bizarre as that sounds, it works

After a few hours on AIrborne it never oscilated with me again, telling me that is just flies differently to other trikes and once I mastered the wing I had no problems.


Many people wind in the luff lines for take off and landing.
This alters the reflex dramatically.
The only time I would do this is when flying straight and level with slower trikes or if I need to reduce my airspeed for any other reason.
I certainly do not allow students/pilots to do this for landings or take off.
What also needs to be done is to release the trim completely.
The ferrule should disapear into the tube and not remain between the slow and fast indicators.
Please try this and then if you can report back on the handling.

[Big-D]

Ok, from the top:

Nicow wrote:

It sounds like a stall to me...

Nope, far from it

Biggles wrote:

What were you doing when it started ocillating? Just turning or maintaining a steady rate turn with left and right inputs?

Important point: This particular airborne cruises at 52 knots, I was doing close to 60 knots, went into steepish left bank, once the level of bank was obtained I wanted I countered by moving the bar to neutral - THis is when the trike started oscilating, and all of a sudden banked sharply right, then sharply left, then sharply righ - I lost control - Untill instructor told me to let go of wing completely - Recovered immediately

Does the trike in question have wheel spats with winglets?

Edge X - Normal spats

Was the wing in the neutral position in the turn? And releasing the wing allowed to to move to the neutral position?

Nope, this is what starts the oscilation - If you fly the Airborne like an Aquilla or Mainair in my experiecne it will oscilate - I was going into left bank and then moved bar towards right to get it back to neutral in order to maintain bank - This is when it started oscilating - What I should have done is given smaller pilot inputs, but you only learn this after an hour or 2 on the Airborne


John wrote:

My logic says it's like a motorcycle getting a speed wobble or a serious tank slap

Ja, something like that except that this "tank slap" gets progressively worse Forget the Suzuki's and get a BMW John - A real bike

Blue max wrote:

Sorry gents. I am try-ing hard to understand this one.
Can some-one plse explain this to me in Afrikaans..

Dis heel eenvoudig: Ek het in 'n vinnige links-om draai gegaan, toe ek tevrede is dis ver genoeg gedraai toe bring ek die bar terug neutral toe, terwyl ek steeds in die draai was - Met die aksie het die trike na regs begin draai, ek probeer toe kompenseer en toe gaan ons weer links, weer probeer kompenseer toe gaan ons regs - So het dit erger en erger geword totdat ek feitlik beheer verloor het - Toe ek die vlerk heeltemal laat gaan op instrukteur se instruksie toe hou dit dadelik op en sy vlieg pragtig


McGuiver wrote:

Many people wind in the luff lines for take off and landing.
This alters the reflex dramatically.

Good point, in my case though I did not role up luff lines at all, cable was interely loose

Cheers

D

[Duck Rogers]

I'm no boffin at this and I am sure the men with the big hats on this forum like Ducky etc. will give their input.

Sorry.........I'm an observer on this one. I know nothing about trikes or PIO, I fly a real aeroplane......

[John Boucher]

And there Ducky goes and disappoints me and Big D.... I finally had a BMW bike but due to Aviation Induced Divorce Syndrome I had to relinquish my ownership!

[Big-D]

I finally had a BMW bike but due to Aviation Induced Divorce Syndrome I had to relinquish my ownership

Eish You will have one again Johno