What is drag over ?

[SandL]

full understanding of PPO and torque over but not sure what drag over is
I have seen Doug mention it a few times. maybe I understand it by a different name. Is it when the frame rotates due to rotor drag eg rotor spins anti clockwise so with power off the friction in the head also pulls the frame around anti clockwise ?
can some one explain with out lots of maths please
Thanks
peter

 

[Jazzenjohn]

It is basically the idea that aerodynamic drag below the center of gravity can drag the gyro into something resembling a bunt. Things like large pontoons don't present too big a drag if directly aligned with the windstream, but as the craft is rotated forward the coefficient of drag, as well as the area both increase rapidly.

 

[GyroChuck]

Things like large pontoons don't present too big a drag if directly aligned with the windstream, but as the craft is rotated forward the coefficient of drag, as well as the area both increase rapidly.

Another example the 18A in a side-slip.

 

[Texasautogyro]

If you have seen the video of the PPO from Japan. The gyro has skis with no nose teather. They drug him right over when the wind caught the tips.

 

[SandL]

got it thanks

more sort of drag under, i guess it's not a sudden effect unless it instigates pio so it's form drag way under vertical C of G drag increases with square of speed so i guess a gyro with floats flying fast would be fulnerable

thanks all

 

[birdy]

I think there is anatha possable type of tumble.
Iv never tryed it [ tumbled that is] but i do know that theres a very unresponcive phase in time from the rotor near the end of an inertia hover, specialy with agressive, high rate inputs. Sumwhere between air over to air under flight, the machine feels more like a rock than an aircraft.

 

[SandL]

Birdy Just when I though I'd got it

you talk of an "inertia hover" and "air over to air under flight " the machine feels more like a rock than an aircraft.

Birdy , i'm on the hook , and it's not April 1st yet , so please can you explain further , what is inertia hover and what do you mean by air over and air under

Thanks

 

[Doug Riley]

Sandl, I'll leave Birdy to explain inertia hover.

Drag-over, unlike PPO, was known during the Cierva-Pitcairn era. There's an account (possibly in the Brooks autogiro book) of a float-equipped tractor gyro dragging over onto its back --even with the huge H-stabs that those gyros had. According to the account, it flew along inverted for a moment, and then -- it righted itself! The pilot landed and walked away.

The typical modern gyro wouldn't fare as well.

Igor Bensen described a near-catastrophe he experienced in a "gyroboat" (a monohull float gyro, but one that's towed by a rope behind a powerboat). The open top of the hull scooped air and forced the gyro down even with full back stick. The tow rope pulled it out of its dive just above the water.

A friend of mine had an unplanned dive into Long Island Sound in a float-equipped, powered Bensen. Again, full back stick was ineffective to pull out. He survived but got pretty banged up.

Floats and open-topped "scoop" pods deserve extreme caution. It's best to design such craft from scratch, instead of bolting the drag-making gadget onto a stock wheel gyro.

 

[Resasi]

My understanding of an 'inertia hover' would be that time period where the inertia of the rotor blades is converted into lift.

In most cases this would probably be immediately prior to touchdown, however I could easily see where in Birdy's line of work he might well be using this phase in some other manoever.

It would be dependent upon the inertia stored in the rotor and would vary from, say the depleted uranium tip loaded Carter copter blades, to DW's which are extremely light blades.

A video of Birdy's, incidentally showing spousal abuse as he showered his wife with rotor wash and debris, seemed to indicate that those Aussie blades he had converted to probably had a reasonable amount of inertia and longer dwell time. (They both seemed to be enjoying the experience.)

Now comes the disclaimer. My understanding inertia hover could be completely wrong. hwell:

I will wait for the rest of the 'air over air under' though it sounds suspiciously like 'arse over tip' or reverting to gravity, and stones in the air syndrome.:help:

 

[Doug Riley]

A gyro can work like a helicopter for short periods of time. If RRPM is increased above cruising level, the stored energy in the rotor substitutes temporarily for an engine drive. This means that the gyro can stand still in the air, drawing air down through its rotor in a way that is inconsistent with autorotation.

But this can't last long. As RRPM decays, the gyro will settle. Specifically, it will settle into its own downwash. That is, the rotor settles into (1) disturbed air that (2) is already travelling downward.

Just like a helicopter in a similar situation, the gyro will descend vertically very fast and can get buffeted on the way down by the turbulent air of its own downwash.

If you have altitude, you'll recover from this predicament by nosing down and flying out of it.

If you are at, say, 20 feet, though, things will not go well for you. You will pancake in at greater than normal vertical-descent speed. Splat.

 

[birdy]

According to the account, it flew along inverted for a moment, and then -- it righted itself!
Bloodyell!!!!
Thatd be one hell ofa yarn to spin to the grandkids, if you lived.

An inertia hover is a handy tool for stubbern moos Sandl.
I recon its kinda hypnotic , and wen you blast out of it, they snap back to reality with their tail between their legs, most times.
As Leigh n Doug says, its useing the stored excess rotor inertia to hover momentarily.
Obviously, if your useing it 5' off unlandable ground, or over a tree, you need to know just how much hangtime you have built up, and snap the throttle open before the sink starts.
Light, tip weighted blades are excellant for the job, as is a reliable 912.

The bad bit [ anythn i dont understand is bad] is a short duration phase between the air over [ helicoptering] and air under [ autorotation] phases.
I cant realy explain it, mainly coz iv never been in a situation where iv had the grey cells to spare to think bout it at the time, but dureing the transition, the stick is non responcive.All iv ever dun dureing this phase is power out. Iv never tryed to command the rotor to do anythn but backstick.
Even so, with the rotors leaning backwards, the machine "wobbles".
Its like the gyroscopic resistance is be'n transfered to the machine, instead of be'n taken up by the air.
CB could explain more wots go'n on, but to be honest, i dont, coz iv never 'studied' it.

A video of Birdy's, incidentally showing spousal abuse
From memory Leigh, that wasnt an inertia blast, i was just side slipn, and directed the blast at the camera.

If you are at, say, 20 feet, though, things will not go well for you. You will pancake in at greater than normal vertical-descent speed. Splat.
Zactly!
Hint, dont push the nose down.
Thats where the dirty air is.

 

[SandL]

helicoptering

helicoptering

I'm getting there but not brave enough to give it a go for the time being
however later in the summer (if we have one this year) I may be tempted to give it a go.
so to perform this manouver (without moos)
I go up to say 1500 ft then ease back on the throttle and gently dive to 1000ft at say 70kts ease the stick back to a hover thus increase G loading (gyro has more weight to lift) so blades increase speed and airflow goes downwards through the disk (would hear the blads slapping the air ?)

I then enter a vertical decent and in effect fall through the dirty air for a few seconds recovering at say 7-800ft lower the nose and gradually open the throttle. returning to straight and Level (S and L as in sandl)

does that sound ok ?

things to watch out for don't pitch up too sharply when entering the hover, keep a little throttle on during the hover to retain rudder authotity. make sure I have plenty of air under me for recovery.

is that it ? I have a single seat Bensen with Pod, CLT and light 22ft draggon wings.
Thanks
Peter

 

[SandL]

air under and air over

are you talking about
air under
normal cruuse where the disk is angled and air flow is from under the disk
air over
air over as in the hover concept where the frame has virtually 0 forward air speed , the blades stay coned supporting the weight and air passed from over the disk to under it thus supporting the frames weight briefly.
It that a correct translation of air over and air under.?
thanks

 

[Resasi]

Nope Birdy I didn't think you were doing this...

An inertia hover is a handy tool for stubbern moos Sandl.
I recon its kinda hypnotic , and wen you blast out of it, they snap back to reality with their tail between their legs, most times.

...just some sideslipn...blasting the poor camera person...and trying out those new Aussie blades you had just got.

And...when you got down, you may just have got just a tiny blast of reality yourself, though she was laughing, so perhaps not.

 

[XXavier]

Sandl, I'll leave Birdy to explain inertia hover.

Drag-over, unlike PPO, was known during the Cierva-Pitcairn era. There's an account (possibly in the Brooks autogiro book) of a float-equipped tractor gyro dragging over onto its back --even with the huge H-stabs that those gyros had. According to the account, it flew along inverted for a moment, and then -- it righted itself! The pilot landed and walked away.

The typical modern gyro wouldn't fare as well.

[...]

The complete account is here... Yes, it's from Brooks' book.

 

[Stan V]

The complete account is here... Yes, it's from Brooks' book.

QUOTE]

What's the full name and author of this book? I can't seam to find it online. I'd like to give it a read. Thanks

 

[XXavier]

The complete account is here... Yes, it's from Brooks' book.

QUOTE]

What's the full name and author of this book? I can't seam to find it online. I'd like to give it a read. Thanks

Cierva Autogiros
The Development of Rotary-Wing Flight

Peter W. Brooks
Smithsonian Institution Press
ISBN 0-87474-268-4

I believe it's currently out of print.

 

[Mike Stone]

This may be the film of the Japan crash


www.youtube.com/watch?v=VmOeMTUqp98

 

[C. Beaty]

The complete account is here... Yes, it's from Brooks' book.

“The floats increased empty weight by 275 lbs.”

I’d say dragover was only one of a plethora of problems. Anything at wheel level that increases AUW by 275 lbs. converts such a machine to one with propeller thrustline well above the CG, a severe case of HTL.
Combine that with rotorblade profile having a high negative pitching moment and the pilot was indeed lucky to have walked away.

 

[Stan V]

Cierva Autogiros
The Development of Rotary-Wing Flight

Peter W. Brooks
Smithsonian Institution Press
ISBN 0-87474-268-4

I believe it's currently out of print.

Amazon has several used copies available, I ordered one of them. Thanks XXavier