Groundloop Explanation

[ChiSau]

Can someone enlighten me as to what a "groundloop" is? I keep reading about them and I can glean that they are undesirable, but what actually are they??????

:confused:

[Evo]

I started on an essay ;) but this explains it better than I could...

http://www.albertvilleaviation.com/taildraggers.htm

[FlyingForFun]

ChiSau,

It's a tail-dragger thing.

Imagine holding a pencil vertically. If you hold it from the top, gravity will cause it to hang straight down, even if you don't grip it very tightly. This is called "stable". Try holding it loosely from the bottom, though, and you'll have to juggle with it a bit to get it to stay upright. This is "unstable".

The Cessnas/PA28s that you learn in are basically stable aircraft on the runway. If the nose is pointing slightly to the left, the momentum of the aircraft (which acts through the centre of gravity, i.e. in front of the main wheels) will pull the aircraft straight. Imagine a piece of string tied to the centre of gravity of an aircraft, then pull that piece of string not quite straight forwards, but a few degrees off to the side - the aircraft will soon line up with the direction you are pulling the string.

Now imagine the same piece of string on a tail-dragger, which is unstable. If you pull the string any more than a few degrees to the side of where the aircraft's nose is pointing, it won't straighten up at all - the back of the aircraft will spin around until it's pointing the other way.

This is a ground-loop. At best, it's embarassing. At worst, the aircraft could tip over, damaging a wing-tip or worse. The way to avoid it is to ensure that every time you land, you are pointing straight down the runway, with no drift at all - things you should do in a tricycle-geared aircraft, too, but they're especially important in a tail-dragger for this reason. Also, when taxying, be ready to correct any deviation from where you want the aircraft to be - a slight gust of wind can catch the tail and induce a ground-loop at very low speeds.

Does that answer the question?

FFF
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[ChiSau]

Sheesh!!!

Very comprehensive..... thank you!

:p :cool:

[FNG]

Also, look at the thread lower down the page (or on page 2 or wherever it has got to by now) re avoiding groundloops, for a description from ace test pilot John Farley

[Flyin'Dutch']

I am obviously not as eloquent as the quoted articles but will try to explain it in 5 sentences.

1. Think of a two-wheeled (side-by-side) wheel barrow.

2. You pick up the handles.

3. You pull the wheelbarrow and the thing will follow you all the time (you being the centre of gravity = nothing more than point at which all forces get together) from here to china and back.

4. You push the wheelbarrow with the wheels in front of you, you now need to make constant corrections to keep the blasted thing going straight.

5 The 3rd wheel is only to stop the thing from falling for or aft depending whether said craft is a nosewheel job (CofG in front of mainwheels) or tailwheel job (CofG behind the mainwheels)

And thats it.

Groundloop is the situation whereby you have not made enough small corrections to stop the centre of gravity overtaking the mainwheels and the craft making itself into a back to front nosewheel job.

Because on takeoff the prop is pulling on the entire affair and helps preventing the above to happening. But beware it is still possible.

HTH

FD

[AerBabe]

The only time I've ever groundlooped was on take off... My instructor said he could have taken control and used more power to get us off the ground, but he wanted me to experience one. He was right, I've never come close since!
Why is it people only see you groundloop, they never see the perfect landings? :confused:

[Flying Lawyer]

ChiSau
If you're on the ground and suddenly find yourself facing the other way, or you've spun round 360 degrees - that was a groundloop.

FFF
Impressive stuff! One further point.
If you're heavy-handed with the throttle, it's easy to ground-loop a taildragger with a powerful engine (even without a gust of wind) on tarmac. It's important to apply throttle gently when moving off eg in a Harvard, Yak 3 or any other more powerful warbird.

It's not a pleasant experience, you look silly ( Sod's Law is that there's always someone watching :O ) and few people make the same mistake a second time!

Been there, done that in a Harvard, got the T-shirt etc. :)
Hope not to repeat the experience in the Yak!! :eek:

[LOMCEVAK]

Embarrassing - I heard an apocryphal story about a wartime FTS that used Harvards. If a student groundlooped he then had to walk (march?) around with a Harvard wheel suspended around his neck until the next student did one! You should never wish ill on your mates but.....

Or was it the South African Air Force? (Never let the facts get in the way of a good story).

[Heliport]

The old saying is that there are two types of warbird pilot, those who have groundlooped and those who will one day. ;)

[Flyin'Dutch']

Say Heliport,

What is the helo equivalent of the groundloop?

:rolleyes:

FD

[Heliport]

I suppose the nearest equivalent is 'Dynamic Rollover' and it's far worse than a ground-loop. I've been in an aircraft which did the latter, but I certainly wouldn't want to do the former!

In a nutshell, it's very important that a helicopter lifts off / lands cleanly and vertically.
If a helicopter drifts sideways whilst one skid (or wheel) is on the ground, the skid can act as a pivot point and the helicopter will begin to tilt over. If it's allowed to tilt over too far, or if the wrong inputs are applied, the helicopter will roll over and thrash itself to bits.

The cyclic (heli equivalent to control column) is much less effective at that point because, with one skid on the ground, the helicopter is not hovering. Beyond a certain point, the cyclic will be ineffective.
The recovery action is to lower the collective immediately - which will plant both skids firmly on the ground. The instinctive reaction, before being trained otherwise, is to raise the collective to try to lift out of trouble - wrong! That only makes the problem much worse.

Not by any means the most common circumstance in which dynamic rollover can occur, but ......
The pre-flight checks when a helicopter has been parked outside on a hard surface overnight in frosty weather include physically moving the skids to ensure they are not frozen to the ground.
There have been incidents where one skid has freed and the other remains frozen to the concrete pad when the helicopter begins to lift. The pilot, either not realising the problem or wrongly trying to free the second skid this way, raises the collective further and - bingo - dynamic rollover. :eek:

Helicopters are the most flexible flying machines ever designed, and can land virtually anywhere - but the ground has to be reasonably level. Slope landings/lifts have to be performed cautiously according to a specific technique for a number of reasons, one of which is the risk of dynamic rollover.

[FNG]

Alas, Flying Lawyer, I have nothing to offer as a proposed trade for a go in your Yak 3 except Cap 10 flits (a bit tame by comparison with warbirds) and a large collection of out of date White Books (useful for chocking if nothing else)

[Heliport]

FNG
Daresay you've noticed it's a single-seater?
A good few hours checking out in a Harvard first methinks! :D

[FNG]

I am confusing it with the rather less pretty but two-seat Yak 11.

by the way, do we win some sort of prize for the most off-thread thread?

[atb1943]

FL

Intriguing. Is it an original Yak-3 as pulled from the Russian Steppe, or a Yak-3M, or a Yak-11-turned 3 (if there are such things)?

Thanks