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What is a ground loop?



 
 
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  #31  
Old July 23rd 03, 10:43 PM
Darrell
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Mike wrote:
I've read the term ground loop in a lot of articles and accident
reports but what exactly is a ground loop?

--Mike


A ground loop is when the airplanes skids around 360 degrees while
continuing to move in the original direction on the ground.


--

Darrell R. Schmidt

B-58 Hustler History:
http://members.cox.net/dschmidt1/



  #32  
Old July 24th 03, 12:55 PM
Robert Coffey
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BTIZ wrote:
and that's why tail dragger pilots have "happy feet"..

never heard of a nose wheel aircraft "ground looping", the CG location
relative to the main gear kinda help keep it straight..


My first solo in a pa28 came real close when I landed in wake turbulance.


  #33  
Old July 26th 03, 11:00 AM
Julian Scarfe
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"David" wrote in message
...

It seems to me that this explanation, though common, is oversimplified.
What we are talking about is stability. When an aircraft (or a car for
that matter) turns on the ground a sideways force is developed on the
wheels. There is also a force generated by the sideways acceleration at
the cg and, also, in the case of the aircraft, a side aerodynamic force.
If the combined reaction of the first two is behind the cg than the yaw
motion on the ground will be unstable and may or may not be able to be
controlled by the pilot with the rudder.

It is not that the main wheels are in front of the cg so much as that
the side force developed by the tail wheel is very small (even smaller
if it is a castoring tail wheel) and too much of the side ground force
will be developed by the 'main' wheels.


I'm not sure that's the case, David.

The problem with a decelerating taildragger is that the inertial force at
the CG associated with the deceleration occurs behind the retarding force of
the mainwheels on the runway. This is unstable. If the two forces get out
of line, the couple tends to increase. By contrast, having the retarding
force on the main wheels behind the CG is stable.

^
| direction of motion in landing roll.

-------------------------------------------------

Tricycle:

^
|
* CG

+ wheels
|
v

-------------------------------------------------

Conventional (tailwheel):

+ wheels
|
v

^
|
* CG

-------------------------------------------------

Look at the stability to a yaw.

Of course the lateral forces you mention are usually available to control
the situation, which is why the instability isn't manifested as a ground
loop every time. If the aircraft starts to yaw it just gets more draggy,
hence the situation just gets worse.

In principle a tricycle gear aircraft should be susceptible to groundlooping
on take-off, but you have the stabilising advantage of increased drag
hampering acceleration as the aircraft starts to get out of shape.

Julian Scarfe



  #34  
Old July 27th 03, 01:51 AM
David
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In article , Julian
Scarfe writes
I'm not sure that's the case, David.

The problem with a decelerating taildragger is that the inertial force at
the CG associated with the deceleration occurs behind the retarding force of
the mainwheels on the runway. This is unstable. If the two forces get out
of line, the couple tends to increase. By contrast, having the retarding
force on the main wheels behind the CG is stable.


Thanks for the comments Julian. My first thought about your suggestions
is that as long as the braking force is directly in the line of
deceleration then there is not a problem but as soon as a yaw develops
then side forces immediately come into play, if they didn't then the
aircraft would not start to turn. It must be very similar to the
oversteer/understeer problem of cars.

In a car if you brake hard and the front wheels lock then the car tends
to go straight on because the yaw stability is still provided by the
rear tyres. If the rear wheels lock up then you will have great
difficulty in stopping a spin. This corresponds to the lack of 'lift'
developed by the tail wheel (particularly if it castors) meaning there
is insufficient yaw stability.

The couple that you mentioned that depends on the retarding force of the
front wheels only produces an effect if a yaw develops. The correction
of the yaw has to be provided by an inbuilt stability or by the rapid
response of the pilot trying, with a big rudder, to introduce
'artificial' stability into the loop.

It has some small similarities to the concept that a high wing aircraft
is more stable because the cg is below the wing. It is more stable but
not due to 'pendulum' stability but due to the way the air flows during
a yaw.
--
-----------------------------------------------------------
David Francis E-Mail reply to
-----------------------------------------------------------
  #35  
Old July 30th 03, 06:19 PM
Grandpa B.
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I'm in the process of a restorating a '58 Champion 7FC/EC that was
groundlooped in Reno, shortly after being converted to a raildragger. As my
neighbor - from whom I purchased the project - said, they converted it just
in time to groundloop it.

It suffered a great deal of harm: broken wing spars, both main gear
partially torn off, along with the fittings, prop curled back (one blade), a
few bent ribs, scuffed and bent sheetmetal - cowl, etc. The lift struts made
it through, as did the bulk of the airframe.

I'm basically rebuilding it from the tires up - airframe has been faithfully
converted to an EC by removing all vestiges of nosewheel paraphernalia,
blasted and powdercoated, new interior, including floorboards. Even the seat
frames got new powdercoating! I'm in the wiring stage, waiting for the radio
trays to be repaired - not from crash damage, just abuse - then I'll finish
the (brand new) panel wiring and plumbing. Covering isn't far off... Then it
will look like an airplane, rather than a skeleton, in the garage. After
that, it's on to tearing the engine down for inspection.

Jon B.
wrote in message
om...
"Mike" wrote in message

...
I've read the term ground loop in a lot of articles and accident reports

but
what exactly is a ground loop?

--Mike


Mike,
If you ever experience a ground loop, you will know it!!!!!
A ground loop will make a bigger impression on you if you happen to be
in the back seat of a tandem tail dragger that you own when the wild
swing happens.
I let some yahoo fly my 7ac Champ from the front seat because he was
interested in buying it.....never again.....we ended up in the weeds
at the side of the runway. Luckly there was no damage and he bought
the airplane AND I was a LOT SMARTER.

Ken Black



 




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