Ground loop?
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For those pilots who regularly fly tailwheel aircraft the following is certain....
"there are those that have.. and those that will groundloop"
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.....it goes so quiet when the goldfish dies.
[This message has been edited by Algernon Lacey (edited 07 October 2000).]
"there are those that have.. and those that will groundloop"
------------------
.....it goes so quiet when the goldfish dies.
[This message has been edited by Algernon Lacey (edited 07 October 2000).]
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STP - a ground loop most usually happens on a tail wheel aeroplane because the center of gravity is behind the two front wheels.
While things are going normally everything is fine, but if the line of travel of the aeroplane starts to swing to one side then momentum makes the C of G keep going in the direction i.e.: out to the side!
This is why, when flying a tail wheel, you have to concentrate on keeping it under control. I was taught to use the rudder pedals as if they were the pedals on a paddle boat and that seems to work!
You can ground loop a tail wheel, even at low speed taking off or landing, if you don't keep on it. At least embarrassing... maybe dangerous. Obviously the heavier the aeroplane the harder it is to keep the C of G under control.
While things are going normally everything is fine, but if the line of travel of the aeroplane starts to swing to one side then momentum makes the C of G keep going in the direction i.e.: out to the side!
This is why, when flying a tail wheel, you have to concentrate on keeping it under control. I was taught to use the rudder pedals as if they were the pedals on a paddle boat and that seems to work!
You can ground loop a tail wheel, even at low speed taking off or landing, if you don't keep on it. At least embarrassing... maybe dangerous. Obviously the heavier the aeroplane the harder it is to keep the C of G under control.
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hear hear fallen eagle
I was under the impression this forum was more like a "staff room" for instructors, whereas Wannabes and R+N were the classrooms.
If I've got a question about what to do to/for/with a student, it comes here, if it's how to fly, it goes to Wannabes.
"But that's just one mans opinion." (Keith Quinn)
I was under the impression this forum was more like a "staff room" for instructors, whereas Wannabes and R+N were the classrooms.
If I've got a question about what to do to/for/with a student, it comes here, if it's how to fly, it goes to Wannabes.
"But that's just one mans opinion." (Keith Quinn)
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Are our ego,s getting so big that we wont answer a question from some one who is clearly not an instructor ?.
Or do we just think that it should not be asked on this forum ?.
Or do we just think that it should not be asked on this forum ?.
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I'm very sorry if I have invaded private territory, I genuinely had no idea what a "ground loop" or how it occurred. I thought it best to ask in this forum because this is where knowledgeable people are most likely to frequent. With many thanks to VIRGIN and OLEO, I am now wealthy in knowledge and moreover, entirely satisfied that I have received more accurate information than I may have received in the wannabees forum.
I am now leaving, banished into exile into the land of the wannabees!
I am now leaving, banished into exile into the land of the wannabees!
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STP,
Don't take too much notice of Fallen Eagle or Chicken 6. Those jackasses just found their way on to the perch! If you want to ask questions of instructors I would think that this is as good a place to start as any.
------------------
Mount'in man,
I luv mountin' women!
Don't take too much notice of Fallen Eagle or Chicken 6. Those jackasses just found their way on to the perch! If you want to ask questions of instructors I would think that this is as good a place to start as any.
------------------
Mount'in man,
I luv mountin' women!
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Thats all fine, but when someone pitches up on the instr. forum with a question like that its OK. but state who he /she is I am so VERY SORRY. BUT, I just thought an instr would know the answer to that one, and it concerned me that that chap did not. ANYWAY I have nearly had enough of the misunderstandings and jumping on people arround here its getting to much like a real flying club. bye
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STP
I was going to stay out of this one, but I am always a tad unhappy to stand by and see slightly duff gen being taken in by an aviator trying to learn. That way off message stuff gets perpetuated. Hence my U turn (sorry)
If you have a paper and pencil, the whole subject takes 30 secs to cover but I don’t know how to put the appropriate diagrams up here, so a lot of words now follow
Ground loops happen because of the force due to friction that exists between a tyre and the ground.
When an aircraft touches down with a zero drift angle we can ignore the friction forces (sure they have to spin up the wheel but once that has happened the wheel just rolls and does not disturb the aircraft)
But when a wheel touches down with a drift angle, friction causes a drag force which acts 180 deg out to the direction that the aircraft is travelling (not the direction it is pointing). Visualising this is easy if you take an extreme case like 90 deg of drift (!)
This force is not in the plane of rotation of the wheel, so for our convenience we can split it into its two components, one in the plane of the wheel and the other at right angles to the plane of the wheel. It is the one at right angles to the wheel that creates the piloting problem.
Any force applied at right angles to the wheel is ACROSS the long axis of the aircraft and so will make the aircraft yaw.
Whether the yaw so produced REDUCES the original angle of drift or INCREASES will either make our day or spoil it.
So, and thinking only about the main wheels, if you land with the nose heading to the left of the runway and with the aircraft tracking down the runway, the nose will tend to snatch further left (bad) if the main wheels are in front of the CG (taildragger) but pull round towards the runway heading (good) if the wheels are behind the CG (tricycle).
This is the crux of the issue, weight is not strictly speaking a factor. What is a factor is the yawing inertia of the aircraft as this RESISTS the tyre induced yaw whichever way it acts. Thus, for a low inertia aircraft (probably light and short) things will get better or worse very much more quickly than for a high inertia aircraft (probably heavy and long)
I think it is important to recognise that during a ground loop the CG continues to move over the ground essentially in the direction it was travelling at touchdown but the aircraft ROTATES in yaw about the CG (as opposed to a notion of the CG being flung out sideways)
The last time I did a ground loop (it was a secret between me and about 6000 people at the airshow) the aircraft stayed on the runway centreline but remorselessly yawed to the right until I was going straight, but backwards, down the runway (at this point I knew what to do – open the throttle, until I finished up going forwards and calmly taxy towards the turn off I had just missed…..)
If I have explained things well enough that you are happy with the above all the rest of the ground loop stuff follows easily:
They are less likely to happen on grass as it tends to produce less friction than tarmac.
If you have a tailwheel lock, then the side force from the tailwheel will be stabilising (behind the CG) If you forget to lock the tailwheel it just castors and produces no stabilising effect (bad)
Now you can see why tailskids provide nicer handling ON GRASS, as they tend to dig in more than tailwheels and so enhance their stabilising effect.
You can also see that ground looping on take off is perfectly possible if you let ANY yaw go uncorrected for more than a moment. If you do this the aircraft momentarily continues on its original tack, but points to the side, and bingo the tyres come into play. With a high powered piston, the initial yaw can easily happen due to a torque induced swing or from raising the tail a tad quick and generating a gyroscopic yaw from the prop.
My ground loop (in Bob Mitchell’s Ryan PT 22) was caused by me being an idiot and lowerering the tail too fast after a main wheel only touchdown – plus a strong cross wind with a tail component, trying to help the busy controller by expediting my arrival between displays and all that sort of stuff that you know you should not do.
JF
I was going to stay out of this one, but I am always a tad unhappy to stand by and see slightly duff gen being taken in by an aviator trying to learn. That way off message stuff gets perpetuated. Hence my U turn (sorry)
If you have a paper and pencil, the whole subject takes 30 secs to cover but I don’t know how to put the appropriate diagrams up here, so a lot of words now follow
Ground loops happen because of the force due to friction that exists between a tyre and the ground.
When an aircraft touches down with a zero drift angle we can ignore the friction forces (sure they have to spin up the wheel but once that has happened the wheel just rolls and does not disturb the aircraft)
But when a wheel touches down with a drift angle, friction causes a drag force which acts 180 deg out to the direction that the aircraft is travelling (not the direction it is pointing). Visualising this is easy if you take an extreme case like 90 deg of drift (!)
This force is not in the plane of rotation of the wheel, so for our convenience we can split it into its two components, one in the plane of the wheel and the other at right angles to the plane of the wheel. It is the one at right angles to the wheel that creates the piloting problem.
Any force applied at right angles to the wheel is ACROSS the long axis of the aircraft and so will make the aircraft yaw.
Whether the yaw so produced REDUCES the original angle of drift or INCREASES will either make our day or spoil it.
So, and thinking only about the main wheels, if you land with the nose heading to the left of the runway and with the aircraft tracking down the runway, the nose will tend to snatch further left (bad) if the main wheels are in front of the CG (taildragger) but pull round towards the runway heading (good) if the wheels are behind the CG (tricycle).
This is the crux of the issue, weight is not strictly speaking a factor. What is a factor is the yawing inertia of the aircraft as this RESISTS the tyre induced yaw whichever way it acts. Thus, for a low inertia aircraft (probably light and short) things will get better or worse very much more quickly than for a high inertia aircraft (probably heavy and long)
I think it is important to recognise that during a ground loop the CG continues to move over the ground essentially in the direction it was travelling at touchdown but the aircraft ROTATES in yaw about the CG (as opposed to a notion of the CG being flung out sideways)
The last time I did a ground loop (it was a secret between me and about 6000 people at the airshow) the aircraft stayed on the runway centreline but remorselessly yawed to the right until I was going straight, but backwards, down the runway (at this point I knew what to do – open the throttle, until I finished up going forwards and calmly taxy towards the turn off I had just missed…..)
If I have explained things well enough that you are happy with the above all the rest of the ground loop stuff follows easily:
They are less likely to happen on grass as it tends to produce less friction than tarmac.
If you have a tailwheel lock, then the side force from the tailwheel will be stabilising (behind the CG) If you forget to lock the tailwheel it just castors and produces no stabilising effect (bad)
Now you can see why tailskids provide nicer handling ON GRASS, as they tend to dig in more than tailwheels and so enhance their stabilising effect.
You can also see that ground looping on take off is perfectly possible if you let ANY yaw go uncorrected for more than a moment. If you do this the aircraft momentarily continues on its original tack, but points to the side, and bingo the tyres come into play. With a high powered piston, the initial yaw can easily happen due to a torque induced swing or from raising the tail a tad quick and generating a gyroscopic yaw from the prop.
My ground loop (in Bob Mitchell’s Ryan PT 22) was caused by me being an idiot and lowerering the tail too fast after a main wheel only touchdown – plus a strong cross wind with a tail component, trying to help the busy controller by expediting my arrival between displays and all that sort of stuff that you know you should not do.
JF
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When I first saw the name "John Farley" being used as a nom-de-plume I thought "what a good name for a pilot to choose", now I wonder if John Farley really is the great man himself. John Farley, are you THE John Farley, the test pilot of the Harrier?
If so, please sign this bit of paper for me. I remember seeing the Paris Airshow er.. how shall we say...errr..yes crash, that is the word I'm looking for.
In the present day idiom 'nuf respect Mr. Farley, and Capt Pprune for letting us listen to these pearls of wisdom.
If so, please sign this bit of paper for me. I remember seeing the Paris Airshow er.. how shall we say...errr..yes crash, that is the word I'm looking for.
In the present day idiom 'nuf respect Mr. Farley, and Capt Pprune for letting us listen to these pearls of wisdom.
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One question, 16 responses, 3 answers. I have to ask why Algernon Lacey, Capt Crash, Fallen eagle, Chicken6. A and C, Mount'in Man, Tallbloke and New Bloke felt impelled to post comments that had sod all to do with the question that was asked. Could it be an ego problem?
Congratulations to Oleo, Virgin and John Farley for making creditable attempts to answer, in a text based medium, what really requires a diagrammatic explanation.
I shall now don my flack jacket and await the inevitable stream of vituperation from those whose over-inflated egos I have dented.
Congratulations to Oleo, Virgin and John Farley for making creditable attempts to answer, in a text based medium, what really requires a diagrammatic explanation.
I shall now don my flack jacket and await the inevitable stream of vituperation from those whose over-inflated egos I have dented.
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Some factors to consider:
A tricycle type is directionally stable ie tends to keep moving in the same direction because the CG is ahead of the centre point of the drag from the wheels.
This means that if the two get out of alignment the inertia of the CG (pulling forward) is acting opposite to the drag of the wheels (pulling backward). Within certain limitations, the combination act as a couple, pulling the a/c back into alignment with its direction of travel.
A tailwheel a/c has the reverse. The drag is centred ahead of the CG. The CG has a tendency to keep moving in the direction it was traveling, while the wheels are trying to do the opposite.
If the wheels & CG get out of aligment with the direction of travel then the a/c will have a tendency to continue to yaw - unless a correcting force is applied. Think of a car skidding.
The correcting forces or factors that are available include keel area & rudder input, tailwheel effects eg locked or not, or steerable, moment arm over which these forces can act, width between the main wheels (Is this called groundtrack? I forget), rolling resistance caused by the surface etc
Spacing of the mainwheels is a factor because the further the wheels are apart the more yaw must happen before the CG moves far enough to the side for sufficient misalignment to cause a ground loop.
Anything that induces a yaw away from the longitudinal alignment of the CG & centre of drag from the gear can precipitate a ground loop.
This can include:
A tricycle a/c can behave like a tailwheel type if it has a relatively light load on its mainwheels & a relatively heavy load on the nosewheel eg if you wheel barrow by landing on the nosewheel, or if you try to force it to stay on the ground too long during the t/off roll.
I have a feeling I've forgotten something in the above...
[This message has been edited by Tinstaafl (edited 11 October 2000).]
A tricycle type is directionally stable ie tends to keep moving in the same direction because the CG is ahead of the centre point of the drag from the wheels.
This means that if the two get out of alignment the inertia of the CG (pulling forward) is acting opposite to the drag of the wheels (pulling backward). Within certain limitations, the combination act as a couple, pulling the a/c back into alignment with its direction of travel.
A tailwheel a/c has the reverse. The drag is centred ahead of the CG. The CG has a tendency to keep moving in the direction it was traveling, while the wheels are trying to do the opposite.
If the wheels & CG get out of aligment with the direction of travel then the a/c will have a tendency to continue to yaw - unless a correcting force is applied. Think of a car skidding.
The correcting forces or factors that are available include keel area & rudder input, tailwheel effects eg locked or not, or steerable, moment arm over which these forces can act, width between the main wheels (Is this called groundtrack? I forget), rolling resistance caused by the surface etc
Spacing of the mainwheels is a factor because the further the wheels are apart the more yaw must happen before the CG moves far enough to the side for sufficient misalignment to cause a ground loop.
Anything that induces a yaw away from the longitudinal alignment of the CG & centre of drag from the gear can precipitate a ground loop.
This can include:
A tricycle a/c can behave like a tailwheel type if it has a relatively light load on its mainwheels & a relatively heavy load on the nosewheel eg if you wheel barrow by landing on the nosewheel, or if you try to force it to stay on the ground too long during the t/off roll.
I have a feeling I've forgotten something in the above...
[This message has been edited by Tinstaafl (edited 11 October 2000).]
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Rolling C this is the first incoming !, i asked "are our ego,s getting to big that we cant answer a question.........."
What i did not like was that some of the posts where critical of some one who clearly wanted to further his/her undestanding of a subject and who better to ask than an instructor? .
It would seem some did not like this on this forum a point that i disagree with.
As instructors we should all be willing to answer questions from students what ever forum we find them.
Finaly thanks to john f for an a post far more eliquent that i could have made.
What i did not like was that some of the posts where critical of some one who clearly wanted to further his/her undestanding of a subject and who better to ask than an instructor? .
It would seem some did not like this on this forum a point that i disagree with.
As instructors we should all be willing to answer questions from students what ever forum we find them.
Finaly thanks to john f for an a post far more eliquent that i could have made.
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New Bloke
Hi. On a point of detail I have just checked my log book and can find no record of a crash.
It was actually my Lord High Master Bill Bedford in XP831 at Paris. After the lads in the hangar at Dunsfold did their body work stuff they gave it to me to take to Bedford (aerodrome) to compare with the Short SC1 which we already had on Aero Flight at that time. There I managed 128 landings in the beast without further modification to its shape – so I was well chuffed. Off topic I know but accuracy is everything (well below 50 ft anyhow).
STP
My pleasure, but there is no need to feel honoured – I’m just another aviator like you.
JF
Hi. On a point of detail I have just checked my log book and can find no record of a crash.
It was actually my Lord High Master Bill Bedford in XP831 at Paris. After the lads in the hangar at Dunsfold did their body work stuff they gave it to me to take to Bedford (aerodrome) to compare with the Short SC1 which we already had on Aero Flight at that time. There I managed 128 landings in the beast without further modification to its shape – so I was well chuffed. Off topic I know but accuracy is everything (well below 50 ft anyhow).
STP
My pleasure, but there is no need to feel honoured – I’m just another aviator like you.
JF