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Loop

Old 25th Aug 2015, 22:23
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Loop

In the light of recent events at Shoreham;

Can I as a non aerobatic pilot please ask a question?

Assuming that you wish to exit a plain loop at or above the entry point in a reasonably powerful aircraft, what is the last point that you can take corrective action if you realise that your airspeed is low?

Top of loop, or is it too late then?

FF
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Old 25th Aug 2015, 22:35
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Loop

Define reasonably powerful.


Then go look at clips of overpowered Su33s and MiG29s and even a Thunderbird F-16 screwing up with tons of thrust to spare, return to PoF regarding lift and stalls, and wait until the AAIB release their report.

I understand your curiosity, but speculating and drawing commentary is neither welcome nor useful at this sensitive time.
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Old 25th Aug 2015, 23:16
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I purposefully didn't ask my question in the forum where the Shoreham disaster is being discussed as it does not contribute to that specific discussion.
Obviously that event did prompt my question about the technical aspects of the aerobatic manoeuvre being attempted and I assumed that this was the best place to ask it and just hoped that a proper pilot would be able to give me an answer.
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Old 26th Aug 2015, 00:38
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You can abort by rolling wings level (resulting in something from a roll off the top to a half cuban) well past the top of the loop. The latest you can do that would depend on roll rate.
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Old 26th Aug 2015, 00:47
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Power [available] is only one element of the equation, there'll be more to it than that. Different aircraft will react differently to the forces in a loop. More power may not be the fix for a erred loop entry. When you were trained in stall recovery, hopefully you were trained to allow the plane to accelerate as you pull out of the dive, to prevent a secondary stall, there are elements of this in completing a loop also. Thinking about, and discussing this is good, attempting it without competent training is bad.

I like altitude for that margin of safety during aerobatics, but, I suppose altitude is not what is ideal for aerobatic displays to a crowd on the ground - it's a dilemma...
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Old 26th Aug 2015, 01:04
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Assuming that you wish to exit a plain loop at or above the entry point in a reasonably powerful aircraft, what is the last point that you can take corrective action if you realise that your airspeed is low?
The problem with powerful aircraft is that their loops are so big, that it's impossible to judge visually if you have sufficient height to complete the loop safely when you are at the top.

Rather than relying on visual judgement of the height available, pilots of these aircraft have previously determined target values for speed, and height they aim to achieve at the top of a loop, known as 'gates'.

If their speed and height are within the 'gates' then they are safe to continue down the second half of the loop. If not, they now have a small window of opportunity to roll erect and fly away.

They would aim to do this by the 45 degrees pitch down position from the top of the loop. Beyond this point the 'window of opportunity' rapidly closes, and is, of course, fully closed at the vertical point, where they are committed to continue the loop.

Factors affecting the height gained during the upward half of the loop, and the minimum height required to complete the downward half of the loop, such as aircraft weight, air temperature/pressure/humidity(density) will vary on the day, and the 'gates' required at the top of the loop, particularly the 'gate' for height, should be based on the worst case.


MJ

Last edited by Mach Jump; 26th Aug 2015 at 01:15. Reason: Punctuation.
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Old 27th Aug 2015, 19:08
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Discussion of proper techniques for performing loops in aircraft common to "private flying" is welcomed here. Let's not expand the "Shoreham" topic to here please....
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Old 28th Aug 2015, 15:41
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If the "reasonably power aircraft" is capable of "reasonably quick" aileron rolls you can take corrective action until shortly before the nose points 90deg downwards by rolling 180deg to next horizon and pulling out... but obviously the earlier you act the better...

In my experience if you end up slow & inverted & unhappy with the situation the best solution is to lower the nose 20 - 30deg below the horizon, accelerate for a moment and then roll upright again.

maehhh
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Old 28th Aug 2015, 23:22
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What maehhh said. Obviously, once in the down vertical there is no way out other than pulling through.

I've sometimes thrown away a loop or other 'pull up' manouevre on the way up, if I'm unhappy about having enough energy to go over the top. I just turn it into a wing-over with no 'pull' and recover to level flight.
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Old 30th Aug 2015, 17:05
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If you do the first half of a loop then roll out to fly horizontal (the right way up) from the top what is that mavouver called?

Thanks for you other replies, exactly what I wanted to know. Pilot myself but have never done aeros (never wanted to).

FF
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Old 30th Aug 2015, 17:34
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That is unsurprisingly called a 'roll off the top', or, an 'Immelmann' as our friends across the Atlantic would call it.


MJ
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Old 30th Aug 2015, 17:46
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Obviously, once in the down vertical there is no way out other than pulling through.
Actually, depending upon aircraft type, you could equally well push with same radius...

( a myriad of aerobatic types most certainly, maybe not in a Yak??)

TOO
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Old 31st Aug 2015, 07:02
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...depending upon aircraft type, you could equally well push with same radius...
Yes, but surely you'd lose a little time, and height, in the transition from pull to push and if the maneuver was in such a critical state any loss would be bad.
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Old 31st Aug 2015, 14:38
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If you do the first half of a loop then roll out to fly horizontal (the right way up) from the top what is that mavouver called
For lower power, lower inertia types, it would be called "very difficult". At that stage in the loop, you're flying rather slowly, and possibly not at one G. The amount of airflow might be inadequate to perform a half roll up there, before you're no longer flying. A lot of drag is introduced by the control input to initiate a roll, and that drag can slow you right down, at a point in flight where you have little speed anyway. For higher power types, and those with engine torque as an aid, this is probably quite different, and possible.

Actually, depending upon aircraft type, you could equally well push with same radius...
If you were to "push" on the downward side of the loop, it would instantly cease being a loop, and become rather scary. However, you certainly can modulate your pull, to affect the radius of the loop. Indeed, a safe loop may be flown by relaxing the pull a little on the way down, and allowing the plane to accelerate, so it has the speed it will need to sustain the G of the pull out approaching the bottom, without stalling. This is a big part of the required pilot judgement, and resisting pulling like heck because you're seeing ground rush.

Ground rush with a 1000 foot AGL "floor" can be alarming, I can imagine the difficulty resisting it when the floor is much more close to the ground!
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