Aerobatic manoeuvre

[CBLong]

Background... I've read a fair bit about aeros though I haven't tried my hand yet, so this question is coming from an interested layman...

It occurred to me the other day that although the stall turn seems to be a very well-known and frequently-used manoeuvre, I've never read about or seen the equivalent manoeuvre around the pitch axis. That is to say, a stall turn is a vertical climb followed by a 180 degree rotation around the yaw axis when the airspeed is close to zero, so I'm thinking it should be possible to perform a 180 rotation around the pitch axis instead.

Do people fly such a manoeuvre? If so, what's it called? And if not, why not? I can't see any obvious aerodynamic- / gyroscopic- / stress-related issues that would affect the pitching version but not the yawing version... I'm aware of the tail-slide and its variations, but that seems like a quite different thing...?

Yours with interest!

cbl.

[FNG]

I am not sure quite what you have in mind. Might you be thinking of the first half of a loop? In a loop the aircraft describes 360 degrees in the pitch axis. At the top of the loop, airspeed is zero or very low. If you have in mind the aircraft flying vertically upwards and then flipping over to fly the same line downwards, I am inclined to suggest, along with Mr Scott, that you canna change the laws of physics, Captain.

If you fly up the vertical (and really vertical, no cheating) until you stop, where will you find sufficient elevator authority to pull through 180 degrees?

Edit: I can see from entries below what you had in mind.

[Evo]

In the Robin 2160 (never tried in anything else) if you pull up to the vertical, centre the controls (and keep them centred, hard) and wait then you'll pitch forward or backwards through 180 degrees once you run out of airspeed - you don't really seem to tailslide far. It's not a controlled manoeuvre, although it is rather fun...

(edit: you keep the controls centred to stop them banging against the stops as the airflow reverses ... which would be a Bad Thing)

[FNG]

As Evo says, that's how you recover from the vertical, and the instructor teaches you this in order to deal with vertical moves going wrong, but the aircraft sort of flops over one way or the other. You hold on tight and keep your feet braced firmly on the pedals. You aren't really driving through a pitch change in this situation.

NB For all of this stuff, of course, you vitally need an experienced aerobatic instructor. PM for some personal recommendations, if you like.

[CBLong]

Hhmmm... thanks for the replies, chaps. I think what Evo describes is what I understand as a tail-slide? What I was thinking of was more of a controlled pitch from nose-up to nose-down *before* the airflow reverses, much like in a normal yaw stall-turn.

In my mind's eye (I've never flown aeros and of course wouldn't ever try this without prior training, an instructor present, etc etc) it would go like this: pull up to vertical climb; close throttle; wait for the airspeed to decay to (almost) zero; stick full back (or forward); blip the throttle to get some air flowing over the fully-deflected elevators. The aircraft would then rotate round the pitch axis and finish pointing nose-down.

It seems like it would make a nice addition to the repertoire of direction-reversing manoeuvres, assuming it is actually technically possible. Perhaps there would be too great a danger of an unintentional tail-slide, leading to damaged tail surfaces??

cbl.

[FNG]

There's a difference between a deliberate tailslide and a recovery from the vertical (in which, amongst other things, you are seeking to avoid damaging the control surfaces). Hopefully one of the aerobatic instructors or competition flyers (I am neither of these) will be along later to discuss tailslides etc in more detail.

Have you seen this site?

http://acro.harvard.edu/ACRO

[Evo]

I'm just talking about a generic bodged manoeuvre in the vertical - it isn't sustained enough to be a tailslide, you swap ends as soon as the airflow starts to reverse.

I'm no aerobatics expert - far from it - so i've got no idea if you could fly what you're suggesting in a controlled way, rather than just letting it happen. I have a hard enough time understanding stall turns. They're complicated things, lots of different effects coming into play at the top of the vertical climb before the turn: torque, gyroscopics, roll as a secondary effect of yaw, that sort of thing. I've never understood quite what's going on, and blame one of the aforementioned for my inability to exit a stall turn along the same line that I entered it.

[AerBabe]

CBLong - sounds like a Lomcevak to me. Well, it sounds like how a Lomcevak was described to me once. :O

[Shaggy Sheep Driver]

There's the 'push over' and the 'Humpty-Bump', or 'pull over'. Both are valid Aresti manouvres. Both are executed off the vertical, in one case pushing over to level flight, or the down 45, or the down vertical. The Humpty Bump is the same, except pulling instead of pushing.

We used to do both in the Yak 52; the push-over was my usual exit from the Yak's 'party piece' near-vertical take-off.

I well remember sitting in the back while one of our other group members went through his 'advanced' routine. We dived for speed, pulled up to the vertical, executed 2 vertical rolls, then went into a Humpty Bump. With 2 hefty lads, this was a bit much for the '52, and we entered the Humpty Bump at quite a low airspeed having used most of the energy in the vertical manouvres. The whole airframe shook and buffeted as we went over the top, and the guy in the front said "I think we may be in trouble here", but she went over, and into the down vertical, OK. So we tried it again..... with exactly the same results. ;)

SSD

[MikeeB]

I shall ask about the above on Monday. Sounds interesting.

With regards a normal stall turn, what happens if you don't correct the turn with opposite rudder when pointing at the ground. i.e. after the flop?

[Shaggy Sheep Driver]

With regards a normal stall turn, what happens if you don't correct the turn with opposite rudder when pointing at the ground. i.e. after the flop?

You actually begin the application of opposite rudder before you reach the down vertical, so the yaw stops exactly on the point of reaching the down vertical.

In the Chipmunk (or Yak), stall turns are generally done to the right (because the direction of engine rotation and resultant low speed yaw forces make it easier that way). As you progress up the up vertical with full power but the speed rapidly bleeding off, you need more and more left rudder (just as you do at take off, when power is high and speed is low).

At the point of rotation, if you were to attemp to go left, there would be very little rudder left to initiate a left yaw. Applying full right rudder, however, results in a crisp rotation in yaw to the right. As the nose drops towards the down vertical, full left rudder is applied to stop the yaw in the down vertical, as explained above.

If the rudder were simply released after the rotation (I presume this is what you mean), the aeroplane would overshoot the down vertical in yaw as it commences descent, then swing back under the influence of directional yaw stabililty as the speed rises in the down vertical. It might fishtail a bit, and descend out of balance as well. The manouvre would look pretty awful.

Vince

[NinjaBill]

A properly executed stall turn, should cause the aircraft to yaw 180 degrees, but with no roll, followed by a vertical decent, and a pitch to level. If carried out correctly, the ac will be travelling in exactly the opposite direction to before the mavouvre.

In a stall turn, the aircraft will not encounter any turbulent airflow over the wing, as there is no load on the wing, and any airflow over the wing will therefore produce lift. The upper wing in the turn will produce more lift due to its faster movelent through the air, and will therfore cause the aircraft to roll. This rolling (roll to right during yaw to right) movement would cause the ac to become slightly inverted during the mavouver, and after the recovery, the path of the aircraft would not be at 180 to the direction of entry.

In order to counteract this rolling motion, opposite aileron must be applied, therefore ensuring that the ac only turns about its normal axis, and not the lateral axis.

In a high powered ac, the torque of the engine will also cause the aircraft to roll, and this must be factored into the amount of aileron required to ensure no roll.

regards

NB

[stiknruda]

CBL

What I believe that you are describing is a humpty-bump. As a previous poster (SSD?) noted there are 2 varieties - a pull humpty or a push humpty.

You will need power (all of it:D ) as the aircraft is so slow that you are reliant upon propwash to energise the tail surfaces. The only problem that I have encountered with these is that if I get too slow, I tend to torque roll out of them - not a major issue on a Sunday afternoon but a real penaliser in competition.

I reckon what happens is that if too slow, you run out of counteracting aileron authority and the fuselage just revolves slowly against the engine until sufficient sped has been built up on the downwards leg to restore aileron control.

In the single seat Pitts, in comps, I try and push or pull over the top at no less than 90mph - any slower and there is a very obvious hdg change and a commensurate low score!

Pull humpties are much nicer than push humpties until you have developed suitable resistance to negative G!

Hope this helps,

Stik

[MikeeB]

I started some aero training the other week, and I have been taught to stick a boot full of opposite rudder before we are pointing at the ground, thus achieving the 180 degree turn. This is at the same time as trying to remember to put in a bit of right stick to counter the lift from the faster wing (turn to the left) and (now I forget) a bit of forward to errrr, stop it doing something else. Oh forgot, that once I'm pointing at the ground, I have to look at my left and right wing, make sure they are level, then pull out.....

However I only asked the question, as it doesn't appear to take very long to swing the 180 degrees on the axis and end up pointing at the bit of terra firma which was on your tail on a second or so earlier.

It's all good stuff anyway, and I'm really enjoying it !!! That in my book is the main thing.

I'm hoping to enter a contest as a beginner before the end of the year, but that will be down to finance (i.e. practice)

[Shaggy Sheep Driver]

I reckon what happens is that if too slow, you run out of counteracting aileron authority and the fuselage just revolves slowly against the engine

I once completely porked up a loop in the Yak and this happened. I just got far too slow over the top, and next thing, we were gently rolling:confused: .

I just went with it (keeping in just enough back stick to stay positive, and no more) until the nose started to drop and we re-gained some airspeed.

It must have looked very odd from the ground:ugh: .

SSD

[stiknruda]

SSD - my current party piece is the avalanche or Porteous loop! I love that roundy roundy sensation at the top of a loop!

Stik

[paulo]

Evo: I was taught the same in the 2160, but interestingly in a Pitts an instructor showed me how, if you go hands off, the direction in which the stick flops gives you an early read on which way the aircraft will flop.

To really prove the point, he did this in cloud. :}

[CBLong]

Hi again,

Thanks for all the replies, espesh from SSD and stiknruda - very interesting. AerBabe, I'm not thinking of one of the Lomcevak things, that's a whole different kettle of gyroscopic fish!

I looked at the link FNG provided, and what I'm thinking of is close to a Humpty-Bump, but the description of the Humpty-Bump (and stik's description) indicate that the push or pull at the top is a flown half-loop... ie with a significant airspeed and the wings un-stalled. What I was trying to describe was getting the aircraft to pitch over while essentially stationary at the top of the up line, as in a stall-turn.

I gather from the lack of recognition that this is not a manoeuvre that is commonly flown, which then leads to the next question - why not?? :)

[Shaggy Sheep Driver]

CBL

Because it wouldn't work. If you held the up vertical until the point at which you'd normally kick in rudder for a stall turn (just below 40 knots in the Chippy, but judged more by the need for left rudder and anti-roll aileron than by the ASI), but instead pulled full back stick or pushed full forward, there would be insufficient elevator authority to flip the aeroplane over. Instead, you would end up in a tailslide from which you'd flip over; nose forward if forward stick had been used, nose back if back stick had been used (probably - but not guaranteed).

Incidentally, the stall turn is ill-named. The wings don't actually stall, and never will in the up vertical since there is no load on them. The Americans call it a 'Hammerhead', and that is probably a better description.

SSD

[djpil]

If you held the up vertical until the point at which you'd normally kick in rudder for a stall turn (just below 40 knots in the Chippy, but judged more by the need for left rudder and anti-roll aileron than by the ASI), but instead pulled full back stick or pushed full forward, there would be insufficient elevator authority to flip the aeroplane over. Instead, you would end up in a tailslide from which you'd flip over; nose forward if forward stick had been used, nose back if back stick had been used (probably - but not guaranteed).

Depends on the aeroplane, SSD.
A Laser will do it quite neatly.

A variation on that is to: nudge the stick forward to start the pitch then ease the stick back all the way to try to hold the nose up. It will stay in approx a level attitude as it accelerates but not enough power to stop it sinking. Just a bit of buffet as it accelerates through the stall and flies away.

[paulo]

SSD - not sure you are right there, I think it's the opposite i.e. stick back = flop forward. Picture the reverse airflow over the elevator.

[Miserlou]

What you describe is a tail-slide w'thout the slide which makes it a humpty-bump with little or no forward speed. Bear in mind the direction in which the manouvre is flown with regard to the wind will influence it's appearance from the ground.

All that is required is that the propwash over the elevators is sufficient to keep the nose going down (or up) at a rate such that the wing remains unloaded.

The gyroscopics and lack of airflow over the rest of the wing make it a slightly fiddly manouvre and easy to screw up. Controls banging against stops and structural damage to wood and fabric control surfaces have left tailslides out of favour.

[Shaggy Sheep Driver]

Depends on the aeroplane, SSD.
A Laser will do it quite neatly.

I can beleive that! The most exotic aeroplane I've aeroed is the '52, which won't. And the Chippy and similar low-powered types certainly won't. Paulo - I think you are right:ok: , but I've had tailslides that haven't gone the way I was expecting:eek: .

SSD

[bcfc]

Great thread!

I've been doing some aero's to get my AOPA certificate in a T67 (Slingsby Firefly). This has some lateral strakes near the fin which seem to counter adverse yaw and also (i think) help in spins, but they mean I don't need opposite aileron in a stall turn - just a smidge of forward stick and she cuts the air nicely.

[MikeeB]

Did my first ever dual spin today......

I now see why people become unstuck !!!

I decided not to try it myself. Leave that until the next lesson. My instructor said, we'll just do one or two each lesson until you get used to it.

I'm learning in a firefly. He said it was a good aircraft to learn in, as it forces you to recover it, rather than some aircraft that recover themselves if you give them the stick.

Also, do we have any other left handers on here? I'm left handed, but nearly always fly with my right hand. Doesn't appear to cause me any problems. Just wondered how other goggy handers found it?

[paulo]

I'm right handed, but fly with my left - just seemed an obvious thing for left seat flying (right hand can do flaps etc). By my logic, a southpaw choosing to fly righthanded is the worst of both worlds! ;) :)

[FlyingForFun]

Also, do we have any other left handers on here?Yes - me.

Most aircraft, I fly with my left hand, but I've flown a few types which need to be flown with the right hand (throttle on the left), and have been flying from the right hand seat (with my right hand) during my FIC. I've never had any problems switching from one to the other. I think I'm probably in a minority, though, from having spoken to other pilots. (And I would gladly swap this not-very-useful talent for an ability to fly more accurately with either one hand or the other, I don't care which!)

Not sure what this has got to do with humpty-bumps. Never heard of the humpty-bump before - excellent thread! Out of interest, why is this manoevre not as widely known or taught as the stall-turn? Is it very difficult?

FFF
-------------

[stiknruda]

FFF

All compound aerobatic maneouvers are made up of components of rolls, loops, spins and turns with straight line segments on the vertical, horizontal or 45.

There are a plethora of different maneouvers detailed in the Aresti catalogue (red book) - as some are more difficult than others they ONLY feature in higher levels of competition.

Eg., in UK standard/US sportsman, there is no negative G maneouvers. Negative and flick/snap maneouvers start to creep into Intermediate.

UK Standard quite frequently feature the pull humpty but the push humpty (negative over the top) will not rear its head until intermediate.

Are either difficult? Not really - but to do a nice high scoring one takes time and lots of Avgas!

Stik

[yakker]

Get yourself "Better aerobatics" by "Alan Cassidy", I think an excellent book. Then get some proper training, ofcourse.

[Slow-Rider]

SSD

You mentioned that you need more and more left rudder to hold the a/c vertical as it slows with full power and therefore stall turn left is not ideal as you have little additional rudder.

If you pull the power back just prior to turn would regain sufficent authority?

In the aircraft I fly it doesn't really matter too much, especially my stall turns, they're cr*p anyway! :ugh:

[Shaggy Sheep Driver]

SR - yes, just about the only way to get it to go left is to pull the power - but then there's good chance of stopping the engine, and it's more 'nose dropping to the left' manouvre rather than a nice rotation in Yaw.

SSD

[stiknruda]

SR - do be aware that SSD is speaking about stall-turning a Yak or a Chippie.

If you stall turn an American engined aeroplane then you face the same predicament but of course on the other side - ie you need increasing right rudder on the way up behind a Lyc/Con and of course at the top, full left rudder pedal will give you more than half the available deflection.

Pulling power (once the nose has started to slice downwards) also reduces the possibility of the aircraft torqueing in yaw.

Accurately capturing the vertical on the up-line also diminishes the real possibility of the aeroplane very obviously scribing a positive (canopy up) or negative (canopy down) yaw when seen from the ground!

Yakker's comment about AC's book is very valid - however, if he'd had it printed in a handy two volume softback A5 format, then I could take it up with me and revise immediately before I tried any new maneouvers!

Stik

[FNG]

On the subject of Aerobatics books, can I plug David Robson's short introductory work as a well written guide to the basics.

[Evo]

I like Robinson's book too - can also recommend Szurovy & Goulian's "basic aerobatics".

[greeners]

Would also echo support for Alan's book - don't be put off by the poor picture on the cover! His description of the basic aeros is excellent, including a good graphic in there on the slow roll which shows the timing and amount (and direction) of aileron, elevator and rudder input all the way around the circle. Great help in keeping the rate of roll constant all the way around and especially through that demanding last quarter, although coming out whilst NOT cross-controlled will take more than a little practice!

[paulo]

Got 'em all! :ok:

Robson is nice summary.

Szurovy & Goulian is beautiful - the 'outtakes' make the book unique. In between the dry technical stuff, the stories add some colour and lots of inspiration.

Cassidy. The most in depth text I've ever read. No other book compares for me. My only irritation - and this is a compliment I think - that reading it only makes me want to ask many many more questions. If I could have made it a perfect book, I would have added some 'asides' - anecdotes to intersperse the instructional text. Nonethelss fascinating. Could easily have been twice the size and still left you wanting more.

[TheAerosCo]

Stall turns
To help you turn against the engine (or with it, for that matter), try introducing a little opposite rudder during the pull up and counteract with a tad of aileron to keep the aircraft straight. So for a stall turn to the right, feed in left rudder and right aileron during the pull up. This will result in you carrying left rudder in the vertical with the aircraft sliding to the right. The turn at the top then becomes much cleaner. This is particularly useful if the wind is from the right and you want the figure to pivot around a point when viewed from the ground.

Humpties
With the humpty bump, as previously mentioned, a difference to the stall turn is that the aircraft has to have a significant angle of attack over the top, whereas the stall turn is performed at zero angle of attack. In fact, to get a constant radius round the top you normally have to pull (or push) into buffet during the second half of the figure. This effectively determines the minimum airspeed you can start the turnaround without allowing the second half to finish lower than where you started.

Having said that, it is possible on some types to achieve CBL’s manoeuvre. It is possible to contrive to have a figure end in the vertical but carrying significant rudder. So, with a lycoming engine, if you end up carrying left rudder at the top of the vertical you can push and at the same time kick in full right rudder. Elevator and precession will (hopefully) neatly cause the aircraft to swap ends. Only some aircraft, though, and lots of stresses and strains involved. (This, incidentally, is not a lomcevak).

TAC

[djpil]

While we're discussing books - don't forget "Aerobatics" by Neil Williams - an oldie but a goodie.

[stiknruda]

djp,

I have this book and agree that it is a good book but IMHO it explains the maneouvers without actually teaching you how to fly them.

The books by Cassidy, Muller, Szuvroy and Goulian are far more prescriptive.

Bill Thomas' books are quite good too, especially for a Pitts pilot.

Williams' book's strength is that the anecdotes make very interesting reading.

(really hope that the apostrophisation in the preceeding sentence is correct before FNG, BEagle and the rest of the apostrophe police descend upon me!)

Stik

[FNG]

All correct, Stik. In fact, your previous convictions may now count as spent, as two of the apostrophe usages in your post are at Advanced or Unlimited Level, and Lynnne Truss would approve.

As you say, the Williams book is more a collection of anecdotes than a manual of instruction. Perhaps he was cautious about giving away trade secrets.