Spinning


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The following was received from Richard Goode and is reproduced here with his permission. Richard is a world-class competition and display pilot. He knows of what he speaks.

After his letter, a personal friend and YAK expert scribbled some opinions on the subject which may be far less authoritative than Richard's but you may find them useful.

RICHARD GOODE AEROBATICS

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Aerobatics and Spinning in the Yak-52

I am writing this because I feel that many of us – and I include myself - have been too casual about the characteristics of the Yak-52, very particularly during spinning.

The Yak-52 is a delightful aeroplane, offering great aerobatic ability and ‘fun to fly’ characteristics with military-build quality for unbelievably little money.

Nevertheless, its spin recovery can be difficult and particularly after a recent accident involving a highly experienced aerobatics pilot I am concerned that too many people are flying Yak-52 in aerobatics, which can intrinsically lead to spins through mishandling, or indeed deliberately spinning without sufficient training to be absolutely certain of recovery.

To be specific:

Ø        It is not difficult to get into a flat spin through a mishandled stall turn – particularly, as is normally the case, power is kept on.  Therefore one should not think that because one is not deliberately spinning that one would never get into a spin.

Ø        The 52 is a heavy aircraft with a significant amount of rotational inertia in a flat spin.  This is because there is heavy engine in the front and a heavy radio and other equipment behind the rear seat and therefore once the aeroplane begins spinning, it will take time for that inertia to be destroyed and for the aircraft then to recover from the spin.

Ø        In particular, if the spin is allowed to fully develop into a power-on flat spin, the rate of rotation can be rapid and disorientating, and importantly, the more rapid the spin, the greater the rotational energy to be stopped before the spin slows down and therefore the longer the spin recovery.

Ø        Closing the throttle will not in itself cause any recovery.

Ø        Once the flat spin has fully developed it can take up to four complete revolutions for recovery to be made and of course much more if the absolutely correct control movements are not used.  Additionally there will be further height loss during the return to level flight.

Ø        It is also possible while recovering from a spin with a lot of in-spin aileron and forward stick, for the rotation to convert rapidly into an inverted spin.  Again, this must only be demonstrated with an appropriate instructor.

Ø        Stick forces on both elevator and rudder in order to move the stick forward and to obtain opposite rudder can be extremely high – requiring a great deal of strength.  This can give the impression of jammed controls if one is not used to it and this can only be achieved through practice with an appropriate instructor.  It is interesting to note that the Russian manual says that the rudder forces can be as high as 100 kilos (220 lbs) and stick forces 40 kilos (90 lbs), and says that two hands maybe necessary to move the stick forward.

Ø        We know of at least two Yak-52 aircraft that after a fully developed flat spin (ie four or so turns) will NOT recover with the conventional  spin recovery of full opposite rudder and full forward stick, but need in-spin aileron to recover.  Again, this should not be experimented but practised with an instructor.

Ø        If practising spinning, total height loss can be dramatic and even with absolutely correct recovery procedures, height loss can be in excess of 2000 ft and a bit more to level regain flight.  For this reason spin practice of this sort should be commenced at a minimum of 6000 ft and recovery initiated by 5000 ft.

Ø        Several 52 accidents have been attributed to one of the pilots harnesses catching the brake lock on the stick.  This obviously varies with pilots, but before any aerobatic flight is commenced, a very complete ‘full and free’ check should be made to ensure that this cannot happen.  Specifically there are two types of brake catch  (the new one dating from approximately 1989) and two types of harness, the early buckle type and the later pin type.  Apart from anything else the old ‘buckle type’ should never be used today, but the newer ‘pin type’ can catch with the old model brake catch.

Ø        Finally, there is the potential problem by virtue of being a tandem cockpit aeroplane that there is misunderstanding between the two cockpits.  This is common to all such aircraft, but it emphasises the need for a thorough briefing on all procedures before any aerobatic flight.  This should also cover all emergency procedures, and a formal understanding about a bottom height during spinning at which the occupants will jump clear of the aircraft if the spin has not stopped. In Russia this is 1000m / 3300 ft.

 

In conclusion, any Yak-52 pilot who intends to do anything more than pure straight and level flight must undertake proper instruction with an instructor who is completely familiar with all aspects of the aircraft’s behaviour, particularly during fully developed spin recovery.

None of the above should deter a potential purchaser or pilot of a Yak-52. The aircraft has a superb safety record despite being used by a huge variety of organizations and people throughout the world. However like any aircraft it must be flown correctly. Recovery from simple power-off ‘competition-type’ one or two turn spins is conventional and rapid. All the above only refers to established flat spins and is why proper instruction should be mandatory for any aerobatic pilots on Yak-52s.

13th March 2001

 

 

The Hammerhead, more than most maneuvers requires very specific and careful training. The words that follow are intended to be used as a reference during that training and NOT to teach you how to perform the maneuver so you can try it yourself.

 The Hammerhead, or stall turn.
(Revised January 25, 2003)

These are my thoughts on the hammerhead, based on some years of performing them and teaching them. Please let me know if you disagree or have a different opinion. I am here to learn too. This is written with the YAK 52 in mind and assumes an engine that rotates in that direction.

Although the HH looks simple to do, it actually requires a good sense of timing and a well developed sense of orientation. I make it one of the last figures taught in a course of aerobatic instruction. In my opinion, the most important part of the figure is to know when it does not look right and abandon it safely, don't hang in there hoping it will "sort itself out". - It won't. The consequences of a badly flown HH can be as described by Richard above, or a tail slide which can be damaging to an aircraft, particularly if fitted with flaps.

This is my procedure:

In preparation for the HH proper, we will fly the "Climb & Dive" exercise: Set aerobatic power (80cm + 82%). Let the aircraft accelerate to a steady speed and ensure that the slip ball is centered (no slip or skid). Now, look straight ahead and pull back on the stick until you have achieved a pitch up of 30 or 40 degrees.  Look at one wingtip and then the other  and check that they look the same with respect to the horizon. (adjust with coordinated movement of aileron and rudder if not). Keeping you feet absolutely still and not allowing the rudder to move at all, return the stick to the elevator-neutral position. The ball should still be about centered.

As you sit there, speed reducing, look at the airspeed and the slip ball. As speed reduces, the ball will move to the left, further and further. At a speed just above the spin entry speed (say 120 kph) push forward to level flight while still looking at the slip ball. Now it is hard over against the left edge of the tube right? Why? - Because as the speed reduced, the fin & rudder became less effective at counteracting the torque,  'P' factor and gyroscopic precession of the engine & prop. The ‘P’ factor and torque are the dominant forces as you maintain constant pitch and the aircraft slows in the climb. The precession is dominant during the change of pitch  as you push to level flight.

Now let's do that again, this time though, use the rudder to keep the ball in the center. You will find that at the point of minimum speed, as you push to level flight, you have close to full left rudder applied to keep the aircraft straight!

So in a hammerhead, would we not expect the same phenomenon to occur? Yes and no. There is little or no 'P' factor because the angle of attack should be zero during the climb but there is still plenty of torque from that big geared engine.  The bottom line is that if you spend the vertical up part of the figure with your feet still, you will be skidding wildly by the time you need to pivot. Skidding is a principle ingredient of the spin remember. 

So now let's look at the hammerhead for real.

We set aerobatic power and dive, if necessary, to achieve the required entry speed. I use 280~300 kph in the YAK52. Return to level flight, check wings level and ball centered. Look straight ahead and pull. Pull hard enough to minimize the loss of energy, at least 3G, 3 1/2 to 4 is better. (In a YAK52, I temporarily use both hands to help avoid unwanted aileron input) Now as you pitch up, two things will happen: You will loose sight of the horizon over the nose and the aircraft will yaw to the right just like it did in the practice exercise.  So look at a wingtip now and anticipate the need for some left rudder to keep the ball centered. Glance at the ball as you pitch. Look at both wingtips, one after the other and check that they are in the same place, relative to the horizon. Correct with small coordinated movement of stick and rudder. When you hit the vertical, check forward with the stick and climb. The slip ball won't work now, it is laid on its face, so instead, we will use the wingtips to judge. Look at one, the other and back again over and over so that you can be sure they are the same distance above the horizon still. Just like in the exercise, you will need to feed in left rudder, a little at first, then more and more as the speed reduces.

At this point comes a vital check. Are you perfectly vertical and straight? If not, immediately abandon the figure and try again. DON'T NOT CONTINUE with an imperfect beginning. Remember that the top surface of the wing is curved so allow for that in judging the vertical but don't overdo it. Not quite vertical (too little pitch) is much better than past the vertical (slightly on your back) - The Russians often use the Attitude Indicator to judge the vertical. In the West, that is unusual.

Assuming all is well, the next item on the agenda is the pivot, or rotation which is the heart of the figure. You are going to pivot to the right of course. In time, you will come to feel the point at which rotation should be initiated but for now,  use the airspeed indicator. A figure of 100 kph is a good starting point.

A little more theory: - All the way up the vertical line, you have been feeding in left rudder so now, at the top of the climb, you most likely have at least half rudder applied. When you stomp on the right rudder pedal, the rudder will move from half left to fully right. It will generate 50% more side thrust than had it moved from the neutral position to full right. Adding that rudder to keep straight on the way up will pay dividends at the top!

Back to the HH! - When you reach the pivoting speed, let's say 100 kph, look at the right wingtip and note EXACTLY where it lines up with the horizon. With your left hand on the throttle, smartly apply FULL right rudder (press hard). Keep your eyes on that same point on the horizon. After the aircraft has rotated through 90 degrees, the nose will be pointing at your reference spot. Keep looking at it! You may use SMALL aileron inputs now to guide the left wingtip so that it will pass exactly thought you reference point.

IMPORTANT STUFF!!

·         Many people teach that as the nose passes through the reference point, you should look at the right wingtip (which is now pointing at the ground) and use this to find a new reference point to use on the down line. I don't do this because, if you use the reference point on the horizon and try to make the left wing pass through the same place the right wing did, you will be sure that you rotated in a perfectly flat plane, with zero angle of attack. Zero AOA means it is impossible to stall and hence to spin.

·         If the aircraft begins to roll on you or fall over onto its back, DO NOT push the stick forward and left to counteract! Those are the control positions for an inverted spin! It is rolling because you screwed up the entry. Your airspeed was incorrect or you were not straight at the point of rotation. Close the throttle and center the controls. Let the aircraft get itself pointing downwards safely and recover. If the controls are centered, you cannot stall.

Now, when the left wing is just above your reference point on the horizon, quickly look over the nose at the ground and swiftly apply left rudder. When the rotation stops, reduce the rudder to a position just slightly left of neutral. Why? Because you are at zero airspeed with a big torquey engine trying to pull you to the right again. As the aircraft gathers steam on the down line, move the rudder to the neutral position and then, even, a little to the right as the aircraft begins to slip. (Check both wingtips again to judge the rudder required). Recover from the dive with a good straight pull. Use the same acceleration (3 1/2 G or so) that you used on the pull up.

Many people will reduce the power setting on the way down. They argue that it prevents the aircraft from building up too much speed and allows for a more comfortable pull out. Others prefer to keep the power constant so that they don't have to consider the sudden change in torque. I prefer to reduce power but you may not. it's up to you.

That is all I know about the hammerhead. I have no doubt that Segei Boriak would apply his trademark "Bull-shiiit" to the above but it works for me.  As always, I remind you that there is no substitute for competent instruction and that you should not try this without first availing yourself of some. There are plenty of good aerobatic instructors around these days. To learn more on the subject, I suggest the excellent book "Flight Unlimited" by Eric Muller and Annette Carson.

A YAK 52 Aerobatic Instructor