Advanced Spinning
ADVANCED SPINNING
There are many instructors and enthusiasts that are either involved in aerobatics or that are building RV aircraft that will need spin testing on completion. This article has been written for these fellows, to peruse and study, in the hope that it will lend a little more understanding to the phenomenon of spinning and advanced spinning.
Some pilots amongst us, certainly those that have competed in the Advanced and Unlimited competition classes, have already explored all the intricacies of advanced spinning, and to these fellows I ask their patience in going through this small treatise. Naturally, any feedback would be greatly appreciated by the author.
Every pilot, for whom this article is intended, has experience in spinning. I will therefore dispense with the aerodynamics of autorotation and the spin, and begin the discourse from the point where the aircraft has already settled into a spin and all forces are in equilibrium. For simplicity and consistency, the discussion pertains to American aircraft where the propeller rotates clockwise as viewed from the cockpit and where the aircraft is spinning to the left.
The stick is right back, full left rudder is in and the throttle is closed…
Once the spin has stabilized, move the stick smoothly over to the right i.e. out of spin. The aileron(s) on the left wing will move downwards, with respect to the aircraft, and the aileron(s) on the right wing will move upwards.
The effect will be to reduce the difference in the lift components on the two wings. At the same time, the left aileron(s), which is deflected downwards, causes far more drag than the right aileron(s) which is deflected upwards.
The reduction in the difference between the lift components on the two wings causes the lower wing to rise, but usually only very slightly.
The difference in drag between the two wings, which is more significant, causes an increase in the rate of rotation of the spin. This increase in the rate of rotation causes an increase in the inertia moments of mass and the nose moves up somewhat towards the horizon.
This then is the first tentative step towards performing a flat spin…
The lift and drag characteristics of the left and right wings were altered by the application of 'out of spin' aileron. The spin motion of the aircraft therefore changed, and a little while later the aircraft settled into a new and different steady state spin, this being a rather insipid but certainly flatter spin with a higher rate of rotation.
Now bring the ailerons back to the neutral position…
Once again there is a change in the amounts of lift and drag that the wings are producing.
The difference between the lift components on the wings increases and the difference in drag between the wings reduces. The left wing lowers, the nose drops somewhat and the rate of rotation reduces.
The aircraft settles into its original steady state spin and it is a good time to recover!!!
For the time being, let us effect recovery in the 'time honoured tradition' of opposite rudder, pause a while and then stick forward…
Now, back to our spin where we had the stick full back, full left rudder in and the throttle back… It is time to look at a more developed flat spin.
We allow the spin to stabilize, and then we apply out of spin aileron. The rate of rotation increases, the wings adopt an attitude of slightly less bank and the nose rises. We're back in our 'insipid' flat spin.
We now start adding power, more and more until we have full power. The spin rotation is to the left and the propeller rotation is to the right. Work the gyroscopic precessional effects out for yourself and you will see that the effect of the application of power is to cause the nose to rise. There is now a significant change in pitch attitude. The rate of rotation is however barely affected because of where the precessional force is being applied, but does in fact increase slightly. (The reason for this will be covered later - the flatter attitude of the aircraft causes more masking of the fin and rudder above the stabilizer and elevators.)
Now throttle back and observe the nose drop, move the aileron back to the neutral position and note that the bank angle increases and that the rate of spin rotation diminishes.
Once again, and for the time being, recover in the 'time honoured tradition'.....
Now, it is as well to mention that before we embarked on flying the flat
spin it was of vital importance to GET ALL OUR DUCKS IN A ROW AS TO
WHAT WE WERE GOING TO DO AND HOW WE WERE GOING TO RECOVER.
A huge amount of importance should be attached to the sequence of events that we will pursue and the method of recovery we will use before we even start with the manoeuvre,
One should put one's self through a thorough mental briefing if flying solo.
The briefing, if giving instruction, should put an airline pilot's RTO briefing or his CAT 111 briefing to shame:-
a) The student should read the entire procedure back to the Instructor - - - There is no room for misunderstanding.
b) Once established in the spin, things happen very quickly, and both pilots have to know and understand what actions they are going to take.
c) The student should be talked through the entire manoeuvre,.
d) If the Instructor goes quiet for more than two rotations, the student must have been briefed to recover without having been commanded to do so.
So much for flat spins…
It is now time to look at ACCELERATED SPINS…
We will look at accelerated spins separately for the time being,
The stick is right back, full left rudder is in and the throttle is closed…
The aircraft is in a steady state spin.
We have already examined the effect of applying out of spin aileron and adding power whilst in the spin.
We have not yet examined the effect of varying the position of the elevator in the spin, so let us do this now…
The aircraft is descending on its spin axis with the relative wind from below. The stabilizer and elevator combination is blanking off the airflow from the fin and rudder above it, The amount of fin and rudder that is blanked off depends on the design of the tailplane. When the aircraft is descending in the spin with the elevator full up, there is a high percentage of the lower part and even mid-part of the rudder that could remain exposed to the airflow.
As the stick is pushed forward in the spin, the amount of rudder below the stabilizer and elevator combination that remains exposed to the airflow reduces, until the point where the stick is fully forward, at which stage the amount of rudder that has airflow effecting it could he as low as 20% of what it was when the stick was fully back.
What is the significance of this?
The rate of rotation of the spin is affected by the resistance or 'weathercock' effect provided by the aircraft's rudder. The more resistance there is, the slower the rate or rotation. As the resistance diminishes, the rate of rotation goes up.
Additionally, with the stick fully hack, the rudder has a certain amount of effectiveness, and when the time comes, there will he enough rudder to stop the yaw. With the stick fully forward, the rudder effectively is lost, because of the small surface area available. This might be insufficient to stop the yaw.
So . . . Whilst in the spin, with full left rudder still applied, gently move the stick forward. As you do this, less and less resistance to the airflow from the rudder is offered and the spin rate begins to accelerate dramatically.
As the spin rate increases, the inertia moments of mass increase, and the aircraft's nose rises, adopting the flat spin attitude.
As the stick is pulled right back again, the drag of the rudder increases, the rate of rotation decreases, and the nose drops.
Time for recovery again, but all of a sudden this 'time honoured' forward stick business has got us thinking…! We need to explore what dangers lurk here.
Back to our basic spin, with stick right back, full left rudder and the throttle back...
Once we are stabilized and spinning nicely, apply more and more forward stick whilst keeping full left rudder in. Notice how the spin accelerates and how the nose comes up. The spin rate can he almost mind-boggling!!!!
Now, with the spin nicely accelerated, the yawing inertia of the aircraft is really high.
IF YOU ARE FLYING A PITTS IT IS TIME TO TRY SOMETHING REALLY INTERESTING…
Apply full right rudder and see what happens…
THE AIRCRAFT JUST CONTINUES SPINNING…
THE ROTATION DOES NOT STOP!
THERE IS NO WAY IT IS GOING TO RECOVER…
In short, the inertial forces exceed the aerodynamical capability of the rudder.
This exercise teaches us two very important lessons;
1. Stop the yaw whilst the stick is fully back because this is when you have the maximum rudder effectively.
2. Refrain from moving the stick forward whilst the yaw in the direction of the spin is still present. The changing elevator position will serve to cause the rate of rotation of the spin to increase.
So, if down elevator is applied before the yaw stops, the best case scenario will be that the recovery is delayed somewhat, and at worst, that recovery is impossible.
As an aside, for those of you that flew Harvards, how many of you remember that if forward stick movement following thc application of rudder was rushed, thc aircraft would "wind up" and often perform as many as three accelerated rotations before recovery was effected?
And so…… for the recovery, we apply full opposite rudder to the direction of rotation, and wait for the yaw to stop. The wings will now be at the same angle of attack, both generating the same amount of lift and drag.
All that is required now is the slightest forward movement of the stick and the aircraft will unstall. In fact all you really need to do is release the stick and it will find its own position.
We are now getting close to the Beggs/MulIer method of recovery from the spin...
These two gentlemen were pioneers in the field of spin recovery and achieved world fame and recognition in the field of aerobatics for the work they did on this subject.
Gene Beggs was a one-time member of the U.S. National Aerobatic Team and the late Eric Muller (heart. attack) was the Swiss National Acrobatic Champion on many occasions.
Today, aerobatic schools worldwide teach the Beggs/Muller Emergency Spin Recovery Technique. There is not better method…!
But more of this later…we still have to fly some ACCELERATED FLAT SPINS.
Our spins are beginning to become more complex and involved now. They are also becoming more hectic and dramatic. As they get faster, flatter and noisier, one tends to become more disorientated. At times the horizon can become a blur. Also, one tends to get pinned in against the side of the cockpit in a really fast spin, and with so much going on, one could lose a certain amount of awareness as to the placement of the controls.
MORE THAN EVER, IT IS IMPORTANT TO GET THE EVER INCREASING NUMBER OF DUCKS INTO A ROW BEFORE YOU START THE SPIN!
We are back in our spin to the left.
Once the machine has stabilized, apply out of spin aileron and watch the rate of rotation increase and the nose come up into a flatter attitude.
Now apply power progressively, all the way up to maximum. The spin flattens significantly. The spin rate increases only slightly however. This, because of slightly more shielding of the upper fin and rudder, and not because of the precessional force.
Now start pushing the stick forward and note how the spin accelerates. The further you move the stick forward the faster the aircraft spins. Eventually you will have the stick up against the forward stop and this is where the highest rate of rotation will occur. Since the moments of inertia increase, the spin flattens even more. This is a wild, wild ride!
Now for the recovery:-
-You can of course retrace all your steps...
Stick hack to reduce the rate of rotation
Power off to get the nose to come down out of the flat spin
Ailerons hack to neutral to get rid of the final vestiges of the
flat spin.
Full opposite rudder to stop the yaw.
Release the stick and allow the wings to unstall themselves.
I doubt whether a pilot is going to get this right in the heat of the moment, particularly if he doesn't precisely know how he got into the spin in the first place.
AND SO… THE BEGGS/MULLER EMERGENCY SPIN RECOVERY METHOD
1. CUT THE POWER
2. APPLY FULL RUDDER IN THE OPPOSITE DIRECTION TO THE DIRECTION OF THE YAW UNTIL ROTATION STOPS AND THEN CENTRALISE IT.
3. LET GO OF THE STICK---YES, THAT'S RIGHT, JUST LET GO OF IT!
You need not remember the order in which to do all three of these actions. Any order will suffice.
My recommendation is that pilots adopt this method of spin recovery and that they
STICK TO IT!
It is important for pilots to have a total grasp as to what effect the controls and what effect power has on the spin. This way they understand and grasp the pitfalls.
NOW, competition spins are a different ballgame. Here into-spin aileron plays a huge part in precision recoveries. Also, it poses no real danger to the recovery of the aircraft and does in fact assist in the recovery.
On certain super-high performance monoplanes it is barely necessary to throttle back for an advanced spin recovery PROVIDED PLACEMENT OF THE ELEVATORS, AILERONS AND RUDDER IS CORRECT.
However, what we are concerned about is a method that will work each and every time, and which covers the worst case scenario.
WHEN FLYING ADVANCED SPINS THERE IS A GREATER POTENTIAL FOR DISASTER. THE RECORD SHOWS THIS.
1. Be sure in your mind that you have thought it all out properly before you do one.
2. If you have a student, make sure you are both on the same wavelength and that he is not going to freeze up or do something stupid. - You never want two fellows fighting their own very different battles on the controls. We all know now what the effect of aileron, power and elevator has on a spin.
3. If you are unable to bring the power back for any reason, be ready to cut the engine on the ignition switch or the mixture control. You can always restart the engine after the recovery.
4. Make sure you make the required amount of control input for the recovery. You will be subjected to huge amounts of centrifugal force in a fully developed accelerated flat spin. Your subconscious might tell you that it feels as if you are applying the right amount of input for the recovery, whilst this is far from the real case. You might not pull the power off completely and you might not apply full opposite rudder.
I am sure that some of you saw this on the Harvard, which could be a handful in a spin. We were taught to make a conscious effort during the recovery of having to stand on the opposite rudder because it was so heavy.
5. Do not perform advanced spins over a featureless landscape or over the sea. Since the ground is often a blur, when the time comes for the recovery, the pilot will need an abundance of landmarks to help him determine that he has stopped the yaw.
The late Professor Art Scholl was out over the sea filming inverted flat spins for the movie 'Top Gun'. During one of his spins he called "I have a problem here". He went into the sea 18 miles off the coast of California. The accident investigators speculated that the reason for the accident could have been two-fold:
1. That a camera came loose or shifted, effecting the c. of g. or that it interfered with a control surface.
2. That Professor Scholl was unable to determine when the rotation of the spin had stopped because he had no feature to relate to.
All aircraft have different spin characteristics and all spins have the potential to be lethal.
Whether you are flying a Pitts Special, Zlin 50, Harvard or Impala, the spin characteristics vary, but the same principles apply.
Irrespective of your background, treat even the venerable Piper Cub, Tiger Moth and Chipmonk with great respect. These aircraft too, can be full of surprises.
I hope this has been of interest and/or value to you. If by now you are not reaching for
a cyanide pill (for either yourself, or me) and you feel you would like some more, I
would be happy to cover the subject of advanced inverted spinning for you.
SOURCES OF INFORMATION
Royal Air Force AP 129, Volume 1, Part 1, Section 1, Chapter 5, Figure 3.
Flight Unlimited - Eric Muller (Swiss Aerobatic Champion) and Annette Carson
Advanced Aerobatics - Geza Szurovy and Mike Goulian (1995 US Aerobatic Champion)
Fly for Fun to Win - Bill Thomas (US Aerobatic Team Member)
Happy flying
Scully
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