Approval for Aerobatics

[Genghis the Engineer]

An interesting issue I spotted the other day.

I was doing some evaluation work on a UK registered light aeroplane which is also quite prevalent (and originated in) the USA.

In the USA it's authorised for aerobatics, in the UK it is not.

Going through the US POH, it lists the normal authorised manoeuvres, but explicitly prohibits deliberate spinning. Not sure if it's relevant, but the POH also recommended a fairly non-standard spin recovery drill, which presumably was properly evaluated.


I don't have ready access to the information, but I'm guessing that the reason that the UK declined to approve it for aeros may well be the opinion that an aeroplane should not be flying aerobatics if it's impossible to practice spin recovery in it. I tend to agree with that viewpoint. [Although, it could of course just be a lack of faith, for example, in the structural integrity - I honestly don't know and UK authorities tend not to be very sharing with such data.]

Anybody got a view on this? Is it ever acceptable to approve an aeroplane for aerobatics when that doesn't include spinning?

(I'm not trying to get it an aerobatic clearance - this is a purely academic question.)

G

[fantom]

Well, I could do a passable loop in My F4 but spinning...

[djpil]

At least one homebuilt type approved (per the old order before we had Experimental category) in Australia for aerobatics but not for spinning.
Somewhere I have a comprehensive report on spin characteristics of the Pazmany PL-2. Personally, I wouldn't aerobat it beyond the barrel roll or two I did in one.
It certainly would not be approved for aerobatics if certified per FAR 23.

[John Farley]

I'm guessing that the reason that the UK declined to approve it for aeros may well be the opinion that an aeroplane should not be flying aerobatics if it's impossible to practice spin recovery in it.

I am sure you are correct in that G.

[Fitter2]

If the spin recovery in the POH reliably recovers, then it might be argued that it is a useful spin demonstration/recovery tool, since it emphasises the need to be familiar with the POH.

I seem to recall a pub discussion with GtE when I referred to 'standard spin recovery' and he (and I agree in principle) told me that there was no such thing, the correct recovery was the one in the POH for the aircraft in question.

On the other hand, I agree that for training purposes, behaviour similar to most types is preferable.

[Zoom-56]

Like Genghis, I can't offer a rationale for the FAA clearance without knowing more about the airplane. (And like fantom, I have flown many high-performance military planes that were cleared for all manner of high-rate, high-AOA dogfighting maneuvers but not cleared for intentional spins.) Whether it makes sense to restrict a plane from aerobatics just because spins cannot be practiced is another question. I can certainly understand the logic, but it may be overprotective. How susceptible is the plane to inadvertent spin entry? If the plane is highly resistant to spins anyway (requires prolonged pro-spin controls to get it into a spin in the first place) then the logic seems to break down to me. On the other hand, if the US clearance for acro allows a wider CG envelope than the UK would, a Yank spinning the plane might have a tougher time recovering than his European counterpart. I don't know the UK certification standards. Maybe it should actually be cleared for BOTH in the UK...

[Pittsextra]

Anybody got a view on this? Is it ever acceptable to approve an aeroplane for aerobatics when that doesn't include spinning?

I suppose it depends what people define aerobatics as. If its simply an abrupt change of the aircrafts attitude, an abnormal attitude or acceleration then maybe but in competition aerobatics, for example, you'd get to figure 4 of the 2014 standard known....

http://www.aerobatics.org.uk/sequences/Power_StandardKnown2014.gif

I'm not sure what kind of aircraft being referred to but in general there is a lot of emotion with spinning and even the RAF have lost a few single engine piston aircraft to spinning.

I don't have ready access to the information, but I'm guessing that the reason that the UK declined to approve it for aeros may well be the opinion that an aeroplane should not be flying aerobatics if it's impossible to practice spin recovery in it. I tend to agree with that viewpoint. [Although, it could of course just be a lack of faith, for example, in the structural integrity - I honestly don't know and UK authorities tend not to be very sharing with such data.]



What does the manufacturer or the test pilot that conducted the initial testing say??

[John Farley]

Back in the '90s when I was flight testing the Sprint 160 for Lovaux they wanted it to be certificated in the aerobatic category. For this to happen BCARs at that time required a full spinning clearance - which we did. Dunno if anything has changed since then. (the Sprint was a developed version of the SAH1 which never achieved a Type Certificate)

[Genghis the Engineer]

What does the manufacturer or the test pilot that conducted the initial testing say??

I'm unable to access that information - I was assessing the aeroplane,which has been around for over a decade for other purposes, and this was just an interesting peculiarity that I picked up whilst learning my way into the aircraft before flying it.

My suspicion is that the US manufacturer found the spinning characteristics compliant with part 23 but a bit unconventional - certainly the POH uses a non-standard spin recovery. That is probably at the root of the "no spinning" requirement.

Why the UK didn't allow aerobatics again I don't know - that wasn't part of my assessment, but the lack of spinning permissions does seem quite feasible. Personally I think that the F4 comparison isn't particularly valid as the height loss in a spin in a fast jet is so great that Martin-Baker rather than Parkes is more likely to be the solution to an inadvertent spin, and partly because piston engined aeroplanes put a big torque generator in the nose which perhaps make a spin more likely from a mishandled aerobatic?

(The other possibility of course is that the UK engineers overseeing certification weren't happy with the structural reports at the higher g limits, which wouldn't be a first. Opinions do differ between regulatory regimes about acceptable practices in that regard as well.)

G

[djpil]

Intriguing. The Pitts S-2 could be said to have a non-standard recovery procedure too.
I'm interested in which type?

[Genghis the Engineer]

Not able to say I'm afraid. Just project confidentiality, nothing sinister.

G

[Pittsextra]

Intriguing. The Pitts S-2 could be said to have a non-standard recovery procedure too.


follows:-

My suspicion is that the US manufacturer found the spinning characteristics compliant with part 23 but a bit unconventional - certainly the POH uses a non-standard spin recovery. That is probably at the root of the "no spinning" requirement.


What / how do the FAA, CAA etc define spin recovery techniques and therefore what defines the unconventional spin recovery which the CAA then prohibit intentional spinning??

I'm not sure this is valid is it?? After all here are some very recent events with pilots who in aerobatic terms are reasonably inexperienced.

Here is the 2014 standard known sequence:-

http://www.aerobatics.org.uk/sequences/Power_StandardKnown2014.gif

As you might be able to see figure 4 is a one and a quarter turn spin. So I think we might be able to agree that in order to fly this figure you need to be able to in control of the machine.

Here are the results from a competition just last weekend.

CD's Report (http://www.aerobatics.org.uk/results/2014/GoldingBarrett/CD%20Report%20and%20Results.htm)

As we can see the 1st and 2nd places at standard level flew Pitts S-2 and actually the 4th and 5th places flew Slingsby T67's.

I don't actually agree that a Pitts S2 has any strange spin characteristics but if it does then we can see that it can be controlled to within a 1/4 of a turn and that goes for the T67. Doesn't it suggest that there are some odd teachings / theories around spinning?

[Genghis the Engineer]

What / how do the FAA, CAA etc define spin recovery techniques and therefore what defines the unconventional spin recovery which the CAA then prohibit intentional spinning??

The "standard spin recovery" - that is what we try to make work first is that in AC23-8 isn't it?

The aeroplane in question has a "stick released" spin recovery - not unique, but unusual and presumably means that there was some reason not to use the "standard" recovery. The prohibition appears to be a decision by the manufacturer, so far as I can see from the documentation I have, rather than an external imposition.

Presumably neither CAA nor FAA felt any urge to try and impose clearances against the desires of the manufacturer. That at-least is totally understandable.

G

[Pittsextra]

Agree, but of course for aerobatic category spinning one may use additional procedures....

[djpil]

yes, my copy of AC 23-8: 8) Recovery. Recoveries should consist of throttle reduced to idle, ailerons neutralized, full opposite rudder, followed by forward elevator control as required to get the wing out of stall and recover to level flight. For acrobatic category spins, the manufacturer may establish
additional recovery procedures, provided they show compliance for those procedures with this section. Not saying that the Pitts has strange spin characteristics at all but one (of several) very good example of the application of the above statement from AC 23-8. Although the hands off method works very well for the Pitts it is not mentioned in the flight manual. S-2A: "For flat spins use aileron with the spin for recovery." - certified before the days of Beggs-Mueller.

I don't see that same statement in my S-2C manual, I must follow up.

To specify the Beggs-Mueller technique these days in such an aeroplane seems very sensible to me. Naturally, the spin tests are done to verify it

[Genghis the Engineer]

"should consist", not "must consist".

It's perfectly permissible to use a non-standard recovery where that is the best, or the only way to meet the cert basis. I've done it myself on an aeroplane which had a very powerful rudder and recovered first time every time with centralised rudder, but opposite rudder created a tendency to try and kick into a spin in the opposite direction.

G

[NutLoose]

Wasn't the Sepecat Jaguar forbidden from intentional spinning as it was nigh on impossible to recover it? But was cleared for aeros.

I remember the first Falcon 2000 that came on the UK register, if memory serves me correctly they were designed not to stall, but the CAA insisted on a stick shaker being fitted on the first as they hadn't tested them, when the first one arrived (with shaker) they test flew it and then told them they could now remove it.


Btw all the USA limits are on the TCDS

See

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame

[Genghis the Engineer]

Jaguar was referred to as having "an aerobatic" - it rapid rolled magically! Not much else it would do.

G

[goldfish85]

For FAA certification, all Acrobatic Category airplanes must pass the intentional spin tests.

There is no single spin recovery technique required for FAA Part 23 spin approval. Whatever spin technique the manufacturer wants is place in the AFM or POH. If the airplane is to be approved for intentional spins, there is a whole gamut of 'abused spin recoveries." to be flown. These are rudder only, elevator only, airlerons with and agains, etc. These can take a large number of spin tests involving hundreds of spins. It's even more complicated by requirements to rig the elevator at 1 deg beyond the normal up stop and 1 deg short of the normal down stop. The rudder is rigged at 1 degree more than the right stop and 1 degree less than the maintenance requirement. (For left spins, switch those two.)

Spin recover using normal controls must be accomplished within 1-1/2 turn. There is no requirement for number of turns for abused spins, only that the airplane must recover eventually somehow.

Thus one will do all left spins one day and all right spins the next day. One will usually (if smart) start with forward cg and work the cg aft.

My most interesting spin test involved a (redacted) airplane. I had done all of the normal recovery spins (1, 2, 3, 4, 5, and 6 turns) in both directions and was now doing the abused recovery. I had down all of the elevator only spins and all of the rudder-only spins to the left. I did 1, 2, 3, and 4 turns spins. On the five turn spin to the right (next to last in the matrix, the spin went flat and continued that way until I decided it wasn't going to recover. I put in pro-spin controls (right rudder, stick was already back) and it eventually went into a normal spin, from which i recovered. The recovery was 17-1/2 turns.

By the way, this was a pass because I was able to recover. I did persuade the company not to pursue spin approval.

In some flight regimes, only God understands the equations on motion. At high angles-of-attack, God's not sure


The Goldfish

[djpil]

FAR 23 simply states that there must not be an unrecoverable spin and my copy of AC 23-8 is quite clear that recovery must not take too long for it to be deemed not unrecoverable: (3) Abnormal Control Usage. ...
Abnormal control usage should be evaluated at several points throughout the spin to ensure that uncontrollable spins do not occur....
Following abused control usage, reversion to normal pro-spin controls for up to two turns is acceptable, prior to the normal recovery control inputs, which must result in recovery in not more than two turns. In addition, going directly from the control abuse condition to the normal recovery control condition should not render the spin unrecoverable. For example, after evaluating the effect of relaxing the back stick input during the spin, it would be reasonable to expect the pilot to apply normal recovery use of rudder and elevator without first returning to full back stick.