Asymmetric in a steep turn

[Timothy]

I occasionally spend time getting photos like this (ftp://www.artifax.net/files/Misc/WestminsterSchool.jpg) out of the side window of my Aztec. As you can see, this entails doing pretty steep turns at relatively low level over built up areas, and I am therefore concerned about the effect of a failure of the inside engine.

The Aztec (http://www.airliners.net/open.file?id=333936&WxsIERv=UGlwZXIgUEEtMjMtMjUwIEF6dGVjIEU%3D&WdsYXMg=VW50aXRsZWQ%3D&QtODMg=S2VtYmxlIChFR0JQKQ%3D%3D&ERDLTkt=VUsgLSBFbmdsYW5k&ktODMp=TWFyY2ggMTUsIDIwMDM%3D&BP=0&WNEb25u=Q29saW4gSy4gV29yaw%3D%3D&xsIERvdWdsY=Ry1MSVpa&MgTUQtODMgKE=Qy9uIDI3LTc0MDUyNjg7IENhbm9uIEQ2MCBJU08gMTAwLCA 3MC0yMDBtbSArMnggY29udmVydG9yLCAxLzE2MHRoIGYxNg%3D%3D&YXMgTUQtODMgKERD=MTgw&NEb25uZWxs=MjAwMy0wMy0yOQ%3D%3D&ODJ9dvCE=&O89Dcjdg=&static=yes) is a very conventional 6 place twin piston aircraft with two 250hp lycomings, MAUW 2.3 T

I am thinking of going and doing some experiments, at a safe altitude, cutting the inside engine during a steep turn (maybe starting at 45deg and building up to 75deg.)

Obviously I will build up from a gentle start to try and avoid surprises, but I am concerned as to whether a point will arise whereby I could enter a manouevre outside the capabilities of the aircraft (obviously ranging from structural damage to the unrecoverable.)

There is no point in my seeing what will happen in an unlikely scenario only to kill myself investigating!

The aircraft is not cleared for intentional spinning, but is very conventional in all other respects, so I am pretty confident that it would recover from a normal spin, but is there any chance that it will flick inverted?

Any sage advice gratefully received.

Timothy

[John Farley]

Timothy

Your post has been up nearly two days and this is the first reply so perhaps that gives you a clue that many will be shaking their heads on reading it and thinking that what you are planning to do is a fairly advanced handling exercise which could go seriously wrong – but then you do appear to realise some of the issues. But not I suspect all of them.

It would be very easy to just say ‘Don’t do it’ because that is sound advice and really the best given that I know nothing about you or your aeroplane – and please don’ take that as implying you might be an incompetent idiot. Literally I have no information other than your post with which to form an opinion.

On the other hand me just saying ‘Don’t do it’ is not terribly helpful. So without in any way encouraging you to ‘have a go’ may I make some comments?

You talk of cutting the engine. I presume you mean chopping the throttle rather than turning off the fuel – which would NOT be on. Chopping the throttle will still give the engine something to think about from a thermal shock point of view and is not without the potential to do harm, especially if it was repeated over and over in a test programme of many points. How much harm I am not competent to say and anyhow it would depend on the power that you normally use in these photo turns.

Even if you decide that is not enough to stop you going ahead, then forget turns and handling issues for a moment and ask yourself how will the aircraft behave at the speed you do your photo turns if you chop the power with wings level? How much slip is involved? What will the fin think of this? It might all be very benign from a structural standpoint but I don’t see how you can be sure of that without flight test instrumentation.

You are right to be concerned about a real inside engine cut when doing your turns. My answer to that concern is that you should mentally rehearse what you would do in such an event before orbiting your target. I would aim to instinctively chop both throttles at once, start rolling to wings level and then feed up power to cruise away and sort out the relevant check lists. It is a bit like sitting on the runway before EVERY twin take-off and getting in the right frame of mind to cope with an engine failure just as if you are about to do an engine failure test ride. You are NOT sitting comfortably, you are not relaxed and looking forward to the trip, you are in fact handling a loaded gun and very much aware of that.

In your case, unless these tests are carried out with the most violent engine cut and under g and high alpha which will exacerbate the roll with yaw issue, then there is not much point to doing them at all as you will only finish up kidding yourself there is no problem with your turns.
But if on the other hand you do find an inside cut is a very bad scene then ask yourself what are you going to do with this information? Stop taking pics?

Right now you feel there could be a problem and that is good – so address it like every take-off and stay ahead of the game

Cheers

JF

PS When you get old things don’t work as well as they did and so you ask the doc for this test or that. He then says do you really want to know that information? If the result it is not what you want to hear there would be nothing I could do about the condition so why find out?

[john_tullamarine]

.. a minor point .. you might check your POH/AFM for maximum bank angle limits ?

Can't comment without the book but the aircraft may well be limited to 60 degrees which would open another Pandora's Box at the Enquiry in the event of an incident/accident....

[fobotcso]

May I suggest that there are a couple of other investigations that might be done before you get to the point of simulating engine failure in steep turns.

Compare the results of left and right engine chops in steady level flight at various power settings. (As suggested by JF.) See which is easier to handle.

Compare the results of departure in left and right steep turns under symmetrical power- gradually - very.

None of these need result in a sharp intake of breath and an iterative approach should ensure that you are able to keep up with the gradual approach to the manoeuvre boundary that you are looking for.

When you get to the "comfort" limit for the engine chops in the turn, decide which way is the better way to turn. One way will be easier to deal with than the other.

Do your photography with the camera on that side.

[Timothy]

Thank you all for your helpful words. All read and understood.

To answer John's first point very briefly, I am, of course, a very, very long way down the curve from you test pilots. I am an ATPL with a few thousand hours, of which probably 2,000 are on light twins and maybe half of those on the Aztec. I was in a University Air Squadron, where Her Maj was kind enough to show me how to do basic aerobatics 'n stuff. I have done most stuff from Tiger Moth to HS125 at one time or another. So, no, not quite an incompetent idiot, but again, no particular training or experience to equip me for this game.

Yes, I meant using the throttle to simulate engine failure.

The only times I have deliberately killed an engine in the cruise is for C of A climbs, but I have also lost an engine at cruise speed due to fuel leakage, and in both cases the effect was utterly benign, with very moderate rudder input to stop yaw. I am not quite sure whether the wing down technique, with the ball half out of the box, actually induces slip, but my understanding is that that is the minimum slip situation. Anyway that is the technique I have used.

I think that the advice of not to experiment, but to be certain what I am going to do in the event is very good, and certainly makes me very glad that I decided to air this issue here!

I have read the POH several times and cannot remember seeing a maximum bank angle, but there are various technical limitations about "utility category" and "no aerobatic manoeuvres" which might, on investigation, turn out to limit bank angle. In fact the technique I use is to sit in a stable 60deg turn and then, when the right angle is coming up for the photograph increase the bank angle momentarily to around 80deg to allow the photographer to take the picture without the wing getting in the way. There is obviously a fair amount of g involved (under the circumstances) which can be quite uncomfortable for the photographer who is twisted around at an angle and looking down through a view finder, so I try and keep the very steep part to a minimum.

I completely take the point about the critical engine. On the Aztec, the left engine is very much the critical one, not only because of all the usual aerodynamic and torque reasons, but also because it drives the only hydraulic pump. For this reason I always make these turns to the right. I assume that the same engine remains critical in a steep turn?

I really do appreciate your comments. I think that John has quite rightly put me off the idea of doing the experiment, but at the same time has given me reason to feel less uncomfortable about the exercise in general.

Incidentally, I heard this evening that, as yet another spin-off of 9/11, all orbiting is to be banned over Central London and there is to be a general minimum transit altitude of 1800'. What a bummer :(

Thank you all,

Timothy

[fobotcso]

That is bad luck Timothy :sad:

So there is no point in suggesting a change to a high wing aircraft...

Or maybe there is. Orbiting would not be necessary - just a change of direction around the target to get the best angle. :O

But it is good to know that you were thinking about these weighty matters.

[safetypee]

Timothy,
I can only endorse the advice not to try potentially hazardous manoeuvres. For more information on the type of problem and the accidents resulting from Propulsion System Malfunction and Inappropriate Crew Response: see the PSM+ICR and ‘asymmetric flight’ files at Turboprop PSM+ICR (http://uk.geocities.com/[email protected]/alf501h.htm ). Remember that some 114 accidents were used for just the turboprop analysis in the main report; most of those were fatal accidents.