Bacon Saver Angle of Attack Indicator

[BRL]

QDM. I don't understand why you have a go on your previous threads. I did e-mail you and explained what i had done and why. If you wanted to know more, why didn't you e-mail me back?

[QDMQDMQDM]

Sorry, Big Red L. I'll go and take a look at that email address.

QDM

[formationfoto]

QDM
I thought the wind vane like device on the early Moth machines was a paddle which was spring loaded and was pushed back by the action of air and therefore a crude ASI rather than AoA indicator?. Not studied this so could be wrong but certainly looked that way when I last saw one at the Moth fly in.

I think we've all taken rude pills - under another guise, and in a different forum, it has been interesting to see how a post can become the prompt for massive unexpected controversy. I guess the relative anonymity of forums along with the 'free speech' ethic leads to beheviour which we would find difficult to justify face to face.

Off topic I know but this is one of the negative and corrosive impacts of e-mail which in most other ways has been a huge benefit to society.

I guess one of the points that some of the posters missed was the fact that the supercub, particularly the larger engine variants, can sit in the air with the ASI off the clock as you describe. Makes tail chasing with less capable machines quite fun, they just go sailing past.

[QDMQDMQDM]

I thought the wind vane like device on the early Moth machines was a paddle which was spring loaded and was pushed back by the action of air and therefore a crude ASI rather than AoA indicator?. Not studied this so could be wrong but certainly looked that way when I last saw one at the Moth fly in.

formationfoto,

You could be right. I was, I admit, basing my assumption on that from what a Tiger Moth pilot told me when we were discussing AoA indicators. He had always presumed this was actually an AoA indicator, so maybe he was wrong.

I think we've all taken rude pills - under another guise, and in a different forum, it has been interesting to see how a post can become the prompt for massive unexpected controversy. I guess the relative anonymity of forums along with the 'free speech' ethic leads to beheviour which we would find difficult to justify face to face.

Yes, indeed. I was just rather surprised such an apparently innocuous topic excites so much controversy.

I guess one of the points that some of the posters missed was the fact that the supercub, particularly the larger engine variants, can sit in the air with the ASI off the clock as you describe. Makes tail chasing with less capable machines quite fun, they just go sailing past.

I have relatively little faith in my ASI above 55 knots and practically none below that, which I suspect is how it should be. Gross position error at the low speeds at which the Super Cub stalls and its relatively low cruise speed make the ASI a severely limited instrument for this aircraft. It's not useless, obviously, but it has severe limitations just when you want to rely on it most -- during a low and slow powered approach.

QDM

[paulo]

I suspect Mr Alan Cassidy would have something to say about this.

"Right, so stall is down to angle of attack?"
"Yes."
"Where's the angle of attack indicator in the kind of aircraft you'll fly?"
"Ummmm..."
"OK, so take a PA-28... you can paint a line on the column.
Keep pulling, you see the line, that where's where it stalls."

Simple really, when a very experienced pilot explains it.

So, err, no - I concur with a few other people here - can't see how it helps vs. 'normal' flying.

[QDMQDMQDM]

"Right, so stall is down to angle of attack?"
"Yes."
"Where's the angle of attack indicator in the kind of aircraft you'll fly?"
"Ummmm..."
"OK, so take a PA-28... you can paint a line on the column.
Keep pulling, you see the line, that where's where it stalls."

I'm not sure I see the relevance of this as one considers whether an airflow-based angle of attack indicator is useful in slow flying an aircraft such as a Super Cub.

The other thing, of course, which a suitably calibrated AoA indicator is useful for is to help achieve both best angle of climb (close to the aerofoil's max lift angle, a few degrees less than stall angle) and best rate of climb. The AoA for best rate of climb will also be very close to that for best glide, helping you to eke out maximum distance in the event of power failure. While the airspeeds for best rate and best angle will alter with factors such as weight and density altitude, the Angles of Attack will not. Once again, in these cases airspeed is merely a poor proxy for AoA.

Admittedly, for the majority of light aircraft, used mainly for touring and in which the low speed / high angle of attack performance is neither critical nor often explored, an AoA indicator is probably a distraction and a confusion to most pilots who don't really understand the importance behind Angle of Attack and who couldn't really care less about it. But I'm not talking most aircraft, I'm talking a 150HP Super Cub which is designed to be flown in this very flight envelope. At present I have no instruments to aid me in doing so. An AoA indicator would / will.

QDM

[stiknruda]

QDM

I'd still love to know how you will accurately calibrate your device, as per my first post!

You've told me why you you've bought one, already!

The 4 or 5 SuperCubs that I have flown have all stalled as the the needle recedes to zero, power off. Full power stalls - I am sure that the needle was tickling about 35-40 mph. At that power/speed/alpha combination the stall was very evident.

Langeweische is a sort of hero of mine, hence my monniker! As an aerobatic pilot I find him and AoA indespensible. I really wish you well with your weight/drag increase and would still love to know how you will calibrate it.

God forbid I like the answer so much, I might even install one on my Pitts! Okay - that was a blatant lie to dissuade Kirstey from her persecution of a fat old bloke!


Stik

[stiknruda]

Alan C's Paint a Line

Paulo's post above:

Totally concur

yes - the aeroplane (light GA) will stall when you pull through a certain stick position and will stall inverted if you push through a certain point, too.

A previous poster mentioned flicking a C15x. That control column back position to induce the momentarily stalled wing that will allow one to induce the flick with rudder at 70mph will be the same back position that stalls the airframe at idle!!

Stik

[andrewc]

Knowing the stick position is fine for level flight, but as soon
as you are in a turn with more heavily loaded wings and
a different air flow then having an AoA makes a lot of
sense.

QDM gave a very rational set of reasons for having one on
his aircraft...stalling/spinning at low level is a rather game
-over event.

-- Andrew

[QDMQDMQDM]

Stiknruda,

Calibration should be quite simple, I hope. Simply stall the aircraft in three configurations -- flaps up, flaps 25 and flaps 50 and note the AoA of each. Then make a best angle and best rate climb and note the AoA of each of those. Then land and mark each of those angles on the AoA indicator with a bit of coloured tape.

It's a very low tech affair, which is why I like it. Rather like the sight level fuel gauges on the Super Cub -- very little ambiguity is possible.

To all the doubters: my reg is G-CUBP. You can look out for it in the AAIB reports.

QDM

[nonradio]

3QDM, here's one for you: tie a little piece of string about a foot long around the pitot tube close to the jury strut and see how the airflow changes at the pitot from hi to lo speed inc stalled condition - it doesn't very much at at all - which surprised me as I was trying to get a free version of the AoA ind. (made me think that suspected ASI error wasn't so bad after all. I guess that's why the store bought versions are on dirty great big poles out the front! In any event I would be careful at low level ie short final and over the hedge ( I'm guessing this is all about STOL) since turbulence and manoeuvring ie aileron use will cause a fair amount of local airflow change which will mean accurate judgement of the stalling angle, or rather your proximity to it(!), difficult to judge. It sounds like jolly good fun though, but I think that looking out front and judging sink rate, attitude, and stick position/feel to be more important (You can also judge when to close your eyes if it gets too exciting!)
Finally, Real Cubs are flown from the BACK seat ... ;-)
(but not very quickly)

[englishal]

In my opinion, certain contributors to this thread, have a very simplistic view on stalls in an aircraft....

Keep pulling, you see the line, that where's where it stalls

Don't forget an aircraft can stall at any attitude, and at any airspeed. The important thing to be aware of is that below Va the aircraft will stall before the wings fall off, above Va the wings might fall off first.

The only thing that detemins the stall is AoA....so if someone wants an AoA indicator, so what?

Cheers
EA

[QDMQDMQDM]

In any event I would be careful at low level ie short final and over the hedge ( I'm guessing this is all about STOL) since turbulence and manoeuvring ie aileron use will cause a fair amount of local airflow change which will mean accurate judgement of the stalling angle, or rather your proximity to it(!), difficult to judge. It sounds like jolly good fun though, but I think that looking out front and judging sink rate, attitude, and stick position/feel to be more important

nonradio,

I totally agree. I don't envisage myself crossing the hedge looking out at the AoA, in the same way as I don't look at the ASi in that situation. That said, it strikes me as a better option to have an instrument for critical phases of flight outside the aircraft a fair distance away (i.e. not near focus) between your 10 and 11 o'clock than shaded down in the instrument panel. It's a low tech head up display, if you like!

Finally, Real Cubs are flown from the BACK seat ...

I'll give you that one.

QDM

[QDMQDMQDM]

Langeweische is a sort of hero of mine, hence my monniker! As an aerobatic pilot I find him and AoA indespensible. I really wish you well with your weight/drag increase...

stiknruda,

The device weighs four ounces and has minimal drag at all realistic speeds. The area of the vane is 0.02 square feet and in tests the load at 400mph is only 8lbs, and that's if the vane is meeting the airflow side on, which of course it never does. In any case, the drag of such a device is not a relevant consideration on a Super Cub with a climb prop that cruises at 80-85 knots on 150HP.

In Langewiesche's book, pp 75-77 are devoted to the Angle of Attack indicator and as you know pretty much the entire book is devoted to angle of attack itself. Among other things, he says:

"The most important fact about an airplane's flight condition is not indicated by any instrument. This is not because such an indicator cannot be built, but because designers don't appreciate the need for one. Perhaps they are right -- too many pilots don't know what Angle of Attack is in the first place, and such an instrument's indications would be meaningless to them."

Later, when referring to the Wright brothers' only flight instrument, a tuft of string AoA indicator...

"On today's airplane we could not put such a tuft on the nose of the airplane, since the propeller blast would make it give false indications. Perhaps it should be carried on a pole extending forward from one wing, well as the Pitot tube of the airspeed indicator is carried now -- only perhaps farther forward, so that it would be in undisturbed air and well in the pilot's field of vision. Perhaps every flying school should have at least one airplane fitted with such a forward mast and pennant, and every student should perhaps have a chance to fly it once in a while and see what Angle of Attack really means."

Sage advice, given almost 60 years ago now. It's bizarre that there should remain so many misconceptions about Angle of Attack and the utility of measuring it. Given the choice between an ASI and AoA indicator, I should certainly choose the latter. The only function of the former is to give readings which approximate (often inaccurately) to the Angle of Attack. That this is not appreciated by the majority of pilots is an indictment of our training.

QDM

[Evo7]

Given the choice between an ASI and AoA indicator, I should certainly choose the latter. The only function of the former is to give readings which approximate (often inaccurately) to the Angle of Attack

Maybe if you navigate using GPS, but if all you're working with is chart, DI and stopwatch then information about your airspeed is a lot more useful than information about your AoA. Now, lets see, I've been on a heading of 270 at 8 degrees AoA for 10 minutes, where am I....

as for

I think we've all taken rude pills - under another guise, and in a different forum, it has been interesting to see how a post can become the prompt for massive unexpected controversy. I guess the relative anonymity of forums along with the 'free speech' ethic leads to beheviour which we would find difficult to justify face to face.

I think this is rather informed and polite for a topic where people hold such different views. Maybe the internet has just made me thick-skinned...

[QDMQDMQDM]

Maybe if you navigate using GPS, but if all you're working with is chart, DI and stopwatch then information about your airspeed is a lot more useful than information about your AoA. Now, lets see, I've been on a heading of 270 at 8 degrees AoA for 10 minutes, where am I....

Alright, touche, for those people who fly aircraft which go places quickly. But why would you want to do that?!

QDM

[nonradio]

hear, hear!

[Final 3 Greens]

Kirstey

A PA28 does have an AOA indicator. It's called the AI (Attitude Indicator), but the PPL syllabus minimises reference to it apart from the instrument appreciation, because (as you infer correctly) PPL students are trained to fly airspeeds because its a less tricky concept at that stage and getting the prospective pilot to look outside rather than fixate on the panel is important at this stage.

As to stalling a PA28, this is very easy; what is not so easy is obtaining a "g" break due to the aerodynamics - it tends to "mush down" stalled, but benign.

If you are interested in stalling, you could do a search - I think that John Farley (a very experienced test pilot) made a super posting explaining the difference between being stalled and a g break.

The only caveat on the PA28 that I know of is that the taper wing versions, when loaded to the rear of the W&B envelope can give you the mother of all wing drops which comes as a nasty surprise when they don't usually break at all.

I understand what Stik and the other guys are saying - I'm not knocking QDM, but you're probably not going to want to fly a Cub in IMC and if you did, you could fly it on airspeed, power and turn co-ordinator. Having said that, we don't know why QDM needs the device, so there may be good reasons, although claibration will be interesting.

[QDMQDMQDM]

A PA28 does have an AOA indicator. It's called the AI (Attitude Indicator),

Final 3 Greens,

Whatever the attitude indicator measures, it certainly has nothing to do with relative airflow over the wings. It is not an angle of attack indicator.

we don't know why QDM needs the device, so there may be good reasons, although claibration will be interesting.

I've outlined it in several previous posts and calibration should be quite simple. The complicated bit in all this (for me) is going to be the small amount of pop-riveting required to assemble it and then getting it approved as a minor mod and any advice on this will be gratefully received.

QDM

[formationfoto]

Lively forum so lets keep it going.
AoA does not equate to Attitude so the AI is not an AoA indicator which of course has to take into account the aircrfat angle of attack with respect to the airflow over the wing. An AI tells you nothing about this condition just the attitude of the aircraft in reference to an established horizon. It know nothing of the airflow.
Easy mistake so not being critical but given the thread is getting quite detailled worth being clear about accuracy for the benefit of all.