Bacon Saver Angle of Attack Indicator [Archive]

Kirstey

5th Jul 2002, 14:14

qdmqdmqdm firstly no idea as to the answer to your questions - sorry!

secondly to all you "top guns" intent on critisising - whats the main reason you use you airspeed indicators??? that's right its to make sure you don't stall! Obviously it's somewhat important when you are DR. but essentially you are using it to make sure you don't stall in slow flight.

Now as you all patently know more about aviation than the rest of us you will be aware that Stalling occurs when an aircraft exceeds its angle of attack NOT when it reaches a certain speed, although the predictable laws of physics mean that an aircraft will be travelling at a certain speed and a certain number of revs when the angle of attack reaches it's critical point.

Surely a better way of monitoring the angle of attack, is an indicator that measures angle of attack???? Instruments are a grand back up and if you ever fly into cloud you'll realise that they are more realiable than we are if we are deprived of any of our senses. If QDM ends up inadvertantly IMC, all other things being equal he'll have a slightly better chance of surviving than you! and he's probably less of an arrogant so and so than the rest of you as well!!

stiknruda

5th Jul 2002, 14:33

Kirstey

No criticism intended or implied - just wonder why and how it will be calibrated.

Given your interest in "principles of flight" as per your post, what do you think he is going to do; calibrate it against an ASI or perform a series of stalls?

The fact that it will increase the weight of the aircraft and the drag would be my only criticism, do think that TTHills has a valid point though!

About as useful as a stall warner in an aerobatic mount in my opinion.

Stik

;)

Kirstey

5th Jul 2002, 14:41

stik,

I do understand that - but I just think every little helps when it comes to staying safe! As for how it's going to be calibrated I can only assume an engineer will do it - I'm afraid I can't spot one gyro from another, the physics of all the instruments are beyond me!

and anyway I fly a PA28 - I think i've stalled it! u can never tell tho'

Evo7

5th Jul 2002, 14:49

Interestingly, Denker says (http://www.monmouth.com/~jsd/how/htm/aoa.html#toc19) that "many airliners .... that do have fancy angle-of-attack sensors don't make the information available to the flight crew — only to the autopilot". That suggests to me that an AoA-instrument doesn't give you very much in the way of useful information.

Oh, and my PA-28 seems to be very good at telling me how close I am to the criticical AoA without any instruments at all - you get a very noticable pre-stall buffet through the yoke. Admittedly the stall itself is a non-event, but you know it's coming.

I guess the washout in the PA-28 wing means that an AoA indicator is meaningless, anyway?

(edit: just noticed a rather odd spelling of critical :) )

Bottle Fatigue

5th Jul 2002, 14:50

I like the noise the stall warner makes in the 152 when you flick roll it.

You can't tell me that isn't useful!:)

stiknruda

5th Jul 2002, 15:11

I believe that I'm correct in saying that many mil fast jets are flown on AoA. In fact IIRC final approach in the Jaguar is 8 Alpha.

I suppose that you use the stall warner in a C15x to ensure that it goes silent as soon as you unload once the rudder has bitten, what with all that plan-form drag and a slow entry speed it would be buzzing for days, otherwise!

Kirstey - if it really was a safety aid, don't you think that they'd have been fitted at Lockhaven? How many other light aircraft have them as standard fit? You and most pilots however have an in-built AoA indicator, your inate ability to recognise the onset of a stall as aerodynamic buffet or tailplane burble is felt. Still not sure? - then go get more stall/spin awareness training until you are sure.

I can see it being a distraction and if not properly calibrated either a useless or a dangerous distraction! Hope old QDM didn't pay too much for his gizmo.

Stik

Kirstey

5th Jul 2002, 15:40

stik,

I am fairly confident I can recognise the early stages of a stall. The fact that light aircraft don't as a rule have an AOA indicator, doesn't mean they are more dangerous with them without! Surely it's similar to GPS - not an essential tool by any means but if a pilot chooses to use one then thats up to them??

I suspect it is a fairly minor mod and won't effect the basic C of G, likewise being as the guy is asking for advice on it's proper installation one can assume he's going to install it properly??? Therefore if it's calibrated properly it can only be helpful!!

Flying an airplane is not difficult the added task of glancing at an extra gague is not going to overload a pilot!!

I won't use GPS I think its "cheating" I get a lot of pleasure plotting a route, tracking VORs and NDBs etc etc.. I wouldn't critise anyone who wanted to use a GPS as a primary nav tool so long as they have skills in other techniques to get them home n case it goes pear shaped!

Ultimatly if QDM can afford an airplane he can afford an AOA! so stop giving it the "I AM" routine and let people enjoy their aviation however they want to do it!

The Ugly Fend Off

5th Jul 2002, 16:22

Military a/c find them very useful indeed, in fact they're pretty much vital on high performance swept wings. I don't think it is so vital on straight winged a/c.

Useful in the event of a pitot-static/CSI failure though. Instead of having to guess at power settings he can now just fly a circuit on alpha, much easier methinks. I'm not sure how confident I would be in a DIY one as opposed to one designed for that particular a/c.

The various important AOAs are usually discovered by test pilots through hours of well supervised flights. Be careful buddy.

kabz

5th Jul 2002, 17:18

Well, there's no stall warning on a Citabria, but it still 'whistles' like mad near the stall ... that's a pretty good indicator.

The wallowy handling and high sink rate also give a couple of clues.

formationfoto

5th Jul 2002, 18:09

I guess we are all different. Whilst I agree that the AOA indicator for a cub / supercub is probably as valuable as an INS, weather radar, and crew bunks if you want to fit one and the CAA doesn't have a problem go ahead. As with any instrument you need to consider carefully what it is telling you and react accordingly.

stiknruda

5th Jul 2002, 18:31

Kirstey,

If it is properly/accurately calibrated then all well and fine and I really hope he enjoys using it.

If it is inadvertently calibrated to under-read, ie 10alpha is really 14alpha then it if he relies on it too much it is inherently very bloody dangerous.

Likewise if it over-reads, it probably won't be helping him at all and will merely be a useless distraction that may not enable him to get the best out of the aeroplane.

Off to my hangar to fit aircon and a dehumidifier to my Aeronca Super Chief. I'll then call it it Stik's Super-Cool and Dry Chief and will accept the 300% increase in runway required.

I'm sure that Mr Aeronca would have installed them as standard if he'd had more money to splash about!:D

Gotta go, the hangar beckons.

Stik

QDMQDMQDM

5th Jul 2002, 19:04

Wow. I've been away for a day and didn't realise what a hot potato this is! I'm gobsmacked that people find it so controversial.

My reasons for buying and, hopefully, fitting an AoA indicator are very simple and two-fold:

1. The airspeed gives only a crude guide as to proximity to the stall, depending on all kinds of factors such as weight and g. The angle of attack in a given wing configuration at which the aircraft stalls is, however, constant. Airspeed indicators are not particularly accurate, especially at low speeds and the Super Cub excels at flying at low speed. What one wants to know at low speed is precisely how close one is to the stalling angle of attack, not the airspeed, which is frankly irrelevant and represents only a very crude proxy for this, as I said. I therefore think that, especially in the Super Cub it will be a highly useful supplementary instrument.

Interestingly, the US Navy flies carrier approaches pretty much entirely by reference to angle of attack. At low speeds and high angles of attack it makes no sense to fly by reference to airspeed if you can actually measure angle of attack directly. They at least understand this.

It is also interesting that the Super Cub, arguably one of the safest low speed aircraft that exists, also has the highest stall-spin fatality rate by far in US NTSB statistics. This shows that if you push any aircraft to its limits it will bite and actually the pre-stall buffet in my machine is pretty minimal. Although the stall itself is 'benign', you get very little warning and certainly NONE from the ASI which is firmly pegged to the bottom of the clock for ages before the stall. In my book, therefore, anything which gives you more direct AoA information has to be beneficial.

2. Quite apart from its utility in everyday operations, I am looking forward to using and calibrating it as a way of better getting to know my aircraft and its limitations and qualities. Of course, experienced pilots with thousands of hours in Super Cubs have no need of an AoA indicator because they can feel the AoA in their bones, at least up to a point. What I hope is that I will be able to advance more quickly in my feel for the aircraft through the information which an AoA indicator will give me in all phases of flight.

The preference for use of airspeed instead of angle of attack measurement in low speed flying is utterly irrational and a result of ingrained prejudice. To show just how irrational it is, the Tiger Moth used to have such a 'weather vane' AoA indicator which was calibrated not in degrees, but in mph. Ridciulous, but a sign of the irrational dependency we have on mph, knots or whatever.

On a separate note, I am interested that the link I put to the AoA indicator website was edited out. It provides a lot of useful info and pictures of the device. I have no interest in promoting it and in fact the man who sells it does not make it easy to send them abroad. He won't do so and I had to get him to send it to a friend of mine in the US who sent him back a US cheque. My friend then sent it on to me. Hardly a highly commercial enterprise. I understand you don't want blatant, excessive plugs, but are the urls of all commercial operations taboo? Seems slight overkill.

I sit back and await responses with interest!

QDM

Evo7

5th Jul 2002, 19:26

It is an interesting website, and I also have no idea why the link was removed - it takes all of five seconds with Google (http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=%22bacon+saver%22+%22angle+of+attack) to find it (and BRL, that isn't a link to the manufacturer - just saving people a bit of typing in Google). Not sure that I'm convinced, but having seen what you're talking about I can't see the harm either.

Must admit I find high-AoA stuff bl**dy interesting, but that's a thread for Tech Log... :)

QDMQDMQDM

5th Jul 2002, 19:34

Evo7,

You probably know it already, but the book for those who find AoA an interesting standpoint from which to approach the practicalities of flying a light aircraft is 'Stick and Rudder' by Wolfgang Langewiesche. Written in 1944, it remains an absolute classic and, in my opinion, is very readable and understandable, if dated in some of its terminology.

You can find it by keying the above details into a certain .com website which sells lots of books and other things and which has borrowed the name of the large equatorial rainforest spanning Brazil, Venezuela and a number of other South American countries.

QDM

Evo7

5th Jul 2002, 19:36

:D

I've got "Stick and Rudder" - very good book indeed. Would recommend it to anyone. Can never spell his name though :)

QDMQDMQDM

5th Jul 2002, 19:44

This will probably induce even greater apoplexy, but it may be useful for anyone reading this thread who wonders what all this stuff is about, so here goes...

The following is a link to an interesting series of pictures showing a DIY AoA indicator in action on a Super Cub in various phases of flight:

http://www.supercub.org/woe/woe0402.php

(It's a .org website, so dear moderator if possible please don't delete the link.)

QDM

BRL

5th Jul 2002, 19:54

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?:confused:

QDMQDMQDM

5th Jul 2002, 20:09

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

QDM

formationfoto

5th Jul 2002, 20:40

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

5th Jul 2002, 21:07

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

5th Jul 2002, 21:22

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

5th Jul 2002, 21:47

"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

5th Jul 2002, 23:36

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!:p

Stik

stiknruda

5th Jul 2002, 23:44

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

6th Jul 2002, 01:24

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

6th Jul 2002, 07:25

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

6th Jul 2002, 08:07

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

6th Jul 2002, 08:52

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

6th Jul 2002, 10:25

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

6th Jul 2002, 10:54

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

6th Jul 2002, 11:42

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

6th Jul 2002, 11:53

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

6th Jul 2002, 12:18

hear, hear!

Final 3 Greens

6th Jul 2002, 18:00

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

6th Jul 2002, 18:35

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

6th Jul 2002, 18:39

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.

QDMQDMQDM

6th Jul 2002, 19:27

I'm at risk of being called a pedant here, but the AI / AoA thing is a common and dangerous fallacy and it's important to nail it on the head very firmly. Here's an example of why:

Take four flight situations.

First, a descent on approach to land, with a slow speed and relatively high angle of attack. In this situation, the AI will show a small degree of nose down attitude.

Second, a near vertical, full throttle, high speed dive at a very low angle of attack. The AI will show a very high degree of nose down atttitude.

Third, a cruise climb. Angle of attack slightly higher than that for level cruise, but not much, so still a relatively low angle of attack. The AI will show a small nose up attitude.

Fourth, a best angle climb, very high angle of attack. The AI will show a high degree of nose up attitude.

Thus, a high degree of nose down on the AI in the situations above correlates to a LOW angle of attack, whereas a high degree of nose up on the AI correlates to a HIGH angle of attack. In other words, there is no consistent correlation between nose attitude and angle of attack. In the first situation above, you are at risk of stalling with only a small amount of nose down attitude on the AI. In the fourth you are at risk of stalling with a high amount of nose up attitude.

Most important of all, is that this shows the AI alone will tell you nothing about your proximity to the stall. To believe that it has the power to do so will be highly misleading and will likely lead to much more than mere embarrassment.

QDM

Genghis the Engineer

6th Jul 2002, 20:45

Stall, for a given flap/slat setting combination (just flaps on a cub) will always be at the same AoA.

AoA is also a much better indication of loading and proximity to the stall than airspeed or a g-meter. But, unless somebody's done some considerable work to produce operating data based upon AoA, calibrated the instrument, etc. it's not a great deal of use. On an aircraft like the Jaguar, Tornado or Concorde, it's essential. I'd venture that on an aircraft like a super-cub, it's usefulness when you have adequate stall warning from things like lack of wind noise, back-stick and buffet, is at best marginal.

If you simply want to fit it, as something to look, then it's probably a minor mod. If it's on a permit, the PFA'll do it for free, if it's on a CofA it'll cost you £62 through your CAA regional office. They'll probably insist on a suitable placard being fitted saying that it's not a primary flight instrument.

If you want to make proper use of it, that requires calibration, flight testing, preparation of a POH supplement and CAA major mod approval. If you want that, the CAA minimum fee is £309 and you'll need the services of an E3 company, or design and flight-test signatory acceptable to the CAA. Offhand, if you were to ask me to do the job, I'd probably charge you around £2-3k. Trick is to find a design signatory who fancies free use of a super cub for a while in payment, that might be me as well, but even at my eminently reasonable consultancy rates, that's a lot of flying!

G

QDMQDMQDM

6th Jul 2002, 21:00

If you simply want to fit it, as something to look, then it's probably a minor mod. If it's on a permit, the PFA'll do it for free, if it's on a CofA it'll cost you £62 through your CAA regional office. They'll probably insist on a suitable placard being fitted saying that it's not a primary flight instrument.

Thanks, Genghis. It's on a CofA. What's the best way to approach the CAA regional office? I was planning to send them the design drawings and FAA Form 337 documentation and tell them what I hoped to do. Is this the best tack to take with them?

It will be there for information only. I certainly don't plan the whole rigmarole.

QDM

nonradio

7th Jul 2002, 11:13

F3G
Please don't Rely on your AI to tell you your AoA! Hold the nose of your aircraft on the horizon - fixed attitude, right? Now close the throttle. Continuing Holding the attitude constant, by your argument means the AoA must be constant...?? It clearly isn't, is it? (unless you have an anti-gravity device fitted, of course)
Put this AI = AoA indicator nonsense out of your mind, "Lest the earth rise up and smite thee....." However, as ol' Lang' said AoA is the difference between where the aircraft is pointed and where it going..... so attitude monitoring is still important

Crossedcontrols

7th Jul 2002, 14:06

It would be intersting to see if the built in stall indicator of a J3 worked on the PA18. It is a bit of a hassel using it in the UK, but works well in Florida.

Oh you want to know what it is.

When the door is left open of the J3 the bottom half start to rise up near the stall, wonderfull device. But bloody parky in the UK.

Show us a picce when you get it fitted

CC

Note the J3 doesn't have flaps

Genghis the Engineer

7th Jul 2002, 15:24

I confess that minor mods on CofA aircraft isn't my strong point, but I'm pretty sure there's a standard application form.

I'd suggest giving the regional office a call (the numbers are all in CAP455 somewhere), ask to speak to a design surveyor, explain what you want to do, and with any luck they'll send you the paperwork you need and explain any significant points.

But, my instinct is that drawings, the FAA documentation, a few sums showing that the CG change is so small as to be insignificant, the CAA's own form, and the all-important cheque, will probably do it.

A couple of steers for you; do make sure that the attachment to the strut is either clamped on the outside or picks up on an existing bolt, don't drill anything - that's sure to cause problems. Don't run any cable near a wing leading edge, and make sure if it's running from the aircraft power supply (if you've got one!) that it's independently fused at about 50% above the maximum rated current. These are the standard sort of things that they'll look for.

Cheers,

G

QDMQDMQDM

7th Jul 2002, 20:23

Thanks a lot, Genghis. It's simply a wind vane on a stick, fixed to the lift strut with a hose clamp, no electrics. Shouldn't be too much of a problem I hope.

QDM

Final 3 Greens

8th Jul 2002, 06:19

3QDM/NonRadio/Formationfoto

Quite right to pick me up gentlemen. What I should have said in the context of Kirstey's post was that there was an instrument (AI) that can be used to keep the angle of attack safe when used in conjunction with other instruments.

Having just looked at the Bacon Saver website, there was one line that caused me a little alarm....

If he's trying to clear a ridge, or make the turn to Final, is it seven degrees, or one degree?

My old mountain flying instructor in the States would have had an apoplexy if any of his students had got so close to a ridge on even a minor hill, due to the potential for windshear.

Just out of interest, does any one know what the effect of gusts on this instrument would be and could they cause spurious indications?

englishal

8th Jul 2002, 08:18

Just out of interest, does any one know what the effect of gusts on this instrument would be and could they cause spurious indications?

I would assume that it would display the correct AoA. If a gust hits the wing then the AoA will change...

Cheers
EA:)

QDMQDMQDM

8th Jul 2002, 08:39

My old mountain flying instructor in the States would have had an apoplexy if any of his students had got so close to a ridge on even a minor hill, due to the potential for windshear.

Well, you can skim ridges as long as you're 100% positive you're approaching from the upwind side, but it's still a mug's game.

The stupidest thing I have ever done in flying was last year agreeing to go in the jump seat of a Cessna turbine 206 dropping parachutists in the Swiss Alps. I know the area well and the pilot ducked into a very high, steep cirque just after take-off and I thought, 'Uh huh, he's going in here for a sightseeing tour and is going to do a speedy 180 and we'll be out', but no he headed up and West for the saddle (prevailing wind is from the West). Sure, this was a turbine 206, but we were at gross and climbing towards the pass. I just prayed and, of course, we got over, but only just. We crossed the saddle with about 200 feet to spare. He'd done it several times already that day and he knew that day it was OK, but one day it won't be.

We dropped at 10,000 feet agl and beat the first free faller to the ground, but that was a breeze after the flight up.

QDM

Final 3 Greens

8th Jul 2002, 09:10

EA

Agree in principle, but what about gusts from an angle and also fuselage blanking effects?

Probably not a major issue, but interesting to think about.

QDMQDMQDM

8th Jul 2002, 11:06

Agree in principle, but what about gusts from an angle and also fuselage blanking effects?

F3G,

It would have to be pretty extreme fopr these factors to have a major effect. The vane sits 20% of the chord forward of the leading edge and outside the prop blast. In the Super Cub, it is clamped to the upper pole of the left lift strut, so is very far out.

If it's that gusty, you'll be approaching faster anyway so the proximity to the stall won't be so critical and you'll be ready with a bellyful of power. You wouldn't fly the approach staring at the AoA shifting in gusts in the same way as you wouldn't fly it staring at the ASI fluctuating.

QDM

Final 3 Greens

8th Jul 2002, 11:15

QDM

Sounds reasonable.

What was interesting to me (at a pedantic level) was taking a reading from one wing and not the other.

Knowing little about these things, I wonder how AoA on jets works ... e.g. a sensor on each wing averaged or some other approach such as a fuselage mounted device.

Best of luck with the installation.

The Ugly Fend Off

8th Jul 2002, 14:14

It's on the fuselage in the jet I use. No snags with prop wash you see. It's slightly more complicated than QDMs job but still does exactly the same thing mind!

Croqueteer

9th Jul 2002, 11:55

A simple A of A indicator is the stick. If you paint a line on the fus wall at the correct place, then if the stick is aft of that you have exceeded the critical A of A and the wing will stall regardles of speed, so the message is, always be aware of the stick position. Suggest you hire an aerobatic a/c with a good instructor for an hour and play test pilot and explore some of the corners of the envelope. Have fun!

englishal

9th Jul 2002, 12:22

A simple A of A indicator is the stick

A very simple one...practically useless....Low speed the stick needs to come back a long way, high speed you pull it back a short distance too fast and you stall the wing (if they don't drop off). So where do you paint the line? right at the back, or just aft of centre?

Cheers
EA:)

QDMQDMQDM

9th Jul 2002, 14:07

A very simple one...practically useless....Low speed the stick needs to come back a long way, high speed you pull it back a short distance too fast and you stall the wing (if they don't drop off). So where do you paint the line? right at the back, or just aft of centre?

Yes, and it would also depend on both the trim and C of G.

It's right in spirit, though, in that the real function of the elevators is to control the angle of attack of the main aerofoil. Just how much elevator deflection is required will depend on speed, as englishal says.

The other thing is that AoA info is not just useful for detecting proximity to stall, but also for flying at best rate and best angle of climb and also best glide.

QDM

nonradio

9th Jul 2002, 14:57

I suspect that the stick position is pretty constant, but clearly the rate at which the pitch change occurred would be greater at higher airspeed. Any aeroplane could be made 'unstallable' by limiting the aft stick travel and hence elevator movement (e.g. the Ercoupe)Not sure if the trim would make a diff as it just helps relieve the control surface force. Anyway 3QDM, hurry up and strap the thing on, we're all itching to find out whether it works or not. And then we can maybe construct our own homebuilt versions by nicking the design.....

QDMQDMQDM

9th Jul 2002, 16:18

Anyway 3QDM, hurry up and strap the thing on, we're all itching to find out whether it works or not. And then we can maybe construct our own homebuilt versions by nicking the design.....

nonradio,

Cor, luvaduck, gimme a chance. The thing only arrived last week and it needs pop riveting together which is way out of my league, so I'm taking it round toi a metalworking friend next weekend.

Also, when it comes to the minor mod approval the CAA say they will only deal with a licenced engineer, not a mere pilot scumbag such as yours truly, so it may take a bit of time.

I posted this way back in the thread, but here it is again, the homemade version, if you dare:

http://www.supercub.org/woe/woe0402.php#

QDM