BM, that will be handy when you land at Mile Hi next month.

To revive this topic once more, I swung by the Alpha Systems booth while at OshKosh and spoke with the owner for a while. I asked him what he thought of the contention that his product is not a "true" AoA system and challenged the utility of AoA in light GA aircraft. He had a strong working knowledge of AoA system design and factors in measuring AoA, to include accounting for asymmetric lift/airflow and prop wash. He produced the original study commissioned by the Air Force (in the 70s I think) that assessed the viability of a pressure-differential AoA system and further pointed out that the AoA system on the F-22 is pressure-differential based.

No doubt there was some salemanship at work but I came away impressed with his level of knowledge and confident that he wasn't just selling snake oil. It's well established that you don't "need" an AoA system on a light GA plane, but then you don't "need" a GPS either - these systems just provide higher fidelity information in a convenient format. If nothing else I would say that the charge that this isn't a "real" AoA system is unfounded. I can't comment further because I haven't had the opportunity to fly behind one of these systems, but I'm certainly open to giving it a fair try if the opportunity arises.

It's a color coded air speed indicator I've got one sitting in my office that my AI gave me a couple years ago. If you look at the probe that mounts on the bottom of the wing it's got 2 holes 1 on the leading point is pitot, 1 on the bottom static. Same with the gauge, pitot in on one line, static into other port. If you watch Bonanza Man's videos the ASI and the "Lift Indicator" needles correspond accordingly as air speed decreases and stall warning happens at the same speed in all videos.

I do believe that a true AOA indicator measures the angle of the wing vs. the relative wind? Not to say that this gauge doesn't give you pertinent and important information, but if you mounted your ASI on your glare shield and color coded it the same I believe you'd have the same information.

OVER

Glidergeek wrote:I do believe that a true AOA indicator measures the angle of the wing vs. the relative wind? Not to say that this gauge doesn't give you pertinent and important information, but if you mounted your ASI on your glare shield and color coded it the same I believe you'd have the same information.

Right, but it's the relative wind that causes the differential in pressure, so this type of system still effectively depicts the relationship between the wing and relative wind, not simply airspeed. Your example doesn't account for AoA in maneuvering flight where you are maintaining airspeed - remember a wing can stall at any speed. Maintain a speed (through power or attitude, doesn't matter) and pull - this system will show the change in AoA as AS remains constant.

There's no question that this system measures and depicts AoA, the question is if the system is sophisticated enough and has adequate sensors to accurately measure AoA. If the answer is no then there is enough error in the system to deem it worthless, if not dangerous.

Vick I do agree with you, I think a good test would entail some more abrupt control input. I'm not talking pulling the wings off.

Glidergeek wrote: If you watch Bonanza Man's videos the ASI and the "Lift Indicator" needles correspond accordingly as air speed decreases and stall warning happens at the same speed in all videos.

Well they should have been the same as the conditions were the same. Weight, temp, etc. Let me load up the plane to nearer gross weight and we'll see a difference.

Well I certainly don't have the technical education to argue aero science with either the AoA Systems salesman or Vick. But it seems to this old model builder that any AoA system that only uses pitot and static pressures has to be subject to some strange inputs from varying airspeeds, yaw angles, etc.

Even with my truncated IQ, I can easily visualize a vane type device always telling the truth about which way the relative wind is blowing it, and I can visualize pressure ports not always telling the truth (since "pressure" and "angle" are not always linked).

I'll bet that the reason for the design of the F-22 AoA system has more to do with radar return and high speed heat than anything else.

But I do know that the high IQ aero guys always talk about the stall angle of a wing, not the stall speed.

BM I do agree that's more info and probably good info. yes load the structure abruptly and increase the angle of attack without pulling the wings off. I'm interested to see if it acts different from the ASI.

[quote="EZFlap"]Well I certainly don't have the technical education to argue aero science with either the AoA Systems salesman or Vick. [quote]

Whoa, hold on. No claims of a big brain here. Aero science is pretty far removed from my Philosophy degree, on a good day I have a pretty good nose for bullshit but that's it. I try to surround myself with smart people and then listen up, try to glean what I can.

Glidergeek wrote:BM I do agree that's more info and probably good info. yes load the structure abruptly and increase the angle of attack without pulling the wings off. I'm interested to see if it acts different from the ASI.

I'll play around with the camera mount some more, those videos were pretty poor. Didn't expect that since the videos with the camera mounted on the passenger window were pretty good. So far my experience is the needle is pretty smooth. It doesn't sit and vibrate around. Even with some yawing going on in some of the roughest air I've landed in two weeks ago at Benchmark the needle only moves about a needles width.

As someone who flies the Alpha AOA I'll chime in again. It is not an airspeed indicator. A given wing will stall at much different airspeeds given different flight configurations. My POH gives stall numbers for straight and level, and steep turns. The lights on my AOA correctly predict the stalling of the wing in every configuration I have tried to a much higher degree of accuracy than my ASI, and in a much simpler way.

So for instance I could either refer to my POH prior to pulling a a canyon turn with 60 degree bank with full flaps and know that the wing will want to stall at 54 KCAS ( I can't remember what it really is) and hope that given plane loading and density altitude that I have a good safety margin. Or I can just go ahead and do the turn and make sure that the all the red lights and one blue light stay on. I can see this in my peripheral vision, I don't really think about it and I am looking outside, If I keep the blue light on I have a good safety margin. If I pull back further and the red's start to blink out I will get a buffet, everytime. And everytime I've checked its been a slightly different airspeed.

Before my AOA I flew my aproaches too fast to be on the safe side and I often bounced, I was scared to turn really slow so I used up more real estate in steep turns 'cause I did not want to stall. After a few hundred hours flying it (AOA) and practicing, I really don't need it anymore as MTV says my butt knows. But prior to the AOA my but had me flying too fast. Sit at any GA airport, grass or dirt strip where folks are landing. Most everyone comes in too fast, because they don't really know when they're wing is gonna stall so they bounce a little.

And, If I am ever flying up a canyon and am too low ( I don't play around with this stuff, but it could happen) and I need to pull a canyon turn as tight as I can I will be refering to my butt and the lights on my AOA.

I think this thing works it had me flying my 185 much better much sooner. In this day and age of $5 gas practicing is expensive and not everyone can do it.

-Brad

I've had my Alpha Systems AOA in my P172D for 1 1/2 years, and in my opinion, it works, and it works well. I have the mechanical version, in a pod on the top of the panel, so I see its indications in peripheral vision while I'm looking where I'm going to land. The difference in airspeeds which are appropriate for approaches between light (just me and dog and quarter tanks) and heavy (full gross) is dramatic. It does what it is advertised to do, regardless of criticism. Yes, the probe looks a lot like a PA 28 pitot, but it's not the same, and it doesn't work the same. But it does work.

The probe in my installation is in an inspection plate just inside where the strut connects to the right wing. My IA did have to do a 337 with FAA approval, because I ordered the electrically heated version, which meant connecting it to the electrical system. Otherwise, it would have been a minor alteration requiring no approvals.

I admit that it took me awhile to learn to trust it, but now that I've flown with it for roughly 75 hours, I do trust it, not as a primary instrument but certainly as an instrument which gives me valuable information. BTW, I'm not a newbie. I've been flying for more than 38 years, I let my CFII lapse back in 1987, and I have some 2300 hours (I'd have more if it weren't for several gaps of more than a year each time), and nearly 2000 of those hours are in 172s and 182s, perhaps 1400 in 172s and 600 in 182s. That doesn't make me any kind of expert, just reasonably experienced. Yeah, I can "feel" what the airplane is doing, too. But just because I have the AOA indicator doesn't mean I shut off my abilities.

So criticize the Alpha Systems AOA if it makes you feel better, but that doesn't change that it works pretty darned well.

Cary

I had it installed on my 180 and can't get it to calibrate. Lots of variables and maybe it's just an install issue. I just don't have the time now to follow thru with it.

I'd like it to work out and I understand they usually do work fine.

Oh well.

RR

Bonanza Man wrote:

Glidergeek wrote:BM I do agree that's more info and probably good info. yes load the structure abruptly and increase the angle of attack without pulling the wings off. I'm interested to see if it acts different from the ASI.

I'll play around with the camera mount some more, those videos were pretty poor. Didn't expect that since the videos with the camera mounted on the passenger window were pretty good. So far my experience is the needle is pretty smooth. It doesn't sit and vibrate around. Even with some yawing going on in some of the roughest air I've landed in two weeks ago at Benchmark the needle only moves about a needles width.

Well How'd you come out with the camera mount and the color coded a/s indicator

The AOA works great. I calibrated mine differently from what the manufacturer tells you to do as I have a different aim for this device. The market for the AOA's is not for back country guys but rather the average pilot who's worried about a stall spin close to the ground. The instructions have you fly in a clean configuration and slow down to minimum controllable airspeed and at that point the needle(or lights depending on the model) will be on the alpha symbol. Well that information is of little use to me so I set the probe so that the needle is on the alpha symbol at stall speed dirty, full flaps and gear down. The alpha symbol is on the red/yellow border. In normal flying the needle is off the scale. It doesn't move down into the green until I slow into the pattern and put the gear down. Stays in the green until I am on final and really start to slow. I can then slow to about the middle of the yellow arc, just below the stall horn speed. I did this before but didn't know where I was in relation to the stall, only that I was slower than stall horn speed. The needle is very stable, those who say it bounces around thus making it of no value simply don't know what they're talking about. It's also repeatable, go flying at any weight, wind, temp, altitude, etc, and the plane always stalls when the needle gets to the alpha symbol.
On takeoff you can yank the plane off the runway as the needle passes thru the alpha symbol on the way up but you'll need a lot of rudder to keep the plane from going left. You can get it off the runway a bit sooner than by starting the takeoff roll with a slight nose up elevator and waiting for it to fly off. It might save me 30-40 feet of takeoff roll. I don't have much use for that but what it reminded me of was when I have seen some low performance taildraggers friends near here trying to struggle off short runways and you can see the pilot rowing the stick back and forth trying to force the plane into the air. If they had an AOA they would simply wait until the needle gets to the alpha symbol which would happen a little faster without the added drag of the tail going up and down trying to fly.
On my low wing the probe is attached to the aileron bellcrank inspection plate which is way back on the wing, making it essentially invisible. If you're not looking for it you'll never see it. I like where I mounted the display on top of the panel as far left as it could go. Makes it easy to see as you concentrate on the runway environment. I still don't have decent video, still working on that, perhaps this weekend.

Bonanza I want to give it the same use as you.
Did you give more angle or less angle to the probe?
Default is 50 I think.

I bought mine, installed it and the unit didnt light up, we tried everything , and nothing!!

Called Mark and he sent me the interface box and display so I test them and keep whatever works and return the faulty parts.
Great customer service.

I moved it three degrees from the default after the first flight. I moved it towards the area of greater possible movement, which you'll understand when you handle it, which is to the rear so I think I'm at 53 degrees. After the second flight that showed it was right I removed it from the wing and installed the set screw so it can't move if it gets bumped. Mine is the analog needle gauge, didn't want the electronic one because I don't think it would work well enough for back country stuff, the graduations are too large. It will be interesting to see what you think.

I have the electronic 2 1/2 vertical, I know what you mean about the analogue one for backcountry.
Mark convinced me this will work as good and its easier to see without looking at it.

Need to try it to see results.

When mine was installed, the most difficult thing was getting the angle of the probe correct. I started it with the angle at the supposed optimum of 50 degrees, but the needle wasn't going far enough toward the red, so that the airplane stalled while the needle was still in the green. So I moved the probe all the way to the back position as allowed by the slot in the mounting plate, and it still wasn't enough. It took some filing of the mounting plate to be able to rotate the probe far enough back. I don't recall how many flights before I was satisfied, but probably 5 to 7.

The Alpha angle is not the stall speed, however. The alpha angle is the slowest airspeed at which full control can be maintained in level flight, so that the needle is at the red/yellow position. That may or may not result in the stall warner going off--mine was buzzing periodically. Whether the alpha angle is determined with flaps or not, should not make any difference. I chose to determine the alpha angle without flaps, and later tested it with different flap angles. I retain full control at the red/yellow, regardless of flap position, and stall occurs with the needle middle to left in the red. Actual airspeed with the needle at the red/yellow varies significantly, depending on load, bank angle, flap angle, etc., as you would expect. Except when fully loaded, the safe approach speeds are much slower than book figures, again as expected.

I've played around with different airspeeds, bank angles, and loads, and as long as I keep the needle in the yellow, the airplane is stable and fully controllable, at pretty low airspeeds. In turbulence at lower speeds, the needle does bounce around a little, but not to the point of being unusable. If I have any gripe at all, it is that I'd like the needle to be wider, so it's easier to see in the dark, but that's pretty minor. All in all, I'm very satisfied that the Alpha Systems AOA works well and adds significantly to safety. Again, criticize the Alpha Systems AOA if it makes you feel better, but that doesn't change that it works pretty darned well.

Cary

Cary wrote:
The Alpha angle is not the stall speed, however. The alpha angle is the slowest airspeed at which full control can be maintained in level flight, so that the needle is at the red/yellow position.

...in the clean configuration. That's how the instructions read. That's not a useful setting to me so I simply made the alpha symbol the stall. Two flights total with the second verifying the adjustment was correct.