Best approach airspeed on short final

[Cary]

EZflap sez: "I don't know of any AOA system for light aircraft that in real world use is worth a shit."
MTV sez: "AOA is important, but as you noted in your initial post, there is no RELIABLE INSTRUMENT in our light general aviation aircraft that provides us with that information."

I disagree. I had the Alpha Systems AOA indicator (the basic analog version) installed in my modified P172D last January (2010), with the gauge mounted on top of the panel so I can see it without taking my eyes off the approaching runway. I've flown roughly 50 hours with it now, including at full gross and at very light weights (just me and a few gallons of fuel) and at different weights in between, and I am very pleased with it.

It took several flights to get the probe angled correctly to calibrate the AOA indicator, so that the needle hovers right at the division between the red and yellow segments, at the slowest speed possible but still with sufficient aileron control. Once calibrated, then I've experimented enough that I'm confident that it works well regardless of weights and flap position.

At full gross, it pretty much agrees with the book stall speed; at much lighter weights, it's pretty amazing how slow the IAS will show while the AOA indicator still shows a safe angle of attack. I have something in excess of 1400 hours in 172s, maybe more, and over 300 hours in this particular airplane, so I can certainly feel the stability of the airplane, with or without the AOA and with or without the ASI. But the AOA still gives me a lot of comfort on short fields with varying weights.

The probe for mine is mounted under the right wing, and I opted for the electrically heated version. It is protected (or I should say, my head is protected) because it is within the area just inside where the strut is attached. I have tried slips both directions, and I can't see any variation in the information it is giving me, whether right or left. I wouldn't think it would, since both holes which are in the probe are in the centerline of the probe, and the probe is far enough from the fuselage that it is not blocked by a left slip (hard right rudder).

The identical instrument was favorably reviewed by Sparky Imeson a year or two before his death, FWIW.

Everyone is entitled to his opinions, of course, but I suggest, don't knock it until you've tried it. I can't speak for any other brand or type of AOA indicator, but the Alpha Systems analog version works, just fine. My airplane is the 4th one I've owned (first 3 were with partners, this one is all mine) and the first one in which I've had an AOA indicator. If I ever have occasion to own another airplane, it will be one of the first modifications that I make to it.

Cary

[Bonanza Man]

A bunch of the Beech guys like it too. I will install one one of these days. Those who say they aren't worth a shit just simply don't know what they're talking about. Here's a couple threads on it.

http://www.ballyshannon.com/air/aoaflighttests35.pdf

http://www.beechtalk.com/forums/viewtop ... &hilit=AOA

[EZFlap]

EZflap sez: "I don't know of any AOA system for light aircraft that in real world use is worth a shit."

That quote was actually not mine. I had initially made a post saying that IMHO an AOA indicator is likely more accurate and more useful than IAS for STOL work, on the basis of Sparky Imeson's web article, and that I understand Navy carrier approaches are all made with AOA as primary reference.

[GumpAir]

That would be my quote.

I see this is a supposidly new system, but... How did they "fix" the problem of asymmetrical wing speed and AOA in a turn while using a single sensor? The ones I've tried have never told me anything that the seat of my pants wasn't telling me way more quickly and accurately than any gauge could. I'm still not "getting" why I need a system like this in a light aircraft with relatively low wing loading and a prop.

Of course I don't look much at the ASI either. Just lucky to be alive I guess.

Gump

[porterjet]

I'll throw my jet experience in here again! Most jets have an AOA, a few older Citations don't but you don't need it with that wing. Our stall warning system uses the AOA so it is a no go item. So the book says.
I use it when climbing to high altitude with best l/d set instead of 1.3Vso. As Gump was getting at, it has a bit of lag and ours does not have a heads up display so it would mean looking down by my left knee so for approach work it is pretty much useless. I did fly one Citation that had a heads up display for the AOA (not one of the new fangled modern HUDs) and that one most of us would use on short final. I suspect that system costs as much as a Cessna 120 today though.

[mtv]

I HAVE flown an airplane with an Alpha Systems "AOA System", specifically a Cessna 185 that we were evaluating the system on to see if it was a worthwhile addition to our aircraft. As such, several pilots, each with extensive Cessna 185 experience, and lots of off airport experience, each took the airplane and worked it for a period of time to evaluate the "AOA System".

The universal response from these pilots was that the device did not provide significantly better information than did the airspeed indicator, and it did not provide anywhere near optimal information for maximum performance approaches and landings. I can't remember, but as I recall, at least four of us flew that plane, and provided feedback on the device.

We never installed another, based on real world experience. And, this wasn't just each pilot flying the plane for a few minutes-we all had the opportunity to use the airplane at work for a while.

Another problem which hasn't been addressed here, wasn't addressed in the article by Imeson and isn't dealt with by the manufacturer is that NONE of these simple systems is STCd. MANY FSDOs will NOT field approve this thing, because they believe (and it is certainly the intent of the manufacturer) that these devices are to be used for "Primary Information". As such, they MUST be STCd.

To say that the Navy uses AOA, therefore these simple systems should be good is like saying the Navy can get a 40,000 pound gross weight airplane airborne in 150 feet, so we should be able to as well. The systems the Navy uses are VERY sophisticated, like the system that Porterjet described, with MULTIPLE sensors to provide accurate data, regardless of attitude. And, this is the big issue...the major problem with airspeed instruments is PROBE PLACEMENT, since the probes are always mounted well within the wash of the wing, and mounted only on one side of the airplane. Basic aerodynamics 101 will tell you that the mid section of one wing moves at a very different AOA than a comparable span-wise section of the other wing, depending on what we're doing with the airplane. Also, mounted in the wash of the wing, airflow is significantly modified by the wing. That's why in flight test, a VERY long probe is used, to try to get the sensor away from the wing during flight test.

REAL AOA systems use more than one sensor, and many jets place the sensor on the fuselage, near the nose, to keep them away from the lifting body. Now, the fuselage also modifies the flow of air, but not in the same way the wing does.

An AOA sensor, mounted in almost precisely the same location as the airspeed probe simple CANNOT provide any better information. In fact, take a close look at a Piper A/S probe as found on the Warrior/Arrow, etc series, and compare it to the "AOA" sensor that Alpha systems provides to mount on your wing....they are virtually identical, with the pitot front, and the static behind. Simple, but NOT an AOA.
I read Sparky Imeson's article and thought it was bunk at the time. I still do, based on real world experience with the very device he was promoting.

MTV

[Littlecub]

RE: AOA indicator by Alpha Systems

First I'll confess to being a 'gizzmo' guy........ And I like as much information as I can get especially if it relates to 'safety'.....
BUT I see some drawbacks right off.
1)Purchase price PLUS installation time/effort/cost
2)Adding weight. Got to think and re-think anything that adds weight to small aircraft.
3)The air pressure pickup that hangs down 4 inches or so below the wing. I donate enough blood already to my high-wings/pitot tubes/struts/trailing edges , I don't need another 'blood' pickup on my plane that may/may-not help me be a better pilot.

Last I knew (several years ago) these things were not 'approved' for certified std aircraft, and you had to do quite a 'dance' and be in the right FSDO's area to get them approved, so they were mostly for the Experimental builders......

YMMV
lc

[nmflyguy]

Since I started this thread, let me try to sum up what's been said so far in this thread about controlling airspeed and/or AOA on short final to a short/soft field:

1) It ain't rocket science - fly the airplane by the seat of your pants
2) It is rocket science - fly AOA
3) It may be rocket science - but light aircraft owners generally can't afford rocket science instruments like the Navy uses

I'm not the grizzled old aviation expert (I have just under 500 hours in my logbook, most of it in my Cherokee), like some who post here certainly are, so I'm in no position to judge.

But for now I will take the advice of the grizzled aviators who recommend #1: I'm going to make a pointed effort this year to learn to fly my bird more by the seat of my pants, and less by the airspeed indicator, and figure out what the real limits of my airplane are in slow flight approaches to landing. And if that makes me a better pilot (it certainly ought to), then I can always decide later on to add the AOA gizmo ... or not.

[Littlecub]

nm,
I'm not the 'hot stick' that some of our guys ARE , but it looks like a good conclusion to me......

Common wisdom-Familiarity (more flying) breeds.........skill

lc

[JimC]

Makes sense to me.

[Littlecub]

Hey Mike, I'll grant you that you are very experienced and are considered the expert by yourself and others on board here, but I find it a quite rude when I make a point in a post (FSDO's don't like to approve) and you edit your earlier post-which is ahead of mine-to include my point. Makes it look like I don't know how to read/or process information and am only parroting your post in less depth with less authority when someone reads through later. Yes, your time says 2 min earlier, but you came back and edited (added) plus had the gall to say:

Another problem which hasn't been addressed here,

before you edit-added the point. Seems pretty damn 'cheeky' to me!

I went back and read the topic review last thing before posting to make sure I wasn't mirroring/trampling someones post, and you had not made that point at that time, and I read yours after I posted mine and even a little later, and it still was NOT there.

Rude, rude, rude. This time the teacher needs a timeout in the corner for being an A$$!

lc

[mtv]

Littlecub,

I hate to break this to you, but I posted that note, went to another thread and recalled I'd forgotten to mention the "no STC" thing, and went back and edited my original post.

In any case, I hardly think that two people actually agreeing about something on one of these threads is cause for name calling.

I have flown some airplanes, but there are a lot of REAL experts out there, and I've had the priviledge to know many of them. I'm not one, however.

MTV

[Jaerl]

I got some really good advise when I first joined this forum. I was talking about putting a STOL Kit on my plane. I got a PM from a long timer and he told me to just buy gas and fly. I thought that was some great advice. I am sure that $4000 worth of gas could probably make me land a lot shorter than a STOL kit could without the experience. Plus I doubt I am a good enough pilot to use all my plane has to offer or even close to it. I'm working on it though.

[GumpAir]

And... Even if your fortunes change or your ex takes it all... You still walk away with the experience and skill. Much better than any gadget ever made.

Gump

[Littlecub]

Mike, If you really are so 'tone deaf' that you missed my point, and actually think agreeing on the subject at hand is all that matters........Well, I forgive you......... for what, well....... for what you apparently completely missed...

lc

[58Skylane]

[Cary]

Like everything else in life, you pay your money and make your choice. I paid my money, I made my choice, and I'm very satisfied with doing so.

In your "tests" of the 185 with the AOA installed, I doubt that you materially changed the weight you were carrying, or the ASI would have shown a much lower airspeed at light weights than at gross weight, assuming that the AOA was correctly installed and calibrated--it's fundamental aerodynamics that minimum controllable air speeds are significantly lower with lower operating weights. Thus, the ASI could not have shown the same information as the AOA.

Not everything aviation has to cost many thousands of dollars to work reasonably well for our purposes. The Alpha Systems AOA is comparably priced with a typical DG, AI, altimeter, etc., all of which work reasonably well for GA aircraft.

As for requiring an STC to install the AOA in a certificated aircraft, no, that's not true. We had to get a 337 because of opting for the electrically heated version, since it ties into the airplane's electrical buss. The Denver FSDO had no problem with that.

The Alpha Systems AOA probe is significantly dissimilar from Piper blade style pitot tubes. They may look similar, they may both have 2 holes, but there the comparison ends. To make a raunchy metaphor, just because a nun and a streetwalker appear to have the same equipment doesn't mean it's used the same.

As I intimated before, I suspect I have as good a set of gluteus maximus sensors as any experienced pilot, and for sure I can fly any airplane that I'm experienced in, without a working ASI--and I have had to do that. But just because I can doesn't mean I want to. I like the benefits of the AOA. If you don't want one, that's your choice--but it's not snake oil, and those who use an AOA are not less talented as pilots.

Cary

[EZFlap]

I have to agree that the AOA sensors mounted underneath the wing are prone to problems and will be affected by the flow field around the wing.

To be honest, the reason I mentioned AOA in the first place is that I've been sketching and head-scratching on an inexpensive AOA add-on that does not have these problems. Unfortunately most of our airplanes are not jets, so using a jet type "swinging wedge" (fuselage type) AOA probe will be negatively affected by propeller slipstream and thus not fully trustworthy. So I'm concentrating now on putting some sort of vane type AOA sensor up on the vertical fin, out of the prop wash and out of the wing wash. The big question there will be what effect a slipping maneuver would have on it. We'll seeee.....

[Zzz]

For those using these AOA indicators: Do you actually operate that close to the critical AOA for sustained periods that the information becomes valuable? Argue in favor all you want, but the scenario of a real world approach requiring such a high AOA is going to likely require more much awareness outside the cockpit. Unorthodox, non-standard approaches like Mile Hi, Dewey Moore, etc. By the time you've considered AOA in a scan you are behind the airplane and thinking too academically. There are times in an aircraft where it's like motocross or skiing. Usually when you're deep in a trench. I want minimal scan data like altitude and airspeed, possibly VSI -- that data is used for a lot more than just stall avoidance.

AOA might be useful for those curious about such things, but it seems more novelty that anything else, at least for a light aircraft. Perhaps as a flight test instrument.

Littlenub-- better to be an ass than a whiner.

[mtv]

Like everything else in life, you pay your money and make your choice. I paid my money, I made my choice, and I'm very satisfied with doing so.

In your "tests" of the 185 with the AOA installed, I doubt that you materially changed the weight you were carrying, or the ASI would have shown a much lower airspeed at light weights than at gross weight, assuming that the AOA was correctly installed and calibrated--it's fundamental aerodynamics that minimum controllable air speeds are significantly lower with lower operating weights. Thus, the ASI could not have shown the same information as the AOA.Cary

Cary,

What I said was that we each took the airplane for a period of time and WORKED it. That does not imply flying around at one weight, it means hauling loads.

And, my point was that the device provided no BETTER information than an ASI. What that means is that all the pilots involved in the trial stated that they could consistently operate the airplane more precisely than EITHER device would permit, if we followed the guidance of either.

A pilot's butt, properly "calibrated", will afford a better handle on where the airplane's at.

As to FAA approvals--your argument may apply in YOUR FSDO district, but not in a lot of others. There is headquarters guidance on this subject that instruments require an stc. Yet, the manufacturer of these things is still letting the buyer figure out how to get them approved. And, in fact, the manufacturer is stating that NO approval is required, which is wrong. Try to get one of the little Dynon EFIS units approved in a certified airplane, for example. VFR only, so this is clearly NOT primary instrumentation......no go. Further, you cannot PERMANENTLY mount ANYthing in a certified airplane without some "basis". Your mechanic may be brave enough to install one of these as a "minor" but I'm betting the FAA in a LOT of districts won't go for that either.

FInally, if these things are SO great, why doesn't the manufacturer go ahead and STC them. After all, they are the greatest thing since sliced bread, so it couldn't take much, and soon they'd have em mounted on every airplane in the country. Of course, that would mean they'd have to actually do some flight testing and documentation themselves....

Or not.

MTV