I have a Advanced Flight Systems AoA indicator (http://www.advanced-flight-systems.com/Products/AOA/aoa.html) which was included in the purchase of my Wilga. I would really like to install it but the instructions say it requires a Form 337. I know that Alpha Systems AoA indicator has a letter from the FAA that says it's OK to install without this form. However the Alpha system does not tap into the original pitot/static system where the Advanced Flight system does. I suspect that because of this tap into the pitot/static lines, the Form 337 still applies.

Does anyone know how big a pain in the ass a Form 337 process is? Is it worth it? Any thoughts?

Thanks for any help,
-Ryan

The company should have a sample 337 & Approved Data, your A&P & IA signs. One copy for you and the other to OK City.

Do $5 Records check next annual to see if the 337 was filed. Optional.

Depending on how your FSDO is about giving field approvals, you may want to run it by them first. Typically if you have a copy of a previously approved field approval its not a problem, but that doesn't always mean they will or have to approve it.

xdillonx wrote:I have a Advanced Flight Systems AoA indicator (http://www.advanced-flight-systems.com/Products/AOA/aoa.html) which was included in the purchase of my Wilga. I would really like to install it but the instructions say it requires a Form 337. I know that Alpha Systems AoA indicator has a letter from the FAA that says it's OK to install without this form. However the Alpha system does not tap into the original pitot/static system where the Advanced Flight system does. I suspect that because of this tap into the pitot/static lines, the Form 337 still applies.

Does anyone know how big a pain in the ass a Form 337 process is? Is it worth it? Any thoughts?

Thanks for any help,
-Ryan

Ryan, Go put 100 hrs on the Wilga before you jump for the AOA, When you get down to the down and dirty of high AOA in the Wilga You won't be looking anywhere inside!
My $.02
You will find it is very very Stick is speed throttle is altitude in any given situation.
There are a couple of gotcha's in that bird that will surprise you.
Don't know if anyone has pointed out to you yet, if you lose power, immediately go to 70 kts!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! if not you will not have enough energy to round out to land?
You can go up and try this at altitude to see it is to believe!!

Tying into the aircraft pitot/static system is a big deal. That's what the big hold-up was getting an original Dynon approved for VFR use only in a friend's Swift. If the AOA gizmo killed the pitot static system, both the airspeed and altimeter would go away. I would get the approved 337 and see what was done and how it was approved preferably before buying anything, and definitely before mounting anything.

When it comes to ANY field approval, ALWAYS have your IA discuss the proposed mod with the FSDO. Then, have it approved by the FSDO, as in signed off. Then and only then do you start buying stuff and installing things.

As to installing one of these so called "AOA indicators" on a Wilga or most any other similar aircraft......buy gas instead.

MTV

I may not of understood the question...

Which type of install, STC (Supplemental Type Certificate) or FA (FSDO Field Approval)? FA requires FSDO sign-off and STC generally just a 337 with installer and IA signatures.

You can verify an STC applicability and procedures here:

http://www.faa.gov/aircraft/air_cert/design_approvals/stc/

FAA field approval guide & checklist:

https://www.faa.gov/aircraft/air_cert/design_approvals/field_approvals/field_approv_proc/

https://www.faa.gov/about/office_org/field_offices/fsdo/ric/local_more/media/Field%20Approval%20Checklist.doc

Looks like an FA:

http://www.advanced-flight-systems.com/Support/AOAsupport/AOA%20Manual%20rev4.pdf

Thanks for all the valuable input! I think M6RV6 and MTV are right that I should log MANY more hours in the Wilga before I go modifying it. After that I may start thinking about installing the AoA indicator. This would be much easier if the airplane was experimental. But since there are many hoops to jump through it will likely not be worth the time money or hassle.

This gauge was included as part of the purchase and is still new in box so no money wasted as of yet. I think that it's time for it to go up on eBay and use the funds to buy more blue.

Bottom line; I won't be installing the gauge.

-Ryan

Before the FAA's more recent AOA decision, there was a dispute in mechanic circles whether a 337 was required, and many IAs chose the conservative route. The FAA's letter solved that problem--no 337 is needed unless the AOA installation somehow cuts into an existing function of the airplane. For instance, my AOA indicator's probe is electrically heated, so a 337 was required to tap into the buss.

But according to the Advanced Flight Systems website, it's a stand alone installation. If it was packaged before the FAA's policy decision, then it would make sense that the instructions might say a 337 is required. But it's not, so long as it's considered a "minor alteration", and so long as AFS has the individual approval letter required by the FAA. Here's the FAA's policy document: http://rgl.faa.gov/Regulatory_and_Guida ... 0-PM01.pdf

I can't find on the AFS website any reference that says that they have the necessary letter of approval, but I'd be willing to bet that they do. You might explore their website more, and if it's not there, then ask them.

If the enhanced features were to be used, such as the gear down warning (whoever heard of a retractable Wilga? ), and if it's electrically heated like mine is, then the 337 route would be necessary. As long as it's stand alone, then it wouldn't.

Since you already own it, and it's a good system, I suggest looking into these issues before getting rid of it, then make your decision whether to install it. I don't want to start another argument about AOA indicators--we've beat that one to death in the past. Most who argue against them have not flown with one, or if they have, it's been a one or two time proposition. I'll leave it at this: I've been flying with mine for about 6 1/2 years and about 400 hours, and if I were to ever have another airplane, it would be one of the first items I'd have installed.

Cary

Steps:

#1 Call/email OEM

#2 Ask "What paper work would be needed legally to install?" (get it in writing too)

#3 Prepare paperwork

#4 install

Opinion: AOA is not needed if you develop your skills (VFR).

Cory,
This system ties into the pitot-static system, bus, and comm so I think that this paragraph excludes it from being installed:

"The AoA system must be a stand-alone unit and must not interface with a
certificated system (e.g., pitot-static system, stall warning, etc.) with the exception of supplying
electrical power to the AoA unit and mounting requirements for the sensor and the display unit."

If it were an easy hassle-free install, I would put in this weekend! But since it will most likely be a pain, I'll wait until I gather thoughts on the pros/cons.

I did e-mail the manufacturer asking them about 337 steps. No reply yet...

xdillonx wrote:Cory,
This system ties into the pitot-static system, bus, and comm so I think that this paragraph excludes it from being installed:

"The AoA system must be a stand-alone unit and must not interface with a
certificated system (e.g., pitot-static system, stall warning, etc.) with the exception of supplying
electrical power to the AoA unit and mounting requirements for the sensor and the display unit."

If it were an easy hassle-free install, I would put in this weekend! But since it will most likely be a pain, I'll wait until I gather thoughts on the pros/cons.

I did e-mail the manufacturer asking them about 337 steps. No reply yet...

As I said, the website indicates that it is a stand alone item, if you don't attach it to any of the electrical system. Since it works exactly like the Alpha Systems system, I'd be surprised if it taps into the pitot-static system. But I didn't read the instructions manual, although that's apparently on their website.

Cary

Cary wrote:...... I've been flying with mine for about 6 1/2 years and about 400 hours, and if I were to ever have another airplane, it would be one of the first items I'd have installed.

I'm curious as to what airspeed differences you see for the same AOA indication at light vs heavy weight? I can definitely see where AOA would be useful on a military aircraft, esp something like a bomber, where the airplane weight changes dramatically as you get rid of ordnance. On a GA airplane where the weight doesn't really vary that much, only about 900# difference for my airplane empty vs loaded to gross weight, not so much.

A friend of mine told me that another guy at his airport put an AOA indicator system in his Glasair and it enabled him to land shorter. I told my friend that he was able to land shorter because he was going slower. The AOA system may have helped him to determine a safe lower speed, but it wasn't a magic wand. My friend put on in his RV6, but I haven't ever quizzed him about it. He's never brought it up, so I suspect that it didn't make an earth-shaking difference in his flying.

hotrod180 wrote:

Cary wrote:...... I've been flying with mine for about 6 1/2 years and about 400 hours, and if I were to ever have another airplane, it would be one of the first items I'd have installed.

I'm curious as to what airspeed differences you see for the same AOA indication at light vs heavy weight? I can definitely see where AOA would be useful on a military aircraft, esp something like a bomber, where the airplane weight changes dramatically as you get rid of ordnance. On a GA airplane where the weight doesn't really vary that much, only about 900# difference for my airplane empty vs loaded to gross weight, not so much.

A friend of mine told me that another guy at his airport put an AOA indicator system in his Glasair and it enabled him to land shorter. I told my friend that he was able to land shorter because he was going slower. The AOA system may have helped him to determine a safe lower speed, but it wasn't a magic wand. My friend put on in his RV6, but I haven't ever quizzed him about it. He's never brought it up, so I suspect that it didn't make an earth-shaking difference in his flying.

I have even less difference between lightly loaded and fully loaded than you do. The lightest I'm likely to fly is just me, quarter tanks, and my usual "baggage" (tow bar, oxygen set, survival kit), which adds up to about 310 lbs, or around 1660 lbs. With a lowered gross to 2350 from 2500 due to the engine conversion, there's a 690 lb. difference. At pretty close to full gross, the approach & landing speeds using the AOA mimic the book, about 65-70 mph. At lightest weights, I knock about 10 mph off that.

I would agree that it doesn't make an earth-shaking difference, but a 10 mph difference is a 15% reduction, and that's at least significant, in touch down speed and roll out distance.

Cary

That is significant.
Your engine upgrade lowers the gross weight? First time I've heard of that, usually it leaves it alone or hopefully increases it. For example, my C150/150TD had a 1760# gross per the STC, vs a 1600# gross stock. Which was good, as it was quite a bit heavier than the normal stock airplane-- 1240 or so empty vs 1100 or so for my first airplane, a stock 1969 C150J.

My biggest reason for wanting one is the incredible inaccuracies in our simple pitot-static systems at any attitude other than level flight cruise.

Flying in aircraft with sensitive p-s systems (orange gear: highly calibrated with swivel-head pitots) and comparing indications with the production equipment showed pretty big differences when the relative wind wasn't aligned with the pitot tube. Though these are sometimes predictable, sometimes there are cliffs. I think getting an honest indication every time will help build consistency. Consistency will give a head start to learning how the plane should feel in more difficult phases of flight.

Plus I think it'd be nice to have an actual indication of wing AoA. But that's my reasons for getting one. Ymmv.

CamTom12 wrote:My biggest reason for wanting one is the incredible inaccuracies in our simple pitot-static systems at any attitude other than level flight cruise.

Flying in aircraft with sensitive p-s systems (orange gear: highly calibrated with swivel-head pitots) and comparing indications with the production equipment showed pretty big differences when the relative wind wasn't aligned with the pitot tube. Though these are sometimes predictable, sometimes there are cliffs. I think getting an honest indication every time will help build consistency. Consistency will give a head start to learning how the plane should feel in more difficult phases of flight.

Plus I think it'd be nice to have an actual indication of wing AoA. But that's my reasons for getting one. Ymmv.

Okay, you're seeing and flying with "real" AOA systems. Before you jump on one of these "general aviation AOA indicators", take a good look at:

1) The sensor: Every one of the sensors I've seen on these things look mysteriously like a pitot/static head for experimental aircraft from Aircraft Spruce, and remarkably similar to the pitot/static head of a Piper Warrior. In other words, the things are "measuring" the AOA based on almost exactly the same data that's being fed into an airspeed instrument. Essentially, you're now using lights instead of a dial to suggest AOA. Maybe.

2) Mounting location of the sensor: These are without exception mounted assymetrically on the airframe, as in out on a wing. For obvious reasons, the most obvious being a propeller. Nevertheless, our wings are not always moving at the same speed, nor are they always at the same AOA in regular flight regimes. Now, maybe this difference between wings isn't enough to make a big difference, BUT every sophisticated AOA sensor system I've seen includes a means of measuring AOA of each wing and averaging.

After all, a spin is a flight regime where one wing has a greater AOA than the other. So, again, I'm assuming that these "AOA systems" for GA figure this into their algorithms (or whatever voodoo they claim to use) and actually INDICATE a slightly higher AOA than the wing actually sees, for saftey's sake.

All of which suggests to me that we can do just as well with an A/S indicator, or better yet with our butts than one of these things can do.

Finally, as Hotrod180 suggests, the difference in weight of a fully loaded F-18 compared to a nearly empty F-18 is vastly different than thatcomparison of a Cub or 172/182.

Put your butt in the plane and work it. I would bet that very shortly, you'll be able to work it quite a bit tighter by feel than you ever will with a "Colored Light Airspeed Indicator" or CLAI for short.

The F/A 18 has a real AOA system.

MTV

There are so many indirect (implied) and direct (explicit) pre stall characteristics in a small Part 23 aircraft. If a pilot can't fly with normal indicators of a stall or is dangerously close to stalling and needs an AOA, then aviation has got a problem.

Opinion....

Go fly and learn what the characteristics are, and don't forget.

Disclaimer: never flown a Wilga so no empirical guidance but, 8GCBC is freaking hard to fully stall

MTV,
I've actually only flown one aircraft with an AoA: the mighty T-38.

To your points, which are good points:

1) I'm going to get a CYA-100. It's not based on differential pressures

2) That's a really good point, but we do the best we can. I still think it'll be fine on one wing as I'm not planning any spins and won't be looking at it if I get into one.

I totally agree that feeling the aircraft is the best way to fly our GA craft, but I also think an AoA will help me personally build consistency and confidence in slowing up as much as I can in the landing phase. I'm sure I won't even need it eventually, but I think it can accelerate the learning process.

Cam

My comment re asymmetry was referring to a condition where you're close to the stall, but closer to the stall with the wing that doesn't have a sensor. It's possible to stall one wing while the other flies.

Gust of wind, vortex, etc could put you there. A well trained butt will feel that. One of these "one size fits all" devices may not.

To prevent that, they're going to have to work with more margin, hence not max performance.

Maybe

MTV