Easiest retrofit stall warning system?

[SwimmingDragonfly96]

Hello awesome people,

I bought a flying 7A and I would like to incorporate some kind of stall warning system into it. Would it be easier to retrofit the vans stall warner or should I go with an AOA system (likely Garmin)? I don't need anything to be fancy, just functional and within my installation abilities (which are minimal at this point but I'm sure I could find someone to supervise). Cost is not as important as functionality and ease of retrofit.

Thanks!

 

[Tommy123]

You'll need a AOA capable pitot tube for AOA and run another hose through the wing

 

[WingsOnWheels]

Hello awesome people,

I bought a flying 7A and I would like to incorporate some kind of stall warning system into it. Would it be easier to retrofit the vans stall warner or should I go with an AOA system (likely Garmin)? I don't need anything to be fancy, just functional and within my installation abilities (which are minimal at this point but I'm sure I could find someone to supervise). Cost is not as important as functionality and ease of retrofit.

Thanks!

Do you currently have a glass panel? If so, most support AOA with the right hardware. If not, then there are a few standalone options.

 

[BobTurner]

I’m at LVK and currently down for annual Condition inspection. I have both Vans simple system and AOA. Stop by if you’d like to talk, As others have said, the ease and cost depends on what’s already in the panel. IMHO AOA is vastly superior but does cost more.

 

[SwimmingDragonfly96]

Hey Bob, thank you but unfortunately I'm in San Diego until Monday of next week or so, otherwise I would totally come check it out.

I do not have a glass cockpit so it's either retrofitting an AOA/pitot (might as well upgrade to heated pitot in the process) or retrofitting the vans stall Warner. I would be interested in the AOA setup, however, the few threads I've read about retrofitting seem to mention issues with running the AOA line through the wing after the plane has been built.

I'm really looking for the easiest retrofit option for a stall warning device... e.g. is it easier and even feasible to retrofit the vans stall Warner vs. retrofitting an aoa?

 

[BobTurner]

Well, I’d say the original stall warning is easier especially if the slot in the wing is still there. Access to get the switch installed is poor, but not impossible. After that you run two wires to a buzzer or better, a tone generator hooked to your audio panel. For AOA you need a second nylon tube attached to a new pitot tube with a second, angled port (both Garmin and Dynon sell them); pressure sensors, plus electronics to compare pitot pressure to the new port pressure, tone generator, etc.
If/when you upgrade the pitot to a heated one, get one with a temperature controller. If you’ve ever burned your hand by touching a hot pitot on the ground, you’ll be glad you did.

 

[lr172]

Hey Bob, thank you but unfortunately I'm in San Diego until Monday of next week or so, otherwise I would totally come check it out.

I do not have a glass cockpit so it's either retrofitting an AOA/pitot (might as well upgrade to heated pitot in the process) or retrofitting the vans stall Warner. I would be interested in the AOA setup, however, the few threads I've read about retrofitting seem to mention issues with running the AOA line through the wing after the plane has been built.

I'm really looking for the easiest retrofit option for a stall warning device... e.g. is it easier and even feasible to retrofit the vans stall Warner vs. retrofitting an aoa?

For AOA, you will need some kind if intrument to process and display. As to the new pitot, that can be dealt with. I had a gretz heated pitot that came with my 10 kit and didn't want to buy another one with the AOA port. I did some research on how Vans does this with the 12. Ended up putting a rivet in the leading edge (same arrangement as static ports) and it works great. Placement of rivet is important

 

[olyolson]

Stand Alone AOA

Amir,

I just did this with my RV-8 and researched a couple options. The Garmin GAP 26 kit may work for you or if you want a bit of “do it yourself work” you can opt for the FlyOnSpeed system (https://www.flyonspeed.org/gen-2). The installation of the Flyonspeed system seemed a bit too complicated for me but you may have more experience in this area.

I have an Advanced Flight Systems EFIS so it was a no brainier to just replace my heated pitot tube with a Dynon heated pitot/AOA probe with controller. I did have to run a separate AOA tube back to the Adhars but it wasn’t difficult, just required a bit of grunt work to remove the lower left wing panels, the left side wing/fuselage fairing for access and of course some of the floors in the cockpit to get the line back to the ADHARS behind the aft baggage compartment.

In your case a Garmin GAP-26 heated AOA system may offer you an easier acceptable solution. Even though Aircraft Spruce says that this cannot be used as a stand alone system this is incorrect according to Garmin. I contacted them directly and they stated that it can be installed and used as a separate AOA system with the GI-260 externally mounted display. According to my e-mails with Garmin, the calibration does not have to be done on the G3X, it can be done directly on the GI-260 display using the Test button. G3Expert can chime in here but all the online data indicates that you have to have the G3X but evidently that is not true.

You will need the pitot mast to mount the probe so hopefully you already have one of those on the wing. The GI 260 display receives AOA input from a GSU 25 air data computer connected to a GAP 26 probe so you will need these plus associated tubing and fittings and of course a pitot mast to mount the probe on the bottom of the wing. This is not a cheap setup at around $1700 but would be a very capable and professional solution. I’ve flown a buddy’s RV-8 with the external GI-260 display (but he also has the G3X) and the display worked perfectly. He had his display offset to the left to stay out of direct view on approach but easily seen. I ended up just listening to the tones anyway and really liked the system. Picture below shows the AOA on the left side of the glare shield but he wired his so it is also displayed in the EFIS as well.

 

[tthrew]

uAvionix AV-30-E

I have no experience with the uAvionix AV-30-E, but I know it has synthetic AoA, which means no cutting a hole in the wing, or pitot tube change, etc. Kitplanes did a review in October 2020, and there are other reviews and explanations of how it works if you Google it. I’m thinking this would be the easiest way to get some kind of stall warning/AoA.
My plane didn’t have any stall or AoA originally either - I flew it like that for years before I did a major panel upgrade (from steam to dual HDX) and then I upgraded the pitot & ran the additional AoA tube. Hardest part was where the wing walk is with the additional ribs.

 

[SwimmingDragonfly96]

I have no experience with the uAvionix AV-30-E, but I know it has synthetic AoA, which means no cutting a hole in the wing, or pitot tube change, etc. Kitplanes did a review in October 2020, and there are other reviews and explanations of how it works if you Google it. I’m thinking this would be the easiest way to get some kind of stall warning/AoA.
My plane didn’t have any stall or AoA originally either - I flew it like that for years before I did a major panel upgrade (from steam to dual HDX) and then I upgraded the pitot & ran the additional AoA tube. Hardest part was where the wing walk is with the additional ribs.

Thank you for this! I have a panel update sitting in my closet with two G5s so a 30 might not fit the bill, however, this got me looking into AV20s which are inexpensive and also have the AOA option. Going to dig in to how functional it is for that.

 

[Ironflight]

I have no experience with the uAvionix AV-30-E, but I know it has synthetic AoA, which means no cutting a hole in the wing, or pitot tube change, etc. Kitplanes did a review in October 2020, and there are other reviews and explanations of how it works if you Google it. I’m thinking this would be the easiest way to get some kind of stall warning/AoA.
My plane didn’t have any stall or AoA originally either - I flew it like that for years before I did a major panel upgrade (from steam to dual HDX) and then I upgraded the pitot & ran the additional AoA tube. Hardest part was where the wing walk is with the additional ribs.

My experience with "derived" AoA has been very mixed - I've had it in the GRT EFIS on my RV-8 for close to twenty years. I also have an AFS AoA Pro on the dash of that airplane, and comparing the two has shown me that the derived AoA is OK in steady-state approach conditions, but if things are changing rapidly (or even sort-of-rapidly), the derived AoA doesn't keep up very well - so I'd be hesitant to call it an acceptable solution for an AoA system by itself.

 

[tthrew]

Thanks Paul

I was hoping my post would get a response from someone with experience using this type of AoA. Thank you for commenting, Paul.

 

[BobTurner]

My experience with "derived" AoA has been very mixed - I've had it in the GRT EFIS on my RV-8 for close to twenty years. I also have an AFS AoA Pro on the dash of that airplane, and comparing the two has shown me that the derived AoA is OK in steady-state approach conditions, but if things are changing rapidly (or even sort-of-rapidly), the derived AoA doesn't keep up very well - so I'd be hesitant to call it an acceptable solution for an AoA system by itself.

+1. I have both the ‘direct measurement’ (second air pressure sensor) AOA with a Dynon D6, and the ‘derived’ (calculated) AOA from a GRT Hx. As ironflight said above, they agree well on smooth approaches to landings, but the derived system lags in any sort of rapid maneuvers. I think GRT itself acknowledges this: newer GRT EFIS boxes use the direct, second sensor method. Note to OP: For the cost of the stand alone Garmin AOA system mentioned earlier, you can buy a complete mini-Efis (Dynon D6, GRT mini (some models)) which include AOA. IMHO the audio warning tones are much more practical than the visual gauges.

 

[FinnFlyer]

Second tube run

Is it really more difficult to run the AOA tube through (half) the wing than the wire required for Van's stall warning device?
I may be wrong but a 1/8" or 3/16" tube would work.

If you already have a G5 in your closet why not install it?

As for AOA rivet near wing leading edge it works for me in my RV-4. Can't easily do it on my RV-3B because of factory-built wings -- no lightening holes in the main spar web. But if you can reach leading edge through inspection hole in bottom of wing, that certainly is a low-cost AOA port solution. But if money is no object go with a pitot with AOA port.

Finn

 

[SwimmingDragonfly96]

Is it really more difficult to run the AOA tube through (half) the wing than the wire required for Van's stall warning device?
I may be wrong but a 1/8" or 3/16" tube would work.

If you already have a G5 in your closet why not install it?

As for AOA rivet near wing leading edge it works for me in my RV-4. Can't easily do it on my RV-3B because of factory-built wings -- no lightening holes in the main spar web. But if you can reach leading edge through inspection hole in bottom of wing, that certainly is a low-cost AOA port solution. But if money is no object go with a pitot with AOA port.

Finn

From my understanding, I don’t think the G5 supports AOA?

 

[Pilot135pd]

I installed an OnSpeed AOA system in my RV-8 with a heated pitot and it's super easy. My knowledge isn't good enough to build a plane but running the tubes through the wing is extremely easy so don't let that part influence your decision. I have a couple more pictures if you want me to email them to you.

I placed a PEX tubing through small holes and pushed the pitot hoses and heater wires inside to protect them. Very easy to do.

 

[SwimmingDragonfly96]

Thanks everyone for all your replies, as mentioned in most of my posts, I have immense appreciation for this group. I decided to go with an AV20s. Not the greatest, but better than nothing, and I'm not ready to cut holes in my airframe
(maybe some day?).

 

[fasilpereira]

AOA

Hi Amir,

I don't have much experience with AOA, but I believe that if you are looking for something really simple, stall warning only, the Vans style is the way to go. Very simple installation with just a switch on the wing (2-wires) and a tone generator with a signal to the intercom.

But if you are looking for an AOA indicator, with approach cue, that depend on what you have on the panel.

If you do have an EFIS that is AOA capable, all you need is an AOA probe and some tubes.

If you don't have an EFIS with AOA capability, a stand-alone AOA is the way to go. The Garmin system is too expensive, but maybe you can find a legacy AFS AOA system or an equivalent one for sale.... by the way, I have one available

Good luck!

Fabricio

 

[Vac]

Applying Derived AOA

Since Amir decided to go with a system using derived AOA, let’s take a short look at what that is…

It means AOA derived by an inertial measurement unit (IMU). If the IMU can compute pitch and flight path angle, the difference between the two is AOA (technically “body angle,” but close enough for what we are trying to accomplish). It’s easy to picture this in level flight as shown in this diagram:

Things get more complicated as the airplane maneuvers or encounters rough air, as Paul points out. The processing power required to compute a tight attitude solution and flight path goes up; and good code is required that can handle the matrix calculus and Kalman filtering required. With the right IMU, processor and software, an accurate all-attitude, high-G capable derived AOA is in the art of the doable.

We currently use derived AOA to calibrate the ONSPEED system. This is a more primitive use of the capability but illustrates how it works using the relationships shown in the picture above. Our current processor doesn’t have the muscle to run advanced derived AOA code and keep up with all of the other functions required for flight test…

A calibration run consists of a deceleration from Vmax (as fast as the airplane will go in level flight) to stall. The IMU computes pitch and flight path angle and compares that to the coefficient of pressure as the airplane slows down and AOA increases. “Coefficient of pressure” is just a fancy way of saying one pressure divided by the other one (or using a geometric function to compare the two). This captures AOA for the entire speed range of the airplane very accurately. When you plot this out, it looks like this:

What’s neat about the physics is that the relationship between AOA the coefficient of pressure is nearly linear as AOA increases. When we take those hundreds or thousands of data points (depending on the clock speed the system is running, this plot shows 50 data points per second), it’s easy for the computer to condense all those points into a simple equation that can then be used to compute AOA from pressure data.

Some folks have pointed out that AOA is non-linear as stall is approached. This is correct, but we can demonstrate that it doesn’t matter to the AOA system. Here is a simple, wing’s level pull from level flight to a stall about 40 degrees nose up. The plot shows pitch (blue line) and AOA (red line). Note that even though the pitch input is linear (constant over time) the AOA increases in the shape of a parabola (increasing over time). That should remind you of the shape of the left side of the flight envelope .

If we compare IMU-derived AOA with coefficient of pressure for this more extreme example, the relationship is still linear:

In a perfect world, the AOA system would compare IMU derived AOA with pressure derived AOA and warn the pilot when the two disagree. We're working on that.

Cheers,

Vac

 

[Pilot135pd]

Since Amir decided to go with a system using derived AOA, let’s take a short look at what that is…

It means AOA derived by an inertial measurement unit (IMU). If the IMU can compute pitch and flight path angle, the difference between the two is AOA (technically “body angle,” but close enough for what we are trying to accomplish). It’s easy to picture this in level flight as shown in this diagram:

Things get more complicated as the airplane maneuvers or encounters rough air, as Paul points out. The processing power required to compute a tight attitude solution and flight path goes up; and good code is required that can handle the matrix calculus and Kalman filtering required. With the right IMU, processor and software, an accurate all-attitude, high-G capable derived AOA is in the art of the doable.

We currently use derived AOA to calibrate the ONSPEED system. This is a more primitive use of the capability but illustrates how it works using the relationships shown in the picture above. Our current processor doesn’t have the muscle to run advanced derived AOA code and keep up with all of the other functions required for flight test…

A calibration run consists of a deceleration from Vmax (as fast as the airplane will go in level flight) to stall. The IMU computes pitch and flight path angle and compares that to the coefficient of pressure as the airplane slows down and AOA increases. “Coefficient of pressure” is just a fancy way of saying one pressure divided by the other one (or using a geometric function to compare the two). This captures AOA for the entire speed range of the airplane very accurately. When you plot this out, it looks like this:

What’s neat about the physics is that the relationship between AOA the coefficient of pressure is nearly linear as AOA increases. When we take those hundreds or thousands of data points (depending on the clock speed the system is running, this plot shows 50 data points per second), it’s easy for the computer to condense all those points into a simple equation that can then be used to compute AOA from pressure data.

Some folks have pointed out that AOA is non-linear as stall is approached. This is correct, but we can demonstrate that it doesn’t matter to the AOA system. Here is a simple, wing’s level pull from level flight to a stall about 40 degrees nose up. The plot shows pitch (blue line) and AOA (red line). Note that even though the pitch input is linear (constant over time) the AOA increases in the shape of a parabola (increasing over time). That should remind you of the shape of the left side of the flight envelope .

If we compare IMU-derived AOA with coefficient of pressure for this more extreme example, the relationship is still linear:

In a perfect world, the AOA system would compare IMU derived AOA with pressure derived AOA and warn the pilot when the two disagree. We're working on that.

Cheers,

Vac

And this is why I love the OnSpeed AOA system and everyone taking part in its development. Thanks Vac !!

 

[Scott Hersha]

I have a GRT Horizon with the AOA function included in my RV6. At first I tried the rivet in the leading edge of the wing for AOA sense and it didn’t work well at all. It may have been my plumbing, but I disconnected it. Then I purchased a Lift Reserve Indicator, which is a stand alone system that I had in my first RV6 20 years ago. It came with a probe that I didn’t like, but was able to get the original LRI probe from a very generous and locally famous VAF’er (Mel) and use that. I mounted the indicator where it would do the most good - right in my line of sight when landing, on top of the glareshield in my slider version…….. actually IN the top of the glareshield.



The probe Mel gave me, mounted under my right wing:



This AOA type system needs no power to operate, but I thought I might want to see it at night, so I took a 3 light LED piece cut off from my under the glareshield strip, soldered appropriate wires to it and taped it to the front of the indicator below the glareshield (behind the panel). It comes on with the panel flood light switch. I get a big grin on my face every time I turn it on, because it looks so cool and retro….



I have tried the “derived” AOA setup in my GRT Horizon, but like PD says above, it doesn’t work very well. So, since I have the AOA functionality in my Horizon, I decided to tap into the tube from the LRI probe that faces downward and connect that to my Horizon (it’s setting right there behind the EFIS). I went up and calibrated it, per instructions, and it works very well. So now I have a visual indication on my PFD, which is a feather that drops down to meet the horizon bar on the PFD when approaching the critical AOA. I pretty much never look at this because I’m not looking there when I’m landing - I’m looking forward and seeing the LRI indicator. But the Horizon system also has an aural tone that gets more rapid as I approach full flaps stall. None of these indications happen until you are slowed to an appropriate final speed on landing. The needle on the LRI is pegged out on the fast end above about 70-75 KIAS clean. It is in the middle of the green arc at about 65 KIAS full flaps, and hits the bottom of the yellow at about 50 KIAS depending on weight. The tone doesn’t start until within about 15% above critical, so it’s not a nuisance. Pretty good setup overall. Most of the times you don’t need this. These airplanes are pretty easy to land, but on a gusty day it might help from having the rug pulled out from under me at the very end.

 

[Ironflight]

Hey Scott, that is the neatest LRI installation I have ever seen! I like the LRI because of its economy, and the fact that it can be installed on “no electrical system” airplanes - I’m goign to show this to the AoA sub-committee I’m serving on, as we’re keeping track of all the available AoA systems on the market, and folks (including me) have always said that yeah, the LRI is neat, but it sure doesn’t “fit” in a modern panel.

I only wish they could figure out a way to give it a 9-volt battery and an audio circuit because I am more and more a believer in variable audio as a way of getting AoA info between the pilot’s ears, since the place I worry most about is turning flight, and when I am turning, I am generally looking in to the turn, and not over the glare shield. This is the problem with all visual AoA indicators - but you’re right that you are far more likely to see it on the top of the glare shield than buried on the EFIS….

Really nice work!

 

[rick9mjn]

i also am saying "SCOTT" ( nice install on your LRI ), also because the LRI uses a different probe and hoses, from probe to the indicator, it is a "real" back up fore the airspeed indicator. and anybody who has had a airspeed quit on them , they know, it a pain to deal with,,,,
fly / be safe / good day rick

 

[Scott Hersha]

Hey Scott, that is the neatest LRI installation I have ever seen! I like the LRI because of its economy, and the fact that it can be installed on “no electrical system” airplanes - I’m goign to show this to the AoA sub-committee I’m serving on, as we’re keeping track of all the available AoA systems on the market, and folks (including me) have always said that yeah, the LRI is neat, but it sure doesn’t “fit” in a modern panel.

I only wish they could figure out a way to give it a 9-volt battery and an audio circuit because I am more and more a believer in variable audio as a way of getting AoA info between the pilot’s ears, since the place I worry most about is turning flight, and when I am turning, I am generally looking in to the turn, and not over the glare shield. This is the problem with all visual AoA indicators - but you’re right that you are far more likely to see it on the top of the glare shield than buried on the EFIS….

Really nice work!

I agree. An audio input is a vital part of an AOA system. I have this with my GRT, but having it as part of a stand alone system, using a low voltage standby source is a great idea. It would be something that anyone could incorporate with little modification in a certified aircraft. Keep it simple.

 

[Walt]

That panel sure looks familiar.