AV-20 or AV-30 for AoA?

Camera's, GPSs and other Gizmos (please let me know if you find an existing thread to be moved into this NEW section)
Post Reply
CRAZEDpilot
Posts: 76
Joined: Thu Jan 24, 2013 4:14 am
Contact:

AV-20 or AV-30 for AoA?

Post by CRAZEDpilot »

Anyone using Uavonix AV20 or AV30 for Angle of Attack? How accurate has it been ?

User avatar
HeavyLoad
Posts: 99
Joined: Wed Jun 21, 2017 9:46 pm
Location: Battle Ground, WA
Contact:

Re: AV-20 or AV-30 for AoA?

Post by HeavyLoad »

I'm curious too. Since it's a probless AOA would be nice to know if it works "good enough"
===========
M5-210C
RV6

CRAZEDpilot
Posts: 76
Joined: Thu Jan 24, 2013 4:14 am
Contact:

Re: AV-20 or AV-30 for AoA?

Post by CRAZEDpilot »

Sadly I emailed Uavionics and their answer was "The AoA data on the AV-20-S is not for improving your short field landings.".

I wish their support people better understood what their AoA can do..... i have a feeling they're WRONG IN THEIR REPLY but it's
kinda sad to get such a response, not confidence inspiring.

-Brendan

User avatar
andy
Site Admin
Posts: 1310
Joined: Mon Aug 06, 2007 2:05 pm
Location: Lake James, NC, USA
Contact:

Re: AV-20 or AV-30 for AoA?

Post by andy »

AV-20 and AV-30 derive the AoA through computerized comparisons of flight path and pitch using the internal AHRS, airspeed and vertical speed. They don't actually measure airflow like other AoA sensors. The AV-30 user guide says that they are only supplemental and they do not replace the aircraft's existing stall warning system. The best AoA would actually measure airflow over the wing and sense when the air on the top is starting to separate. Here's a good explanation of the two main methods: https://www.flyingmag.com/how-it-works- ... indicator/. I think direct measurement of air pressure using a calibrated probe is a more reliable method of sensing an imminent stall than derived measurements from an AHRS.
Andy
1986 MX7-180

Lmjr
Posts: 12
Joined: Sat May 18, 2019 8:03 am
Location: Anchorage
Contact:

Re: AV-20 or AV-30 for AoA?

Post by Lmjr »

I have a AV-30 which I really like. With that being said I would not install one for the AOA feature alone - especially to use on landing. I don't think it is precise enough nor is it in the pilots line of sight during short final to be of much help.

Kirk
100+ Posts
Posts: 567
Joined: Tue Oct 17, 2006 3:07 pm
Location: KGCY
Contact:

Re: AV-20 or AV-30 for AoA?

Post by Kirk »

I’ve always been skeptical of the probeless AOA. It will only be as accurate as the airspeed and attitude input. The airspeed indicator’s acurracy and response rate decreases at lower airspeed. Haven’t flown with either system, but my gut instinct is that the probeless systems won’t add much to what the seat of your pants should be telling you.

Not many of the probe systems display values fine enough to really work the ragged edge of a stall either. You’d have to get down to 1 degree or so increments. Liability concerns will keep most manufacturers from producing a system that you would truly use for primary pitch and airspeed control. More of an awareness system.

Personally, I wouldn’t bother with a probeless system, but keeping an open mind until I fly one or both.

Fun fact: If you have an EFIS that displays Flight Path Vector (FPV) you already have an AOA. The difference between indicated pitch and the FPV is your AOA.

Kirk

User avatar
captnkirk
100+ Posts
Posts: 940
Joined: Wed Dec 25, 2013 4:54 pm
Location: Cherryville NC
Contact:

Re: AV-20 or AV-30 for AoA?

Post by captnkirk »

I have a SafeFlight AoA installed, I love mine it is very easy to adjust flight path to make a landing. I flew many aircraft in my past with AoA systems once you get use to using one you won't want to be with out it. I chose SafeFlight based on their history of making stall warning systems for many years. The only downside to their system is the indicator can be a little hard to see if there is a lot of glare. I added a small hood to block that and all is fine now. I mounted mine on the glare shield in my line of sight . I have seen the Alpha systems unit and it has a big display and I know Gbarrier likes his. They operate on different theories but basically give the same results. One of the great values is knowing how close you may be to the stall is handy when making a short field landing keeping airspeed low but in a safe margin. A lot of people will say all you need is the feel of the airplane but it sure helps to have a way to quantify it.
Kirk Johnson
If god had meant man to fly he would have given him more money

User avatar
andy
Site Admin
Posts: 1310
Joined: Mon Aug 06, 2007 2:05 pm
Location: Lake James, NC, USA
Contact:

Re: AV-20 or AV-30 for AoA?

Post by andy »

Airspeed Indicator
We are all taught to use the airspeed indicator as a guide to knowing when the wing is approaching a stall but it's not very accurate at low airspeeds. When I flew in the Idaho back country in 2016, Lori MacNichol's flight instructor Gary and I did stalls in every flap configuration and maneuver at altitude and recorded the airspeed and configuration when the actual stall occurred. The result was a data card that I Velcro'd to the panel in the airplane. However, we were still using the airspeed indicator. At full flaps (48), the airspeed indicator barely registered during actual stalls and I know it wasn't accurate. The vortex generators helped to delay the stall and made the airplane much more controllable at low airspeeds. I'm a true believer in vortex generators.

Stall warning indicator
The stall warning indicator in my Maule is a panel light activated by a microswitch coupled to a metal tab on the leading edge of the left wing. That's a better indicator of actual airflow but still not very accurate at low airspeeds since it doesn't sense the separation of air over the top of the wing - just the pressure difference on the top and bottom of the metal tab. The microswitch is an on/off sensor with nothing in between so it has to be installed in such a way that it operates prior to a stall. You don't have any way of determining how close you really are to the stall when the light comes on. At altitude you can always continue to raise the nose until a buffet, break or mush occurs to figure that out, but you don't want to try that on landing when you're too low to recover. Another problem with the microswitch arrangement is that it doesn't account for a change in stall characteristics caused by after-market vortex generators like I have on my airplane. The metal tab on the microswitch would have to be re-calibrated with vortex generators installed. Maybe the new Maules coming out of the factory with vortex generators have been calibrated differently.

AoA
An AoA sensor helps most in the area between when the stall warning indicator comes on and when the actual stall occurs. It's most valuable on landing in my opinion. It's not a perfect solution since it still doesn't directly sense the beginning of air separation over the top of the wing. The AoA sensor is usually mounted in a different location than the top of the wing. You could always tape a bunch of string or yarn segments to the top of the wing and watch them wobble on a low wing. Of course you can't see them on a high wing unless you mount a camera up there. Maybe two sensors in the leading edge and trailing edge in front of the flap that measure the difference in pressure would be close to ideal. When the air starts to separate on top of the wing the pressure at the aft sensor would be much lower than the pressure at the forward sensor.

AoA sensors can also help during cruise to detect a fuel-efficient angle of attack. More power results in a lower angle of attack at the same altitude but also produces more fuel burn. Less power reduces fuel burn but requires a higher angle of attack to produce enough lift to maintain altitude. Some AoA indicators have markings or lights that show optimal AoA for fuel efficiency. You could also use that to determine the best balance between prop RPM and MP with a constant speed prop. It would be better than relying on the engine manufacturer's charts, which ignore the airplane's lift and drag characteristics. You could start with the engine manufacturer's setting for a particular altitude and then reduce the throttle/MP while pitching aft to maintain altitude and watching the AoA until it moves to the edge of the green range. Then you could see what effect changes in prop RPM have on AoA, ground speed and fuel burn at that throttle setting.

Here's a good article from Boeing on AoA: http://www.boeing.com/commercial/aeroma ... story.html . Maule drivers don't have to worry much about mach speeds or takeoff performance charts but there are several cautionary notes about over-reliance on AoA sensors.

Many of us have flown our Maules so long that low airspeed handling is as good an indicator as AoA. That doesn't help a new Maule pilot very much. However, AoA can help experienced pilots too. The point at which a wing stalls is set in the design of the curvature of the top of the airfoil. We fly at different AoA depending on weight, CG, wing load, flap setting, wind and power setting so the difference between the AoA and stall point is a product of multiple factors that are difficult to calculate mentally while flying. Sometimes even experienced Maule pilots get into a situation where some combination of these factors is unfamiliar. AoA indicators can give us a good idea of how close we are to a stall before we feel the buffet or mushiness without going through a lengthy and distracting mental process to evaluate all of the factors. That could result in a faster reaction to counter an imminent stall, which is even more important during a critical phase such as landing.
Andy
1986 MX7-180

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest