Angle of Attack Indicator installation

Henry L. Heaberlin · Post by **Henry L. Heaberlin** » Tue Aug 14, 2012 6:32 pm

I have always been interested in an angle of attack indicator for my M5-235C. The old LRI system was looked at, but I was concerned about FAA legality and approvals. AOA Systems seems to have "worked around" the FAA issue with their system being classified as a minor modification. Have any of you guys (or ladies) successfully installed one of these systems in your Maule? If so, where did you install the probe and how did you do it?
AOA appears to push the idea of using an inspection plate "replacement" on aircraft with screwed on inspection plates. Of course we have the snap on
inspection plates. So, that leaves either installing another inspection plate with the ring on inside of the wing skin (i.e. Cessna) or use their pitot mast/plate as a doubler installed externally on the wing. Maule wing skin is
notoriously thin and tends to "oil can" some what in the slip stream. Any thoughts on methods of mounting and possible issues would be appreciated.

noe flightrisk · Post by **noe flightrisk** » Tue Aug 14, 2012 10:23 pm

Do you mean Alpha Systems? If so, my experience with the old LRI may help.

I mounted an old-style LRI at an inspection plate location just forward and inboard of the pitot on my M7-235C. I replaced the snap-on inspection plate with a round disk of about 1/8" thick stainless having a slot for the probe and holes for screws that fasten to the plate that the probe comes on. The probe plate is mounted inside the skin, and the SS disk outside. If I recall correctly, the probe plate is wider than the inspection hole, so tightening the screws secures the whole assembly.

The assembly does have some slight slop due to oil canning, but in flight the LRI behavior is very consistent (I'm a quant jock, so trust me, I've measured). Due to interference with a structural tube behind my panel, I had to mount the readout low on the panel. I thought this would be an issue, but have developed a method that works: On approach I first use the LRI to adjust AOA to desired value, note the ASI reading to the nearest mph, then fly by reference to airspeed.

At your target approach AOA and full flaps you'll see up to 5 mph difference in approach airspeeds depending on load state, which is certainly enough to make a big difference in the flare. Note that the target reading on the LRI will be different for each flap setting.

Henry L. Heaberlin · Post by **Henry L. Heaberlin** » Wed Aug 15, 2012 6:24 am

Yes, I did mean to say Alpha Systems.... Sounds like you arrived at the same overall conclusion I did. Thanks for the ideas... Seems like the LED display would be easier to interpret at a glance than the older mechanical
guage they still offer. I take it from your discussion that you like the system. I have "reinforced" the pitot mast installation in years past with a doubler channel from the back side to reduce the vibration and possible metal fatigue of the skin there, so I am familiar with the issue. Sounds like a project I need to undertake...

Philouamt · Post by **Philouamt** » Tue Aug 21, 2012 1:07 pm

Hi,
i'm very interested by your discussion because i'm quite familiar with the alpha system and i would like to work with for mountain fly (short landing with differents weight...) on my maule. I have a M7c235. Could you give more detail about this ? A stc is available ? could you send me some pics ?
I'm in france and we have only few maule under France reg, so i have some difficulties to found infos....
Thanks very much for your help.
Regards,
philou

Henry L. Heaberlin · Post by **Henry L. Heaberlin** » Tue Aug 21, 2012 1:59 pm

Philou: As I understand it the FAA in the U.S. consider the installation of this device as not critical to flight, but as a useful addition. As such they have issued a letter indicating that it is considered by them to be a minor modification and an STC is NOT required in the U.S. for installation. In France I doubt things would be so simple. Jeremy or so one more familiar with overseas requirements might be able to shed some light on the question. I would encourage you to read all of the available data on the Alpha Systems web site and possibly call them and talk to a tech rep to see if they have any ideas. Prior to the minor modification letter people were installing the units here in the U.S. with field approval from the FAA as I under stand it. The factory folks might have some experience with the French or European aviation authority. That is way outside my level of expertise. Good luck.

maules.com · Post by **maules.com** » Tue Aug 21, 2012 11:36 pm

I took an M7 over to Vanuatu with the AOA installed and it was accepted there under New Zealand rules but I have no idea of the French certificate rules.

Philouamt · Post by **Philouamt** » Thu Aug 23, 2012 6:49 am

Thanks a lot for your reply, the Caa in France is a pain... i called them today and they request a technical study. I'm quite sure that they will request a proving fly blablabla. If someone who has the system on board could you send me some pics ?
If someone in Europe did it before with the EASA i will maybe avoid the suicide

Enjoy

Philouamt · Post by **Philouamt** » Mon Aug 27, 2012 10:55 am

Hi Jeremy,
where was the AOA sensor on the Maule ? i'm thinking to put it under the wing...in the middle and in the front of the shroud.
Thanks

maules.com · Post by **maules.com** » Mon Aug 27, 2012 12:04 pm

The sensor probe was mounted under the left wing.
The forward edge of the mounting plate was about 9" back from the leading edge skin joint and the outboard side of plate was adjacent and inboard of the wing skin joint behind the left landing light .
This is an M7-235B.

Philouamt · Post by **Philouamt** » Thu Aug 30, 2012 1:37 am

Thanks, I have started my file for the French CAA, i'll study this option but for me we have to put the sensor somewhere on the left of the aircraft and not closer than 50cm of the wing... i ask a quotation for the full kit.
Cheers,
philou

FARMAULE · Post by **FARMAULE** » Sat Feb 09, 2013 10:46 am

Just read an article on this system. Seems like it could be a good addition in terms of safety to a somewhat new pilot as in myself. I see you guys have talked a little about the install but how about the performance of the gauge. I don't see myself relying on it but more as a piece of mind. I'm not to the point of flying by the seat of my pants yet. <100hrs I think it could help me in slow flight while turning. Just not too comfortable there yet. Advice would be appreciative.

gbarrier · Post by **gbarrier** » Tue Mar 25, 2014 5:13 pm

Been doing some measuring and some thinking. I have an inspection plate on my M-6 in the place Jeremy described. In fact that plate and one near the wingtip are the only ones near the front of the wing where it looks like a probe should be. There is however a lot oil canning there. On the M-6 that location is barely outboard of the seam between the aileron and the flap. Hope there is no difference of air flow there. Other option is the plate near the tip. I think it is far enough inboard to meet the requirements there. It is a little stiffer. Any thoughts?

I'm thinking of the Alpha Systems Legacy unit. The display looks a lot like the unit we fly in the Citation. Seems to be a lot of units coming on the market. The King unit looks a lot like Alpha systems stuff and appears to be a little cheaper but the display is just too busy for me. Garmin's unit has some similar looking stuff also but says different technology and again the display looks pretty busy.

Anybody in the middle of this right now?

beaver · Post by **beaver** » Tue Mar 25, 2014 6:03 pm

I have the old Alpha differential pressure system with a gauge and needle, great system. I have installed the newer electronic one, useless in my opinion

MauleWacko · Post by **MauleWacko** » Tue Mar 25, 2014 6:07 pm

It's a Maule. Look out the window and fly it by the seat of your pants and your brain.

gbarrier · Post by **gbarrier** » Tue Mar 25, 2014 6:24 pm

Beaver, where is your probe located?

Is the newer electronic ones just a digital versus analog representation?

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