LRI Angle of Attack Installation

[cgruby]

I have completed fabricating and installing the Lift Reserve Indicator (LRI). I don't remember where I got the write-up, but if you're interested you can Google it up.

Basically it consists of a probe that you must fabricate, which consists mainly drilling a few holes reasonably accurate, and purchasing a differential pressure gauge with a range of 0 to 2 inches of water.

I've just completed calibrating the probe angle relative to the bottom surface of the wing and test flying. At the moment, the airspeed indicator is toast so I haven't had the opportunity to really get serious evaluating the setup. I'll write more as I become smarter.

[cgruby]

It's interesting you asked for additional details. I have just returned from a flight where I was checking out a newly installed airspeed indicator. This is indeed the first time I have flown this thing with a reliable A/S indication. What a Godsend!!

The LRI was built just like the author presented it in his article.

I removed the bezel on the differential pressure gauge and color coded the ranges as the article recommended. I then went out and test flew and adjusted the probe per the instructions. Remembering that the ports on the probe are at 45 degrees to the mast, the first landing was at a reading of .35 with the setting of the probe at 64.5 deg.
I readjusted the probe to 70.5 degrees and shot a landing with a reading of .40 on the gauge. I again readjusted the probe setting to 80.1 deg and shot another landing with a readout of .50 on the gauge. According to my arithmetic my critical angle of attack is 80.1 - 45.0 = 35.1 deg. That's an astronomical AOA!! I'm more accustomed to seeing in the neighborhood of 12 deg. But anyhow, I'll let the experts chew on that one for a while.

As far as for mounting the probe, I glued a spacer block to the outside of the rib where the pitot is mounted, so that the LRI probe would clear the lower cap strip and mounted it with a singe\le 3/16th bolt. I glued a captive nut to the probe so that tightening was not a problem.

The lines I the ran to the outer end of the rear spar facilitated by an inspection port I cut in the wing tip in that location. I fished the two lines through the spar, and routed them to the instrument. As far as folding the wing, the lines are routed the same as the other lines ine that area.

Mounting the instrument was no simple solution as it was a huge 4" instrument you'd expect to see in a power station. I cut a rectangular hole in the glare shield and buried 2/3 of the instrument beneath the level of the glare shield, so just the meter scale is protruding. I got to admit, it doesn't look bad.

As far as flight testing it with flaps at different settings, I haven't done that, however the author says that the system reads the same flaps deployed or not. I'll have to see that, because, lowering flaps will increase your angle of attack, and that's basically what this instrument is.

That's about it. I'm looking forward to flying it more and gaining more confidence in the system, so I can get my landings much more predictable.

[KFfan]

Chuck

Thanks for the followup.
I own a KF2 that I have not yet flown. I have to get that pesky license thing first. Your original post intrigued me and I did some searching. I had seen AOA devices in a number of videos I have watched. Being a aspiring pilot I wondered if it was advantageous. Everything I found indicated it is a desirable addition. I look forward to your final finding and impression/recommendation.

[napierm]

You are probably aware that an airspeed indicator is a differential pressure gauge. I made an LRI indicator using a 2 1/4" Falcon 0-80 MPH Airspeed. Use a loop of clear tubing to measure inches of water column. Just make a "U" with water in the bottom. Connect one end of the tube the to "P" input. Move the "U" so that there is 1/2", 1", 1 1/2", etc. difference in water levels in the tube. Tap on the Airspeed a bit so the needle will settle on the new reading each time. Write down the answers.

The front glass can be removed with a thin sheet of steel (1/32) cut to fit the grooves in the locking ring. Unscrew the ring and the glass comes out. Paint over anything you don't like of the face with flat black Testors paint. Put new markings on it with Florescent Testors paint (I used Green, Yellow, Red, White). Might want to practice a bit with fine brush 1st.

Put back together. Works just as well as the differential pressure gauge and mounts in a standard hole. I even put a light ring on mine.

Note it doesn't have to be perfect, it is just a visual reference.

Cheers,

Mark Napier

[cgruby]

Well, I've got to say, that's surely a heck of better than a 4" steam gauge. Do you remember the airspeed numbers that related to .5, 1, and 2 inches of water? That would be good information for someone who might want to go that route (like me).

[jiott]

KFfan, I have the Dynon AOA indicator in my plane and have found it to be a very desirable, advantageous addition. Being a relatively new pilot (400 hrs) I find it very useful in short landings where you are pushing the limits on slow approach speeds. In using it I have found two things:

1- Down near the ground where you really need it, I don't have time to look inside the cockpit at a colored indicator.

2- My Dynon AOA has a variable tone that starts a slow beep in my ears at about 5 mph above stall. The beeps get progressively faster until it becomes a solid tone at impending stall. I just listen to the beeps and never take my eyes off the outside; I could care less about the indicator in the panel. The ones that just start saying "angle, angle, push" are no better than an old fashioned stall horn in my opinion. If you are buying a ready made AOA kit I would highly recommend one with a progressive tone, since not all of them have this feature.

Just my 2 cents on the subject.

[cgruby]

Jim, My observation on your method of relying on stall speed as opposed to AOA is, IMHO, upside down. You can always trust AOA to always adjust for density altitude and weight, whereas indicated airspeed will not. I would suggest you remount your LRI indicator in a location where it's in your peripheral vision during landing and cross check between it and airspeed.

We've all used airspeed for years to safely land our planes, but utilizing AOA is head and shoulders over simply airspeed.

Cheers,

[jiott]

You completely misunderstood my post. The beeps I am talking about have nothing to do with stall SPEED (even though that is what I said in a few places), they tell me how close I am to critical AOA. It is a true AOA (LRI) system with progressive beeps. I do not need to refer to the colored LRI indicator.

[cgruby]

Hey, I gottcha and apologize if I came across as being instructional. Now if I could instrument mine where it would give a tone readout when approaching critical AOA.

[jiott]

Hey no problem Chuck. I guess I am just plugging the Dynon system because its working out really well for me. I do admire you guys that can build an AOA system from scratch.