Yea people love AOA indicators
Looking for first hand feedback from those that have flown without one and then later installed one in an RV.
Thanks in advance, Tom - looking for a spring project.
People who have them (any AOA indicator) love them and swear by them. I've not used one in a RV. I have used them in other planes. This is a must read for you. Sam's builder site has a nice right up of the LRI installation and operation,
LINK.
"Lift Reserve Indicator" or LRI is a trademark or brand name of one AOA (angle of attack) on the market. The LRI is indeed a AOA indicator. It is all pneumatic, meaning it does not use electrical power to work. The gauge is a sensitive differential pressure gauge. It uses two air ports at different angles, like a pitot. The difference in pressure between ports is calibrated to indicate AOA on the gauge. I have not personally used the LRI product.
There are many other AOA products on the experimental market, and except for the LRI, all of other ones I know of use electronics to get the job done. Many (including LRI) use differential pressure on two port method. One brand (AFS) uses flush ports installed in wing wing tips surface. Others require some kind of "mast" exposed or sticking out (LRI, Dynon). One brand,
Rite-Angle AOA, uses an actual "AOA vane" like the big jets do. This AOA vane (like a weather vane) is attached to a little transducer, that measures actual angle of the relative air flow, no differential pressure at all. Both differential pressure and vane method work. The vane method is a direct reading of AOA and the Diff press is a "derived" method.
Just to mention it there is the "Piper stall tab" mounted in the leading edge. Near stall (critical AOA), it gives you a buzzer warning but no AOA gauge or display. Cessna does a similar thing but their stall warning is totally pneumatic, like a flute player blowing over the mouthpiece, which is closer to the LRI. The Piper tab is like the rite-angel AOA vane in a way. Both Piper and Cessna mount in the leading edge of the wing. You can buy a Piper style stall tab from Spruce for $90,
Reddish. This at least will give you a wake up call, "hey dummy you are near stall". The down side it gives no other AOA indication other than when you are near stall. Some AOA indicators like the LRI require you look at it; they have no buzzer or aural warning. That might be the biggest negative to the LRI, there is NO aural warning or flashing light. So it is critical you place it in the panel so its in you normal scan. Some folks mount the AOA on-top of the glare-shield, since on visual approach you will most likely have your eyes outside. Also the LRI does not make that small adjustment for flaps up or down like other units. The Dynon does not adjust for flaps but the AFS and Rite-angle do.
The LRI is passive, no electronics, just pitot lines. The electronic ones add bells and whistles like audio/voice alarms or other display options, as well as flap position compensation. They all work on similar principals regardless, relative air flow to the chord of the wing, ie AOA.
Some of the most popular AOA's are ones integrated with EFIS products like
Dynon and
Advance Flight Systems Inc., which makes a stand alone and EFIS integrated AOA. The Adv Flt Sys AOA has both stand alone and EFIS displays. Then Dynon comes with the EFIS but requires you buy their special pitot mast.
*Reddish stall tab (buzzer only, no AOA $100)
*The LRI has dedicated two port mast sticking out
LINK ($450-$550)
*The Dynon integrates the AOA port with a
pitot. ($200-$400 opinion with EFIS)
*Adv Flt Sys, two flush ports in wing upper/lower surfaces
LINK ($890 stand alone or EFIS option)
*Rite-Angle AOA
Lancair,
Wingtip vane,
Pitot/Vane combo,
RV AOA vane ($800 stand alone)
As you know regardless of "attitude" or indicated airspeed you can stall. Also stall IAS varies with weight and load factor (e.g., pulling g's in a turn).
The critical AOA (stall) is the same no matter what. Knowing AOA is a good thing.
Can you fly without AOA? Sure most GA pilots do fly just on indicated air speed. We use the 1.3 or 30% margin to a "known" Vso or Vs1 on approach (w/ some extra for the kids or wind). You have to consciously be aware IAS to stall goes up when ever you "pull g's", sustained steep turn or pulling back on the stick, pitching up in any attitude. Our gross weight from min to max does not vary much, so we can pretty much use one conservative value for 1g stall (Vso/Vs1) at max weight, which is about a 5 mph spread. If you really want to fly at the edge of the envelope for short fields, than yes, AOA and weight counts, a lot. In a large jet, weight difference from min to max is great, so stall speed varies significantly. That's why pilots of larger planes must do detailed weight and speed calculations before every takeoff and landing. When you're on the airline, you hear the obligatory Captain PA, "we're doing some last minute paper work", it really means the FO is calculating W&B and speeds while the Captain talks. It's that or they're adding up their per diem check for the month.
You have lots of choices. LRI is a good one, just not as fancy as others. Another choice, is the DIY, study the principle and make your own? There are plans on the web to make your own LRI style AOA indicator for $60 + sweat equity. I have the Dynon AOA only because I had the EFIS already. It was only a $200 option. My older Dynon does not have an audio warning for critical AOA (stall), but I think the new ones do. Audio is kind of a good idea. Say you lose you engine and are gliding, maneuvering and you are distracted. That buzzer or flashing light might save you back side. On the down side I saw a video of T/G's using the AFS AOA. The AOA warning was going off on takeoff and landing and was distracting and annoying. On the other hand, why do people stall with an airspeed indicator? They're not looking or conscious of their airspeed. The RV gives OK aerodynamic seat-O-pant stall warning, but close to the ground, near stall you have a high sink situation. That is not pretty. If you don't have speed approaching the ground to flare you're in deep kimchi. An AOA can give you that margin in an emergency if you know who it use it. Regardless, know your V-speeds and practice your approach to stall and full stall recoveries (at altitude).
An AOA is no substitute for airmanship. Be careful.
PS HUD - Heads Up Display idea for LED AOA indicators:
LINK