AOA Dynon or AFS
If you are going with the Dynon already, than in my opinion it is a no brainier, get the Dynon AOA. You are not going buy the Dynon just for the AOA, which is a secondary instrument. The AOA function is standard with the Dynon so why not use it, if that is what you already have. Assuming you are going to use the Dynon. It only requires you buy the optional pitot probe for about $200**. The negative with the Dynon I have heard is the display is a little small and gets lost in the overall display, which has attitude and other data, i.e., display is crowded. I have the Dynon with the AOA but have not flown yet. It is still visible and works well, however the best or ideal location for the AOA indication would be in your line of sight, like on top of the glare-shield.
AFS AOA indicator could be located in a central high location for a better view. One idea is to mount the LED indicator in the glare-shield facing the windscreen. The reflection can be seen reflected in the Plexi, allowing you to stay heads up while having the AOA in view with out blocking the glare-shield. (note: In the picture the LED indicator is on top, but you could mount it flush. When flying at low angle of attack you will see no light or one green light. Just an idea I got from the RiteAngle AOA web site, another good choice of AOA indicators.)
If you went with the Dynon and AFS it would cost a little more for this stand-alone system and a bit of a waste not taking advantage of the Dynon's built in function. The AFS uses ports in the wing. Both work on the same principle, differential pressure. The Dynon does not look at flap position but you do need to calibrate it, but RV flap's have really no affect on the AOA. Remember clean and dirty stall speeds are with in 5 MPH (corrected:was 2 MPH) on the RV. Flaps are more drag than lift for the RV.
The aural is nice. I feel that the AOA is a back-up to airspeed and control (seat-O-pants) feel. AOA to me is a cross ref / back-up to airspeed, which is easy on the Dynon, since it is on the same display, but you have to look it and keep it in your scan. If you want the AOA to warn of impending stall even if you are not paying attention the AFS is better with sound. It would be nice if Dynon would add sound. Why not. I am sure they could add it. I did see a video of the AFS aural warning in action and it was a pain with nuisance warnings on takeoff and landing.
You can make your own AOA easily for $60. See the post in the general forum under: "$60 Angle of attack indicator"
Cheers George
**When Dynon gets the heated Pitot version it would prove to be cost effective, vs. standard heated pitot?s, which are very costly. However the unheated one is fine for VFR and occasional IFR. If you are getting ice on the pitot you should not be there.
Mel said:
(From below) I'm not sure what RVs you are flying, but I've been flying RVs for about 13 years (all models from the -3 thru the -10). And I generally see a difference in stall speed between clean and dirty of about 7-9 mph. My -6 stalls clean at 60 IAS and 51 IAS with full flaps. Mel...DAR
Calm down Mel, you are right 2 MPH might be on the low end; I stand corrected. The max delta of Vso/Vs1 is about 5 mph (TAS) at best, not 2 MPH as I stated. However I still stand that 2-3 mph IAS is common. I don't know about the RV-10 or RV-9.
According to Van's Aircraft own data (recommended airspeed placards) and Cafe Foundation testing, max True airspeed difference between clean/full flap stall is 4-5 MPH. In my own personal experience, full flaps only got me 2-3 MPH IAS (indicated). I also flew out a field with 20 RV's and every one of my buddies noted only about 3 MPH (indicated) delta between clean and full flap (power off) stalls. Since we fly by indicated airspeed I stated 2-3 MPH. Mel the reported 9 MPH lower stall speed your RV-6 gets with full flaps sounds too high. Your indicated airspeed and calibrated airspeed may be off quite a bit. As you and I both know, flight test data at very low speeds and recording data at stall is not easy, especially discussing a few MPH on an analog AS indicator. No one I know has ever got a real 9 MPH TAS lower stall with simple hinge flaps.
According to flight test with and without vortex generators (VG), by Terry Jantzi, the max delta between clean and flaps full down, without VG's, was 2 Kts (2.3 MPH CAS which was also equal to IAS):
http://www.ontariorvators.org/pitot/pitot.htm
The test data (above link towards bottom) shows that with VG's installed full flaps MADE NO DIFFERNCE in stall speed from clean! That is an indication how effective (or not) the flaps are. I think if you are honest Mel and look at True Airspeed and not indicated, the flaps are only good for about 2-5 MPH max, real world. AOA does not care about airspeed. IT is also intersting to note Terry's clean stall (no VG's) was 51 mph IAS not 60 mph IAS as you state for your bird? Hummm 60 mph sounds high, where you at gross weight?
Since AOA does not care about airspeed only angle of attack it is not subject to airspeed instrument error, weight or load (G) factor, which is its true advantage. RV's have simple hinged flaps, and yes flaps 15 can reduce ground roll on takeoff. As I stated, since the flaps do very little to critical angle of attack on RV's. Flap adjustment to the "AOA computer" is a good thing but not crucial for a RV. IF you have triple slotted flaps and leading edge devices like the Boeing I fly, yes you need to account for the secondary "high lift" devices. As the flaps come out you can see the critical pitch angle change on the PFD (primary flight display).
In regards to AOA calibration and variations with flaps up or down, it would more accurate to account for flap position as the AFS does as I stated. The approach Dynon uses for AOA is to account for the most critical condition during calibration. So with flaps up the top of the red AOA indication on the Dynon be the critical angle, and with flaps down it would be conservative with a small buffer (approx 2-3 MPH).
Take Care George
