Make an AOA for $60!, Why you need AOA and why not?
rv8ch said:
I spoke to Sergy at the Dynon booth at SNF in 04
and told him that I had just spent 600 for the AOA sport because his
system did not do sound. I understand they have now added sound.
They are leaving a lot of money on the table by not offering an
external AOA indicator as an option, IMHO. They're already doing
the hard work, and for $20 worth of hardware and a SMOP, they
can easily charge $100, it seems. I'd probably charge more if I
were them!
There are TWO reasons to have a AOA:
One) to warn of stall
Two) Know your lift reserve
Item ONE is really all the Cessna/Piper stall horn does. Since RV's
do not usually have a stall horn/tab it could be useful. Clearly that
function is best served with an AURAL alert. I agree with Mickey that
aural stall warning function could be added on to the Dynon for cheap,
but I am not an electronic expert.
Item two is more for performance flying. Flying slower, closer to stall
and more precisely to gain the most performance such as during short
field approaches.
Right now the AOA on the Dynon does neither ONE or TWO well. One,
it has no aural alert (at this time) and Two the display is too small and
not ideally position in pilots line of sight while looking out the windscreen.
The solution first mention is a remote display and add aural warning.
There is a $60 solution for item TWO.
I agree they should be able to add the aural tone at min cost to the
Dynon, which to me is of most use to me. I don't want to intentionally
fly near stall, and quite happy to fly by airspeed and add a few knots
for margin. However the below should make a few happy and you can
make it for cheap, and it does not matter if you have a Dynon or not.
HOW TO MAKE AN AOA for $60 or
ADD a Secondary AOA display to your Dynon
http://www.vansairforce.com/community/showthread.php?t=794
I posted the above a while back. You can mechanical "lift reserve"
gauge display to the glare shield, for max performance operation,
like min speed short field approaches. For these use the display
needs to be in the pilots vision while looking out the window. The
mechanical display does not provide a warning tone or is as pretty
as a LED display, but it works for cheap. One comment from a glider
pilot of this design was G's affect the needle display but others say
not so? The down side is the drag from the probe (two tubes in
the breeze). I don't think it would work by just taping into the
Dynon "AOA pitot". Since the gauge is calibrated but changing
the two probes angle to the wing chord line.
WHY AOA should be stand alone?
Mickey, I usually agree with you, but do you really think they
are leaving money on the table and it can be done for $100,
at least for a $100. For one they need to add a flap sensor
to really really make it a full UP AOA. Right now it is a bit
of a compromise as is. You calibrate both clean and dirty,
and it sets a conservative AOA setting. Since RV's have simple
hinge flaps that don't change the critical angle of attack
much, it works OK. I don't think Cessna or Piper adjust for
flaps up or down. However all but one stand alone AOA have
that extra level of flap position sophistication.
Of all the Dynon features these are the ones I think most
pilots care about:
Attitude Gyro (pitch/roll),
Airspeed (TAS is nice),
Altitude (DA is nice),
Mag heading,
VSI
The other items a Dynon EFIS offers in order of importance to me:
OAT (Density Alt/TAS), G-meter, Slip/Skid, Clock/Timer and
Voltmeter.
I left AOA out not because its not important, but knowing I want
a low cost EFIS that will give me the basics. I also think a stand
alone AOA has some advantages. For one thing is display postion
and aural warning. However the Dynon price is right.
WHAT IS AVAILABLE
Stand alone systems either use a VANE (riteangle) or differential
pressure from "pressure taps" at differnt angles of attack:
Rite Angle (
http://riteangle.com/RiteAngle/photos.htm) ($700)
Dynon
http://www.dynondevelopment.com/ ($200 add on)
Advance
http://www.advanced-control-systems.com/ ($900/$1500)
Liftreserve
http://www.liftreserve.com/ ($450)
You can see the Dynon is a bargain. The Adv is the best for several
reasons, not the least of which low (no) drag, although the others
should cost only 1/3-1/2 MPH at 200 mph. The Dynon should be the
least added drag. I think the riteangle, the only Vane (airliner) style
AOA is cool. I noticed all the prices of these have gone WAY up on
all AOA's, Which is a hindrance to a cheapskate like me.
The lift reserve is the same as the one I mentioned can be made.
It does not have aural warning, but should work well as a the name
implies, lift reserve indicator.
AOA is really best served, IMHO, as a stand alone system. Yes
using an existing pitot, microprocessor and display are cool, but the
last item is the complaint, display position. Granted large scale
integration of avionics is nice. In jets there are the ADC and FMC
(Air Data and Flight Management Computers) which take all
aerodynamic/config/NAV/Attitude data and combine into one
display.
I know how wonderful AOA is. I don't want to make it a debate
about AOA usefulness. Since stall spin is a killer and RV's do not
have a stall warning system (eg, Cessna/Piper indicator of "critical
angle of attack, aka "stall" horn or buzzer); it is a practical safety
item. The debate is not if useful, but I do have complete confidence
in my calibrated seat of the pants and ability to maintain flying
airspeed at all times and flight conditions, but we all can be
distracted, like during an engine failure. Here are some alternatives
below.
WHY YOU DON'T NEED AOA (or ALTERNATIVES)
I have to admit the only planes I have flown with AOA are
commercial airliners, both turbo prop and jet. Of these planes only
one turboprop had an AOA indicator you could see, which was an
after thought. Most airliners do have a stick shaker/pusher that
warns the pilot of stall, with no direct AOA indication. With the
flaps out on some planes show you a "critical pitch attitude" bar
across the top of the EFIS display (artificial estimate of the pitch
attitude that would give you critical angle of attack for current
flight condition/power/config). This is like little planes which only
indicate critical angle with the stall warning. It's up to the pilot
to "feel" the controls approaching the stall and speed awareness.
Jets don't rely on the pilot to SEE the AOA and react, they have
stick shakers and pushers and you fly "BY THE NUMBERS". Besides
strict adherence to air speeds, you are trained to "respect the stick
shaker". The reason is jets have no real "feel", so artificial feel is
added to the controls. It is impossible to ignore the yoke vibrating.
However the old joke is, The pilot made a gear up landing and said,
"I would have made a good landing if it was not for the dang HORN
blaring in my ear". Pilots ignore stall horns and instruments all the
time. AOA indication will not save your butt if you ignore it or don't
know how to recover.
You can train your BUTT to feel the AOA by practice of stalls,
1g power on,/off, 2g, 3g stalls, awareness and recovery. Also slow
flight is wonderful practice. Remember flying on the edge, buzz......
buzzz, buzz.........buz... I would rather the pilot flying my family be
proficient in these maneuvers than have a AOA and be rusty and
not current in stall awareness. The RV is fairly docile for a "HOT"
plane. The airframe does give warning, if you pay attention and
recovery is not spectacular, difficult or dramatic. So I think you
can be safe in a RV with out AOA or stall warning, but practice
stalls at a safe altitude.
When was the last time you practice
stalls or slow flight?
I don't think everyone is Jones-ing for an AOA as a their top priority.
Although to those who want them, I concede they are useful, but
you are better served with a stand alone system. I can't argue with
adding safety equip, but to use a superior instrument like an AOA
you should match it with superior airmanship skills, to effectively use
it; otherwise its just an expensive fancy gadget, if that. How often
do you REALLY think YOU are going to FLY near stall intentionally?
In the pattern you fly airspeed. If a field is that short I don't need
to get into it. If the engine fails I am going to FLY the plane and
keep the speed around 100 mph indicated.
Spruce sells a cheap STALL TAB for $85.
http://www.aircraftspruce.com/catalog/inpages/redstallwarner.php
(I think this is cool, but I like most don't want to cut holes into the
wings leading edge. You can make your own, someone has plans?)
George
(not anti-AOA, just pro safety and cheap-ness)
