ANGLE of ATTACK INSTRUMENT

2012/04/12

 

Functionally identical to many of the higher priced units yet may be the lowest priced one available.

A “Mechanical” A0A with no power requirements.

Dozens of satisfied users.

 ****     New  price: $235 plus shipping. ***

FAA now allows these in certified aircraft as long as airspeed instrument is retained

Installation in aircraft, where they should not be a primary control device, is at your own risk.

 

Installation Instructions

 

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Differences compared to higher priced units

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This simple, inexpensive instrument quickly becomes your instrument of choice when maneuvering at slow speeds. I’ve heard from several other pilots who confirm this (see some comments from users at the bottom of the page and a comment from my first user).

                                                                                               

Why use this kind of an instrument?

 

The reason that the angle of attack indicator is more useful than airspeed is because a stall can occur at different indicated airspeeds depending on the angle of bank and weight so that if you want to maneuver at the edge, the airspeed indicator is not the best indication. For example, at a bank angle of 75 degrees, the stall speed has doubled. On the other hand, "they" say that no matter what the conditions, stall always occurs at the same angle of attack of the wing to the air stream. This device gives an indication of the angle with a needle moving into the red bar when at the stall angle. Overall, the green, yellow, red segments on the gauge make for an easy to read instrument.

 

The gauge measures the difference in pressure at two points on a probe mounted outboard of the prop slipstream (or on a pusher, anywhere in smooth air at the nose). It could be described as a non electronic or mechanical instrument. 

 

Above, the gauge is mounted on the surface of the panel over a 2 1/8” hole (not inserted). This location gets the gauge mounted nice and high and easy to latch onto when you look at the panel.

 

If there is room, a good place to mount the gauge is on top of the glare shield on top of the panel. This area is close to your line of sight:

 

 

Below is a similar bracket curved to fit the glare shield of a Rans S6 (and the probe bracket is for an S6 jury strut):

You can make these mounting brackets or purchase with our instrument.

 

The gauge body, at 2 5/8”, is an odd size. This one will mount in a 3 ¼ instrument hole using the optional  adapter plate:

 

 

This probe is mounted at the end of the lift strut on this S7

 

I used a length of 3/16 steel rod pushed out to the inspection hole from the cabin to tape the tubes to for pulling through the wing into the cockpit. The top hole is for the high pressure line.

 

The tubes follow the pitot/static lines out to the strut where the probe is mounted.  An alternate routing is down the inside of the strut and into the cabin near the bottom of the strut.

 

On the production version, the shaft is a slightly different shape which puts the probe a little further ahead and the spacer is not used. Also the probe is ½” 6061 aluminum.

 

 

If you fly a pusher, the probe could be placed at the front of the fuselage. One guy put his at the front of a wheel pant. It is not necessary to go right out to the end of the lift strut either. On a SuperCub, a logical place is at the top of a jury strut. In this case the shaft need not be bent as it is above.

 

Here is a jury strut mount on the Rans S7.  It is the same as the previous bracket but  with a 2nd  plate made out of thinner stock so that it just clamps around the jury strut.  Further down in the “Feedback” section is a picture of another jury strut mount using a plastic block made by a customer.

 

 

The probe must be in unobstructed free air away from the prop blast and at least 6” away from the wing.

 

Here are a couple of instruments showing the two faces available.

 

 

 

Setup:  also see:  Installation Instructions

 

Start with the centre line of the probe tilted about 35 degrees nose down to the center line of the aircraft. Take a flight and stall the plane. As the nose goes up and speed drops the needle should come off the right hand stop and move towards the red area. Note the position of the needle when the stall occurs. You want the needle to be near its zero speed, at rest position in the red arc at the stall (on most gauges this is not right at the left stop). If the needle gets to the left side before the stall then the nose of the probe is too high so rotate it down before the next flight.

 

Conversely, if the needle is still in the yellow at stall, then the nose of the probe is too low so raise it some before the next flight.  When you have it set where you want it, tighten the mounting bolt and put a mark on the mounting bracket so you can see that it hasn’t been moved later.  Now, when you set up on final approach, you can experiment with where in the yellow arc you feel comfortable.

 

The Ready-To-Install kit includes the following:

          Instrument with either black or white face (and  white needle or black needle),

Mounting hardware for flush or surface mount but not glare shield mount or adapter

 plate for 3 ¼ hole,

          Adapter tubes to go from hose barbs on instrument to 3/16 lines,

Up to 28 feet of 3/16 tubing  (the length required for through the wing routing on an S7

                                      where strut attaches 8’ out from the fuselage, 22’ for jury strut mount,

          Probe (aluminum) with all drilling complete,

          Probe support shaft in 6061 aluminum drilled and optionally bent for Rans S6,7 end of wing strut

 mount,

          Hardware to attach probe to shaft.    This is what you receive but with whatever tube length you need:

 

Price: $  235 Cndn. Or US  Plus $15 shipping (in Canada and US).

                   Ask about price reduction on orders for more than one unit.

 

Mounting plate to put gauge in a 3 ¼ instrument hole                  $  30

Mounting bracket for top of glare shield/panel                              $  40     

Jury strut mounting bracket                                                             $  30        

 

Tandem option:

          If you have a tandem seating aircraft and fly from the back seat, it is very useful to put a second instrument

up high where you can see it without the front seat passenger shifting sideways so you can see the panel.

Since the AOA is pretty much all you need on approach it makes things a lot easier and safer.

Here is mine mounted in an S7.  Even with a passenger or student in the front seat you have an unobstructed view and it is in your line of sight.

 

 

One probe can drive two instruments so this option gives you a second instrument with modified barbs to enable you to easily splice this gauge into the existing tubes. It also includes the mounting plate shown in the picture.     Specify  flat mounting surface or bent to conform to tubular spar carry thru as in the Rans S7.  Price: $165

 

  Installation Instructions

         

Differences compared to higher priced units:

               Pretty much all “mechanical” units utilize a probe in the airstream with holes at 90 degrees to each other as does this one.

One manufacturer provides two different colours of  tubing; mine are both clear.

My gauge is a non standard size at 2 5/8”. It is not 2 1/8 or 3 ¼ so some adaptation is required.

My probe setup with exposed tubes may not look as elegant!

My price is a fraction of what some manufacturers are charge for functionally the same instrument.

 

If you need flashing LED readouts or audio alarms you should look at the other offerings.

 

 

If you want one, I’ll need to know:

                   Length of tubing if not going on a Rans S7  or S6

                   White or black face

                   Bent, straight, or Jury strut bracket

Options

                   Your address

                   How you want to pay:  (Western Union, PayPal, money order)

 

                   Reply to:  Peter  Cowan         PayPal account id is  peterc@pipcom.com )

                   Telephone:   705 8778404     Eastern time

 

                   Mailing address is  996/ RR 2 Lakefield

                                                  Ontario   Canada

                                                  K0L2H0  

 

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 First feedback (2009/03/31) from a purchaser (Danny Hayman, Challenger):

 

“Very pleased but thanks for the heads up. I am now to a point that airspeed is no longer my primary gauge, instead it's the AOA.............”

 

Feedback from Mike Arnold C-150: 

 Well I got it hooked up and after several trips up to set the stall point I took this into the shortest strip I have ever gone into. It is a 1000ft long paved private strip at about 7000ft AGL. At 90 deg OAT,. it worked just as advertised. So I would give you good  feedback. 

 

This one is on an X-Air:

 

 

Peter,

Some more feedback for you at last.

Photos attached of installation on an Xair "H" (Hawk over here), bit temporary at the time but tidied up now.

Mounted the head on the jury strut with a nylon block, gauge is not really line of sight but there were two handy bolts to mount it without cutting the panel

I intend to move it down onto the top of the dash panel soon. Did have a problem with a sticky needle but sorted that.

 

Works just like it says on the tin, quite interesting to see just how much excess speed you can carry on approach if you use conventional methods.

Takes a little practice to have confidence in the AoA, but then it makes for much easier low speed handling.

 

Many Thanks,

Nick

 

Here is an opinion from one user of a similar instrument:

 

I finished an RV-8 two & a half yrs ago and have flown it over 425 hrs all over our great country. During flight testing (after very little adjustment for calibration) the LRI gauge indicated the imminent and actual stalls at the same points on the gauge, regardless of loading, acceleration/deceleration or attitude. In fairness, I will admit I have never purposely stalled the RV-8 while inverted, but, due to the orientation of the probe, would not expect it to indicate properly (all my stall testing was done while in positive-g flight).

Since completing the stall testing, I can sincerely say that I've flown every landing pattern, particularly at unfamiliar airports, referring almost exclusively to the LRI gauge when my eyes are in the cockpit. My only complaint with the instrument has nothing to do with its value or effectiveness: my complaint is that the small gauge was not available when I installed mine, and mine is larger than I need. It certainly is easy to install/calibrate and you incur very little weight penalty for having it on board.

Having flown 2 late-model Couriers, I find the wing to be exceptionally forgiving or docile or whatever adjective you prefer, and the handling is most impressive at the low-speed range. However, when I'm close to gross, and it's high and hot (I live in Albuquerque), I'll appreciate being able to make that base-to-final turn with more evidence than my fingertips and butt cheeks telling me that I have plenty of "reserve lift" to keep me, my plane and  passenger from becoming a statistic.

One man's humble opinion and personal experience.

 

And another who flys a Rans S7:

 

I have one, I use it a lot, and I really like having it.

 

Here is how I look at it:

Maybe some of the benefit or the reason I am comfortable with it is the simple, colour coded read out which, to some extent, would be achievable with an airspeed also. But knowing that the information it gives is the same no matter the circumstances of the plane is a big plus. I find that while I occasionally cross check to the airspeed, for the most part, I set up my approach by glancing at the AOA indicator. While I rarely go into short strips and have lots of room ahead, my "thing" is to get down in the shortest distance in a variety of inlets around the lakes so safely coming in at minimum speed is important.

 

And one more thoughtful opinion from a non user:

 

I have to say that I've been watching this thread with interest.
Whilst I don't have any great feeling for or against the LRI I think
that some stuff needs to be clarified. The LRI is not a true AoA
system because it does not measure the actual relative airflow and
compare it against the aerofoil chord datum. What it does is
approximate the angle of attack by measuring differential air
pressures acting on a probe in the free airstream. As does the
system described by another poster, where the sense ports are on the
wing upper and lower surfaces. That particular system cannot be
anything more than a sophisticated stall warning setup because it
senses air pressures at the aerofoil surface – incidentally similar
system is in common use in high performance gliders to set optimum
angles and speeds for reflex flap use.

Because these systems are using air pressure as a reference they are
subject to errors just as the ASI, ALT etc etc are. As far as the LRI
goes its main limitation is that it is therefore necessarily
inaccurate outside the confines of straight and level un-accelerated
flight [not so with a true AoA system] – which incidentally is
exactly where it is calibrated?? It could however still be a
valuable tool in a light recreational aircraft for use in takeoff and
landing where it gives a visual indication of how close you are
getting to a stall – providing it has been calibrated correctly. But
then the same applies to the ASI it does pretty much the same in the
S7 – again provided it is correctly calibrated – and bugs don't take
up residence in the small orifices.

Where the difference is in presentation of the information. I have
not used the LRI so cannot comment on its practical operation but
see it as an aid to safe slow flight particularly in the S7S which as
I have said before only has two flaws 1; no step to get in it, and 2;
exceptionally good low speed handling. I had the opportunity to fly
my first S7S flight on its very first flight since build with an ASI
that failed on climb out so the whole flight was conducted without
meaningful airspeed information What this revealed was that the S7S
controls are effective right up to and into the stall without as much
reduction of `feel' as say a C152 or Cub etc as the airspeed decays,
so I flew the first approach faster [by way of feel] than gut feeling
was saying I could be. I have many hundreds of landings now into
short strips with the S7S and even yet I still like to keep one eye
on airspeed as I pass over the hedge just to make sure I am not
getting dangerously close to the stall flying by feel.

I look forward to testing the LRI in my S7S to see how its
theoretical limitations affect its practical operation, but I do
suspect that it will turn out to be a valuable aid. My day job is in
aircraft accident investigation particularly light recreational stuff
and it remains a fact even today that a high percentage of fatalities
occur from stall/spin related accidents and these often being in
aircraft that have stall warning devices. So flight using the ASI
alone clearly wasn't enough for some unfortunate folk. Using
something like the LRI, providing it is used with due regards to its
capabilities and limitations [as with everything else], ought to
provide the pilot with additional valuable safety information.

At the price being given by Peter, his was hardly a commercial
venture, and you were not being forced to buy it. Lets face it you
can always give Spruce £1000 for a device which will likely give no
more reliable information if you feel the need.

 

The following note is from Jim Covington on the Titan group:

 

So many follow-up posts - this is a good discussion! I'll try to answer
a lot of questions in one post.

The fundamental point I have here is that I don't think the instrument
Peter described is a true AoA instrument, but I *do* think it's very
valuable and I encourage anyone who doesn't have one to look into it. If
you gave me the choice between an airspeed indicator and Peter's
instrument and said I could only have one (FAR's notwithstanding) I'd
choose Peter's.

Also, for all of the assumptions below, I'm assuming *no flaps.* Also,
for the discussions of pressure, all discussions are about differences -
so I'm ignoring static pressure (since it will be the same at both
ports; only the dynamic pressure changes.)

Lucien's statement: "Stall is determined only by angle of attack and can
happen at any airspeed or loading"
Absolutely right!

Hugh's instrument sounds like a true AoA instrument - a vane in the
wind. From Hugh:
"I have heard the assertion that an AOA indicator will always tell you
when your wing is about to stall."
Yes, that's true.

"But when you're in a steep bank, meaning higher G forces, how does that
happen? I guess it's because the wing has to generate higher lift in the
turn, so it must be at a higher angle of attack."
Exactly! You do need to carry a higher AoA at any given airspeed to
generate the extra lift required to hold the plane at a constant
altitude. If that given airspeed is just below stall in level flight,
you will stall in a steep bank if you try to maintain altitude with the
same airspeed - because your AoA has increased.

 Now onto Peter's fundamental question - you got it right in the last
email I received. "Jim was saying that there is a reason why this is not
a true angle of attack instrument and I'm curious about that reasoning"
Yes, that's what I'm saying. Here goes:

This instrument measures the difference in dynamic pressure at two
ports. The pressure at each port is proportional to two things - the
dynamic pressure due to airspeed, as would be measured by a perfect
pitot tube, and the cosine of the angle of the axis of port opening
relative to the angle of the oncoming air - the angle of attack of that
particular port. As the angle of attack of the instrument changes, the
difference between the dynamic pressures at the two ports also changes.
As you increase the angle of attack, the angle of attack of the top port
increases and the bottom one decreases, so the pressure at the top one
decreases and the bottom one increases, so our instrument shows a change
in the difference between the two. So far, so good - it's pretty close to
an angle of attack instrument.

Here's where the problem is - changing the angle of attack is not the
only way to change the difference in pressure between the two ports. You
can also change this by changing the airspeed without changing the angle
of attack. Imagine the top port is directly into the wind, and the
bottom port is angled downward about 45 degrees. The pressure at the top
port will be 100% of the dynamic pressure, and the pressure at the
bottom port will be about 70% of the dynamic pressure. Our instrument
shows us some reading (I don't know what reading - it depends on how
it's calibrated.)

Now imagine you double the airspeed in the wind tunnel. The dynamic
pressure with go up by a factor of 4. Here's the important point: *The
difference in pressure between the two points will also go up by a
factor of 4.* So the differential pressure gauge changes! This is why
one of the major manufacturers of a similar system calls it a "Lift
Reserve Indicator." It shows the *lift* your wing is producing, not the
angle of attack. Now if you're not turning hard tight turns, this really
doesn't matter all that much. You do want to know how much lift you're
making, especially during landing and when trying to maintain Vx, Vy or
best glide.

How does the $1800 system avoid this? They *also* take input from the
pitot tube, and do some math on the differences in pressure at all
*three* ports to come up with a real AoA.

So why is the cheaper instrument useful? Because for the majority of
flight, and for almost all one G flight, your airspeed doesn't generally
double at a given angle of attack. You typically only get high angles of
attack at very low airspeeds and low angles at high airspeeds, and the
instrument can be calibrated to show you valuable information in both
these flight regimes.

So to sum up - it's a great instrument. If you don't have one, consider
getting it. It's well worth the investment. Your landings will be
smoother and shorter, guaranteed. But don't count on it to tell you when
you're about to stall in a 5-G pull-up from a split S. For that you need
a real AoA instrument with a display readout near the center of your
field of vision.

 

This is from another RV-8 guy:

 

Flying with AOA - it's about Maximum Performance

----------------------------------------------------------

I must admit that, as an Aeronautical Engineer by training, I have always wanted to have an Angle of Attack indicator in my airplane because, well, we all know that is how wings stall, and geeks like instrumentation. However, I also leaned to fly many decades ago in J-3 Cubs (and the like), and have spent many, many more flight hours without an AOA than with one. In fact, most of my AOA flying is in simulators at hypersonic velocities - very important there, but bearing no resemblance to using it at low speeds. I know many Naval Aviators who have never flown without an AOA, and learning to use one from scratch probably gives on a unique perspective on the device. But picking it up "later in life" is interesting, because, well, I tend to feel the wing first, and then look at the AOA later. (To be fair, I don't generally have to look at my ASI in a light plane that I am used to on final either - you get to know what it feel like - unless my loading is way different from normal).

But flying with the new AOA software on my GRT EFIS for the past couple of months has given me some interesting insights into how it can be useful - even for those of us that "don't need it". The bottom line is that if you operate away from the edges of the low-speed envelope, it is not going to dramatically change your scan or habit patterns. But if the goal is to get the maximum performance out of your bird at the low end , then yes, AOA can really help!

The best example that I can give is that at my normal approach speeds in the -8, I can land and stop in about 1,000' - 1,200' of runway. Because I almost always have 3,000' or so available, I rarely worry about doing a short field landing (and I get at least two years on a set of brake pads), and concentrate on being safely over the threshold, and working on a nice touchdown. This is easily accomplished with an approach speed of about 70 knots, and the C/S Prop brakes you pretty quickly when it's time to dump speed. At my normal approach speed, the GRT AOA indication doesn't even appear on the screen until I am down below 70 knots (calibrated to a 1.3Vso approach speed), popping on with a pitch up indication as I come over the fence. You can say that I am carrying plenty of margin over the fence - or that I am flying way faster than I need to. Either way, the AOA works fine - I am just choosing to have a little better "penetration" speed down final.

Now, if I go out for some short field landing practice, the AOA is fantastic! Pitch up until I get the green dot, and the plane just seems to hover its way down final - in fact, there almost isn't enough energy to flare - a little bump of the throttle makes the touchdown much softer. And, of course, it re-emphasizes just how short an RV can land - I spend more of my time enjoying the high speed aspects of the design than the low speed. Playing around with slow flight at altitude, the AOA is a great tool for seeing when you are getting the most out of the wing - but it just reinforces what my seat-of-the-pants already knows.

So I guess I will never be accused of being an "AOA Cripple", unable to fly comfortably without one, but that is just because I have flown without one too much in my life. But, for precise speed control on an approach where it makes a difference, the AOA is a very handy tool to have. I guess that sort of sums up many of the features I have built in to my aircraft - Synthetic Approaches, HiTS, ILS, multiple GPS's..much of the time, they are superfluous. But when you really need that one tool to make the flight safer and more successful, it sure is nice to have! (Let's face it, that's how we justify buying shop tools as well.right?)

Paul
__________________
Paul F. Dye
RV-8 - N188PD - "Valkyrie" - 890+ Hours!

 

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