Lift Reserve Indicator

[Yenn]

Another thing to put in the cokpit, because it will make it safer. So far all the cockpits I see have far too many instruments. Most Jabs seem to have enough to go IFR, but the pilots seem to be lacking in sense enough to keep well away from IFR.

 

 

[eightyknots]

Seat-of-the-pants versus Instruments

 

Those who have an awareness and feel for what the AC is doing,have the best instrument of all.

Frank.

The Human Factors syllabus tends to suggest otherwise: too much reliance on the seat-of-the-pants at the same time discounting what the instruments are saying may result in a potentially dangerous situation.

 

[facthunter]

Quote -- without qualifications..

 

80 K., You have quoted me without the very specific qualifications/ limititations, I put on that statement.

 

In IMC you have NO help from your "seat of the pants" input. In fact it will mislead you. Once you can "see" where you are your eyes over-ride everything else, and become the primary sensory input. In the absence of an outside visual reference, your INTERPRETATION of what information the instruments give you becomes the way of orientating you and navigating the ship.. In this situation you must absolutely "trust" the instruments and ignore totally the "seat of the pants" thing.

 

The feel for the plane is appropriate where things change suddently like when you are flaring to land, and hit a willy- willy etc.

 

You don't have time to look at instruments, when a student has put the plane into a ground loop situation either. You sense the swing and hit rudder and power immediately, if the thing is going pear shaped. Nev

 

 

[eightyknots]

Yes, I agree, facthunter, trusting in the seat-of-the-pants is definitely different for VFR and IMC. Thanks for clearing that up.

 

 

[Old Koreelah]

Hi RalphA while back I was hunting up how to build an AOA indicator, not sure I'd actually build one, curiosity as much as anything. Couldn't find anything on the net at the time. Came up with a few ideas of my own, vane with optical sensors, 2 ports above and below the LE with some sort of electronic pressure sensor(s) to give the differential etc.

 

Do you have any specifics or references on how to build/calibrate ?

 

Ta Mark

An old post, but I wonder if anyone has actually found (or built) a reliable electronic AoA or Reserve Lift Indicator?

 

I like the simple pressure-tube type, but I have a specific reason for needing an electronic version. An audible tone (like sailplane drivers hear from their variometers) would be even better.

 

Lyle

 

 

[facthunter]

A strand of wool on a glider or pusher is hard to beat. and nothing could be more simple.

 

Having used the real high tech ones, I can't see an easy way to do it electronically. You have to use sensors which I think is where the difficulty lies. While the problem is simple in that angle of attack is what you are measuring, if the aircraft is reconfigured (with flap), you have to apply a new datum, for each flap setting.

 

If it is not working well it is just another gadget/distraction in the cockpit . Nev

 

 

[eightyknots]

An old post, but I wonder if anyone has actually found (or built) a reliable electronic AoA or Reserve Lift Indicator?I like the simple pressure-tube type, but I have a specific reason for needing an electronic version. An audible tone (like sailplane drivers hear from their variometers) would be even better.

Lyle

You would need something that is able to work out the difference in pressures, using pressure transducers perhaps? Then, you would need to work out an appropriate 'trigger' point when either an audio or visual signal would be given to the pilot.

 

Alternatively, you could resort to analogue (steam) instruments such as the commercially made unit: http://www.liftreserve.com/

 

...or the home made one: http://tincantimes.dcsol.com/LRI.html

 

There is some technical information that you might find useful at the following two sites:

 

http://www.pipcom.com/~cowcam/AOAr.htm

 

http://www.sonex604.com/misc/AirsoobLRI.pdf

 

Perhaps, with this information you could adapt this to an electronic version via an analogue-to-digital conversion process?

 

 

[Powerin]

An old post, but I wonder if anyone has actually found (or built) a reliable electronic AoA or Reserve Lift Indicator?I like the simple pressure-tube type, but I have a specific reason for needing an electronic version. An audible tone (like sailplane drivers hear from their variometers) would be even better.

Lyle

This one seems to be totally electronic with voice warning...not cheap though.

 

 

[eightyknots]

This one seems to be totally electronic with voice warning...not cheap though.

I haven't come across this one before, Powerin. It's pricey but just great if you don't have much available panel space ...and, it's electronic.

 

 

 

[jetboy]

Lyle,

 

You mention specific need for electronic; that would be relatively easy to do

 

Differential pressure transducers are found in a lot of things these days. The voltages are small so they need precision balanced amplifiers for the signal, then feed it to a bargraph IC to drive the indicators or alarms.

 

But I would visit carefully what you are trying to achieve; as the LRI does not appear to be very useful if you have flaps or differing loads to calibrate for.

 

Cessna style stall warnings are much more useful in my opinion. Because theyre mounted in the wing it appears they accurately indicate the attitude when the air starts peeling out in the bad direction and flight is about to be interrupted.

 

I like the flap/switch type of the early models - reminiscent of a heart monitor - irregular chirps= caution, flatline tone=flight terminated

 

The later reed type systems give more gentle and progressive alarm, but sound like strangling the turkey if youre having a difficult day. I never did get used to that. As the turkeys get older, they squark less too.

 

Ralph

 

 

[facthunter]

A stall warning is an on/off thing. Doesn't really do much for me. They are a legal requirement in some planes. They annoy you in a tailwheel plane if you regularly do 3 point landings. An LRI is a performance instrument, not a warning. Nev

 

 

[moz]

As already stated, all aircraft already have one - the control column

 

 

[Powerin]

Lyle,But I would visit carefully what you are trying to achieve; as the LRI does not appear to be very useful if you have flaps or differing loads to calibrate for.

Load doesn't matter, wings will always stall at the same critical angle of attack. What will happen is that you need more lift to compensate for the extra load. So you either need more AoA or more speed to increase lift. But you can only increase the AoA so far before the wing stalls, so you need more speed to give you the extra lift before the wing stalls.

I was going to say the same applies to flaps, but on researching it I can't find a definitive answer yet as to whether flaps change the wing's critical angle of attack. Most seem to say flaps will decrease the critical angle, which I guess means an angle of attack indicator may be incorrect when flaps are deployed?

 

 

[Powerin]

As already stated, all aircraft already have one - the control column

So Moz, following on from my above post....does the stick position at which a stall will occur change with the deployment of flaps? If so, I wonder is an AoA indicator a reliable indicator of an impending stall with flaps deployed.

I'm too inexperienced to be able tell if there is much difference in stick position between clean and dirty configuration.

 

 

[djpacro]

... does the stick position at which a stall will occur change with the deployment of flaps? .

yes.Most significant variation is with cg.

Can also change with power setting and pitch rate.

 

And with G.

 

 

[facthunter]

Cof G change is critical ..when you change it you change the whole design of the aircraft. It can go from a benign thing to a beast. Docile stall planes have a nose heavy situation, where you may run out of elevator before you can stall it . The elevator controls your ability to present the wing at whatever angle of attack you command it to be . Hence the concept of " stall stick position" .. Planes don't stall ..Pilots make them stall...Nev

 

 

[Thalass]

As far as an electronic AoA/LRI goes, it shouldn't be too tricky. A potentiometer with a normal wedge-shaped vane would work, with some kind of microcontroller to trigger the output stall warn/ident lights and sounds. Such a thing could even have an input from the flap selector to alter the levels, as well as an input from airspeed if you're going that fast.

 

But to get the reliability and precision you need for aircraft (even a single seater homebuilt) you're looking at a fairly complex system with layers of redundancy. Even a homebrew one would start to be expensive! And being such a vital system you'd have a hard time finding someone to put their name on it!

 

 

[Old Koreelah]

Thanks for the thoughtful replies, comrades. In the short term I'll go with Moz's stick position as a stall warning. In the medium term I'll perhaps get help to design an electronic system, but the long-term fix is to redesign the wing to improve slow-speed performance so that the stall is less likely to sneak up on me.

 

I hope to increase wing area and incorporate the leading edge profile of the later D18, which is reported to handle better at slow speed. Adding slotted flaps should make a huge difference, and bring stall speed back to respectable territory.

 

Lyle

 

 

[facthunter]

Some types display a good prestall buffet (DH 82) and don't need a stall warning as such. Thin wings with small radius leading edges are not as forgiving. So-called laminar flow wings similar. A LRI is not a stall warning as such although one could be built into it. They even build stick shakers to wake you up. Nev

 

 

[ossie]

great !!

 

another damn gauge we have to teach people to stop looking at......

 

 

[old man emu]

There area couple of things that interest me with this instrument.

 

Firstly, is it correct to call it an Angle of Attack indicator, or is it a Dynamic Pressure indicator (and therefore an indicator of the amount of Lift a wing is producing). From my reading of the various articles linked in the preceding posts, I believe that the instrument should be described by the latter term, and then by extension, a Lift Indicator.

 

Secondly, I don't like the title "Lift Reserve Indicator" because the word "reserve" tends to imply that the instrument is showing something that could be used, and this could lead some pilots to go too far into a danger zone. Having said that, if the indicator was used as intended, ie, it is safe to fly in the green arc, but watch out in the white, and stay out of the red, I think that it is a much better tool for use at low airspeeds than an ASI.

 

ASI's, like all pressure instruments have a lag time, and are do not show speeds accurately to one or two knots. That's why they are called "indicators". They are fine to use as navigation aids to help work out groundspeeds, but I bet there are a lot of you who can tell me that your AIS gives a different reading from your GPS in cruise conditions. These Lift Indicators are measuring Dynamic Pressure, which can be related more accurately to the amount of lift a wing is producing. Provided the instrument is tuned to the particular airplane it serves, I believe that it would provide more information than an ASI in relation to the state of the airplane's aerodynamics.

 

As a final point, the display of this instrument (and I refer to the analogue instrument) is more readily interpreted than that of an ASI. Next time you are in your airplane, grab the POH and look up the Table of Stall Speeds. Then quickly look at the ASI and see if you can determine where the needle would be pointing to indicate those speeds. I'll bet you'll agree that it is easier to determine that a needle position on the LI indicates either a safe, or unsafe speed at which to be operating the airplane.

 

Old Man Emu

 

 

[dazza 38]

I dont know it sounds like crap to me.Its not needed in the aircraft we fly.

Going back to what I said 5 months ago.It would come in handy flying at night I guess or IFR etc. I still think we dont need it in RAA. We have even lasted over 20 plus years without a stall warning horn. I guess RAA guys have better stick and rudder skills than GA.(GA aerobatic guys alot better than we have)

 

 

[old man emu]

I'd rather have one of these Lift indicators fitted to a plane I flew than a whizz-bang GPS system. We didn't have a GPS when I learned to navigate, just a map with a pencil line; a compass and the ability to do mental arithmetic.

 

I have seen Angle of Attack instruments advertised for sale. Basically they are a slip ball mounted longitudinally.

 

OME

 

 

[facthunter]

If they are I hope they don't call them an angle of attack indicator, because they are not. The tiger moth had such an instrument and it could be a crude pitch indicator in steady flight. Nev

 

 

[Wayne T Mathews]

great !!another damn gauge we have to teach people to stop looking at......

Hear hear... Basic is good... Attitude + power = performance...