[Andy_RR]

Just wondering out loud here...

When people use the Dynon (for example...) pitot-based angle of attack sensing, what happens to it in inverted flight? Does it cease to function or return rubbish data?

Just curious...

A

 

[TX7A]

It doesn't seem to me that the AOA/pitot would give a hoot wheather it was upside down or right side up. I would think that realitive flow calculations would work out the same. Now, the Dynon unit itself may be affected...I don't know. Just my $.02
dynonsupport ?

 

[az_gila]

The only thing in the Dynon...

It doesn't seem to me that the AOA/pitot would give a hoot wheather it was upside down or right side up. I would think that realitive flow calculations would work out the same. Now, the Dynon unit itself may be affected...I don't know. Just my $.02
dynonsupport ?

...that should care if it's upside down in the AHRS....

The electronics don't care.

 

[Andy_RR]

It doesn't seem to me that the AOA/pitot would give a hoot wheather it was upside down or right side up. I would think that realitive flow calculations would work out the same. Now, the Dynon unit itself may be affected...I don't know. Just my $.02
dynonsupport ?

What angle of attack would it measure?

 

[Chris Meredith]

This is actually an interesting question since the lifting surfaces of the wing are reversed. I would imagine that it would show you at a very low angle of attack (even if you were about to do an inverted stall) but I don't think any of the AOA sensors out there were designed to give meaningful data in such a flight attitude. It would be interesting to hear from somebody who's tested this with the Dynon or AFS systems.

 

[PCHunt]

The AoA presentations that rely on pressure differential between two sources are actually calculating the AoA. My guess is that the calc's assume positive "G", or positive AoA. [BTW, these "calc's" can be analog calc's, as in just a pressure differential gage marked with AoA information.]

If you look at a photo of an experimental test flight vehicle, you will likely see a long probe off the nose, and at the end of that probe, an angle-of-attack vane.

That vane could be built to show angles of attack in a 360 degree range (0 to +179, and 0 to -179.) (+ or - 179 would be a tail-slide.) Some of those test probes also show yaw angle, or yaw angle-of-attack, also in a 360 degree range.

The pressure-differential AoA's can't do that.

Can someone go up and fly inverted, level, (which assumes negative 1 G,) and report their results?

 

[Rainier Lamers]

Just wondering out loud here...

When people use the Dynon (for example...) pitot-based angle of attack sensing, what happens to it in inverted flight? Does it cease to function or return rubbish data?

Just curious...

A

I can't speak for any manufacturer other than MGL.
The AOA would measure increased pressure on the wing "top" (the real top) and reduced pressure on the wing bottom. This means the angle would at the end of the day calculate negative. In our case it would read "0" as we have not made provision for a negative AOA.
It's an interesting question and to be honest, not something I have even considered when I designed our AOA measurement system.
Hmmmmm.....

Rainier
CEO MGL Avionics

 

[Veetail88]

Why ponder it?

Not like anyone is going to be making a turn from base to final while inverted. This is almost as bad as wondering if Bret Favre is going to retire or not. Who cares?

 

[N941WR]

Not like anyone is going to be making a turn from base to final while inverted. This is almost as bad as wondering if Bret Favre is going to retire or not. Who cares?

I've seen this done. On short final the Pitts rolled upright and landed as if nothing was going on. Legal and safety issues a side, it was kind of funny to watch.

 

[Ironflight]

This discussion has me wondering what the "computed" AoA would do in the GRT while inverted....but I'm not going to go negative G in the Val to find out - unless someone wants to donate a bunch of oil and a good airplane belly cleaning afterwards....

 

[Dynon]

Like MGL, Our calculation of the pressure differential just bottoms out when you get to zero AOA. Negative will still read as zero.

It is possible to build a differential probe that reads while at negative AOA, but ours is not optimized for that at all, even if the math up in the display tried to deal with it.

 

[rv7boy]

AOA while inverted...?

I'm wondering why anyone would be looking at an AOA while inverted. The few times I have been inverted in an airplane I sure wasn't looking at no instrument panel. Momma, get me back to straight and level!!!!

 

[hendrik]

I'm wondering why anyone would be looking at an AOA while inverted.

Don't have AOA in a glider, but I surely look at the air speed when I'm flying inverted. Not only for avoiding stall/spin, but also for making absolutely sure that I'm not too fast before pulling half a loop to level flight. It's just too easy to exceed vne. Of course this requires that you can trust your ASI in inverted flight (calibration!).

 

[DGlaeser]

Inverted AOA options

The pressure type of AOA indicators would not be useful, because they are installed to read positive angles of attack, and inverted flight is a negative angle of attack.
You could mount a second unit on the top of the wing and calibrate it for inverted flight

A vane type of AOA could be designed to work for both upright and inverted flight. It would need to provide the range of motion for the vane for both upright and inverted flight and the display would have to be designed to display both positive and negative AOAs.

ASIs will work inverted, but may be inaccurate for two reasons. First the angle of the airflow at the pitot intake may cause inaccurate readings, especially at high negative angles of attack. Second the static source may provide inaccurate readings while inverted. You'd have to do some flight tests to develop an actual vs. indictated table for inverted flight.

 

[Rainier Lamers]

Depends on the type of AOA sensing.
Some have a hole on the top and bottom side of the wing, near the leading edge. We call this "differential" AOA. This method could work upside down provided the pressure sensor used goes both ways and the following electronics and finally software can deal with it.
The other type is the "single ended" AOA such as used by Dynon (for example). This uses a special probe and uses airspeed and static to make up the missing information. I am not sure how this would work out upside down but I suppose it could work (perhaps after a fashion).
In our case you are free to choose either method (you need to tell the EFIS which method you are using of course) - but as mentioned before, currently our system would not give you a negative angle anyway.
I did look into this after this thread started (for interest sake) but it would require a hardware modification in our case. While the pressure sensor that we are using can go negative, we biased the following electronics for positive operation to allow maximum range so it would work negative only for the slower airspeeds as the electronics would quickly "bottom out" in this case.

Rainier
CEO MGL Avionics

The pressure type of AOA indicators would not be useful, because they are installed to read positive angles of attack, and inverted flight is a negative angle of attack.
You could mount a second unit on the top of the wing and calibrate it for inverted flight

A vane type of AOA could be designed to work for both upright and inverted flight. It would need to provide the range of motion for the vane for both upright and inverted flight and the display would have to be designed to display both positive and negative AOAs.

ASIs will work inverted, but may be inaccurate for two reasons. First the angle of the airflow at the pitot intake may cause inaccurate readings, especially at high negative angles of attack. Second the static source may provide inaccurate readings while inverted. You'd have to do some flight tests to develop an actual vs. indictated table for inverted flight.

 

[Andy_RR]

OK, I'll confess why I asked...

I've been wasting precious fuel tank building time surfing http://diydrones.com/ and looking at all the seriously cool stuff people are doing with the Arduino IDE and other open source embedded platforms.

Part of this surfing, reading and pondering has me thought-experimenting on how the pitot AoA works and how useful that would be for the control algorithms that have yet to be developed...

I am also doing thought experiments on the autoland capability of an RV-8.

I have heard that Cirrus would like to augment their emergency parachute handle with a "I give up - take me home and park it" button on the instrument panel. I don't know whether this is true or not.

Andrew

PS: Please don't PM me and tell me to get back to my rivetting like folk have done in the past. I'm experimental for the education as much as the recreation.

PPS: Thanks a bunch for taking the time to consider the question, especially Rainier and the Dynon guys!

 

[Andy_RR]

OK, I've just felt the need to expound my ideas further. Someone is probably already considering it and I'm sure there are a mountain of issues, but...

...one of the ideas I'm playing with is how to navigate and glide from a random point in space down to a pre-defined landing strip. Now, the next evolution of this idea is to develop it into a HITS-style guided emergency landing route at the punch of a button.

Now I know we should all drive around in cars with spikes on our steering wheels and all that, but please humour me a little here. Anyone know of such a project?

 

[Ironflight]

...one of the ideas I'm playing with is how to navigate and glide from a random point in space down to a pre-defined landing strip. ...... Anyone know of such a project?

Space Shuttle?

Couldn't resist! But that is essentially what the guidance software does. Of coure, there are serious limitations as to what landing strips are reachable from any random point in space.

Paul

 

[Will_S]

...one of the ideas I'm playing with is how to navigate and glide from a random point in space down to a pre-defined landing strip. Now, the next evolution of this idea is to develop it into a HITS-style guided emergency landing route at the punch of a button.

Anything that has VNAV capability creates the profile to an airport, or a user specified height above the airport. I use it all the time on Garmin 430/530 - although I try very hard to not be gliding! Tie that in with the "nearest airport" function and its not many button pushes to achieve what you want.

Wouldn't this then display as a flight-path for HITS capable displays?

As Paul intimated, realising that you're not able to make your chosen airport is perhaps more important..... How about using TAS & Rate of Descent to create a glide-range ring on a map display that takes into account current wind and terrain? That would be very useful!

 

[Andy_RR]

Space Shuttle?

Couldn't resist! But that is essentially what the guidance software does. Of coure, there are serious limitations as to what landing strips are reachable from any random point in space.

Paul

Yes, good example! I guess the glide ratio of the STS adds some limitations too!

 

[n5lp]

...As Paul intimated, realising that you're not able to make your chosen airport is perhaps more important..... How about using TAS & Rate of Descent to create a glide-range ring on a map display that takes into account current wind and terrain? That would be very useful!

I guess that would look something like this.

 

[Will_S]

I guess that would look something like this

Wow!! Sure is hard to come up with a new idea now-a-days!!

 

[dmaib]

Anything that has VNAV capability creates the profile to an airport, or a user specified height above the airport. I use it all the time on Garmin 430/530 - although I try very hard to not be gliding! Tie that in with the "nearest airport" function and its not many button pushes to achieve what you want.

Wouldn't this then display as a flight-path for HITS capable displays?

As Paul intimated, realising that you're not able to make your chosen airport is perhaps more important..... How about using TAS & Rate of Descent to create a glide-range ring on a map display that takes into account current wind and terrain? That would be very useful!

You have just described the Chelton EFIS system!

 

[Dynon]

In devices that have SynVis and a flight path indicator, you can look at the FPI and see if it's beyond the airport you are hoping to make.

 

[nucleus]

Synthetic vision not necessary

My old GRT Horizon has a 3D depiction of the runway and the flight path indicator tells you where you are going to be. They also have a display arc that pops up as you approach the airport that tells you at what point you will reach pattern altitude, which I find really handy for everyday flying, no more calculating, just adjust your pitch to put the arc where you want it.

Hans