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  #1  
Old 06-27-2021, 09:07 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 487
Default What Sideslip Sounds Like

For an airplane to depart controlled flight, the pilot has to exceed the aerodynamic limit with yaw present. This is a short video clip of a skidding departure. In this case, the stall occurs with uncoordinated rudder. The airplane stalls, then immediately begins a snap roll. Note the significant wing drop that occurs as soon as the airplane stalls:

https://youtu.be/cLg_LGjpL9Q

One RV handling characteristic is how well the flight controls work approaching and during the stall. This characteristic combined with a lack of aerodynamic warning (buffet) prior to the stall at 1G, can give the pilot a false sense of security as he "eats up the aerodynamic margin," i.e., increases AOA and gets closer to the limit. The airplane feels solid, until it isn't and there is some unintended yaw present.

To address this, we decided to capitalize on the human brain's excellent evolved response to figure out what direction a sound is coming from. Garmin calls this "3D audio." Most of us call this stereo . In this short video clip, you can hear the tone moving left and right in the sound field if you play the audio through stereo speakers or wear a stereo headset or ear pods:

https://youtu.be/049M6zlendY

The tone mimics the behavior of the ball. To coordinate, you "step on the tone" the same way you "step on the ball." A handy feature when you are trying to max perform the airplane and may be intentionally operating at reduced margin (i.e., flying close to stall). It's drawn my attention to inattentive feet more than once.

Fly safe,

Vac
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  #2  
Old 06-27-2021, 10:29 AM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,946
Default

What a cool idea.

We use audio variometers in sailplanes so that we can be 'eyes out' in thermals and get climb-rate cueing to help us stay centered in the thermal. After awhile, it becomes second nature, and you don't even realize you are responding to the audio input until it is taken away and you realize you miss it.

I can imagine Reno Racers benefiting from this as a very precise yaw cue to maximize efficiency while operating in a high-workload environment. It would have to be low enough volume so that any radio calls would be heard over it, but loud enough to compete with the ambient sound levels.

The other question is what the source of the input? Inertial? Could that be accurate enough with sufficient filtering for a very turbulent environment? It would be hard to devise an aerodynamic sensor because of the prop swirl, but a cone probe outboard on the wing could work. One would want resolution to a small fraction of a degree.
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RV-8 N825RV
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WW 200RV
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  #3  
Old 06-27-2021, 11:50 AM
larosta larosta is offline
 
Join Date: Dec 2010
Location: Redlands, CA
Posts: 188
Default

The application for an aircraft that is raced at Reno would be interesting. I discussed this with a couple of Biplane pilots and a team that was working on a new entry in the F1 class. I did not think that the biplane folks would be too interested based on what I have seen. If someone came up with a new one off design that incorporated some real drag reduction and optimized airfoil design and was willing to embrace some technology like “Phantom” did many years ago I think that a tone based AoA / slip feedback system would be pretty useful. The F1 team I talked too was too caught up with making it pretty to be too interested in wringing out a better line around the pylons. I did not talk to any of the Sport Class teams but I think that the several competitors in the bronze class could get a lot of bang for not a lot of bucks by being able to optimize their AoA. Something to be trained in an environment with other aircraft on the course as the airmass can become pretty turbulent if you are not the guy in front.

I would have liked to see a F1 team try it as the class is pretty close and small improvements in areo efficiency can make a big difference on Sunday night.

Just a few observations. - larosta
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  #4  
Old 06-27-2021, 12:17 PM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 487
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Our primary objective is keeping folks alive in the traffic pattern. The AOA system is actually very accurate (1/4-1/2 degree) across the speed band of the airplane (Vs to Vmax), even under G. Our tone logic is only active at speeds below L/Dmax since it is optimized for maneuvering flight, approach and landing.

Steve, you are spot on--works very similarly to a variometer. It's readily internalized as you said and exists peacefully with radio and intercom. Here's a short clip with some voice over (intercom) and radio on top of the basic tone pattern as the airplane decelerates. Volume and radio "cut out" logic are pilot controllable. When the tone transitions from ONSPEED to "slow", the brain perceives the higher frequency as a higher volume. We augment the stall warning volume a bit as well to make sure that annoying warning comes thru loud and clear:

https://youtu.be/X59y9Song3U

An accurate beta (sideslip) cue at high speed would be practical with the right probe--the physics would support it. We are actually working on probe geometry now to see if we can get past the sideslip limitations of conventional pitot/AOA (e.g., Dynon, Garmin, etc).

v/r,

Vac
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Last edited by Vac : 06-27-2021 at 12:20 PM.
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  #5  
Old 06-27-2021, 02:48 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
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It would take a little training for a pilot to pay attention to this, especially if they are already at least somewhat experienced without it. With that, though, this is an excellent idea. Good work!

Dave
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  #6  
Old 06-27-2021, 03:55 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Quote:
Originally Posted by Vac View Post
An accurate beta (sideslip) cue at high speed would be practical with the right probe--the physics would support it. We are actually working on probe geometry now to see if we can get past the sideslip limitations of conventional pitot/AOA (e.g., Dynon, Garmin, etc).

v/r,

Vac
A conventional 5-hole cone probe would work well for AOA and beta. Needs 5 pressure transducers and a microprocessor to compute the AOA and beta from the calibration map. Lots in the technical literature for how do do this. Extra accuracy and angle change can be gained from a 7-hole cone probe but that is beyond the requirements here. See for example Zilliac, G.,et al from NASA, circa late 1980's.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
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  #7  
Old 06-27-2021, 10:26 PM
dmn056 dmn056 is offline
 
Join Date: Aug 2014
Location: Sydney, Australia
Posts: 44
Default Flush air data

If you're looking at a 7-hole probe, with associated transducers and computation, you might also consider a flush air data system distributed over the wing tip leading edges. Four transducers on each tip would work.

Note also that the over-determined solution obtained would allow real-time uncertainty monitoring. And, you would get Mach number as a by-product...
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  #8  
Old 06-28-2021, 06:19 AM
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Steve Ashby Steve Ashby is offline
 
Join Date: Jul 2006
Location: Stone Mountain, Georgia
Posts: 492
Default What an incredible safety feature!

Mike,
This is a game changing safety feature. Will you make this available to the masses?
Thanks!
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  #9  
Old 06-28-2021, 08:39 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 487
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Hi Steve,

We are working on that! We are currently coordinating to have production units available for folks that don't want to build a system. If you're handy with a soldering iron and can do basic electronic assembly, instructions and parts list are available on our GitHub site: https://github.com/flyonspeed. We have more info available on our website as well: flyonspeed.org.

Using the logic is pretty simple: don't pull harder than optimum AOA (ONSPEED) and keep the tone centered in the sound field. For more of a deep dive, we've got academics up on the site with embedded video: https://www.flyonspeed.org/what-is-onspeed. Click on "how to use the AOA tone" in the menu bar at the top of the page.

As an open-source, non-profit, shoestring budget group, we also hope that manufacturers notice the logic and adapt it to existing systems. We are also happy to collaborate with anyone interested in reducing loss-of-control mishaps. Find us up at OSH--contact info is on our home page if you want to talk AOA, energy management or training.

All of this is proven military technology--our objective is to make it accessible to the EAB community.

v/r,

Vac

P.S. We are grateful for the engineering inputs. Very helpful. There's a deep bench in the VAF family
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