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  #1  
Old 06-23-2021, 04:10 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 491
Default What Energy Sounds Like

We know that "energy" is the algebra of how we convert thrust into altitude and/or airspeed, and how we use a combination of pitch, roll (lift vector placement) and throttle to work the variables in that equation. For example, if we are straight and level at 5000 feet at Vmax, and we pull back smoothly on the stick, we can convert that kinetic energy (speed) into potential energy (altitude). If we keep pulling over the top (fly a loop), then we will convert the potential energy we just gained, back into kinetic energy and end up where we started.

The other important energy concept is "P sub S" or "specific power." This is another trade-off problem for the pilot. If we have more thrust than drag (for a given weight), then our “p sub s” is positive: we can go up, accelerate or both. If, however, there is more drag than thrust, then “p sub s” is NEGATIVE. The airplane is going down, slowing down or both; unless the pilot does something and the ground doesn't get in the way. If thrust and drag are balanced, then "p sub s" is zero, and the airplane achieves best sustained turn performance for that power setting. The cool thing is that thrust and drag are balanced when an airplane is ONSPEED. If you can hear ONSPEED (or read it on a gauge--it's when the wing is producing 60% of it's total lift capacity) and ascertain whether you are fast or slow relative to that angle of attack, you have instant SA about your energy state.

A loop is a vertical turn. If we want to optimize sustained turn performance (best turn rate and turn radius over time), we turn ONSPEED. I had to do some test video editing, and thought this short clip might illustrate the paragraphs above with "a picture that's worth a thousand words" that is only 16 seconds long:

https://youtu.be/X5NzOUNJavA

You don’t have to fly aerobatics to want optimum turn performance…the same physics apply when you turn base to final or any time you maneuver the airplane.

Fly Safe,

Vac
FlyONSPEED.org

P.S. "MIL power" = wide open throttle
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Mike Vaccaro
RV-4 2112
Niceville, Florida

Last edited by Vac : 06-23-2021 at 06:46 AM. Reason: defined MIL power
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  #2  
Old 06-23-2021, 08:49 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,700
Default

Interesting.

For those of us that have EFIS based AOA, how do we figure ONSPEED? Is that the green dot that I get (calibrated when at 1.4 X stall speed). I remember you guiding me that I should slow my final down until I get the green dot and then keep the green dot all the way down final.

Larry
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  #3  
Old 06-23-2021, 09:57 AM
Vac Vac is offline
 
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Location: Niceville, Florida
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Hi Larry,

Yup. Your "green dot" if it's calibrated properly...it's the AOA associated with the speed = .76 x L/Dmax speed; and that's gonna' be 1.25-1.35 x stall in most airplanes (at 1G).

It does vary with flap setting, so if your AOA system doesn't have a flap position sensor, there will only be one correct calibration point. If that's the case, it's probably best to calibrate it for your standard landing flap configuration; that way it will be most accurate when you want it most: during approach and landing. It'll be off slightly for other flap conditions (but not by too much in RV's with NACA wings and plain flaps--bigger difference with the proprietary airfoils and slotted flaps [9, 10 and 14]).

v/r,

Vac
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  #4  
Old 06-30-2021, 09:15 AM
00Dan 00Dan is offline
 
Join Date: Nov 2016
Location: Atlanta, GA
Posts: 235
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Energy is always an interesting topic that is probably not taught well to most private pilots; instead, focus is spent on airspeed and pitch attitude, both of which are acceptable analogues for energy state in normal, non-maneuvering flight. Where it rears its head for most people is during departure and approach. On departure most people will pitch to accelerate to Vy/Vx or a faster cruise climb of choice - pretty simple, right? It's an inexact method since of course from a mathematical standpoint the plane is looking for an angle of attach that best balances lift and drag to accomplish the desired performance, while airspeed can be affected by environmental factors and weight, so we just get close enough. On approach a similar concept applies just going down instead of up - we use an approach airspeed to approximate the angle of attack where the airplane's lift and drag, and in combination with power its overall energy state, to configure the airplane in such a way that we have sufficient energy to make the runway while minimizing any excess we need to bleed out in the flare.

I have a set of the FlyONSPEED beta hardware and I've been flying with it for a couple months now. Vac sent me some calibration curves from his RV-4 which I re-used as is, assuming (reasonably, I feel) that our airplanes are likely very close from an aerodynamic perspective. The box was simple to install - Power, ground, a volume knob installed in the panel, and an audio connection of some sort. Since I don't have an intercom, I soldered mine to a 3.5mm headphone jack I bought on Amazon and plugged it into the aux port on my Lightspeed headset. Wiring the system from an electrical standpoint was very simple - installing a pitot mast and running lines to a Dynon pitot/AoA probe I bought was more labor intensive.

The first thing that stood out to me, having only ever before flown pitch/power/airspeed as I described in the opening to this post, was the relatively quick response of the system compared to letting indicated airspeed stabilize. It also served to expose some weaknesses in my static port configuration. It did open my eyes to the airspeed differences that weight, altitude, and yes, static port configuration, can have on various regimes of flight. The ONSPEED tone, letting me know I'm at approximately the approach angle of attack, came on consistently even though indicated airspeed changed due to a passenger, or because I was trying to fix my static ports. What let me know that it was working was just a day of pattern work. I flew some landings with traditional airspeed and then using just the tone. My landings with the tone resulted in much more consistent approaches and landings with minimal floating, indicating to me I was approaching in an optimal energy state. Over a few more sessions at various weights, I saw that the indicated airspeed required to equal that performance changed by several MPH; It's easy to see now where the assumption we have that at the weight and speed ranges of our airplanes a single approach speed is usually "close enough" falls short.

From a safety perspective, having the tone is of course great for gliding flight, which Vac's previous videos showing some "impossible turn" practice demonstrate. An scenario I encountered that many people sometimes discount as a time to be vigilant for maintaining control is a go-around. We all have had a late go around for some reason or another, I was flying on a gusty day and made a low level go around after a bounce. While getting rocked around at my usual pitch attitude, I heard the slow tone going off in my ear. A quick peek at the ASI to confirm and I lowered the nose to give my self a little extra margin in the shear field that occurs at 50-100' above the field at my home airport.

Overall, with a solid multi-point calibration I found the system to have made my energy management much more consistent across even just the normal regimes of flight. Where previously pitch/power/airspeed got "close enough," and we just shrug off the good landings and the bad landings, now I don't have many bad approaches where I floated down half the runway because I was too fast for conditions, despite flying an "optimal" airspeed. On departure, I fly best rate or best angle without issue - previously trying for best angle airspeed with the deck angle our RV's use can be tricky, especially in windy conditions. All of this culminates with the fact the audio tone lets me stay eyes outside.
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  #5  
Old 06-30-2021, 11:21 AM
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uk_figs uk_figs is offline
 
Join Date: Jan 2005
Location: Tulsa, OK
Posts: 1,185
Default Green dot

I have the Dynon D-100 AoA setup and with the early work you have done with the Dynon AoA probe what would be the closest position on the chevron indicator to correlate with the green dot optimum AoA indication. I use the tone and I can set the progressive tone onset to start at the bottom/middle/top of the yellow chevron area.
Thanks
Figs
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  #6  
Old 06-30-2021, 01:26 PM
Vac Vac is offline
 
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Location: Niceville, Florida
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Figs,

Short answer: fly some practice approaches at 1.25-1.35 times Vs Flaps 40 in still air and note the indication with your current calibration. Dynon has a selectable tone pattern; so, pick one that covers the part of the graphic that is lit when you are stable at that condition. Whatever that graphic/tone combo is your ONSPEED cue. You can repeat the drill at best glide speed, flaps 0 and that’s your L/Dmax cue for your airplane. Because of the way the Dynon calibration works (especially the older DY-10/100 systems), it will be hard to get your display to have ONSPEED correspond to say, the middle of the yellow chevron.

Long Answer: The Dynon AOA is a good progressive stall warning system; but it doesn’t appear to be designed to provide accurate performance cues (i.e, measure actual AOA accurately throughout the flight envelope). When we used the Dynon EFIS originally, we had a work-around that used an off-board processor that read the percent lift signal produced by the EFIS. We simply used a percent of a percent (i.e., a simple ratio) to make the tone work.

If you download your Dynon data into a spreadsheet, you can look at your percent lift plot. It will look something like this:



You can see the stall is occurring at about 80% total lift in this case, not 100. Now ONSPEED still occurs at 60% of peak (i.e., .6 x 80%); but I don’t think the Dynon graphic display makes allowance for this. It appears to be a simple look-up table (i.e., at X%, light Y graphic), thus my recommendation to use the calibration you've got instead of trying to chase a perfect calibration or calibrate to get your graphics to line up (if that makes sense).

Good on 'ya for using the system you've got! Hope this helps, but if it's clear as mud, or you've got more questions, post, drop an email or PM. Happy to help if I can.

Vac
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RV-4 2112
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Last edited by Vac : 06-30-2021 at 01:50 PM.
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  #7  
Old 07-04-2021, 10:58 PM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 491
Default More Dynon Info

Figs,

I found some old slides from our OSH briefing in 2018. If (big if) your Dynon is measuring 100% lift during stall with landing flaps, then the first two slides apply:





This is our best guess for the Dynon % lift associated with the visual display on the 10/100 EFIS. Now in all likelihood, you are NOT getting 100% lift at stall (see graphic in previous post); so the logic I laid out in the "short answer" is summarized on this slide:



Hope this helps clarify. Offer to help stands, if not.

Cheers,

Vac
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RV-4 2112
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  #8  
Old 07-05-2021, 07:02 AM
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uk_figs uk_figs is offline
 
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Location: Tulsa, OK
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Default

Vac
Thanks the charts are really useful as I can go fly some configuration runs and select the progressive tone start point that results in a distinguishable tone at the approximate Onspeed point. Also looks like at that point there is still some margin to react if taken by surprise due to rapid onset.
Only issue I can see is whether the tone will be distracting/annoying as it will likely be on for longer than it currently is.
Cool stuff
Figs
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Last edited by uk_figs : 07-05-2021 at 07:02 AM. Reason: correction
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  #9  
Old 07-06-2021, 08:04 AM
Vac Vac is offline
 
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Location: Niceville, Florida
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Figs,

Excellent. Sound plan.

We worked hard to make the fast tone and the ONSPEED solid tone cues pleasant so that it's "readily internalized" as the human factors folks would say--you only notice it when it's NOT there. We also attenuate it with radio or intercom so it blends into the background. We do, however, want the slow tone and stall warning to get your attention. We think it's important for the pilot to know that the airplane is in a negative energy state (more drag than thrust unless you do something). Not sure how the Dynon logic works, but interested to find out what you learn--post again after you've experimented.

We realize that flying using an aural cue as a reference is an alien concept for most pilots. Fighter and glider pilots have been doing it for years. We run into comments so often from folks that haven't tried it, we've got a name for it: green eggs and ham syndrome

Here's how we've got ours mech'd:

https://youtu.be/X59y9Song3U

And, we added a big, old-fashioned volume knob, so it's easy to adjust any time.

Cheers,

Vac
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  #10  
Old 07-08-2021, 01:11 PM
larosta larosta is offline
 
Join Date: Dec 2010
Location: Redlands, CA
Posts: 188
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Is anyone in the RV community other than Vac actually using the FlyOnSpeed in their aircraft?

If so what do you think about the experience?

-larosta
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