ONSPEED Angle-ofAttack Energy Management: Thinking Past the Airspeed Indicator
Today’s Discussion • What is ONSPEED? • How do you find ONSPEED in your airplane?
• ONSPEED Aural Tone System • Listening to your AOA
• How do I use ONSPEED when I fly? • AOA Rules of Thumb
• Building a Tone Generator • MGL Avionics Adaptation
What is ONSPEED Angle-of-Attack (AOA)? • Optimum AOA for maneuvering + approach and landing • Occurs when the wing is producing about 60% of its total lift capacity
• Why it’s handy to know • Optimum from an energy management (EM) perspective • VREF • Always the same AOA: compensates for changes in bank angle/G, weight and density altitude • Simplifies maneuvering and pattern operations and improves consistency • IAS “automatically” varies, as required, when maintaining ONSPEED
Where has ONSPEED AOA been all these years? • Hiding in plane sight: Nothing in this briefing is new information! • 1907: Orville and Wilbur discuss “angle of incidence device” • Military adopted AOA in the 50’s and 60’s • Extremely effective • Nearly universal in US military fixed wing aircraft • Reference for “max performance” maneuvering (including approach/landing)
• No inexpensive civilian equivalent until coefficient of pressure technology (60’s and 70’s) married up with the tech revolution in the 21st century • Energy Management is still a grey area for many pilots • “1 G mindset”
Full Disclosure… • “There are several flight conditions where airspeed is an easier and better performance parameter than angle of attack.” • “It must be emphasized that angle of attack is not a panacea for all that can go wrong with a flight maneuver…The major difference between angle of attack and airspeed/bank limitations is that angle of attack shows the pilot precisely what his aircraft is doing with relation to the aerodynamic limitations...” -USAF Report IFC-TR-72-3 (1972)
How Can Flying ONSPEED Improve My Flying? • Unless you fly aerobatics, you probably spend 99% of your flying time at AOA’s lower than ONSPEED • It’s that small portion of time you are “flying the back side of the drag curve” that matters: Takeoff and Landing Operations = Maximum Performance Flight
• If you fly ONSPEED, you can’t depart controlled flight and you are maintaining optimum energy • ONSPEED not affected by G load, attitude, gross weight or density altitude • If you do fly all-attitudes, ONSPEED is an outstanding learning aid for maneuvering
Academics
Energy Management 101 • Energy comes from power (thrust) converted into altitude and airspeed • Throttle controls total energy • We add thrust to gain energy • We reduce thrust and/or add drag to lose (or “bleed”) energy
• Basic Maneuvering Energy = Altitude + Airspeed
• Constantly trading one for the other—it’s a zero sum game! • Roll to manage lift vector • Throttle to control power • Pitch (G/Lift) to control drag
How we manage the thrust, drag and lift vectors
• Maneuvering limits: Speed, G and AoA
Load Factor (G’s)
8
Aerodynamic Limit
7 6
13 . 14 2 .6 16 .7
6. 0 7. 4 9. 0 10 .7
9
3. 3 4. 0
1. 0
Aerodynamic G Available Structural Load Limit
+ G Limit
5 4
+ Asymmetric Limit
3
S Gu P F 50
2
Dynamic Speed Limit
st
1 0
Structural Speed Limit
-1 -2
- Asymmetric Limit
-3 -4
- G Limit 0
Maneuvering Speed Corner Velocity
100
150
165 180
Airspeed MPH
200
250
Drag Curve Drag/Power Required
“Region of Reverse Command”
S
ll a t
A DM
L/
X
Wing is producing about 60% total lift capacity ONSPEED
AOA + ON
SP
D E E
Airspeed +
13 . 14 2 .6
7. 4 9. 0 10 .7
9
3. 3
1. 0
Aerodynamic G Available Design Load Limit: + 9.0 G’s
Load Factor (G’s)
8 7 6
+ G Limit
RV-4 S/N 2112 Flight Envelope
5 4
+
Asymmetric Limit
3 2 1
1375 Lbs or Less Gross Weight
ONSPEED BAND
0 -1 -2
- Asymmetric Limit
-3
- G Limit
-4
Design Load Limit: - 4.5 G’s 0
50
100
150
Airspeed MPH
VNO
200 VNE
250
“Optimum” Turn Performance Key Instantaneous Turn RATE
Instantaneous Turn RADIUS Sustained Turn RADIUS
ONSPEED @ 2.5G’s
Sustained Turn RATE
Aero
ONS PEE D
Lim it
How to find ONSPEED CLmax
CL
αzero lift
α – αzero lift / αcrit - αzero lift = CL / CLmax = 1 / (V/V
α
αcrit
Simple proportion that varies as the square of speed… that ratio at the end is VREF 😎
Caveman math… • ONSPEED occurs when the wing is producing about 60% of it’s lift capacity… • That means that: .6 ≈ 1 / (IAS/IASSTALL)2 • You already know that ratio (IAS/IASSTALL) as “VREF” • • • •
It’s 1.2-1.4 VS 1/(1.2)2 = .695 1/(1.3)2 = .591 1/(1.4)2 = .510
• Practice Drill:
• IAS for stall is 63 MPH IAS, what IAS is approximately ONSPEED? • 75-82 MPH IAS
Drag vs Power Required Drag
Option B: Work Backwards from L/DMAX
V
Power Required V = Velocity VMP = Min Power VMD = Min Drag
0
VMP
VMD = 1.32 VMP
V
What about flaps? ONSPEED ≈ 1.3 VS*
CL
ONSPEED ≈ 1.2 VS*
Flaps Down
Clean
α
*Compromise ratio if system is only capable of displaying AoA for a single configuration. Multiple configurations require flap position sensor. If only one “curve” can be displayed, should be lowest AoA stall.
Calibration
Only 2 data points required… Stall Coefficient Of Pressure (CP) or Vane
e n i L
a
la e rR
hip s n tio
Zero Lift Stall Warning
RV-8 Test
EFIS Recorded Data, 1 Second Intervals
60%
EFIS Recorded Data, 1 Second Intervals
Airspeed (MPH CAS) / % Lift
RV-4 Test
Airspeed % Lift (AoA)
Flaps 0 Max Lift 75%
Elapsed Time in Seconds
Flaps 20 Max Lift 82%
Flaps 40 Max Lift 87%
EFIS Recorded Data, 1 Second Intervals
Airspeed (MPH CAS) / % Lift
RV-4 Test
Airspeed % Lift (AoA)
Flaps 0 Max Lift 75%
Elapsed Time in Seconds
Flaps 20 Max Lift 82%
Flaps 40 Max Lift 87%
Bias or Sluing ONSPEED • ONSPEED has to be verified by FLIGHT TEST • Start here: VS (IAS) x 1.25 ± 4-5 KTS/MPH
• It may be desirable to bias the ONSPEED band based on empirical evidence • Trust, but verify!
• Verify nominal performance with known airspeed
• Can adjust band up or down
• Perception Consideration:
• If you’ve been flying IAS, you may be carrying too much energy during approach and round-out/flare • Flying ONSPEED properly requires experience
What does ONSPEED look like? • Using your graphic indicator and progressive stall warning to approximate ONSPEED • 60% Rule of thumb based on YOUR calibration • Examples: Standard military display, adopting a commercial display and progressive stall warning tone… • Perfect World: Stall at 100% Lift • Real World: Stall at Y% lift, ONSPEED approximately .6 x Y
Bendix “Standard” Military Indicator
Slow
Slightly Slow
ONSPEED
Slightly Fast
Fast
Adapting a Graphic Display and Progressive Stall Warning Tone 99% 75% 74% 65% 60% 50%
55% 49%
Step 1: Figure out what % lift your airplane stalls in lowest AOA configuration (flaps) Step 2: Find 60% of that value Step 3: Figure out what that looks like on your graphic display Step 4: If you have progressive stall tone, chose an option that allows you to clearly differentiate ONSPEED (and L/DMAX), if practical
Practice Drill 99% 75% 74% 65% 60% 50%
55% 49%
• Airplane stalls at 99% lift with full flaps… • 5 Different progressive stall warning tone options available: • • • • •
Always off What would ONSPEED On in the red look like, and which tone Start yellow top option would provide the Start yellow mid most information? Start yellow bottom
Practice Drill (Continued) 99% 75%
74% 65% 60%
Slow
Slightly Slow
ONSPEED
55%
Slightly Fast
50%
Fast
Listening to your AOA
AOA Tone Concept • Simple, intuitive cues increase precision and warning, mitigate LOC risk • Pilot listens to AOA in region of reverse command
• Real-time AOA feedback simplifies energy management during maneuvering flight, approach and landing • Inexpensive, easily adaptable “heads up/eyes out” technology
Background • Adapted from proven McDonnell Aircraft F-4 logic • Reduced LOC mishaps in service use
• Modified logic for light airplane aerodynamics • Allows pilot to discern L/DMAX, ONSPEED and stall
• Runs on inexpensive hardware and software • Homebuilt system tested in representative EAB aircraft • Circuit design and software available to EAB community via open-source
• Adopted by MGL Avionics • Pilot-programmable user mode available
-Improves Training Effectiveness -Standard cues/concept could ease transition between types
Drag/Power Curve
Aural AoA Logic “Slow” Tone 1600 Hz Beeps
Airspeed
20 PPS
15 . 1
6.5 PPS
VS
1.5 PPS
ON
SP
Stall Warning
Vs E L/ ED Dm ax
Drag/Power Req
AOA Tone Region
ONSPEED Steady Tone
“Fast” Tone 400 Hz Beeps
60% 6.5 PPS Total Lift
Airspeed DECREASING / AoA INCREASING
A DM
L/
1.5 PPS
X
AOA Tone Logic Demonstration • Click on slide title to view video
Terminology “Stall” Tone
“Slightly Slow”
High Pitch “Slow” Tone
“Slightly Fast”
“ONSPEED” Steady Tone
Low Pitch “Fast” Tone
Basic Maneuvering Demonstration • Click on slide title to view video
Works Throughout Flight Envelope 9
Design Load Limit: + 9.0 G’s
8
STALL WARNING TONE
7
Load Factor (G’s)
6
+ G Limit
OW L S
5 4
+
Asymmetric Limit
N TO
S FA
3
E
ON T T
RV-4 S/N 2112 Flight Envelope
E
2
1375 Lbs or Less Gross Weight
1
ONSPEED BAND
0 -1 -2
- Asymmetric Limit
-3
- G Limit
-4
Design Load Limit: - 4.5 G’s 0
50
100
150
Airspeed MPH
200
250
Maneuvering Under G Demonstration • Click on slide title to view video
How it Works • When AOA is stabilized, it can be used as a “control” indication • Pitch feedback for optimum performance • Accurate trend information • Warning when approaching aerodynamic limit
• Pilot can easily differentiate between L/DMAX, optimum AOA and aerodynamic limit • Ergonomics
• Decreases reaction time (multi-modal input) • Uses “free RAM:” little demand placed on auditory system • Sound more effective than vision helping brain compute timing inputs; sound processed faster than vision • Full disclosure: Effect of acute stress on auditory perception
How It Helps the Pilot • Tone logic simplifies energy management • Energy management is how we trade altitude and airspeed • Pitch/power/roll
• ONSPEED = best PS/turn rate/radius = optimum AOA for maneuvering flight = VREF for approach and landing • Compensates for roll, G, density altitude, weight
• Bottom Line: Maintaining proper energy is key to aircraft control and optimizing performance
Approach and Landing • ONSPEED = VREF at 1G • Stabilizes airspeed and attitude during approach and landing • Highly effective for pattern corrections • Energy Cues + Warning = positive aircraft control • Simplifies pattern and glide path corrections • Proper energy at round-out/flare
• ONSPEED base and final • “Heads Up and Eyes out” reference; compensates for bank angle/G, density altitude, weight
Maneuvering Flight • ONSPEED = maximum performance AOA • Assists with maneuvering at or near aerodynamic limits • All attitude, “eyes out” cue
• Out-of-Control avoidance/recovery aid • Prevention • Mitigates reduced static stability and/or limited stall warning risk • High AOA maneuvering aid
• Recovery • Secondary stall avoidance • Reduce altitude loss during recovery
Flying ONSPEED
ONSPEED Rules of Thumb • When AoA is stabilized, it can be used as a “control” indication • During Takeoff
• Best Angle: full power + rotation to known pitch ➔ transition to ONSPEED • Best Rate: full power + rotation to known pitch ➔ transition to L/DMAX
• During Maneuvering Flight
• Start from known parameters (energy condition) ➔ apply target G ➔ optimize turn performance by using ONSPEED AoA
• During Approach and Landing
• Slow and configure airplane for approach and landing ➔ trim ➔ maintain ONSPEED until flare, touchdown in slow or stall tone, as appropriate
• Maximum endurance glide ONSPEED • Maximum range glide at L/DMAX
Video Demonstrations • Takeoff • Normal Pattern and Landing • High, fast over-shooting Base to Final • Low, slow over-shooting Base to Final • Low, slow, under-shooting Base to Final • Glide • Split-S Comparison • “Beating the system” Accelerated Stall
Additional ONSPEED Video Resources • Short (Various Pattern Demonstrations) • https://youtu.be/BCQF8B49tgw
• Long (“How to”) • https://youtu.be/-kbA6NxMpmQ
AOA Tone In a Nutshell • Proven in service use, successfully tested in EAB type • Inexpensive and easily adapted • Easy to learn • Simplifies and improves EM • Improved training effectiveness • Facilitates precise instructor commentary and reduces need for instructor input
• “Heads Up/Eyes Out” solution • In work: pilot selectable portions of the logic, “null” tone for nonaerobatic operations, stand-alone system/simplified calibration
Tone Generator • Hardware and Software • https://github.com/dinglewanker/aoa-tone-efis-serial
Test set installed in RV-4 testbed equipped with dual Dynon DY-10A EFIS
MGL Integration
MGL Integration 1) Use iBOX AOA differential air pressure input Ports --OR-2) Build a Vane type sensor that provides a variable voltage into iBOX Analog sensor input corresponding to changes in angle of attack
Differential
MGL iEFIS – 2 ways to integrate AOA into system
45Deg Offset
Then program (load) AOA text file and tell system to use it VA N
AI
R
E
OW FL
Electrical ANGLE of ATTACK SENSOR Vane
Add Wing Upper/Lower Differential Pressure Ports
Pitot Tube Port with 45Deg Offset Differential Pressure Port
Pilot Programmable MGL Text File (iEFIS G2/3) ;User AOA tone sequence table
;Minimum indicated airspeed to activate AOA tone followed by maximum airspeed. Speed in MPH.
;
30,105
;
;Each line consists of 5 numbers in the following order:
;1-Frequency
;2-Tone duration in milliseconds (=.001 second) ;3-Pause between tones in milliseconds (if tone repeat > 0)
;4-Repeat count (set to a value of 10 or greater for continuous), Tone parameters will be updated at a rate of 8 Hz in EFIS.
;5-Volume Attenuator 0,1,2,3 (0=High volume -> 3=low volume, each step is 6db)
;
;This table must have exactly 38 lines. This covers the AOA range from 0 to 18 degrees in 1/2 degree steps.
Example Text File (Continued) 0,0,0,0,0 ;5.5
400,100,1000,5,3 ;6
400,100,900,5,3 ;6.5
400,100,850,5,3 ;7
400,100,800,5,3 ;7.5
400,100,700,5,3 ;8
400,100,600,5,3 ;8.5
400,100,500,5,3 ;9
400,100,400,5,3 ;9.5
400,100,300,5,3 ;10
400,100,100,5,3 ;10.5
400,100,0,10,3 ;11
400,100,0,10,3 ;11.5
400,100,0,10,2 ;12
400,100,0,10,2 ;12.5
1600,100,1000,5,2 ; 13
1600,100,800,5,2 ; 13.5
MGL Bench Test Video • Click on slide title to view video • Note: IAS in video is not accurate
Recap • When AoA is stabilized, it can be used as a “control” indication • During Takeoff
• Best Angle: full power + rotation to known pitch ➔ transition to ONSPEED • Best Rate: full power + rotation to known pitch ➔ transition to L/DMAX
• During Maneuvering Flight
• Start from known parameters (energy condition) ➔ apply target G ➔ optimize turn performance by using ONSPEED AoA
• During Approach and Landing
• Slow and configure airplane for approach and landing ➔ trim ➔ maintain ONSPEED until flare, touchdown in slow or stall tone, as appropriate
• Maximum endurance glide ONSPEED • Maximum range glide at L/DMAX
Questions?
