No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

[DesertFox4]

https://youtu.be/m_tKShlf_gU
Video by FlightChops.


I’m sure some members have seen this already and it sounds like airline pilots already live this.


DMMS= Stall Speed (Clean Configuration) X 1.404.

Example: 48 mph X 1.404 = DMMS of 67.392 mph.

Low altitude, loss of speed scenarios = loss of good friends.😢

[Norm]

Good info Steve. I have had a couple of motor outs on take off but had just finished training in a pusher type aircraft where my instructor had drilled into me push forward first then look at options. (pushers tend to balloon up on no power) Because of training both motor outs were non issues and ended safely for both me and the airplane.

[DesertFox4]

It can happen at any time anywhere to anyone Norm. Glad yours were successful too.

I’ve experienced 4 loss of power on takeoff events in just under 3,000 total flight hours. Also with no injuries or even a scratch on the aircraft. Instant and correct reactions were critical to all 4 successful outcomes.

Early training in my student pilot days from my CFI (Thank You Lyle) instilled the only useful action during these events. An instant realization of the loss of power with an immediate and deliberate HARD push on the controls to unload the wings and retain some forward airspeed. Land fairly straight ahead to remain out of a stall/spin scenario. On the way down or during rollout, with the fuselage, try to hit the smallest thing directly in front of you. I doubt any of my four events took longer than 10 to 15 seconds before I was on the ground and stopped. No time for any alternate action than described above including any “OMG is this really happening to me” time. Certainly no “ what should I do now” time. This has to be trained and engrained in the pilot before a loss of power scenario occurs or the natural instinct kicks in to PULL to keep from impacting the ground. I guarantee that this instinctual reaction is what killed two of my friends in their Kitfox a few years back when they lost power on takeoff.

In an event such as these, the aircraft becomes your survival capsule and has no other value at that time. When all four events happened, I was not high or fast enough to analyze anything. No time to flip a switch or change fuel tanks or even look at the panel for any indications of trouble. Get it on the ground without stalling is the only mission.

All four events were similar. An immediate reduction in power from wide open to idle power. No engine quit running but all failed to produce useable power to maintain flight. All four resulted from fuel delivery issues to the engine. All four events were in tried and proven aircraft and not during first test flights of a newly completed aircraft where you would and should expect an issue like this to arise.

This video struck a chord as I’ve lost friends to this power loss on takeoff scenario that may have survived with this info and procedure instilled in them.

Call me “still learning after 39 years of aviation.”👍

[aviator79]

This is a great video. I teach my students many of the same things, including an aggressive push. I like the "light in the seat" criterion. I'll be teaching that going forward.

[korbike]

Thanks Steve,
Great video, thanks for posting! David

[Cherrybark]

My initial instruction and the subsequent teaching I did as a CFI/Glider was with auto tow launches. Chop the top off something bit old Pontiac so the driver and passenger can see the glider, stretch out 1000' feet of rope, hook up the glider, give the appropriate signals, and you're off. Once the glider leaves the ground the stick is eased all the way back and held in your lap till the top of the tow. Real world rope brakes are a fact of life and instruction includes multiple simulated breaks with the instructor surprising the student by releasing the hook. You quickly learn the instant response of stick forward before you start working on the problem of whether to land straight ahead or do a 180. Top of a good tow might be 750' - 800'. A rope break in the 500' range makes for a tough decision. Slip for a straight ahead landing or turn and have any headwind become a headwind as you try and land back at the take off point. Fun times and the club charged $0.50 a flight.

[tracstarr]

I watched this the other day. Great video. I was never taught this in my training nor was there any emphasis on the need to make that push instinct and instant. It's something I want/need to work on for sure.

Additionally, does anyone know with the G3X if you have any options/settings to add an indicator for something like this?

[PaulSS]

Keep it simple and just remember 45kts in a Kitfox as your min manoeuvring speed.

[rcbif]

My initial instruction and the subsequent teaching I did as a CFI/Glider was with auto tow launches.

Started with gliders as well. Those 200ft, 180 turn rope break drills get the blood flowing.

When I was doing my powered transition training, I had the tenancy to go nose down a bit too long for stall recovery, dive during landings, and fly level building up speed a bit too long during the go-arounds.

The Cessna felt like a brick that could stall at any moment in the pattern to me, and I tended to over compensate by using the only power a glider pilot has - pushing the nose down.

[PapuaPilot]

Additionally, does anyone know with the G3X if you have any options/settings to add an indicator for something like this?

It appears that there are 4 custom speeds that you can program on the G3X in the Aircraft Configuration page. The instructor in the video suggests marking 1.404 times your stall speed. This speed could be slightly different for various Kitfox models, but you could program the DMMS on the airspeed tape.

Another option would be to use the AOA indicator as a reference for a safe maneuvering speed. The AOA will compensate for changes in aircraft weight and DA. When you setup the AOA Garmin suggests using 1.5 Vs as the speed when the AOA will first appears on the PFD. They also suggest having the approach target AOA at 1.3 Vs, which is the green dot. Awareness of being too slow could be as soon as the AOA appears on the PFD screen. Always keep the AOA in the green and well above the 1.3 Vs dot.

[Rik]

So are the AOA's merely trying to you keep you at >1.3Vs?

[PapuaPilot]

An AOA shows you your margin from stall and compensates for weight. You can fly whatever AOA you want for approach and landing, but flying at 1.3 or higher gives you a safe margin. It will do the same if you want to use it for a DMMS reference.

[Rik]

You say weight changes. How does it know the weight change?? I thought it was merely a stall plus factor gauge

[PapuaPilot]

This article talks about the relationship of airspeed & AOA:
https://airfactsjournal.com/2015/03/airspeed-vs-angle-attack-pilots-dont-understand/

Unfortunately there is an incorrect statement in the article:
"The five that are marked on the airspeed indicator are aerodynamic or structural limits. They are fixed and do not vary with weight."

WRONG! Vs and Vso DO change with weight, air density and G loading. That is why airspeed is not a good indicator of stall margin. An AOA is always going to tell you how close you are to your critical AOA (stalling) regardless of all of these factors.

[rv9ralph]

Correct Phil.


How does it know the weight change??

The wing stalls at the same AOA regardless. Density altitude can change, weight can change... but the wing will stall at the same AOA. So.. knowing the critical AOA, and having that displayed in the cockpit will give you the most important information on safety margins. Airspeed doesn't matter, as long as the AOA is above the critical point, with margin to spare.

Ralph

[109JB]

WRONG! Vs and Vso DO change with weight, air density and G loading.

While you are right that the actual stall speed (TAS) itself does vary due to certain factors, Vs and Vso DO NOT change and are defined as the IAS (CAS) corresponding to the clean stall speed, or stall speed in landing configuration, both with maximum gross weight, forward CG, defined configuration and a 1g stall. So they don't change with weight because they are defined at maximum weight, they don't change with air density because the IAS stall speed is the same (TAS is different but IAS is same), and they don't change with G-load because they are defined as 1g stall speeds.

[PapuaPilot]

I think you are missing the whole point of the discussion. You are correct that Vs and Vso are defined in the conditions mentioned, but what happens to the stall speed when you are not at gross weight or at 1g? It changes.


These are excerpts from Wikipedia: Stall_(fluid_dynamics) (https://en.wikipedia.org/wiki/Stall_(fluid_dynamics))

STALL SPEEDS
Stalls depend only on angle of attack, not airspeed (https://en.wikipedia.org/wiki/Airspeed). However, the more slowly an airplane goes, the greater the angle of attack it needs to produce lift equal to the aircraft's weight. As the speed increases further, at some point this angle will be equal to the critical (stall) angle of attack (https://en.wikipedia.org/wiki/Critical_angle_of_attack). This speed is called the "stall speed". An aircraft flying at its stall speed cannot climb, and an aircraft flying below its stall speed cannot stop descending. Any attempt to do so by increasing angle of attack, without first increasing airspeed, will result in a stall.
The actual stall speed will vary depending on the airplane's weight, altitude, configuration, and vertical and lateral acceleration.

IN ACCELERATED AND TURNING FLIGHT
The normal stall speed, specified by the VS values above, always refers to straight and level flight, where the load factor (https://en.wikipedia.org/wiki/Load_factor_(aeronautics)) is equal to 1g. However, if the aircraft is turning or pulling up from a dive, additional lift is required to provide the vertical or lateral acceleration, and so the stall speed is higher. An accelerated stall is a stall that occurs under such conditions.

Warning and safety devices
An angle-of-attack indicator for light aircraft, the "AlphaSystemsAOA" and a nearly identical "Lift Reserve Indicator", are both pressure differential instruments that display margin above stall and/or angle of attack on an instantaneous, continuous readout. An AOA indicator provides a visual display of the amount of available lift throughout its slow speed envelope regardless of the many variables that act upon an aircraft. This indicator is immediately responsive to changes in speed, angle of attack, and wind conditions, and automatically compensates for aircraft weight, altitude, and temperature.

[109JB]

I didn't miss the point at all. All I was doing is pointing out that Vs and Vso are defined with certain criteria and as such do not change.

Vs and Vso are the worst case 1g stall speeds for clean and dirty configurations. I'm just saying leave them defined as such and if you want to talk about how the stall speed changes with weight, g-load, etc, just talk about the speed, not the narrowly defined V-speed.

[David47]

I watched this video and wondered why this isn’t part of basic pilot training. I’ve never had an engine out on takeoff, other than my instructor reaching over and pulling the throttle, but it would be a disarming feeling if you’d never experienced it before. This is a great video, to the point I’ve included an additional step in my check list when I’m pre takeoff. In bold letter: Think Engine Failure.

[Rodney]

I just finished installing an AOA yesterday - haven't flown it yet to calibrate it.
(CYA-100)

I understand the concept of DMMS - but no where in this discussion is the use of flaps mentioned. My CYA system says to place the aircraft in a landing configuration and reduce airspeed to just above a stall. You then push a programming button and that defines the angle of attack where the airplane stalls.

Wouldn't it be natural, if you lost an engine to pull in at least one notch of flaps?

I can understand folks with electric flaps wouldn't have time to mess with them in a take-off engine out situation, but our manual flaps can be pulled in so quickly that why wouldn't one pull them in?

Any thoughts???

Rodney

[jiott]

I believe that the DMMS can be defined for any configuration you want; it makes the most sense to me to define it in my normal landing configuration (1/2 flaps).

You never want to pull flaps on an engine out situation if you want to maximize your glide distance. Best glide is speed is always set with clean configuration. Only after the landing spot is assured would you pull flaps to add drag and steepen your approach.

[PapuaPilot]

In the video the instructor said that DMMS is 1.3 Vs plus 8% or (1.3 * 1.08 = 1.404). He said the 8% is the increase in stall speed in a 30 degree bank which has to do with the increased load factor in a bank. I believe his rational is that if you keep your plane above DMMS you can safely maneuver and bank up to 30 degrees with out risk of LOC or stalling.

Using Vs (your clean stall speed) is the most conservative choice. If you add flaps or are flying at a lower GW your stall speed will be even lower, giving you more margin from stall at DMMS.

[aviator79]

You never want to pull flaps on an engine out situation if you want to maximize your glide distance.

Thanks for saying this Jim. I hear other flight instructors tell students things like "The first 15 degrees of flaps give you more lift than drag, after that, they give you more drag than lift." Unless your airplane is of a very stupid design, this is a false statement that leads people to do dumb things like try to add flaps to extend their glide.

[109JB]

Thanks for saying this Jim...

Not entirely true. You should always use what the POH/AFM says to use and not rules of thumb one way or another.

In the case of at least one airplane that I know of, the DA20-A1 Katana, the best glide is accomplished with T/O flaps and not full up. This is likely because the "0 degree" flap setting is a reflexed position for increased cruise performance. Now later versions of the Katana aren't the same and use flaps up (Cruise position) for best glide angle.

In the case of the Kitfox, at least my KF IV, the flaps have an infinitely variable range and are also used as the pitch trim. In the takeoff position there is a fair amount of up flap still available. So is glide in a Kitfox better with flaps fully up, at takeoff position, or somewhere else???

[aviator79]

Okay, there are some designs that aren't "stupid" that have some combination of flap setting and airspeed that yields a higher L/D than the flaps up position at any speed. And I very strongly agree that the POH/AFM is the authority on what do do when your engine quits.

I still maintain that instructors who categorically state that the first notch of flaps gives more lift than drag very much misunderstand what flaps do and are propagating information that could lead their students to do something dumb if applied in the wrong context.

[Flyingmike]

I’ve been sitting in PANC enjoying the reserve life of the celebrated international airline variety and just came across this thread.

What this instructor is teaching is spot on and should be taught to all students, regardless of their experience level. Traditionally what has been taught and ingrained is to pitch for best glide, look for a spot to land, and commit. In the airline industry this is taught completely different and we’ve moved away from the “don’t lose altitude” mindset into the “don’t lose control and hit cumulus granite mindset.”

The training after the Colgan crash in Buffalo has further pushed this training to include EET (extended envelope training), or in layman’s terms extreme upset recovery. Pilots have been taught forever when in an upset condition to level the wings and then lower the nose; modern and advanced practices (including aerobatic/military training) are now focusing on unloading the wing. The ONLY way to unload when in an upset recovery (extreme nose high and extreme bank scenario) is to push, regardless of bank angle. The same applies to engine failure after takeoff, you push to ensure no loss of AOA which leads to a decrease in speed at a very critical phase of flight.

The concept of a DMMS is knowing the slowest you can go at EVERY configuration setting so that you have both stall AND bank protection. As long as you do not allow yourself to get slower than DMMS at XYZ configuration you have maneuvering capability. Once you get slower than that speed you have two options, lower the nose or add more lift (extend the flaps).

By experimenting with each flap setting and applying the DMMS formula you can set a safe DMMS speed for each flap setting. This would best be recreated at the worst case scenario, i.e. max gross weight/cg limit. That often times isn’t feasible, but it gets you closer than you were before without this knowledge; it also helps prevent the student from initially pitching for Vg and trying to “extend” the glide or try to make the impossible 180° turn. If they can unload and stay in control being forced to choose options in front of them, their survival rates increase tremendously. The simple act of immediately lowering the nose in a takeoff may reveal potential landing options that they may not have seen before, and likely would miss as they continue to pitch back and end up in an uncoordinated state of flight.

This is especially important in mountain flying as the “off-field” options and maneuvering room are severely limited. Your only option with an engine failure after takeoff from a mountain airstrip may require at least a 30° bank to make an acceptable landing area. Knowing the DMMS for different configurations is literally the difference between life and death.

[Hawkertech]

Here is another of his videos with some very good info,

https://www.youtube.com/watch?v=4vlNtDWE0f8