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

[DesertFox4]

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.

[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]

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.

[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.

[PapuaPilot]

This article talks about the relationship of airspeed & AOA:
https://airfactsjournal.com/2015/03/...nt-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.

[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)

STALL SPEEDS
Stalls depend only on angle of attack, not 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. 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 V_S values above, always refers to straight and level flight, where the load factor 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.