Vertical, deep stall landing command produces stable controlled descent for vehicle recovery. Permits recovery in unimproved locations not accessible to normal skid landing approach methods.
There's also a reference to "deep stall" landings in the Micropilot MP2028 Autopilot's description
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I know what a stall is, but have never heard of a deep stall, much less how one would perform a landing with it.
Generalizations first so you can throw this response out as useless. Lets define stall as not generating enough lift to maintain the airframe altitude without some changes in the energy or angle of attack. IOW you (but NOT me) can mush along gently loosing altitude in a stall and not be worried.
At the beginning of the stall, dropping the nose will prevent it from 'growing' as would the addition of power.. Usually a deep stall needs some serious nose down and full power to be recovered from although there are conditions where even that would not be enough for some time. In GA terms it means some time after the wing stall has begun to propagate with no state change from the very beginning of the stall. In MOST airframes this tends to lead to nastiness known as stall spin accidents.
I guess you need to investigate the definition of "deep stall". I would worry about the possible (probable?) need for roll control as the craft makes its vertical descent while in the deep stall. That is where most control surfaces are not as effective as normal. I suspect that this (these) airframes have some sort of flow energizers to prevent loss of control as the craft slows down into the deeply stalled regime. There be small airframe eating dragons there for the unaware.
"Deep stall" as you used the term is an induced configuration that causes the plane to just drop out of the sky. The old free flight planes used to do this by having a timer pop the entire elevator up 45 degress and the plane just drops to the ground fast, but safely.
The second method is to pop the wing down severely. The plane - or uav - falls out of the sky sort of like Rutan's new "spaceship one" does a reentry.
If you do a Google 'advanced search' using "deep stall" as the argument you will come up with lots of hits. One of the documents that I found particularly interesting was at
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Interesting subject. I was not familiar with the term before this and am glad you asked the question. Gord Schindler MAAC6694
Stall occurs when the angle of attack increaases to the angle at which the airflow over the top of the wing begins to break up, losing its smooth flow and becoming turbulent. The low pressure is lost and much of the lift disappears. This typcally occurs at aroun 17 degrees AOA. A deep stall occurs when the angle of attack is well beyond the stall angle. In sime aircraft the hoizontal stabilizer may also be stalled due to the extreme angle, and the stall may be unrecoverable since pitch control is lost. Some T-tailed airliners had this problem, caused by the stabilizer being immersed in the turbulent wing wash, and the bose would continue to rise and cause deep stalling.
Before I posted the question, I did do a google search and, as you say, got lots of hits. None of them in the first 6-7 pages of results managed to satisfactorily say what the definition of a deep stall was. You must have slogged through a lot of screens to find that document. Thanks for the effort and thanks for posting your finding. The document certainly gives a clear explanation of how a deep stall works, and I can infer from that that a deep stall landing must be just to go into a deep stall and let the aircraft plop straight down onto the ground. I'd never have suspected that you could do that without damage, but it must be the case.
In the document, it states that the program had a floor of 5,000' AGL. They never actually put a plane on the ground while it was in deep stall, but they gathered mucho good data in-flight! They were just exploring the flight envelope at those extreme AOAs. The descent rate in deep stall was around 4,000 fpm. There is no airframe that could handle impact at that rate of descent without severe damage.
A vertical descent of 4,000 FPM is just over 97 miles per hour STAIGHT DOWN. Yeah, that would be pretty tough on the landing gear. . .
I worked in the Aerodynamics Department at Douglas Aircraft when they were certifying the DC9-80. (The "Super 80") One of the required certification items is "minimum runway length" that the aircraft can land on. Basically the pilot, or in this case Test Pilot approaches the runway at a fairly high rate of descent and then locks up the brakes when he touches down.
As it turned out, the pilot hadn't stabilized his rate of descent and was coming down twice as fast than was planned. In the "controlled crash" that ensued, he broke off the tail, severely wrinkled the fuselage, and blew out the front tires and broke the wheels. Fortunately the only human injury was relatively minor. An FAA inspector was standing* in the airplane as it "landed" and he was thrown down so violently that he broke his leg.
The aircraft had been pre-sold to Swiss Air, but they cancelled the order on that aircraft within a day and the corporation ended up with it. It was repaired and returned to flight for test purposes. I don't know what eventually happened to it but I think it was forever barred from commercial use.
I worked for the Director of Aerodynamics at the time. Since the event was an official certification event the landing was at Edwards Air Force Base with high speed cameras recording the event on film, and the aircraft was fully instrumented to record all the flight control parameters. Our Director gave me a private showing, frame by frame of the whole event. I'll never forget it!
Too early in the morning, and too little caffeine in the bloodstream, makes one's fingers less than 100% accurate. As for Van Halen, I prefer Mozart on my Bose.
I like Mozart but prefer something from the 70's/80's rock while building. Well, that or contemporary country (which is mostly the Eagles re-worked...LOL)
Just for grins try establishing some weight and calculating the G loads on "arrival"! Might water your eyes.
THEN you will see why the Navy is SO interested in replacing the aging A6 fleet as its LG reaches it max capacity and the load factor for electronics keeps going up.
This is all VERY interesting stuff!!! Being relatively new to flying the 1:1 scale aircraft, I haven't had the chance to experience these extreme attitudes, unforunately. That T-38 must be one slippery bitch to peg the VVI like that! Apparently, the plane they used for those experiments had a substantially higher drag coefficient.
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