Came back from flying field over the weekend.
Saw a glider dropping straight down vertically with little forward speed.
Apparently that was a deep stall landing.
It was used as the landing area of kind of small to land safely.

Wonder what is needed to do a deep stall landing?
Oversized tail? Dihedral wings? etc?
Must it be a glider? Can flying wings do deep stall landing?

Thanks.

Delta wing planes can do the deep stall very easily, but I'm not sure about wings.

In the 3D area, you'll find an "elevator" is a near vertical descent. Some planes do it with elevator control only, others require spoilers. Altitude is controlled with throttle. You come in near vertical controlling altitude with throttle and forward progress with elevator-release elevator and you move forward. Steering is with rudder. Ailerons keep the wings level. It takes some practice, but is a fun maneuver.

Powered airplanes can perform the "elevator" because they are basically flying at very low airspeed and using propeller thrust to hold the airplane up. The wing's not developing enough lift for the airplane to actually fly. The airstream of the propeller flowing over the ailerons, rudder, and elevator provide the control forces needed to keep the airplane in the desired attitude.

A "stalled" descent of a glider would require a model that is very stable in roll, that is, one with fairly high dihedral/polyhedral, such as is found on free-flight models. You would then have the elevator be able to go to a very high deflection to allow the model to stall. What you wind up with is a basic parachute effect. With all flight surfaces effectively angled away and upward from the center of the model, it will descend very steeply. It's the same effect as if it were a badminton shuttlecock, but with larger surfaces at less acute angles.

Recovery would take some altitude, because the model would have to go nose down to gain speed.

A "true" deep stall is usually found when certain types of aircraft with high stabilizers get the tail blanked by the turbulence coming off the wing in a stall. The airplane will not recover because there's no way for the tail to get airflow to lower the nose so that the wing can get proper airflow and "unstall". In testing, full-size aircraft have a parachute mounted in the tail that can be ejected a distance away so that the nose of the airplane can be forced down to accelerate the airplane out of the stall. Such 'chutes are also used in spin-testing aircraft for the same purpose if they cannot recover on their own. Of course, the production aircraft don't have that provision, but they also have devices built into the aircraft to force the nose down before the wing has enough AOA to stall (called "stick pushers").

If the wing was fully stalled at landing, the sink rate must have been extreme - about the same as with a parachute with area roughly equal to, or less than, the wing area - at least 1000 feet per minute, probably more, depending on the wing loading. If it was still in deep stall mode at ground contact, it must have hit the ground pretty hard, since power could not be used to horse the nose up and create upforce.

Very interesting - something that I have never seen, although I have made vertical landings with 3d-capable models by applying lots of power just before impact, and even then, only with some wind on the nose.

Was it windy that day? Because with a strong headwind, I can land my Zagi while its moving slightly backwards...

Alfa, what you saw sounds a lot like a dethermalized free flight returning to earth. They do that by popping the stab up to about a 45 degree angle, the plane doies one or two stalls and then settles striaght down.
I don't know if the plane would recover to regular flight if the stab were returned to its normal angle.

gliders use spoilers and on models, sometimes a Crow setup - which is up/down surface deployment for high drag.- inner panels down outer panels up
depending on design - you can drop like a rock--just leave room to get back to maneuvering speed.

You can force an F-16 in this kind of situation by inducing a snap roll while slightly inverted and nearly stalled when going straight up. The plane will flop over on its back, and begin "shaking like a leaf and falling like a rock". There will be some gentle back-and-forth rocking along the pitch and roll axes (more pitch than roll), but attempting to pull out of it won't work.

You have to disable the AOA circuitry and then begin "rocking" the stick back and forth, in time with the rocking motion of the aircraft. Normally, you can recover in 7-10,000 feet of altitude. If you do this below 5,000 feet, good luck, because your plane will come right down on your head if you punch out...

(Way too much time spent on a flight simulator and yakking with my brother, who was a fighter WSO before going cargo, retiring, and going commercial...)

I also routinely deep-stall (isn't it also called a "Harrier"?) my Delta model to land it in limited space. I can get the descent down to about 2-3 feet per second, and gun the throttle or pitch down to get out of it. Very occasionally, I can manage to maintain altitude with an extreme nose-up attitude and 3/4 throttle, and just coast along at less than walking speed. I haven't quite gotten the knack of doing that consistently yet, though.

--
Matt B.

Bax,

Glad you mentioned what a deep stall is.

Thanks to all, esp Bax.

I built my glider with high wing dihedral + high stabiliser .... using salvaged parts from my other birds.
Bingo! Got it to deep stall and land.

However, my bird was too weak to take the landing shock (plus, it didn't come down totally level). Broke my tail boom instead!

NASA has looked into this...
http://www.dfrc.nasa.gov/Gallery/Pho...ECN-26847.html

http://www.dfrc.nasa.gov/Gallery/Pho.../ECN-26847.jpg

I'm glad someone has already brought up the terminology issue.

I think it aids everyone's understanding if they use the right terms.

Just to re-iterate what Bax said............

A Deep-stall is unrecoverable. It's unrecoverable because elevator authority is lost.

What you guys are describing are just stalls, unless they genuinely are unrecoverable. It is quite conceivable to deep stall a model and get away with it, as a great number of models are drastically overpowered and easily have the power to impart forward airspeed again.

Please note that if the glider seen was genuinely deep stalled, then the landing really would have been something to behold, because it's not possible to flare out and check the rate of decent, because it is, of course, stalled.

OR-------------
use a flying stab to commit the deep stall-then rotate the stab to push nose over and gain flying speed.

Next ----------

Doesn't matter if its elevators or an all-flying tailplane though. By definition the deep stall means that the tail is masked by turbulent airflow off the mainplanes, which means you can stir the sticks around all the way to mother earth and it wont make a jot of difference.

For anyone who wants to read about a true deep stall incident, look up the story of HS Trident G-ARPI which was deep stalled at around 11,000ft or there abouts and fell like a brick into grasslands. The CVR revealed the crew trying all sorts of things with the flight controls and they achieved nothing.

If your pitch control surfaces can get you out - it's NOT a deep stall

Deep stall is a relative term when applied to modern aircraft.
A Deep Stall is fatal for a human pilot in todays jet fighters, because they have basically in everyday language moved the C O G to a minus % to gain better turning in a close in fight.
If he goes too slow the plane goes into a "departure" from which HE can not escape as long as he fights the plane.
If he lets go of all controls, the computer saves his butt.
It is all relative.

Thanks for pointing out the difference between deep stall (non recoverable) and stall landing.
BTW, would stall or deep stall have any difference during landing? More reliable? etc?

Thanks!

This clip shows an aircraft in steep descent (not deep stall).

http://s8.yousendit.com/d.aspx?id=2D...72BGIZR9PPMWH3

In a model aircraft (the 3D craze type)- the deep stall is called a "harrier" or a parachute or whatever .
All of my sorta scale aerobatic models wil do em easily .
one did it a month back at about 30 ft -a friend was waltzing it around in very high angle flying -when the engine abruptly cut.
There was no room to drop the nose and regain flying speed so he just held full up and the thing settled -on about an 80 degree slope -directly to the runway -which collapsed the gear and did some structural damage up front .
The model is a H9 260 weighs 13 lbs with wing loading in mid 20's. (oz /sq ft)
. The only thing that saved it was the rather low wing loading and the fact it was simply small and light.
The amazing thing is how stable these models are in dropping with all the surfaces just acting as plates.
The thing I have learned with this 3D craze , is that you can maneuver (well sorta) and control (within limits) a plane which is simply --falling .

It's unlikely the glider was stalled at all. More likely it was flying into a headwind that nearly matched its airspeed, providing a vertical descent angle with respect to the ground. The angle through the air mass would not be vertical. If the glider had spoilers deployed, its descent rate would have been greater than without.

If it was stalled, then the landing could fairly be called a crash

....cos it's impossible to slow the rate of decent of a stalled glider without shoving the nose down and regaining airspeed. One certainly can't flare out and land......

In WW II, Feisler built a plane, the Storch, that looked very much like our Piper Cubs.
Difference was they had installed leading edge slats, flaps all over the wing and a type of flap, a Foweler ?, that extends the wing flap rearward and also downward to improve the stall speed so low that the plane could hold altitude in a moderate breeze and also land going backwards.
Were they the genius of all times in sloww speed or what ?

The Fiesler was not unique. Many planes used that sort of setup at the time. The Lysander being another. But most of them were of heavier design than the Storch so while they were impressive they often could not match the Storch for STOL.

Alpha, unless you happened to be passing a free flight field I'm inclined to agree with mesae about a light and floaty glider flying into a strong headwind.

However there's at least one RC glider that uses a third servo to tilt the all flying stab up to a DT angle for flat vertical landings. And you guys are right about the wing shock loads. It's harsh on heavier models. My rubber stuff doesn't need to worry but a buddy that flies spark ignition Old Timers has broken at least two stock wings due to the fact that the original designs did not know about DT'ing and did not have to deal with the shocks of a 56 oz 6 foot span model "arriving" to earth vertically.

Models in a DT mode will recover nicely if the stab goes back to neutral. But I suspect that has a lot to do with the generous tail moment arms. Jets do not have such generous proportions and I suspect that's part of what hurts them in a deep stall. I've seen videos of them spinning and otherwise tumbling and I don't think the tail is in the wing wash any longer but rather that other factors are at work. Perhaps since the stabilizers are presumably stalled as well they just do not have the proper force distributions to force the nose down and recover?

In any event "deep stall" is not a regular or perhaps not a bonifide aerodynamic term. I suspect it can be used for lots of conditions. But the one that seems to be recurring is that it indicates some form of unrecoverable stalled condition for whatever reason. I know it came into popular use with the F104 but I doubt that it is tied to T tails since other aircraft do not recover nicely from "deep stalls" and they do not have T tails.

The "terminolgy" looks to be doing some handiwork here.
I really don't know which term is best to use -but like porno -I know the thing when I see it .
So what is the preferred term for a very stalled almost vertical sink?

Or a fully stalled vectored flight -like the Russian fighters did after BACKING UP-(the Cobra maneuver.)
I see more and more of full scale show flyers doing stuff I have been told flat out that full sized aircraft will not do.
The airshow filmed in Japan ; Haute-Voltige shows some maneuvers that are simply unreal for full sized birds to do.
Even tho they are duck soup for models .

I've seen a lot of F-16s and others doing wierd manuvers over EAFB.. with the engine contrail marking the flight path..
The plane will be kinda wings level, slightly nose up, and descending vertically... about like a dethermalized free flight.
The utility of such a manuver escapes me.. as it puts the plane in a zero-airspeed no-manuverability condition, which in a 1V2 would be fatal!
I have an SETP report on testing the SAAB Draken at EAFB in '96.. 3 interesting "super stall" modes.
Abrupt full aft stick at 140 knots...pitch oscillations between +100 and -20 degrees... oscillations!!.. +1.5 to -.5 g
Inverted super stall... stick full aft at 140 knots, then full forward after the initial +100 degree pitch up.. results in a -2 g pitch down, stabilizing
at -60 alpha, nose slightly above the horizon.
Tactical entry superstall.. rolled inverted to a Split-S.. at -90 degrees pitch, full aft stick.. the plane pitches up with oscillations between +40 and -20 in pitch.
Full longitudinal stick -in phase- with the pitch oscillations (pitch rocking) recovers the plane to near vertical nose down pitch.

I was a USAF Air Traffic Controller for ten years, and I worked a lot of F16 traffic during that time. I was stationed at Luke AFB for 6 1/2 years, and more than 200 F16s are stationed there. I even got to fly an F16 for about 20 minutes (Thanks again Col. Spence!) and did a bunch of aerobatics in it. I have never seen an F16 fly in a way that meets the above description, descending "vertically". Your reference to engine con(densation)trails makes me think they are very high when this is going on, which is even more puzzling. If they are indeed descending vertically or nearly so, it might be a training maneuver, perhaps to teach how to recover from that "target" flight condition.