Trainer Flat Spin
 

Is it possible to do a flat spin with a trainer ? I'm not even sure I know what a flat spin is :eek: but all answers and ideas are welcome. Thanks

RE: Trainer Flat Spin
 

If you move the CG back a whole lot and up the control throws you proably can as long as it's not too extreme a design. But it sure won't be a trainer any more with the CG and controls set that way. Then you need to do all the tricks to get the basic spin to tighten up.

RE: Trainer Flat Spin
 

OR--even with minimal control movment - you may accidently throw one into a flat spin
(To clarify, a flat spin is a slow rotation with the fuselage at a low angle of attack-a normal spin is faster in rotation and th nose is angled down much more steeply -the plane will easily fly out of a normal spin but NOT a flat spin)
Let's say your trainer is a heavy , flat (no dihedral ) BARF
Not uncommon
Now lets say yo do "something" that yanks the nose way up and the thing hangs in a hover-then falls back and you hang on th sticks trying something --------
Not uncommon.
As it falls -it may start to turn (yaw ) and you hang in there with full elevator and rudder.
the turn becomes tighter and the model seems to level out -but still keeps turning .
so you frantically stir the sticks - nothing changes .
What has happened is that your trainer - with little surface control - simply can't over power the flat spin-- which has all of the surfaces moving around a pivot point .
Some full scale craft were designed to be spin proof (ERCOUPE)
And flown properly -they were.
There is always the expert who will teach the plane a thing or two and some tried .
Once the plane got into an attitude where it departed from normal flight -- other forces started it it spinning . prop forces contribute here.
The spin proof craft -designed to never have much control throw - ,now simply rotates -all the way down--
Most decent trainers -setup properly are spin proof but some trainers -balanced on the edge of stability -can hit that magic window -and fall into a dropping spiral -which may thru operator error -become a very low angle rotation (flat spin).
I have flown some supposed sport models which were very nasty in this respect.
Once in a flat spin -just turn off the TX and watch.
Most models will if simply "released " will eventually recover -unless the ground comes up too fast.

I had a flat spin save a new model last spring - A wing panel on a new (first flight) 33% CAP released and slid out 6" from the fuselage.
I had just done a 45 degree upline snap and the plane went wild .
Instantly I shut down power and the plane could be seen to be rotating slowly to the right. (right panel slid out.)
I held full up and right rudder and watched - the spin was very flat and slow -so I just let it continue - The field below was 18" tall spring grasses wet with morning dew.
The model hit -I walked over to pick up the pieces.
Total damage- a bent landing gear.

RE: Trainer Flat Spin
 

A true flat spin requires a rear cg. If the cg is well forward of the neutral point there is no combination of control inputs that will result in a stabilized flat spin. Exactly how far back the cg must be to give a flat spin is only determined by experimentation, but a flat spin isn’t a maneuver, it is a flight condition dependent on configuration and cg position. (In a spin, flat or normal, the angle of attack is very high and the wing is basically stalled.)

As far as the Ercoupe, if the cg is within limits, it’s not possible to make it spin with any combination of controls. It can’t even be made to stall, which is necessary for a spin. I’ve tried.

RE: Trainer Flat Spin
 

If you can't seem to get out of a flat spin you can sometimes just give full throttle and full rudder opposite spin and blast it out of the spin. One of my 1/4 scale cubs could be put into a flat spin and that was the only way I could get it to pull out.

RE: Trainer Flat Spin
 

As said above, trainers can most certainly flat spin.

I have a Great Planes Trainer 20 (the one with the low-dihedral symmetrical airfoil) that flat spins very nicely, thank you. I found this out after I'd been messing with the CG to make the model more aerobatic. The only problem was that once it was in the flat spin it wouldn't recover. The model kept spinning right into the ground. Throttle would only alter the spin rate slightly, so I closed the throttle and watched the model go down.

When I got to the model, I found that it had hit hard on the landing gear and cracked the fuselage sides where they joined the bottom, and the servo rails had all jarred loose. An hour or two at home and the model was fully flyable again. Sometimes you just luck out.

RE: Trainer Flat Spin
 

Lou -I beg to differ - rear cg is not required .
The distribution of lateral area may be enough as when the flat spin starts -- the wing is stalled .
Once the spiral starts you may never be able to push/pull out.
I can put a well setup EXtra /CAP whatever into a flat spin from a very low angle of attack
The key is to get it to kick into a yaw -hard - and kill the wing.
the elevator has to be at the right angle and the ailerons typically left out of the game -or reversed a bit
It is also possible to increase AOA of a true spin by playing elevator input and shifting aileron position
the spin slows /speeds up as the nose drops or returns closer to level .
just like an ice skater -
Conservation of angular momentum at work.

You actually tried to spin an Ercoupe?
early model w/coupled rudder and ailerons?
My brother and his buddy also tried to slip one -and damn near paid the price for it

RE: Trainer Flat Spin
 

I have to agree with Dick on this. It's as much related to fin, side area and dihedral as CG.

I was trying to help out a newbie that had an ARF Piper Cub. But it was a Piper Cub with a devil complex. I've never flown a model that was so prone to stalling and spinning. Checks showed no bad warps, decent weight to wing area for a moderate loading and a decent CG position. The second time they brought it out it even had some washout. Nothing helped. Even from level or only slightly climbing flight it would hiccup and snap roll into a very hard to recover spin. It eventually bought the farm as you can well imagine and the father and son were looking at the bits with an eye to rebuilding. I recomended they burn it instead and move on to a model that could actually fly. They did and never looked back.

RE: Trainer Flat Spin
 

Thanks fellas for all of the information. I'm still not sure what a flat spin is and gather from ready some ones post that it isn't a manuver. Does't Patty Wagstaff pull off a flat spin in her shows ? Any way I have made a drawing from paint, and the question is looking at the top of the plane and the arrows, if this plane was spinning nose and tail rotating counter clock wise with the belly of it facing horizontal to the ground , I gather this would be a complete flat spin ? Or lets say the planes nose was following the arrows with the belly facing horizontal to the ground and main wing level not tilting one bit, would that be a flat spin. Or did I create a new manuver for us to try [:-] Thanks

Dave.

PS had to draw by hand . BMP not supported for some unexplained reason.

RE: Trainer Flat Spin
 

I will throw in a flat spin experience many years ago. It was a moderately powered .15 glow shoulder wing model. It flew nicely and looped and rolled and could spin nicely. The recovery was OK and not scarey at all. The airplane had a rather small vertical tail but it flew OK. I decided to add a canopy and pilot over the center of the wing.

The next flight I dropped nto a spin and it went from normal into a really flat spin. The descent rate was so slow I was able to try all variations of power, control throw, begging and praying and all were to no avail. Remember this was a moderately powered airplane with small surfaces that couldn't be powered out of the spin. The true flat spin was also maintained with no control inputs.

It came on down and gently settled on the grass. Pretty nice landing if rotating counts. I took off the canopy and all returned to normal.

There are a lot of 3D designs that can be pushed into and out of spins, flat spins, flat spins going horizontal, etc. but the pure flat spin that is based on the combination of inertias, CG, configuration and corresponding aero inputs of a non-augmented kind (no propwash across deflected surfaces) has a spin boundary that is defined by a ratio of damping to forcing parameters and can be stabilized by several combinations of the mess (my aero friend in the next desk to mine did the F-15 test, spin evaluation and report, and tried to explain it to me as I had to proof read it, but there were times I got lost in the math model).

Trainers may be very resistant to entering a spin but if that combination hits, it will drop into one, if not the combination, then never. It would be fun with a foamy for something like a basic Extra design to run a series of experiments with CG and vertical tail/lateral areas and see where the magic location/areas are. Too scarey to do with a real model.

Dick is a good example of if you aren't good - be lucky. ......... did I word that right?

RE: Trainer Flat Spin
 

If you want to see a great flatspin go to http://www.flyingcirkus.com/default.asp?content=home
In 3DU they have a nice video demonstrating a very clean flatspin. Keep in mind they did it inverted because the airframe "preferred" to spin inverted. Not all planes are like that though. For example Bill Hempel's bipe spins very well upright, but I don't think it will do it very well inverted.

RE: Trainer Flat Spin
 

I had a Unionville Tiger Moth that could be put into and out of a flat spin at will.

I would pitch up slowly to lose airspeed, and just before stalling, would give it hard aileron and rudder together. So long as I held the rudder, it would flat spin beautifully. As soon as the rudder was released, it would straighten out and fly.

My record was, I think, 35 rotations.

Recently I rebuilt the same airplane, with slight modifications. (see http://www.members.shaw.ca/ccflyers/funfly.htm) The biggest difference is that the CG is now where it is supposed to be. It won't spin.

I'm not sure it was a true flat spin. It's just that the Tiger Moth has a very small fin, and a huge rudder. When there is lots of throw in the rudder, it effectively disappears in the spin as a stabilizing force. As soon as it is returned to neutral, it stops the rotation. That's my theory, for what it's worth.

RE: Trainer Flat Spin
 

Thanks Ultra Stick , the site is truly remarkable, some very stunning 3D manuvers. I feel I can pull off the inverted flat spin for 5 seconds. I will have to be up quite a bit and to get out of it I think I will have to use the ailerons becasue like it was mentioned above the motor will not have enough power to pull it out .

My dear Watson I think I've got it ;)

Thanks again.

PS I was told a dihidraled winged trainer couldn't fly inverted , [:-] somebody lied [:-]

RE: Trainer Flat Spin
 

Ben - I recall watching a few spin tests on full scale including as I recall the F15.


Why would a prop plane not be counted in the "True flat spin catagory?"
I guess I am lucky -very lucky in the case of my CAP but flat spin is a flat spin --and it can be controlled on some dsigns . I have a few models which can be put into a flat spin - carfully stabilized into a slow rotation --then-- carefully adding elevator and power be made to slowly gain altitude.
and they are truly spinning . The apparant axis is about at the trailing edge of the wing -

RE: Trainer Flat Spin
 

Dick from the context of your comments it appears that you are using the term “angle of attack” to mean the pitch angle of the airplane with reference to the horizon. The more conventional use of the term means the angle with which the wing moves relative to the air. Using the latter definition, in a true spin the AOA is always very high and the wing is stalled. You also seem to use the term “spiral” and “spin” to mean the same thing. In a spin the wing is mostly or completely stalled, and the airspeed is relatively slow. Whereas in a spiral, the wing is not stalled and the airspeed (and “g” load) builds rapidly. To an outside observer it is sometimes hard to tell the deference.

So far no one has defined “flat” spin. An airplane has a normal spin mode that results from a yawing moment introduced at or slightly before the wing stalls. Typically full up elevator and full rudder deflection is held as the spin becomes stabilized. The resulting spin may be steep or flat and may or may not be recoverable depending on the configuration. The various factors mentioned (cg., distribution of side area, inertia, etc.) all effect the character of the normal spin mode. Use of ailerons during the spin may steepen or flatten the spin as will use of power and varying rudder and elevator deflection. When I said that a “flat” spin wasn’t a maneuver it is because the spin characteristics of an airplane are fixed by the configuration and control deflections normally have only moderate effect. An exception may be 3D type models that are designed to operate in a stalled condition using high power and thrust deflection to force the machine into maneuvers that would not be possible with aerodynamic forces alone.

As to whether a spin is “flat” or not is a fairly arbitrary definition. It obviously involves the pitch angle, but also is often used to describe a spin that is not recoverable. The flatter the pitch angle during a spin the more likely the rudder and elevator will be in the wake of the stalled wing and lose effectiveness. The slow descent mentioned in several comments, is also typical of a true flat spin. The wing is stalled and in a high drag condition and the descent resembles that of a free flight model with the dethermalizer deployed except with a rotation.

Bruce, when I commented that a flat spin requires a rear cg, I was referring to typical trainer type models. As the cg is moved rearward, the spin will flatten until at some point it will obviously qualify.

Dick, I have only flown the two control Ercoupe. I tried every way to stall it including zooms from a dive, and it really won't stall. There is just not enough elevator to stall the wing. Obviously if it can't stall, it can't spin. It will however build up a fairly rapid rate of descent in sort of a mush. It's really a strange airplane to fly.

RE: Trainer Flat Spin
 

I understand your comments but - I can put a model into a flat spin right from level flight - Once the wing is rotating -like a prop - it acts much like a prop spinning.
the rotation is quite slow but will prduce no forward motion - simply a "auto rotation" type descent.
I would say the wing is stalled as one panel is moving backwards during rotation yet the plane does not roll over.
The angle of attack relative to direction of "flight" (?) is really high-- 90 degrees -
I have to call this flat spinning .
I love the Ercoupe -the design intent was really a great approach to a plane for the masses. the crap that got guys in trouble resulted from exceeding recommended speed envelope when trying to loop it-------.
You can't protect fools from themselves.
(Same thing happened here with a Bonanza)

RE: Trainer Flat Spin
 

I did about 10 hours in a 2 place pitts. When screwing oup a simple loop, got to slow at top and plane started to stall so Ifigured I`d just roll it over to recover. Luckily the instructer had about enough and recovered the plane later warning me that upside down stalling a pitts and not coordinating the rudder with the ailerons was a real good way to put that plane in a flat spin. He also suggested that if I was foolish enough to get it into a really tite flat spin only a big blast from the prop MAY pull it out. Not long afterward Art Scholl while filming a flat spin for the movie
Top Gun in a Pitts died being unable to recover. Though he had done this countless times before in this same plane it would not recover. Eventually it was determined that the added weight of the camera altered the cg just enough to cross the line. I never forgot that lessen and was obssesed with determing that any plane I flew was within cg tolerances. You really notice a rear cg when slowing to flair at landing.

RE: Trainer Flat Spin
 

I have a trainer that I fly on a regular basis. It will do a "flat spin" quite nicely. The fuse is nearly level, and the wing is stalled.

Entry is engine at idle, full up elevator.

Just as the nose drops, full left rudder and a quick blip of full throttle then back to idle. This creates a ton of yaw, and stalls one wing much more than the other.

After a about a half rotation, the ailerons are moved slowly to full right aileron, which keeps the nose up and the angle of bank level.

Throttle is bumped up to a couple of clicks above idle to sustain the spin.

If I just release the controls, I get anywhere from 3-4 rotations before the plane recovers on it's own. Opposite rudder and down elevator and full power will pull it out quickly.

The trainer has a fair amount of downthrust, so much engine power seems to pull the nose down and break the spin. I also never use aileron with rudder to spin, the ailerons seem to overpower the stalll, and the result is a rolling dive, regardless of rudder or elevator.

This trainer has the CG moved way way WAY back, a ton of elevator and rudder travel, and now has a bigger rudder than stock, though it actually was better with the smaller rudder. I should cut down the vertical stab, and keep the larger rudder, that would probibly help.

I've surprised many "experts" at my field with this trick. Most of them have said things like "trainers can't spin" or "it won't be a true spin". The first time I actually got the spin to flatten out, I almost lost the plane, I wasn't ready for the 3-4 rotations after releasing the controls, so I didn't get right on the opposite rudder and elevator.

The same plane will spin inverted, but won't raise the nose, and the rate of rotation is much faster inverted than upright.

All in all, it's a heck of a lot of fun.

RE: Trainer Flat Spin
 

Now , How high do I have to be to begin the flat spin ? [X(] I tried to do one this weekend and I was so afraid to lose the plane I just couldn't complete one spin. The plane you are talking about is it a low winged trainer? mine is high. Oh well I like the way 3d planes can have so much control but I'm not ready to risk crashing some expensive 3d plane trying to complete tricks.

I will say I did a knife edge this past weekend. The nose was high about 35% in angle and I held it for about 15 seconds. The wind was so calm I was trying every thing in the book. :) My invert is so sweet, I have it mastered to the point I can make one turn.

Thanks guys.

RE: Trainer Flat Spin
 

The trainer I use for spin is a typical high-wing primary trainer type. Flat bottom airfoil, tons of dihedral, the whole nine yards. It's a Hobico Airvista. They don't make them anymore (a good thing, it's junk from a construction point of view). Oh, typical trainer power, OS .40LA, not enough power to get out of it's own way, never mind climb vertically.

Here's a picture of it (when it was fairly newish, before the covering got brittle):

http://www.wheek.org/airplanes/trainer1.jpg

RE: Trainer Flat Spin
 

an artistic masterpiece of vacuum formed plastic-----

RE: Trainer Flat Spin
 

I have a Magic that will not only flat spin at will, but with the right amout of cross aileron (if in a left hand flewt spin then right aileron) and throttle will maintain altitude and when the tank is low actually gain altitude. Several guys at my field have seen the Magic do this. To recover all I need to do is release the ailerons back to neutral and reverse the rudder with a bit of throttle. It will pop right out of the spin. Having said this I had a cannard airplane of unknown origin (I bought it off of a hobby shop ceiling) that once put in a flat spin was unrecoverable. And I had plenty of time to try various things as it was a very flat spin that lost altitude at a relativly slow rate. After I recovered the airplane and fixed the minor damage, I added a pair of ventral fins under the rear of the fuselage and tried again. It was much harder to get into the flat spin, but the results were the same.

RE: Trainer Flat Spin
 

My wingeroned vee-tail CR Turbo had (sob!) a flat spin mode available on demand. Rotational rate too fast to count, but instantly recoverable... except for the last time... :(

RE: Trainer Flat Spin
 

In full scale the flat spin is deadly for some
In one of my old Private Pilot(Ithink) mags - there was an article about a test pilot who was testing a canard - after dozens of attempts - he got it into the flat spin .
Next try to get it out
all std attempts failed - so he unbelted -crawled under the panel -no luck - opened the hatch - stuck one leg out on the forward plane- no help
belted back up and tried agin the std fixes - then he noted that the rate of descent was extremely low - much lower than ever considered possible in any engine off situation
so he rode it down into the pond
He got hurt but survived.
His take on it was that there was a rotational lift being formed which slowed the thing down.
Ok what's the textbook say about this "rotational" lift ?
I know for a fact I can get it to happen on my models as they are apparantly flat (fuselage in horizontal plane) and yet I can make em climb or drop --depending on power and elevator setting

RE: Trainer Flat Spin
 

Sorry, Dick, your information on that canard incident is incorrect, unless there was some flat-spin incident with a very similar sequence of events that I do not know about (which is of course possible). You are probably refering to a deep stall that occured during the "Velocity" flight testing. At the time, it was flown by Carl Pascarell. He was doing stall testing with the aircraft with the CG at different locations inside the designed CG envelope. The incident occured when flying with the CG in the most rearward of these positions. Here is a good summary of the incident:
http://www.aeroman.de/html/best_pilot.html
It was later discovered that the descent rate was probably quite a bit higher than the pilot thought at the time.

That particular incident wasn't the only deep stall incident with a canard - one of them (an inverted deep stall) killed the pilot. These deep stalls have also happened on Long-EZ's. The deep stall is quite different from a flat spin since there is no rotation present at all. The similarity, however, is that in both cases the angle of attack is almost 90 degrees (aircraft descends vertically with the fuselage in a horizontal attitude). From the link I posted above: "The aircraft was neither yawing nor rolling, and the ride was strangely comfortable. Rudder and elevator were useless." The pilot was able to make it turn, but it did not help to recover from the deep stall.

I think the "rotational lift" that you are talking about is actually "vortex lift". It is something you often see on delta's at high angle of attack, but it can be present on other aircraft as well. It will certainly be present on your small foamies with low aspect ratio wings when you fly them at high AoA. After the velocity incident, there was a lot of speculation that vortex lift was the reason the aircraft descended so slowly. Further research and testing shows, however, that the descent rate was not quite as low as initially thought (as I also stated above), so if vortex lift was present it was not quite as powerful as originally speculated. For what it is worth - vortex lift as a phenomenon is very well known and also quite well understood, it is discussed in most of the aerodynamics text books I own, and if you looked at published NASA and AIAA papers over the years you will see many occurences of this term. A google search should also turn up some discussions on the theory if you are interested...

Cheers,
Bennie