Quantcast

Anti-Spin Ideas

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
The problem as I see it, is not that an aircraft is unstable, but that it is stable in undesired ways. Such as merrily spinning down into terra firma. If you want an aircraft to be truly spin proof, it needs to be unstable in all spin modes. While we are at it, lets make spiral dives unstable, too.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,608
Lastly, there are regular spins, and then there are flat spins (usually entered after a misapplication of power).
Flat spins are often a result of an aft CG or rapid spin rate. The masses of the tail and of the engine want to come into the same plane of rotation, which pulls the tail down and nose up. Loading of the airplane is important, but too many pilots ignore the many warnings and get into trouble. The "why" of the rules escapes them. That's why training is so important, but the attitude is just as important.

And you will never design an airplane that will forgive the pilot that pushes things that far. He will find a way to crash. When I was young and building lots of boats and other interesting stuff, I had an old Mechanix Illustrated magazine that had plans for a kid's boat in it. The author said something I never forgot: You can build something strong enough for an adult, but never strong enough for a kid. I have seen that played out in so many ways in the 40 years since then. Like the old saying: You can't build an idiot-proof airplane (or whatever). Someone just comes up with a better idiot.
 

Autodidact

Well-Known Member
Joined
Oct 21, 2009
Messages
4,513
Location
Oklahoma
One of the things that Al Bowers is saying - and is revolutionary if true - is that there is not only proverse yaw with BSLD, but that the induced drag near the wing tip is actually negative, in other words it is thrust. This seems to mean that not only does BSLD mean yaw stability, but that it is also the most efficient lift distribution arrangement. Essentially, you have a wing that is slightly longer span than an elliptically distributed wing, creates the same lift, requires the same structural weight, and has less drag as well.

Bowers described a phenomenon of upwash at the tip, and stated that this would mean the lift vector has rotated forward and voila, you have thrust! My first visualization of this upwash was upwash due to negative lift where circulation would actually be opposite from the inboard part of the wing which would just be more induced drag, but with negative lift. But, if the circulation is the same direction as the inboard portion of wing, meaning that the upwash was just downwash rotated so that it is now pointing upward, ostensibly due to the induced upwash ahead of the wing as well as a negative angle of incidence (not to be confused with negative angle of attack, that would still be positive), then there would actually be thrust because the wing would be lifting forwards; if there is no lift at the tip and the induced drag is negative, then it means that the wing in that part of the span is actually lifting forward - as strange as that sounds.
 

REVAN

Well-Known Member
Joined
Dec 6, 2016
Messages
230
Location
Tucson, Arizona USA
One of the things that Al Bowers is saying - and is revolutionary if true - is that there is not only proverse yaw with BSLD, but that the induced drag near the wing tip is actually negative, in other words it is thrust. This seems to mean that not only does BSLD mean yaw stability, but that it is also the most efficient lift distribution arrangement. Essentially, you have a wing that is slightly longer span than an elliptically distributed wing, creates the same lift, requires the same structural weight, and has less drag as well.

Bowers described a phenomenon of upwash at the tip, and stated that this would mean the lift vector has rotated forward and voila, you have thrust! My first visualization of this upwash was upwash due to negative lift where circulation would actually be opposite from the inboard part of the wing which would just be more induced drag, but with negative lift. But, if the circulation is the same direction as the inboard portion of wing, meaning that the upwash was just downwash rotated so that it is now pointing upward, ostensibly due to the induced upwash ahead of the wing as well as a negative angle of incidence (not to be confused with negative angle of attack, that would still be positive), then there would actually be thrust because the wing would be lifting forwards; if there is no lift at the tip and the induced drag is negative, then it means that the wing in that part of the span is actually lifting forward - as strange as that sounds.
A wing grid will also produce thrust at the 'wing tip' (i.e. - in the grid itself). It works similar to Bowers' wing, in that the "downwash" through the grid is actually an upwash. A wing-grid is what should be used if you need the benefits of the BSLD as Bowers described, but also have a span constraint that prevents using a long wing. The wing grid is amazingly stall resistant, and with tip thrust, it's spin resistant also. But, a longer wing with washout may be easier to make with traditional construction methods if span isn't a constraint.

I think positive yaw stability could be achieved with a smaller wing section washed out than what Bowers used on Prandtl-D if something other than a typical aileron were used for the control surface. A little more thought going into "engineering" how the control surfaces manipulate the induced drag of the wing could have a lot of benefits. By the way, I'd control a wing-grid, not with ailerons, but by moving the grid sections to change the amounts of lift and drag they produce. I'm not a fan of normal ailerons.

PS - Please note that an 'upwash' at the wing tip does not necessarily mean that the wing tip is lifting down (a common misconception). It is still lifting up, but it is surfing the updraft created by the inboard sections of the wing. So, the flow is still up, but it gets slowed by the washed-out wing tip that is recovering its energy instead of allowing it to flow up unconstrained in a strong tip vortex.
 
Last edited:

REVAN

Well-Known Member
Joined
Dec 6, 2016
Messages
230
Location
Tucson, Arizona USA
So how about variable washout wings? One way to do it would be to have the outer wing panels rotate around the lateral axis and the way I'm seeing it they could be interconnected with the elevators so that with up or down elevator you would get the appropriate lift distribution (BSLD) regardless of in upright or inverted flight. It seems a little backward to have the greatest lift potential (whole wing stalls at once) when in the cruise condition, though.
I was thinking of linking the ailerons to the elevator to provide variable washout. Both ailerons would move up with full aft stick. The aileron up movement could act only on the last bit of aft stick. Seems fairly simple. Must have been tried in past?
I too, have been thinking about a variable washout wing concept. I hadn't considered just reflexing the ailerons to do it, but it might work. This gets into that realm of starting to engineer the induced drag profile of the wing to make it behave the way you want it to. This is the thought trajectory on which I wanted to get people going. I'm not sure about tieing it to the elevator. Maybe it would work, but tied to an AOA indicator seems more direct. Although, simple is better, if it works.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,318
Location
Port Townsend WA
I too, have been thinking about a variable washout wing concept. I hadn't considered just reflexing the ailerons to do it, but it might work. This gets into that realm of starting to engineer the induced drag profile of the wing to make it behave the way you want it to. This is the thought trajectory on which I wanted to get people going. I'm not sure about tieing it to the elevator. Maybe it would work, but tied to an AOA indicator seems more direct. Although, simple is better, if it works.
I think the key is simply that the pilot should not be capable of stalling the outer wings even with aileron use. He should only be capable of stalling the inboard wing with full aft stick. Of course, this could be done with lots of washout. But I just read that a Cub would need 8° of washout to be spin proof. That much washout would be very inefficient in cruise, of course.
But instead, if full aft control stick was linked and activated inboard stall strips that might be an alternative to washout.
I noticed the 737 sometimes uses inboard spoilers for roll control when maneuvering slowly in a holding pattern. Same idea, I think.
 
Last edited:

REVAN

Well-Known Member
Joined
Dec 6, 2016
Messages
230
Location
Tucson, Arizona USA
...I just read that a Cub would need 8° of washout to be spin proof. That much washout would be very inefficient in cruise, of course.
Washout doesn't have as much impact on cruise drag as people tend to think it has. They forget about the surfing effect which will recover a good portion of what people imagine is being lost. This idea, that the straight untwisted wing, is both easier to build and will provide more performance isn't really true. It's only easier to build, and that's only true if constructing it on a flat table instead of using a jig.

That said, I completely agree with you that there are things that can be done with the control system to reduce the amount of washout that is required to achieve the desired control characteristics.
 

Autodidact

Well-Known Member
Joined
Oct 21, 2009
Messages
4,513
Location
Oklahoma
Getting BSLD right seems a little more complicated than your average Schrenk computation; is there a simple way to do it, or do you need CFD?
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,597
Location
Fresno, California
I've wonder if split surface ailerons (upper and lower surfaces split like drag brakes) could assist in spin recovery?
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
2,295
Location
Sahuarita Arizona, Renton Washington, USA
So how about variable washout wings? One way to do it would be to have the outer wing panels rotate around the lateral axis and the way I'm seeing it they could be interconnected with the elevators so that with up or down elevator you would get the appropriate lift distribution (BSLD) regardless of in upright or inverted flight. It seems a little backward to have the greatest lift potential (whole wing stalls at once) when in the cruise condition, though.
An outboard "free wing" section would prevent the outboard section from stalling and provide the variable washout desired. I suspect CG control and trim will soon become an issue to deal with as this design concept moves forward.

Right you do not want the whole wing stalling at cruise AoA but how would you get that condition?
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Getting BSLD right seems a little more complicated than your average Schrenk computation; is there a simple way to do it, or do you need CFD?
The Hortens achieved it without computers.

Of course you can get fancier if you want. Wasn't the design of Prandtl-D refined by fancy CFD? I think someone posted the geometry of it on this forum someplace. I may be wrong about this, but my impression is that you can fudge the twist by scaling it up and down for different design lift coefficients.
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
2,295
Location
Sahuarita Arizona, Renton Washington, USA
The designers of the GlaStar/Sportsman wanted an airplane that could be flown in slow flight (not like the new FAA definition, but true slow flight a knot or two above stall) and still have aileron control of the roll axis. They accomplished that for the flaps retracted configuration. The Sportsman (I haven't flown the GlaStar) retains aileron control through the flaps-retracted stall throughout the power range. Power off, with full back stick, it settles into a stable sink with full aileron control. With full flaps, some rudder is required to keep the wings level. I'm still, slowly, evaluating the effects of different aileron rigging.



The Sportsman will spin. One has to intentionally make it spin with flaps retracted. It is easier to enter a spin with full flaps. I have no experience spinning the Sportsman with half flaps.

The crash that started this discussion, the ICON over the lake, would have been easily avoided in the Sportsman (and likely the ICON also) with the turn technique that I described in that thread.

A free-wheeling discussion about methods to make better and safer flying airplanes will be interesting, but may not lead to any useful conclusions. (To me, a better flying airplane would be one capable of pulling to vertical without losing too much speed, like a modern monoplane, but still have snap roll - spin - charactersitics of a Pitts.)

The first step necessary to find a way to eliminate a problem is often overlooked because it is assumed that the problem is clearly understood. The first, and necessary, step is to clearly and succently state the problem.

Please state the spin problem that you would like to fix.

Thanks.

BJC
The problem is the unintentional spin. It is OK and perhaps even desirable to be able to spin the airplane. The problem is that some aircraft have a tendency to enter a spin from what could be a stable stall.

In short, some aircraft are prone to spin and some are not. The goal here is to create a design that is not prone to spinning without detracting from performance and without creating weight, cost and manufacturing or maintenance issues.

To begin with I think we need to have a common understanding of what constitutes a spin resistant airplane.

I will propose the following statements to see what agreement or disagreement follows.

1. The Ercoupe is not a spin resistant design. It is stall resistant and therefore does not have a spin problem. The stall resistant design is a performance limitation that is a limitation for (some or many, pick one) pilots.

2. "The Sportsman retains aileron control through the flaps-retracted stall throughout the power range." This does not make the Sportsman a spin resistant airplane. If the Sportsman is held in a full stall, a wing will drop and without corrective pilot action of aileron and/or rudder the aircraft will spin or spiral dive depending on the CG and amount of elevator control. In short it takes pilot action to prevent a spin at a high angle of attack.

3. It is possible to build a spin resistant aircraft. I can give examples from typical kids kites to ultralights to airliners. I just now built a spin stable paper plane in less than 5 minutes. The Air Bus A330 operated as AF flight 447 made a full stalled descent from several miles high into the South Atlantic ocean without spinning. A TWA B-727 made a deep stall descent from about 20,000 feet with iced pitot tubes. and the Air Bus 320 crashed at the French airshow without spinning. The Cascade Ultralights "Kasper Wing" can make a deep stall descent without spinning. The SGS 2-33 must be forced to spin. What about the Concord crash, Does it look like a spin entry in the final second?

I am sure there are many other examples of spin resistant design as well as spin prone designs. I suspect the Lear jet is a good example of a spin prone design but do not have personal experience to support that statement. I solicit comments on other designs from personal experience. I am particularly interested in comments about the Sonex as it was the Sonex Acro N123SX crash that killed Jeremy Monnett, CEO of Sonex that started the recent interest in this subject. Many aircraft will be average or typical when rated for spin resistance. It would be nice to have some sort of grading scale to cover the range.

4. Before we get into the ideas and merit of design we need to determine the usefulness of the study. There appears to be a large segment of the pilot population that that see no benefit to a spin resistant airplane. Some even see an apparent benefit to a spin prone design. I solicit your opinions.

IMG_0104.JPG

Note aft CG and generous up elevator above and forward CG and neutral elevator below.
Incidentally, these happen too be flying wings for ease of construction with low cost (scrap) material. Normal Paper Plane.JPG

The stalled plane makes a slow stable glide with a 2 or 3 to one glide ratio. The normal configured plane glides with a much faster 5 to one or greater glide angle. We can do better than many existing aircraft designs.
 
Last edited:

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
I recall a control system where the ailerons were connected so that the controls determined the angle difference between the ailerons, but they floated together. Or maybe this was rotating wing tips?
 

Autodidact

Well-Known Member
Joined
Oct 21, 2009
Messages
4,513
Location
Oklahoma
The Granger Archaeopteryx; I have the urge to put wing fences at the break between wing and elevons - I wonder if it would help or hinder? On a tailless, would you even need variable washout? It seems like the act of trimming for attitude (the flight kind) would or could accomplish the washout needed. I wonder if the Archaeopteryx had BSLD and if so, did the designers understand it? From http://aviastar.org/ :

granger_arch.jpg

By the way, there were many interesting little aircraft powered by the Bristol Cherub and other small engines and it would be very nice to see them all replicated with the Pegasus o-100.
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Since I don't see a horizontal stab, I suspect the tips on the Archaeopteryx were used as elevators as well, so they couldn't float in the manner I described. OTOH, the resulting washout probably reduced or eliminated adverse yaw anyway. A more recent aircraft with this arrangement was the Short SB.4 Sherpa.
4530218888.jpg
Incidentally, the Sharpa was probably one of the slowest jets ever built. I think the top speed was supposed to be 170 mph!
 

Autodidact

Well-Known Member
Joined
Oct 21, 2009
Messages
4,513
Location
Oklahoma
On the Granger they were elevons; it's interesting that they were still being investigated up into the jet age. It would be interesting to know what criteria they were being designed to as far as calculating the spanwise distribution - were the designers getting good results that they didn't quite understand? Or did they understand just fine? I don't remember if I heard a reference to the Brits' experiences in Al Bowers' talk - I'll have another listen... From Wikipedia page on the Sherpa:

Handling characteristics
"The Sherpa's first trials, with Shorts' Chief Test Pilot, Tom Brooke-Smith at the controls, proved very satisfactory and the small black and silver plane has been quoted as being 'one of the most graceful aircraft now flying'."
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
12,337
Location
97FL, Florida, USA
2. "The Sportsman retains aileron control through the flaps-retracted stall throughout the power range." This does not make the Sportsman a spin resistant airplane. If the Sportsman is held in a full stall, a wing will drop and without corrective pilot action of aileron and/or rudder the aircraft will spin or spiral dive depending on the CG and amount of elevator control. In short it takes pilot action to prevent a spin at a high angle of attack.
That comment was in response to
Posted by wsimpso1
Boundary layer devices near the leading edge that energize entire tip portion of the wing. These can be classic vortex generators, or the tiny elevated little delta shaped fence used on the Glastars. These have a tendency to keep the wing flying way into stalls even when cross controlled.
I went on to say that the Sportsman will spin.

4. Before we get into the ideas and merit of design we need to determine the usefulness of the study. There appears to be a large segment of the pilot population that that see no benefit to a spin resistant airplane. Some even see an apparent benefit to a spin prone design. I solicit your opinions.
I don't think that a spin resistant airplane will significantly reduce the number of loss-of-control crashes. See my previous posts on that subject.

I do not know what "resistant" means. It takes a conscious effort to make a Cessna A152 spin. In my view, the A152 is spin resistant, so some more definition of "resistant" may be useful.

Any semi-modern type certificated light aircraft, other than a very few aerobatic models such as the S-1 and S-2 series, require gross mis-use of controls to get into an unintentional spin. Are you proposing that E-AB aircraft have similar characteristics? If you are, then you are also proposing designs that will not have the handling chracteristics that make them fun to fly.

Since it takes yaw, usually from inappropriate rudder control, to enter a spin, one might try a full authority yaw damper with a control switch that would allow the pilot to select "ride" or "fly" control modes.


BJC
 

Swampyankee

Well-Known Member
Joined
Dec 25, 2015
Messages
1,433
Location
Earth USA East Coast
Of course, with digital fly-by-wire it's quite straightforward, albeit not trivial, to prevent stall-spin accidents without compromising other areas of flight performance: all modern combat aircraft have DFBW to prevent [possibly the most highly trained] pilots [in the world] from breaking the boundaries of the aircraft's flight envelope.

Overall, I think that it's both more practical and more worthwhile to make sure that aircraft provide good stall warning and have good spin recovery characteristics, as the former will permit avoidance of spins and the latter will make exiting a spin easier.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,318
Location
Port Townsend WA
The fatal spin record is quite different for each model. The C-182 is best, apparently too much force is needed for full aft yoke.
Lucky I survived my early time in the Chief, at other extreme.

image.jpg
 
Top