The Spin Debate

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
13,224
Location
Port Townsend WA
I was reading through Rich Stowall's book STALL / SPIN AWARENESS.
Rich says the ball bank guage is just too slow to prevent spins because of the fluid dampening and spins can happen even with the ball almost centered. So I guess the yaw string wins!

Anyway, the book also covers just about every anti-spin design trick even invented, I think.
 

Toobuilder

Well-Known Member
Log Member
Joined
Jan 19, 2010
Messages
4,758
Location
Mojave, Ca
Odd question but do you have a picture of that or any information on materials etc? I figure if the U-2 can have one, I can fit one on the Praetorian since we will be much slower than the Vne of the U-2...
Does your airplane have a tractor engine? That will screw up that scheme.

In the U-2, it is nothing more than a hole in the top of the windshield bow with the string knotted and sealed with RTV. The string is about 18 inches long, and trails back along the top of the canopy. There are some reference marks painted on the inside corresponding with coordinated flight, and a few degrees off.
 

Toobuilder

Well-Known Member
Log Member
Joined
Jan 19, 2010
Messages
4,758
Location
Mojave, Ca
...Rich says the ball bank guage is just too slow to prevent spins because of the fluid dampening and spins can happen even with the ball almost centered...
Ok, let's back the bus up a bit... The inclinometer (ball) does not "prevent" spins, nor any other flight condition. It is simply a pilot aid to cross reference what his butt should be telling him.

If you are "flying" the ball in the visual pattern, you're doing it wrong.
 

Richard6

Well-Known Member
Joined
Aug 14, 2010
Messages
700
Location
Plymouth, MN USA
I know this is the spin debate, but I was thinking about how the spin starts, because of a stall.

I was watching a video of an eagle flying just above a ridge with the wind blowing up from it. The bird was almost stationary, with the wind coming up from below. I am guessing that it was flying with it’s wings stalled. I noticed that some of the feathers on the top of it’s wing, about half way from the back edge, were lifting up. It appeared to me that these feathers were blocking the stall effect by blocking the disconnected air flow from moving forward to stall the whole wing.

Thoughts ?

Richard
 

Head in the clouds

Well-Known Member
Joined
Mar 11, 2012
Messages
1,983
Location
Gold Coast, East Coast of Australia
Yawstring? How many inches long; you don't want to be considered showing off? "It's like my wife says, "it ain't no big thang!"
Yes, of course, I hadn't considered that. I think I'll start a poll and find out how long is long enough....

I was always going to have one, I just hadn't had a good opportunity to announce it before. The thought is to make my pitot tube good and stiff and stick it out in the breeze ahead of the windshield and tie the yawstring onto it good and tight. What do you think?
 

Head in the clouds

Well-Known Member
Joined
Mar 11, 2012
Messages
1,983
Location
Gold Coast, East Coast of Australia
I know this is the spin debate, but I was thinking about how the spin starts, because of a stall.

I was watching a video of an eagle flying just above a ridge with the wind blowing up from it. The bird was almost stationary, with the wind coming up from below. I am guessing that it was flying with it’s wings stalled. I noticed that some of the feathers on the top of it’s wing, about half way from the back edge, were lifting up. It appeared to me that these feathers were blocking the stall effect by blocking the disconnected air flow from moving forward to stall the whole wing.

Thoughts ?

Richard
Hi Richard,

No, not stalled at all. Detego and others were discussing just this on another thread and Detego posted a great video. The lifted feathers are actually preventing the stall, I'm sure he'll post a link to it for you. Cheers.
 

SVSUSteve

Well-Known Member
Joined
Aug 20, 2007
Messages
3,894
Location
Evansville, Indiana
Yes, of course, I hadn't considered that. I think I'll start a poll and find out how long is long enough....
It's a shame that there aren't more female members on this forum because it would be interesting to see that poll be split out across the genders. LOL
 

Topaz

Super Moderator
Staff member
Log Member
Joined
Jul 29, 2005
Messages
14,110
Location
Orange County, California
...Eat your hearts out folks, Duncan and his lovely wife are coming for some of Christmas with us, so we get to spend time with the twice AUSTRALIAN BALLROOM DANCE CHAMPIONS - CONGRATULATIONS DUNCAN AND GLENDA !...
I was just reading back through some posts, and I missed this tidbit! Without derailing this thread, let me say it's great to see HBA members meeting up "in the real world". :) Some of the SoCal members have met a couple of times for the Flabob airport airshow, and I've had the privilege of visiting PTAirco's shop more than once.

And hello, how is it, Duncan, that we never heard about your wins in "Hangar Flying"???? Congrats, man! That's something of which to be very, very proud!

I'm just putting it out to the membership - "Hangar Flying" is exactly what it says: Shooting the breeze among friends. We try to keep it at least nominally about aviation, even there, but let me say this: If you've just won a national award, tell us for heaven's sake! :gig:
 

SVSUSteve

Well-Known Member
Joined
Aug 20, 2007
Messages
3,894
Location
Evansville, Indiana
I was just reading back through some posts, and I missed this tidbit! Without derailing this thread, let me say it's great to see HBA members meeting up "in the real world". :) Some of the SoCal members have met a couple of times for the Flabob airport airshow, and I've had the privilege of visiting PTAirco's shop more than once.

And hello, how is it, Duncan, that we never heard about your wins in "Hangar Flying"???? Congrats, man! That's something of which to be very, very proud!

I'm just putting it out to the membership - "Hangar Flying" is exactly what it says: Shooting the breeze among friends. We try to keep it at least nominally about aviation, even there, but let me say this: If you've just won a national award, tell us for heaven's sake! :gig:
Congrats Duncan!!

So does this mean I can put up a "Who wants to meet Steve and Kat while they are on their honeymoon in Washington state next September?" thread? LOL
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,340
Ok, let's back the bus up a bit... The inclinometer (ball) does not "prevent" spins, nor any other flight condition. It is simply a pilot aid to cross reference what his butt should be telling him.
keeping the ball centered is no guarantee of spin avoidance.

The angle of attack of the left and right wings is often different.

In level flight, wings, level, they are the same.

In a wings-level climb or descent, they are the same.

In a level altitude, coordinated banked turn, the angle of attack of both wings is the same, but the speed difference between the wings creates an overbanking tendency that usually requires some top aileron. That downgoing aileron on the inside wing increases the angle of attack over that section of wing, and it will stall first and drop that wing into the incipient spin.

In a descending coordinated turn the angle of attack is larger on the inside wing. If we stall the airplane in that turn that inside wing will stall first and drop the airplane into the spin. If we skid the airplane, the AoA difference increases, which is why a skid is such a killer in the base-to-final turn. If we slip the airplane in that descending turn, the AoA difference diminishes, making the turn safer.

In a climbing turn, the outside wing is at a higher AoA and will stall first. The airplane will roll away from the turn.

Go here: Pushover from Pattern Altitude - Page 4 - Pilots of America Message Board

And scroll down to post #93. Pictures of an AoA demonstrator I built a few years ago. You can see how the helical path of wings in a climbing or descending turn are seeing the wind, and what effect a slip or skid has on AoA.

Dan
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
13,224
Location
Port Townsend WA
keeping the ball centered is no guarantee of spin avoidance.


If we slip the airplane in that descending turn, the AoA difference diminishes, making the turn safer.

Dan
Great post Dan. So are you advocating slipping on every turn to final to avoid the dreaded skid stall?
If so how would that be done?
For example on a left turn to final, you mentioned the over banking tendency requires a bit of top aileron to stop that, so should a bit of top rudder be held as well through the turn? And if the pilot is blown downwind past the runway, should the bank be steepened but still keep slipping with top rudder?
And finally, coming out of the turn, would you use a bit more rudder than aileron , as I suggested earlier
thanks Dan

p.s. your link requires registry, no time for that now...
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,340
A slipping turn is used to lose altitude. It's just a slip combined with a turn. It will need top rudder, unless the airplane has a really bad adverse yaw anyway. I'm not advocating a slip in the turn just because it's safer. The skidding-turn stall also requires decaying airspeed, and that often comes when the pilot is a bit low and starts pulling back to stretch the glide in the turn. The throttle should go forward instead.

Being blown downwind (I presume through the runway centerline) the pilot should just maintain the turn until he's approaching the centerline again, then establish the airplane on final. A slipping turn has a larger radius, so he should coordinate the turn and if he's now too high, the whole thing is messed up anyway and he'd better go around and start over, plan better, and start his turn sooner. Too many accidents happen because the pilot is determined to land when there's no real reason to carry through with it.

Dan
 

SVSUSteve

Well-Known Member
Joined
Aug 20, 2007
Messages
3,894
Location
Evansville, Indiana
Too many accidents happen because the pilot is determined to land when there's no real reason to carry through with it.
It was drilled in my head when learning to fly ultralights that one should approach every landing (pun intended) as though it will result in a go around/missed approach. The mantra was more or less to actively seek out reasons why you should abort and try again until your wheels are on the ground. Even then, I have had a few balked landings (going around after touchdown with the intention of a full stop) in my day.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
13,224
Location
Port Townsend WA
I have two thoughts about advocating go arounds.
First, is obvious to me as a glider pilot, it is drilled in my head that the go around is not possible, so every landing must be planned right the first time.
Second, I think when a scared power pilot attemps the go around, at this point the go around maneuver itself might trigger the stall spin.
Something like this:
The pilot already is sloppily skidding the left turn to final and holding top aileron to avoid too much bank and gradually pulling the stick back because the ground speed seems so fast( from the tailwind on base).
So he decides to go around and shoves the throttle to firewall while still cross controlled. And now the torque/P factor adds in additional left yaw. And worse, the pilot slams the wheel full right to level the wings ( ailerons only, no rudder)and there he gets his first and only non recoverable left spin.
Also, the rudder and elevators get more control for a more spectacular stall/spin with power on.

The amount of rudder needed to get perfect coordination varies with airspeed. The pilot has near zero experience with low speed coordination..

This situation is similar to the Alaska Moose Hunter Stall Turn/Spin. In this case, the hunter (with almost no recent slow flight experience) does tight and slow circles around a moose at half throttle. Each circle eats up some energy because turning takes more power. So the pilot keeps adding back stick and a bit of skidding rudder to stay with the moose. Then suddenly gets too low and/or a gust tips the wing down more and the pilot slams in full aileron and full power for a nice spin from about 100 feet.
Happens almost every hunting season.

This is why I think proper turn exit is more important than turn entry, yet virtually ignored in training, I think.
 
Top