snap roll question
Craig Good
Last night I saw the ghouls on some tabloid TV show doing a story about
the airshow pilot who died at Three Rivers a while back. The video (which
they ran over and over) showed his Pitts entering a snap roll. During the
roll two of the wings failed and folded back along the fuselage, leaving
him nothing to do but hit the river. The show said that the cause of the
accident was traced to "cracks in the wings". I must assume they meant the
spars; one can't expect the TV reporterette to get it right.
I understand that with metal fatigue failures can happen at the strangest
times, but it led me to a question about snap rolls which I'm sure someone
here can answer. I've never done a spin (got part way into one in a
Marchetti SF260 with Air Combat USA, but that's another, much more
pleasant story) so I cannot speak from experience. But I've been told that
spins are actually fairly gentle on airframes since the loading goes so
low. I'm also under the impression that a snap roll is little more than a
spin done while flying sideways rather than down. Which would make me
think that snap rolls aren't particularly rough on the airframe. This
accident would tend to mean otherwise.
So what sort of forces are involved in spins and snap rolls? Thanks, as we
used to say ten years ago on the usenet, in advance.
--
--Craig
go...@pixar.com
Amore, Mangiare, Famiglia, Pace
Alan Constant
Craig Good wrote:
>
> So what sort of forces are involved in spins and snap rolls? Thanks, as we
> used to say ten years ago on the usenet, in advance.
>
> --
> --Craig
> go...@pixar.com
> Amore, Mangiare, Famiglia, Pace
I'm no expert on aerobatics, but I built a Pitts and asked lots of questions (had to
quit flying because of vision problems before I got to fly it). In the early 1970's, we
used to go to competitions in Centralia, Ontario and during the show the announcers
would say that a pilot pulls 6 G's in a snap. I questioned Gord Price, former Canadian
Aerobatic Champion, and he said "a snap is 4 G's max - pulling 6G's would rip the wings
off". If I'm not mistaken, I think you are only pulling 1G during a spin.
A Pitts also snaps quite rapidly, probably one of the fastest snappers around, and would
likely be more violent than one in say a Stampe or Citabria which is considerably
slower, even though you might pull the same G loading.
Alan Constant
Kyle Hendrickson
Craig Good wrote:
>
> Last night I saw the ghouls on some tabloid TV show doing a story about
> the airshow pilot who died at Three Rivers a while back. The video (which
> they ran over and over) showed his Pitts entering a snap roll. During the
> roll two of the wings failed and folded back along the fuselage, leaving
> him nothing to do but hit the river. The show said that the cause of the
> accident was traced to "cracks in the wings". I must assume they meant the
> spars; one can't expect the TV reporterette to get it right.
>
> I understand that with metal fatigue failures can happen at the strangest
> times, but it led me to a question about snap rolls which I'm sure someone
> here can answer. I've never done a spin (got part way into one in a
> Marchetti SF260 with Air Combat USA, but that's another, much more
> pleasant story) so I cannot speak from experience. But I've been told that
> spins are actually fairly gentle on airframes since the loading goes so
> low. I'm also under the impression that a snap roll is little more than a
> spin done while flying sideways rather than down. Which would make me
> think that snap rolls aren't particularly rough on the airframe. This
> accident would tend to mean otherwise.
>
> used to say ten years ago on the usenet, in advance.
>
> --
> --Craig
> go...@pixar.com
> Amore, Mangiare, Famiglia, Pace
A snap roll is an induced spin along the horizontal axis. Typically
conventional spins are executed by first entering a conventional stall
ant then inducing a spin at or just before the moment the plane stalls
thus, at entry, the plane really doesn't experience anything much
different (in terms of G loading) than in a normal FULL stall. A snap-
roll, however, is entered through an accelerated stall, meaning the
aircraft is above its normal stall speed and must be "G loaded" in order
to achieve the critical angle of attack. This "G loading" is
accomplished by a sharp backward movement of the stick and the "roll" is
achieved by a simultaneous input of left or right rudder. Throughout
the entire maneuver the plane is ABOVE its normal sall speed thus it can
be recovered without gaining airspeed. In short, a snap roll involves
more G loading than a normal spin. The faster the plane is traveling
the more G's that will be required to "stall" the airplane and thus
enter into a snap roll. All planes have a speed at which structural
failure will occur before a stall (this is similar to the concept of
maneuvering speed). He probably had a deffective plane and entered into
a snap roll at a pretty good speed. It would be very hard for an
experienced aerobatic pilot to accidently rip the wings off of a Pitts
from over acceleration or G loading--ie. The difference between the
normal entry speed into a snap roll and the speed at which the same
maneuver would cause mechanical failure of a sound airframe is quite
significant.
Edward Schreyer
Snap rolls place loading on the tail to induce the stall break necessary
to initiate the autorotation, and the asymmetrical lift on the wings
which causes the roll also places loading on the airframe. None of this
is a problem if you enter the maneuver at the appropriate airspeed. For
an S1-T Pitts or Christen Eagle (both aircraft I've flown quite a bit),
entering at 100 mph indicated is fine. It's pretty tough to get more
than a single roll and be able to maintain a crisp finish at that speed,
which is why a lot of pilots who fly airshows or compete at upper levels
may choose to initiate a snap at a higher airspeed. In a recent issue
of Sport Aerobatics, a graph displaying entry speed versus structural
loading indicated that an entry speed of greater than 140mph indicated
could exceed design limitations for an S2-B Pitts. (Sport Aerobatics,
August 1996, p 12, article by Budd Davisson).
Don't try this without some proper acro instruction, and a good base of
spin recovery training.
--
Edward Schreyer e...@sgi.com
Education Marketing (415) 933-1086 (voice)
Silicon Graphics Computer Systems (415) 390-6060 (fax)
http://www.sgi.com/silicon_campus/ (800) 949-9708 (pager)
DSowder
The flight manual for the Pitts S-1S specifies a max. IAS of 140 (mph) for
an inside snap roll, and 110 mph for an outside snap. "G" loading on the
airframe (required to stall the wing for the snap) increases as a square
of the speed, so if you snap at a higher IAS, the G loading can be
significantly higher. And there's not just plain old G's to worry about. A
snap imposes significant gyroscopic and inertial loads on the airframe and
its various parts, and these loads aren't always symmetrical. The S-1S'
maneuvering speed is 154 IAS, but they say to keep the snaps at 140 or
below, I presume because of these other loads.
So why would someone snap at more than 140 IAS? To do multiple snaps
without losing too much altitude, typically, or perhaps because a snap is
called for at that point in the sequence of maneuvers and the speed just
happens to be too high. If you see an airshow Pitts pilot fly three or
more consecutive snaps on an apparently horizontal line, you can bet he
pulled the trigger at more than 140. And his Pitts is suffering for it.
While wood doesn't have a defined fatigue limit like steel does, the wood
in the wings gets pretty beat up after a life of snaps. Ribs break, spar
attach holes loosen up, drag & anti drag wire blocks get crushed, etc.
These acro airplanes lead a hard life. Don't forget that the S-1S is
certificated for load limits of +6 and -3 G's. Can you do a ROUND outside
loop within 3 G's? I can't. How about an inside-outside "8"? If you pull 5
G's on the inside portion, you're going to have to push -5 on the outside
portion or the part-loops won't be symmetrical. Sorry this is a little
wordy. Spent the weekend rebuilding a Pitts lower wing (though it was more
crash damage than in-flight damage).
Doug Sowder
Rex Root
Wasn't there an AD out for the S1's wing spar a few years ago? I seem
to remember something about it, and if so, don't recall which wing.
As a matter of fact, Patty Wagstaff had an inflight wing failure a couple
of years ago but managed to nurse it to the ground. Wasn't that in an S1?
Course maybe I'm just dreaming .. she's only been flying Extras'. What
in the world would she be doing in a Pitts? :-)
-rex Flying inverted over the
Information Superhighway
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| ( ) |
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T
Don Peterson
DSowder wrote:
>>How about an inside-outside "8"? If you pull 5
> G's on the inside portion, you're going to have to push -5 on the outside
> portion or the part-loops won't be symmetrical.
Hmm. Although a little new to this maneuver, I always figured that if I
was going slightly faster on the backside of an inside/outside 8, then a
slightly lower g load would produce the same diameter loop. Comments?
Don
Guy York
Craig Good <go...@pixar.com> wrote in article
<good-27099...@buttle.pixar.com>...
> Last night I saw the ghouls on some tabloid TV show doing a story about
> the airshow pilot who died at Three Rivers a while back. The video (which
> they ran over and over) showed his Pitts entering a snap roll. During the
> roll two of the wings failed and folded back along the fuselage, leaving
> him nothing to do but hit the river. The show said that the cause of the
> accident was traced to "cracks in the wings". I must assume they meant
the
> spars; one can't expect the TV reporterette to get it right.
>
> I understand that with metal fatigue failures can happen at the strangest
> times, but it led me to a question about snap rolls which I'm sure
someone
> --
> --Craig
> go...@pixar.com
> Amore, Mangiare, Famiglia, Pace
>
I believe the aircraft in question flown by Clancy was an S1 Pitts and
unless modified, had a wood wing. Several factors may have come into play
including the age of the aircraft, and g loading it had been sujected to
over the years. In a recent IAC magazine there was an artical concerning
the longerons on the Pitts S2 aircraft failing. The artical basically
stated the Aviat (makers of the Pitts) believed entering maneuvers
including snaps at higher than recomended airspeed was probable cause for
the failures. The NTSB also agreed with Aviat saying it thought that
opeeration beyond the flight manual operation was the probable cause of the
falures in the S2.
You might get away with exceeding the limits of an aircraft a few times.
Then again, unaware to you, long term damage to your aircraft may have been
done. Flown by the book the Pitts is a very safe and strong aircraft.
Guy York
love...@peop.tdsnet.com
Jim Smolen
r...@Glue.umd.edu (Rex Root) wrote:
>Course maybe I'm just dreaming .. she's only been flying Extras'. What
>in the world would she be doing in a Pitts? :-)
Slumming??
Jim (yes, I love the Pitts) Smolen
Dennis N. Yugo
If the part-loops are to be symmetrical, then higher airspeed will
require MORE g's (assuming zero wind).
--
Dennis Yugo
http://www.hooked.net/~dyugo
DSowder
For a given radius of loop, a higher speed requires more "G". The formula
for centripetal (i.e., "towards the center") acceleration is A=V^2 / R.
Thus, for a given radius, "G" force increases as a squared function of the
speed. Double the speed, and 4 times the "G" is required. That's why jet
fighters fly such big loops and turns. And why a clipwing Cub flys such
small ones. Algebraic rearrangement shows that R=V^2 / A, so if you reduce
"G", the radius increases in direct (but inverse) proportion. But if you
increase speed, leaving "G" load constant, the radius increases
proportional to the square of the speed. BTW, we're sort of using "G" and
"A" interchangeably here.
Doug Sowder
Don Peterson
Actually, I knew this, but hit the send button before I re-read my note
and realized I stated it bassackwards. Of course, our engine rotates the
"right" way around rather than left, so maybe centripetal force will work
in reverse. :)
Anyway, my main point was that it does not require identical g forces on
both sides of an inside-outside 8, with the outside being flown at lower
g if one uses the corrent lower entry speed for that portion. See
earlier post.
When one flies a +6 -4 airplane, you just gotta find ways to get around
the corners that won't tear things off in the process.
Don
Brian Grinter
dso...@aol.com (DSowder) wrote:
>The flight manual for the Pitts S-1S specifies a max. IAS of 140 (mph) for
>an inside snap roll, and 110 mph for an outside snap. "G" loading on the
>airframe (required to stall the wing for the snap) increases as a square
>of the speed, so if you snap at a higher IAS, the G loading can be
>significantly higher. And there's not just plain old G's to worry about. A
>snap imposes significant gyroscopic and inertial loads on the airframe and
>its various parts, and these loads aren't always symmetrical. The S-1S'
>maneuvering speed is 154 IAS, but they say to keep the snaps at 140 or
>below, I presume because of these other loads.
My instructor owns an SF-260 and told me the gyroscopic forces are
quite strong esp. on the engine mounts of the SF-260. The manufacturer
recommended flick-roll (snap-roll to you guys) speed caused enough
movement in the engine mounts to make the spinner rub against the
cowling surrounding it. He now uses a lower speed...
Brian Grinter
Sydney, Australia
bgri...@onaustralia.com.au
ph 61 2 6228970
Alan Peake
announcers
>would say that a pilot pulls 6 G's in a snap. I questioned Gord Price, former
>Canadian
>Aerobatic Champion, and he said "a snap is 4 G's max - pulling 6G's would rip
>the wings
I hope not! The pitts is supposedly stressed to +/- 12G and unlimited pilots
regularly pull +7/-5
Alan
Travis Leonard
Alan Peake <Alan....@defence.dsto.gov.au> wrote in article
<Alan.Peake...@defence.dsto.gov.au>...
Now I'm no aerobatic pilot, but it would seem to me that the g-limits of
the wing are expressed as static load, and not a full dynamic load. If you
suddenly apply a load of 12G's to a Pitts wing, it probably will fail. I
don't think that 6G's would do it, but it is just important how the load is
applied (snap roll being one of the more violent) as how big the load is.
Travis Leonard
1946 7AC Champion
And no, I don't even try aerobatics in it!
Alan Constant
Alan Peake wrote:
>
> announcers
> >would say that a pilot pulls 6 G's in a snap. I questioned Gord Price, former
> >Canadian
> >Aerobatic Champion, and he said "a snap is 4 G's max - pulling 6G's would rip
> >the wings
>
> I hope not! The pitts is supposedly stressed to +/- 12G and unlimited pilots
> regularly pull +7/-5
>
> Alan
I built a Pitts (though I never got to fly it - had to quit flying for medical reasons).
Anyways, all the manuals said that it was "certified to +6 and -4 G's", which according
to other information meant it was tested to 1.5 times these loads or +9 and -6 G's so +7
and -5G are well within the "test limits" but, apparently if you exceed the "certified
limits", "permanent distortion of the materials may occur" (presumably bending and
fatigue of the airframe).
In Neil Williams' book on Aerobatics, he mentions a particular model of Zlin that was
certified to the limits the Pitts was (+6/-4) and if flown within those limits it had a
fatigue life of somewhere around 2000 hours or so, but flown in unlimited competition to
+9 and -6, it's fatigue life fell to 100 hours!
I understand serious competition and airshow pilots also rebuild their wings (and other
damaged assemblies every winter when the season slows. (Some, I'm told, also scrap their
engines at 500 hours instead of 2000).
Pulling 6 G's in a snap is very different than pulling 6 G's in a dive pullout. In a
pullout, the G's would be applied basically in one direction (downwards), but in the
snap, the forces are applied in a very different way - twisting the airframe (you also
have the engine torque twisting too). The speed and sharpness of the maneuver make a
difference - fast, abrupt maneuvers cause a very sudden flexing of the airframe. Snaps
in a Pitts last about a second. Someone else posted a very good description of the
forces involved in a snap roll earlier.
Incidentally, Gord Price told me that most of the wing damage he found on his aircraft
was not caused by snap rolls, but by hesitation rolls - claiming the rapid start and
stopping did a lot of damage breaking lots of ribs. He had added an extra set of flying
wires to the rear spar on his highly modified Pitts to stop this twisting and eventually
developed the "Ultimate Wing" for the Pitts used by several well known U.S. airshow
pilots (including the guy who has a set of wheels on his upper wing and lands inverted).
Alan Constant
Mike Yukish
In article <325D21...@kanservu.ca> Alan Constant,
arc...@kanservu.ca writes:
>Pulling 6 G's in a snap is very different than pulling 6 G's in a dive pullout. In a
>pullout, the G's would be applied basically in one direction (downwards), but in the
>snap, the forces are applied in a very different way - twisting the airframe (you also
>have the engine torque twisting too). The speed and sharpness of the maneuver make a
>difference - fast, abrupt maneuvers cause a very sudden flexing of the airframe.
It is well known in engineering literature on fatigue
cracking ( indecipherable as it may be ) that the G onset
rate, sometimes known as 'jerk' has a major impact on
fatigue life of structures. Typically the transient loads,
such as the start or stop of a rapid roll or pull, have a
disproportionate effect on the total 'damage' suffered.
This is because airframe structures are like big
mass-spring-damper systems, and pulsing them gets them
vibrating much more than a slow application of force.
Mike Yukish
Applied Research Lab
may...@psu.edu
http://elvis.arl.psu.edu/~may106/
Alan Constant
Brian Grinter wrote:
>
> My instructor owns an SF-260 and told me the gyroscopic forces are
> quite strong esp. on the engine mounts of the SF-260. The manufacturer
> recommended flick-roll (snap-roll to you guys) speed caused enough
> movement in the engine mounts to make the spinner rub against the
> cowling surrounding it. He now uses a lower speed...
>
> Brian Grinter
First, a dumb question. What's an SF-260?
One guy I knew in Aerobatics Canada agreed about the snap causing the spinner to rub
against the nose bowl of the Pitts - he also claimed that a snap could cause the
crankshaft to move as much as an inch off center on its rubber lord mounts. I can
believe it. (Love the sound of a Pitts snap-rolling).
Also, Rolly Cole, son of Duane Cole was killed sometime in the 1960's, I think at a show
in Rockford, Illinois when, as I'd been told, he snap rolled and his engine separated.
They are pretty violent maneuvers. I am told many aerobatic pilots have a steel cable
attached to the engine just in case they do throw it - at least they'd still have the
dead weight of the engine there and could hopefully glide in.
The most I've ever seen in a row was a guy do five consecutive on a 45 degree downline,
and there was a guy I read about a number of years ago who had a Pitts with a
six-cylinder Continental engine with nitro injection who claimed he could do a maneuver
called the "tornado" which was essentially six consecutive VERTICAL snaps - anyone know
what ever happened to him? Most of us figured one day he'd switch on the nitro and about
10,000 pieces of airplane would shower down.
Alan Constant
Dave Swartz
Alan Peake wrote
> >would say that a pilot pulls 6 G's in a snap. I questioned Gord Price,
former
> >Canadian
> >Aerobatic Champion, and he said "a snap is 4 G's max - pulling 6G's
would rip
> >the wings
The G's pulled in a snap can be calculated as (V/Vs)**2 (The ratio of
speed to stall speed is squared). For a Pitts S2B with a stall speed of
60, a snap initiated at 120 will produce +4 G's. A snap in an S2B at 140
(the rated maximum speed for snaps) will produce +5.4 G's. Attempting a
snap at 180 would result in +9 G's if everything held together long enough
to register on the G meter.
Snaps load the airframe very asymmetrically. A positive snap right will
put far more stress on the right upper longeron than on the left. Normal
pulls (pulling vertical) will load both the left and right longerons
equally allowing the stress to be divided between them. A right snap that
results in 5.4 G of load will put far more stress on the right upper
longeron than would result from a 5.4 G pull to vertical.
DSowder
Don,
Do I recall that you're flying a Stampe? Yes, I'd agree that if you fly
the second (outside) part loop of a laydown "8" at a lower airspeed than
the first half, fewer G's will be required to make the radius of the
second loop the same as that of the first. But, do you actually reduce
throttle? In the Pitts (180 hp.), seems like I am always looking for more
energy....reduce throttle to spin or to land!
Re. centripetal acceleration, I've never been south of the equator, but
maybe it works the other way there! Or perhaps just in conjunction with a
backwards rotating motor. I've always wondered about Australians...do they
build their toilets as a mirror image of an American Standard?
Doug Sowder
DSowder
Brian,
You're right about the gyroscopic forces being quite strong in snapping
("flicking?") manouvers. In the Pitts S-1, being a short, light airplane
with a big engine and relatively quite heavy propeller, they're VERY
noticeable. Gyroscopic forces are why most Pitts pilots usually snap to
the right. And when pulling for a loop or to vertical, etc., a healthy
dose of left rudder is needed to keep the nose straight. Similarly, when
pushing over the top of a push humpty, a lot of right rudder is needed to
avoid heading change. I've never noticed this trait in other airplanes
which are physically larger relative to their propeller. Haven't flown an
SF-260, but would like to (of course!).
Doug Sowder
Don Peterson
>> Are you sure about that? In twenty-odd years of going to airshows and aerobatic
> competitions, I don't recall ever seeing a Pitts (or any other aerobatic aircraft) snap
> to the right - always to the left. I'm told the torque of the engine makes it much
> easier to snap that way.
>
> I have many photos of Pitts, Eagles, and Lasers snaprolling, and they are all doing it
> to the left.
>
> Alan Constant
Yep, in competition most Lycoming engine pilots snap to the right, unless
they are on an ascending 45 or vertical line, in which case some go to
the left. The slower rotation to the right makes the maneuver more
controllable, while going to the left causes a bit less sideways
displacement and resulting yaw, which is important in partial snaps.
Don
Brett Wayne
In article <326264...@kanservu.ca>, Alan Constant <arc...@kanservu.ca>
wrote:
> Are you sure about that? In twenty-odd years of going to airshows
> and aerobatic competitions, I don't recall ever seeing a Pitts (or any
> other aerobatic aircraft) snap to the right - always to the left. I'm
> told the torque of the engine makes it much easier to snap that way.
>
> I have many photos of Pitts, Eagles, and Lasers snaprolling, and they
> are all doing it to the left.
>
My Pitts S-1C will snap significantly faster to the right than to the
left. Not that it _won't_ snap to the left, it does that just fine - but
markedly slower. The gyroscopic and control inputs contribute much more
than any torque moment developed off a clockwise turning motor (as viewed
from the cockpit).
The torque of the motor is a small effect. It becomes most pronounced
when there is almost no airflow over the wings - at the tops of vertical
maneuvers such as humpty-bumps, tail-slides, and yes - torque rolls. Snap
rolls are generally entered between 80-100 KIAS - definitely enough for the
lift component off the wings to significantly overshadow the torque
effects.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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| .====== .__. /~| \
| ____ |_ /____~-._.'__|__) /------------------~
<( ( |. _|_.'......./ Brett M. Wayne |
| ~-..======-....----~ \o \ b...@ccnet.com |
| |_/ \------------------~
(_)
Benton Jackson
Don Peterson wrote:
>
> >> Are you sure about that? In twenty-odd years of going to airshows and aerobatic
> > competitions, I don't recall ever seeing a Pitts (or any other aerobatic aircraft) snap
> > to the right - always to the left. I'm told the torque of the engine makes it much
> > easier to snap that way.
> >
> > I have many photos of Pitts, Eagles, and Lasers snaprolling, and they are all doing it
> > to the left.
> >
>
> Yep, in competition most Lycoming engine pilots snap to the right, unless
> they are on an ascending 45 or vertical line, in which case some go to
> the left. The slower rotation to the right makes the maneuver more
> controllable, while going to the left causes a bit less sideways
> displacement and resulting yaw, which is important in partial snaps.
I saw the Holiday Inn team do a group snap roll from a tight
diamond formation, with the lead, slot, and wing man going one
way, the other wing going the other way. It spread their formation,
then they were back tight in just a moment. The really amazing part
was that they did this ON TAKEOFF!! Only 50 feet up or so!
Quite a flashy way to start your routine.
--
Benton Jackson, Goat Rider at Fenris Wolf Electronic Games
ben...@fenriswolf.com
http://www2.bitstream.net/~benton
AcroDrew
One post indicated that rotation during snap rolls to the right right is
(ref: Lycoming engine) slower than to the left and therefore more
controllable. I beg to differ with the analysis given. The initial pitch
upward to stall a wing causes a simultaneous right yaw from gyroscopic
precession, thus making the entry easier. Then, once the rotation has
begun, the yawing around the rotation axis not aligned with the crankshaft
actually tries to move the aircraft axis back into alignment with the axis
of rotation. If you're familiar with power on spins, this is exactly the
same phenomenon that causes the nose of an airplane to pitch downward as
power is applied in a spin to the right and upward as power is applied in
a spin to the left. The only difference here is that the power is on
during the commencement of autorotation. A snap roll to the left appears
to the pilot to be rotating faster than a snap roll to the right because
the difference between the airplane's longitudinal axis and the axis of
rotation is larger than in a snap roll to the right. The pilot is looking
over the nose at point further from the apparent point of rotation and
therefore it appears to travel a much greater distance. In reality there
are many influencing factors affecting the rate of rotation. The comment
about stopping the rotation is correct, a snap roll to the right is easier
to stop properly (i.e., level flight and wings level). This is because
the airplane's axis does not need to be moved as far in recovery as in a
snap roll to the left. It is not related to rate of rotation.
Drew
Alan Constant
Don Peterson wrote:
>>.....
> > I have many photos of Pitts, Eagles, and Lasers snaprolling, and they are all doing it
> > to the left.
> >
> > Alan Constant
>
> Yep, in competition most Lycoming engine pilots snap to the right, unless
> they are on an ascending 45 or vertical line, in which case some go to
> the left. The slower rotation to the right makes the maneuver more
> controllable, while going to the left causes a bit less sideways
> displacement and resulting yaw, which is important in partial snaps.
>
Okay! I admit I never really watched the competition flights themselves closely (usually
wandering around looking at the planes and watching the airshows afterwards). But I am
certain I am right about snaps to the left in airshows. Do the airshow pilots do it just
to "thrill the crowd" with the rapidity so to speak, because it's physically easier, or
to make triple and quads easier perhaps?
I'd also been told that pilots in general do not feel as comfortable snapping (or even
rolling) to the right because of some unexplained reason - either physically more
difficult or something psychological - they seem to be more comfortable going to the
left. Ever hear that?
Alan Constant
DSowder
Well, most snaps that I see, and 90% of the ones that I do, are to the
right. Speaking of upright snaps here. The reason is simply that when the
nose pitches up, the gyroscopic precession of the Pitts' rather large
propeller yaws the nose strongly to the right. My Pitts snaps much more
quickly and cleanly to the right, and ends the snap on the original
heading. When snapped to the left, the snap is slower, messier, and it's
hard to end with the nose on-heading. The roll seems to end (i.e., wings
level) before the nose yaws back onto heading. This would all be opposite
for a backwards turning engine (Renault, DeHavilland, Vedeneyev, etc.)
The easy way to see the yaw, other than by playing with a toy gyroscope,
is to go flying. Build up some speed, the higher the RPM the better, and
pull about 4 or 5 g's while holding the rudder neutral. You'll see the
nose yaw markedly to the right. Then try snaps both ways. This assumes
American engine, of course.
When I first learned aerobatics some 25 years ago in a 115 hp. Citabria, I
always snapped left because I assumed that the "torque" would help. Now I
realize, of course, that the 7ECA had neither torque nor gyroscopic force
to worry about! If I ever get a chance to fly one again, I'll try snaps
both ways.
Doug Sowder
Dennis N. Yugo
Torque certainly has effect in a snap roll, but the sudden pitch and yaw
inputs cause gyroscopic effects which are even greater. These effects
vary with the rpm and the weight of the propeller. I notice different
snap characteristics in my Pitts with my wooden prop than with my
previous metal one.
Basically, after an inside snap to the right is begun, the initial pitch
up will cause a gyroscopic effect of yawing further to the right (that
is good). Also, the initial right yaw will cause a slight pitch down,
tightening the snap (that is also good).
Conclusion? Damned if I know. I snap to the right all the time, unless I
have to snap left in a vertical maneuver.
Brian Grinter
Alan Constant <arc...@kanservu.ca> wrote:
>Brian Grinter wrote:
>>
>> My instructor owns an SF-260 and told me the gyroscopic forces are
>> quite strong esp. on the engine mounts of the SF-260. The manufacturer
>> recommended flick-roll (snap-roll to you guys) speed caused enough
>> movement in the engine mounts to make the spinner rub against the
>> cowling surrounding it. He now uses a lower speed...
>>
>> Brian Grinter
>First, a dumb question. What's an SF-260?
Marchetti SF-260. An Italian aerobatic trainer aircraft, low wing
three seater, very sexy looking. That mob AIR COMBAT USA for Tom
Cruise wanna be's use them (that's the most famous I can think of)
>One guy I knew in Aerobatics Canada agreed about the snap causing the spinner to rub
>against the nose bowl of the Pitts - he also claimed that a snap could cause the
>crankshaft to move as much as an inch off center on its rubber lord mounts. I can
>believe it. (Love the sound of a Pitts snap-rolling).
A famous Aussie aerobatics pilot, Chris Sperou apparently lost a prop
on his Pitts during a flick roll.
Regards
BRIAN
Don Peterson
Alan Constant wrote:
> Okay! I admit I never really watched the competition flights themselves closely (usually
> wandering around looking at the planes and watching the airshows afterwards). But I am
> certain I am right about snaps to the left in airshows. Do the airshow pilots do it just
> to "thrill the crowd" with the rapidity so to speak, because it's physically easier, or
> to make triple and quads easier perhaps?
>
> I'd also been told that pilots in general do not feel as comfortable snapping (or even
> rolling) to the right because of some unexplained reason - either physically more
> difficult or something psychological - they seem to be more comfortable going to the
> left. Ever hear that?
>
> Alan Constant
I am probably not a good source for the definitive answer, because almost all of my acro time is in an
anachronistic old Stampe, with a Renault engine that rotates the "right" way around, rather than "Left" way
around like a Lycoming. As a result, virtually all of our rolls are to the right. The engine is such a big
torque producer that rolling left against its rotation is just an awful chore. I get pretty sloppy when I get
into a Pitts or Decathlon and have to roll left. My body just fights it after all the aclimitization.
Oddly enough, I also snap right in this aircraft, because the rate of rotation going left is so slow that it
often un-snaps before I get all the way around - particularly in an avalanche where the entry airspeed and
G-load are fairly low. The other post describing how his Pitts has an uglier snap to the left may not match up
with everyone's experience. Snaps are highly variable maneuvers for most of us, and each airplane/pilot
combination can produce somewhat different results.
Don
David Lee
b...@ccnet.com (Brett Wayne) wrote:
>My Pitts S-1C will snap significantly faster to the right than to the
>left. Not that it _won't_ snap to the left, it does that just fine - but
>markedly slower. The gyroscopic and control inputs contribute much more
>than any torque moment developed off a clockwise turning motor (as viewed
>from the cockpit).
>
>The torque of the motor is a small effect. It becomes most pronounced
>when there is almost no airflow over the wings - at the tops of vertical
>maneuvers such as humpty-bumps, tail-slides, and yes - torque rolls. Snap
>rolls are generally entered between 80-100 KIAS - definitely enough for the
>lift component off the wings to significantly overshadow the torque
>effects.
Another factor may be the fact that the entire bird is rigged to help you
stand on that right rudder during take-off. With plenty of airflow, without
full power to overcome, it just turns right easier. Pointed down/power-off,
it WILL turn right unless you stop it. Seems like it just naturally breaks
that direction at stall... That all makes it snap-right quicker.
Of course, my "Down-Under" friends will tell me that I'm just a backwards Yank
because I'm on the "wrong" side of the equator, and it's really all Coriolis's
fault because he saw water drain the other direction... ;^)
David
-------
I pledge NOT to patronize any business that:
sends unsolicited e-mail advertisements or
spams multiple newsgroups with off-topic advertising.
Brett Wayne
In article <32656B...@kanservu.ca>, Alan Constant <arc...@kanservu.ca>
wrote:
> Okay! I admit I never really watched the competition flights themselves closely
> (usually wandering around looking at the planes and watching the airshows
> afterwards). But I am certain I am right about snaps to the left in airshows.
> Do the airshow pilots do it just to "thrill the crowd" with the rapidity so to
> speak, because it's physically easier, or to make triple and quads easier perhaps?
>
> I'd also been told that pilots in general do not feel as comfortable snapping
> (or even rolling) to the right because of some unexplained reason - either
> physically more difficult or something psychological - they seem to be more
> comfortable going to the left. Ever hear that?
Okay. So now you've admitted that you weren't actually paying very close
attention. And after at least a half dozen posts to the contrary from real
pilot's with real experience - your still "certain" that all airshow
snaps are to the left. Then you try to substantiate your position with
even more idle speculation.
I suspect you won't be convinced until you go out and rent a Pitts and
see for yourself that snaps to the right are faster.
Alan Constant
>> Okay! I admit I never really watched the competition flights themselves closely
>> (usually wandering around looking at the planes and watching the airshows
>> afterwards). But I am certain I am right about snaps to the left in airshows.
>> Do the airshow pilots do it just to "thrill the crowd" with the rapidity so to
>> speak, because it's physically easier, or to make triple and quads easier perhaps?
>
>> I'd also been told that pilots in general do not feel as comfortable snapping
>> (or even rolling) to the right because of some unexplained reason - either
>> physically more difficult or something psychological - they seem to be more
>> comfortable going to the left. Ever hear that?
Brett Wayne wrote:
>
If someone wants to criticize what I have to say, I WISH THEY WOULD READ WHAT I HAVE
WRITTEN FIRST!
> Okay. So now you've admitted that you weren't actually paying very close
> attention.
ONLY referring to competition flights that I wasn't paying close attention to. If you
read what I said you would know that, but the rest of your posting tells me that you
haven't read it carefully (or for that matter, any of the postings by others you refer
to).
>And after at least a half dozen posts to the contrary from real
>pilot's with real experience - your still "certain" that all airshow
> snaps are to the left.
Hmmm. Doesn't know the difference between your and you're. I learned that about grade
one.
Did you ever bother to check the posting dates? That response of mine you are quoting
from was sent to one of the first to post, not after a half dozen or more had done so,
so reading it out of order (which you obviously have) means that your conclusions that I
am still "certain" are groundless.
>Then you try to substantiate your position with
> even more idle speculation.
What, exactly is my position?
You've only included a tiny portion of the thread of messages and it is not apparent to
anyone reading it, nor can it be deduced. What you have quoted is out of context, and
your analysis is ridiculous. The first paragraph makes no sense whatsoever without the
previous author's message. The second paragraph, as anyone who can interpret what they
read, is a question (note the "?" at the end!) and not "idle speculation".
> I suspect you won't be convinced until you go out and rent a Pitts and
> see for yourself that snaps to the right are faster.
>
Why should I do that? If you read my postings, you would find I never asked which
direction a Pitts snaps faster, nor do I care.
How do you know snaps to the right are faster? You just state it as fact with no
evidence you are an aerobatic pilot or have any knowledge of aviation. (Sounds like a
well known character in another aviation group).
One well explained response I got seems to indicate that it, in fact, does not snap
faster to the right. Due to some reason beyond my understanding, although related to the
torque of the engine and movement around the horizontal axis, a snap to the right only
"appears" to be faster to the pilot. I'll take his word on it until someone can prove
otherwise. (And if he's correct, taking a ride in a Pitts will only prove that it
"appears" to snap faster to the right and not that it actually does).
What value is this posting of yours to the group anyways? Is it really important for
them to know you think I'm an idiot? I'm sure they really care. Ordinarily I wouldn't
waste my time answering, but this is the second time you've made unnecessary comments
about my postings because you didn't like something. Haven't you got anything more
constructive to do instead of criticizing others when you think they are stupid, boring
you or don't seem to see things your way?
For anyone else reading, I will admit that after reading the postings of others, I may
very well be in error about which way most pilots snap a Pitts. It's something you see
so often at airshows you tend to not really think about it or pay a great deal of
attention to (unless you do it of course). I'm one who likes to see proof I am wrong,
and my "snapshots" (pun intended) show more lefties than righties. -- I just thought
that I know someone with a video of that awful movie "Cloud Dancer" - I'll borrow it and
see which way the Pitts snap (they might also have some airshow videos too).
As for my aerobatic background - no flight experience, but I'm trained as an aircraft
mechanic and built a Pitts. No, I never flew it - grounded for medical reasons before I
got it finished. I had a strong interest in aerobatics and read whatever I could find
about them for quite a while. Never professed to be an authority, merely ask questions
because I like to learn and have misinformation corrected and try to answer what I can.
Alan Constant
*** Don't bother to try and flame me unless you have a spark of intelligence with which
to light the fire ***
Brett Wayne
In article <327483...@kanservu.ca>, Alan Constant <arc...@kanservu.ca>
wrote:
>
> one.
Oooooohh scorch....that was real constructive criticism. Of course, it
doesn't
detract from what I was saying nor does it support your position any
more....
>
> Did you ever bother to check the posting dates? That response of mine you are quoting
> from was sent to one of the first to post, not after a half dozen or more had done so,
> so reading it out of order (which you obviously have) means that your conclusions that I
> am still "certain" are groundless.
>
Nope. And my ISP is not so hot when it comes to providing me with the
threads in a real coherent order. I may be guilty of criticizing you,
but your response may be just as far off the mark. I sent an earlier
reply explaining why snaps to the right tend to be faster which was
further substantiated by others. Perhaps you haven't read or received those
replies yet?
> How do you know snaps to the right are faster? You just state it as fact with no
> evidence you are an aerobatic pilot or have any knowledge of aviation. (Sounds like a
> well known character in another aviation group).
Oh, and I suppose the fifteen years of flight experience and six years and
400 or so hours I have logged in a Pitts don't qualify as having experience
or expertise or "any knowledge of aviation" ?
> One well explained response I got seems to indicate that it, in fact, does not snap
> faster to the right. Due to some reason beyond my understanding, although related to the
> torque of the engine and movement around the horizontal axis, a snap to the right only
> "appears" to be faster to the pilot. I'll take his word on it until someone can prove
> otherwise. (And if he's correct, taking a ride in a Pitts will only prove that it
> "appears" to snap faster to the right and not that it actually does).
I never said it "appears" to snap faster to the right. It's not an optical
illusion. It _does_ snap faster to the right and it has more to do with
gyroscopic precession, technique, and perhaps rigging than torque (your
original
conclusion).
> What value is this posting of yours to the group anyways? Is it really important for
> them to know you think I'm an idiot? I'm sure they really care. Ordinarily I wouldn't
> waste my time answering, but this is the second time you've made unnecessary comments
> about my postings because you didn't like something. Haven't you got anything more
> constructive to do instead of criticizing others when you think they are stupid, boring
> you or don't seem to see things your way?
>
> For anyone else reading, I will admit that after reading the postings of others, I may
> very well be in error about which way most pilots snap a Pitts. It's something you see
> so often at airshows you tend to not really think about it or pay a great deal of
> attention to (unless you do it of course). I'm one who likes to see proof I am wrong,
> and my "snapshots" (pun intended) show more lefties than righties. -- I just thought
> that I know someone with a video of that awful movie "Cloud Dancer" - I'll borrow it and
> see which way the Pitts snap (they might also have some airshow videos too).
No - the intention wasn't to make you look like an idiot. You posed a good
question and started a good discussion. My gripe was when you appeared to
get lots of great feedback and then draw a conclusion contrary to that
feedback,
and then appeared to be an authority when your only real experience is
watching
from the ground. My gripe is when you've been given great feedback, the
only one you seem to listen to is the one that supports your original
conclusion, ignoring the other explainations and real experiences from
pilots such as myself.
> As for my aerobatic background - no flight experience, but I'm trained as an aircraft
^^^^^^^^^^^^^^^^^^^^
(...no comment...)
> mechanic and built a Pitts. No, I never flew it - grounded for medical reasons before I
> got it finished. I had a strong interest in aerobatics and read whatever I could find
> about them for quite a while. Never professed to be an authority, merely ask questions
> because I like to learn and have misinformation corrected and try to answer what I can.
...except, of course, when the misinformation being corrected is your own.
Tim Bastian
"Travis Leonard" <Gle...@ix.netcom.com> wrote:
>Alan Peake <Alan....@defence.dsto.gov.au> wrote in article
><Alan.Peake...@defence.dsto.gov.au>...
>> >would say that a pilot pulls 6 G's in a snap. I questioned Gord Price,
>former
>> >Canadian
>> >Aerobatic Champion, and he said "a snap is 4 G's max - pulling 6G's
>would rip
>> >the wings
>>
>> I hope not! The pitts is supposedly stressed to +/- 12G and unlimited
>pilots
>> regularly pull +7/-5
>>
>> Alan
>Now I'm no aerobatic pilot, but it would seem to me that the g-limits of
>the wing are expressed as static load, and not a full dynamic load. If you
>suddenly apply a load of 12G's to a Pitts wing, it probably will fail. I
>don't think that 6G's would do it, but it is just important how the load is
>applied (snap roll being one of the more violent) as how big the load is.
>Travis Leonard
>1946 7AC Champion
>And no, I don't even try aerobatics in it!
The load limmits published for an aircraft are working loads. in the
case of an aerobatic aircraft with a published G limmit of 10 g's it's
aultamit failure load would be 150% to 200% greater or 15 to 20 G's.
So a snap roll even at 10 G's probably won't pull the wings off. It
may however tear your head off.
Tim Bastian
I'm an aerobatic instructor with over 2200 hours of aerobatic dual
give and I compete in the advanced catigory with an extra 300.
Are Barstad
Tim Bastian <timot...@earthlink.net> wrote in article
<snip>
> So a snap roll even at 10 G's probably won't pull the wings off. It
> may however tear your head off.
Just curious, what is the speed/G ratio for a snap roll in the Extra 300?
i.e. How many G's at 120 kts.
Are Barstad
ACRO...@msn.com
In article ,
"Are Barstad" wrote:
>
> Tim Bastian wrote in article
> > So a snap roll even at 10 G's probably won't pull the wings off. It
> > may however tear your head off.
> Just curious, what is the speed/G ratio for a snap roll in the Extra 300?
> i.e. How many G's at 120 kts.
> Are Barstad
there is a very simple mathematical rule if one snaps at 2times the stall speed
the G force will be 4g's for example if an Extra stalls at 60mph the 120mph
stall is 4 g's 120/60=2 2squared = 4 Its the ratio of the snap speed to the
stall speed squared.
A Pitts stalls around 58 so a 140mph snap = 140/58=2.41 2.41Squared=
5.8 G's thats about the load limit for the Pitts.
Darwin Jones
CFI-IA
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