CG hook on aero tows??

On 6 Jan 2004 12:41:34 -0700, (Mark James Boyd)
wrote:


First of all, if the manual says to not use the C.G. hook
for aerotow, I personally wouldn't try it, even once.
But that's just me.


But what do you do with a glider like our ASW-27?
If only a CG hook is installed (yes, there are at least 150 27's
flying like this), it's fully certified for aerotow on the CG hook.
Since the new rules came out, all new 27's have a nose hook installed
and therefore this one MUST be used for aerotow.

Does the installed nose hook suddenly make the aerotow on the CG hook
dangerous?


OK, be prepared for me to completely change my tune. Are you guys
telling me the manual says that if it has only a CG hook, you can
aerotow with it, but if both hooks are present, the manual
prohibits aerotow on the CG hook for the ASW-27? And the
W&B limits and CG hook locations are identical for both
gliders?

If THIS is the case, a certainly can't argue with those
who see it as a simple paper shuffle. But I'd also say that in
this case a factory test pilot has surely flown that exact type of glider
with the CG hook in the exact position and flown it aerotow
that way. This means anyone who does it is NOT therefore a
test pilot.

Sounds like removing the nose hook just to "legally" aerotow
off the CG hook is a ridiculous paper shuffle hassle...
And yes, I did read the reasons why one might want to remove it.
Hmmm...so much for the manual, eh?

[Apologies if this is a double-post - Google seemed to have lost the
first one. This version is shorter and more to the point anyway.]

Earlier, Ian Strachan wrote:

... If only one hook is fitted then it
will be somewhat forward of the pure
"C of G" position because its location
is a compromise for both air tow
and winch and it will be tested for
both before the initial C of A is
given for the type.

From the perspective of an amateur sailplane developer:

That might have been true some time ago. However, increased demand for
better performance have made such compromises less tenable in the last
generation or two of sailplane.

The way I understand it, there are only two good locations for a tow
hitch: At the stagnation point on the nose of the glider, and aft of
the point of maximum thickness of the fuselage.

With the tow hitch buried in the nose vent at the stagnation point,
there is no particular disruption to the airflow, and you can
reasonably expect to get laminar flow over most of the forward
fuselage. At least, until the air encounters a disruption such as a
canopy separation line or passes the point of maximum thickness and
encounters an adverse pressure gradient.

With the to hitch located aft of the point of maximum thickness, the
airfow will already have tripped over into turbulent flow, and the
extra drag of that flow encountering the tow hitch will be minimal.

However, with the hitch located in the "compromise" area as Ian
suggests, it will almost certainly disrupt the laminar flow there, and
trip it over into draggier turbulent flow. Furthermore, the area of
turbulence will spread laterally at about a 7-degree angle aft of the
disruption. So you end up with a triangular patch of turbulent flow on
the belly with an included angle of about 14 degrees. That means extra
drag and poorer performance.

My own next glider will have a nose hook in the air vent duct at the
stagnation point on the nose of the glider, and a mounting location
for an optional CG hook that will be covered by the landing gear
doors.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

On Sun, 4 Jan 2004 16:53:58 -0700, "Ted Wagner"
wrote:

A few seconds into take-off roll today in a Pilatus B-4, while applying left stick to correct for a dipping right wing, the right wing suddenly dipped all the way into the ground. The glider lurched to the right, and a second or two later popped up into the air, a good 20 feet up and 30 or more feet out to the side. By that time I had full left rudder in addition to full left aileron, so the glider recovered rather quickly, and I was able to bring it to normal take-off position right about the time the tow plane started to climb. I was amazed he had maintained his heading directly down the runway. The winds were light and variable. It was my ninth flight on the B-4.

After landing, the tow pilot apologized, saying it was his fault -- something about the wake turbulence. But I'm still puzzled about what, if anything, he did wrong; it looked like a completely normally take-off roll to me.

I had thought that maybe a sudden tail wind had reversed the effective correction of my aileron deflection during take-off, causing the right wing to dip harder instead of leveling off. Does this make sense to anyone with more experience on an aircraft like the B-4?

Also, I'm curious to know how much the CG hook location on the B-4 contributed to the squirrelly sequence of events after the right wingtip hit the ground. How many 15+ meter gliders have CG-only hooks? Are such exciting events more commonplace with CG hooks?

Other than the wobbly tows, I'm loving the B-4, it's the first 15-meter single-seater ship I've flown, and the first with retractable gear...

~tw

How long was the rope?

Most of the towplane wake turbulence or whatever problems go away if
you use a 250 foot rope. Lots more time in the event of a pitch up and
less likely anyway due to lower energy in the wake turbulence.

I once saw three gliders damaged in one day at Waikerie(all unflyable
the next day) due to aero retrieves out of fields with short ropes and
nose hooks. Problem with a nose hook is that if things get out of hand
and you release they instantly get a lot worse.

Short ropes are deadly. It is the angle that counts. Longer rope =
smaller angle = recoverable situation. I find this so bleeding obvious
after observation, experience and thinking about it that if I was an
insurance company I'd refuse all claims for ground loops or towplane
upsets that used a shorter than 250 foot rope.

Anyway I gave up aerotowing and bought a TOP.

Mike Borgelt

we use a 200ft rope as standard.. we had 230ft ropes.. great for training..

160ft ropes really get your attention..

BT

"Mike Borgelt" wrote in message
...
On Sun, 4 Jan 2004 16:53:58 -0700, "Ted Wagner"
wrote:

A few seconds into take-off roll today in a Pilatus B-4, while applying
left stick to correct for a dipping right wing, the right wing suddenly
dipped all the way into the ground. The glider lurched to the right, and a
second or two later popped up into the air, a good 20 feet up and 30 or more
feet out to the side. By that time I had full left rudder in addition to
full left aileron, so the glider recovered rather quickly, and I was able to
bring it to normal take-off position right about the time the tow plane
started to climb. I was amazed he had maintained his heading directly down
the runway. The winds were light and variable. It was my ninth flight on
the B-4.

After landing, the tow pilot apologized, saying it was his fault --
something about the wake turbulence. But I'm still puzzled about what, if
anything, he did wrong; it looked like a completely normally take-off roll
to me.

I had thought that maybe a sudden tail wind had reversed the effective
correction of my aileron deflection during take-off, causing the right wing
to dip harder instead of leveling off. Does this make sense to anyone with
more experience on an aircraft like the B-4?

Also, I'm curious to know how much the CG hook location on the B-4
contributed to the squirrelly sequence of events after the right wingtip hit
the ground. How many 15+ meter gliders have CG-only hooks? Are such exciting
events more commonplace with CG hooks?

Other than the wobbly tows, I'm loving the B-4, it's the first 15-meter
single-seater ship I've flown, and the first with retractable gear...

~tw

How long was the rope?

Most of the towplane wake turbulence or whatever problems go away if
you use a 250 foot rope. Lots more time in the event of a pitch up and
less likely anyway due to lower energy in the wake turbulence.

I once saw three gliders damaged in one day at Waikerie(all unflyable
the next day) due to aero retrieves out of fields with short ropes and
nose hooks. Problem with a nose hook is that if things get out of hand
and you release they instantly get a lot worse.

Short ropes are deadly. It is the angle that counts. Longer rope =
smaller angle = recoverable situation. I find this so bleeding obvious
after observation, experience and thinking about it that if I was an
insurance company I'd refuse all claims for ground loops or towplane
upsets that used a shorter than 250 foot rope.

Anyway I gave up aerotowing and bought a TOP.

Mike Borgelt

"BTIZ" wrote in message
news:HK7Kb.46875$m83.26542@fed1read01...
we use a 200ft rope as standard.. we had 230ft ropes.. great for
training..

160ft ropes really get your attention..

BT

The only bad take off I had in my Pilatus was at HusBos, it was downwind and
slightly cross, plus I was towed by a not very powerful Chipmonk. All other
takeoffs with our supercub are fine though these are all into wind as we
have three runways to play with. Its a great aircraft with few vices, and
can outclimb some newer glass ships.

Peter S

DLA
lakesgc.co.uk

05-01-2004 06:46, BTIZ:

we use a 200ft rope as standard.. we had 230ft ropes.. great for training..
160ft ropes really get your attention..
In Poland 200ft ropes are used for training, but pilots prefer shorter,
130ft ropes. For tows in very turbulent air (like tows for wave flying)
the ropes are even 60ft long.

Longer ropes gives more time for reaction to tug's turns, but shorter
ones are less springy, which makes easier to maintain steady speed
during tow. Especially if the tug is not so powerful.

--
Wojtus'.net __|__
FidoNet: 2:484/47 `--------o--------'

So does any one have an actual list of tug upset accidents with
towplane type, glider type and circumstances?
Just off hand I can't remember any in Australia and yes even when you
use low tow the upset possibility exists after liftoff and before
transition to low tow.
We've had plenty of towplane/glider midairs which makes existence as
a tow pilot 10 times as likely to kill you as cropdusting per hour.

Mike Borgelt

Mike,
There was a tug upset on takeoff in Tasmania a few years
ago. I don't remember the year, or other data. Sorry.
There must have been several in the more distant past to
cause GFA to mandate nose hooks for aero tow on new gliders
or those changing ownership. (Came in in the early 1980s I
think)
John G.

"Mike Borgelt" wrote in
message ...
| So does any one have an actual list of tug upset accidents
with
| towplane type, glider type and circumstances?
| Just off hand I can't remember any in Australia and yes
even when you
| use low tow the upset possibility exists after liftoff and
before
| transition to low tow.
| We've had plenty of towplane/glider midairs which makes
existence as
| a tow pilot 10 times as likely to kill you as cropdusting
per hour.
|
| Mike Borgelt

ASW 27B is only certificated for aerotow operation when the forward tow
release is used!

On 6 Jan 2004 08:21:29 GMT, Ray Payne
wrote:

ASW 27B is only certificated for aerotow operation when the forward tow
release is used!

This is correct.
And an ASW-27 where no nose hook is installed is certified for aerotow
operation on the CG hook.

Bye
Andreas