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Airspeed control during ground launch?



 
 
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  #11  
Old March 30th 07, 06:35 PM posted to rec.aviation.soaring
Bill Daniels
external usenet poster
 
Posts: 687
Default Airspeed control during ground launch?


"toad" wrote in message
oups.com...
Ok, thanks. That's the physics as I understood it.

With a modern winch, I won't have to worry about reverse control. But
with an old technology ground launch, I do.

Todd


Actually, it's neither difficult nor expensive to eliminate the worst
problems with an automatic transmission.

Replacing the stock valve body in the transmission with a "manual valve
body" allows the winch driver to lock out 1st and 2nd gears. (Google "manual
valve body"). These gadgets replace the stock "PRND2L" shift pattern with
"RN321" which can be further restricted to "N3" with a simple shift gate.
This results in the transmission starting in 3rd and remaining there
throughout the launch.

For a bit more money and little more effort, the stock 1800 RPM stall torque
converter can be replaced with a "high stall" TC that lets the transmission
slip up to say 2800 RPM during power up for a softer but still energetic
launch. It also prevents a heavy glider in strong wind conditions from
bogging down the winch engine. Don't do this without adding an effective
transmission cooler.

It won't be perfect, but it's FAR better than the stock setup.

Bill Daniels


Ads
  #12  
Old March 30th 07, 11:55 PM posted to rec.aviation.soaring
John Galloway[_1_]
external usenet poster
 
Posts: 215
Default Airspeed control during ground launch?

Bill,

If you were to stand beside a Skylaunch winch (which
has a big American petrol/LPG V8 and a fully functioning
3 speed auto box) you would notice that the box is
in 3rd gear by the time that the glider is leaving
the ground and the rest of the launch is normally carried
out in 3rd gear.

John Galloway


At 17:36 30 March 2007, Bill Daniels wrote:

'toad' wrote in message
roups.com...
Ok, thanks. That's the physics as I understood it.

With a modern winch, I won't have to worry about reverse
control. But
with an old technology ground launch, I do.

Todd


Actually, it's neither difficult nor expensive to eliminate
the worst
problems with an automatic transmission.

Replacing the stock valve body in the transmission
with a 'manual valve
body' allows the winch driver to lock out 1st and 2nd
gears. (Google 'manual
valve body'). These gadgets replace the stock 'PRND2L'
shift pattern with
'RN321' which can be further restricted to 'N3' with
a simple shift gate.
This results in the transmission starting in 3rd and
remaining there
throughout the launch.

For a bit more money and little more effort, the stock
1800 RPM stall torque
converter can be replaced with a 'high stall' TC that
lets the transmission
slip up to say 2800 RPM during power up for a softer
but still energetic
launch. It also prevents a heavy glider in strong
wind conditions from
bogging down the winch engine. Don't do this without
adding an effective
transmission cooler.

It won't be perfect, but it's FAR better than the stock
setup.

Bill Daniels





  #13  
Old March 31st 07, 12:20 AM posted to rec.aviation.soaring
Bill Daniels
external usenet poster
 
Posts: 687
Default Airspeed control during ground launch?

Actually, John, I've done better than that. I have several cable tension
traces from a Skylaunch made with a tensiometer load cell at the glider.
The data shows horrific tension surges as the transmission shifts up and
down during the launch. These surges were violent enough to break weak
links and the cable. Surges such as these would be unacceptable in a $200
junkyard winch. Given the price of the Skylaunch, we should expect MUCH
better.

I stand by exactly what I wrote. It's extremely foolish to allow a winch
transmission to shift - particularly when it's easy to prevent it. Just
because big American V8's and automatic transmissions are dirt cheap is no
reason to use them without the needed modifications.

BTW, I do like the Skylaunch paint job.

Bill Daniels


"John Galloway" wrote in message
...
Bill,

If you were to stand beside a Skylaunch winch (which
has a big American petrol/LPG V8 and a fully functioning
3 speed auto box) you would notice that the box is
in 3rd gear by the time that the glider is leaving
the ground and the rest of the launch is normally carried
out in 3rd gear.

John Galloway


At 17:36 30 March 2007, Bill Daniels wrote:

'toad' wrote in message
groups.com...
Ok, thanks. That's the physics as I understood it.

With a modern winch, I won't have to worry about reverse
control. But
with an old technology ground launch, I do.

Todd


Actually, it's neither difficult nor expensive to eliminate
the worst
problems with an automatic transmission.

Replacing the stock valve body in the transmission
with a 'manual valve
body' allows the winch driver to lock out 1st and 2nd
gears. (Google 'manual
valve body'). These gadgets replace the stock 'PRND2L'
shift pattern with
'RN321' which can be further restricted to 'N3' with
a simple shift gate.
This results in the transmission starting in 3rd and
remaining there
throughout the launch.

For a bit more money and little more effort, the stock
1800 RPM stall torque
converter can be replaced with a 'high stall' TC that
lets the transmission
slip up to say 2800 RPM during power up for a softer
but still energetic
launch. It also prevents a heavy glider in strong
wind conditions from
bogging down the winch engine. Don't do this without
adding an effective
transmission cooler.

It won't be perfect, but it's FAR better than the stock
setup.

Bill Daniels







  #14  
Old March 31st 07, 09:08 AM posted to rec.aviation.soaring
Z Goudie
external usenet poster
 
Posts: 8
Default Airspeed control during ground launch?

Chris Reed wrote:
(a) the pitch over to a proper recovery
angle is much higher than a pilot trained on aerotow
only would expect,
(b) there is a further trap in these circumstances
in that G is reduced
during the pitch over, so that any attempt to turn
before full G returns
can lead to a stall and spin (stall speed reduces with
lower G)


Also a reminder that a rapid pitchover from a high
angle/energy cable break can result in a 'Vomit Comet'
reduced/negative G sensation which has over the years
convinced some pilots that the glider is stalled.
They then keep pushing until the glider reaches the
near vertical or the ground whichever comes first.

This difference between stalling and stick induced
negative G may not have been sufficiently well demonstrated
to pilots trained on aerotow.



  #15  
Old March 31st 07, 11:18 AM posted to rec.aviation.soaring
Bruce Greef[_2_]
external usenet poster
 
Posts: 3
Default Airspeed control during ground launch?

Bill Daniels wrote:
Actually, John, I've done better than that. I have several cable tension
traces from a Skylaunch made with a tensiometer load cell at the glider.
The data shows horrific tension surges as the transmission shifts up and
down during the launch. These surges were violent enough to break weak
links and the cable. Surges such as these would be unacceptable in a $200
junkyard winch. Given the price of the Skylaunch, we should expect MUCH
better.

I stand by exactly what I wrote. It's extremely foolish to allow a winch
transmission to shift - particularly when it's easy to prevent it. Just
because big American V8's and automatic transmissions are dirt cheap is no
reason to use them without the needed modifications.

BTW, I do like the Skylaunch paint job.

Bill Daniels


"John Galloway" wrote in message
...

Bill,

If you were to stand beside a Skylaunch winch (which
has a big American petrol/LPG V8 and a fully functioning
3 speed auto box) you would notice that the box is
in 3rd gear by the time that the glider is leaving
the ground and the rest of the launch is normally carried
out in 3rd gear.

John Galloway


At 17:36 30 March 2007, Bill Daniels wrote:

'toad' wrote in message
egroups.com...

Ok, thanks. That's the physics as I understood it.

With a modern winch, I won't have to worry about reverse
control. But
with an old technology ground launch, I do.

Todd


Actually, it's neither difficult nor expensive to eliminate
the worst
problems with an automatic transmission.

Replacing the stock valve body in the transmission
with a 'manual valve
body' allows the winch driver to lock out 1st and 2nd
gears. (Google 'manual
valve body'). These gadgets replace the stock 'PRND2L'
shift pattern with
'RN321' which can be further restricted to 'N3' with
a simple shift gate.
This results in the transmission starting in 3rd and
remaining there
throughout the launch.

For a bit more money and little more effort, the stock
1800 RPM stall torque
converter can be replaced with a 'high stall' TC that
lets the transmission
slip up to say 2800 RPM during power up for a softer
but still energetic
launch. It also prevents a heavy glider in strong
wind conditions from
bogging down the winch engine. Don't do this without
adding an effective
transmission cooler.

It won't be perfect, but it's FAR better than the stock
setup.

Bill Daniels







Hi Bill

I don't understand the mechanics well enough, but this is what we have.

Our little red monster - which looks scrappy but has served well for nearly 30
years consists of:

1x Ford 352 V8 Windsor in stock condition - (Removed from a galaxie I believe.)
1x Standard manual transmission
1x Ford Ranchero one ton truck axle with the differential and one axle locked.

The Single drum is driven from the other hub.

I presume we have the 1,800 RPM stall torque converter as I have not seen any
modifications, and the transmission acts locked from around 2000RPM.

Shifter is 'RN321' manual override.
We launch in 2nd gear - to prevent the engine bogging down. Typically RPM is in
the 3,500 - 3,800 range with a 55-65kt launch in the glider. We only shift to
third manually when needed to retrieve the cable fast. First is locked out.

Am I right in assuming the locked differential and axle are changing the gearing
on the axle. (I think it is a nominal 3.59:1 ratio)

By the way - this setup is nearing the end of it's life at around 50,000 launches.
There is now runout on axle bearings, and oil weeping from the transmission, the
guide rollers are worn beyond machining and the drum rim is deformed. The winch
driver thus gets exposed to quite a lot of vibration, although the cable appears
to absorb most of the vibrations as they are not noticeable in the glider. The
engine is still running well, although it goes through fuel pumps with
distressing frequency (about every 4,000 launches.)

The "capital" cost per launch is tiny.
Fuel is around one litre per launch - less than 1US$.
Maintenance cost is negligible. Filters and batteries mainly.

Now we have to build a replacement - and I wonder where we will find components
as robust.
  #16  
Old March 31st 07, 03:51 PM posted to rec.aviation.soaring
Bill Daniels
external usenet poster
 
Posts: 687
Default Airspeed control during ground launch?


"Bruce Greef" wrote in message
...
Bill Daniels wrote:
Actually, John, I've done better than that. I have several cable tension
traces from a Skylaunch made with a tensiometer load cell at the glider.
The data shows horrific tension surges as the transmission shifts up and
down during the launch. These surges were violent enough to break weak
links and the cable. Surges such as these would be unacceptable in a
$200 junkyard winch. Given the price of the Skylaunch, we should expect
MUCH better.

I stand by exactly what I wrote. It's extremely foolish to allow a winch
transmission to shift - particularly when it's easy to prevent it. Just
because big American V8's and automatic transmissions are dirt cheap is
no reason to use them without the needed modifications.

BTW, I do like the Skylaunch paint job.

Bill Daniels


"John Galloway" wrote in message
...

Bill,

If you were to stand beside a Skylaunch winch (which
has a big American petrol/LPG V8 and a fully functioning
3 speed auto box) you would notice that the box is
in 3rd gear by the time that the glider is leaving
the ground and the rest of the launch is normally carried
out in 3rd gear.

John Galloway


At 17:36 30 March 2007, Bill Daniels wrote:

'toad' wrote in message
legroups.com...

Ok, thanks. That's the physics as I understood it.

With a modern winch, I won't have to worry about reverse
control. But
with an old technology ground launch, I do.

Todd


Actually, it's neither difficult nor expensive to eliminate
the worst
problems with an automatic transmission.

Replacing the stock valve body in the transmission
with a 'manual valve
body' allows the winch driver to lock out 1st and 2nd
gears. (Google 'manual
valve body'). These gadgets replace the stock 'PRND2L'
shift pattern with
'RN321' which can be further restricted to 'N3' with
a simple shift gate.
This results in the transmission starting in 3rd and
remaining there
throughout the launch.

For a bit more money and little more effort, the stock
1800 RPM stall torque
converter can be replaced with a 'high stall' TC that
lets the transmission
slip up to say 2800 RPM during power up for a softer
but still energetic
launch. It also prevents a heavy glider in strong
wind conditions from
bogging down the winch engine. Don't do this without
adding an effective
transmission cooler.

It won't be perfect, but it's FAR better than the stock
setup.

Bill Daniels







Hi Bill

I don't understand the mechanics well enough, but this is what we have.

Our little red monster - which looks scrappy but has served well for
nearly 30 years consists of:

1x Ford 352 V8 Windsor in stock condition - (Removed from a galaxie I
believe.)
1x Standard manual transmission
1x Ford Ranchero one ton truck axle with the differential and one axle
locked.

The Single drum is driven from the other hub.

I presume we have the 1,800 RPM stall torque converter as I have not seen
any modifications, and the transmission acts locked from around 2000RPM.

Shifter is 'RN321' manual override.
We launch in 2nd gear - to prevent the engine bogging down. Typically RPM
is in the 3,500 - 3,800 range with a 55-65kt launch in the glider. We only
shift to third manually when needed to retrieve the cable fast. First is
locked out.

Am I right in assuming the locked differential and axle are changing the
gearing on the axle. (I think it is a nominal 3.59:1 ratio)

By the way - this setup is nearing the end of it's life at around 50,000
launches.
There is now runout on axle bearings, and oil weeping from the
transmission, the guide rollers are worn beyond machining and the drum rim
is deformed. The winch driver thus gets exposed to quite a lot of
vibration, although the cable appears to absorb most of the vibrations as
they are not noticeable in the glider. The engine is still running well,
although it goes through fuel pumps with distressing frequency (about
every 4,000 launches.)

The "capital" cost per launch is tiny.
Fuel is around one litre per launch - less than 1US$.
Maintenance cost is negligible. Filters and batteries mainly.

Now we have to build a replacement - and I wonder where we will find
components as robust.


Bruce, It sounds as if the builders of your 'little red monster' got it
right 30 years ago to the standards of that day. If I understand correctly,
your transmission has a manual valve body allowing you to over ride any
automatic shifting. The axle undoubtedly has the differential gears welded
to eliminate their action and make the axle act as a simple right angle
drive. Your simple machine has returned the original investment many
thousands of times over. It deserves an honored retirement. Some current
winch builders could benefit from studying your winch.

When you build your new machine thee are a lot of new ideas to consider.
Electronically controlled, common rail diesels are available either new or
used at reasonable prices. I just located a brand new 425HP Mercedes Benz
14.2 liter diesel for $10,000 USD. These engines produce constant, massive
torque from just above idle to redline. They are very well matched to the
job of launching heavy modern 2-seaters. These engines should last forever
in winch duty. If desired, they can be fueled with biodiesel.

Hydrostatic transmissions and hydrostatic drive systems are now available in
many configurations. They allow absolutely precise control of cable tension
and speed under all conditions.

Since both engines and tranmissions are now electronically controlled, this
makes near full automation both possible and highly desirable. This means
the pilot can expect absolutely smooth, high performance launches every time
regardless of wind, turbulence, thermals, glider type, even rough pilot
technique and inexperienced winch drivers.

There seems to be a trend toward fully enclosed cabs with climate control to
make the winch drivers day more pleasant.

New synthetic cable materials like Dyneema and Spectra have eliminated
virtually all cable related problems. With them, winch builders can make
their creations far more user friendly.

Bill Daniels


  #17  
Old March 31st 07, 06:47 PM posted to rec.aviation.soaring
none
external usenet poster
 
Posts: 14
Default Airspeed control during ground launch?

Roger Worden wrote:
I also understand that a properly balanced glider using a CG
hook for winch launch will tend to nose up initially, and will seek an
optimal climb angle naturally. Altering the climb angle with elevator will
necessarily result in a less-than-optimal altitude gain.

This applies to some gliders, e.g. ASK-21, G103, Puchacz, DG500, Pegase,
ASW19/20 and Discus to quote some I know to be benign on the winch, but
not to all gliders.

An ASK-21 trimmed to around 55 kts can be winched without moving the
stick. I haven't done it but our CFI uses this as a demo for students
who are wrecking the launch by misusing the stick. He claps from just
after lift off all the way to the top to prove he isn't flying the glider.

Ka-8s are known to need full forward stick through the ground run and
rotation due to their light weight the large moment arm between wing the
hook. I haven't winched one so can't comment further.

Libelles will snap-rotate as they lift off if you leave trim for
approach speed and leave the stick at that position - at least mine
will. There's nothing in the operator's manual about this. OTOH if I set
full forward trim and apply a little additional pressure past the full
forward trim position I get an nice lift off followed by a nice, slow
rotation into the full climb.

Gliders with heavily cranked sticks (Libelle again) may exaggerate this
effect because the stick will tend to flop backwards during the initial
burst of acceleration and its possible that having to hold the stick
forward may mitigate this tendency.

Get briefed about what the glider you're flying will do during the
launch BEFORE trying it. Snap rotation at lift-off is very dangerous -
the glider can stall and snap roll, which is why the BGA is currently
pushing slow rotation rates.

Remember to RELEASE IMMEDIATELY if a tip touches the ground during the
ground roll. The force vectors make your chances of getting the wing up
again rather remote and you won't have time to think about the
situation, so start the launch with your hand on the release. Mine stays
there all the way up. Remember that on a good winch, 0 to 50 kts is
about 5 seconds: you need to react rather than think if it goes wrong.


--
[email protected] | Martin Gregorie
gregorie. | Essex, UK
org |
  #18  
Old April 1st 07, 12:06 AM posted to rec.aviation.soaring
ucsdcpc
external usenet poster
 
Posts: 10
Default Airspeed control during ground launch?

Speed control is OPPOSITE to that during aerotow and gliding

I'm sure if I asked this of one of our instructors the answer would be "you
don't" You control the attitude, the winch driver controls the speed. Lowering
the nose is the signal to the driver that you are too slow, wagging the rudder
the signal for too fast. If the winch driver doesn't or cannot respond you
abandon the launch.



Roger Worden wrote:
What is the correct relationship between pitch angle and airspeed during
ground launch, either by auto or winch? Different sources make conflicting
statements:

1. Speed control is OPPOSITE to that during aerotow and gliding

* SSA Soaring Flight Manual, page 13-10: "Under most circumstances, the best
way to reduce the airspeed is to raise the nose. During ground launch,
however, the opposite is true ... pulling the nose up results in an increase
in airspeed, assuming the launch vehicle has adequate power."

* FAA Glider Flying Handbook, page 7-16: "The pitch attitude/airspeed
relationship during ground launch is unique. During the launch, pulling back
on the stick tends to increase airspeed, and pushing forward tends to reduce
airspeed. This is the opposite of the normal pitch/airspeed relationship."

* This is what I was taught during autotow training. I can't say that I have
varied the pitch enough in my few launches to have demonstrated it.

2. Speed control is the SAME as during aerotow and gliding

* British Gliding Association Instructors' Manual, page 16-2: "If the launch
speed starts to tail-off, lower the nose." Page 16-3: "monitor the airspeed
trend. If it is falling back towards the minimum safe speed, lower the nose
or relax any back pressure on the stick." BGA does not mention attempting to
slow down: "If the glider is starting to go too fast, maintain the normal
climb attitude, and signal. If it remains too fast, or gets even faster,
release."

* During presentations on winch launch at a recent seminar, two leading
instructors discussed lowering the nose to increase speed and raising the
nose to decrease speed.

* This is what my experience with the Condor flight simulator winch launch
has shown.

It seems to me that this is a critical point on which to be clear, since I
will be winch-launching for the first time soon. I understand that the
vectors involved are different than in aerotowing, because the wings are
converting forward rope travel to angular motion (just like the skeg on a
water ski!). I also understand that a properly balanced glider using a CG
hook for winch launch will tend to nose up initially, and will seek an
optimal climb angle naturally. Altering the climb angle with elevator will
necessarily result in a less-than-optimal altitude gain. But what is the
actual effect of raising or lowering the nose in a stable ground launch
climb?

A. Is it different depending on the angle of climb? In my experience,
autotows tend to achieve a 25- to 30-degree climb angle, winch launch a 40-
to 45-degree climb. Does that cause a difference in the effect of pitch
angle?

B. If #2 above is true, how did the SSA and FFA manuals get it wrong?

C. If #1 is true, is it reversed in Britain? (Just kidding...)


  #19  
Old April 1st 07, 02:43 AM posted to rec.aviation.soaring
Bill Daniels
external usenet poster
 
Posts: 687
Default Airspeed control during ground launch?


"ucsdcpc" wrote in message
...
Speed control is OPPOSITE to that during aerotow and gliding


I'm sure if I asked this of one of our instructors the answer would be
"you don't" You control the attitude, the winch driver controls the speed.
Lowering the nose is the signal to the driver that you are too slow,
wagging the rudder the signal for too fast. If the winch driver doesn't
or cannot respond you abandon the launch.


And your instructor would be wrong in most cases. Pilots who think they are
controlling attitude are at risk of stalling while on the cable. We are in
a transition period in winch launch where old ideas are giving way to the
new. New gliders launched by new winches operate by somewhat different
rules.

In the modern view, the winch driver controls POWER and the pilot controls
AIRSPEED. The relationship is the same as in airplanes where throttle
controls power and pitch controls airspeed. As the glider leaves the ground
on a winch launch. the pilot smoothly pitches up to hit a target climb
airspeed. In an airplane, this would be Vy. In the typical glider, it
will be between 55 and 65 knots depending somewhat on headwind. It's
helpful to think of the winch driver as your flight engineer with his hands
on the power levers.

A modern trainer such as a ASK-21 would need a very powerful winch indeed
for its pilot to be unable to control airspeed. In most cases, the entire
launch will be flown with neutral elevator leaving considerable up elevator
to control airspeed.

An important exception is with gliders which have hooks too far forward
and/or have too little up elevator authority - for example, most Schweizers.
When flying these gliders the pilot will reach full up elevator before the
airspeed can be controlled. Since the pilot cannot control airspeed, the
winch driver has to. A further complication is that these gliders, which
require the winch driver to control airspeed, will not reach more than 1/2
to 2/3's the height of the modern 2-seater with a properly positioned CG
hook.

This exception case also introduces complications in the event of a cable
break. With the elevator positioned at full up, the glider will pitch up
strongly at the cable break - sometimes beyond the point where a safe
recovery can be made. In any event, a very quick and positive action will
be required of the pilot. This contrasts with gliders like the ASK-21 which
will continue on the same trajectory giving the pilot additional seconds to
handle the cable break.

Bill Daniels


  #20  
Old April 2nd 07, 04:05 PM posted to rec.aviation.soaring
Andreas Maurer
external usenet poster
 
Posts: 345
Default Airspeed control during ground launch?

Hi Bill,

On Fri, 30 Mar 2007 09:49:23 -0600, "Bill Daniels"
[email protected] wrote:

The winch should be constructed such that it is not be possible for the
airspeed to increase as a result of raising the glider's nose. Otherwise,
the winch should be regarded as dangerous.


Is it such a problem to teach the pilot to pull the release if his
airspeed exceeds the desired prameters?



Bye
Andreas
 




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