| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 426.1 | put the hook slightly forward of the CG | BPOV09::ERICKSON | | Fri Feb 20 1987 14:45 | 19 |
| (a) The tow hook really should be slightly in front of the CG, as
suggested in 61.0. You must have it near the CG as that will
allow the glider to fly with full controllablilty while under
tow---the same reasoning applies to launching with a Hi-Start.
Too far in either direction and the results will be equivalent
to a misplaced CG.
(b) Using "full-down" elevator is the only real option. Since the
glider will be above the tow during a proper tow launch, one
would run the risk of pulling the glider away from the tow;
the added tension might make releasing increasingly difficult
or impossible.
Granted, the actuation will take place so quickly that the glider
PROBABLY won't respond to the transient control movement, but
why not play it safe? Use "full-down!"
(c) There are some hang-glider schools around the Groton area; perhaps
you can gain access to their hills during off-hours.
|
| 426.2 | Down may spell disaster | SPKALI::THOMAS | | Fri Feb 20 1987 15:53 | 13 |
| If I have been reading the responces correctly people are telling
you to use an application of down elevator to release the plane
from the tow. This is a technique used but for different reasons
than what has been stated. When you are on two stay headed in the
direction you want to go and as the ship passes over the end of
the tow it will slip off of the hook by itself. Application of down
elevator would cause the tow to pull the ship downward. this will
in turn add speed to the ship. Up elevator at this time woild make
the ship pivot and the tow to release. The manuever is called a
power launch. It puts great stress on the airframe. Make sure your
airframe is up to it. The gentle lady isn't.
Tom
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| 426.3 | Tow Point of view | ROYCE::HORNBY | | Mon Mar 02 1987 16:04 | 39 |
|
Where to put it.....Don
The general rule, if your not realy sure and haven't
perhaps got the plan, is to project a line from the centre of gravity
under the wing downwards and forwards approx 30 degrees. The pulling
point on the hook should be in line with this. As you become more
experienced both in flying skills and knowledge of the specific
glider the hook can be moved more rearward (closer to the C.G.)
to improve the launch height but beware the glider usually becomes
more unstable the further back the tow point. Conversly with the
hook too far forward you will tend to generate more speed and less
height and Up elevator on the launch will be less effective.
______________________________
_______________(_________^________Wing________\__________
/ /|C.G.
/ / | FUSELAGE
\ /30|
\______________________/__________________________________
L
The hook should be short, strong and simple.... I usually reinforce
the inside bottom of the fus. with a piece of ply and then cut
down and reshape a cup-hook...
/ \ Thread
_| |_ Flange
| |
| |____ Reshaped hook approx 0.3" x 0.3"
|______|
Launching..... I agree with Tom's comments
|
| 426.4 | "Active" Tow Hook | BPOV09::ERICKSON | | Tue Mar 03 1987 15:33 | 16 |
| When I wrote .3 I had an "active" tow-hook in mind, in which the
act of "full down" will cause the mechanical release of the tow-line.
Such a system is obviously more complicated than the "cup-hook"
approach, as it requires the mechanical linkage to the elevator
servo, but it allows the tow-ee to abort independant of speed,
altitude, etc. In other words, you need not "fly" your plane off
the towline.
I built such a system into a "Dyke Delta" slope soarer, with the
intention of piggy-back launching (Space Shuttle/747 style) from
my Uncle's 80-powered YAK. We built the launch bracket, but neither
one of us had the gonads at the time to try it!
HAve a great one,
John
|
| 426.5 | 36 to 38 percent of the wing cord for both | CSC32::M_ANTRY | | Sat May 13 1989 13:58 | 33 |
| I am entering this reply after reading note 997.
The CG of the glider should be about 35-38 percent of the wing cord at
the root. The Tow hook should be anywhere from 0-2 percent less than
this. As previously stated, if the tow hook is the same as the CG or
behind it the glider may be unstable and want to pop off the launch
unless you are using a releasable/capture tow hook. I generaly set my
CG at 36% and the Towhook the same.
The percentage measurement means that the you take the cord of the wing
at the root say 10 inches and the CG would be at 36% or 3.6 inches back
from the leading edge. We have built a balance box that makes this
very simple. Here is a small diagram:
side view end view
^
=================/ \========= | |
= = = =
= = = =
= = = =
============================= ==========
the piviot point is a small triangle piece that is put on the top of
the box sides and then the top rail can be marked in inches starting
ath the point of the triangle and going forward. Then to balance the
plane place it in the middle of the box with the wing resting on the
two triangles and position it until it balances. Then look from above
down onto the box and sight from the leading edge down to the top of
the box. You can then read the measurement and then figure the percent
at which the plane is balanced.
|
| 426.6 | Tow hook positions??? | KAY::FISHER | Stop and smell the balsa. | Mon Jun 17 1991 11:52 | 35 |
| Here's a question that has been puzzling me.
The old buzzard says that you should have the tow hook location slightly
aft for a winch compared to the correct location for a hi-start.
I'm not sure if I read that in his book or where but I've been curious
ever since.
Now I must admit I have never had a truly adjustable tow hook - but I did
attempt to solve bad launch problems with my Sagitta by moving it forward,
but I didn't notice any difference. The ultimate problem with my Sagitta
and Hobie Hawk was my procedure and not the tow hook position. In both
planes you must stay on the winch longer with faster heavier planes in
order to get them flying above stall speed at those steep angles of attach
you get on launch. The hi-start seems more forgiving because it doesn't
stop pulling till it's ready.
Anyway - I have noticed that I must add significant down trim for launch
on the winch. I can take it out after I travel about 50 feet up.
So my intuitive feel is that if you changed the tow hook for winches
you would want it more forward. On the other hand if you only consider
super winches then maybe were looking at the possible that compared to
a standard hi-start - we can develop more horsepower. Since stall is a
function of angle of attack and forward speed, then we could say that
with the winch I won't stall as easy therefore I can have a higher angle
of attack - therefore I can move the tow hook back. There is some
assumption here that the hand stays off the elevator and you don't
have a special trim (launch switch) setting for launch?
What to you experts have to say about tow hook position movement?
Bye --+--
Kay R. Fisher |
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| 426.7 | Launch speed..work to increase it. | ELMAGO::TTOMBAUGH | A Fistful of Epoxy | Mon Jun 17 1991 13:36 | 36 |
| Kay,
My own experience agrees with yours, on having the tow hook forward
for winch launches.
For normal sport/contest flying by mere mortals, the biggest danger
on winch launches is insufficient launch speed, during the first
1 or 2 seconds after release.
With a more forward hook the nose stays lower and speed builds more
quickly.
Your experience with having to add down trim on launch is puzzling.
I find that I can use a few more clicks of up trim on the winch
as compared to the hi-start. I never touch the trim after release.
With the Algebra, I sometimes horse the nose up more steeply with the
elevator on downwind launch, after the plane is out 100 ft. or
so, and moving fast. But that is due to the Algebras' dislike of
downwind launches, and the need to keep the nose well down for the
first few seconds.
It's worth noting that on a really hot launch ,ie the typical F3B
launch, where the plane holder hangs on to it until the winch is
nearly stalled, then javelins it up nearly vertical with two hands,
a rearward hook reallys pays off because the plane wants to stay
vertical and a lot of altitude is gained in the first few seconds.
These sort of shenanigans are a little too thrilling for the average
sport flyer, but I've been gradually learning to get more tension
on the line before release and find that this helps a lot.
I've never tried an adjustable tow hook, but have used two hooks
mounted ~1/2" apart. It was so long ago I can't remember any details
of how it worked.
Terry
|
| 426.8 | Launching - continued | KAY::FISHER | Stop and smell the balsa. | Mon Jun 17 1991 18:25 | 16 |
| > <<< Note 399.834 by ELMAGO::TTOMBAUGH "A Fistful of Epoxy" >>>
> -< Launch speed..work to increase it. >-
> For normal sport/contest flying by mere mortals, the biggest danger
> on winch launches is insufficient launch speed, during the first
> 1 or 2 seconds after release.
...
> Your experience with having to add down trim on launch is puzzling.
Terry, for exactly the reason you mention above - to help me get sufficient
launch speed during the first 2 seconds I have my launch switch set up
for down trim and I take if off as soon as I am stable on tow.
Bye --+--
Kay R. Fisher |
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| 426.9 | | HPSPWR::WALTER | | Mon Jun 17 1991 20:48 | 10 |
| I agree with Terry, I feel I can use a little more up elevator for a winch
launch. I've often considered making an adapter for the tow hook that would
attach to the existing hook (which is permanent and not adjustable) and
effectively move the tow point back a quarter inch or so. But I don't understand
WHY this is so. Obviously, the high start pull decreases during the launch;
maybe that means the plane has to nose down more to keep its speed up?
As for Kay's need to add down trim, you don't think that's because you barely
spool up the winch, do you?
|
| 426.10 | Put the pedal to the metal | SNAX::SMITH | I FEEL THE NEED | Tue Jun 18 1991 12:16 | 7 |
| Kay, I tend to agree with Dave. Virtually all of the "high performance"
gliders I see are spooled up to the point of not being able to hold
on to them anymore before their let go. I think you may get better
launches if you stomp on the winch and DON'T LET GO until it's about
to get ripped out of your hand.
Steve
|
| 426.11 | two hook position for winches - continued | KAY::FISHER | Stop and smell the balsa. | Tue Jun 18 1991 17:08 | 12 |
| > Kay, I tend to agree with Dave. Virtually all of the "high performance"
I'm not disagreeing with you guys but I am talking in general here.
My Chuperosa will pop off every time on a winch. My Sagitta, and Hobie Hawk
are dangerous to launch without some down elevator - I agree that
more power at the start helps - but my real question is why would
the tow hook be more aft for a winch?
Bye --+--
Kay R. Fisher |
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| 426.12 | Here's a BS idea | SNAX::SMITH | I FEEL THE NEED | Tue Jun 18 1991 17:32 | 7 |
| The only thing I can think of right now is just that the winch has
more power. More power means that the winch can overcome the planes
climbing ability and "drag" it off the winch. A more rearward tow hook
increases the angle of attack which in turn overcomes the "drag" effect
of the more powerful winch.
Steve
|
| 426.13 | Ain't so! | MR4DEC::ANKER | Anker Berg-Sonne | Wed Jun 19 1991 12:09 | 13 |
| Re: <<< Note 399.836 by HPSPWR::WALTER >>>
>WHY this is so. Obviously, the high start pull decreases during the launch;
>maybe that means the plane has to nose down more to keep its speed up?
Ain't so!
The winch pulls harder on the plane at the end of the
launch. As the plane picks up speed and the wings generate lift
the force on the plane increases. Wings almost always get ripped
off at the end of the launch.
Anker
|
| 426.14 | | ZENDIA::REITH | Jim Reith DTN 226-6102 - LTN2-1/F02 | Wed Jun 19 1991 12:14 | 3 |
| Yes, with a very nice kaboom I might add.
Jim (who did it on sunday)
|
| 426.15 | Same hook position..winch & hi-start | ELMAGO::TTOMBAUGH | A Fistful of Epoxy | Wed Jun 19 1991 12:43 | 34 |
| Since I had a meeting with some club members last night, I put this
tow hook location question to them.
The consensus was that the optimum position is the same for both
winch and hi-start.
However, since the hi-start is more unforgiving if something should
go wrong on launch, ie, you can't get off the power, a more forward
hook position may be safer, if you like to crowd the performance
envelope.
One guy with a lot of A1 Nordic towline (FF) experience, said that
a too far forward hook position will result in snaking and weaving
on tow, but that this condition usually isn't experienced with RC
gliders because no one experiments with such extreme positioning.
He, and others, agreed that the absolute best way to get the steepest
launch angle was to put the tow hook behind the CG, then use down
elevator trim to keep it under control until flying speed was reached,
then take out the down trim and , Zowie!, it will rocket straight
up. Whether such on the edge techniques are worth it in the long
run are debateable.
Dave wasn't there so I couldn't ask what he meant about hook placement,
in Old Buzzard.
I did get to see what an Omega wing looks like after flutter has
ripped off the aileron and flap in a high speed dive.
It put a 45 degree crease across the top off the wing, and crumpled
a section of the t.e. near one of the arrow shaft hinge pin points.
It was still stiff in the spanwise direction, so Phil thinks he
can repair it for sport flying but is leery about full bore F3B
flying with it. It uses the hollow wing, monococque construction
with balsa, CF, glass laminate.
Terry
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| 426.16 | Is this how you Danish guys have an argument? | HPSPWR::WALTER | | Wed Jun 19 1991 16:33 | 18 |
|
#>WHY this is so. Obviously, the high start pull decreases during the launch;
#>maybe that means the plane has to nose down more to keep its speed up?
#
# Ain't so!
#
# The winch pulls harder on the plane at the end of the
# launch. As the plane picks up speed and the wings generate lift
# the force on the plane increases. Wings almost always get ripped
# off at the end of the launch.
#
# Anker
Anker, unless I'm missing something here, we seem to be in violent agreement.
The winch continues to pull on the plane at the end of the launch, whereas
the high start loses its pull.
Dave
|