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Old Jul 03, 2006, 04:35 PM
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Europe - Belgium
Joined Mar 2005
1,521 Posts
Whoops!
Got my first "parachute catch tail" today

Fiddling with towhook, chamber, elev-preset, 10 flight ok, 11th = tailcatch . Unstearable the plane floats (full breaks employed) down lika leave, no damage done by hitting the ground. Inspection: the speedline (mono) drove itself 1" into an elevator and went sideways at the carbon parts. See pict.

How comes? It (dip-zoom) all happened so fast i cannot record. Only to say for sure: i was deliberate longer (1 sek. estimated) on the line than else for checking out hightgain.

What are the secrets to avoid tail-catches? I dont want this anymore
Does the pro's also suffer tailcatches sporadically or is it just dummy learning stuff?
Any tips how to repair damage like this?

Thx in advance, Jurgen.
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Old Jul 03, 2006, 06:36 PM
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Huntsville
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don't dive quite so deep or long when you enter the zoom.
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Old Jul 03, 2006, 09:26 PM
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Keremeos, BC Canada
Joined Mar 2004
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Wow, I've been flying sailplanes for 30 years, and I have never had a tailcatch, must be doing something wrong... If the model is at the end of the launch and the line is slack, I can see it happening, but at that point floating off the ring would be the option. If there is still any tension on the line (enough to generate acceleration), use up that acceleration then pull up...

Wow, a tailcatch....
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Old Jul 03, 2006, 10:14 PM
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Melbourne
Joined Apr 2005
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I have seen this happen a few times and is caused generally from not keeping the power on until release. Don't back off on the winch during the zoom phase, keep power on until after you have released.

cheers Brad
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Old Jul 04, 2006, 02:19 AM
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I can guarantee the line was at max tension, almost stalling the winch before i started the dip, ready for a 70 meter (200ft.) zoom like i had in the previous launches (alt recordings checked). So tha catch happened when the plane pulled up for the zoom at max speed, hence the damage. I did not realy dove that much to loose all tension from the line. I suspect the pullup was too agressive.
Jurgen.

PS:when i said i stayed deliberately 1 sek longer on the line that was before doing the dip, not during dipping.
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Last edited by Jurgen; Jul 04, 2006 at 02:59 AM.
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Old Jul 04, 2006, 08:06 AM
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Sorry it happened Jurgen, glad you have it basicaly in one piece. Amazing how fast you can out run the end of the line.

Marc
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Old Jul 04, 2006, 08:15 AM
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Huntsville
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Sounds like you did a deep dip that allowed the plane to outrun the chute before pullout. I've done the same and seen others do it as well.

I found that when zooming my speed, and elevator effectiveness, is much greater than any other time during flight. If I have trouble with fine pitch control during the zoom I will add some expo to the elevator for this flight mode. That usually fixes the above problem for me.
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Old Jul 04, 2006, 08:53 AM
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Jyvaskyla, Finland
Joined Aug 2003
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That damage does not look too bad. First secure the spar and tube with plenty of CA. Then try to fix the core to its original for with CA. Last some sanding and spacke or tape for the surface. Alternatively you can make a new section of airfoil from foam that is easy to sand.

It also very impotant to secure the LE joint. Fix with CA just to be in the safe side.

I just repaired the center panel from my Snake to fly my best F3J contest ever It looked rather bad but spar was intact.
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Old Jul 04, 2006, 08:58 AM
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Vienna, VA, USA
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I've done that too. It all happens so quickly that it's hard to be sure, but I think it's a combination of an over-enthusiastic (too steep/too deep) dive and getting off the winch power too early.
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Old Jul 04, 2006, 11:04 AM
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USA, CT, Hamden
Joined Oct 2002
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Quote:
Originally Posted by Resurgam
I've done that too. It all happens so quickly that it's hard to be sure, but I think it's a combination of an over-enthusiastic (too steep/too deep) dive and getting off the winch power too early.
It's been repeated, and that's it!
Once it's happened, circle the turnaround, release the brake and shout for someone to grab the line and run towards the turnaround with it. If the line gets taut the game is over.
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Old Jul 04, 2006, 07:56 PM
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Joined Apr 2006
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I had this happen off a high start after trying a zoom with not enough tension left on the bungee... THe tail caught the floating paratchute. Luckly no damage.

Lesson learned, start the zoom earlier while the bungee is pulling with authority or dont zoom at all.
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Old Jul 05, 2006, 01:45 AM
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Europe - Belgium
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Quote:
Originally Posted by Robglover
.....If I have trouble with fine pitch control during the zoom I will add some expo to the elevator for this flight mode. That usually fixes the above problem for me.
I think this nails the problem. How can we expect to master a plane that is superspeeding with elevatorsetting made for gliding? Actualy this is asking for trouble. I gonna make special dual-rate reduction for launching next time and see how it works out.

Tuomo, too bad for the Snake, hope you get it fixed. The damage is not only the plane but also some soul-pain when this happens to a fairly new plane. Thx for the repair tip, the elevator is almost flyable after one evening of tinkering. We had 37C (98F) today, the cristalised harder went fluid of its own and the mix hardened 5X faster than usual. We were living in an oven

Rcko: "not zooming at all"? No way man, its a reason to live . Some aspects of live are worth some thrill of danger, that carbon wing has to work for its price. Lets try to master that dip-zoom rather than avoid its beauty.

Jurgen.
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Old Jul 05, 2006, 01:56 AM
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Quote:
Originally Posted by Resurgam
I've done that too. It all happens so quickly that it's hard to be sure, but I think it's a combination of an over-enthusiastic (too steep/too deep) dive and getting off the winch power too early.
You mean too early starting to zoom while there is still too much tension on the line, or too early stopping the winch-pedal so there is too less tension on the line for dip-zooming (like what happens when one dives too far) ?

When i make a very tiny little dip followed by the zoom, then the parachute makes a WHACK-sound, snapping open powerfully due to the big tension that was still on the line when detaching. I was always wondering if this type of release is a good one. It sure gives a kick to hear that parachute open like this but on the other hand i might spoil some unused tension. Any suggestions?

Jurgen.
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Old Jul 05, 2006, 04:20 AM
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Australia, NSW, Sydney
Joined Sep 2003
1,145 Posts
Tail catch

The monofilament line used for F3B type winches has a little bit of stretch but it isn't that much. Winch line speed isn't all that fast either compared to the speeds the aircraft can achieve during a launch.

The line gets stretched by the aircraft going up in the climb with full pedal on the winch. The dip is the time we try to convert all that stored energy in the line to speed and then we pull up to convert speed to altitude in the zoom. If the dip is too steep (or too long) then the stretch in the line is taken out very quickly by a rapidly accelerating aircraft and soon the parachute slips off the tow-hook due to no tension in the line. Here is where the aircraft tail actually runs over the parachute and if you are trying to pull up at that moment the tail snags the parachute or the line. If you dip down very steeply (nearly vertical) the line can get wrapped around the wing. I've heard of situations where the entire tailplane has been severed from the aircraft by the line cutting through the tailboom, through carbon, pushrods, everything.

The solution/prevention is to not dip so steeply or as long, so that there is still line tension to pull the parachute away from your aircraft as you pull up. Sure the parachute snaps open and produces a loud sound but if you have extracted almost all the energy then that's the best that can be done. Dipping down for too long also means that the zoom starts from a lower altitude hurting your final launch height. The maximum acceleration during the dip is when you first start it (maximum line tension) and from then on line tension is decaying rapidly, so there isn't much to be gained by staying on for long. Watch the top guys do it - a very quick dip and a sharp pull up.

It's a fine balance between maximum energy extraction for top performance and a mishap. Personally I'd err on the side of caution and try to avoid the mishaps side of the possibility matrix.

Your damage doesn't look too bad actually. Provided the spar is intact then a fibreglass patch over the cut should suffice.
F
Edited for spelling
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Old Jul 05, 2006, 05:33 AM
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Jyvaskyla, Finland
Joined Aug 2003
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I agree totally: the acceleration for zoom does not have to be a deep dip.

Below you can see a selection of my loggings. 1.2mm mono with 150m to turnaround. All tows are quite long for max height, but surprisingly there is no relation between altitude gained and the dip. Actually the best tow with more than 100m has almost no acceleration phase

In competition it is very important to make a fast launch, 5 sec max. In this case I rarely do any dip, just flick the switch to slight reflex (with snap flap) and pull hard to vertical.

Other pictures are from the repaired wing (for damage, see post #8). Just to encourage you in the repair job
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