Scale Soaring UK

I’ve been doing a bit of towing with an electric Riot XL and a towline, both of which were given to me. I’ve been asked by the owner of a Bolus Baby Albatross, which weighs about 6lb, what breaking strain would be appropriate for a weak link to be incorporated in his release fitting line.

Is there a rule of thumb for weak link strength vs. glider weight?

Weak links are a waste of time. Don't bother.......

BC

275 Paracord for the tow line 100-120’.......braided winch line for the loops at the sailplane end of the line with a heavy duty snap swivel.

Buy a 30m length of orange builders line from B&Q or your local hardware shop and tie a loop in one end to go on the tug release and a heavy duty fishing swivel with a snap link on the other. Glider pilots provide whatever they need to go between the swivel and their own release in the nose of the glider.
Do NOT use a weak link....it will only end in tears !!!

AEB

Trevor, in the 80s when we were aerotowing at Romanway with relatively low powered tugs and sailplanes of all sizes we never saw the need for the full size practice of weak links. We did however have 100% reliable releases.
Regards John.

Thanks guys. The line I was given seems to work well, so if a glider pilot wants a weak link, it’s up to him to provide it in their release adapter connection. I will though pass on your advice not to bother!

Never mind a weak link, just make sure you use the most powerful servo on the release that you can afford, whether it is the tug or the glider and not a retract servo. One day you will have a hang up on tow and you will need it to work immediately without stalling in order to save both models at the same time. A standard servo like a 3001 or a JR 507 won't cut it, they will just stall and make you crash. I would say at least a 10kg pull if not a lot more. My tugs have 20 to 25 kg servo's as I don't want to get sucked into a caught wingtip induced crash.

Ray

Like I say, one day you'll need it and no, this isn't photoshoppped, it was my first ever towing sortie about 12 years or more ago

Ouch! Point taken Ray. However, I'm not sure I'd react fast enough to save the tug in that situation! As I said, the tug is a battered Riot XL which spent most of its previous life stuck up in the top of a pine tree before it was donated to me for use as a club tug. I'm very impressed with how well it copes. I usually put a 5s LiPo in it instead of the normal 4s when towing and it pulled the 6lb Albatross up without problems. Given it's history, we do tend to worry more about the safety of the gliders than the tug.

On the second tow with the Albatross, there was a violent line snatch a second or so after the glider pilot pulled the release. Post flight inspection revealed that the tow release fitment at the end of the line was missing, as was the brass undercarriage skid, suggesting that somehow the line had snagged on the skid after release. This is what has triggered the glider pilot's interest in a weak link!

Ray

That looks just like the attitude my DG600 got into last year, before the retract servo (travelling slowly) released the line.
Nearly finished the repairs now (cosmetics still to do) and did re-maiden it at the Long mynd a couple of weeks ago.
So yes, best advice is strongest/fastest servo in the model on the tow release.

John M

Fellow Tuggers,
To be contrary: I have used a weak link on my tow line for a number years now. I use 60lb mono filament fishing line which stretches under load but snaps if snagged. It is at the "tug" end of the line and is designed to save my tug, particularly on landing if you come in over a hedge or fence etc. where the trailing line can easily snag. Mine did once and the weak link snapped saving my tug. I tow 6 metre scale gliders with out any problems with this set up although it is essential to take up tow line slack before going "All Out" (which we all do anyway)

I bought a full reel of 50lb line and if anybody wants a metre or two just ask.

The weak link should not be relied upon to save the tug and glider in the situation depicted in the preveous photo. I strongly recommend both tug and glider pilot have their finger's on their release buttons before setting off. I am amazed at the number of glider pilots, some with lovely models, who cannot release quickly in times of stress. If you have to think about where the release switch is, it is allready too late. Anyone hitched up behind my Wilga will hear me shout "finger on button..." before every tow.


Cheers,

John

Hi John

This isn't personal, just my thoughts.

In the full size world, I believe it is the glider that has the weak link and this is calculated to go with that particular glider.

I see your point about saving the tug if the line snags a fence or anything and I have snagged fences at least 3 or 4 times and been lucky so far. I have the ripped windsocks from the end of the line to prove it. However the problem is when you go to an aerotow event and put yourself forward to tow whatever comes along in the queue, and this can be a 3 and a half kilo woodie like the seagull K8's or a 38 to 40 kilo half scale glider which are becoming increasingly common. In that case your weak link would snap before the glider had even started rolling. Conversely if the weak link was strong enough to withstand the necessary drag of the heavy glider, then it wouldn't snap with a fence snag, so it is a tough call.

Last year at Shrivenham, we tried towing John's Vienna with my Decathlon, but without the take off dolly for the Vienna. I went to full throttle and the Decathlon got airbourne with zero movement from the glider. 3 people pushed the Vienna to start it rolling and we got going. I dread to think what the strain was on the line that day, and if the line had broken, the sudden release of energy on the tug probably wouldn't have done it any good either.

It is all these variables that make towing such a fascination for me and make me want to do it over and over again. You never know what you are going to get next.

Ray

Ray, just to,clear up a point on full size weak links. You are right that every glider has a colour coded different weak link on winch launch. On Aerotow there is a one strength fits all at the tug end to save the tug . This can break with a snatch in severe turbulence or out of position situations. However in mountain flying in the Pyrenees we did not use weak links. May I suggest in obstacle critical approaches we have dropped the line and done a short circuit with the tug.
Regards John.