Don't forget to check your spam folder if you don't get an activation email after joining!!

Towhook question

General discussion on any topic which doesn't have a natural home on any of the other boards.
Post Reply
harry curzon
Posts: 100
Joined: 21 Jul 2018, 09:32
Location: Gloucestershire

Towhook question

Post by harry curzon »

I have bought a Nimbus 4D, 7metre span, weight approx 13kg. It is fitted with a towhook of the type with a rotating arm, rather than a multiplex style. Several people at aerotow meetings have said to me that the rotating arm type of hook is not totally reliable and can snag the tow wire. I can think of several design flaws in the rotating arm style, and certainly if I try and operate it it by hand while pulling hard on the tow wire I can feel the roughness as the wire drags along the arm.

Should I try and remove this hook and fit the model with a Multiplex style of hook? I doubt that the thin wires of the Mpx unit are strong enough for a model of this weight but I have no problem in making my own more sturdy unit in the lathe.

FrankS
Posts: 320
Joined: 18 Mar 2015, 14:29
Location: Gloucestershire

Re: Towhook question

Post by FrankS »

Harry, I'm not a fan of this type of release but have flown models with them in, what I found I needed was a thicker wire tow loop, I made mine out of pushbike gear cable and that stopped it getting trapped and jamming up. I think in a recent magazine article that Chris had made some releases from welding wire and that would be another option.

Looking forward to seeing the Nimbus, have you got somebody to chuck it off Selsey for you..............

Elliot Howells
Posts: 243
Joined: 18 Mar 2015, 08:18
Location: West Wales
Contact:

Re: Towhook question

Post by Elliot Howells »

Harry, all the big stuff use the cam and loop as you describe, as Frank says, it's down to the type and strength of the loop and of course a whcking great big servo using all it's mechanical advantage.

Me and Paul Watters have fitted Let pin in the hole style releases on our biggest models, but only because there's a motor in the snout. The pin has to be very stiff metal, as supplied the Let pin is too soft, Paul found his didn't release. I've personally never had a failure with the cam style.

Of course the really neat thing would be to make a tost release, not often found in model gliders, but can be done easily without machine tools.

Best of luck, see you at Milson!

Ell.

harry curzon
Posts: 100
Joined: 21 Jul 2018, 09:32
Location: Gloucestershire

Re: Towhook question

Post by harry curzon »

Ok, it will save a lot of work if I can leave it there. Got a 20kgcm HV servo for it.
Just remembered that a friend bought a glider with one of these, but it came with a link to use in it - a solid aluminium rod with a slot milled in the end for the cam to lock into. Easy enough for me to make. Worth trying, or is thick wire better?

John Vella
Posts: 240
Joined: 20 Mar 2017, 22:09
Location: UK

Re: Towhook question

Post by John Vella »

Harry, I have used the rotating cam hook release for years and never had a hang up. The need for a thick wire loop and a 100% reliable servo is the answer for peace of mind on the aerotow. Regards John.

User avatar
B Sharp
Posts: 729
Joined: 19 Mar 2015, 17:18
Location: Perthshire

Re: Towhook question

Post by B Sharp »

Harry, I also have used the rotating cam release for many years without problems. I manufacture my loops from 2.5mm plastic strimmer line fashioned into a large figure 8. They also function as a weak link in case of a violent tow. The only time I had a problem with this release was when I inherited a machined aluminium rod such as you described. It worked fine on the ground under tension but locked solid in the air. It turns out that the tolerances in the slot were too neat. The result? Aerobatics with my 1/3 BG135 behind a Greenly over Buckminster. I didn't enjoy that one small bit!
Brian :(

Tom Pack
Posts: 84
Joined: 18 Mar 2015, 23:33
Location: USA

Re: Towhook question

Post by Tom Pack »

Have been using cam releases for years......all I use is braided winch line as the tow loops......no fancy metal rods or steel wire loops.....the key is to make sure the edges of the cam itself are rounded over so that there is no chance for it to “wear” at the loop......

harry curzon
Posts: 100
Joined: 21 Jul 2018, 09:32
Location: Gloucestershire

Re: Towhook question

Post by harry curzon »

Thanks for your replies, I have decided to keep it, and rounded the 90 degree edges of the hook as Tom Pack suggested. I have some multi-strand bowden cable that will work as a towline loop. See my Nimbus 4D thread in the build forum for more info on what I did

Post Reply