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Jef Ott

Aerotowing advice wanted

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Jef Ott

A friend has built an electric tug. Spec is quite impressive; the motor is capable of handling 3kW.

To my knowledge, he has not yet towed anything more expensive than a banner.I am quite keen to have a go at aerotowing some of my gliders, and had never even seen a model aerotow before this month.

The way I see it, it would be foolhardy to attempt to be my friends first tow glider pilot, without some kind of tuition first.Anyone got any advice? And I mean any advice !

Has anyone towed RES models, or are ailerons a minimum requirement?Naturally I would be happier trying it out on an old scrapper than something of a valuable / desirable / irreplaceable nature.

We both fly at the Damyns Hall Aerodrome in Upminster, Essex and would hope to eventually do our aerotowing there.

Thanks,

Jef.

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Gary B

Hi Jef, Yep, I've towed a 'scrapper' earlier this year and it survived!

The glider was a Thunder Tiger Explorer 2M (given to me before anyone says anything!) and the tug was an electric Multiplex Mentor.

The glider release was just a hole in the plastic nose cap with a wire pushrod coming forward off the elevator servo (arranged to release on momentary full up elevator).

We tried it off the ground but not good without ailerons, hand launching worked but was also tricky, best results were achieved borrowing a wheeled dolly but the tug struggled to get the combined weight moving.

The glider followed the tug fine in flight and the release worked well.We were just messing about really but it proved the concept.

Cheers

Gary

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Jef Ott

Thanks Gary.

I found a proprietary tow-release mechanism on ebay, but I do like the simplicity of the system you described.Sounds like the glider would certainly benefit from ailerons during the ground handling bit.

With 4HP on tap, I don't think that the tug would need the glider to be on wheels, but a dolly makes sense never-the-less, as the time spent with the coupled aircraft moving on the ground wants to be minimised, as I see it.So what does the ideal dolly design incorporate?

Best regards,

Jef

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Phil.Taylor

I've had several aerotows, by an experienced tug pilot, towing up my 100" bitsa glider - just off the ground, no dolly neededIts all very simple & straightforward (*)

most important is that you have an ultra reliable nose-mounted tow release in the glider - and keep your fingers on the Tx release switch in case something does go wrong - and for when you do want to release. I'm using the "Flair products" aerotow release gadget.

my plane has ailerons - not sure I'd like to try it with a rudder/elevator planeand here is a link that was posted on another forum - may be useful - havent looked through it yet

Phil.

(* I have seen it go spectacularly wrong for other folks :) )

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Phil.Taylor

and the easy version - as in "Easy Glider" version - Multifun glider with an improvised hook on the nosesimple - what could possible go wrong?

http://youtu.be/KIMO9R5agCY

vid by Mike / Isoarquite possibly the funniest thing we've seen at an F3F comp (that wasnt cos there was zero wind, in February)

Phil.

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Jef Ott

Thanks Phil,

The rc aerotow forum link is quite useful.Enjoyed the video - it's very humorous.Have made contact with someone that has the perfect model for my first aerotowed flights, and hopefully I will collect it on Sunday.

In case anyone is interested, this is the tow release I bought

http://cgi.ebay.co.u.....0666731999

Best regards,

Jef

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isoaritfirst

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isoaritfirst

First few aerotows we did during the last foot & mouth when we were all going stir crazy. Just used a piece of bent wire taped onto the top of the nose of various models, such as Phoenix MP Rico-she's etc.

Just like a larger tow hook and mounted more forward and on top. To release just mean't that the tug slowed down and the glider dived to speed up. Worked flawlessly. Advice on being tugged = Fly the model on the ground, before you have speed you need to be ahead of the game to keep the wings level.Once up and flying just keep the wings level don't try to steer to follow the tug,

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Jef Ott

What a great facility internet fora are, for those with no experience to learn of the possible stumbling blocks, without paying the normal learning fee! (Heartache and more balsa bashing.)

Thanks for posting the video again isoar, in an even more user-friendly link. It is funny every time I watch it.Also the comment regarding "don't steer the glider to follow the tug" sounds like a very valuable one.

Thanks also for the "fly it on the ground" comment - by which I think you mean control the ailerons to keep the wing horizontal, a great tip, which got me thinking of fitting a pair of gyros (one on each aileron) and only controlling the elevator during the tow. Or would one gyro be able to control two aileron servos? In amongst my rocketry bits and pieces I do have a gyro and a unit to enable and disable the gyro from the Tx.

Has anyone done this? Or am I just overcomplicating everything before I have even got my tow-release?Best regards,

Jef

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Steve J

I did a bit of aerotowing earlier in the year and enjoyed it. Here are a few 'lessons learned' -

1) The tug needs to be 'adequately' powered. If it all goes to pot in the air, it's nice if the tug can power though the problem and not have to dump the glider.

2) Make sure that there is a weak link in the tow line. Use the longest line that is practical for your takeoff area. We used a line with a rigid section where it went over the tug's tail surfaces.

3) Discuss the tow beforehand. Communicate during the tow.

4) I found it easier with a glider where the wingtips are rounded rather than square as they are less likely to catch on the ground while the glider is being dragged and it's wings haven't started flying.

5) The tug shouldn't rotate until the glider is airborne. The glider pilot should call out when the glider is airborne.

6) The glider should try to keep above the tug during the tow with the wings level.

7) Don't let the towline go slack. Don't try to turn the glider inside the tug.

8) The tug pilot should announce his manoeuvres and avoid 'bank and yank' style turns.

HTH Steve

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Jef Ott

Thanks Steve J ! :clap:

Excellent post.I will print that list and show it to the tug pilot.What breaking strain line would you use in the weak link for a relatively lightweight 3.4m span model?Just got some models that will be going on tow, when they have been flown on the slope to ensure thay have no 'nasty surprises' and had their tow releases fitted…Then it's heart in the mouth time again! :rolleyes:

Jef

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Steve J

My towline is around 25m of 2mm nylon climbing cord with a short length of nylon fishing line at the tug end to provide a weak link. I have a weight (an M10 nut) a few metres from the glider end.

The heaviest glider that has been towed with this line weighed around 1.5kg. 9) Have a finger on the release switch during the takeoff. If you catch a wingtip, you may need to release in a hurry.

Steve

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Jef Ott

Steve,

Thanks for advising again - 2mm line sounds heavy to me, would otherwise have used 1mm nylon line, so that would have been a pitfall, I would also have put the weak link at the glider end - which now I think about it is wrong too - so I am really glad you posted that! Any idea what diameter or breaking strain fishing nylon you used at the weak link? I reckon about 2 to 3 times the glider weight but am happy to be put straight on that one too.

The 9th point is probably the most important one - I will use a momentary switch for the tow release, and will also set the failsafe to open the release on signal failure. I regularly use the left momentary switch for my electric model as a safety device mixed on the throttle control, so it will be natural for me using that on the tow release too.

Thanks very much,

Jef

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Steve J

The weak link is there to protect the tug. I once got a bit low coming over a fence with the tug with the line attached after a tow…. luckily the weak link did it's job. The nylon that I use for the weak link came with my old EasyGlider.

Jef said:

In case anyone is interested, this is the tow release I bought http://cgi.ebay.co.u.....0666731999

This is very similar to the release that I have in a couple of gliders. I would suggest replacing the hinge pin with a bolt and nyloc and making sure that there are no sharp edges on the bit that holds the cable. Here is a photo of a clubmate's glider at the moment of takeoff. The tow line being used is a lot fancier than mine.

DSC_0208.jpg

Steve

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Jef Ott

OK, thanks Steve.

In the picture, it looks like the glider pilot is holding in full up elevator at this stage. The edges of the catch are all rounded off already (obviously a CNC milled item). I can see good reasons not to use a pivot with rough edges too, so why would you bin the pin in favour of a bolt and Nyloc?

I was going to open up the hole to the pin diameter, on one side, clean the swarf from inside the tube, then insert the pin (through the tube and catch) and push the pin into the un-enlarged hole on the otherside, with a press.

Cheers,

Jef

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Steve J

Jef said:

I can see good reasons not to use a pivot with rough edges too, so why would you bin the pin in favour of a bolt and Nyloc?

If you don't think that the pin will ever work loose or you will be able to get to it if it does, then there is no problem sticking with the pin.

My Graupner releases came with a bolt that I thought was marginal on length and a plain nut, so I replaced them with a slightly longer bolt and a nyloc.

Steve

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Jef Ott

On my 'scrapper' a 2.5m aileron model, I will be fitting the tow release inside the keel, then running some carbon tows around the woodwork to keep the release in the right place and the keel in one piece.

Hopefully the pin will not move anyway - as it will be a tight interference fit in the ally tube, but the woodwork should keep it in place as well.Sketch not to scale...

aerotow-scrapper-nose.jpg

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Jef Ott

or better still... if I fit a longer pin, that can transfer the tug loads directly to the airframe and keep the tube from turning. 

aerotow-scrapper-nose-2.JPG

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Steve J

Tow line at the tug end. 

DSCN1086.jpg 

Steve

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Phil.Taylor

You dont seem to have a line release on the tug?

Extra protection for both tug and glider in case something goes very wrong, and you can drop the line before landing, so no chance of snagging it

Phil.

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