bogbeagle

I thought that you might like to see my friend's new twice-size Ivory Gull having it's first flights. The model was aerotowed after a few test-glides.

We have developed a very safe and easy launching technique for our gliders ... almost foolproof, in fact. The aerotow, being demonstrated in the video, was only the 2nd flight of the model and the second occasion upon which the glider-pilot had ever flown an aerotow. The pilot had experienced his first aerotow that same day ... and his first tow coincided with the first flight of his new Ivory Gull!

The tug is a T240, with a 40cc petrol engine. A towing mechanism is fitted beneath the fin.


[youtube]http://www.youtube.com/watch?v=CUhQc6ErzxE&list=UU4HLk42VM0CCjglQ2KPcYdA&index=1&feature=plcp[/youtube]

N1EDM

My Feedback: (2)

Thanks for the video. Could you fill in more of the blanks for us - this will probably get a lot of interest with people wanting details. Here are a few questions that I had:

I'm curious about the two mechanism on the tow plane. Most RC models that I've read about have you put the tow point at the TE of the wing. What was it like to tow a plane with the tow point under the fin? What was the tow mechanism like on the tug?

Did you release the towline over the field before you landed (so that it wouldn't snag on something when you came in, resulting in a 'sudden stop'?

How did you release the glider? I am presuming that you brought the tow plane throttle down to idle and let the glider zoom on ahead, dropping the tow off the gliders tow hook.

I have a J-3 Cub rigged for two but have not done that yet. So, you can see my interest.

Thanks a lot,

Bob

guamflyer

First of all ...the Ivory gull is very Beautiful...airtow technique was interesting..seemed to work..i did some airtowing" being the glider pilot and the tow plane had a release mechanisim in case something went wrong..I'm also acustomed to the tow at the TE of towplane..if there was some drag on the part of glider or towline or caught and can't release, would'nt the tow plane go into a nose down attitude as full scale...anyways very interesting..but add more pics please as I LOVE THOSE THERMAL PLANES...Built a couple of vintage stuff...Pretty airplane indeed...


SLOPE FAST - SOAR DEEP

guamflyer

bogbeagle

OK.

I will get some pics of Dave's Ivory Gull at the next opportunity. It's very pretty and I can't believe that it was sold to him for just £75.


I don't have the T240 on hand, but I have uploaded a couple of pics which show the "release mechanism" as fitted to my Bi-stormer. The mechanism on each aircraft is quite similar. The Bi-stormer has the towing bridle (trace wire) secured to a strong internal bulkhead via a steel pin. The steel pin passes through a hole in the aircraft's bulkhead. The pin can be withdrawn by servo' action. The bridle passes down a plastic tube to an exit point at the rear of the aeroplane. The plastic tube ensures that the towing bridle cannot snag on any internal structures.


We've been using this aerotow method for about 18 months, now and we usually land with the tow-line attached to the tug. A little care is required, to ensure that it doesn't snag on trees. A bit of rag acts as a drogue and a visual marker, indicating the terminus of the tow-line. As you will see from the video, landings are best made with a little engine power. If you cut the throttle early, there is enough drag to rapidly slow the tug.

Each of our gliders is fitted with an independent release mechanism ... but I've heard that some people use a simple hook, quite successfully. I saw one video in which the tug was a Multiplex electric foamie; and it was towing quite large gliders.

We found that towing from the ground, or from a dolly, is much more risky than the hand-launch method. Of course, hand-launch might not work if the model was very large or a heavily-loaded type. The only requirement of the glider pilot is to keep the wings level and to prevent his model from climbing too high above the tug... so a little forward stick may be required. The tug pilot must fly smoothly, reasonably slowly and must maintain a positive climb... if he descends, he takes the risk that the glider will accelerate, leading to the tow "snatching". This can be very violent.

So, good piloting is required by both parties, as is communication.

N1EDM

My Feedback: (2)

Thanks for those pictures... That's an idea about towing with a release pin inside the fuse. I like that idea. But it seems like you would have to take the wing off each time that you want to tow in order to rig up the towline again. This is very interesting. Learning a few new angles here.

Bob

bogbeagle

I leave the towing bridle attached to the aeroplane, whether I'm towing or not. There's just a couple of inches of trace wire protruding from the tail end of the model. I attach the long towline to this protruding trace wire, when I want to aerotow.

If I had to ditch the towline, for some reason, then I would have to gain access to the fuselage, so as to re-attach the bridle.

Our T180 tug ... a smaller version of the T240 in the video ... has the release mechanism fitted by the tailwheel. A wire connects the release mechanism to a servo inside the fuselage.

There's lots of ways to skin the cat. But, I do think that there is more load on the delicate after-parts of the fuselage when the release mechanism is located right at the tail. Everything is usually more robust as you go towards the nose of the fuselage.


In fact, the release mechanism on the T240 is mounted underneath the fuselage and close to the main gear, such that there is ample access without removing the wings. The bridle then passes through a stirrup beneath the tail surfaces. You still need to make provision such that the towing bridle is guided clear of the aeroplane if it becomes necessary to discard the tow-line. A light-weight plastic tube will do the job ... snake outer is favourite. If something can possibly "hang up", you can be sure that it will.




Good fun, though. The collaborative nature of aero-towing has absolutely rejuvenated my interest in aeromodelling.


You can see our smaller tug (T180) here towing two gliders together.



[youtube]http://www.youtube.com/watch?v=k74EqrITs6E&list=UU4HLk42VM0CCjglQ2KPcYdA&index=10&feature=plcp[/youtube]

bogbeagle

Normally, the glider pilot launches his own model ... so only two people are required.

We had a third person launch Dave's Gull, owing to his inexperience with the aerotow.

BarracudaHockey

My Feedback: (11)

The general theory is yes, you want the tow point at or near the CG of the tug for the reason stated, if there's a problem and the glider ballons it can yank the tail up and the nose down.

bogbeagle

Ah, well, Barracuda, the "general theory" does not stand the test of practical experience. Therefore, I reject it. There's more than one way...