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How much power needed for tow?

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How much power needed for tow?

Old 02-18-2002, 05:38 PM
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wjjones
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Default How much power needed for tow?

I need some opinions on aerotowing. I want to use a Senior Telemaster and a 3W-24 to tow 4-meter scale sailplanes. Some say I need a bigger engine, but others say even marginal gassers on a ST will haul the planes aloft, albeit slow and scale-like.

I can see the value of something like a Pegasus with a montrous motor on it when you want to tow as many planes up as fast as you can. I don't need or want to tow planes up that fast. Can I get by with a smaller engine?
Do
Old 02-19-2002, 02:47 AM
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Ollie
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Default Power Loading

The combined weight of the tow plane and sailplane should result in a power loading of less than about 14 pounds per cubic inch of engine displacement. It's the weight of the sailplane and the lightness of the tow plane rather than sailplane span that count.
Old 02-20-2002, 02:01 AM
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Wyohi
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Default tow plane

OK Ollie lets get exact. In your opnion will a telemaster with a tower 74 on it , swigning a 12 inch prop tow a paragon. My guess both planes together will be less than 12 lbs. Les make it more interesting we will be at 7200 ft up when we start/. Been going to try this for several years just never got my act together.
Old 02-20-2002, 03:53 AM
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Ollie
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Default How much power needed for tow?

At an altitude of 7,200 feet ASL, the Tower 74 will have about as much power as a similar .60 CID engine does at sea level. To minimize the extra thrust required to tow the Paragon, it is necessary to match the speed of the tow plane to the best L/D speed of the Paragon. The Paragon has a best L/D of about 17:1. A 3 pound Paragon only needs about 2.7 ounces of tension in the tow line to maintain altitude at its best L/D airspeed but, a lot more is required to climb. My guess is that it will take some very careful piloting, prop selection and a high nitro fuel for the Telemaster to produce much of a climb rate while towing the Paragon. BTW the air speed to produce a given coefficient of lift at 7200 feet ASL will be about 10% higher than at sea level.
Old 02-20-2002, 01:46 PM
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Wyohi
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Default Towing

OK you have told me what I expected thats why I am a little leary of the project. Now lets look at a lighter plane like a gentle lady everthing the same situation smaller & lighter plane. {easier to rebuild after the crash}. We towed a gentle lady with a astro hog but the guy flying the hog said he couldn't slow down it would stall. It was flopping behind the hog like a dirty dish rag. & all I wanted was off the hook. The telemaster is slow & will stay in the air if it is getting any flow over the wing at all but it is going have to pull fast enough to keep the glider up. Your opinion is appreciated.
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Old 02-20-2002, 03:51 PM
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Default Towing

The problem with towing gliders with much dihedral or polyhedral is that the location of the tow line causes yawing when the glider gets a little out of line. The yawing results in rolling that is hard to control. Worse yet, the tow line induced yaw gets worse as the airspeed increases. Polyhedral ships should be launched piggyback instead of towed.
Old 02-21-2002, 01:18 AM
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Default power for towing

Yep that is what happened. I had a windfree from marks models & sold it who would want a straight wing. Got a bunch of plans have to look thru them.. A Moetery would be too heavy. Had plans for a Malibu . Have to find a light straight wing for just towing won't care how it thermals after as the tow would be the thing.. THANKS Have had the idea to buy a cheep freeflight glider & piggyback it on my telemaster . Have to look into this
Old 02-23-2002, 06:09 AM
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Default How much power needed for tow?

I've tried lots of extremes with aerotowing. Our club had a Telly 40 with an Astro 40 cobalt on 18 cells, that would tow up 3m woodies like my Paragon and my BOT with aplomb. One tow per charge, though.

Once, Bob Marchi pulled me up with his Sr Telly ( wimpy OS60FP), my sailplane was the Rodel 1/4.5 scale ASK21 (165" span, 10.5lb). It was slow-going, but we did it. I came off the tow at about 700 feet, and got a nice, long flight. We had to be very careful, though, to keep everything straight, and all turns had to be shallow and large.

I also got towed up behind Steve Dentz' 1/4 scale Frisch Wilga, with a Brison 6.4 twin. My sailplane this time was the diminuitive Gerasis 2.2m Fox. Yup, it worked! Like a gnat on an elephant's butt. The Wilga didn't even know the Fox was there. I came off tow at about a thousand feet, could barely see the little thing, and landed 19 minutes later. Yeah, I found lift! What fun. We had the Fox on a wheeled take-off cart that time, so as to not have to run the wing tip on the little guy.

Most of our towing is done with Bob Marchi's Pegasus (DA100 power) and Steve Dentz' new Airworld Cmelak (Moki 2.15CID five-cylinder radial power). In most cases, we have to throttle way back for the 4m and under ships, but the 6m (25lb) and 7m (35-40lb) ships need the power, as you might expect.
Old 02-23-2002, 11:42 PM
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GeorgeR
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Default How much power needed for tow?

I have a Telemaster with a Precision Eagle 70 cc alcohol burning motor. The RTF weight of the Telemaster, which is outfitted with dive brakes/flaps, is 17 lbs. I use a Bolly 24 -10 carbon fiber prop and put out around 35 lbs of static thrust. I have towed a variety of sailplanes, the largest around 35 lbs, and it is nice to have the extra power. Mostly I tow my own ASW-27 4M, using another pilot of course, and the tows are ballistic, about 30-45 sec until we speck out. The tow plane is a blast to fly by itself. I have used a variety of motor on this Telemaster, Webra 120, OPS 30cc and ended up liking the current one the best.

George Rada

Ps, Ollie you are right that polyhedral wings are harder to tow. I towed a two meter wood sailplane aloft once. The key was to tow vertically straight up, hehe. I worked great, lot a jaws were hittin the floor there.
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Old 02-24-2002, 01:02 AM
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wjjones
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Default How much power needed for tow?

OK...my original question was whether or not my Sr. Telemaster with a 3w-24 would do the job of towing a 4 meter ASH26.

It looks like Don Bailey (of S&E Modeler fame?) thinks it can be done.

Unless someone else feels I'm making a huge mistake, I'm going to mount the engine and give it a try. Again, I'm not looking to "speck out" the glider in 30 seconds. All I need is the power to safely tow a 4 meter.
Old 02-24-2002, 02:52 AM
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GeorgeR
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Default How much power needed for tow?

I have aerotowed a 4m ASW-27, wt 11 lb., using a Telemaster with a 20cc webra, I can tell you that it can be done. It will take several circuits to get high enough. The 3W 24 gas is about equal to the webra 20cc alcohol motor with the latter combo weighing less.

I hope that answers your original question.

George R.
Old 02-24-2002, 04:31 PM
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Default How much power needed for tow?

wjjjones,

You betcha, that 3W-24 will haul a 4m ship. Don't even worry about it, it'll have enough power. At Yakima last year, we were towing all the 4m ships with a Sr Telly that had a Moki 1.80 in the nose. Plenty enough to get us up there.

See my write up in the June/July 2001 (Vol 6-6) issue of S&EM on towing with an electric-power quarter-scale Sig Cub. It had an Aveox 1817/3Y brushless on 32 cells, and it hauled my quarter-scale Ka8b up (9.5lb) just fine. The climb was slower than with a gassie, but it was plenty enough to get the job done. It was also VERY scale in appearance. Everyone remarked about that.

The notion that you need a nuclear powerplant in the nose to do effective towing is pervasive these days, as everyone tries to out-do everyone. More power is nice when you are doing lots of heavy-duty towing, like at an event, but if it's just for sport, your combination will do just fine.
Old 02-24-2002, 04:54 PM
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Default How much power needed for tow?

Thanks George and Don. I do feel a lot better about that plane and engine combo.

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