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Tow line attachment point?

earthsciteach

Moderator
Moderator
#1
Random question in my brain at the moment - where should a tow line be attached to a tow plane for pulling sailplanes to altitude? Behind the CG is pretty obvious. Should it be attached to the back end of the fuselage, or more forward on the belly?

Thanks!
 

pgerts

Old age member
Mentor
#2
Top of the wing - close to CG is one way.
Try to find the manual for the Multiplex Mentor - MPX is one of the oldest model plane companies with a lot of experience and 1st class models.. The Mentor is prepared to tow.
The sailplane should always fly higher than the towplane.

In full scale the tow line is normally fastened at the rear of the towing plane.

If the towing plane is really strong you can tow the sailplane as an ancor straight up but that is not beautiful.
http://scalesoaring.co.uk/
 
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earthsciteach

Moderator
Moderator
#3
Thank you, pgerts! I am surprised the tow line doesn't interfere with the tail and rudder on the tow plane.

I have been thinking of rigging up a tow line on my Super Cub for a while. I've sketched out a Red Tail Hawk glider, similar to the Alula, to tow up and get footage of hawk attacks. I don't want a motor or any sharp surfaces, such as a prop, to harm the hawk. I'll have to come up with a clever way to conceal and protect control rods.
 

pgerts

Old age member
Mentor
#4
A thin wire or nylon string can be fastened from the top of the rudder to the ends of the stab if the tow line comes by it will glide off. You will see it if you are searching the tube for glider towing.
Why not using an electric motorglider with folding prop. It it almost silent and the prop is not going to harm when it is folded. But that is not what you want if you are trying to get attacked. Gliders don't normally have any control rods or horns you can see. They are small and hidden to get the smallest amount of air disturbance.
The HK http://www.hobbyking.com/hobbyking/store/__6998__Servo_Covers.html is much to "bulky" compared to the paper thin fiber glass push rod covering from the servo all the way to the control horn protruding just 1/8" from the control surface.
 

earthsciteach

Moderator
Moderator
#5
I will probably put a motor on eventually. I just want to play around with towing it and releasing. Any thoughts on the proper length for the tow line?
 

pgerts

Old age member
Mentor
#7
I will probably put a motor on eventually. I just want to play around with towing it and releasing. Any thoughts on the proper length for the tow line?
See if you can translate this http://www.svensktmodellflyg.se/for...193423&page=1&CurrentMainTopic=4&replypage=99

Some hints and a very smart way to tow and release the glider without any extra servo in the glider.
30 meter line - hook and strap to attach the glider - full up with the glider to release from the hooks.
 

earthsciteach

Moderator
Moderator
#8
Too many variables at once!

x=attachment point of tow cable to Super Cub
y=method of attachment to Super Cub
z=length of tow cable
r=release mechanism
t=method utilized to prevent tow cable from wrapping around tail
a=my ability to fly the tow plane with no previous experience
b=my friend's ability to fly the yet untested RC modified chuck glider with no previous experience
N=any number of unforseen problems that may occur.

Chance of an unsuccessful flight for either aircraft = N/(x+y+z+t)a^b+(z*r)b^a

As the equation approaches 1, the probability for success approaches zero.

Simple as that!
 

Ak Flyer

Fly the wings off
Mentor
#13
The tow line needs to be attached close to the wing or you will lose the effectiveness of the rudder and elevator on the tow plane. The wing is the pivot point and all the control is gained by pushing the tail around. If you are pulling it straight back all the time you are limiting the tails effectiveness. This could result in a difficult time flying or even a crash.

The new UMX Carbon Cub with the built in tow point has it up behind the wing as well.