Aerotow release question - which servo?

[surfimp]

Hello all, I'm thinking to retrofit an aerotow release into my 1/16 scale Waco CG-4A cargo glider, and I'm trying to decide on an appropriate size servo to use. The plane is small (1.5m wingspan) and relatively light (~50oz. AUW), so I'm thinking I can probably get away with a relatively small servo for this application. I plan to do a simple brass tube & steel rod type release, similar to the type shown on this page (http://www.sailplanes.com/asher.htm) of the Sailplanes Unlimited website.

So, do you all think an HS-81 (36oz. torque) be sufficient for this application? Is it overkill? Could I go with something like an HS-50 or HS-55? I have plenty of room in the boxy nose of my CG-4A so space isn't really an issue, but all the same smaller would be nice.

Thanks for any tips! And yes, I know that 1.5m is quite small for aerotow and all that, but it's what I've got to work with, would be tons of fun to tow, and so it's going to have to do. I'm a reasonably proficient pilot and the plane flies great on the slope (plus it's EPP hehehe).

Steve

[VincentC]

For that size and weight you should have no problem with the Hs-81

[surfimp]

Thanks Vincent, much appreciated!

Steve

[Ben Diss]

I'm not sure I agree. After you build it and install the servo, do a test and make sure it's enough. I've saved many gliders by dumping them the moment they start to get into trouble. I'm sure I saved my tow plane a few times too. If it doesn't work, you're screwed.

Hang your tow plane by the tow line and activate your release. Obviously, have someone assist so they can catch your plane if it works. If the release struggles the least little bit, put a 225 on it and make sure you've got sufficient voltage to the servo.

-Ben

[dgliderguy]

I agree with Ben. Hand testing the release is essential. The most important factor is the friction in the system. I like using a pullwire-over-hole, or pullwire-over-wire hoop, as this has minimal friction. The pullwire must be smooth! No rusty baling wire here. Gotta be polished, shiny, SMOOTH music wire. A pull test is a great way to determine the amount of friction (trust your ability to feel it).

If you've got a low-friction system, then an HS81 ought to be enough for a small 3lb glider. The highest load it will ever see is in a bad cross-up, with the glider dangling beneath the tug like a pinwheel. It happens!

Don Bailey

[surfimp]

Thanks guys! I appreciate it. I was planning to do a pullwire over hole type of release. I will try building it with an HS-81, and if that doesn't work I'll still have room for a larger servo.

Now then, any suggestions for a suitable towplane for a glider this size? Preferably electric? I was thinking a 1/10 scale (60") Pilatus Porter with a brushless motor and lipolys might do the trick ;)

Steve