Author Topic: Aerotow : How to ?  (Read 3151 times)

Nhalyn

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Aerotow : How to ?
« on: July 27, 2016, 13:31:51 PM »
How to perform aerotowing?
Please find here my contribution about aero towing… A short “how to”, certainly not exhaustive, but a good help for beginners, I hope…
1.   The glider:
All gliders can be aero towed, some more easily than others, but it’s always feasible.
1.1.   Two axes:
The two axis rudder/elevator are the worst ones because they are too stable and as they are over speeded during towing they only do waves downside the cable… It feasible when the tow plane fly at nearly the same speed as the natural speed of the glider, just a little over for cable tension purpose. Strangely, it’s not for pure beginners…
The two axis aileron/elevator gliders are way easier and will be considered here after as the three axis gliders.
1.2.   Three axes:
All three axes glider can be aero towed, whatever the “shape” of the glider. It can be classical, duck style, flying wing, PSS, old style, modern F3B, etc… The important points are:
-   The position of the cable hook
-   The speed during aero towing
Let’s have a look at these points….
1.3.   The hook:
Position? In the nose! More seriously, the position of the hook is not that important, you don’t need to be mandatory on the far nose end in the axis.
Sometimes it’s not the best place to have an easy towing. For example, the scale 1/1 Fox glider has its tow hook below the fuselage at middle length from nose to the wing leading edge. It’s the best place to put this heavy and speedy glider at the right angle of attack and position behind the tow plane. That’s an important thing to think…
For most of the gliders, the best place is the nose, in the axis. In this case, you need a tow hook glued in the nose wood block or fiberglass fuselage. Think to the actuating rod and to the nose lead…
A very good second solution for a very simple tow hook is to simply machining a guide slot on the fuselage flank or below the nose some few centimeters or inches from the nose end. The non-axial position of the hook for only few centimeters or an inch is barely unnoticeable for 99% of pilots…
This slot is just to pass through the tow cable. Inside the fuselage, a simple piano wire coming from the hook servo close or open the slot, letting the cable slip around when it’s close. The piano wire should be not too big in order it can cut the fuse cable if stress is too high.
Always put the best servo you have for the tow hook! It’s mandatory that the hook should always open on order! A good test, put a cable inside the hook, applies a traction equivalent to the full weight of the glider, and releases the cable via the transmitter. It should release directly.
1.4.   Speed during aero towing:
This point is most important, and is solved by a good communication between the two pilots, glider and tow plane. Too slow, it’s evident, will cause problems of controllability, stalling, etc., for both glider and plane. Too much speed is also a problem as glider will overreact and can be quickly overstressed. The correct speed is always in the upper range of your glider one’s, so keep it in mind when moving the sticks.
Some gliders have a wide speed range and are the easiest to aerotow. “Problems” comes when your glider has a narrow speed range, aka vintages, flying wing, old scale gliders, beginner’s gliders…
The solution to control speed is not the power setting of the tow plane but the angle of climbing. It’s not easy and even dangerous for the plane to tow with half power of changing power setting during climbing (this aims to high secondary effect, loss of controls, etc.). The best solution is to keep the usual power (most of time maximum!) and to climb with a high angle to keep speed slow. If this angle is too high for the style of your glider, change the tow plane for a less powered one!
2.   The tow plane:
The tow plane has to be a simple plane, with a good reliability, well known by the pilot. It has to be very stable and simple to fly. Tuning of the controls should be smooth to achieve that point. Lots of plane can be tow planes. Remember it has to fly smooth trajectory and to do 20 landings a day…
3.   The cable:
The important thing is that the cable should not be an elastic one… It’s very difficult when there is some tension variation… Check the forums and experienced guys to find some suppliers.
Cable should have some fuse at each end. The glider side one should be weakest in order to break first, and then the tow plane come back with the cable, put a new fuse, and try again… Use nylon cable from fishermen’s.
Cable length is another important parameter. The longer the cable is, the easiest it is.
-   Up to 2 meters span glider, use a 15 to 20 meters long cable
-   Standard cable length see on fields is 25 meters, for every gliders up to 6 meters span
-   Over 6 meters span glider, use a 30 meters long cable
4.   How to do?
4.1.   Take off:
Ask somebody to maintain the glider leveled horizontal. Maintain it by the trailing edge with just two fingers. It has to be able to escape from his hand without resistance.
Cable in line and tensed, tow plane goes to full power in a short time and keep the axis.
Your only work in the first few meters is to keep the wing horizontal!
Use ailerons mostly and in priority.
After a very short time your glider should take off by itself, or with a little help of elevator. Don’t try to climb, only put your glider at 5 to 10 feet altitude and wait for the tow plane to take off and climb. The glider should always take off first.
If you take off from a dolly, you have nearly no work. Just take off and go up to avoid the dolly to shock your glider. I don’t like dolly, it’s only for special gliders with no wheel or skid that can’t take incidence on ground, or with wing too narrow of the ground (no dihedral, low fuselage, low wing…). There is a high risk than the dolly bounces and hit your glider or tailplane, and after your take off it needs somebody to run after it on the runway.
4.2.   Position:
During the entire climb, the pilot works is to maintain its position behind the tow plane.
The good position for the glider is in the axis of the tow plane, a few feet upside of it on the trajectory, whatever the climb angle. Never under, but not too much high…
Always use smooth and moderates orders on the sticks!
4.2.1.   Vertical position:
Use your elevator to reach the good vertical position and maintain the order to keep that position. For slower glider it’s not unusual to maintain a bit of down elevator.  If you feel it’s too much or if speed is too much, asks the tow plane to climb more. If you can’t reach the upper position, ask the tow plane to climb less before you stall.
4.2.2.   Lateral position:
Use mainly your ailerons to stay in axis with the tow plane trajectory.
Keep your wings horizontal or parallel to the tow plane. The glider will automatically line up with the cable by itself.
If not lined up and if you know which side to go, use only 5 to 10 degrees banking, no more, then go back to horizontal before your reach the axis.
4.3.   Turning:
The tow plane will take a smooth turn. Have an eye on the plane, an eye on your glider.
Apply ailerons only to reach half the banking of the tow plane (and keep the vertical position with elevator).
That’s the secret!
By doing this, the cable will always stay taut, your glider will take a smooth turn, and you will need very few orders.
When the tow plane goes out the turn, simply apply ailerons to go back horizontal or parallel to tow plane’s wings.
Never go inside the tow plane turn!
4.4.   Release the cable:
On your transmitter, release the cable, without prevent to tow plane pilot. Apply a smooth aileron order to quit the tow plane flight axis smoothly.
If the cable is released, you will see a smooth turn and can confirm a positive release to the tow plane pilot, which will also see it. He can now break and go down.
If the cable is not released, your glider will react and go back to the axis of the plane. You now have a problem! Most of time your tow servo is not strong enough or you are way off the flight axis…
Try again the same action, maybe ask the tow plane to slow down a little in order to reduce the cable tension. Check a positive release, confirm to the tow plane pilot, and enhance you tow hook!
5.   Conclusion:
Try it! In fact it’s simple and everybody can do it. The most part of the work is for the tow plane pilot. If he is working well, you glider pilot will have nearly nothing to do, just steer the course! 8)
Last tip: whatever something goes wrong or out of control, release the cable immediately, glide back, and try again. Don’t wait for the crash. ;)
"Flying is just the time between take-off and crash"

Fred

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Re: Aerotow : How to ?
« Reply #1 on: August 02, 2016, 09:20:28 AM »
Very Good Nhalyn! Thanks for taking the time.

And I put it as a sticky  :)
Education is important, but flying RC planes and gliders is importanter!

Nhalyn

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Re: Aerotow : How to ?
« Reply #2 on: August 02, 2016, 10:43:09 AM »
Thanks...
That's my gift as a newby here...  ;)
"Flying is just the time between take-off and crash"