Fatal Towplane Accident 5-9-20

An artificial horizon and electric guillotine is a complex solution. Is the tow rope at a sufficient angle in these situations to simply position a sharp knife above the rope such that it cuts itself if the angle is too high? Surely that has been thought of and rejected for good reasons?


I'd been thinking along the same line. I don't think it's quite that simple though. No matter how sharp the blade, it won't cut a line that is merely kissing against it. The blade needs to be hot enough to melt through the line or actively sawing. And, obviously it has to all happen very quickly..

How about this: Imagine two permanent magnets (strong magnets) that when joined together create a magnetic junction in the tow line just a bit aft of the tugs two hook. Similar to the knife blade idea, a horizontal bar is mounted off the back of the tow plane above the tow rope such that when the rope raises to a critical angle, the bar presses along the alignment between the two magnets. The relatively small orthogonal force exerted at the magnetic juncture will have a leverage effect to pry the magnets enough to break the magnetic circuit. To improve and optimize the leverage action on the magnets, each may have an attached bar of defined length that is rigidly affixed such the tow line attachment point is positioned at the distal end of these leverage bars. In fact, the tug side's lever bar may have a ring at the end to be attached directly to the tug's tow release. The tug will be instantly freed predicated on the existence of a strong enough pull on the line above the critical angle of bar contact.

On Thursday, May 14, 2020 at 12:28:22 PM UTC-7, Steve Koerner wrote:
An artificial horizon and electric guillotine is a complex solution. Is the tow rope at a sufficient angle in these situations to simply position a sharp knife above the rope such that it cuts itself if the angle is too high? Surely that has been thought of and rejected for good reasons?


I'd been thinking along the same line. I don't think it's quite that simple though. No matter how sharp the blade, it won't cut a line that is merely kissing against it. The blade needs to be hot enough to melt through the line or actively sawing. And, obviously it has to all happen very quickly.

How about this: Imagine two permanent magnets (strong magnets) that when joined together create a magnetic junction in the tow line just a bit aft of the tugs two hook. Similar to the knife blade idea, a horizontal bar is mounted off the back of the tow plane above the tow rope such that when the rope raises to a critical angle, the bar presses along the alignment between the two magnets. The relatively small orthogonal force exerted at the magnetic juncture will have a leverage effect to pry the magnets enough to break the magnetic circuit. To improve and optimize the leverage action on the magnets, each may have an attached bar of defined length that is rigidly affixed such the tow line attachment point is positioned at the distal end of these leverage bars. In fact, the tug side's lever bar may have a ring at the end to be attached directly to the tug's tow release. The tug will be instantly freed predicated on the existence of a strong enough pull on the line above the critical angle of bar contact.

Perhaps simpler and smaller than the magnetic method would be to instead incorporate a metal weak link analogous to a Tost weak link used on winch tows. In this case, the link is designed to bust specifically by leverage action across the weak link junction. There will be leverage bars on both sides of this angular weak link. The fulcrum of action could comprise two annular elements with the weak link element joining the two sides in the center of the annular elements. As with the magnetic case, a bar above the line imparts an orthogonal force that results in a powerful leverage action that busts the weak link when the combination of line angle and pull force exceeds the intended critical threshold.

Has anyone investigated placing the tow hook directly over(or under) the tow planes center of gravity? This would keep the out of position glider from yanking the tow planes tail out of acceptable limits? The RC tow ships, I have seen, place the tow hook over the towing ships CG.
My 2 cents,
JJ

seen, place the tow hook over the towing ships CG.
My 2 cents,
JJ

Mic drop?

Clever concept. Would the release have to be precisely at the CG/CM? If for example it were above the CG/CM point, then would the tow pilot have to apply constant down elevator to overcome the asymmetric leverage caused by the glider's drag? Would the glider pilot be much busier trying to fly in line with the longitudinal axis of the tug?

The moment arm up (or down), from the tow ships CG to a tow hook directly above, would be quite short....... not much more than say 4 feet. I would think correcting for pressures applied at 48� would be well within flight controls to compensate. Constant back pressure could be trimmed out. In the RC world, the tow ships are normally quite stable, as is Glider..........problems arise when too much pilot input is applied on either end of the rope! Guide wires from the top of the rudder fin to the tip of both stabilizer tips could keep the tow rope away from the tows tail feathers.
Just thinking outside the box,
JJ

Has anyone investigated placing the tow hook directly over(or under) the tow planes center of gravity?

I'm trying to envision what that would look like. To be at the CG, there would have to be as much behind and below and ahead and above. How would you rig this without hitting the tail on low or high tow?

Maybe 'over' the CG would eliminate above and below, but still don't see how.

Not seeing how, does not mean there isn't a way, so how do the RC folks do it?

Might have to rig a yolk-type system like the old Blanik L-13 yolk, but installed on the tug end. Model it using a toy Piper Pawnee; tie a string around the outboard strut wing attachment points on both sides (close enough to the CG). Tie the two strings together with a ring in a "Y" well beyond the tail feathers. Attach the tow rope to the ring and voila! If the glider climbs above the Pawnee, the yolk just pivots through the CG, avoiding a tail pull-up.

I thought through the hard stuff, you solve the little details.

I thought through the hard stuff, you solve the little details

Cadd drawings of CG-yolk attachment to discourage tail-lifting by kiting glider.

https://www.dropbox.com/sh/rjcl6hugl...rTU8p2W5a?dl=0

It has been done in Germany during WWII with military gliders. It was called "Hubschlepp". It was tested with a DFS 230 transport glider and a Junkers Ju 87 B-1 as a towplane. The system was very stable, only one of the two pilots had to steer his plane, the other just followed. Climb rate was roughly double that of the normal tow: 5–7 m/s against 2–3 m/s. Service ceiling, autonomy and maximum speed increased also.

https://de.wikipedia.org/wiki/Flugze...epp#Hubschlepp (in German)
See also: Ernst Peter: Der Flugzeugschlepp von den Anfängen bis heute. Motorbuch Verlag Stuttgart, 1981.

How about banning all sideways/aft opening canopies from gliders? An unlocked canopy is a non-event in my LS6 with it's forward hinged canopy. Grobs? Deathtraps!

Or, just ban all canopies, period. Open cockpits are much more relaxing, and there is one less thing to mess up prior to takeoff.

OR, we could switch to using helicopters to aerotow...just put a CG hook on the TOP of the glider, lift vertically to 3000', and cut'em loose. Yee Haw! With a Chinook you could even daisy-chain several gliders and take up the whole club at once - just make sure you release from the bottom up...

Seriously:

1. Replace ALL Schweizer tow hooks with TOST releases (or equivalent) with the release lever close to the throttle. This is a no-brainer.

2. DO NOT TOLERATE ANY out of position/out of view flying by ANY glider pilot. At a minimum, talk to them after a flight with an "incident"; worse case, hand them the rope as soon as they get out of position (within gliding range of the field, of course, if possible).

Kirk
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