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#11
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Tow Plane Upsets......
Sounds great to me! In the US, high tow is predominate although low tow is taught.
Our club is one of 2(?) in the US that predominantly use low tow although we also teach high tow. We have tested "going too low" and the towplane still has elevator available whereas going to high runs the towplane out of elevator. If the glider pilot gets way out of position, the time difference is not much between the 2 tow types in my opinion. Not trying to start a "conversation regarding which to use", just noting what we do. This can turn ugly fast, even worse than US contest rules discussions....... PS, lost a friend during tow a couple decades ago while he was towing with a "known squirrel" on the glider end. The towplane was a L19 and went in from about 300' when the glider went too high in front of a couple dozen onlookers. Not sure low tow would have helped. |
#12
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Tow Plane Upsets......
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#13
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Tow Plane Upsets......
On Monday, April 24, 2017 at 3:45:05 PM UTC+3, Chris Rollings wrote:
A large proportion of the tow-plane upsets, including most of the fatals, happen very shortly after take-off, before there is an opportunity to get into low tow. Also, descending into the prop-wash can be a trigger to the momentary loss of control that leads to the upset, if the glider is on a C of G hook. Do these upsets *only* happen with a C of G hook? I've done a fair bit of flying in a C of G hook Janus, including on days with wave and pretty bad rotor. Never had a problem. Does an upset really happen because the glider pilot simply flies out of position? It seems unlikely to me. You need not only to be high but also with significant pull on the rope. All the times I've gotten high it's because the towplane suddenly ran into sink (of at least out of lift), and the result has been a slack rope, not the tight rope required for an upset. Simply maintaining station (even though high) until the slack starts to come out, and then descending back into position with a constant amount of bowing (i.e. low tension but not slack as such). Without having actually been there myself, I suspect that upsets may be caused not by being out of position, but by having a slack rope suddenly come tight. With a C of G hook this causes a reasonably large nose up pitching moment which may not be able to be countered by the elevator. The glider can get significant angle of attack and lift and upwards and (as the angle increases) backwards acceleration. If you're towing at 68 knots (or more) with a stall speed of 40 knots then you can generate 3 G of acceleration. With 3 G of acceleration you've only got to get to 10 degrees nose up to tension the rope to half the glider's weight, 20 degrees nose up to put a full 1 G of force onto the rope, and 30 degrees for 1.5 times the glider's weight in tension. The glider being out of position is most likely the very quick *result* of the glider going into winch launch mode, not the cause of it. I can't see that low tow would make any significant difference to this. Slack being taken out violently (but not quite enough to break the rope) will have exactly the same effect as in high tow. |
#14
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Quote:
Walt |
#15
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Quote:
There will be Tost hooks and release handle modifications post haste on all three of our tugs or I will commence my full retirement. There is NO logical reason why a longer handle cannot be fabricated and installed....FAA or NO FAA. Walt |
#16
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Quote:
Walt |
#17
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Tow Plane Upsets......
Does anybody have actual experience or testing with the McFarlane product that uses a roller bearing instead of a mechanical connection between the latch and the finger? Again - I am looking for actual experience - not opinions.
See: http://www.mcfarlaneaviation.com/new.../march2007.htm ROY |
#18
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Tow Plane Upsets......
"Time to get to low tow"?!?!
You're doing it wrong. Towplane and glider start rolling, glider lifts off and stays a few feet off the ground in ground effect, towplane lifts off and climbs out, when sight picture looks correct, glider starts climbing. The propwash is not really a factor since it has not quite come together yet with normal ropes, maybe felt a bit on rather short ropes. By the time the turbulence has come together, it's over the glider. BTW, I am not an AandP or IA, just an ex CFIG, long time glider pilot with some power time. As to a release with a roller, any roller is better than a sliding surface, although keeping it rolling while operating on grass or dirt may be an issue. On a sliding type release, at least make sure the edges of the hook where it goes into the release are smooth, not mushroomed out. A flat file now and then to smooth it out helps this. Also some lube on release cable guide rollers, inside guide tubes and release pivots helps out a bit. |
#19
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Tow Plane Upsets......
As mentioned elsewhere in the thread, this topic comes up every few years. As I've posted in the past, I actually sat in a lab with John Campbell and built/tested a rig to measure release forces on the Schweizer release mounted on our PA-18 Supercub. We used various towropes, a simple protractor and a strain gauge.
I can't for the life of me find the handwritten notes and mimeographed (!!) handout that we created, but the conclusion is very clear. - It only takes a fairly small amplitude kiting event to load up the Schweizer hook to a point where the release forces are significant. Don't quote me, but I believe the magic angle was less than 20 degrees above the longitudinal axis of the release hook with a relatively low load (100lbs IIRC) - Beyond that point, the pilot in the towplane couldn't apply enough force on the release cable to effect a release. Compounding the problem is the fact that the routing of the release cable drastically reduced the effective force that was applied at the release point (cable bowed and routed around several pulleys). We had a separate version of the release we used for auto tows, and that one had a direct pull with a lever that actually worked under much higher loads. Bottom line is that the towpilot was very unlikely to be able to release once the glider got significantly outside of normal tow envelope. Erik Mann (P3) On Sunday, April 23, 2017 at 8:43:12 PM UTC-4, Walt Connelly wrote: I have been towing for about two and a half years and have logged over 6,500 tows. Having recently experienced a couple of rather violent glider kiting incidents, one at about 300 feet AGL I decided to investigate the experiences of other tow pilots in these circumstances. I have spent several hours reading posts about gliders kiting and upsetting the tow plane, many of the posts deal with creating an automatic release that will recognize the actions of the glider and release without input from the tow pilot. Nice idea, some really creative approaches and the bottom line is anything can be done if you have enough money and can get the FAA to buy into it and give approval. Lots of opinions and ideas as to why these things happen. Bottom line is that they do happen, they have resulted in loss of tow pilot lives and the causes are well known. Of my two most recent experiences one was with a 67 year old licensed private pilot, glider only, no other pilot ratings who at 2000 feet tried to release, “slipped back in the seat pulling back on the stick and going vertical.” I took a stab at the release to no avail, the pressure was too great and I soon found myself at about 75 degrees nose down at full power. The natural instinct at this point is to pull back the power and try again to release. He managed to release before I could try for a second time and I recovered. If this has to happen to you, 2000 feet is a good place to be. My understanding is that this was his first tow in more than a year. Something to think about. My second experience in the same week was with a 15 year old student on her 3rd solo pattern tow. At about 250 to 300 feet I started a turn from the downwind drift to the right. I felt a tug on my tail pulling my nose to the left. After a few seconds I tried again to turn to the right knowing that she was behind me to the right. Could not see her, no mirror on the right. (much easier if she was a little to the left) The second time the pull of my tail to the right and nose to the left was a bit more violent…..followed by a very hard tug of my tail UP and to the right. We could not have been much more than 300 feet when I found myself nose down and trying to release….again the pressure was too much to overcome and I needed to retard the throttle. Before I could make a second attempt at release I heard a loud BANG as the rope broke, I regained control and recovered just above the trees. (glad that I had made a pit stop before I started towing). She made it back to the field and didn’t seem at all concerned……I shall withhold my comments at this point. I had to straighten out the Schweizer hook which was off to the right about 30 degrees before I could make the last 8 tows of the day. While I have concerns with both of these pilots my major concern is that the difficulty of actuating the release when the glider kites is well documented. To make matters worse, the release in the tug I was flying, although a bit more manually accessible than the other two I fly requires that the pilot pull it back and push down to fully actuate the release. Not an easy thing to do under the circumstances. The other two release handles are down on the floor to the left and for someone of my height, sitting on a cushion and trying to grab the release is very difficult. It would seem to me that an easy fix would be to simply make a longer handle curved up so one could both see and feel for it in an emergency. A longer handle would also provide a bit more mechanical advantage although having read many of the posts I am not sure this would overcome the pressure on the Schweizer hook. Of course I hear all the noise about needing to apply for a 337 and get FAA approval….next I will need approval to put a cushion on the seat or to have an inspection after washing the airplane. So, the fixes appear to be going to a Tost hook or inverting the Schweizer hook which I understand can be done with an available STC. In my case I would also like to see a more accessible release handle…would (or should) an STC be required for this? This would be the short term fix I would like to see. If the handle was made from the same stock as the current device, just a foot or so longer it would seem that this should be able to be done without a long drawn out approval process. I love flying, enjoy the gliderport environment and people but I am NOT willing to give up my life. When the glider kites things happen very fast. Unless your hand is on the handle (not feasible in my circumstances) you will not be able to release before the pressure gets too great. If it happens much lower than I experience it will be lights out. So remember my glider pilot friends….fly well….the life you save might be your tow pilot. Walt Connelly -- Walt Connelly |
#20
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Quote:
Walt |
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