Actual Rope Break

On Monday, June 2, 2014 4:08:14 PM UTC-5, Bill D wrote:
"I know someone will point out that a Schweizer hook is limited to 1,200 Lbs-F so it's impossible to comply with 91.9 and 91.309 using this hook. Yep, that's what it means. It IS possible to comply using the Tost tow plane hook."

Only flaw in that logic, Bill, is that the HOOK may be approved for that load, but the AIRPLANE it is attached to may NOT be approved for that load. Sort of like how on that old TV show "The Six Million Dollar Man", he could pick up the multi-thousand pound rock with his bionic arm, but they ignored the fact that his still human spine couldn't take the load and he would have been crushed.

I agree with you 100% that there are better things out there than Schweizer tow hitches. But, you can't suddenly legally pull 2000 lbs on the back end of your Cessna or Piper just because your tow hitch is now good for that much load. You have to know where the weakest link is, and either not exceed its limit, or you must increase the strength of it.

As to reliability, I have never known a Schwiezer release to let go of the still intact ring because the ring was worn. I have known of worn Schweizer releases releasing without pilot command, just like a Tost can do if the ring is worn, possibly beyond its allowed limits. So, neither one is perfect. If you have a choice as to which you want to use, make your decision and be willing to listen to the opinions of others.

Interesting that this thread is called "Actual Rope Break" when the rope in question doesn't appear to have broken? :-) We now return to our regularly scheduled programming...

Steve Leonard

On Tuesday, June 3, 2014 8:01:50 AM UTC-6, Steve Leonard wrote:
On Monday, June 2, 2014 4:08:14 PM UTC-5, Bill D wrote:

"I know someone will point out that a Schweizer hook is limited to 1,200 Lbs-F so it's impossible to comply with 91.9 and 91.309 using this hook. Yep, that's what it means. It IS possible to comply using the Tost tow plane hook."



Only flaw in that logic, Bill, is that the HOOK may be approved for that load, but the AIRPLANE it is attached to may NOT be approved for that load. Sort of like how on that old TV show "The Six Million Dollar Man", he could pick up the multi-thousand pound rock with his bionic arm, but they ignored the fact that his still human spine couldn't take the load and he would have been crushed.



I agree with you 100% that there are better things out there than Schweizer tow hitches. But, you can't suddenly legally pull 2000 lbs on the back end of your Cessna or Piper just because your tow hitch is now good for that much load. You have to know where the weakest link is, and either not exceed its limit, or you must increase the strength of it.



As to reliability, I have never known a Schwiezer release to let go of the still intact ring because the ring was worn. I have known of worn Schweizer releases releasing without pilot command, just like a Tost can do if the ring is worn, possibly beyond its allowed limits. So, neither one is perfect. If you have a choice as to which you want to use, make your decision and be willing to listen to the opinions of others.



Interesting that this thread is called "Actual Rope Break" when the rope in question doesn't appear to have broken? :-) We now return to our regularly scheduled programming...



Steve Leonard

Steve, you have a point. My defense is that the installation of a Tost tow plane hook requires an STC which, one presumes, would take aircraft structure into consideration. The Tost Hook itself is approved for 2,570 Lbs-F. If the aircraft structure is weaker, the STC should state a lower limit.

Most composite 2-seater flight manuals (Grob 103, ASK-21 etc...) call out a 600 daN blue weak link for aero tow so the tow plane link would be a red 750 daN link (1,686 Lbs-F) That's more than a Schweizer hook could take but much less than the Tost.

On Tuesday, June 3, 2014 8:01:50 AM UTC-6, Steve Leonard wrote:
On Monday, June 2, 2014 4:08:14 PM UTC-5, Bill D wrote:

"I know someone will point out that a Schweizer hook is limited to 1,200 Lbs-F so it's impossible to comply with 91.9 and 91.309 using this hook. Yep, that's what it means. It IS possible to comply using the Tost tow plane hook."



Only flaw in that logic, Bill, is that the HOOK may be approved for that load, but the AIRPLANE it is attached to may NOT be approved for that load. Sort of like how on that old TV show "The Six Million Dollar Man", he could pick up the multi-thousand pound rock with his bionic arm, but they ignored the fact that his still human spine couldn't take the load and he would have been crushed.



I agree with you 100% that there are better things out there than Schweizer tow hitches. But, you can't suddenly legally pull 2000 lbs on the back end of your Cessna or Piper just because your tow hitch is now good for that much load. You have to know where the weakest link is, and either not exceed its limit, or you must increase the strength of it.



As to reliability, I have never known a Schwiezer release to let go of the still intact ring because the ring was worn. I have known of worn Schweizer releases releasing without pilot command, just like a Tost can do if the ring is worn, possibly beyond its allowed limits. So, neither one is perfect. If you have a choice as to which you want to use, make your decision and be willing to listen to the opinions of others.



Interesting that this thread is called "Actual Rope Break" when the rope in question doesn't appear to have broken? :-) We now return to our regularly scheduled programming...



Steve Leonard

Thinking about this a bit more, a bigger problem is tow planes which are only approved for use with the Schweizer hook. Ex: Cessna 182's. Technically, they are only legal when towing gliders with a 965 Lb-F (439 daN) or less weak link which would exclude composite 2-seaters. FAR 91.9 trumps FAR 91.309 if the glider's Approved flight Manual contains an aero tow weak link specification.