Ground launches and weak links

All,

After some research I came to a conclusion that in the USA, there is
no legal requirement to use a weak link during a ground launch,
regardless of the rope/wire strength.

First question: Am I missing something? Is there something like a
ground launch version of 14 CFR 91.309?

Second question: If the glider's POH does not offer any guidance (say,
1-26), what would be an appropriate range of rope breaking strength?

Thanks!
Bart

At 05:28 03 December 2012, Bart wrote:
All,

After some research I came to a conclusion that in the USA, there is
no legal requirement to use a weak link during a ground launch,
regardless of the rope/wire strength.

First question: Am I missing something? Is there something like a
ground launch version of 14 CFR 91.309?

Second question: If the glider's POH does not offer any guidance (say,
1-26), what would be an appropriate range of rope breaking strength?

Thanks!
Bart


I'm sure there is.
It's a long time since I read it but I'm certain it was a fundamental back
in the day and it is probably still applicable...... try Googling 'Darwin'

It doesn't include old US types but here is a link to the BGA
recommended weak link strengths.

http://www.gliding.co.uk/bgainfo/tec...eets/weaklinks.
pdf

John Galloway


At 05:28 03 December 2012, Bart wrote:
All,

After some research I came to a conclusion that in the USA,
there is
no legal requirement to use a weak link during a ground launch,
regardless of the rope/wire strength.

First question: Am I missing something? Is there something like
a
ground launch version of 14 CFR 91.309?

Second question: If the glider's POH does not offer any
guidance (say,
1-26), what would be an appropriate range of rope breaking
strength?

Thanks!
Bart

On Sunday, December 2, 2012 10:28:45 PM UTC-7, Bart wrote:
All,



After some research I came to a conclusion that in the USA, there is

no legal requirement to use a weak link during a ground launch,

regardless of the rope/wire strength.



First question: Am I missing something? Is there something like a

ground launch version of 14 CFR 91.309?



Second question: If the glider's POH does not offer any guidance (say,

1-26), what would be an appropriate range of rope breaking strength?



Thanks!

Bart

Actually, there is a legal framework of sorts. Look at 91.9 which requires you to operate all aircraft in compliance with their POH/AFM. AFAIK, all gliders except Schweizer will have a weak link specified for ground launch in their POH/AFM. 91.9 requires you to use the POH weak link. OTOH, 91.309 exclusively applies to aero tow.

The problem is with Schweizer who never bothered to publish weak link strengths for ground launch. In fact, ground launch in general seemed to greatly confuse them. For example, the 2-33 posits the winch launch redline (Vw)as HIGHER than the maneuvering speed (Va). While I believe Schweizer knew how to calculate Va correctly, the 2-33's published Vw is pure fiction. This doesn't make me feel good about any Schweizer Vw number.

Vw is normally set at 70 - 80% of the maneuvering speed which makes a great deal of structural/aerodynamic sense. With this as a guide, the 2-33's Vw should be 44 - 50mph which would be impossibly slow for a safe launch. The bottom line is if you thinking of winch launching a Schweizer, you're a test pilot.

Vw is normally set at 70 - 80% of the maneuvering speed which makes a great deal of structural/aerodynamic sense. *With this as a guide, the 2-33's Vw should be 44 - 50mph which would be impossibly slow for a safe launch. *The bottom line is if you thinking of winch launching a Schweizer, you're a test pilot.- Hide quoted text -

- Show quoted text -

I disagree with the last portion. Va can be approiximated by the
SQRT(N) * stall speed. N or load factor, might be as determined by
utlity category (4.4) limit load, or gust load factor, typically north
of 5gs as specified by the BGCDH of 1962 or much later by JAR22.

"sorta" CG hooks are/were made for the 2-33 and 1-26, so they have
been test flown. Winching with a nose hook is not likely to enable
significant loads before stalling the tail, so I can see why Vg might
be higher than Va in some cases. Les at K&L would be best to answer
this question.

aerodyne

On Monday, December 3, 2012 12:22:50 PM UTC-7, aerodyne wrote:
Vw is normally set at 70 - 80% of the maneuvering speed which makes a great deal of structural/aerodynamic sense. *With this as a guide, the 2-33's Vw should be 44 - 50mph which would be impossibly slow for a safe launch. *The bottom line is if you thinking of winch launching a Schweizer, you're a test pilot.- Hide quoted text -



- Show quoted text -



I disagree with the last portion. Va can be approiximated by the

SQRT(N) * stall speed. N or load factor, might be as determined by

utlity category (4.4) limit load, or gust load factor, typically north

of 5gs as specified by the BGCDH of 1962 or much later by JAR22.



"sorta" CG hooks are/were made for the 2-33 and 1-26, so they have

been test flown. Winching with a nose hook is not likely to enable

significant loads before stalling the tail, so I can see why Vg might

be higher than Va in some cases. Les at K&L would be best to answer

this question.



aerodyne

OK, I hear you. But, these gliders sometimes require full back stick in a winch launch which is prohibited at airspeeds above Va even without the large winch launch loads. With up to 1000 pounds-force applied to the hook in a downward direction, flying them faster than Va seems insanely dangerous. I still think a reasonable 2-33 Vw would be less than 50 knots which makes them impractical for winch launch.

Yes, they were flight tested but I think it went this way. "Gee, we need up to 65 mph to get a decent launch while staying safely above the loaded stall speed so lets set the winch red line at 69." Thus ignoring maneuvering speed which is 65mph. Ref: http://www.harrishillsoaring.org/doc/sgs2-33manual.pdf

I love winch launch but I'm putting my marker down on this one because I expect a 2-33 wing failure probably sooner than later.

On Monday, December 3, 2012 3:00:07 PM UTC-6, Bill D wrote:
On Monday, December 3, 2012 12:22:50 PM UTC-7, aerodyne wrote: Vw is normally set at 70 - 80% of the maneuvering speed which makes a great deal of structural/aerodynamic sense. *With this as a guide, the 2-33's Vw should be 44 - 50mph which would be impossibly slow for a safe launch. *The bottom line is if you thinking of winch launching a Schweizer, you're a test pilot.- Hide quoted text - - Show quoted text - I disagree with the last portion. Va can be approiximated by the SQRT(N) * stall speed. N or load factor, might be as determined by utlity category (4.4) limit load, or gust load factor, typically north of 5gs as specified by the BGCDH of 1962 or much later by JAR22. "sorta" CG hooks are/were made for the 2-33 and 1-26, so they have been test flown. Winching with a nose hook is not likely to enable significant loads before stalling the tail, so I can see why Vg might be higher than Va in some cases. Les at K&L would be best to answer this question. aerodyne OK, I hear you. But, these gliders sometimes require full back stick in a winch launch which is prohibited at airspeeds above Va even without the large winch launch loads. With up to 1000 pounds-force applied to the hook in a downward direction, flying them faster than Va seems insanely dangerous.. I still think a reasonable 2-33 Vw would be less than 50 knots which makes them impractical for winch launch. Yes, they were flight tested but I think it went this way. "Gee, we need up to 65 mph to get a decent launch while staying safely above the loaded stall speed so lets set the winch red line at 69." Thus ignoring maneuvering speed which is 65mph. Ref: http://www.harrishillsoaring.org/doc/sgs2-33manual.pdf I love winch launch but I'm putting my marker down on this one because I expect a 2-33 wing failure probably sooner than later.

that manual says:

Speed to begin manuevering with Caution - 65 MPH

If you look at the following V-n diagram, what we would traditionally consider Va actually occurs at a bit over 70 mph. It isn't immediately clear to me but i'm guessing that chart is based on max gross weight.

the manual also says "Winch or Auto towing can produce high loads, but if the auto-winch placard speed is observed, this will be within safe limits. The best ground launch climb is achieved at speeds well below placard limits"

there are many 2-XX's out there with LOTS of ground launches. I think that if they really had mis calculated it there already would've been a wing failure.

For those operations who are ground launching their 2-33, what weak link are you using.

The Canadian Air Cadet manual for winch and auto launch of 2-33's specifies the weak link should be 2 x max gross weight and this gives 2080 lbs.

We recently winch launched a 2-33 at a neighbouring club and used a 1925 lb rope for the weak link.

For a 1-26, I would use the same (2x) rule of thumb.

With the weak link at this level, you can not put more than 2g on the airframe.

On Monday, December 3, 2012 5:12:22 PM UTC-7, Dave Springford wrote:
The Canadian Air Cadet manual for winch and auto launch of 2-33's specifies the weak link should be 2 x max gross weight and this gives 2080 lbs.



We recently winch launched a 2-33 at a neighbouring club and used a 1925 lb rope for the weak link.



For a 1-26, I would use the same (2x) rule of thumb.



With the weak link at this level, you can not put more than 2g on the airframe.

I feel a cold knot forming in my gut. A 1925 Lb-F weak link can put far more than 2G on the airframe. PLEASE read some winch launch guidance.