Maximum allowable forces on nose and CG hooks

Is there a general rule of thumb for the maximum design forces for hooks? And is the nose hook spec'ed for more than the CG hook?

I'm assuming the design load is mostly driven by the fuselage/hook connection, the hooks themselves are rated to as much as 14kN.

On Thursday, June 4, 2020 at 9:31:34 AM UTC-4, Kenz Dale wrote:
Is there a general rule of thumb for the maximum design forces for hooks? And is the nose hook spec'ed for more than the CG hook?

I'm assuming the design load is mostly driven by the fuselage/hook connection, the hooks themselves are rated to as much as 14kN.

The bible for this is CS-22 BOOK 1 Subpart C – Structure. If you're interested in things like this, use your favourite search engine for "CS-22_Amendment 1 revised.pdf" and it's all there. Quick download which cures insomnia...

"CS 22.585 Strength of launching hook attachment
(a) The launching hook attachment must be designed to carry a limit load of 1·5 Qnom, as defined in CS 22.581(b), acting in the directions specified in CS 22.581 [ed.-airtow conditions] and CS 22.583 [ed.-winch conditions].

(b) The launching hook attachment must be designed to carry a limit load equal to the maximum weight of the sailplane, acting at an angle of 90° to the plane of symmetry."

"CS 22.581 Aerotowing
(a) The sailplane must be initially assumed to be in stabilized level flight at speed VT with a cable load acting at the launching hook in the following directions:
(1) horizontally forwards;
(2) in plane of symmetry forwards and upwards at an angle of 20° with the horizontal;
(3) in plane of symmetry forwards and downwards at an angle of 40° with the horizontal; and
(4) horizontally forwards and sidewards at an angle of 30° with the plane of symmetry.
(b) With the sailplane initially assumed to be subjected to the same conditions as specified in CS 22.581 (a), the cable load due to surging suddenly increases to Qnom, assuming the use of a textile rope.
(1) The resulting cable load increment must be balanced by linear and rotational inertia forces. These additional loads must be superimposed on those arising from the conditions of CS 22.581(a).
(2) Qnom is the rated ultimate strength of the towing cable (or weak link if employed). For the purpose of these requirements it must be assumed to be not less than 1·3 times the sailplane maximum weight and not less than 500 daN."

On Thursday, June 4, 2020 at 9:50:57 AM UTC-4, Dan Daly wrote:
On Thursday, June 4, 2020 at 9:31:34 AM UTC-4, Kenz Dale wrote:
Is there a general rule of thumb for the maximum design forces for hooks? And is the nose hook spec'ed for more than the CG hook?

I'm assuming the design load is mostly driven by the fuselage/hook connection, the hooks themselves are rated to as much as 14kN.

The bible for this is CS-22 BOOK 1 Subpart C – Structure. If you're interested in things like this, use your favourite search engine for "CS-22_Amendment 1 revised.pdf" and it's all there. Quick download which cures insomnia...

"CS 22.585 Strength of launching hook attachment
(a) The launching hook attachment must be designed to carry a limit load of 1·5 Qnom, as defined in CS 22.581(b), acting in the directions specified in CS 22.581 [ed.-airtow conditions] and CS 22.583 [ed.-winch conditions].

(b) The launching hook attachment must be designed to carry a limit load equal to the maximum weight of the sailplane, acting at an angle of 90° to the plane of symmetry."

"CS 22.581 Aerotowing
(a) The sailplane must be initially assumed to be in stabilized level flight at speed VT with a cable load acting at the launching hook in the following directions:
(1) horizontally forwards;
(2) in plane of symmetry forwards and upwards at an angle of 20° with the horizontal;
(3) in plane of symmetry forwards and downwards at an angle of 40° with the horizontal; and
(4) horizontally forwards and sidewards at an angle of 30° with the plane of symmetry.
(b) With the sailplane initially assumed to be subjected to the same conditions as specified in CS 22.581 (a), the cable load due to surging suddenly increases to Qnom, assuming the use of a textile rope.
(1) The resulting cable load increment must be balanced by linear and rotational inertia forces. These additional loads must be superimposed on those arising from the conditions of CS 22.581(a).
(2) Qnom is the rated ultimate strength of the towing cable (or weak link if employed). For the purpose of these requirements it must be assumed to be not less than 1·3 times the sailplane maximum weight and not less than 500 daN."

This is great information. If you had to guess, for how long has this been the standard? Can it be reasonably assumed that the 20+ years old gliders can meet these requirements?

On Thursday, June 4, 2020 at 8:05:48 AM UTC-6, Kenz Dale wrote:
On Thursday, June 4, 2020 at 9:50:57 AM UTC-4, Dan Daly wrote:
On Thursday, June 4, 2020 at 9:31:34 AM UTC-4, Kenz Dale wrote:
Is there a general rule of thumb for the maximum design forces for hooks? And is the nose hook spec'ed for more than the CG hook?

I'm assuming the design load is mostly driven by the fuselage/hook connection, the hooks themselves are rated to as much as 14kN.

The bible for this is CS-22 BOOK 1 Subpart C – Structure. If you're interested in things like this, use your favourite search engine for "CS-22_Amendment 1 revised.pdf" and it's all there. Quick download which cures insomnia...

"CS 22.585 Strength of launching hook attachment
(a) The launching hook attachment must be designed to carry a limit load of 1·5 Qnom, as defined in CS 22.581(b), acting in the directions specified in CS 22.581 [ed.-airtow conditions] and CS 22.583 [ed.-winch conditions].

(b) The launching hook attachment must be designed to carry a limit load equal to the maximum weight of the sailplane, acting at an angle of 90° to the plane of symmetry."

"CS 22.581 Aerotowing
(a) The sailplane must be initially assumed to be in stabilized level flight at speed VT with a cable load acting at the launching hook in the following directions:
(1) horizontally forwards;
(2) in plane of symmetry forwards and upwards at an angle of 20° with the horizontal;
(3) in plane of symmetry forwards and downwards at an angle of 40° with the horizontal; and
(4) horizontally forwards and sidewards at an angle of 30° with the plane of symmetry.
(b) With the sailplane initially assumed to be subjected to the same conditions as specified in CS 22.581 (a), the cable load due to surging suddenly increases to Qnom, assuming the use of a textile rope.
(1) The resulting cable load increment must be balanced by linear and rotational inertia forces. These additional loads must be superimposed on those arising from the conditions of CS 22.581(a).
(2) Qnom is the rated ultimate strength of the towing cable (or weak link if employed). For the purpose of these requirements it must be assumed to be not less than 1·3 times the sailplane maximum weight and not less than 500 daN."

This is great information. If you had to guess, for how long has this been the standard? Can it be reasonably assumed that the 20+ years old gliders can meet these requirements?

JAR-22 preceded CS-22 and offers similar considerations as it was the derivative document. Prior to that there was OSTIV guidance. At one time, TOST (producer of glider hooks, winch and aerotow weak links and other rigging) had some notes that in the absence of of other guidance a weak link of 1.3X the AUW of the glider for ground launching. That is no longer published.

Ultimately the structure the hook is attached to is more important, as is the wing loading. The hook itself must be able to operate for several thousand cycles, in all types of conditions, between overhauls, so it will obviously be capable of safety margins over operational loads. I'm not an engineer, but that may be 5X the expected operational load, or more.

Have a look at the BGA glider data sheets.
https://members.gliding.co.uk/library/datasheets/

Frank Whiteley