Is there a nose hook modification for a standard cirrus

Amen!

Using simple engineering (physics, if you like), the CG hook is about 1
foot displaced from the CG of the glider.Â* Assuming around 25 lb of
force applied to that arm (after the initial force required to overcome
inertia during acceleration (and you're on the ground at that time with
the tail wheel resisting the torque)), that yields about 25 lb-ft of
torque.Â* That's really not much to overcome.

It is my opinion that the real cause of a kiting incident is that the
glider pilot is either asleep at the helm and doesn't recognize what's
happening or that he wants to salvage the tow to avoid inconvenience or
expense.Â* Say all you want how quickly this develops, that too is anecdotal.

On 10/17/2017 8:54 AM, Tango Whisky wrote:
Le mardi 17 octobre 2017 16:13:50 UTC+2, a écritÂ*:
On Monday, October 16, 2017 at 8:29:08 PM UTC-5, Andreas Maurer wrote:
100000 hrs". Or something to that effect.
100% agree.

For 25 years my club has had two DG-300: One with nose hook and one
without. We had exactly one incidence where a DG-300 got the tow plane
out of control by pulling up its tail.

It was the one with the nose hook.
Andreas, pre Newtonian physics (Galileo) suggest that the nose hook is providing more stability, no non-stochastic statistics necessary to prove that! Why is it so hard to accept that you're better off with the tow line attached to a point far forward of the cg? Anecdotal stories are BS.
Of course a nose hook provides a little bit more of stability.
Now, if you *need* this little delta to stay safe, you shouldn't be flying solo in the first place.

--
Dan, 5J

On Tuesday, October 17, 2017 at 10:13:50 AM UTC-4, wrote:
On Monday, October 16, 2017 at 8:29:08 PM UTC-5, Andreas Maurer wrote:
On Mon, 16 Oct 2017 01:17:26 -0700 (PDT), krasw
wrote:


Statistical data would be like "we have a group of Std.Cirrus gliders with nosehook and similar group with C/G hook, and we can say that this group exhibits XX accidents during tow per 100000 hrs, and other group YY accidents per 100000 hrs". Or something to that effect.

100% agree.

For 25 years my club has had two DG-300: One with nose hook and one
without. We had exactly one incidence where a DG-300 got the tow plane
out of control by pulling up its tail.

It was the one with the nose hook.

Andreas, pre Newtonian physics (Galileo) suggest that the nose hook is providing more stability, no non-stochastic statistics necessary to prove that! Why is it so hard to accept that you're better off with the tow line attached to a point far forward of the cg? Anecdotal stories are BS.

"True" nose hook is higher and more in line with the center of mass, thus reducing the pitching force when rope tension is really high. This helps with kiting to a degree. It is possible to yank hard enough that this pitching force can exceed the ability of the horizontal tail to overcome, especially at high weight and aft CG. Dick Johnson did an article about this in late '86 or early '87.
Also provides some straightening effect in yaw obviously.
FWIW
UH

"True" nose hook is higher and more in line with the center of mass, thus reducing the pitching force when rope tension is really high. This helps with kiting to a degree. It is possible to yank hard enough that this pitching force can exceed the ability of the horizontal tail to overcome, especially at high weight and aft CG. Dick Johnson did an article about this in late '86 or early '87.
Also provides some straightening effect in yaw obviously.
FWIW
UH

Per UH's note, see Dick Johnson's Tail "Stall While Towing", Soaring mag, May 1987. For those who aren't aware, Dick's article arose from discussions I had with him and (independently) Air Force test pilot Jim Payne following Robert Robertson's fatal towing accident in 1986. I had spoken to each about my suspicion that there was more going on in that tragic accident than just all-up weight, CG, or tow speed. Both experts reached the same conclusion: i.e., in some circumstances, a robust tow plane, high/ballasted glider weight, CG towhook, and/or slower tow speed could possibly make the tail susceptible to stalling, with disastrous consequences.

To this analysis I offered another twist, with not much agreement in this group: if the glider pilot were hanging on, nose high, with the stick in his/her lap desperating hoping for the tow speed to increase and then decided to give up and release, then pushing the stick over might itself trigger tail stall because of the near instantaneous increase in effective elevator angle of attack resulting from the up-to-down change in elevator deflection.

Years ago, my LS-3 popped the nose up sharply for a moment rolling out behind a powerful towplane just as I lowered the flaps to lift off and we flew out from behind a row of hangars that had sheltered us from the wind. In that case, a quick full-forward-stick motion reversed the incipient kiting (I could never recall whether I moved the flaps back to zero, but that would have helped) and my heart rate returned to normal.

As far as directional control, I've been flying gliders with CG hooks since 1978 (LS-3, ASW 24). I never thought having a nose hook was a big deal until I rolled off the runway last summer in Nephi after my wing dropped early with full water ballast. I'm not sure if a nose hook would have provided enough steering force to prevent hitting a landing light. But I could have avoided doing so simply by releasing, as I've done several times before (and once since!).

We do mostly aerotow here in the U.S. A CG hook isn't unsafe. But if I had the choice, I'd take a nose hook just because of the modest benefit.

Chip Bearden

On Tue, 17 Oct 2017 01:47:08 -0700 (PDT), wrote:

So, Andreas, do we conclude the the physics and maths of tow hook placements are wrong or that there is always someone who sometime can manage to do something especially stupid?

Well...
let me put it this way:

As you probably know, the test flights that proved that the nose-up
momentum of a CG hook have been made by a German Akaflieg (project
pilot was a friend of mine, btw). And of course these flight tests
(using a Ka-8) proved that using a CG hook indeed made a huge
difference.


But:
Based upon these flight tests Germany introduced a law that aerotows
on CG hooks were only allowed if the pilot had recent aerotow
experience (3 aerotows during the last 6 months), and of course new
gliders had to be equipped with a nose hook.

Many people assumed that these limitations would affect aerotow safety
in a positive way. But it turned out that there was no influence of
these new rules on aerotow safety, not was there ever a hard
statistical proof that gliders with a CG hook had a higher aerotow
incident rate than gliders with nose hook (the odd man out being some
notorious gliders with problematic geometry and CG hook, especially
the Ka-6).


So last year this law was removed.


My conclusion:
In theory and flight test the maths and physics are correct, but in
practics they are not related to incident numbers.



p.s.
I usually fly an open class double seater with only a CG hook, and my
club's ASK-21 and Duo Discus XL. When teaching upset aertow situations
in the ASK-21 I never noticed any useful stabilizing effect of the
nose hook, nor did Iever in the Duo Discus. The same goes for the
DG-300 with and without nose hook which I had many chances to compare.

The only real advantage I can see to a nose hook is to the ground
crewman who doesn't have to lay on his back to attach the rope. :-D

On 10/17/2017 7:01 PM, Andreas Maurer wrote:
On Tue, 17 Oct 2017 01:47:08 -0700 (PDT), wrote:

So, Andreas, do we conclude the the physics and maths of tow hook placements are wrong or that there is always someone who sometime can manage to do something especially stupid?
Well...
let me put it this way:

As you probably know, the test flights that proved that the nose-up
momentum of a CG hook have been made by a German Akaflieg (project
pilot was a friend of mine, btw). And of course these flight tests
(using a Ka-8) proved that using a CG hook indeed made a huge
difference.


But:
Based upon these flight tests Germany introduced a law that aerotows
on CG hooks were only allowed if the pilot had recent aerotow
experience (3 aerotows during the last 6 months), and of course new
gliders had to be equipped with a nose hook.

Many people assumed that these limitations would affect aerotow safety
in a positive way. But it turned out that there was no influence of
these new rules on aerotow safety, not was there ever a hard
statistical proof that gliders with a CG hook had a higher aerotow
incident rate than gliders with nose hook (the odd man out being some
notorious gliders with problematic geometry and CG hook, especially
the Ka-6).


So last year this law was removed.


My conclusion:
In theory and flight test the maths and physics are correct, but in
practics they are not related to incident numbers.



p.s.
I usually fly an open class double seater with only a CG hook, and my
club's ASK-21 and Duo Discus XL. When teaching upset aertow situations
in the ASK-21 I never noticed any useful stabilizing effect of the
nose hook, nor did Iever in the Duo Discus. The same goes for the
DG-300 with and without nose hook which I had many chances to compare.




--
Dan, 5J

Gliders with CG hooks are kinda like airplanes with tailwheels; if you know what you are doing they are no problem and can be more fun (i.e. need more skill) than nose hooks or nose wheels.

BUT

They both can setup situations that can rapidly escalate out of control. Crosswinds, unbalanced wings dropping, poor aileron control at low speed, tall grass - you have to be aware of the system dynamics and prepared to cope.

Now if we had CG hooks on towplanes..!

Kirk
66

On Monday, October 23, 2017 at 11:12:44 AM UTC-6, kirk.stant wrote:
Gliders with CG hooks are kinda like airplanes with tailwheels; if you know what you are doing they are no problem and can be more fun (i.e. need more skill) than nose hooks or nose wheels.

BUT

They both can setup situations that can rapidly escalate out of control. Crosswinds, unbalanced wings dropping, poor aileron control at low speed, tall grass - you have to be aware of the system dynamics and prepared to cope.

Now if we had CG hooks on towplanes..!

Kirk
66

I have seen a concept sketch for a specialty tow plane, automotive powered, large prop driven by a reduction drive, and cg tow tow hook and twin boom tail. Only a few hurdles to overcome, like FAR's (allow experimental to tow) and/or certification (difficult) and limited market. Break even point would be about 200 builds. It could equal or beat on of these as a tow plane
https://en.wikipedia.org/wiki/SIAI-Marchetti_SM.1019

Keep the CG hook and buy a winch is easier and cheaper.

Winter's coming;^)

Frank Whiteley