Glider Handling on Tow

A question for any aerodynamicists out the why does low aero tow speed adversely affect the handling of a glider so drastically?

Occasionally I’ve received an aero tow in my LS-8 (dry) at 55 kt (minimum recommended aero tow speed is 54 kt). The plane is heavy and unresponsive at that speed; it’s an extremely stressful experience! But once off tow the same plane handles like a dream at speeds down into the upper 30 kt range.

Before anyone asks, yes, I do immediately ask the tow pilot for 10 kt more speed - right now! I’d just like to understand what the root aerodynamic cause of the poor handling might be.

-John, Q3

The Discus 2 exhibits the same behavior. It's a problem mostly seen in newer unflapped racing ships because of the angle of incidence of the wing. This results in a nose-up attitude at low speeds and on aerotow this results in a downward pull on the nose from the towrope. This down-pull has to be counteracted by up elevator. With ballast, I run out of up elevator around 60 knots or so, and I have had my glider sink into low tow a couple of times with a slow tug and have had to release a couple more. In free flight, the glider will stall at its placarded speed and handles fine. Tows below 60 knots have very poor aileron and elevator control.

There may be other things going on, but I suspect the relative angle of the towrope to the fuselage on tow is responsible. Flapped ships alter their pitch and hardly suffer from this effect.

Mike

Discus 2b

On 6/11/2013 05:32, Mike the Strike wrote:
The Discus 2 exhibits the same behavior. It's a problem mostly seen
in newer unflapped racing ships because of the angle of incidence of
the wing. This results in a nose-up attitude at low speeds and on
aerotow this results in a downward pull on the nose from the towrope.
This down-pull has to be counteracted by up elevator. With ballast,
I run out of up elevator around 60 knots or so, and I have had my
glider sink into low tow a couple of times with a slow tug and have
had to release a couple more. In free flight, the glider will stall
at its placarded speed and handles fine. Tows below 60 knots have
very poor aileron and elevator control.

There may be other things going on, but I suspect the relative angle
of the towrope to the fuselage on tow is responsible. Flapped ships
alter their pitch and hardly suffer from this effect.

Mike

Discus 2b


In that case, flying in low tow should reduce the problem.

Somebody care to experiment?

GC

Mike,
You said that poor handling during low speed towing is mainly felt by newer standard class racing ships. This is probably correct if we accept Andreas’ explanation that downwash interaction (requiring higher AOA which leads to tip stalling) is the root cause of the poor handling problem, as flaps would allow a lower AOA than with a standard ship. However, a look at section 4 of several pilot handbooks showed that the 15/18 m ships have higher minimum tow speeds:

Ship, dry min tow, wet min tow
D2, 54 kt, 65 kt
LS-8, 54 kt, 65 kt
Duo, 54 kt solo, 65 kt dual
V2, 65 kt, 70 kt
ASW-27, 65 kt, 70 kt

Do you know what the 15/18 m pilots experience when being towed below 65 kt?

-John, Q3

On Tuesday, November 5, 2013 1:32:35 PM UTC-5, Mike the Strike wrote:
The Discus 2 exhibits the same behavior. It's a problem mostly seen in newer unflapped racing ships because of the angle of incidence of the wing. This results in a nose-up attitude at low speeds and on aerotow this results in a downward pull on the nose from the towrope. This down-pull has to be counteracted by up elevator. With ballast, I run out of up elevator around 60 knots or so, and I have had my glider sink into low tow a couple of times with a slow tug and have had to release a couple more. In free flight, the glider will stall at its placarded speed and handles fine. Tows below 60 knots have very poor aileron and elevator control.

There may be other things going on, but I suspect the relative angle of the towrope to the fuselage on tow is responsible. Flapped ships alter their pitch and hardly suffer from this effect.

Mike
Discus 2b

On Tuesday, November 5, 2013 1:10:33 PM UTC-5, John Carlyle wrote:
A question for any aerodynamicists out the why does low aero tow speed adversely affect the handling of a glider so drastically?



-John, Q3

Is it Winter already? This is one of those frequent threads (along with gelcoat maintenance, is the PW-5 the spawn of Satan, and the Downwind Turn) that come up every few years. As recently as two winters ago it was "Aerodynamics of Towing". If you search on some combination of "aerodynamics" and "tow" or "aerowtow" you'll see at least three primary generations of the thread. For instance:

https://groups.google.com/forum/#!searchin/rec.aviation.soaring/aerodynamics$20of$20towing/rec.aviation.soaring/C69yZmsaFe0/JqUTgv_G5HQJ

On Tuesday, November 5, 2013 2:58:54 PM UTC-5, Papa3 wrote:
On Tuesday, November 5, 2013 1:10:33 PM UTC-5, John Carlyle wrote:

A question for any aerodynamicists out the why does low aero tow speed adversely affect the handling of a glider so drastically?







-John, Q3



Is it Winter already? This is one of those frequent threads (along with gelcoat maintenance, is the PW-5 the spawn of Satan, and the Downwind Turn) that come up every few years. As recently as two winters ago it was "Aerodynamics of Towing". If you search on some combination of "aerodynamics" and "tow" or "aerowtow" you'll see at least three primary generations of the thread. For instance:



https://groups.google.com/forum/#!searchin/rec.aviation.soaring/aerodynamics$20of$20towing/rec.aviation.soaring/C69yZmsaFe0/JqUTgv_G5HQJ

I don't think there is anything wrong with renewing a few classic discussions. There are always new pilots like myself who can benefit but wasn't around back in the day. I have flown Hang Gliders for nearly 40 years and managed glider blogs and know there are from time to time repeated topics.I don't see the harm in reintroducing them.

On Tuesday, November 5, 2013 3:06:37 PM UTC-6, HGXC wrote:
I don't think there is anything wrong with renewing a few classic discussions.

Classic discussions. Hmm. Ginger, or Mary Ann?

;-)

On Tuesday, November 5, 2013 1:35:15 PM UTC-8, Steve Leonard wrote:
On Tuesday, November 5, 2013 3:06:37 PM UTC-6, HGXC wrote:

I don't think there is anything wrong with renewing a few classic discussions.



Classic discussions. Hmm. Ginger, or Mary Ann?



;-)

Mary Ann, Definitely.

Craig

On Tuesday, November 5, 2013 4:06:37 PM UTC-5, HGXC wrote:

I don't think there is anything wrong with renewing a few classic discussions.

The problem with searching for old discussions before posting a question is that newbies (like me) pick up a lot on RAS from questions that we never think to ask. So if people search for their question and don't repost the question, our ignorance remains unrequited.

And that ignorance is deep and wide. I did not even realize that the PW-5 was Spawn of Satan. Seriously, there seem to be an endless stream of "good to know" and even a few "really important to know" topics. You make us less dangerous to you by educating us.

I wish there were a book of "soaring lessons learned". Last Fall I learned the hard way that the "caster wheel" on a glider trailer tends to vibrate loose and drag on the pavement. Where am I suppose to have learned that? My pappy did not get his hands dirty very often and my education is deficient in many areas of practical knowledge.

Civilized online communities maintain FAQ lists. In lieu of that... keep the repeat questions coming.

I didn't mean to be snarky - I promise. I forgot the smiley emoticon :-) I figured the parenthetical examples would be a clue that I meant this somewhat tongue-in-cheek.

BTW, this is one of the best discussions on R.A.S. where some good (and not so good) information has come out.

On Tuesday, November 5, 2013 4:06:37 PM UTC-5, HGXC wrote:
On Tuesday, November 5, 2013 2:58:54 PM UTC-5, Papa3 wrote:

On Tuesday, November 5, 2013 1:10:33 PM UTC-5, John Carlyle wrote:



A question for any aerodynamicists out the why does low aero tow speed adversely affect the handling of a glider so drastically?















-John, Q3







Is it Winter already? This is one of those frequent threads (along with gelcoat maintenance, is the PW-5 the spawn of Satan, and the Downwind Turn) that come up every few years. As recently as two winters ago it was "Aerodynamics of Towing". If you search on some combination of "aerodynamics" and "tow" or "aerowtow" you'll see at least three primary generations of the thread. For instance:







https://groups.google.com/forum/#!searchin/rec.aviation.soaring/aerodynamics$20of$20towing/rec.aviation.soaring/C69yZmsaFe0/JqUTgv_G5HQJ



I don't think there is anything wrong with renewing a few classic discussions. There are always new pilots like myself who can benefit but wasn't around back in the day. I have flown Hang Gliders for nearly 40 years and managed glider blogs and know there are from time to time repeated topics.I don't see the harm in reintroducing them.