Glider Handling on Tow

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.

Oh, and of course, Mary Ann.


On Wednesday, November 6, 2013 10:40:26 AM UTC-5, Papa3 wrote:
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.

On Wednesday, November 6, 2013 9:43:21 AM UTC-6, Papa3 wrote:
Oh, and of course, Mary Ann.





On Wednesday, November 6, 2013 10:40:26 AM UTC-5, Papa3 wrote:

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.





I wonder if doubling the length of the tow-rope would help (runway length permitting. That would get the glider further above the downwash. From my many winch tows back in Germany I can confirm that the glider comfortably flies at 55 knots at a steep enough angle (not to be confused with AoA) that you get to 1,400' in 35 sec.
Herb

No problem, Erik. I picked up on your clues. :-)

-John, Q3

On Wednesday, November 6, 2013 10:40:26 AM UTC-5, Papa3 wrote:
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.

I did a search as Erik suggested. After reading a lot of posts, I found a very good explanation by Andreas Maurer, which I partially quote below. His explanation seems to account well for why the glider handling is so poor at slow tow plane speeds. But for me, several things are still unexplained:

1. Why does increasing the tow plane speed cause the poor glider handling to go away?

2. If the answer to (1) is that the down wash and wing tip vortices are now further below the glider, then why doesn't simply moving up higher above the wake of the slow tow plane remove the poor handling?

-John, Q3

===========

The following was written by Andreas Maurer, and posted on RAS 1/5/11:

The main factor for the seemingly odd flying characteristics behind
the tow plane is the downwash of the latter.

Let me explain:

The downwash has a significant angle (the air is deflected downwards
behind the tow plane's wing to up to four degrees!), but due to the
larger span of the glider it only affects the inner part of the
glider's wing.

Therefore, if the glider if lying laterally displaced, only one wing
is affected by the downwash of the tow plane - four degrees of AoA
difference between left and right wing need a lot of aileron to
correct.

Likewise, if the glider is flying straight behind the tow plane, the
downwash *decreases* the AoA of the affected inner part of the wing.
Getting the nose up by pulling back will restore the lift of the inner
part of the glider's wing, but now the outer parts of the wing have a
much higher AoA than they have in free flight.

Voila, meet the the conditions for poor aileron efficiency (high AoA!)
and tip stall.

The downwash is reduced by
- wingloading of the tow plane
- wing span of the tow plane

In other words: The more a tow plane looks like a motorglider (say, a
Dimona, or Katana Extreme), the less the flight characteristics of the
glider are affected.

Anyone who has ever been towed behind a motorglider or a microlight
will testify that problems like poor lateral control or running out
of elevator don't exist there, despite a far slower tow (55 kts
compared to a typical 70-75 kts behind a typical tow plane like
Reorqeur or Pawnee).

===========

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