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high tow vs low tow



 
 
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  #1  
Old February 25th 19, 04:27 AM posted to rec.aviation.soaring
Steve Koerner
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Default high tow vs low tow

As a US pilot, I've flown low tow a few times but mostly just high tow as that is the convention here. I'm wondering what all of the trade-offs are by the two methods? Might it be time to reconsider this?

As pointed out on another thread, low tow would seem to be safer against the problem of glider kiting up to overpower the tugs up elevator. I'm wondering if it's ever possible for a low tow glider to go too low and overpower the tugs down elevator?

Also, how does low tow compare in the other common dangerous towing situation wherein the tug flys too slow for a highly ballasted glider? My own experience with a seriously too slow tug is that I end up falling to low tow whether I like it or not.

Has anyone done a lot of tows both ways and have reasons as to which way is better?
  #2  
Old February 25th 19, 05:06 AM posted to rec.aviation.soaring
John Foster
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Posts: 354
Default high tow vs low tow

On Sunday, February 24, 2019 at 8:27:25 PM UTC-7, Steve Koerner wrote:
As a US pilot, I've flown low tow a few times but mostly just high tow as that is the convention here. I'm wondering what all of the trade-offs are by the two methods? Might it be time to reconsider this?

As pointed out on another thread, low tow would seem to be safer against the problem of glider kiting up to overpower the tugs up elevator. I'm wondering if it's ever possible for a low tow glider to go too low and overpower the tugs down elevator?

Also, how does low tow compare in the other common dangerous towing situation wherein the tug flys too slow for a highly ballasted glider? My own experience with a seriously too slow tug is that I end up falling to low tow whether I like it or not.

Has anyone done a lot of tows both ways and have reasons as to which way is better?


The risk of the tow rope wrapping around the glider is higher if you have a rope break on low tow.
  #3  
Old February 25th 19, 05:42 AM posted to rec.aviation.soaring
BobW
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Posts: 504
Default high tow vs low tow

On 2/24/2019 8:27 PM, Steve Koerner wrote:
As a US pilot, I've flown low tow a few times but mostly just high tow as
that is the convention here. I'm wondering what all of the trade-offs are
by the two methods? Might it be time to reconsider this?

As pointed out on another thread, low tow would seem to be safer against
the problem of glider kiting up to overpower the tugs up elevator. I'm
wondering if it's ever possible for a low tow glider to go too low and
overpower the tugs down elevator?


Having performed low tows only by way of demonstrating 'em during BFRs
(remember them?), the aerospace engineer in me has little doubt that 'all that
glider mass back there' *could* 'cause alarming things to happen to the tug'
if Joe Glider Pilot is either seriously asleep at the stick or intentionally
and unilaterally plays Joe Test Pilot.

That said, my visual take on low tow is that 'well before' a tug-upsetting low
tow position is likely to be reached, Joe Glider Pilot will almost certainly
find the visual picture so alarming that he'll take corrective action. Clearly
that's not the case with high tow...

So, OZ glider pilots, how do you folks manage to kill your tow pilots? Too
much beer?

Bob W.

---
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  #4  
Old February 25th 19, 05:59 AM posted to rec.aviation.soaring
JS[_5_]
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Posts: 624
Default high tow vs low tow

(Other than landing on tow)
High tow makes the most sense to me, even in Australia.
Fly the glider!
Jim
  #5  
Old February 25th 19, 09:07 AM posted to rec.aviation.soaring
Charlie Quebec
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Posts: 253
Default high tow vs low tow

It only makes sense if you like towplane crashes. When a glider kites on high tow down low there is no time for the tow pilot to recover.
Had this been a low tow, the likely hood is very strong that the pilot would have survived. In Au, we only do low tow training, and I’ve never seen
any problems or even the slightest upset of the tow plane on low tow. Some years ago we used to go to high tow to release, but even that was scrapped.
It needs to be remembered that low tow means just below the slipstream. C of G hooks make high tow even more dangerous.
  #6  
Old February 25th 19, 01:26 PM posted to rec.aviation.soaring
Cookie
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Posts: 152
Default high tow vs low tow

High tow, low tow....

One of the (many) arguments in aviation that you just can't win.

I teach my students to be proficient at both.

The I give them my lecture, "when in Rome......."

-Cookie
  #7  
Old February 25th 19, 01:49 PM posted to rec.aviation.soaring
Charlie M. (UH & 002 owner/pilot)
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Posts: 1,383
Default high tow vs low tow

Since this topic comes up every few years, very diplomatic reply you posted Cookie.

Yes, in the US, high tow is the norm except for training demonstration/practice.

Our club is an exception, we have been doing low tow as the norm since I started flying some 45 years ago. We do teach high tow, I use high tow at other fields...."When in Rome...."
Others flying at our place are given the option of which to fly, we tell the towpilot if a high tow is to be expected.
  #8  
Old February 25th 19, 02:28 PM posted to rec.aviation.soaring
Tango Eight
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Default high tow vs low tow

On Monday, February 25, 2019 at 3:07:36 AM UTC-5, Charlie Quebec wrote:
It only makes sense if you like towplane crashes. When a glider kites on high tow down low there is no time for the tow pilot to recover.
Had this been a low tow, the likely hood is very strong that the pilot would have survived. In Au, we only do low tow training, and I’ve never seen
any problems or even the slightest upset of the tow plane on low tow. Some years ago we used to go to high tow to release, but even that was scrapped.
It needs to be remembered that low tow means just below the slipstream. C of G hooks make high tow even more dangerous.


I realize that you come here chiefly to wind people up, but let's just set that aside for a moment.

If you have a shred of actual evidence for the relative safety of low tow, cite it. The guys who studied the problem and test flew upset scenarios at altitude don't agree with you.

Chris Rollings:

"The belief that low-tow significantly reduces the risk of sling-shot tug
upsets is mistaken. The trigger is if the glider pitches up to about 30
degrees above the line of the rope. Being in low-tow when that happens
simple makes the sunsequent event take about half a second longer - not
enough extra time to greatly increase the chance of releasing before the
critical point."

Critical point: it's the acceleration of the kiting glider that does the tow pilot in. The towplane is suddenly slowed, probably below 1g stall speed, accompanied by loss of elevator authority, then it's pitched over and put into a deep negative angle of attack. Take away: low tow doesn't and can't prevent this from happening. The glider pilot has the task of preventing this from happening. See figure 2 here https://members.gliding.co.uk/librar...owing-booklet/

Rope length is far more important to tow (in)stability than either tow position or hook location. Anyone can test. Try a 150' rope and a 225' rope. Difference is obvious and dramatic. In contrast, the difference between high and low tow is pretty subtle as far as control pressure goes and I honestly feel no difference in stability. We use 225' because it's the longest our tow pilots can safely manage on final approach (road crossing). I have on rare occasion towed on even longer ropes (275') and felt that was over doing things.

Nose vs CG hook is another myth. It would take a lot of work to assemble the data, but anecdotally we already know: the vast majority of tug upsets and upset/accidents involve nose hook equipped gliders. Most CG hook gliders (e.g. ASW-20s and such) tow very nicely.

T8
  #9  
Old February 25th 19, 02:34 PM posted to rec.aviation.soaring
Cookie
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Posts: 152
Default high tow vs low tow

Charlie M.

Regarding Valley Soaring...where low tow is used...

I avoid using the term "high tow" because over the years I've seen many pilots who interpret this as meaning to "fly above the tow plane"...I've done many an uneasy check ride where the pilot, thinking they were doing high tow, flew way above the tow plane...

Of course the term high tow, means to "fly above the wake", NEVER above the tow plane!
So I started using the terms .."low tow", and "normal tow"...but one of the Valley pilots aptly pointed out that low tow is "normal" for them!!!!

So now I have to teach my students what I call "below the wake" tow and "above the wake tow"

BTW...with the powerful tow planes we have at our field, which can climb quite steeply...above the wake, is actually quite a bit below the tow plane....

Conversely, on a cross country tow, when the tow plane is flying level, and the wash goes straight back...."low tow" (just below the wake) is not really all that low...(almost the same sight picture as above the wake in a steep climb!

Cookie




On Monday, February 25, 2019 at 7:49:03 AM UTC-5, Charlie M. (UH & 002 owner/pilot) wrote:
Since this topic comes up every few years, very diplomatic reply you posted Cookie.

Yes, in the US, high tow is the norm except for training demonstration/practice.

Our club is an exception, we have been doing low tow as the norm since I started flying some 45 years ago. We do teach high tow, I use high tow at other fields...."When in Rome...."
Others flying at our place are given the option of which to fly, we tell the towpilot if a high tow is to be expected.


  #10  
Old February 25th 19, 02:54 PM posted to rec.aviation.soaring
[email protected]
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Posts: 2,124
Default high tow vs low tow

On Sunday, February 24, 2019 at 10:27:25 PM UTC-5, Steve Koerner wrote:
As a US pilot, I've flown low tow a few times but mostly just high tow as that is the convention here. I'm wondering what all of the trade-offs are by the two methods? Might it be time to reconsider this?

As pointed out on another thread, low tow would seem to be safer against the problem of glider kiting up to overpower the tugs up elevator. I'm wondering if it's ever possible for a low tow glider to go too low and overpower the tugs down elevator?

Also, how does low tow compare in the other common dangerous towing situation wherein the tug flys too slow for a highly ballasted glider? My own experience with a seriously too slow tug is that I end up falling to low tow whether I like it or not.

Has anyone done a lot of tows both ways and have reasons as to which way is better?


I've done something over 20,000 flights at both ends, 12k or so at the back and something over 8k at the front.
Properly flown, as high as possible without being in the wake, the glider is very closely aligned with the thrust line of the tug and has almost no effect on trim.
Flown too low, the glider pilot can have a poorer view of the horizon.
Being a bit high is obvious.
The rope wrapping hazard happens if there is slack caused by a fairly quick, big descent. I have never witnessed this happening in operations I have been involved with.
We tested the "pull the tail down" risk and could not accomplish it. The angles don't work. In trying this we had our Cub down to below 45 MPH with the glider behind hanging low. It was more stable with the glider on at that speed.
My experience is that low is easier to teach and do at the beginning because the view is a bit better and the wake is not anywhere near as much of an issue.
Get slack- Move to the side to take it out, just like high(normal?) tow.
Rope will hit the glider. Could happen if way too low when tug releases it. If the glider is in proper position when releasing the rope doesn't go much up or down. If the tug releases the rope drops below and behind and probably, but not surely back releases.
Rope will wrap around the glider- I have yet to figure out how a rope can go upwind against a 60 mph headwind.
The rope will scratch my belly when using a CG hook. No scratches on my ships in 40+ years of low tow.
Most training, from my experience, teaches pilots to fly too low.
If one wants to get better at this, a couple dual flights with an experienced instructor can be useful.
Also note that many tugs have mirrors set up such that the tow pilot can't see the glider in low tow.
Tell your tow pilot what you plan to do. Trim settings are different so he or she may want to adjust.
To finish. Both options can be done safely. I believe low tow is more easily done safely.
Flame suit on.
UH
 




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