high tow vs low tow

On Tuesday, February 26, 2019 at 10:16:56 PM UTC-5, Ramy wrote:
Sounds to me that this method of staying low in ground effect for low tow position will increase the time we spend in the dangerous zone below 200 feet, in addition to transitioning through the wake while low and slow. Personally I prefer to spend as less time as possible down low, and would rather transition to low tow position at safe altitude and safe speed. Especially at high density altitude such as we have in the west, fully ballasted combined with not so powerful towplane, the last thing I would want is to purposely stay in ground effect at the end of the runway while the tow plane slowly climbs higher. I never tried this, so maybe it is not as bad as i think it is.

Ramy

One reason I will never do this in a ballasted glider is wind shear.

Low tow increases the glider pilot's vulnerability to a slow tow.

best,
Evan

On Tuesday, February 26, 2019 at 10:16:56 PM UTC-5, Ramy wrote:
Sounds to me that this method of staying low in ground effect for low tow position will increase the time we spend in the dangerous zone below 200 feet, in addition to transitioning through the wake while low and slow. Personally I prefer to spend as less time as possible down low, and would rather transition to low tow position at safe altitude and safe speed. Especially at high density altitude such as we have in the west, fully ballasted combined with not so powerful towplane, the last thing I would want is to purposely stay in ground effect at the end of the runway while the tow plane slowly climbs higher. I never tried this, so maybe it is not as bad as i think it is.

Ramy

My experience is that the slightly improved takeoff performance puts the glider at an equal to slightly higher height shortly after transition to the tug climbing attitude.
UH

And I think this is an example of not being properly trained in low tow.
You are in ground effect until the towplane reaches the proper sight view in front of the glider which is not too far off the ground.
If you are looking up at the bottom of the towplane, you waited too long. This would accentuate the negative effect of wind gradient.

OK, I will start with.....I am biased to UH, he was one of my early instructors and we have other connections.

The "only" time I see an issue with low tow is with a VERY high wind gradient and someone being waaaayyyyyy too low near the ground.
The relevant airspeed of the tug vs. the glider (especially on a weaker tug) may put the glider in a poor position speed wise.

I will say, I have towed out of our field on very gusty days with, about a 45* cross wind, near gross weight (say, a ASW-20 A or C, so, about 9lbs/sqft.).
Yes, it ''twas sporty down low", why not? Big cross wind, over trees, higher wingloading, etc.

I have had rope breaks and a few TP dumped ropes while low tow, the rope just drops below the glider, try to drop a broken rope over the field on the grass.

As to the towpilots, what I have heard is that low tow allows them to trim a climb in their ship, thus less tiring over a day. High tow is usually outside the trim limits, thus always using your arms to maintain a climb pitch.. Part of this is a correct low tow puts the glider basically on the pitch line from tug spinner and down the rope to the glider...

I remember decades ago in upstate NY at a contest. Summer day, ballast, weak towplane (leaving site and tug out, not trying to slam the site). I started in high tow. We were attempting to do circles close to the field to clear terrain, I ended up in low tow since I was just hanging on. It appeared that it helped climb a bit, but I was not happy.

In general, the "perfect world" done wrong/incorrect still sucks and may be dangerous.

At our place, we teach both.
Other places, we do as they do, but if it gets bad, we may fall back to what we have more time with.

A search on RAS will likely pop up multiple threads with the same basic question, which tow is better?

I guess this discussion is akin to, "what contest rules should we use?", sheesh......

I flew at Valley Soaring for a while and did low tow. Worked fine. The only negative I heard was that the glider appears to be lower in the first critical phase of climb so it takes longer to get to the 200' safe 180 turnaround point. But I've also heard that low tow is more efficient because there's less/no trim drag from the towplane using up elevator to keep the tail down and therefore climbs faster. So perhaps it's a wash.

I'll move into low tow on cross-country aerotows if I've briefed the tow pilot or can communicate with him/her because it seems easier to hold position.

Yes, kiting a glider is going to upset the towplane regardless of the tow position. But at least if you're in low tow, you'll feel the wake as you pop up thru it, which provides an alert that might help prevent situations as was described in the NTSB report where the glider pilot may have taken his eye off the towplane for a few seconds.

Chip Bearden

To add a tiny bit, some high tow proponents have said, "I want to clear low obstructions, thus I fly high tow....!"
I usually counter with, if the towplane clears, there is typically enough energy for the glider to clear, even from low tow. Also, as Chip stated (and I agree), low tow does not require as much parasitic drag from the towplane tail to maintain a climb angle, thus more efficient. This also means the towplane is marginally higher clearing an obstacle, thus more energy for the sailplane to clear even if too low doing low tow.
Again, big wind gradient can be a negative factor if too low.

We break ground, sit in ground effect (pretty much the most efficient place for any aircraft), let towplane accelerate, break ground, then establish a climb. Once the sight picture looks good, the sailplane starts a climb.
Turbulence from towplane wing wash/vortex is essentially "0" since that does not really form until some climb is done. By the time it starts, the sailplane should be starting up.

As stated before, any method done wrong/incorrect is still poor.

On Sunday, February 24, 2019 at 7:27:25 PM UTC-8, 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?

Steve.

First reading this post brought back memories of the R11 Truckee contest in 2015.
If I remember correctly, you struggled tremendously to take off each day.
It is understood that R11 was hosted at an advanced site, though even in a fully loaded racing glider, it does not require superhuman skills to get off the ground and tow safely.
Note also that ground looping half way down the runway is not the fault of the wing runner...
Further reports from towpilots indicated that they could rarely see you in their rearview mirrors. In fact, there were several occasions where you were almost released by the towplane.

My best advice is to consider practicing normal takeoff and tow, where you keep the towplane's wheels on the horizon and the rope tight with basic techniques.
Intentional high tow and low tow in heavy, high performance gliders on rough days make things scary for the towpilot and their friends and family.
It is important to be able to recover from unintentional position upset, but there's no reason to intentionally upset your position.
Please, do us all a favor and stay in the standard tow position.

P.S. I hope to never have to see your gear doors up close again...

On Monday, February 25, 2019 at 2:28:18 PM UTC-7, Cumungus wrote:
On Sunday, February 24, 2019 at 7:27:25 PM UTC-8, 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?

Steve.

First reading this post brought back memories of the R11 Truckee contest in 2015.
If I remember correctly, you struggled tremendously to take off each day.
It is understood that R11 was hosted at an advanced site, though even in a fully loaded racing glider, it does not require superhuman skills to get off the ground and tow safely.
Note also that ground looping half way down the runway is not the fault of the wing runner...
Further reports from towpilots indicated that they could rarely see you in their rearview mirrors. In fact, there were several occasions where you were almost released by the towplane.

My best advice is to consider practicing normal takeoff and tow, where you keep the towplane's wheels on the horizon and the rope tight with basic techniques.
Intentional high tow and low tow in heavy, high performance gliders on rough days make things scary for the towpilot and their friends and family.
It is important to be able to recover from unintentional position upset, but there's no reason to intentionally upset your position.
Please, do us all a favor and stay in the standard tow position.

P.S. I hope to never have to see your gear doors up close again...

Hello there Cumungus.

Who are you?

Why would you choose to ridicule me and make your wise suggestions over the internet?

And, why four years after the fact?

Low tow isn't common in Italy, and in the EU as far as I know. We practice the low-tow position during basic training, then it's at the pilot's discretion. Occasionally during the season I use it for a minute or so, and every time I make my first flight on a new type.

What's the standard low-tow procedure? Do you still take-off in the high-tow position then transition to low-tow at a given altitude?
Or do you watch the towplane climb, then start climbing when "it looks about right"? the latter seems scary to me (as I've never done it).

Thanks!

Aldo Cernezzi

Low tow is.....sailplane breaks ground, stays close to ground (since close ground effect basically negates the sailplane drag), let towplane accelerate, lift off, when towplane "looks about right" follow it up.

This is the short version.

Having, taught newbs for both, low tow seems easier and safer.

There is ALWAYS the outlier where, "I think high tow would have been better".
To me, sorta like, "I won't wear seat belts because I knew of a case where they were thrown free in a crash and survived because they didn't wear seat belts".

I stick with low tow, but teach and fly both.

As I stated before, this is a "no win" conversation.