high tow vs low tow

On Monday, February 25, 2019 at 10:11:36 AM UTC-5, Steve Koerner wrote:
Hank -

Do you have any thoughts on the separate problem of tow too slow with a ballasted glider? Wondering which might be better for that big problem. Maybe that problem is the same either way.

Second, I'm wondering about how glider lift off occurs for a low tow. Do you typically lift off with the towplane then immediately transition to low position or does the glider attempt to hold it down on the runway until the sight picture is correct for low tow?

Too slow is obviously a problem in either position- duh! That said the first thing most will feel in high tow is poorer position control when sinking into the wake. Control isn't as much an issue in low tow but it still feels bad.
In a flapped ship adding some more flap can get a bit of lift without pulling the leading edge up and reducing control.
Ships with no flaps are just screwed.
On takeoff I teach:
Lift off normally and get stable at a comfortable height, say 6- 8 feet.
Hold that position as the tug accelerates and lifts off.
When the tug starts to climb hold the glider down a bit so the tug outclimbs the glider . The glider stays in ground effect and the tug wake is dissipated.
As the tug wake starts to be above the glider smoothly transition to climb in the low tow position. Avoid doing this late and then having to climb hard to catch up.
Easier to do than describe but it feels very odd to someone not famailiar.
UH

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

In Australia we now transition higher, I use around 200’ before going into low tow.
I have flown high tow at many overeas comps and still find low tow much more stable.
The only time I fly high tow at home is on long cross country tows where I also pull the gear up (nose hook only!) and let the tug pilot accelerate in level flight.
The issue of tug pilots ignoring what type and weight of glider behind them is much more of a safety issue than the simple high/low equasion.
(I am a tug pilot too!)
Tom

Some gliders have the CG hook just forward of the gear doors.Â* I always
raised the gear in my LAK-17a on tow (at a safe altitude, of course) to
get a marginal improvement in climb rate.Â* Everyone says that low tow is
best for XC tows.Â* I've only been on the front end of the rope on an XC
tow, so I can't address the back end.

On 2/27/2019 12:02 AM, wrote:
In Australia we now transition higher, I use around 200’ before going into low tow.
I have flown high tow at many overeas comps and still find low tow much more stable.
The only time I fly high tow at home is on long cross country tows where I also pull the gear up (nose hook only!) and let the tug pilot accelerate in level flight.
The issue of tug pilots ignoring what type and weight of glider behind them is much more of a safety issue than the simple high/low equasion.
(I am a tug pilot too!)
Tom

--
Dan, 5J

On Tuesday, February 26, 2019 at 11:02:17 PM UTC-8, wrote:
In Australia we now transition higher, I use around 200’ before going into low tow.
I have flown high tow at many overeas comps and still find low tow much more stable.
The only time I fly high tow at home is on long cross country tows where I also pull the gear up (nose hook only!) and let the tug pilot accelerate in level flight.

Weird, because long cross country tows is exactly the one time the rest of us use low tow!

The height difference between a good low tow and a good high tow isn't much anyway. Twenty feet / six metres maybe? Maybe less.

Yes!

Above the wake during a level (not climbing) tow, will place the glider quite a bit above the tow plane...not a good place to be...

Low tow during level tow, just barely below the wake will place the glider only very slightly lower than the tow plane...a good place to be...

So...anybody winning the argument yet? LOL


Cookie



Weird, because long cross country tows is exactly the one time the rest of us use low tow!

The height difference between a good low tow and a good high tow isn't much anyway. Twenty feet / six metres maybe? Maybe less.

You do realise high and low refer to the slipstream don’t you!?

Speed of tow is the most important thing, I have not had so much flying in the USA but it is a problem at comps here when tug pilots used to towing slow two seaters and empty older gliders and turn up at a comp to tow heavily ballasted gliders. I understand there have been accidents over there from this.
ASGs and JSs need more speed than 2-22s but some tug pilots cannot seem to see that!

I have always believed the wake basically goes DOWN behind the tow plane, being compressed, i.e. heavier, air, and/or maybe for other reasons. I don't remember feeling any wake turbulence just following the tow plane at the same height, climbing or level flight.

On Wednesday, February 27, 2019 at 2:21:01 PM UTC-8, Cookie wrote:
Yes!

Above the wake during a level (not climbing) tow, will place the glider quite a bit above the tow plane...not a good place to be...

Low tow during level tow, just barely below the wake will place the glider only very slightly lower than the tow plane...a good place to be...

So...anybody winning the argument yet? LOL


Cookie

On Wed, 27 Feb 2019 18:12:56 -0800, Tom BravoMike wrote:

I have always believed the wake basically goes DOWN behind the tow
plane, being compressed, i.e. heavier, air, and/or maybe for other
reasons. I don't remember feeling any wake turbulence just following the
tow plane at the same height, climbing or level flight.

Its caused by a wing generating lift. If you assume that the wake's
downward angle is 1/3 of the wing's AOA you won't be far wrong.


--
Martin | martin at
Gregorie | gregorie dot org

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