Sideslip or crab immediately after takeoff on tow in crosswind?

[[email protected]]

I was wondering what the conventional wisdom is on whether to sideslip or crab the glider on takeoff under tow in a crosswind. I've always crabbed to follow the tow plane because of the low altitude and not wanting to risk catching a wingtip just after becoming airborne -and after a very short climbout you can sideslip without the risk of ground contact, though I usually continue to crab. However, doesn't crabbing the glider add a lot more drag to the towplane/glider combo?

[[email protected]]

On Monday, March 6, 2017 at 9:48:13 AM UTC-8, wrote:
> However, doesn't crabbing the glider add a lot more drag to the towplane/glider combo?

No, a slip creates drag. A crab is clean.

[Dan Marotta]

Crab to stay over the runway until you have enough altitude to clear
obstacles, e.g., wind sock should the tug drift downwind. The tug
should also crab so you'll both be flying clean, as Tom said. After
you've got sufficient altitude, say 50-100 feet, slide back behind the tug.

On 3/6/2017 11:05 AM, wrote:
> On Monday, March 6, 2017 at 9:48:13 AM UTC-8, wrote:
>> However, doesn't crabbing the glider add a lot more drag to the towplane/glider combo?
> No, a slip creates drag. A crab is clean.

--
Dan, 5J

[Charlie M. (UH & 002 owner/pilot)]

This. I do keep the upwind wing a bit low until flying, then crab as needed to track over the ground even with the towplane until it's flying. Our towpilots turn upwind once about 200' AGL so getting back to the runway is easier in case of any issues on tow, this goes for the towplane as well as the glider.

[Jim[_33_]]

On Monday, March 6, 2017 at 10:16:37 AM UTC-8, Dan Marotta wrote:
> Crab to stay over the runway until you have enough altitude to clear
> obstacles, e.g., wind sock should the tug drift downwind. The tug
> should also crab so you'll both be flying clean, as Tom said. After
> you've got sufficient altitude, say 50-100 feet, slide back behind the tug.
>
> On 3/6/2017 11:05 AM, wrote:
> > On Monday, March 6, 2017 at 9:48:13 AM UTC-8, wrote:
> >> However, doesn't crabbing the glider add a lot more drag to the towplane/glider combo?
> > No, a slip creates drag. A crab is clean.
>
> --
> Dan, 5J

This is likely just a consequence of poor flying technique but I seem unable to sustain a crab behind the tow plane without holding a fair amount of up-wind rudder. The pull of the tow plane seems to pull the glider's nose out of the crab otherwise.

[Dan Marotta]

Maybe you're right. Since the 80s all of my gliders have had CG
releases so not much, if any, rudder was required to stay in the crab.
I can see that, with a nose release, you'd need some rudder to offset
the side load of the rope. Still not a problem.

On 3/6/2017 5:07 PM, Jim wrote:
> On Monday, March 6, 2017 at 10:16:37 AM UTC-8, Dan Marotta wrote:
>> Crab to stay over the runway until you have enough altitude to clear
>> obstacles, e.g., wind sock should the tug drift downwind. The tug
>> should also crab so you'll both be flying clean, as Tom said. After
>> you've got sufficient altitude, say 50-100 feet, slide back behind the tug.
>>
>> On 3/6/2017 11:05 AM, wrote:
>>> On Monday, March 6, 2017 at 9:48:13 AM UTC-8, wrote:
>>>> However, doesn't crabbing the glider add a lot more drag to the towplane/glider combo?
>>> No, a slip creates drag. A crab is clean.
>> --
>> Dan, 5J
> This is likely just a consequence of poor flying technique but I seem unable to sustain a crab behind the tow plane without holding a fair amount of up-wind rudder. The pull of the tow plane seems to pull the glider's nose out of the crab otherwise.

--
Dan, 5J

[Martin Gregorie[_5_]]

On Mon, 06 Mar 2017 16:07:36 -0800, Jim wrote:

> On Monday, March 6, 2017 at 10:16:37 AM UTC-8, Dan Marotta wrote:
>> Crab to stay over the runway until you have enough altitude to clear
>> obstacles, e.g., wind sock should the tug drift downwind. The tug
>> should also crab so you'll both be flying clean, as Tom said. After
>> you've got sufficient altitude, say 50-100 feet, slide back behind the
>> tug.
>>
>> On 3/6/2017 11:05 AM, wrote:
>> > On Monday, March 6, 2017 at 9:48:13 AM UTC-8,
>> > wrote:
>> >> However, doesn't crabbing the glider add a lot more drag to the
>> >> towplane/glider combo?
>> > No, a slip creates drag. A crab is clean.
>>
>> --
>> Dan, 5J
>
> This is likely just a consequence of poor flying technique but I seem
> unable to sustain a crab behind the tow plane without holding a fair
> amount of up-wind rudder. The pull of the tow plane seems to pull the
> glider's nose out of the crab otherwise.

Seems reasonable to me: if you're on track, i.e. your CG's velocity
vector is pointed at the tow-plane's CG, your nose hook is upwind of that
track and the towplane's tail hook is downwind of it. IOW the tension in
the rope is trying to rotate you round your CG so you point at the
towplane's tail. If the rope tension wins you'll be way out of position,
so it follows that you need to hold sufficient upwind rudder to prevent
the rope pulling you round and to keep your velocity vector aimed at the
towplane CG.

The amount of rudder deflection needed depends on what type of glider
you're flying.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Monday, March 6, 2017 at 3:07:40 PM UTC-9, Jim wrote:
> On Monday, March 6, 2017 at 10:16:37 AM UTC-8, Dan Marotta wrote:
> > Crab to stay over the runway until you have enough altitude to clear
> > obstacles, e.g., wind sock should the tug drift downwind. The tug
> > should also crab so you'll both be flying clean, as Tom said. After
> > you've got sufficient altitude, say 50-100 feet, slide back behind the tug.
> >
> > On 3/6/2017 11:05 AM, wrote:
> > > On Monday, March 6, 2017 at 9:48:13 AM UTC-8, wrote:
> > >> However, doesn't crabbing the glider add a lot more drag to the towplane/glider combo?
> > > No, a slip creates drag. A crab is clean.
> >
> > --
> > Dan, 5J
>
> This is likely just a consequence of poor flying technique but I seem unable to sustain a crab behind the tow plane without holding a fair amount of up-wind rudder. The pull of the tow plane seems to pull the glider's nose out of the crab otherwise.

Jim, If you are holding rudder you are not crabbing. Crabbing is with the yaw string straight.

[Jim[_33_]]

On Thursday, March 9, 2017 at 3:10:50 PM UTC-8, wrote:
> On Monday, March 6, 2017 at 3:07:40 PM UTC-9, Jim wrote:
> > On Monday, March 6, 2017 at 10:16:37 AM UTC-8, Dan Marotta wrote:
> > > Crab to stay over the runway until you have enough altitude to clear
> > > obstacles, e.g., wind sock should the tug drift downwind. The tug
> > > should also crab so you'll both be flying clean, as Tom said. After
> > > you've got sufficient altitude, say 50-100 feet, slide back behind the tug.
> > >
> > > On 3/6/2017 11:05 AM, wrote:
> > > > On Monday, March 6, 2017 at 9:48:13 AM UTC-8, wrote:
> > > >> However, doesn't crabbing the glider add a lot more drag to the towplane/glider combo?
> > > > No, a slip creates drag. A crab is clean.
> > >
> > > --
> > > Dan, 5J
> >
> > This is likely just a consequence of poor flying technique but I seem unable to sustain a crab behind the tow plane without holding a fair amount of up-wind rudder. The pull of the tow plane seems to pull the glider's nose out of the crab otherwise.
>
> Jim, If you are holding rudder you are not crabbing. Crabbing is with the yaw string straight.

Yes. That is my experience.

[Dan Marotta]

On 3/9/2017 4:10 PM, wrote:
> Jim, If you are holding rudder you are not crabbing. Crabbing is with the yaw string straight.
The rudder is to offset the pull of the tug on a nose release. If
you're using a CG release, you won't need rudder. Likewise, should the
rope break or be released, you can maintain your angle into the wind and
track down the runway. To my mind, that's crabbing.
--
Dan, 5J

[Bret Hess]

The crab is clean for glider and tow only if both have CG hooks.

[son_of_flubber]

On Saturday, March 11, 2017 at 3:35:20 PM UTC-5, Bret Hess wrote:
> The crab is clean for glider and tow only if both have CG hooks.

A tug with a C.G. hook?

[Jonathon May[_2_]]

At 21:20 12 March 2017, son_of_flubber wrote:
>On Saturday, March 11, 2017 at 3:35:20 PM UTC-5, Bret Hess wrote:
>> The crab is clean for glider and tow only if both have CG hooks.
>
>A tug with a C.G. hook?
>
Tug with a CofG hook,sounds fun !
First dibbs on camera man job!

[[email protected]]

On Sunday, March 12, 2017 at 3:15:04 PM UTC-7, Jonathon May wrote:
> Tug with a CofG hook,sounds fun !
> First dibbs on camera man job!

Giant scale radio control typically have the rope attach at the tow plane's CG and on top. :-)

Could do it with a Pawnee, but the tail feathers would need reinforcement to handle the rope dragging along them at times.

-Tom

[Martin Gregorie[_5_]]

On Tue, 14 Mar 2017 20:29:41 -0700, tom wrote:

> On Sunday, March 12, 2017 at 3:15:04 PM UTC-7, Jonathon May wrote:
>> Tug with a CofG hook,sounds fun !
>> First dibbs on camera man job!
>
> Giant scale radio control typically have the rope attach at the tow
> plane's CG and on top. :-)
>
> Could do it with a Pawnee, but the tail feathers would need
> reinforcement to handle the rope dragging along them at times.
>
I know that RC towplanes usually have a CG hook on top but have wondered
about rudder-rope interference. Obviously it isn't a major problem, but
does it damage either the fin and rudder structure or kill the rudder
servo?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Sunday, 12 March 2017 17:20:14 UTC-4, son_of_flubber wrote:
> On Saturday, March 11, 2017 at 3:35:20 PM UTC-5, Bret Hess wrote:
> > The crab is clean for glider and tow only if both have CG hooks.
>
> A tug with a C.G. hook?


Apologies to the original poster for staying off topic.... cg tow hook equipped tug would eliminate take off accidents due to the sailplane getting out of position.... no?

[Tango Whisky]

Le mercredi 15 mars 2017 14:33:56 UTC+1, a écritÂ*:

> Apologies to the original poster for staying off topic.... cg tow hook equipped tug would eliminate take off accidents due to the sailplane getting out of position.... no?

The tug pilot hitting the ground after the tow rope snatched off his tail feather might say "no".

TW