Slips in turns and landing with winglets

kirk.stant wrote on 2/8/2016 9:55 AM:
Extra bonus - you get some lift off the fuselage!

Maybe this is intended as joke, but the last thing you want is a very
low L/D "airfoil" like the fuselage involved in providing any lift.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

On Monday, February 15, 2016 at 6:17:13 PM UTC+3, Eric Greenwell wrote:
kirk.stant wrote on 2/8/2016 9:55 AM:
Extra bonus - you get some lift off the fuselage!

Maybe this is intended as joke, but the last thing you want is a very
low L/D "airfoil" like the fuselage involved in providing any lift.

I don't agree.

As I've already said once in this thread, you're going to get a certain amount of drag from the fuselage anyway. If the presentation to the airflow for minimum drag generates zero lift then, by the calculus definition of "minimum" of a continuous function, the first little bit of lift will not add any drag. The optimum thing to do is to use it. It might be *very* little, and a very small AoA, but it's nonzero.

If the presentation to the airflow for minimum drag generates non-zero lift ... then of course you'll take it!

Yes, the fuse has a low L/D. But that's better than the 0.0 L/D if you don't take what lift you can from it...

Le lundi 15 février 2016 16:32:27 UTC+1, Bruce Hoult a écrit*:

I don't agree.

As I've already said once in this thread, you're going to get a certain amount of drag from the fuselage anyway. If the presentation to the airflow for minimum drag generates zero lift then, by the calculus definition of "minimum" of a continuous function, the first little bit of lift will not add any drag. The optimum thing to do is to use it. It might be *very* little, and a very small AoA, but it's nonzero.

If the presentation to the airflow for minimum drag generates non-zero lift ... then of course you'll take it!

Yes, the fuse has a low L/D. But that's better than the 0.0 L/D if you don't take what lift you can from it...

Why do you assume that the fuselage has zero lift in a perfect airflow?
Why do you assume that the increase of drag is zero for small slip angles?

If you slip, you will trade a part of the wing's lift (with a good L/D) for lift from the fuselage (with amn extremely low L/D). Your choice - it wouldn't be mine...

On 2/15/2016 8:16 AM, Eric Greenwell wrote:
kirk.stant wrote on 2/8/2016 9:55 AM:
Extra bonus - you get some lift off the fuselage!

Maybe this is intended as joke, but the last thing you want is a very low
L/D "airfoil" like the fuselage involved in providing any lift.


Eric,

That's pretty dogmatic. Why do you say so? Thanks!

Bob W.

Perhaps a good rule of thumb while landing with winglets is to land with the same number of winglets you took off with.
This didn't work for the Voyager's round-the-World flight, but most times it does.
Jim

On 2/15/2016 11:05 AM, JS wrote:
Perhaps a good rule of thumb while landing with winglets is to land with the same number of winglets you took off with.
This didn't work for the Voyager's round-the-World flight, but most times it does.
Jim
And yet the Voyager succeeded in its flight and landed safely, to boot.
--
Dan, 5J

No theory: After talking with Dick Johnson at a Hobbs contest I tried a slight sideslip in thermals in my winglet-free 20B. It seemed to help so I kept doing it. It did not help in my 27, which was designed to have winglets, so I stopped doing it.
I never flew the 27 with only one winglet and compared results turning to the winglet and away from it, so no idea if it would have made any difference or not. (PS: The only guy I saw, after landing, who had lost one winglet in flight on a 27 said he hadn't noticed any impact on his flying at all.)




On Sunday, February 7, 2016 at 3:09:42 PM UTC-7, wrote:
I know this is a silly question, but I was reading an article by Dick Johnson that talked about holding a slight slip while thermally. This article was written before winglets and I was wondering if the same idea applied to gliders with winglets. Also, as for slipping to lose altitude for landing in a glider with winglets, does this place a lot of side load on the winglets. Should you not slip in landing with winglets?

Sorry for the questions, but would appreciate any help in this.

Go up, fly your ship, do whatever works best for your bird after testing things out yourself. If it worked for butler or AJ or Moffat, they must have known something they discovered with their particular ship. My 1-26 doesnt care all that much but I do have the advantage of being able to work the core of the core while most others dont have the turn radius to get and stay in there unless they are flying minden or marfa thermals.

On Mon, 15 Feb 2016 07:16:51 -0800, Eric Greenwell
wrote:


Maybe this is intended as joke, but the last thing you want is a very
low L/D "airfoil" like the fuselage involved in providing any lift.


Depends on the type of glider.

An open class ship needs a lot of sideslip while thermalling.

I learned that a long time ago from Uli Schwenk, who told me that he
learned that from a guy named Klaus Holighaus.

Thermalling with the yawstring 30 degrees outwards makes a huge
difference in climb performance. Huge.

Explanation:
The yaw costs a lot of drag due to the "low L/D fuselage" - but it
saves even more drag because you barely need any opposite aileron
anymore, therefore you get a much better lift distribution (and
therefore much less induced drag) on the wing.


One other glider that needs a lot of yaw in a thermal: Arcus.



Best regards
Andreas

On Monday, February 15, 2016 at 7:13:43 PM UTC+3, Tango Whisky wrote:
Le lundi 15 février 2016 16:32:27 UTC+1, Bruce Hoult a écrit*:

I don't agree.

As I've already said once in this thread, you're going to get a certain amount of drag from the fuselage anyway. If the presentation to the airflow for minimum drag generates zero lift then, by the calculus definition of "minimum" of a continuous function, the first little bit of lift will not add any drag. The optimum thing to do is to use it. It might be *very* little, and a very small AoA, but it's nonzero.

If the presentation to the airflow for minimum drag generates non-zero lift ... then of course you'll take it!

Yes, the fuse has a low L/D. But that's better than the 0.0 L/D if you don't take what lift you can from it...

Why do you assume that the fuselage has zero lift in a perfect airflow?

I don't. I present the argument for both cases: zero and non-zero lift at minimum drag.


Why do you assume that the increase of drag is zero for small slip angles?

Follows directly from the definition of "minimum" for a continuous function..

The minimum is, by definition, at the point at which the function (the drag) has zero change for small changes in the input (the AoA or slip angle).