Slips in turns and landing with winglets

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.

On Sunday, February 7, 2016 at 5:09:42 PM UTC-5, 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.

For certification, winglets must withstand a 50 lb force in ant direction at the tip without permanent deformation or damage. Flight loads are a small fraction of that.
UH

Dick Johnson's recommendations are still correct even with winglets. Each glider is different but I have found that S-H gliders climb better with aft cg and a slight slip. Does not require much and generally the glider feels like it has found its groove.

Winglets are strong enough for slips to final and increase the safety as the glider is less likely to spin with the winglets, especially earlier generation models like the ASW-20 and Ventus.

On Sun, 07 Feb 2016 14:09:35 -0800, ucanemailmoi 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.

Doesn't this follow from the fact that the yaw string is a fair distance
in front of the wing?

Think about it: if the tipwise axis of the wing is exactly aligned with
the radius of the turn, which it should be for maximum climb efficiency,
the yaw string should also be at right angles to the turn radius but,
being a good 2m/6ft or thereabouts in front of the wing, the turn radius
it is on is angled forward of the turn radius the wing is on, which
therefore makes it point out slightly out. This looks like a slight slip
to the pilot.

Draw this situation on a piece of paper, but exaggerate the situation by
drawing the circle diameter and about twice the wingspan and you'll see
what I described.

If you redraw the diagram with correctly scaled turn radius and wingspan,
the angular difference between the wing radius line and the yaw string
radius line will be very small, but this needs to be adjusted because the
curved shape of the canopy will amplify the angle of yaw string in a
slip. Now Dick Johnson's advice makes perfect sense.

Practically, if the yaw string is central or pointing slightly out in a
thermal you're doing it right. If its pointing a long way out or to the
inside of the turn you're sideslipping while turning and this is hurting
your climb rate by generating excessive drag.


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

On 2/7/2016 3:09 PM, 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.


Not silly questions at all!

UH, Tim T. and Martin G. have each provided insights.

Arguably (reality always rules, of course!), because of the additional
side-surface drag, slipping in the presence of winglets should be more
effective than in their absence...which, of course, is not the same as
suggesting that slipping in a particular glider "will *always* increase the
sink rate." (See below.)

As to whether you should slip or not, if the ship has a POH, that's the best
place to start for specific input, followed by practice aloft before trying it
"near the ground." In any case, your expectation should be that nothing will
break off due to aerodynamic forces of a slip performed at pattern airspeeds.

(Kinda-sorta related, I've flown one non-spoilered,
large-deflection-landing-flap-only equipped, 15-meter glass, glider having
*reduced* sink rate when straight-ahead-slipped with full landing flap in.
That informational bit is simply by way of sharing a perhaps-non-obvious
tidbit regarding "the obvious usefulness of slipping" as a landing aid. The
devil is in the details...)

Bob W.

Originally Posted by Tim Taylor

Dick Johnson's recommendations are still correct even with winglets. Each glider is different but I have found that S-H gliders climb better with aft cg and a slight slip. Does not require much and generally the glider feels like it has found its groove.

snip

I fly a Ventus a and a Nimbus3D and they both climb better with the yaw string indicating some slip. In the case of the Nimbus it can be having the yaw string 30 - 40 degrees off centre at times which tallies with advice I was given by a 4 time world open class champion.

The cross flow over the Nimbus canopy exaggerates the string position in relation to the actual amount of slip but if I'm not having to hold off bank I'm pretty much in the ballpark for getting the best climb. The Ventus has Masak winglets and climbs well with the slipping but because of the trailing edge brakes doesn't often call for sideslipping for landing although it does it well enough

:-) Colin

On Sunday, February 7, 2016 at 6:11:14 PM UTC-6, Martin Gregorie wrote:

Doesn't this follow from the fact that the yaw string is a fair distance
in front of the wing?

Think about it: if the tipwise axis of the wing is exactly aligned with
the radius of the turn, which it should be for maximum climb efficiency,
the yaw string should also be at right angles to the turn radius but,
being a good 2m/6ft or thereabouts in front of the wing, the turn radius
it is on is angled forward of the turn radius the wing is on, which
therefore makes it point out slightly out. This looks like a slight slip
to the pilot.

Draw this situation on a piece of paper, but exaggerate the situation by
drawing the circle diameter and about twice the wingspan and you'll see
what I described.

If you redraw the diagram with correctly scaled turn radius and wingspan,
the angular difference between the wing radius line and the yaw string
radius line will be very small, but this needs to be adjusted because the
curved shape of the canopy will amplify the angle of yaw string in a
slip. Now Dick Johnson's advice makes perfect sense.

Practically, if the yaw string is central or pointing slightly out in a
thermal you're doing it right. If its pointing a long way out or to the
inside of the turn you're sideslipping while turning and this is hurting
your climb rate by generating excessive drag.

Martin, I believe this is only part of the answer. You are correct that a perfectly coordinated turn (slip ball in the center) should show some slip if the yaw string is forward of the CG (and conversely, a centered forward mounted yaw string indicates a skidding turn - beware in the pattern!) but there is also the overbanking effect of long wings seeing different local airflow velocity in a turn; this can be countered by holding aileron out of the turn (inefficient and draggy) or by adding a little bit of slip via top rudder. This slightly increases the angle of attack of the lower wing and decreases the angle of attack of the top wing and voila, no overbanking, ailerons are flush and efficient, and you gleefully outclimb the newb with the perfectly aligned yaw string. It's really noticeable in my LS6 (probably due to the dihedral) - it settles into a nice slipping climb with the yaw string off about 10 degrees to the outside, no aileron deflection, and just a touch of top rudder. Extra bonus - you get some lift off the fuselage! (See "String Theory").

Kirk
66

On Mon, 08 Feb 2016 09:55:16 -0800, kirk.stant wrote:

but there is also the overbanking effect of long wings seeing
different local airflow velocity in a turn; this can be countered by
holding aileron out of the turn (inefficient and draggy) or by adding a
little bit of slip via top rudder. This slightly increases the angle of
attack of the lower wing and decreases the angle of attack of the top
wing and voila, no overbanking, ailerons are flush and efficient, and
you gleefully outclimb the newb with the perfectly aligned yaw string.

True enough, and having reasonable amounts of dihedral is essential for
this to work. I didn't mention this primarily because I wanted to talk
about the effect of having the yaw string in front of the wing.

Of course I understand how yawing a dihedralled wing causes roll: when I
were a lad I used to fly single channel RC models before I discovered
free flight models and thermals.



Kirk 66



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

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.

There are two other considerations:

A. The side of the fuselage meeting the airflow in a slight slip produces some lifting force.
And:
B: A bit of top rudder reduces the back pressure on the stick needed to hold your turn. That reduces the induced drag at the horizontal.

So what do you think?

Bob

On Wednesday, February 10, 2016 at 8:03:15 PM UTC-5, Bob Caldwell (BC) wrote:
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.

There are two other considerations:

A. The side of the fuselage meeting the airflow in a slight slip produces some lifting force.
And:
B: A bit of top rudder reduces the back pressure on the stick needed to hold your turn. That reduces the induced drag at the horizontal.

So what do you think?

Bob

I think both are a crock of stuff. Lift is better generated by a wing and top rudder only serves to make the turn rate lower than it should be for the bank angle.
UH