Dogtooth wings?

[Antonsoarer]

Anyone know what the dogtooth wing design does?

Used on some transonic jets like below....

[steve lewin]

The leading edge notch/extension (dogtooth) is a flow control mechanism similar to the wing fences currently being discussed in "What is this ?". It's supposed to be as effective at fixing the unwanted flow along the span but with less drag than a wing fence.

Steve

[Antonsoarer]

Thanks Steve, I thought it might have something in common with a fence, it was the fence thread that triggered the question. What I am curious about is what it does at both high and low alpha.

I seem to remember reading somewhere (not sure if it was a dogtooth or something similar) that it may also create a vortex at high alpha and make a medium aspect ratio swept wing (like the hunter) look like a delta and so make landings easier.

I am thinking of employing devices like this on a design I am working on to achieve extreme manoeuvres even at low speeds but keep the efficiency of medium aspect ratio wings.

Tony.

[steve lewin]

Entering "dogtooth wing aerodynamics" into Google will find you some discussion. I rather doubt that fences or LE notches will do anything useful at the Re values we're usually working with but I've never tried them....anything is possible :).

Steve

[HELModels]

I would think that at loooow reynolds, the best way to augment flow would be with leading edge Slats. Slats being a little airfoil that goes in front of the main LE. Slooow speed implies reduced reynolds.

[Antonsoarer]

Electrostorch, I already have leading edge slats on the menu of devices to try out, my minimum operating Reynolds on this design is root 300k and tip about 170k.

I now have several devices I am considering applying to this slope-soarer, it's the culmination of several decades of intermittent development and fun.

Wing-fences
Dog-tooth leading edges
Leading edge slats (German Storch style, is that where you get your call sign from?) or leading edge droop (camber changing)

Probably just end up with a drag-monster but all good fun.

A lot the experimenting is now made feasible by EPP. I was inspired many years ago watching a couple of Phase-5s doing stunts the likes of which I have not seen since. What made them unique was way they could pull tight square manoeuvres with little loss of speed. They used coupled flaps and very light construction, lots of high alpha stuff, great to watch.


Steve, thanks for the google tip I will have a good read.

Tony.

[AndyOne]

I was told that the "Dog Tooth" on fast jets was to prevent stall in the turn close to or beyond the speed of sound. If this is the case it's going to do very little for any model.

Andy.

[chrisgood]

The new Hobbico Nexstar 46 RTF airplane has leading edge extensions at the tips that have a similar effect to the sawtooth and wing fences. While they primarily allow for the airflow to remain attached at the tips at higher alpha, the vertical transition on the bottom of the wing from flat airfoil to rounded has the same effect as a bottom wing fence (!?).

As the air on the top of the wing tries to get to the bottom, it takes any path it can. As you approach the wingtips, especially on a wing with sweep, the top air flowing towards the wingtips can actually flow forward over the leading edge, causing a tip stall. The sawtooth adds to the distance that air has to travel, keeping it on the top of the wing longer.

All that being said, if it worked for all circumstances, every plane would have fixed leading edge extensions at the tips. Most passenger jets have movable leading edges for low speed, higher lift. They are usually along the entire leading edge, but some have movable tip extensions. It is a question of trade-offs between complexity of components, weight, desired airspeed ranges and desired alpha range.

Chris Good

[HELModels]

It is a question of trade-offs between complexity of components, weight, desired airspeed ranges and desired alpha range.

I wouldnt argue with that when talking about fullscale. The considerations with models seem to be, will it even get off the ground with all the claptrap required to make it work.

EDIT Added 03/21
Complexity(of functionality) seems harder to achieve as you go from full scale down to small model. In other words, very low Reynolds arena, very little claptrap; Higher Reynolds, more claptrap possible.

I Would also Add, and I am sure there is much more to it, that The Nexstar device is a different animal than dogtooth or fence because it abruptly changes the shape of the wing by increasing thickness and camber and occupying many more spanwise stations than a thickness of a sheet of aluminum. I'd bet that the Nexstar contraption is about 1 root chord length in span (untapered), cause that is about how far from the tip all the trouble starts.

Fixed LE slats can also work on a model.:)

[Ollie]

Swept back and tapered wings are very prone to tip stall because the sweepback shifts the lift distribution to the tip and the taper reduces the ability of the wing near the tip to carry the additional load. Much like fowler flaps an extended and drooped leading edge increases the wing area near the tip and also increases the washout and maximum lift coefficient. All of this is to lower the stalling speed by preventing premature tip stall and the associated loss of control. Enough washout improves low speed handling but, then is too much for high speed efficiency by producing too much drag at high speed.

The highly swept and tapered wings of a typical jet transport have 8 to 10 degrees of washout to produce an efficient lift distribution at crusing speed but not enough to prevent tip stall at very low speeds. That's why they are universally equipped with devices to increqse washout and lift production at slow speeds.

See:
http://aero.stanford.edu/WingCalc.htmlUse
Use this on line Java applet to see the effects of sweepback on lift distribution at both and low high angles of attack for the same wing with and without sweepback. The lift distribution that has the least induced drag is elliptical. When the lift distribution is distorted to put too much load on the tips, premature tip stall results. When the lift distribution is distorted to put too little load on the wing tips at low (crusing) angles of attack the induced drag also becomes excessive.

The one and only important justification for sweepback is to avoid compressibility effects as the plane approaches the speed of sound.

[Grejen]

The one and only important justification for sweepback is to avoid compressibility effects as the plane approaches the speed of sound.

And for (non scale) models if it's the look your after go for it.:D
- well - this is a modeling science forum.:rolleyes: :D

[HELModels]

Hmmmm!

I'm looking at the Tower Hobbies Tower Talk and right on the cover is a Nexstar with the "contraption" on the wing. This is not the same device I had in mind when replying to ChrisGood. The Nexstar device only appears to increase chord length and does not reach all the way out to the tip. It extends the leading edge and blends smoothly into the upper and lower wing surfaces.

I have no idea where I got the impression that the Nexstar device increased camber, thickness, And Chord length, And reached all the way out to the tip. The one I imagined might be worth building, just to see what it does. My device would increase the thickness, camber and chord without going all the way out to the end of the wing, as the Nexstar does not, nor the wing fence. It would differ from the wing fence by being wider than just a sheet of Alum.