Peter wrote:
The TBs have no washout… how does it work?
Silvaire wrote:
Slightly different wing sections at the tips? That’s one way.
Just a rectangular plan form does it too, a triangle taper does the opposite, an eclipse is supposedly perfect, any sweep changes it all together.
For a square or rectangular plan form the lift is reduced as you approach the tip, yet the chord length and profile remains the same the upwash and the downwash are all reduced and in this section it will stall a little later than it would otherwise. The pressure gradient which creates the lift and adverse pressure gradient that ultimately results in a stall are all reduced.
You can use twist to make a rectangular wing behave like an elliptical one, this is probably the cheaper smarter option, you use twist to make an elliptical wing behave like rectangular one making it more expense, but look nicer and maybe sell more 
You can substitute different profile instead of the twist.
Or back to the original post you could add a negative flaps to a wing that is too big, and sell it as a must have
RobertL18C wrote:
The Harvard may be one of the types which publishes Va for the different axes.
Could be. I also recall a friend talking about US Navy instruction on the issue of maneuvering speed as a pitch only calculation. i.e. roll level before pulling etc. in relation to training on the A4 Skyhawk.
Peter wrote:
The TBs have no washout… how does it work?
Slightly different wing sections at the tips? That’s one way.
The TBs have no washout… how does it work?
On Va 1. It only applies to one axis, full control movement in more than one axis may cause structural damage and 2. Va is different for different axis with typically Va being higher on the longitudinal axis (roll), than the horizontal axis (pitch) which in turn is higher than the normal axis (yaw)
The Harvard may be one of the types which publishes Va for the different axes.
Then Va is a function of mass, being lower at lower mass.
You can also apply a force that will destroy the aircraft below manovering speed, below Va it would normally stall before the g limits are exceeded but not in all cases, specifically a dynamic one is not considered.
I.e. an a310 lost is tail this way.
No taper or a square tip has a similar effect to adding washout. Ie it changes the span wise distbrution of lift. It is even cheaper.
alioth wrote:
So negative flaps in a certified plane are generally not worth it. To make the aircraft meet certification requirements on stalls, you would need so much washout to have a negative flap setting that doesn’t result in the tips stalling first, that you might as well have less washout and no negative flap setting.
Or maybe reflexed full span flaperons, which might alter washout effect on the wing as a whole to a lesser degree and leave benign stall characteristics intact.
A friend of mine designed and built his first aircraft at around age 20, years ago. It looks a lot like the Glasair designs, photo below. In his first iteration he decided to build the wing with no washout, to maximize speed. It was apparently “interesting” so he built a new wing with washout.
there’s no disturbed air now flowing over the tail so no buffet
I didn’t know the stall buffet comes from disturbed air hitting the elevator.
Learn something every day!
Airborne_Again wrote:
I don’t see why a minimum flap setting which is negative would be more dangerous that a zero flap setting?
I think it’s “dangerous” in the way it will remove washout from the wings. Most light GA aircraft have washout (and if you look down some plane’s wings spanwise it’s really very visible) – the wing has a twist in it which means the inboard section is at a higher AoA than the outboard, so the inboard stalls first, leaving the ailerons at least somewhat effective at the onset of a stall. So you will get a warning of an impending stall (some stall buffet) during the onset, but all the aircraft’s controls continue to work as expected.
Now if you put in negative flaps (enough to be worthwhile), now the washout is “backwards” – the wing tips are at a higher AoA than the inboard section of the wing, and the outboard section will stall first. You also will not have much warning of this – there’s no disturbed air now flowing over the tail so no buffet. You might put some aileron in not realising the outboard section of the wing is about to stall, immediately causing the outboard wing on the downgoing aileron to stall, leading to control reversal (e.g. if you turn the wheel right, the plane will start to bank left instead, which will cause you to add even more right aileron input, causing the stall to deepen and the roll rate to the left to increase, causing you to add even more…till all the aileron is in and the aircraft rolls on its back).
So negative flaps in a certified plane are generally not worth it. To make the aircraft meet certification requirements on stalls, you would need so much washout to have a negative flap setting that doesn’t result in the tips stalling first, that you might as well have less washout and no negative flap setting.
Airborne_Again wrote:
I don’t see why a minimum flap setting which is negative would be more dangerous that a zero flap setting?
OK I must admit that I don’t remember the details, nor can I puzzle it out now. This is stuff from when I was young, more than 20 years ago, when I was flying gliders with such features. I was told to not stall or go in thermals with negative flap setting, as this could end real bad. So I can’t contribute more to this, sorry.
