if a wing has down incidence, what is the effect?

thanks RCU

Maybe the airplane would fly better inverted?

The fuselage would be flying with the nose up and you would have up thrust, an unstable thing
and if it were real you could not see where you were going.
Darryl

Down with respect to what? If you mean it has less incidence than the stabalizer/elevator you would have to have a large amount of down elevator throw just to fly level. If you mean relative to the waterline of the aircraft you would also have to specify what the stabalizer and/or thrust line was set at in order to answer your question.

It would be a ground lover.
No problem with it crashing, since it couldn't take off.

If it was wide and flat [as in barn door] might not take to much up elevator to keep it up there. Have you ever heard of the test pilot that bragged , give him power enough ,he could fly a barn door.Well he got into one new design that he found that is about what he had once he got it in the air. I suppose you could come out something like that!

You can't just look at the wing alone. You need to compare the angles of the wing, stab and thrustline to see the whole picture. This stuff doesn't care what angle it is to the fuselage but it DOES care what the angles are between each of those three things.

So to help us give you a proper answer other than the ribbing you've mostly see so far you need to give us more information.

Many airfoils still provide lift at negetive angles of attack with respect to the airflow. Depending on the weight and the speed the model is designed to fly, it is not unusual for a main wing to fly at negetive incidence.

Incidence shown on a plan however is a different story. It is relative to an arbitrary 'datum line' chosen by the designer by which the wing, stabilizer, and thrust angles are compared. So you could have negetive incidence of two degrees on the wing, stabilizer, and thrust line reletive to the 'datum line' but yet they would all be parallel to each other. So when you look at the big picture of an airplane design you need to take into account the incidences of all the components and how they relate to each other via the datum line.

the whole problem was or is that the wing saddle did not match the airfoil, on this aircraft, by manufacturer, so i went back to the basics and leveled the fuse at the thrust line, because there is no datum line, from front to aft , its fine, then i measured
up from the floor at each wingtip , first the center of the leading edge , than the trailing
edge, the numbers came out close to the same at these points on the left and right tips. IF the leading edge measurements were lower than the trailing edge numbers,
than i would have had neg incidence. I probably will ck it with an incidence meter.

Maybe, maybe not.

If the airfoil is symmetrical, yes you'd have negative incidence to the fuselage if the fuselage was parallel to the floor when you measured the wing. But if the airfoil is cambered, it would depend on the airfoil whether or not it was actually negative, positive, on zero.

And understand that it wasn't an idle suggestion about the airplane not being able to take off. Think about it.

The F-86 -couldn't- take off if the pilot let the airspeed get too high on the takeoff run!
A warbird Sabre ran off the end of a runway out here many years ago because of this, and hit an ice cream parlor well off the end of the runway.
Insufficient control power from the elevator to rotate the airplane if the pilot delayed and let it too fast.

Well, if you used the thrust line as your datum and the wing is negative to that line then you've definetly got a mess on your hands. Either that or there's a significant amount of upthrust.

It sure sounds like the wing saddle is at fault. But just in case did you measure the stab leading and trailing edge as well? If not then put the elevator to dead neutral trim and measure it and the wing and let us know what you set to level if it was not the thrust line. GIve us the numbers so we can figure out the angles and suggest what needs changing if anything. Also what model it is or what sort of model it is.

Be sure you are measuring at the furthest forward point of the leading edge, this is where the air is split between the airflow over the top and bottom of the wing and is the true incidence...........I think.

its a wing P-40, NEVER AGAIN!!!! will i build a wing kit, i'm going to get an incedence meter and check it.

Keep in mind that it doesn't require an incidence meter to measure incidence.

A flat floor and a ruler is all it takes. Most of us have both. And it's dead simple to do.

I checked it with the floor ruler method and it doesn't look bad , sometimes you can't depend on the manufacturer, you have to be warry of everything.

I have a dennis bryant typhoon , thats in the bones and its a very difficult build, but the wing saddle is perfect.the parts were cut by laser lizzard .in my opinion theres no excuse for a poor fit at the wing saddle, by any manufacturer. , as far as this p-40 is concerned, i think the foam wing plan doesn't match
the aircraft plan , which has probably been updated many times throughout the years.

some kits just require you to double and triple check every step, its just too time consuming and exausting, i like a challenge, but i don't want to spend needless time
messing with something thats designed wrong from the start.

I’ve seen videos of the take off roll leading to that crash. What happened is that the inexperience pilot over rotated the F-86 at low airspeed. The over rotated position of the airframe kept it from accelerating to a normal takeoff speed but the pilot realized it too late and ended up yanking it off the runway with low airspeed. It didn’t gain much altitude and ended up in the ice cream. It was so over rotated that the tail was almost hitting the runway. I also recall the runway used was short for a F-68. He should have started his rotation at about 105 knots by just gently rotating so the nose gear comes off the runway. Very sad event.

I used to work with Kjell The Mad Norwegian Fighter Pilot. He really had been a Norwegian Fighter Pilot. He mostly flew the Republic ThunderStreak when he was in the Norwegian AirForce. He had an interesting story or two. One favorite was about how bad the thrust to weight ratio was on that airplane.

A couple of stories themes were based on "getting the airplane behind the power curve." It seems that on takeoff the pilot had to be very careful to not rotate until a safe speed. The airplane had enough wing to get it into trouble and not enough power to get it out, especially on takeoff. If it was rotated just a bit too soon, the lift would be sufficient to get the sucker flying, but the AOA would then throw some more drag at the sucker. The engine was doing all it could, which wasn't enough to actually accelerate the lump out of that altitude (which was runway altitude + 10-20') and in fact wouldn't accelerate at all. And the wing wouldn't give any additional lift. And the pilot couldn't get more airspeed by pitching the nose down, 'cause there wasn't any down available from that altitude. So the pilot was stuck at that altitude and speed and "climb" angle until some fuel burned off. Well, until the fuel burned off, or his flight path encountered terrain of any significance.

He told of one guy who wound up flying across the North Sea at wavetop, riding the pipe. He didn't know for sure he had enough altitude to push the nose down until he was almost to England, and was afraid to mess with the stick until then.