blown flaps/wings question

You would be correct. Usually bleed air is taken off the compressor section and injected over the flaps. It increases lift and increases angle of attack. Others will know more.

Dean

thanks mate

any idea if the effect diminishes at higher speed

eatthis

any idea if the effect diminishes at higher speed

Yes, as speed increases the volume & pressure of the air flowing over the wing also increases, so unless you were to increase the amount of blown air, the effect will diminish. Also remember that engine power is used to create the blown air - engine power is required to increase the speed of the aircraft, therefore the faster the aircraft is going, the less engine power is available for blowing.

Internal flap blowing is / was predominantly used to reduce speed on landing, where high engine power is generally not used, allowing plenty of scope for blowing.

thats pretty much what i thought

would it be fair to assume that given enough spare engine power (what im planning will have somewhere around 120,000 lb of thrust in a plane with an empty weight of 60,000 lb that given enough bleed air it could be usefull at higher speeds?

At higher speeds it isn't needed because the wing itself is creating plenty of lift. Remember more lift is needed at lower speeds hence the use of flaps at takeoff and landing.

Dean

the plane im thinking of has a small wing

I'm having a guess here, but I would imagine that the power required would increase exponentially in relation to the speed. As that speed increases, the wing generates more lift & consequently doesn't require assistance, I imagine that flap blowing would also become a drag issue as speed increases.

when you say a drag issue do you mean that the blown air will be slower than the natural air flowing over the  wing?

Probably and it will also disturb the boundary layer of air flowing over the wing. That can open up another can of worms. 

eatthis

when you say a drag issue do you mean that the blown air will be slower than the natural air flowing over the  wing?

Possibly, but the wings on a high speed aircraft are usually optimised for high speed, meaning that there is no need for blowing at those high speeds - look at the X-15. Many modern high performance aircraft now use Leading Edge Extensions in the form of slats, as these are more effective & less maintenance intensive in comparison with blown flaps, in addition to take off / landing, they are also used in flight to improve turn performance & what not;

thats a great picture :)

im planning on using slats and blown surfaces basically every trick in the book lol

The best use of BLC was for carrier aircraft, like the F-8 Crusader.  Conventional, land-based planes do not normally need such a system for landing because they have such a long runway, but carrier aircraft do not.  On the F-8 Crusader, the -J variant  and the French Crusaders were equipped with a "blown flap" system in order to reduce the landing speed.  But they also had slats on the leading edge--in fact, they actually had a "double droop" system, where the front portion of the slat would lower more than the rest of the slat would.  So, in effect, you would have two slats. 

At higher speeds, BLC becomes nothing more than extra weight that is added to the airframe.  The bleed air does not do anything to help the plane's performance.

First I just want to say I'm definetly not a flight engineer.

But I thought the main reason to use a blown flap was to delay flow separation that occures when the boundary layer has lost it's energy. By mixing "energized" airwith the boundary layer separation will be postponed. Thus will this "mixing air with the boundary layer" really be affected by the flow around the wing? Still I guess transonic/supersonic flows will make things myghty more difficult.

/Carl

Short answer is, Yes. At higher speeds, the flow OVER the wing can't be disrupted without consequences.

can slats be used at high speed?

eatthis

can slats be used at high speed?

Dean and others pretty well covered it all.  Flaps and slats have speed liminations and to prevent damage most aircraft have a speed blow up system.  Flaps and slats are effective at lower speed to increase the area of the upper wing for increased lift.  At higher speed enough air flow is going over the wing to produce more than enough lift.  Many aircraft have to trim out the horz stab at high speed to make up for increased lift generated by the wing.  When you see the slats or flaps deployed on an aircraft in flight, it is at low speeds.

The only exception that I know of is the F-16 where the slats can deploy at high speed but only by a very small amount.  They are controlled by the fligh control computer.  The Euro Fighter may also have this same feature, but I am not sure. 

The slats, in combination with the flaperons on the Typhoon are controlled by the FCS to give the best wing camber & lift for any given situation, the pilot has no control over the flaps. I imagine that the maximum deployable speed would be limited by their structural strength