Q14676

[dee dee]

Question: Upon wing spoiler extension in straight and level flight, if the speed and load factor remain constant:CD increases but CL remains unaffected.


Am I right in saying that Lift will decrease? The whole point of spoliers is to induce airflow seperation and reduce lift - right???

[Dick W]

Re: Q14676

The question says speed and load factor are constant, that is throughout the changes you maintain level 1G flight at the same speed. From the lift equation this means overall CL must remain the same. You get this by raising the nose a bit. Simiarly, you maintain speed by increasing thrust to counteract the increased drag

Dick

[dee dee]

Re: Q14676

Can you please show me with some number using the actual equation?
I am trying to balance the lift formula with respect to the question.
thanks
d

[Dick W]

Re: Q14676

The Lift Equation is L = CL x 1/2rho x Vsqd x S. If lift is constant, then the other side of the equation is also constant. V is the same, rho is the same, S is the same so CL is also the same.

CL depends on a mix of factors, like airfoil shape and Alpha. Here you are reducing CL over part of the wing by putting out the spoilers so to get back to the same overall CL you have to increase overall Alpha

But how you do it is not part of the question. It only asks if CL stays constant if you maintain level flight at constant speed - and it does

Just for interest, load factor is a measure of up or down. 1G is level flight, more than 1G and you are climbing, less than 1G and you are falling earthwards. Cross refer this to the G Demand control law in some autopilots, page 9.5 in Instruments

Dick

[Jacques Keulder]

Thanks your explanation just helped me a Ton in understanding the thought processes of POF!!