Air Brake effect

[EVVFCX]

Hi all,

can anybody explain why the F18 and maybe others pitch  up when the spoiler/airbrakes are deployed?

They are'nt wing based so not directly effecting wing created  lift but they are body spoilers, is this why because they are towards the rear of the plane?

I'm learning to be ready for it now, noticed it on the expert carrier landing challenge, no navigation but imc conditions.

regards

Steve

[Lima-Victor-Mike]

My guess is the air resistance pushes against the airbrake and, since it's aft of the centre of gravity, makes it rotate about the lateral axis

[CAFedm]

In case you may want to edit this (of course, keep a backup of the original)..open up the aircraft.cfg (I use AirEd), open table #1101 - Flight Dynamics, then scroll down to Spoilers Pitch Effect=xxx (an increasing negative number increases the pitch effect, a positive number would result in nose-down tendencies when airbrake is deployed).

[EVVFCX]

Hi CAedm, thanks for that, I may try it to see the effect.
I started placing my aircraft below my wingamn when catching up with the effect that the spoiler then pitched me back up, giving height gain for short and reduced my speed.

It was just that I've not see this happen in the past and FSX is still pretty new to me.

I started with FS1 or in other words before microsoft got their hands on it - yes I am that old, actually older than that, now 30 years in simulators.

regards
Steve

[CAFedm]

Hello,

BTW, am not advocating adjusting the airfile for a better sense of reality...dunno if the real F/A-18 shares the same trait, rather it's intended as a tweak if it makes the aircraft fly more to your liking. If interested, the value I used for my own aircraft under this same table entry, is Spoilers Pitch Effect = -0.022500. Other flight dynamics in place may or may not yield a favourable result, but in my case, causes the aircraft to descend fairly rapidly without dropping the nose.

p.s. - Regarding the placement of the F-18 airbrake, it could likely act somewhat as an elevator surface. The designers most probably added in some other characteristics to negate the tendency to pitch up too much, after all a fighter ought to be highly controllable, eh. Maybe someone having experience with the real aircraft might provide some enlightenment. Cheers.

[RaptorF22]

That's cool, I have noticed that effect before.
I wonder if you put the number in that .CFG entry very high you could make the aircraft preform a Pugachev's Cobra.

[DaveSims]

Being as the real world F-18 is a fly-by-wire aircraft, all of its movements are computer controlled.  I would venture to guess the computer automatically would compensate for the speed brake.  Just look at how the F-18E SuperHornet slows down, it doesn't actually have a speed brake, it just deflects all of its control surfaces at the same time to increase drag, but the computer keeps the aircraft stable.

[EVVFCX]

Hi davysims, thanks for that.

What was really on my mind when I thought about it, was that it's a body based airbrake, just for drag, but the fuss gives some lift as well,  In my mind it's not a spoiler because it's fuselage based but it must be upsetting the lift at the rear, so the rear drops increasing drag and increasing alpha at same time.

It just caught me out when it happened, wasn't expecting it.

In real life my flying with spoilers is with gliders so they are purely lift spoilers.

All these aircraft in drag and no change of clothing