Air brakes and flaps?
 

Anyone have the real reason why they can't be used together? Did ask a distinguished aerodyanmist this week and after scratching his head suggested it might have something to do with turbulence breaking up the laminar flow with landing flap but my question related to intermediate descent with LE flap and possibly first stage TE.
my thoughts were that it was a certification thingy with the manufacturer not considering the case of speed restriction with requested or needed increased ROD.

Wiggy, everything I've flown bar F100 which had a split tail.
so Trident,VC10, DC9 (32 to 51) MD 80, DC 10. Plus a couple of Sims.
should add I've flown some high performance flapped sailplanes where it wasnt a problem

As Wiggy says, it depends on the type. I flew the VC10, 747, A320/1 and A330 and all were different. the VC10, I can't remember; the 747 up to F20 on both Classic and 400. The A320 is up to Config 3 and the A321 up to Config 2. the A330 is up to Config 3 normally, but ours have the steep approach modification so we can land in Kathmandu which allow up to Config full - but don't give you all the spoilers. The couple of times I forgot which aircraft I was flying in the 321 led to some buffet, so clearly the wing doesn't like it.

Yep, on B727 it was a no no.
On A300/310/320/340 it's allowed up to a certain flap position.

Having a guess as most of the kit I flew was second generation the traffic density wasn't envisaged, no speed controls and fly as low and fast as you want regardless of fuel consumption and noise, hence it wasn't needed. One day actually intercepted 10R ils some 35 miles out and steamed down at 365 knots. The jock captain closed the taps around 3grand and I thought no way, chiltern here we come but around the marker he just heaved the nose so high I could only see blue, dropped everything, followed by a mild bunt and greased it on.
and you tell that to the youngsters and they won't believe you ( greasing it on that is!)

320 kts at 8 DME in a MD80 doing a visual, greased it on as well...

All right kids, carry on with the thread.

I believe it is because the tendency of the airplane to roll.

The limitation to use speedbrakes with flaps extended might have something to do with an engine failure. If you lose a donkey with full flaps and the speedbrakes don't retract in time and you are close to the ground I don't know how much margin you would have left.

It depends on type.

Nimrod had an authorised approach of 30 degrees flap plus airbrake.

HS125 on the other hand it was a no-no to have airbrake with flap it caused flap flutter and fatigue.

Iggy
 

Yes believe that especially as we had to have land flap and gear SELECTED by 400ft..but down ils 14 with a tailwind in ZRH it was select additional flap at the limit...lovely aircraft and the aerodyanmist at Toulouse on Tuesday pointed out that his boss had patented the strakes on the nose and got lots of lolly from M.D..
All to do with vortex and lift..something new to me.

Allowed, but "not recommended" for F25 and F30 on the 744. I've done it on occasion, but it does give a significant descent rate along with a lot of rumble from the turbulence. Not a lot of practical-use situations (e.g., speed restricted, intercept glide path from above)...

Reason why Toulouse got the money I guess.

The shedding of vortices from the forward portion of long and slender fuselages at incidence can cause lateral instability which is aggravated if the aircraft is flying at small angles of yaw. This condition only occurs at low speed and few aircraft have a sufficiently high overhang ratios (the ratio of length of fuselage ahead of the centre of gravity to fuselage diameter) to give a problem. The rear-engined DC-9-50 has an overhang ratio of about 6:1, very similar to that of the long-bodied, wing-engined DC-8-61/63, which was not fitted with strakes. Small, very low- aspect-ratio forward fuselage strakes act to prevent any lateral instability by fixing the vortex pattern. Concorde is the only other airliner to make use of such strakes and the DC-9-50 is the first subsonic airliner to follow suit.

The DC-9 strakes are probably insufficient in area to provide anything but a minimal nose-up pitching moment or contribution to lift during low-speed flight and therefore serve a completely different purpose from that of the retractable foreplanes on the Tu-144. The primary role of the latter is to provide a trimming force which also contributes to lift. The strakes were not shown on earlier general-arrangement drawings of the DC-9-50 (although they have been apparent on drawings of the longer DC-9-60 project shown to airlines) and were probably added after wind-tunnel testing.

Good point. Good thing that the speed brake retracts automatically on the A319/320 in conf full and conf 3 and conf full on the A321.

Bonus question: Anyone knows why on A320 with AP ON we only have half speed brake?
Thank you.

Thanks megan
 

The lecture at Toulouse was one of the guys who worked on the arrow, super caravelle and Concorde.

If you don't mind me guessing again I think it has to do with the dramatic increase of Vls with full extension. If you are already on manual flying and a protection kicks in on a undesired way the AP wouldn't be following the FD and you would override them.



Well, except if you are a Children of the Magenta (green in Airbus) :E

And then of course the Lockheed L-1011 Tristar deployed partial spoiler-speed brakes on both sides on approach in the Direct Lift Control (DLC) mode. They were then raised or lowered to control rate of descent without any change of the angle of attack. In DLC mode the aircraft maintained a constant body angle. You still got differential spoiler operation to assist roll control. Very neat.

The A320 depends on config status as well, with the steep approach modification the speed brake is usable in all configs and actually extends automatically to allow the london city approach on the smallest one.

Ejet and CS100 both use Spoiler against flap for steep approach.
CS can use spoiler with all flap settings.
Ejet normally restricted to Flap 1 if not steep approach.

Of course they deploy asymmetrically for roll assist too.