Vent as Speed Brake and Rear Aero CG Device

dbuds2 · #1 02-07-2008, 05:25 AM

I met a RV pilot at Sun N Fun last year with the scissor style of speed brakes on his wings. He said besides helping to slow down (don't remember if CS or FP) they also help to move the aerodynamic CG aft and helped to keep his tail dragger going straight down the runway.

What do you think of using something like Van's RV10 vent mounted on the underside of the fuselage near the tail with the opening (but blocked to stop air from really coming in) facing forward? ON decent you could push/pull a cable to open the vent, get additional drag and from aft end to help resist any misalignment of CG and forward motion.

I was out for a long run this morning and this idea popped in my head and I thought bouncing it off this wonderful world of Van's AirForce experts should be the first step

Kevin Horton · #2 02-07-2008, 10:35 AM

The force created by the speed brake would not vary much when the aircraft yawed on the ground. The restoring moment from the speed brake pushing the aircraft straight would be equal to the drag from the speed brake times the distance that the speed brake was displaced sideways from the tire contact point. This would be quite a small restoring moment, unless the speed brake was very large.

If you believe that there is a problem to be solved (and the service history would tend to suggest that there is no problem), then it would be much more effective to add a ventral strake. The restoring moment would be equal to the side force created by the strake times the fore and aft distance from the wheel contact point to the strake. And, the amount of side force from the strake would increase as the yaw angle increased. Thus the ventral strake would produce a much larger restoring moment than the speed brake.

Lockard · #3 08-25-2011, 04:12 AM

Quote:

Originally Posted by Kevin Horton

If you believe that there is a problem to be solved (and the service history would tend to suggest that there is no problem)...

It's phrases like the one above that remind me of how often I like to tinker with things that aren't broken.

But seriously, if a FP prop RV wanted to add some yaw stability, sink rate, slow an approach or shorten landing distance, would a speed brake like this...

...installed under the horizontal stabilizer on the right and left side be feasable? Nothing too big, maybe 8 inches tall and 4-6 inches wide and hinged on the leading edge? Would that destroy the rudder effectiveness? Is there room with all the other control linkages? Is this something that could be accomplished with a lever and a closed cable loop?

Toobuilder · #4 08-25-2011, 01:07 PM

Quote:

Originally Posted by Lockard

It's phrases like the one above that remind me of how often I like to tinker with things that aren't broken.

But seriously, if a FP prop RV wanted to add some yaw stability, sink rate, slow an approach or shorten landing distance ...

Problem solved!

gnuse · #5 08-25-2011, 03:57 PM

Quote:

Originally Posted by Toobuilder

Problem solved!

A good friend flew B-47's and stated the reason for the chute was to create enough drag to allow the engines to be kept spooled up. He said that the time to spool those engines up was in the 15-20second range

Think about what go-arounds must have been like.

Shockwave · #6 08-25-2011, 06:12 PM

A split rudder maybe? Space Shuttle style.

What happened for subsequent landing attempts in the B-47? Was the chute able to be reeled in?

flyboy1963 · #7 08-25-2011, 10:13 PM

...Bud, how about just standing on the pedal, activating the nice, big rudder already at the back end of your -8?
I'm no fighter pilot or aerodynamicist, but that has GOTTA create a bunch of drag!
.(....okay, not recommended in some flight attitudes, altitudes, or airspeeds)

Lockard · #8 08-26-2011, 06:23 AM

Quote:

Originally Posted by gnuse

...to create enough drag to allow the engines to be kept spooled up. He said that the time to spool those engines up was in the 15-20second range

...

Amazing. Ross Perot's giant sucking sound is actually the fuel flow rate on those horrible turbojets. Thank God for the high bypass turbofan.

Does anyone have a good photo of the inside of the rear fuselage with the linkages? I'm still curious about the amount of room back there. Sorry, I don't have access to any drawings.