View Full Version : Tailwheel doors for speed?

09-21-2004, 08:47 PM
I remember seeing somewhere this week a good photo of "Blue Thunder" on edge in a Sport Class race and the tailwheel doors were clearly only partly closed. It made me wonder if aerodynamically this would be a very big penalty to speed? My guess would be 5 mph or more, but it is only a guess.
I've thought in years past that Czech Mate could have seen some speed increase if she had tight sealing tailwheel doors installed (maybe she does now, I haven't really looked the last couple of years...). Who can comment from an aero engineering standpoint please?


09-21-2004, 11:12 PM
Not an engineering viewpoint, but...

Common sense would say that anything on an airframe that increases drag or turbulence reduces maximum speeds. By how much depends on the size and shape of the obstruction, and the speed of the airflow around it

Smooth wings, gap seals on movable surfaces such as ailerons and elevators/rudders, etc. are all used to get a few more mph's....Anything sticking out in the airstream or prevents smooth airflow will slow one down a bit, including wheel-doors.

I wonder....was Thunder Mustang's exposed tail wheel an accident due to G-forces or malfunction? Doesn't make sense to build it that way intentionally in a high-speed racer.

09-22-2004, 07:55 AM
I've noticed the same thing for years with White Lightnin's nose gear door.
I always thought it was g-forces and door adjustment working together, but I'm not a mechanic.
Can't be good for speeds tho.
The mustang had a problem with up-locks early on which allowed doors to open. The stress could fail a wing.


09-22-2004, 09:34 AM
"...was Thunder Mustang's exposed tail wheel an accident due to G-forces or malfunction..."

It is NOT a design problem in the Thunder Mustang,at least that we ever had to deal with at PAPA 51 for the 3-1/2 years that I observed the flying of three of the early Thunder Mustangs. We had some early micro-switch problems that caused some headaches for a time with the sealing of the main doors/inner doors but those were solved.

Probably this was just one of those race week gremlins that John and everyone else had to deal with. I hope it didn't cost him the extra ummphh needed Sunday though.

W J Pearce
09-22-2004, 07:11 PM
The tailwheel doors have been a problem for a while. It only happens at high speeds but it happens with no Gs also. Current theory is that the air comes off the canpoy and pours into the canpoy slide slit on the top of the fuselage. This creates pressure in the aft fuselage which then pushs on everything, but the gear doors give, so that is the exit point.

Just a theory.


09-22-2004, 09:09 PM
And a very interesting theory it is.....perhaps something as simple as a vent in the tail section could relieve the pressure and solve the problem. Hard to say, since simple fixes often lead to new "gremlins"...

If it happens even with no G's applied, then it does sound like high air pressure behind the doors pushing them open, or a low pressure area is being formed outside of the doors, sucking them open.....I can only speculate, but I can't imagine any other potential cause if all the mechanicals are working fine under lower speeds...

Eric M
09-23-2004, 07:49 AM
The air entering the cockpit is just a theory, from first hand experience in a mustang, if you put anything to close to the area between the canopy and the fuselage it will be sucked out, granted that it will fit through that space. I believe that its more a form of suction/lift that causes the tailwheel doors to open or give a little. If you leave a gas cap off of the wing of an airplane, it does not pressurize the tank, rather it sucks the fuel from the tank.

Kilo Hotel
09-23-2004, 10:06 AM
Putting a tail vent behind the tailwheel isn't a bad idea. Any time you've got NACA vents or scoops bringing air into the fuselage, that air is gonna exit the airframe again, somewhere. If it exits where you don't want it to, it'll create drag by disturbing the airflow. Why not let it out where it can't hurt you, with a rear-facing vent in the tail? It's a common practice on racing sailplanes, which represent the last word in aerodynamic efficiency.

W J Pearce
09-23-2004, 07:12 PM
Personally, I want to due away with the tail wheel and go to a magnesium tail skid. Blue Thunder would then be called Sparky II, or maybe Lil Sparky.


09-23-2004, 11:26 PM
Personally, I want to due away with the tail wheel and go to a magnesium tail skid. Blue Thunder would then be called Sparky II, or maybe Lil Sparky.

BillBill, you know, you are demented, just a little mind you but you are, indeed, demented...

I like that in my friends...


09-24-2004, 06:43 AM
Would be more like the Parker Rocket.... :D


09-24-2004, 07:47 AM
Unless they changed things, Race 86 uses the tail wheel opening as an exhaust outlet for the oil cooler.