Inflatable boattail

[drrbc]

Once upon a time in the massive number of clicks across the web…

I recall going stumbling upon a diagram of a dirigible (IIRC) in whose tail fins were inflated by a ram air type opening- so more of a parachute than balloon.

The obvious problem being the induced drag of the opening versus the reduction benefit of such a mechanism.

Materials wise it doesn't seem (on the surface at least) much more difficult than a little plastic, parachute type nylon, and a needle and thread.

Anyone seen similar or heard of such?

[user removed]

I like aluminum battens and sailcloth.

regards
mech

[freebeard]

I recall going stumbling upon a diagram of a dirigible (IIRC) in whose tail fins were inflated by a ram air type opening- so more of a parachute than balloon.
...
Anyone seen similar or heard of such?

More likely a Blimp? Losing control without forward motion sounds like a recipe for disaster.

[drrbc]

Originally Posted by freebeard

More likely a Blimp? Losing control without forward motion sounds like a recipe for disaster.

You'd think, huh? It'd almost be like trying to control a sailboat with no wind!

Can't recall it's construction, but I'm tending to think dirigible because of how that construction contrasted with the rest of the aircraft. Also, on reflection, I'm wondering if it wasn't part of the rudder but dunno.

[drrbc]

Originally Posted by Old Mechanic

I like aluminum battens and sailcloth.

regards
mech

I too prefer more rigid construction, but I always imagine what ever the mod is bouncing down the road and into someones windshield.

[aerohead]

Originally Posted by drrbc

Once upon a time in the massive number of clicks across the web…

I recall going stumbling upon a diagram of a dirigible (IIRC) in whose tail fins were inflated by a ram air type opening- so more of a parachute than balloon.

The obvious problem being the induced drag of the opening versus the reduction benefit of such a mechanism.

Materials wise it doesn't seem (on the surface at least) much more difficult than a little plastic, parachute type nylon, and a needle and thread.

Anyone seen similar or heard of such?

I've seen towed targets for military weapons testing which inflate this way,and one boat tail,by Bruce Ruefer of the Lubbock area.I think his patent drawing is given in the appendix of the book,"FAIRING WELL",which is available online for free.It also appeared as a photograph in "ENGINEERING TODAY',published by Texas Tech's Engineering Dept. in 1996.

[UltArc]

Originally Posted by drrbc

Once upon a time in the massive number of clicks across the web…

I recall going stumbling upon a diagram of a dirigible (IIRC) in whose tail fins were inflated by a ram air type opening- so more of a parachute than balloon.

The obvious problem being the induced drag of the opening versus the reduction benefit of such a mechanism.

Materials wise it doesn't seem (on the surface at least) much more difficult than a little plastic, parachute type nylon, and a needle and thread.

Anyone seen similar or heard of such?

Obviously exhaust is dangerous. Just saying...BUT, what if the boat tail ran off exhaust, until reaching full size where it would "lock" or "snap" into form- and then the exhaust could come out of a flap in the back, or whatever. Or, design it so the pressure needed to fully inflate is X, and the pressure to release from exhaust/switch to going to rear wake is X+5 (PSI?). Then when you get to the destination, bend the joints back, and let it fold into place. Obviously letting the car idle to inflate would be a poor idea, but if it could be unfolded length wise while driving, or before hand (cities with tailgater's), then it would probably work. I would guess this is more trouble than worth for commercializing, but seems like a reasonable project for some of our more advanced members.

(CRX donkey? I think that's his handle. The one with the BMW tornado bead seats.)

[freebeard]

Engine exhaust is corrosive. And the added back-pressure would harm engine performance.

A double-walled envelope (like a U-shaped air mattress) would need less air volume, and could be inflated, as aerohead suggests with an auxiliary fan.