Too Tense Boat Tail
 

Question to those with/on boat tails: how stiff do the panels need to be in order to be effective?

It would appear to me that they wouldn't need to be since they are guiding airflow rather than deflecting. Is this correct?

The reason I ask is that I am working on a idea. Think of it as an inside-out pop tent/ Teepee boat tail. Structure and cover like a tent using clear greenhouse film. The rear joint tied together like a teepee, with a cable attachment on joint to body. This cable would keep it attached and provide a slight bend to rods and tension to outer skin.

This concept would be easily collapsed and stored in the car for in town, and setup quickly as well. Rod attachment points would be easy to hide, and would be in 6 locations: Under roof spoiler, top of wheel arch, and the front of the wheel arch (incorporating a rear wheel skirt).

Thoughts?:confused:

Title fyi (cleaned for PC reasons): Man walks into a psychologist's office and says "doctor, I've been having these really odd dreams". Doctor: "tell me about them". The man says "At first, I'm a wigwam, then a teepee, then a wigwam. Doctor, what wrong with me?". Doctor says, "I know your problem. You're two tents! (too tense).";)

The flapping noise seems undesirable whilst driving downtl the highway at 70 mph. But give your idea a shot.

Think of it in the same manner as a convertible top. They still stretch/inflate due to the air pressure/vacuum as the air rides over the skin. With the exception of the hard top convertibles, all soft topped convertibles inflate to some degree. ;)

My 1985 Toyota Celica GT-S convertible does it all the time and the fabric is tight against the frame. :(

how stiff
 

*the envelope should be inflated to some minimum pressure (which I never quantified) which can be achieved with a BOSCH 12-VDC heater fan from a VW Westfalia Campmobile and should have a sewn-in,internal truss structure for triangulation,both vertically and horizontally.
*Without inflation pressure and trusses,the envelope will rise into high-velocity/low-pressure air,then reach an angle-of-attack which triggers burble,then stall,'falling' away from the airstream until it's slope is gentle enough for reattachment,then the whole process repeats itself,setting up a cyclical whip-sawing of the structure which cannot be dampened.
I encountered this on my T-100.
You can use a rigid spar to reinforce the structure,but then you've got to deal with that.
You can probably find online patent drawings of GoodYear Tire's Aerospace Division's U.S.ARMY inflatable airplane of the 1950s,which will show you their internal truss structure.
Without something like this to reinforce the structure,you'll have a rattlesnake's tail to deal with.:eek:

This was my thought:

http://ecomodder.com/forum/member-fr...pe-ii-boat.jpg

A stowable rigid lower difusser panel, fiberglass ribs and a ripstop nylon sock over it. At the time I thought it could be inflated with scoops along the front edge. More lately I'd go with a multicellular construction with internal transverse walls.

Edit: Actually, here's a sketch I made in the 1980's that shows something similar:

http://ecomodder.com/forum/member-fr...nd-inflate.jpg

rigidity
 

The diffuser panel would get you most of the way there.It would kill any pitching,kill any yawing at the bottom.Any tension of the envelope would stabilize the top.
Werner von Braun's V-2 underwent aeroelastic deformation which he fixed with sheet metal reinforcments.
It might have been the Redstone Missile which suffered similar aeroelastic deformation.They ended up inflating it's body with compressed gas to achieve the rigidity without any real weight gain.
Bruce Ruefer (I think it is) in Lubbock,Texas has an inflatable boat tail he was developing,which just used scoops to harvest ram-air for inflation and tensioning.Texas Tech,who was helping him didn't say a lot about it.

That was why I showed those little half-moon scoops on the model. It's silly when there's 1500 cubic feet/minute of engine cooling air blowing past.

It's funny that the sketch (intended as a camper pop-out) is so similar, from 30 years ago. :eek: