The "Kamm-back" (K-form)

[aerohead]

Originally Posted by Ecky

Has there been any talk of production of inflatable boat tails for existing vehicles?

Yes,we've been kicking the idea around on a number of threads.
Fachsenfeld invented the inflatable boat tail in the mid-1930s,and Hucho has promoted the notion that we reconsider the technology.
I did a crude one for the C-10/T-100 and it performed very well.
I started with a bean-bag envelope stapled to a wooden box,using a 12-VDC auto HVAC blower for the inflation.

[aerohead]

Originally Posted by freebeard

246 people have looked at my Beetle Aerodynamics thread. Were you one?



This follows Breers more than the Template.

Yes,I've wanted to keep up with the project.
With respect to the DeSoto Airflow test mule,Breer got it down from Cd 0.51 (very close to the Beetle),to Cd 0.244.Not too shabby for 1934.And this was actually the first "Kammback",a year ahead of Fachsenfeld,although the technology was not reported until just after the Pearl Harbor attack.
Lay found,in 1933,that an optimized windshield would deliver Cd 0.12 just as well as the 'ideal' windshield (as we see in Tamai's canopy drag table).Hucho infers that we can kinda cheat on the nose,but never the tail.
Hucho also cautions that if the glass is too steep,that all we'll see is a reflection of the dashboard top and our kneecaps.
Aerodynamically,your cowl/windshield is delicious,but potentially challenged optically.
A guy did a complete Plex bubble windscreen for his Mobil Economy Run car of the 1950s,and you can see some distortion looking through it into the car.

[spacemanspif]

Thanks for the clarification on my question, Aero.

On windshields: Ever drive in a ~2000 Camaro/Firebird? Very raked windshield with about a mile of dash board under it, accompanied by the same mile of reflection...

On inflatables: Could the exhaust be used to inflate the boat tail? By using electric cut-outs you select whether the gas goes in or out of the bag. The bag would have to be pretty "leaky" to make sure the the engine isn't choked down; but then again, with you could use the cutout and not fully divert flow. Allowing exhaust to inflate the bag and allowing the excess pressure to bleed off through the regular tailpipe.

[freebeard]

Originally Posted by aerohead

Aerodynamically,your cowl/windshield is delicious,but potentially challenged optically.

The lines coming to a point in the center are for finding the line over the top. Note how they run from the top corners of the windshield to the driprail at the B-pillar, and lift off the roof in the center close to that same point.

A more practical and buildable approach would follow Disk Dean's Shalako:


I used that in the VLV sketch:

I haven't measured the angle, but it's actually pretty steep.

spacemanspif -- exhaust gases are hot and corrosive. Given an adequate heat shield, I think they could be used for wake filling. Basically, a rocket nozzle that would slow down the exhaust to match the velocity of the air moving into the wake.

an alternative to an inflatable would be base plate[s]:

from Base Pressure Recovery using Rear Cavity and Base Plates (not a direct link, the PDF is in there somewhere)

[freebeard]

I didn't make it out to the barn today, so I approximated things in Photoshop. It looks like the angle of the windshield is 32°, I would have guessed ~45°.

[aerohead]

At 32-degrees you'll have no trouble.
The Shalako is configured very much like Grumman's US Postal vehicles,with the 3-pc layout,making it very doable with flat pieces of laminated DOT safety glass.
Kamm did these segmented windscreens.

[freebeard]

I was out there today. I didn't confirm the angle, but I took some measurements.The center piece would be 42" across at the windshield, 30" at the nose and 60" tall.

The triangular side pieces would only be as long as the top 2/3 of the center piece. Baja fenders could be fitted and/or the headlights could be under glass.

Kamm did these segmented windscreens.

So did Bucky Fuller, Tatra, my Cortez motorhome.

[aerohead]

I added two additional drag tables from Kamm's FKFS a couple weeks ago if you didn't catch them.
They illustrate the drag difference between pseudo-Jaray and 'K'-form aft-bodies.Cds are included for each type.
I'm about a week away from posting Walter Lay's 1933 aero research,of which stimulated Kamm's FKFS research.I'll post it as a separate,dedicated thread.

[freebeard]

Thanks.

I see there's another believer.

[aerohead]

I just posted 3-new images with the others on page-1:
*Kamm's personal Cd 0.23 car
*The only surviving K-car
*and a tuft-study wind tunnel image demonstrating upper edge vorticity