Welcome to Montana ... Please!

This is the place where you can introduce yourself, and include a photo if so desired.

Re: Welcome to Montana ... Please! - Rough TDT Drag Calcs

Postby jim_manley » Sat Jul 01, 2017 6:59 pm

During a filling breakfast of oatmeal with fruit Saturday, I searched the forum for discussions about TDT drag and didn't find any specific calculations, so I did some of my own. I assumed a worst-case shape of a flat-front, rectangular box, as the difference between that and the most aerodynamic shape is a factor of about 30% less for the still-boxy cross-sections of our TDTs.

F = A x P x Cd (F is Force, A is cross-sectional Area, P is wind Pressure, and Cd is Coefficient of drag)

P = 0.00256 x V^2 (V is Velocity in mph, and P is pressure in pounds/square foot)

Cd (long rectangular box solid) ~ 2.0 (no dimensions)

So, F = A x 0.00256 x V^2 x 2.0 (F is total Force in pounds)

Here are the numbers for my Corto designs:

Code: Select all
           4 x 4 x 8 foot (H x W x L) Corto
Vehicle     Wind      Area    Coefficient    Wind Force
 Speed     Pressure  (ft^2)  of Drag (Cd)      (lbs)
 (mph)    (lbs/ft^2)
    5       0.06      30.0       2.0             2
   10       0.26      30.0       2.0             8
   15       0.58      30.0       2.0            18
   20       1.02      30.0       2.0            33
   25       1.60      30.0       2.0            51
   30       2.30      30.0       2.0            74
   35       3.14      30.0       2.0           100
   40       4.10      30.0       2.0           131
   45       5.18      30.0       2.0           166
   50       6.40      30.0       2.0           205
   55       7.74      30.0       2.0           248
   60       9.22      30.0       2.0           295
   65      10.82      30.0       2.0           346
   70      12.54      30.0       2.0           401


Code: Select all
           5 x 6 x 12 foot (H x W x L) Corto
Vehicle     Wind      Area    Coefficient    Wind Force
 Speed     Pressure  (ft^2)  of Drag (Cd)      (lbs)
 (mph)    (lbs/ft^2)
    5       0.06      30.0       2.0             3
   10       0.26      30.0       2.0            15
   15       0.58      30.0       2.0            34
   20       1.02      30.0       2.0            61
   25       1.60      30.0       2.0            96
   30       2.30      30.0       2.0           138
   35       3.14      30.0       2.0           188
   40       4.10      30.0       2.0           245
   45       5.18      30.0       2.0           311
   50       6.40      30.0       2.0           384
   55       7.74      30.0       2.0           464
   60       9.22      30.0       2.0           553
   65      10.82      30.0       2.0           649
   70      12.54      30.0       2.0           752

While I'm working on my TDT, I'm running some more accurate computational fluid dynamics (CFD) modeling using the actual profile of my TDT designs, but those are computationally intensive. They're usually done on massively-parallel, high-performance computational systems with thousands of processors (way more powerful than the old supercomputers). So, they'll take some time to complete at a reasonable level of precision on my desktop system with hundreds of floating-point processors on a 3-D graphics card.
"Education isn't the filling of a pail, but the lighting of a fire." -- Plutarch ... or W.B. Yeats ... or ...

"In theory, theory and practice are the same ... in practice, they aren't!" -- Some Engineer

"Just when you think you have all the answers ... they change all the questions!" -- Murphy of Murphy, Dewey, Screwem, and Howe, LLP


What I'd love to build: ... What I'll probably wind up with:
.....Image................ Image
User avatar
jim_manley
Teardrop Advisor
 
Posts: 52
Images: 61
Joined: Wed Jun 21, 2017 3:20 pm
Location: East Glacier Park, Montana

Re: Welcome to Montana ... Please! - FRP-to-Foam Adhesive?

Postby jim_manley » Sat Jul 01, 2017 9:43 pm

In preparation for buying my foam, FRP, etc., I've been poking around the forum and doing web searches looking for the right adhesive to use to stick non-porous FRP panels to non-porous blue or pink extruded polystyrene foam in an exterior application. I've found a few low/non-VOC, odor-free, adhesives for non-porous surfaces (they cure with moisture, so misting accelerates it), and they're rated UV-proof, but are only designed for interior applications. I assume that means they can fail when heated, and while my FRP panels will be white/very-light-gray, and so should stay pretty cool even in direct sunlight, but I may wind up transiting through hot areas at some point, and I don't want to take any chances.

Thanks and All the Best,
Jim
"Education isn't the filling of a pail, but the lighting of a fire." -- Plutarch ... or W.B. Yeats ... or ...

"In theory, theory and practice are the same ... in practice, they aren't!" -- Some Engineer

"Just when you think you have all the answers ... they change all the questions!" -- Murphy of Murphy, Dewey, Screwem, and Howe, LLP


What I'd love to build: ... What I'll probably wind up with:
.....Image................ Image
User avatar
jim_manley
Teardrop Advisor
 
Posts: 52
Images: 61
Joined: Wed Jun 21, 2017 3:20 pm
Location: East Glacier Park, Montana

Re: Welcome to Montana ... Please! - Roof Joint Details

Postby jim_manley » Sun Jul 02, 2017 10:00 pm

Here's a drawing for the wall/roof joint that shows how the plastic sheet on the outer FRP layer of the raise-able roof overlaps the FRP-covered edges of the side walls panels:
Image
The locator pins are attached to the overlapping FRP edge and pass through locator holes in the edge FRP layer in the tops of the wall panels. The pins enter the holes as the roof is lowered onto the side walls, providing lateral reinforcement of the latter. The window frames are attached to the underside of the roof edges, running fore-and-aft and allowing the windows to hang and slide just inside the inner edges of the side walls. There are gaskets along the outer edges of the bottoms of the window frames, which seal against water intrusion when the roof is raised.

The foam core of the roof section is cut along the long edges so that the outer top edges of the side walls are located directly above the outer edges of the floor panel. So, the width of the roof section foam core section is reduced by twice the thickness of the sidewall panels, plus 1/8th of an inch for 1/16th of an inch of clearance on each side of the roof section for movement, while minimizing the probability of moisture intrusion along the bottom of the window frames:
Image
"Education isn't the filling of a pail, but the lighting of a fire." -- Plutarch ... or W.B. Yeats ... or ...

"In theory, theory and practice are the same ... in practice, they aren't!" -- Some Engineer

"Just when you think you have all the answers ... they change all the questions!" -- Murphy of Murphy, Dewey, Screwem, and Howe, LLP


What I'd love to build: ... What I'll probably wind up with:
.....Image................ Image
User avatar
jim_manley
Teardrop Advisor
 
Posts: 52
Images: 61
Joined: Wed Jun 21, 2017 3:20 pm
Location: East Glacier Park, Montana
Top

Re: Welcome to Montana ... Please!

Postby Roly Nelson » Tue Jul 11, 2017 12:51 pm

wow, Jim, you are still at it. After discussing your build with my good friend and aeronotical engineer (and 4 star General of aviation), he rightfully suggests that you start building and do less progragulationing. He said Oskosh is 2 1/2 weeks away and getting your dream on the road and back to Wisconsin, is highly improbable......no, actually impossible! Never-the-less, keep plugging away and hope for the best. Good for you, checking out the air flow and wind loads on the front of your tear. My calculations, as primative as they are, find the tumbling air flow behind my Chevy Cruze, when striking my tear's front end, have zero affect on gas mileage or ground speed. However I have noticed there is not as much slush and snow build up as there is on my car grille. I wonder why. Keep plugging away (on that laptop), and keep us informed, and by the way, how are you going to prevent water from entering the roof/sidewall connection? Weatherstripping? I fail to see it on your details.
:) :? 8) :thinking: Roly, the li'l ol' woody td guy, awaiting pics of your creation at Oskosh in 2 weeks or so.
See the little 1/2 Nelson Woody constructions pics at: http://gages-56.com/roly.html
User avatar
Roly Nelson
L'il Ol' Woody Builder
 
Posts: 2971
Images: 13
Joined: Sun Jan 30, 2005 12:45 pm
Location: Wildomar, Calif
Top

Previous

Return to Newbies, Introduce yourselves

Who is online

Users browsing this forum: No registered users and 7 guests