Hello all - it's been awhile since I've been on here but I've gotten a bit of the build bug again. I am working on a clone of one my first rockets, the Estes Marauder #1922. I've gathered donor parts from a couple of other kits, but I have a question on the fins. I pulled up the plans and fin sheet from YORF and printed out the fin sheet. The directions state that when printed, they are at their correct size, but I don't think they are correct. There are two smaller balsa standoffs for the launch lugs and the size in the directions are different from the printed plan sheet.

I am wondering if someone could get me the actual dimensions of the fins? I could take the plans and compare actual size to the printed size, come up with a ratio, multiply and divide a whole bunch of numbers, yada yada yada and come up with a pretty close size for the fins. But if anyone a Marauder on a shelf, a physical and accurate measurement would be awesomely appreciated.

Thanks in advance......Rick

Rick,

Try using Gimp set for 300 dpi. I think that's what I used when I drew the image so long ago...

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Craig McGraw

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SAM 0044
AMA 352635

If I print at 300 dpi, the lug standoffs come out a little larger than the size mentioned in the instructions — 1" on the root edge, 3/4" on the tip edge, and 3/8" high. Instructions say 7/8", 5/8", and 1/4", so the pattern dimensions are too large by 14%, 20%, and 50% respectively. Clearly the standoff's proportions are different than what's implied in the instructions, and there's no way of using the standoff dimensions to rescale the fins.

So maybe the fins come out the right size printed at 300 dpi, but you'd still need to measure an actual fin to verify it.

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Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com

Hmmnnn...

OK, the following dimensions are taken from my clone, and the fins were cut to match an old original kit. I thought the drawing was correctly sized, but it's been so long ago...

Root edge: 1 3/8"
Tip edge: 1 1/4"
Leading Edge: 3 3/8"
Trailing Edge: 2 3/4"

The upper LE-to-Tip angle is 90 degrees, as is the Tip-to-TE angle.

As you experienced, the drawing does come out much larger than the original when it's printed out from some graphics packages. I run linux, and it came out way too large in Image Viewer. When I look at it now using GIMP, the image properties show that it is sized at 300 dpi. Printing a quick sheet through my laser printer out of GIMP gives me the following dimensions:

Root Edge: 1 3/8"
Tip Edge: 1 1/4"
Leading Edge: 3 3/8"
Trailing Edge: 2 13/16" (1/16" longer than my clone)

LE-to-Tip angle and Tip-to-TE angle remains at 90 degrees.

Lugs --

Root Edge: 1"
Lug Edge: 3/4"
Height: 3/8"

(The lug stand-offs may be a bit taller than stock, but I think they're close...)

Use GIMP (free download, Windows and Linux) or Photoshop Elements (~$100, Windows only) to view and print the image instead of Paint or Image Viewer. Some simple programs don't know how to correctly deal with TIF archives. They just blow the image up to fill the sheet. See if there might be a setting in your program to print "original size", or "do not enlarge", or something to that effect.

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
BARCLONE Forum -- BARCLONE Forum

BARs helping BARs

SAM 0044
AMA 352635

From a real Marauder, including balsa grain from 80's finishing skills.
Tip edge/Width is 1 1/4inch
Leading Edge is 3 3/8 inch
Trailing edge is 2 25/32 inch

Attached Thumbnails

     

Any chance you could verify the height of the fin, as well as the root chord? While you're at it, the sweep length and angle would be helpful. I'm trying to sim this in OR, and it's getting to be a PITA.

Thanks
Jim
.

__________________
.
.

Dreaming of making the rockets I dreamed of as a kid (and then some).

"The Guide says there is an art to flying", said Ford, "or rather a knack."
"The knack lies in learning how to throw yourself at the ground and miss."

Launching is Optional... Landing? That Depends on Trees.

I can't right now, but the fin is a basically a rectangle truncated at the root, so if you draw the fin using the other dimentions you can measure the root.

The fin is a trapezoid, but one with the leading and trailing edges parallel, not the root and tip. So in OR you'd have to do it as a free form fin. To get the coordinates of the corners requires some trigonometry (specifically, figuring out the sweep angle and then applying a rotation). I get:

0 0
1.448 3.049
2.577 2.512
1.384 0

Look right to you?

__________________
Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com

Thanks for the measurements...

I've run the numbers through OR and created a file for it. However, I've got a conflict on some of the numbers (from a source on TRF), so I've created a 2nd version with the 2nd set of numbers. Both look really close, I've just got to look at the printouts and figure out which version I want to build.

Thanks again!
Jim

__________________
.
.

Dreaming of making the rockets I dreamed of as a kid (and then some).

"The Guide says there is an art to flying", said Ford, "or rather a knack."
"The knack lies in learning how to throw yourself at the ground and miss."

Launching is Optional... Landing? That Depends on Trees.

Thanks folks for all of the help. I think I can now get started on my Maruader - after I hit my LHS for some fin stock. Thanks again!