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banco
01-22-2008, 10:03 AM
I'm cloning the Honest John K-27. The original plans called for a BT-50 tube that was 9.5 inches long. The forward end of this tube was partially covered by a paper fairing which gives the HJ its distinctive flared shape. Now here's the problem: The nose cones available now for the HJ from BMS and others already include this flare in their profile, obviating the paper fairing of the original kit. That means I must shorten my body tube to compensate for that portion originally covered by the fairing. But by how much? Does anyone know? Thanks much in advance.

rocketguy101
01-22-2008, 12:55 PM
can you scale it from either of these Pete Alway drawings?


M31--early big fins (http://members.aol.com/petealway/Rocketdrawings/HonestJohnM31.gif)

M50--later small fins (http://members.aol.com/petealway/Rocketdrawings/HonestJohnM50.gif)

mojo1986
01-22-2008, 01:53 PM
The instructions call for the rear edge of the shroud to be located 7 7/8" from the rear edge of the BT-50 body tube, so presumably that should also be your modified tube length.

Joe

banco
01-22-2008, 02:04 PM
Thanks mojo and rocketguy!

Carl@Semroc
01-22-2008, 10:19 PM
The instructions call for the rear edge of the shroud to be located 7 7/8" from the rear edge of the BT-50 body tube, so presumably that should also be your modified tube length.

JoeThe math does not work out on the Honest John. If the tube is 9.5" long and the shoulder on the nose cone is .3" long, then the shroud length of 2.32" would place the end of the shroud at about 7.5" instead of 7.875".

The only explanation is that the nose cone is about .375" from completely seating in the BT-50. This could explain why the shoulder length of the nose cone was changed from .5" in the catalog to 1" in the actual cones. The correct scale length for the body tube for a BT-50 sized HJ should be about 7.8", so I would probably go with the 7-7/8".

banco
01-23-2008, 02:12 PM
Carl,

Thanks for this additional detail (and for the fins).

ghrocketman
01-23-2008, 03:10 PM
Carl is right on the nose cone on the K-27....it does NOT seat completely to the Bt-50 shoulder; a slightly reduced from max-diameter upper shoulder on the cone seats against the paper transition instead.

jbuscaglia
01-23-2008, 03:15 PM
The only explanation is that the nose cone is about .375" from completely seating in the BT-50.

I believe that you are correct about that, Carl. I partially built one of these back in the '70s and as I recall the BT-50 shoulder on the nose did not go all the way in.

I messed up the construction on the body somehow. I remember making the shroud and test-fitting the nose cone. The body is long gone, but I still have the nose cone, and I think I may still have the decals. Maybe I need to clone one myself.

rocketguy101
01-24-2008, 06:34 PM
Carl,

Thanks for this additional detail (and for the fins).

I used built-up fins made from balsa and 110# cardstock--saved lots of sanding :D

banco
01-24-2008, 09:58 PM
I used built-up fins made from balsa and 110# cardstock--saved lots of sanding :D
You've clucked, now you gotta lay: Please explain your technique. I doubt sanding those tapers will produce an accurate result, so I'm all ears!! (Nice job BTW.)

rocketguy101
01-24-2008, 11:24 PM
Basically take the fin pattern and mirror it about the leading edge--this will become a fold line. You need to create two more fold lines that will form the high point of the wedge cross section. You then need some balsa spacers to support the inside of the fin.

I believe I just used a single spar running from the root to tip along the high point, and just used "Fill n Finish" to fill in the root and tip and sand smooth. The model in the pics is about 10 years old.

The fin "skins" will be cut out of 110# cardstock or even file folder material.

Check out the instructions for the Estes Little Joe II or the Saturn I those are built-up fins, with more internal support.

The attached pdf may explain better than my text. It should print out full scale--there is a 1" by 1" square to check your printer setting.

BTW, go easy on the glue w/ the spar, you will warp the paper. You may go with CA (super glue) or something else not water based. Also, you can really strengthen the fins by applying CA to the paper after the fin dries. Do this in a well-ventilated area the fumes are atrocious!! :eek:

mojo1986
01-25-2008, 07:45 AM
David, that is a REALLY nice technique and makes what was a very tricky sanding job obsolete. I always prided myself on the job I did on the fins of my old K-27, but if I had to do it again, it would definitely be by using your method. One question though............did you taper the internal balsa support so that it was thicker at the root edge?

Joe

banco
01-25-2008, 10:34 AM
David, Thanks much for this idea. I also have the same question about the tapering.

On another matter, what kind of paper stock did you use for the banding and nozzle cutouts?

rocketguy101
01-25-2008, 05:29 PM
David, that is a REALLY nice technique and makes what was a very tricky sanding job obsolete. I always prided myself on the job I did on the fins of my old K-27, but if I had to do it again, it would definitely be by using your method. One question though............did you taper the internal balsa support so that it was thicker at the root edge?

Joe
Thanks--like I said I came across the technique building an Estes Little Joe II and Saturn 1B. Oh, the CMR D-Region Tomahawk (http://www.oldrocketplans.com/cmr/cmrS1/cmrS1.htm) uses a paper covered fin too. It is also covered in Pete Alway's "Art of Scale Modeling". I am lazy, so any highly tapered/angled fin like a Nike or such I use built up fins.

Yes there is some taper from the root to the tip (including the card skin it runs 0.12" at the root to 0.09" at the tip). My thickness is greater than a true scale dimension (0.078" to 0.032"). Subtract the card thickness and you're left with a tiny toothpick for a spar!

David, Thanks much for this idea. I also have the same question about the tapering.

On another matter, what kind of paper stock did you use for the banding and nozzle cutouts?

I used 110# cardstock, available in the paper section at WalMart. I have found a nice coated stock at a stationary store, so you should be able to find it at Office Max, etc.

Here is another fin I did for a Terrier-Sandhawk semi-scale--I haven't flown this one yet. The Sandhawk's fins were done similar to the D-R Tomahawk.