cherokee-d inspired rocket

ooo, decisions, decisions. not sure how closely I want to get to the original with regards to the launch lugs, the original cherokee had 2 lugs one at the aft end and one at the forward end of the Bt centered between two fins, most of my rockets have a lug just aft of the cg and one further aft along a fin root. what do you all think, should I follow the original? or go with my usual placement? thanks.
rex

if you are trying to get something that is close to the original, then i would personnally try and match the original placement.
if you are going with a different colour scheme etc, then go for your usual placement.

Rex R said:

ooo, decisions, decisions. not sure how closely I want to get to the original with regards to the launch lugs.
rex

Click to expand...

Tough choice. Flip a coin.

Rex R said:

ooo, decisions, decisions. not sure how closely I want to get to the original with regards to the launch lugs, the original cherokee had 2 lugs one at the aft end and one at the forward end of the Bt centered between two fins, most of my rockets have a lug just aft of the cg and one further aft along a fin root. what do you all think, should I follow the original? or go with my usual placement? thanks.
rex

Click to expand...

Personally I've never understood the manufacturers placement of Ugly, drag inducing lugs centered between fins.

If we're gonna use LL's at least put them where they are least obtrusive and perhaps just a tiny bit least dragy. My vote would be tucking the aft lug into a fin root fillet and aligning the other just FORWARD of the loaded CG.
That's SOP when I'm building if using Launch lugs. The Cherokee's i've built have flown just fine that way for years
Hope this helps.

I REALLY dislike painting w/ gloss white . think I'll go with my current preference and tuck the aft lug next to a fin etc. right now its just a pile of parts(well I did get the mmt assemebled), fins weigh in at 2g each. pics later. thanks for the insights.
rex

How big is the Cherokee D you are building?

I made a BT-5 downscale for T engines and used two 1/8" lugs. One small one at the bottom, one small at the top like the original.

It looks rediculous. The lugs are too big and out of proportion for this size model. On this size model I should have went with a single lug.

21.6" as listed in the '74 estes cat . so it'll be getting the upgrade to 3/16" lugs. unless I goof things up totally in regards to weight it will not be getting the stock size (18") chute however .
rex

If it were an upscaled Cherokee, would it be a Grand Cherokee? :roll:

lol, and get two companies miffed if you decide to market it .
rex

took me awhile to get the sub-assemblies done(white glue takes forever to dry in hot humid weather) but, the pace should quicken a bit now.
rex

I built a Cherokee Deuce designed for a cluster of two mini motors.

latest entry into the 'cherokee nation', still needs clear coat (& install shock cord/parachute),and needs to pass stability testing...other than that pretty much done .

it got its maiden flight at bong aug 28. nice straight flight, a small hitch in the recovery apparently I goofed a smidge when I made the baffle, the chute got a bit warm in one spot(guess I'll have to use some wadding after all), aside from that no damage (and the 'stick and paper' fins came back fine).
rex

Rex R said:

it got its maiden flight at bong aug 28. nice straight flight, a small hitch in the recovery apparently I goofed a smidge when I made the baffle, the chute got a bit warm in one spot(guess I'll have to use some wadding after all), aside from that no damage (and the 'stick and paper' fins came back fine).
rex

Click to expand...

I'm curious. Why did you go with stick and paper fins? Great looking rocket, by the way!

thanks. bit of a departure(for me) from the 'hard' line between colours, wasn't sure how it would turn out...
heheh, well made the 1st fin just to see if I could(and how hard)...found that (for me) it was easy and it was stiffer than the solid fins. so I made two more fins to match. did get a few odd looks from folks when they noticed that they were hollow.

Micromeister said:

Personally I've never understood the manufacturers placement of Ugly, drag inducing lugs centered between fins.

If we're gonna use LL's at least put them where they are least obtrusive and perhaps just a tiny bit least dragy. My vote would be tucking the aft lug into a fin root fillet and aligning the other just FORWARD of the loaded CG.
That's SOP when I'm building if using Launch lugs. The Cherokee's i've built have flown just fine that way for years
Hope this helps.

Click to expand...

I played with Computational Fluid Dynamics (CFD) of an Alpha to see if lug location mattered as far as drag effects were concerned. The CFD results show that the area between the fins is "booger air" anyway, so it should not matter whether the lug is attached to the fin root, or whether it is centered between the fins. This has not been tested experimentally, but Chan Stevens did show lugs mounted on the fin root have lower drag than lugs mounted out on the body at the CG (see his NARAM-47 R&D report "Analysis of the Launch Lug Drag on Model Rockets")

The CFD results also show there is a low pressure area on the body tube just aft of the base of the nose cone. This is why the altimeter folks tell you to place your pressure ports more than 1 BT diameter aft of the nose. Seems to me it would be better to place your forward lug in this low pressure area.

I like split lugs, widely spaced, for another reason--it reduces the contact force on the lug if the rocket tries to rotate during liftoff. Increasing the moment arm of the contact forces reduces the force for a given torque, or moment. The force = the moment divided by the length between the reacting forces. If the moment is equal to say, 0.5 in-lb, then the reacting force on a 1.25" long lug would be 0.4 lb. Same rocket, using lugs spaced 10" apart would have a lug force of 0.05 lb.

I saw this when Rex brought it to Bong. I was quite impressed by the fins, seemed light, but solid.

This inspires me to try something similar, but with Lexan and clear packing tape.

Instead of papering wood fins, I could plastic plastic fins...?

p 'n' p fins hmmm. two things that would be of concern to me; 1) getting the skin, tight. and 2) anchoring the skin. the outer surface carries the tension load, and you need to be able to transfer the load to the skin(this applies to 'normal' fins as well but, we don't usually have to worry about it unless the paint cracks ). be interesting to say the least, go for it jeff! :dark: