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-   -   Semroc Pro Cherokee (http://www.oldrocketforum.com/showthread.php?t=20631)

Initiator001 05-31-2022 12:59 AM

Semroc Pro Cherokee
 
I bought one of these kits when they were released last year.

Now it is time to build it! :D

I already purchased the correct nosecone for the model.

I have two questions and would like some input from the members:

1) Round the leading/trailing edges of the fins or leave them square?

2) Which version to build? The original with the 16.35" BT-55 body tube or the later full 18" BT-55 body tube?

I reserve the right to ignore any and all answers. ;) :chuckle:

Thanks.

ghrocketman 05-31-2022 01:10 AM

I only ever leave fin edges square if required for a scale build.
On almost every 3 or 4FNC rocket I round the leading edge and taper the trailing edge to a sharp knife like edge. It really makes a performance difference.
For futuristic rocket types such as a Scorpius, Trident, Star Speeder, or Manta Bomber, I just round all edges. Square fin edges on rockets make about as much sense as blunt stubby nose cones - ZERO.

astronwolf 05-31-2022 08:50 AM

1) I'd at least round the leading edge.

2) I'd build the original shorty only because my original Cherokee was a shorty. IMHO the longer profile is a better flier though.

BEC 05-31-2022 02:32 PM

Agree with both GH and Wolf - at least round the LEs (and I'd do tips, too).

I have a friend who was a test engineer at Grumman who found that square TEs, at least for the Reynolds numbers that small RC airplanes operate at, were just fine and even better than tapered ones with respect to drag. I haven't done the calculations to figure out the Reynolds number of, say, an Alpha fin at 200 mph (a reasonable speed for 2/3 of the way through a C6 burn) actually is to see if this applies to rockets like it does to an RC airplane at 40 mph with a 7 inch wing chord. But I have used that bit of info as an excuse to leave trailing edges square on many of my rocket builds.

Note that this has nothing to do with the Cherokee design itself.

Gus 05-31-2022 04:12 PM

Bob,

I always round the edges on sport models, only because I feel negligent if I donít, LOL.

MarkB. 05-31-2022 06:44 PM

Well,

I just finished painting my Semroc Cherokee.

I rounded leading, trailing and tip edges. But I also feel like a slacker when they mention "for those of you scoring at home" during televised baseball games.

I didn't have an option; it came 16.35 "long.


Suggestions: 12" parachute, drill and add a 2" long piece of 1/2" hardwood dowel in the nose cone for both weight and strength

Extra OCD fun: figure out where the CP and CG decals really should be placed.

Royatl 05-31-2022 07:10 PM

Iíd round all edges. Otherwise it just doesnít look right.

I like the looks of the shorter model, but my original Cherokee in 1970 flew away, mostly horizontally, on its first flight as it changed course about 70 ft up, prob due to near neutral stability.

barone 05-31-2022 07:40 PM

Round leading, taper trailing. Check CG with the shorter BT. Mine, years ago, was slightly unstable. :D

ghrocketman 05-31-2022 07:58 PM

My RC airplanes fly a LOT faster than 40mph.
The slowest one does about 80mph.
Most of mine are capable of flying over 120mph.
Ballistic (old school) Pattern aircraft, Pylon aircraft, and Jets.

BEC 05-31-2022 11:21 PM

Yeah, I know.

The sort of model I was referring to is a small (3 foot span) moderately-powered (under 100 W, a little over 1 lb. flying weight) electric model. The person I was referring to designed a number of airplanes, and kitted some of them, which were made almost entirely with 1/8 x 1/4 inch strip stock. Consequently, they have 1/8th inch thick, square trailing edges on both he wing and the tail surfaces. I was thinking in terms of cruise speed for such a model, not top speed or landing/stall speed.

Your old school pattern ships probably are landing at not much under 40 mph.


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