dixontj93060
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Been doing some design work on a planned build during the last 24 hours... It is the rocket which will utilize the superb nosecone that Dan Schwartz of Python Rocketry completed from this purchase: https://www.rocketryforum.com/showthread.php?66980-SOLD-Discount-Python-Rocketry-nose-cone. I sure wish I had an independent picture of the nosecone as it is soooooooo nice (maybe I can post it later). In any case, I decided to do a upscale of the Estes Cherokee K-47 (original kit) as shown below.
Obviously this type of upscale has been done before. Here is an example of an 8" upscale of the Estes #1247 kit version. Personally I wanted to make the shorter K-47 version work because it was the first rocket kit I built at a young age. The problem is this kit is a bit tough with respect to stability and for sure I cannot use solid plywood fins as shown in the example above because of the weight and stability penalties. As most know, the Cherokee fins are honking big, so something needs to be done to build these correctly.
This particular build will utilize the mid-size range of 10" Sonotube which is 10.25" O.D. actual. Fins at this 7.74X upscale end up with a root cord of 27", tip cord of ~16" and fin span of ~17". So, to save weight, the planned fins are 1/2" ply frame with "paper" honeycomb inserts with a couple of 5.7oz. biased carbon fiber layers as skin. The "frame" of the fins will be ~1.5" around the perimeter with the TTW tab kept intact.
With the background above, now comes the need for a mechanical engineer (which I am not)... Doing flight simulations along with laminate and flutter modeling, it looks like the structure is good to ~1.5 Mach; which is great. Still, for some reason I have a compelling drive to stabilize the leading edge/tip of these large fins. This may, or may not be needed(?). I would like to add a single "stringer" or "spar" (I don't know the right term) from root to tip. Again the question(s)... Is this needed? Does this help with flutter damping (I think it would)? If the first two questions are "yes" or partially "yes" then the question is, what shape/size/location is best? My current thought is to cut out a rounded triangle and rounded parallelogram leaving one "spar" shown as Position 1 below extending from the approximate center of the root chord to the fore of tip chord (cut outs again filled with paper honeycomb). Other options considered were Position 2 and Position 3 below which may be better or worse(?). So, are there any mechanical engineers here on TRF that can help provide feedback on the internal fin structure?
Obviously this type of upscale has been done before. Here is an example of an 8" upscale of the Estes #1247 kit version. Personally I wanted to make the shorter K-47 version work because it was the first rocket kit I built at a young age. The problem is this kit is a bit tough with respect to stability and for sure I cannot use solid plywood fins as shown in the example above because of the weight and stability penalties. As most know, the Cherokee fins are honking big, so something needs to be done to build these correctly.
This particular build will utilize the mid-size range of 10" Sonotube which is 10.25" O.D. actual. Fins at this 7.74X upscale end up with a root cord of 27", tip cord of ~16" and fin span of ~17". So, to save weight, the planned fins are 1/2" ply frame with "paper" honeycomb inserts with a couple of 5.7oz. biased carbon fiber layers as skin. The "frame" of the fins will be ~1.5" around the perimeter with the TTW tab kept intact.
With the background above, now comes the need for a mechanical engineer (which I am not)... Doing flight simulations along with laminate and flutter modeling, it looks like the structure is good to ~1.5 Mach; which is great. Still, for some reason I have a compelling drive to stabilize the leading edge/tip of these large fins. This may, or may not be needed(?). I would like to add a single "stringer" or "spar" (I don't know the right term) from root to tip. Again the question(s)... Is this needed? Does this help with flutter damping (I think it would)? If the first two questions are "yes" or partially "yes" then the question is, what shape/size/location is best? My current thought is to cut out a rounded triangle and rounded parallelogram leaving one "spar" shown as Position 1 below extending from the approximate center of the root chord to the fore of tip chord (cut outs again filled with paper honeycomb). Other options considered were Position 2 and Position 3 below which may be better or worse(?). So, are there any mechanical engineers here on TRF that can help provide feedback on the internal fin structure?
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