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Madcow DX3 Fin Discrepancy

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dhkaiser

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Picked up a DX3 SD last weekend and while testing parts fit discovered one fin's tab is 1/16th longer than the others. Overall it is the same height but when press fit it stands off the BT by 1/16. If I sand to fit the BT the height will be 1/16th shorter than the other two. Would this concern you or should I not worry?

I have sent word to Madcow but not heard back yet.
 

markkoelsch

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Not a huge deal. You could talk to Madcow about a new set of find, but I doubt a 1/16" will make a big difference.
 

TMJ

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If it were 'me'... I'd leave the fin and its root at its current length and simply fill the gap between the fin and the body tube with epoxy. Maybe even shove a 1/16" shim between the fin/tube before gluing. I say this because we are talking more of 'aerodynamics' here than we are talking structural integrity. One short fin will create less drag in that one area, dissimilar to the higher drag produced by the 'other' two longer fins... likely causing the rocket to not fly so straight. Keep the fins all the same length from body tube to tip. I'm big into overbuilding and adding a lot of questionable structural bracing. I'm somewhat of a 'lone-wolf' in that department, so I'll not advise you as to how to make things strong. I'll simply advise you to keep all three fins the same length.
 

DavidMcCann

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Sand it. I'd say 97% of rockets with bevels are off more than this.
 

cerving

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I got a DX3 recently and had the same issue. I simply trimmed down the tab. Flown it quite a few times already, it's a nice flyer.

Picked up a DX3 SD last weekend and while testing parts fit discovered one fin's tab is 1/16th longer than the others. Overall it is the same height but when press fit it stands off the BT by 1/16. If I sand to fit the BT the height will be 1/16th shorter than the other two. Would this concern you or should I not worry?

I have sent word to Madcow but not heard back yet.
 

dhkaiser

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Thanks guys. Still have not heard from Maddow will wait a bit longer.
 

timbucktoo

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Thanks guys. Still have not heard from Maddow will wait a bit longer.
Have you called? Mike usually answers the phone. Then again, he may be at a launch & it is now the weekend!
 

dhkaiser

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I went ahead and sanded the fin tang to fit. I am going ahead with the construction and should have it finished this weekend. Won't be able to fly it until Sept. We'll see how it goes.
 

TMJ

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After reading your post, I checked the DX3 that I too just purchased. I got lucky, I guess. My fins are all just fine, however. You've brought up a good point that makes for 'food for thought'. "Just how much of a discrepancy can be tolerated in fin length, etc. before it actually starts to degrade the flight performance of the rocket. Thanks to 'you', I'm now wondering about the drag created by rail buttons, external switches, etc. Does it really matter? I'm honestly not sure. I like to think that it 'would' matter, due to the laws of physics, but then again. Maybe it doesn't really matter all that much! I'll be keeping an eye on this thread. Curious to see what develops.
Enjoy...
 

DavidMcCann

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To see the effect, make a part the size of the items in question and put them into the open rocket file.... see how far the CP shifts.



spoiler alert- it won't be far ;)
 

TMJ

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Pay close attention to what Mr. McCann says. He's yet to steer 'me' wrong! He knows what he's talking about!
 

Buckeye

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Thanks to 'you', I'm now wondering about the drag created by rail buttons, external switches, etc. Does it really matter?
Yes, it all matters. To what degree depends on you. Most fliers don't care about the impact, but performance junkies do. Hence "minimum diameter" and launch towers.

Run some simulations with and without rail buttons or launch lugs. You may be surprised.
 

DavidMcCann

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I would only take my advice on whisky and women. Everything else is questionable at best. ;)

(BTW: I like whisky and women to be about the same age)
 
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Crash-n-Burn

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I would only take my advice on whisky and women. Everything else is questionable at best. ;)

(BTW: I like whisky and women to be about the same age)
So... based on your Bushmill's photo in the 'how you relax' thread... errr... you like your women at about the minimum age of consent?

I joke, I joke.
 
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