18mm MD 2000 ft on a C6

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I just finished my 18mm MD C6 project this summer. It took two extra spotters and a lot of tracking powder to get it back. I am really interested to see what you come up with. :pop:
At this time of year, the field is all covered in hard snow so hopefully it shouldnt be hard enough to find it.
 
What about this design? The fins are highly swept so it gets more altitude. With larger composite motors I wouldnt do this due to flutter but the max velocity is not too high so i could probably get away with it.

View attachment 314037
 
Swept fins are great way to add stability. But with a tumble or streamer recovery a broken fin is almost guaranteed. I am a fan of the simple delta. Leading edge profile is the same and with OR you can easily play with it until you get the desired stability.
 
Swept fins are great way to add stability. But with a tumble or streamer recovery a broken fin is almost guaranteed. I am a fan of the simple delta. Leading edge profile is the same and with OR you can easily play with it until you get the desired stability.
Yeah probably. Ill use a clipped delta.
 
Now heading off to cut the tube and mark it....fin sheet and nose cone shuld arrive next week or so.
 
Those launch lugs will rob your altitude. I'd recommend using a fly away guide. You can find the article on how to do them on the Apogee website.
 
Those launch lugs will rob your altitude. I'd recommend using a fly away guide. You can find the article on how to do them on the Apogee website.

(Based on what I've read,) Launch lugs have less drag than is typically assumed, and fly away guides as well as tower launchers create lots of friction which can diminish or negate any the benefits.

For the lugs, cut the leading and trailing ends of the lugs at a 45 degree angle and fillet them. For weight reduction, you might be able to sand fillets out of balsa pieces.
 
(Based on what I've read,) Launch lugs have less drag than is typically assumed, and fly away guides as well as tower launchers create lots of friction which can diminish or negate any the benefits.
Oh really
 
Oh really

I recall that the stated figure was 2-3% (or maybe it was 3-5%) of total drag on a competition rocket (vs the 10% normally used)
I could have forgotten. The poster of the amount could be wrong.
 
I believe I also read that one longer launch lug is actually less draggy than two smaller ones.

One other suggestion... Make it a 3FNC instead of 4FNC to reduce even more drag.
 
Maybe. Personally, I prefer three, but playing with sims doesn't bear that out. Once upon a time I was a staunch adherent to the three over four argument. What started me thinking otherwise was a comment that there is less "wobble" with four fins for a given polar moment of inertia and "wobble" dissipates energy that would otherwise contribute to altitude. I haven't been able to simulate that, but the reduction in individual fin surface area needed to achieve an equivalent stability margin in a four vs three configuration can, under the right circumstances, equal out. If the four fin configuration is spending less time off verticle axis anything close on fin drag should result in more altitude.

I believe I also read that one longer launch lug is actually less draggy than two smaller ones.

One other suggestion... Make it a 3FNC instead of 4FNC to reduce even more drag.
 
(Based on what I've read,) Launch lugs have less drag than is typically assumed, and fly away guides as well as tower launchers create lots of friction which can diminish or negate any the benefits.

For the lugs, cut the leading and trailing ends of the lugs at a 45 degree angle and fillet them. For weight reduction, you might be able to sand fillets out of balsa pieces.
I'm planning to cut them at a 45 degree angle but i'm either going to fillet them with wood glue or CA.

And I dont think that a tower launched rocket wouldnt get as much altitude as a rocket with a launch lug. If you compare the two you'll find that the tower launched rocket get a ton more altitude then the ones with a launch lug.

I believe I also read that one longer launch lug is actually less draggy than two smaller ones.

One other suggestion... Make it a 3FNC instead of 4FNC to reduce even more drag.
I already cut the launch lugs so i dont think i'll be able to try a longer launch lug.

And I did try 3 fins in the sim but they got alot less altitude than a 4 finned rocket (i enlarged the 3 finned version to get the same stability as the 4 finned version).
 
...

And I did try 3 fins in the sim but they got alot less altitude than a 4 finned rocket (i enlarged the 3 finned version to get the same stability as the 4 finned version).

Enlarging the fins probably added weight and that was what reduced the altitude.
 
Also, with bigger fins, you'll get more drag regardless of weight. So many factors. After all, it is rocket science. Try the Rocket optimization tool in OR. That can help automate tweaking the design a bit.

All-in-all though the main thing is to have fun with your build. At the end of the day, it's yours and you need to do what will make you happy with it. Looking forward to the launch report!
 
Ohhh...I just got finished building a Yankee. Wonder what one of those Klima D 18 mm engines would do with it...
 
I'll try it with the mass override and see what i get.
Yea, it still gets less altitude.

Also, with bigger fins, you'll get more drag regardless of weight. So many factors. After all, it is rocket science. Try the Rocket optimization tool in OR. That can help automate tweaking the design a bit.

All-in-all though the main thing is to have fun with your build. At the end of the day, it's yours and you need to do what will make you happy with it. Looking forward to the launch report!
Yeah that's true. But with 3 fins it's not all that bad since you lose a fin which also helps on lowing drag.

What kind of finish will you have? Also, what will your fin edges be like? You can gain some altitude if you play with those variables.
My painting skills aren't that good yet so i think ill go for a regular paint finish. I do plan to bevel the fins but there isnt much i can do with 1/32" thick fins.
 
Airfoil them or round the edges, since most if not all of the flight will be below mach 1.
Max speed is mach 0.5. I still doubt that i could airfoil the fins completely, a bevel is probably all i can do.
 
Here is a idea for a simple beveling jig. I made it on the table saw years ago. With different wedges you can change the angle and blend them together for an airfoil. Just tape the fin to the wedge and draw the paper across. The sand paper is cut to just miss the wedge. Works great for small fins.

IMG_1468.jpg
 
"Launch lugs have less drag than is typically assumed, and fly away guides as well as tower launchers create lots of friction which can diminish or negate any the benefits."

I will agree in part. A poorly set up tower can be a real drag. Ha! Sorry...but a well prepped tower yields dramatic results. Proper length and rail surface prep are many times over looked. The compulsion to "just make the rocket fit" without a rattle is another factor. With all that in mined a tower will be the optimal launcher in most situations but it takes a lot of prep. One thought on lugs is presented profile. What is the ratio of the lug to body tube as you look at the front of the rocket. Smaller rockets the lug is large with corresponding drag. As the body tube diameter increases and the launch hardware gets smaller the effect diminishes.
 
Here is a idea for a simple beveling jig. I made it on the table saw years ago. With different wedges you can change the angle and blend them together for an airfoil. Just tape the fin to the wedge and draw the paper across. The sand paper is cut to just miss the wedge. Works great for small fins.
That's a nice idea, may use it on my builds from now on.

"Launch lugs have less drag than is typically assumed, and fly away guides as well as tower launchers create lots of friction which can diminish or negate any the benefits."

I will agree in part. A poorly set up tower can be a real drag. Ha! Sorry...but a well prepped tower yields dramatic results. Proper length and rail surface prep are many times over looked. The compulsion to "just make the rocket fit" without a rattle is another factor. With all that in mined a tower will be the optimal launcher in most situations but it takes a lot of prep. One thought on lugs is presented profile. What is the ratio of the lug to body tube as you look at the front of the rocket. Smaller rockets the lug is large with corresponding drag. As the body tube diameter increases and the launch hardware gets smaller the effect diminishes.
Yea true.
 
Haven't made any progress on the MD today, but got the fin sheet. Progress should start on sunday.
 
Please use idea of the beveling jig. If you can improve it let me know. I have successfully used it all the way down to .5mm carbon plate. Checking the bevel at .5 is another story. Many times I need to wear a jewelers loop.:)
 
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