Blaze Rocket- Build Thread

markkoelsch said:

I would really run a layer of full tip to tip. Easy to do.

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I second that! Tip to tip would be best. Or at least across each valley and half way up each fin. Something to break up the harmonics of fin flutter.

BayouRat said:

I second that! Tip to tip would be best. Or at least across each valley and half way up each fin. Something to break up the harmonics of fin flutter.

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I was thinking only half ways of the fin, but now I thought why not just do the whole thing, since the fins will have the secondary bonding peel ply texture.

Igotnothing said:

To cause to flutter: "fluttering her bristly black lashes as swiftly as butterflies' wings" (Margaret Mitchell).

Just because they are bonded well won't mean they will not flutter and cause significant drag.

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They can flip flap all they want. My point being with the attachment methods and reinforcment. Those fins aren't going anywhere.

SinfulDarkLord said:

They can flip flap all they want. My point being with the attachment methods and reinforcment. Those fins aren't going anywhere.

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Thats really not true... it's amazing how much more force is created when fins flutter, plus if they flutter enough the fin material will fail and break off even if the joint doesn't.

With some quick finsim analysis assuming basic clipped delta fins and 0.0625" CFRP (which any handmade CF most likely is neither as stiff nor strong) you get flutter values anywhere from M1.4 to M2.4, depending on the semi-span and overall fins size. Thats cutting it way to close IMHO. It's easy enough to thicken the plate to 0.1'' or 0.125" with some more layers of CF, so why not give yourself some safety margin?

RocketHunter said:

Thats really not true... it's amazing how much more force is created when fins flutter, plus if they flutter enough the fin material will fail and break off even if the joint doesn't.

With some quick finsim analysis assuming basic clipped delta fins and 0.0625" CFRP (which any handmade CF most likely is neither as stiff nor strong) you get flutter values anywhere from M1.4 to M2.4, depending on the semi-span and overall fins size. Thats cutting it way to close IMHO. It's easy enough to thicken the plate to 0.1'' or 0.125" with some more layers of CF, so why not give yourself some safety margin?

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Turns out the carbon plate I have is really 0.097" thick. I guess that's why I felt okay with it. I thought it was 0.0625" thick.

Still I wouldn't mind 1/16" thick. I've seen so much that it has led me to believe that I dont have to take it that far.

SinfulDarkLord said:

Turns out the carbon plate I have is really 0.097" thick. I guess that's why I felt okay with it. I thought it was 0.0625" thick.

Still I wouldn't mind 1/16" thick. I've seen so much that it has led me to believe that I dont have to take it that far.

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Sounds good then, that should be plenty thick/strong enough!

I flew a 38 minimum to M-2.8 with 1/16 carbon plate fins only held on with fillets....no issue. 6xl I-max.

Put a spare set of BlackHawk 24 fins on a 38 thin wall tube.

SinfulDarkLord said:

They can flip flap all they want. My point being with the attachment methods and reinforcment. Those fins aren't going anywhere.

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The flapping can cause delamination of your composites.

Here is an example of fin flutter in action and the next photo is the results.

blackjack2564 said:

I flew a 38 minimum to M-2.8 with 1/16 carbon plate fins only held on with fillets....no issue. 6xl I-max.

Put a spare set of BlackHawk 24 fins on a 38 thin wall tube.

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Just curious, how did you get that rocket stable? I'm guessing the BH24 fins had a semi-span of less than 1.25" since they were on a 24mm rocket, and considering you hit M2.8 you must've weighed less than ~10oz, which leaves no room at all for nose weight, which overall would seem to put you way unstable very quickly even with the electronics in the NC.

RocketHunter said:

Just curious, how did you get that rocket stable? I'm guessing the BH24 fins had a semi-span of less than 1.25" since they were on a 24mm rocket, and considering you hit M2.8 you must've weighed less than ~10oz, which leaves no room at all for nose weight, which overall would seem to put you way unstable very quickly even with the electronics in the NC.

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Pretty good ciphering.... it weighted 9.6oz. Back then the 24 & 29mm BH's had the same size fins, they were actually for the 29mm

I did this in 3 days just trying to prove a point, guess I was lucky [+ Open Rocket said it would be stable...for what that's worth]

Used the Raven Av-bay.

blackjack2564 said:

Pretty good ciphering.... it weighted 9.6oz. Back then the 24 & 29mm BH's had the same size fins, they were actually for the 29mm

I did this in 3 days just trying to prove a point, guess I was lucky [+ Open Rocket said it would be stable...for what that's worth]

Used the Raven Av-bay.

View attachment 268979 View attachment 268980

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Cool thanks, those don't actually look as small as a I was expecting, they look pretty close to 1.5''. OR has been said to be a bit pessimistic in stability values @ higher mach, and your flight seems to prove this a bit. Also, if they were less than 1.5'' finsim does predict that they'd probably be fine, and since you used commercially made CF the small safety margin is OK. I just don't personally trust mine or anyones home made CF to be 100% as strong as ideal CF. Semi-span really does have a huge effect on fin flutter - @ 1.4'' or less your rock solid, 1.5'' OK, 1.6"-1.7'' definitely not good....

edit: sorry for hijacking the thread a bit

No worries about the hijacking fellas. We are all having a legit conversation about fin flutter.

SinfulDarkLord said:

No worries about the hijacking fellas. We are all having a legit conversation about fin flutter.

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Agreed, it has been quite educational.

I have decided to ditch the carbon plate I already have and make a new one. Now before anyone asks why, it is because, no matter how hard I sanded on that carbon plate I can't get these foggy sections on the board to disappear. I don't want a fin that has fog on it, it just ruins the beauty of the carbon. I also was thinking of going just a tad thinner. How thin? I don't know for sure. I have carbon left over and 8"x8" floor tiles. I have just enough carbon for 6 ply's, but that only gets me to 0.06" thick. In order to increase the thickness I was thinking of doing 5 ply's of carbon along with some 3oz. satin fiberglass cloth in-between each layer of the carbon. This should get me close to 0.07" thick, but with the compression of the floor tiles I don't know just how much thinner its going to be. I'll keep you all posted on how that goes.

Clear Lacquer will make that Carbon Plate glow!!

BayouRat said:

Clear Lacquer will make that Carbon Plate glow!!

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Its undearneath the epoxy. I've sanded it multiple times with 60 grit sandpaper and it wont go away. I'd rather just make a new one than continue to sand through it.

Looks like no parts for me this week, because Rocketry Warehouse shipped USPS and for the reason that my house is not set up for home delivery they could not verify my address and thus is being returned.

Once more I say this world needs to follow the KISS method. Not putting blame on Rocketry Warehouse. I definitely have to blame USPS for this nonsense of subscribing to home delivery.

This whole week is my vacation from work so I will be working on the carbon/glass hybrid plate.

Already got started by cutting out the layers. 5 layers of 3oz. Satin glass and 6 layers of 6oz. 2X2 twill carbon. Only showing the carbon, the glass frays too much. But wait, doesnt the carbon also fray? Not when you have low melt fiberglass strands holding the fabric together. I really recommend this fabric to anyone that hates those annoying strands from falling off. You can get this fabric at Composite Envisions.

15 hours have passed and I was able to remove the peel ply. You got to love those room temperature cure epoxies. You got to however, not love those pain in the neck to remove polyester peel plys.

Anywho I am going to wait until 24 hours to cut it into a 7"x 5.5" piece. It still has some flex to it and I am assuming thats, because it has only been 15 hours.

Looks like the plate turned out thicker than I thought. Note to self, the math is always right.

Either way I am happy the way it turned out. It has the secondary bonding ready for strong attachment.

Okay so I have hit an issue with the design. I still have some weights un-accounted for and by the looks of it. I will not end up hitting Mach 2. I will have to re-desgin. Basically I will be getting rid of the top 7.75" body tube section. This means a custom nose cone is in order, but I will definitely get right on that some time.

Small update,

First off I have decided to take the fins to a different approach. Being 0.09" thick I thought, why not diamond airfoil the fins?

Now before you ask why, it is because I wanted less weight on the aft end of the rocket. To relief some of you on fin flutter concernces. I will be doing a tip to tip.

Having plenty of carbon plate to work with. I have been practing on the airfoil. It is not easy to do, but very do-able.



Please give me tips on how I can better do this.

Those shoes man, those shoes.

grouch said:

Those shoes man, those shoes.

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WoW...the soles have a nice wedge air-foil!

I don't think your fins are large enough, or thick enough to benefit very much at all from a true airfoil. I would just stick to nice beveling job.

With out a CNC you will drive yourself nuts, for little reward.
It's for you to decide however.

grouch said:

Those shoes man, those shoes.

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Exactly what I was thinking... Maybe to keep one's toes clear of the workshop floor? I wear sandals myself, but....

blackjack2564 said:

WoW...the soles have a nice wedge air-foil!

I don't think your fins are large enough, or thick enough to benefit very much at all from a true airfoil. I would just stick to nice beveling job.

With out a CNC you will drive yourself nuts, for little reward.
It's for you to decide however.

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This was only practice. It is very do-able, but not without a good perma-grit file. I plan to get one, but I think I will go with a normal bevel job like you said.

I'll show pictures tomorrow of the intended airfoil.

Oh and fellas the shoes aint mine lol.

grouch said:

Those shoes man, those shoes.

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Too funny!

blackjack2564 said:

WoW...the soles have a nice wedge air-foil!

I don't think your fins are large enough, or thick enough to benefit very much at all from a true airfoil. I would just stick to nice beveling job.

With out a CNC you will drive yourself nuts, for little reward.
It's for you to decide however.

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I agree with the fin recommendations, .09 is just not enough to contend with... If you are dealing with a 1/4" you would have plenty to get creative with.

As long as your carbon plate was made correctly , you will be fine. Your fin shape will determine if the fins will flutter or not. My old shadow composites raven had carbon fins right around .08 thick and it survived countless close to mach 2 flights. the fins where surface mounted with high temp epoxy with Kevlar pulp mixed in. no tip to tip.

I'm sure everyone will agree with this type of airfoil.



Very easy to do except for not having a table that I can sand at an angle to it. Before I make the others I want to get me a perma-grit sanding file. Its rigid and will easily sand the heck out of it to give me straight bevels.

This is just a teaser so you can get an idea of how the fins will look on the rocket. The fin span has been reduced down to 1.625". It is just a tad less than a body diameter and therefore I find it as the perfect balance for the stability and fin flutter.