No Big Deal

[cryoscum]

Hi All

After the recent trip to the US I thought I had better come up with a nice performing rocket that is easier to travel with, i.e. make sure all parts are shorter than 1m and can break down to low diameters, including being able to disassemble the fincan. You'll notice from the design that it builds on the work of Mike P, Scoop and Rocketstar - credit where it is due!

So it's a relatively small vehicle that would be able to fly on many different motors, but is intended for a 6G 75mm M.

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The single break occurs at the top of the motor (using an aluminium coupler that clamps to the top of the motor case), so the NC and the section of BT is to be made monolithically. Strangely enough, the sims indicate for this design that a 7:1 ogive performs better than a VK. I'm OK with that, happy to make something other than a VK for once!

Started with the NC design:

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Then cut the profile box parts, assemble and hotwire the EPS plug:

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I did the layup with 10 layers of 165GSM 2x2 twill S-glass and K3600 making a wall thickness of approx 2.2mm and heat treated the monolithic NC/BT overnight with the prescribed ramped method with an apex of 80 deg C.

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Made the 5000-series alu NC tip on the lathe in a shape that completes the 7:1 ogive profile. According to the sims I'll need approx 200g of nose ballast to ensure stability throughout the burn and the tip weighs approx 190g. The piece of threaded rod for attachment would provide the rest.

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So the alu coupler is next. The design is easy, but my lathe is not big enough for it, so I'll have to get some help for that...

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Will keep you posted on progress...

[ROCKet STAR]

Looks great, Nic!

I really like the monolithic NC/BT design. Should both improve strength, reduce weight and increase aerodynamic performance. Very interested to see how it all works out.

So the alu coupler is next. The design is easy, but my lathe is not big enough for it, so I'll have to get some help for that...

If I can make a 3" aluminium coupler on my pipsqueek little lathe, I reckon you should be able to make this on yours!

[cryoscum]

If I can make a 3" aluminium coupler on my pipsqueek little lathe, I reckon you should be able to make this on yours!

I had a good look at it. It's really close, but the lathe just doesn't have the x-axis travel to do it comfortably. The inner face cutting is a whole extra level of complexity, so I reckon it's just better to get some help on this one. A bigger lathe would be nice, but I'm already struggling with space in the shed.

[SpaceManMat]

The advantage of having a metal nose cone tip is you can use it as a mounting point during storage without worrying about your paint - nice

[BerowraRocketBoy]

Another one...

Seriously though, good work so far and I really like the concept.

I'm Assuming that the NC tip was made from aluminium, but was it? I don't know why, but to me it seems like an object that size would weigh less if made from Al.

Can't wait to see how it looks finished.



Campbell

[strud]

This coupler is a great job for my newly running NC lathe

I'll post pics of it as I make it in the near future.

CS

[CATO]

Made the 5000-series alu NC tip on the lathe in a shape that completes the 7:1 ogive profile.

Hey Nic, looks great as always, a newbie question, what was the reason you went with the "5000" series alu (what variant did you go with) as opposed to the normal 6061. Just asking to increase my knowledge of the hobby.

Thanking you in advance...

http://en.wikipedia.org/wiki/Aluminium_alloy

[BerowraRocketBoy]

just saw Catos comment and re read your post (really should read things thoroughly sometimes) so I guess that answers my question well enough.

(thanks for saving me more embarrassment than necessary CATO)

[cryoscum]

There's not too much to the choice of alloy.

I believe it is 6060-T5 bar stock as this is a simple, cheap and available alloy here. I usually buy off-cuts and it's not always entirely clear exactly what alloy you get, but the machinability gives you a good idea. The places I frequent don't often have 6061 in many different tempers, usually just T6 if at all, making it a bit more resistant to machining. I think 6061-T6 has a tensile strength of something like 250 or 300MPa, i.e. approaching that of mild steel, where as anealled 6060 is maybe 90 or 100MPa. Obviously easier to machine... In this case the ultimate tensile strength of the tip makes no difference.

For something like fins I think you'll have to be a bit more careful, but using the excellent 7075, which has a higher tensile strength than high-end structural steels, costs big $$$ and hence a 6061-T6 would likely be ideal. The short lived aerodynamic heating is unlikely to make much of a difference to the temper...

[CATO]

Cheers Nic,

So, when are you applying to be a TAP....

[rocket_troy]

With regards to machining Al-Alloys - there's a simple rule: harder = better. What's more, the same rule also applies to the tensile strength of Al-Alloys ie. harder=stronger so the mathematicians here may therefor equate that better machining = higher spec Al-Alloy and that's pretty much universally true.
Soft Al-Alloys are not only gummy to machine, but they can also blunt tool bits and should be avoided if possible for turning.

TP

[cryoscum]

May be so. My small lathe doesn't like stuff that is too hard, vibration issues become really problematic. I get better results with the softer stuff...

[ROCKet STAR]

With regards to machining Al-Alloys - there's a simple rule: harder = better. What's more, the same rule also applies to the tensile strength of Al-Alloys ie. harder=stronger so the mathematicians here may therefor equate that better machining = higher spec Al-Alloy and that's pretty much universally true.
Soft Al-Alloys are not only gummy to machine, but they can also blunt tool bits and should be avoided if possible for turning.

TP

On a related note, what method does everyone use for cutting down their aluminium barstock? I have always just used a hacksaw, but the diameter of materials that I am using now is making that a fairly miserable experience. I am thinking of investing in a horizontal band saw... something like this: http://www.machineryhouse.com.au/B009 Do you guys reckon that is the best option?

[rocket_troy]

On a related note, what method does everyone use for cutting down their aluminium barstock? I have always just used a hacksaw, but the diameter of materials that I am using now is making that a fairly miserable experience. I am thinking of investing in a horizontal band saw... something like this: http://www.machineryhouse.com.au/B009 Do you guys reckon that is the best option?

Definitely! We have 3 bandsaws here up to 12" capability and they're the most used bits of kit in the fab area. I do all my cutting on the bandsaw unless I'm at the lab where there isn't one (and that's often a PITA!).
I would recommend one with coolant and as preference, but even without, it's an investment you'll never regret!

TP

[strud]

Definitely get the horizontal bandsaw !

I have an old clapped out one but it still is awesome.

Mill or Lathe squares up any wonkiness of the cut.

CS