Bertha 6X???

[edwinshap1]

So i'm getting to that point where my level 2 is ready to go...for the second time...but hey, that damned nose cone is secure!!! regardless, all i can think about is what my L3 will be on. I want it to be something iconic to me, and the most iconic rocket i can think of is the big bertha. It was the first rocket i made when i first got into rocketry 7-8 years ago (or so?), and it was the first rocket i ever lost. I'd love to build myself a new one, but first i gotta ask, has anyone done it before that has pics or vids or drawings or rocksims?

I'm thinking of doing appx a 6x upscale to bring the rocket to a 10" diameter with about 40" long fins from leading edge to the flat bottom.

My concerns lie mostly with the edges of the fin that will be directly adjacent to the blast from the M motor. something tells me i'll have to put a decent strip of aluminum to give enough heat dispersion if i go through with it. that and how to make sure the fins don't get cracked (bunch of glass?) on landing, or a big chute?

[cbrarick]

fin flutter?

[bandman444]

I have a chute you can borrow!

LOL

Bryce

[cwbullet]

Test, test, test. I flew a 5.5 inch big bertha this weekend and shreaded the fins off due to fin flutter. Watch the velocity and keep if below 600 ft/s/

[stantonjtroy]

My concerns lie mostly with the edges of the fin that will be directly adjacent to the blast from the M motor. something tells me i'll have to put a decent strip of aluminum to give enough heat dispersion if i go through with it. that and how to make sure the fins don't get cracked (bunch of glass?) on landing, or a big chute?

There is a paint called Pyromark 1200 that can withstand temps up to 1200DegF. We used it as part of a heat protection system for the fin can of a full sized target rocket. Here's a couple of links http://www.bjwe.com/tempil/pyromark.htm http://www.tempil.com/closeup.asp?cid=26&pid=32&theme=0

[edwinshap1]

fin flutter?

thinkin pretty hefty fins and a pretty slow lift off. i'll probably need some real reinforcing, any ideas besides just more lamination?

[UPscaler]

CF fins and an M650?




Braden

[JPVegh]

This sounds like a project that I could really get into.

One of the great things about this design is that it is overstable to begin with. This gives you some room for overbuilding the tail. For the fins I would go with 3/4 inch cabinet grade plywood. That should be strong enough to withstand the landing forces if you are using a large enough chute. I would not worry about fin flutter, choosing the right motor should eliminate that scenario from occuring.

As for scorching on the backside of the fins I really don't know. It could be an issue I suppose. I can tell you that in 1995 we launched a 5.5 inch Big Bertha on a K550 and had no problems with fin flutter or scorching and in 1996 we launched a 7.5 inch Bertha-ish rocket on a 5 engine cluster for an awesome flight.

A 6X BB would really be a fun L3 and one that many rocketeers could relate to. GO for it!

[blackjack2564]

Make fins from sandwiched 1/4 or 1/2 foam and carbon fiber. That will take the landing & the heat.

Mega fins are: second set for new fincan [which are surface mounted] center is carbon then 1/4 foam on each side, then carbon on exterior. For the P-motor.

First set [pictures] are 1/2in foam with 3 layers of 5oz carbon on each side.

They don't flex and have a couple flights on them. One landing on concrete hard Playa.

Nothing fancy [not bagged or vacuumed] just regular layup.

Will be light weight and keep the CG where it belongs

[MClark]

We had a local member in about the same time as Jeff make a 7.5" with a K550, flew great.
The fins were ply with carbon, no flutter, just sand and repaint after flight or leave it as a badge of honor.

Mark

[edwinshap1]

hmm, a layer of CF would definitely make sure nothing ignites at all, but 3/4" ply would be nice and thick as well as it'll be taking the brunt of it.

also the fins are 39.75" long in all, that's a lot of CF :P

oh yeah and jim, you're welcome for the playa scrape

[troj]

I'd go with something more structural than foam as the core -- end grain balsa, or even light plywood, would be a better choice.

No matter what you do, weight in the fins is your enemy.

Probably need to oversize the chute a bit, especially for a cert attempt. Use a smaller motor, to keep the velocity (and altitude) down.

-Kevin

[edwinshap1]

Did a very very quick rocksim upscaling of the rocket, leaving just about everything except major structural components out.

first thing i realized is i have no idea how much the cone will weigh until i make it. I'm going to use this method to make my nosecone. I'm unsure how much the wood/foam will weigh (i expect not much), but i will be putting a center tube in to add nose weight.

The total weight is definitely lower than what i will actually be seeing once i add the mass objects for other components that i haven't tabulated yet, but even on an M1939W (largest motor you can fly in Ca right now) i only get to 350mph and 5400ft, and with a 28' parachute (who would have one of those ) it'll come down at 13fps which i think is just about perfect for the fins.

What does everyone think, should i just do single deploy at apogee? I'd need a pretty hefty pilot chute to yank the thing out quickly enough, or i'd have to DD it at like...2000 ft and i don't want to buy an expensive altimeter to accomplish it.

As for altimeters, i intend to use a perfectflite stratologger and adept 22

more to come soon, but i got physics to get done with for tomorrow XD

[bandman444]

Did a very very quick rocksim upscaling of the rocket, leaving just about everything except major structural components out.

first thing i realized is i have no idea how much the cone will weigh until i make it. I'm going to use this method to make my nosecone. I'm unsure how much the wood/foam will weigh (i expect not much), but i will be putting a center tube in to add nose weight.

The total weight is definitely lower than what i will actually be seeing once i add the mass objects for other components that i haven't tabulated yet, but even on an M1939W (largest motor you can fly in Ca right now) i only get to 350mph and 5400ft, and with a 28' parachute (who would have one of those ) it'll come down at 13fps which i think is just about perfect for the fins.

What does everyone think, should i just do single deploy at apogee? I'd need a pretty hefty pilot chute to yank the thing out quickly enough, or i'd have to DD it at like...2000 ft and i don't want to buy an expensive altimeter to accomplish it.

As for altimeters, i intend to use a perfectflite stratologger and adept 22

more to come soon, but i got physics to get done with for tomorrow XD

I wish I knew someone with that big a parachute ! Lol

What is your timeline for this project?

TRA I am assuming?

Bryce

[edwinshap1]

timeline is pretty much unknown. i need to gather up the funds for it all before i start buying any of it, so it'll be a few months at least.

and yeah i think im gonna cert under TRA, allows for more flexibility in the wording of when building can begin.

[troj]

first thing i realized is i have no idea how much the cone will weigh until i make it. I'm going to use this method to make my nosecone. I'm unsure how much the wood/foam will weigh (i expect not much), but i will be putting a center tube in to add nose weight.

Seems like a lot of work, to me. Why not just stack foam, hot wire it (or spin it and shape it, the Vatsaas way), and be done? A Bertha nosecone will be short and blunt, anyway, so structure isn't really critical.

The total weight is definitely lower than what i will actually be seeing once i add the mass objects for other components that i haven't tabulated yet, but even on an M1939W (largest motor you can fly in Ca right now) i only get to 350mph and 5400ft, and with a 28' parachute (who would have one of those ) it'll come down at 13fps which i think is just about perfect for the fins.

A C9 at 5400 foot apogee, with 13fps recovery? You better hope for zero wind, or it'll be in the next county.

Try to find an unmodified T10, which is 24 foot, and likely more appropriate.

What does everyone think, should i just do single deploy at apogee? I'd need a pretty hefty pilot chute to yank the thing out quickly enough, or i'd have to DD it at like...2000 ft and i don't want to buy an expensive altimeter to accomplish it.

The trick to reliable dual-deploy on a parachute that big is that it must be bagged. When a C9 is bagged, a 60" drogue can extract them quickly and easily.

Any altimeter that can do deployment can do dual deployment.

-Kevin

[edwinshap1]

Any altimeter that can do deployment can do dual deployment.

but how effectively i can get it at 1100 ft is different. also, i looked at the stratologger and it can do main at upto 3k ft.

hmm, i could tender descender it with the deploy bag connected to the drogue?

a 2500 or so foot main deploy with a C9, or the same alt with a smaller chute would be fine.


also kevin, at lucerne the wind goes west to east, and there's nothing east for like 20 miles, it's all desert and lakebed

[troj]

but how effectively i can get it at 1100 ft is different. also, i looked at the stratologger and it can do main at upto 3k ft.

Yup, and getting a canopy that large to inflate quickly is very much dependent upon how it's packed.

hmm, i could tender descender it with the deploy bag connected to the drogue?

a 2500 or so foot main deploy with a C9, or the same alt with a smaller chute would be fine.

Packed properly, you can do the C9 at about 1500; I wouldn't go much beyond that -- they take about 500 feet to fully inflate.

also kevin, at lucerne the wind goes west to east, and there's nothing east for like 20 miles, it's all desert and lakebed

Yep, but if there's much of a breeze, getting dragged far can do horrendous damage not only to your rocket, but also to the parachute -- as the canopy bounces, the nylon gets abraded. We lost a C9 that way.

-Kevin

[DAllen]

but how effectively i can get it at 1100 ft is different. also, i looked at the stratologger and it can do main at upto 3k ft.

hmm, i could tender descender it with the deploy bag connected to the drogue?

a 2500 or so foot main deploy with a C9, or the same alt with a smaller chute would be fine.


also kevin, at lucerne the wind goes west to east, and there's nothing east for like 20 miles, it's all desert and lakebed

In considering drift, I like to do these sorts of calcs (assuming I am doing my math right):

5400 ft descent, 13 fps, 10 mph cross wind = 1.2 miles drift
@ 15 mph = 1.7 miles drift
@ 20 mph = 2.3 miles of drift

AND if the winds are strong enough, once the rocket lands the chute can re-inflate and drag that project a looooooong ways down the playa. I saw a project get dragged about a 1/4 mile across a plowed field at LDRS this weekend. That was pretty ugly.

Just something to ponder. And while I am at it...more things to ponder...

Why are you considering going the tender descender route? Is that thing really capable to handle a gigantic chute like that? I mean, you are talking about a itty bitty fishing line being the only thing that is holding a 30 lb chute from inflating as it is flailing around in the air stream as it descends (maybe I am missing something here).

Not only that but a tender descender is a timer not an altimeter. An alt can deploy a chute at a given altitude regardless of time in the air. Weather cocking is going to be an issue with this bad boy so your time to the optimum altitude for main deploy will vary significantly.

Also, if you REALLY do want a 28' chute I would recommend looking up military surplus stores for man rated chutes.

[troj]

Why are you considering going the tender descender route? Is that thing really capable to handle a gigantic chute like that? I mean, you are talking about a itty bitty fishing line being the only thing that is holding a 30 lb chute from inflating as it is flailing around in the air stream as it descends (maybe I am missing something here).

Yep, you're missing something.

A Tender Descender is a hold-down device, similar to the ARRD or Tether. It will only be holding the load of the drogue to an attachment point, such as a bulkhead, and not be trying to hold in the main.

Even if the main were external to the airframe, as long as it's in a deployment bag held closed by the TD, there's no real load there.

Not only that but a tender descender is a timer not an altimeter. An alt can deploy a chute at a given altitude regardless of time in the air.

It's a hold down device. http://www.tinderrocketry.com/assets/pages/l2.html

-Kevin

[DAllen]

Yep, you're missing something.

A Tender Descender is a hold-down device, similar to the ARRD or Tether. It will only be holding the load of the drogue to an attachment point, such as a bulkhead, and not be trying to hold in the main.

Even if the main were external to the airframe, as long as it's in a deployment bag held closed by the TD, there's no real load there.



It's a hold down device. http://www.tinderrocketry.com/assets/pages/l2.html

-Kevin

*FACEPALM SELF*

Wow I am an idiot sometimes. I read "tender descender" and thought "chute tamer."

Troj, this forum needs a, "Disable posting prior to morning coffee consumption" button. Either that or I gotta stop hitting "Submit Reply" so quickly.

[troj]

*FACEPALM SELF*

Wow I am an idiot sometimes. I read "tender descender" and thought "chute tamer."

Troj, this forum needs a, "Disable posting prior to morning coffee consumption" button. Either that or I gotta stop hitting "Submit Reply" so quickly.

Just as soon as I figure out how to implement such a feature, you can be second in line for it to be setup for.

I'm first.

-Kevin

[gdjsky01]

also kevin, at lucerne the wind goes west to east, and there's nothing east for like 20 miles, it's all desert and lakebed

This is a generalization. Saturday it was strong east to west.
and

[edwinshap1]

This is a generalization. Saturday it was strong east to west.
and

even better, it floats across the lakebed til it bumps into the side of a mountain


Also, does anybody know the thickness of 10" sonotube, or the appx mass of a 10' section of it?

I asked quikcrete about it, and i got a pretty useless answer.

The QUIK-TUBE® will have a nominal diameter of 10”. Because of QUIK-TUBE®’s fiber laminate construction it’s weight is almost negligible. Are you asking about the weight of 4’ section of 10” tube filled with QUIKRETE® Concrete? If that is the weight about which you are inquiring, it would be approx. 305 to 315 lbs.

now that i think about it, that would be so much more fun than a bowling ball launch Q50,000?

[troj]

QuikCrete makes three sizes of tube, each of which nests inside the other, for shipping purposes.

Find somewhere that sells concrete tools and ask them where to buy SonoTube. You'll get better consistency on size that way, plus you can buy it in 12 foot lengths and not have to splice tubes together.

-Kevin

[edwinshap1]

ah, well then, sonotube it is

[G2Rockets]

QuikCrete makes three sizes of tube, each of which nests inside the other, for shipping purposes.

Find somewhere that sells concrete tools and ask them where to buy SonoTube. You'll get better consistency on size that way, plus you can buy it in 12 foot lengths and not have to splice tubes together.

-Kevin

Andi its cheaper for those who like to blow it up.

[JPVegh]

SONOTUBE

10" 2.1 lbs/ft. 0.190" Wall Thickness

12" 2.3 lbs/ft. 0.190" Wall Thickness

[edwinshap1]

Thanks Jeff, and I assume that the 10" diameter is internal?

[JPVegh]

Yes, 10" ID.