Design for G37-10?

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astronboy

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I have simmed a rocket for my 24mm Ellis Mtn G37-10s I picked up at NARAM.

I named it the Blitzen as I am sure that it will just go like lightning!!

The delay is loooooong, so I went for a light, yet strong rocket with as almost little drag as possible. I do not like minimum diameter rockets, so I went with mostly ESTES parts, and plywood TTW fins designed using G Harry Stine's rules for low drag clipped delta fins.

Recover is by a BIG streamer so that there is a small chance in heck of getting it back.... I do live in Upstae NY, so there are no dry lakebeds nearby.

The rocket is BT-60 based, and I have included a rocsim. I would appreciate any comments, suggestions, or thoughts as I have never built a rocket that flies this high, or this fast.

Fred
 

GL-P

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Good luck! I have the demo of rocksim so I can't read it but it sounds interesting. I think estes tube should be good enough. Just keep the tube from getting any dents and it might just survive!!!

What are Stine's rules for low drag fins??? Just curious cuz I can see how low Aerolab puts the drag at.

Use a mylar streamer. They glitter real nicely so are easy to see.

My fins will be 30-60-90 shape as seen on the original machbuster and vb extreme and many loc kits. the tube will be carbon fibre to keep it light and will have a fibreglass avionics bay for a mini alt and Rf locator.

I'd love to see maybe a 3D view. You might want to think of a 29mm tube cuz it isn't minimum diameter but will get you real high!!!

Keep us updated!
 

FredT

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Originally posted by astronboy
I have simmed a rocket for my 24mm Ellis Mtn G37-10s I picked up at NARAM.

I named it the Blitzen as I am sure that it will just go like lightning!!

The delay is loooooong, so I went for a light, yet strong rocket with as almost little drag as possible. I do not like minimum diameter rockets, so I went with mostly ESTES parts, and plywood TTW fins designed using G Harry Stine's rules for low drag clipped delta fins.

Recover is by a BIG streamer so that there is a small chance in heck of getting it back.... I do live in Upstae NY, so there are no dry lakebeds nearby.

The rocket is BT-60 based, and I have included a rocsim. I would appreciate any comments, suggestions, or thoughts as I have never built a rocket that flies this high, or this fast.

Fred
I flew a G37-10 in a mostly stock Estes Black Brant II... got it back and flew it again! The only mod was to add at little clay in the nose and a mylar streamer. No damage other than ripping most of the decalls of the BT. I had previously flown it on an F21-8. This was my third post-BAR rocket; build only with wood glue and plastic cement.

Also flew a G37-7 in an almost stock Pheonix.

I don't think plywood fins are necessary.

You should make the drive down to METRA. Not to far from Albany.

...Fred
 

astronboy

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OK, For those without rocsim:

18" BT-60
PNC-60AH (Mean Machine nc)
BT-50 heavyweight engine tube (od is .99)
Centering rings are .125" lite ply.
I doubled the engine block just in case.....
engine tube runs more than 1/2 the length of the rocket as a stuffer tube, in order to keep the recovery system up front, and to stiffen the airframe...

3g of noseweight brings the rocket up to oprtimum weight for this motor.

There is a 1.6" long paper boat tail from the rear of the BT-60 to the BT-50.

G Harry's fin rules are as follows:

root = 2 x Diameter of airframe
clipped tip is 1 x D
span of fin is 2D

with of root of fin is .1 root length (max)
with of fin material at fin tip is .1 tip length (max)

My fins have a 3.274 root, a 1.637 tip
Span is 3.5 (Harry says that you can add to span if needed)
I am now leaning towards .25 balsa fins sanded to .125 at the tip, and then doped with silkspan for strength.

Here is a jpeg of the design

Phred
 

GL-P

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The span is kinda big but it really is only gonna fly one! :D
 

astronboy

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Yeah, I am pretty sure that this one may just fly away....

The fin span is needed to balance out the G37 motor which is 7.125" long!!

I will start cutting tubes this afternoon at my break time, and I should be able to build most of it tonight.

Phred
 

shockwaveriderz

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you could always redesign it for dual deployment....use the engine ejection chargabe to push out the drougue and use a timer or altimeter to push out the main chute say at 500 ft......to prevent it being lost....also use alot of good tracking powder....
 

astronboy

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I thought of that. Unfortunately, in order to get a full 10 second coast after burnout, weight is a critical factor. A time or altimeter, and a second recovery system would add way too much weight.

I believe that I will simply go with a slightly too small streamer....

Ph
 

GL-P

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Make the fins smaller and the tube longer. I've managed a design to do this.
More likely to survive M1. Not that you'll ever see it again!

Just build the fins tough and use a tiny streamer. Oh yeah, get some people spread out around the field. Someone may see it.

I found on wRASP that the delay was too short by 2 sec or so. Not that I'll be on the optimal mass!
 

cls

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this is a fun design project. I like the boat tail.

I always thought eliptical fin tips were lower drag than Harry Stein's trapezoids. but if you're breaking mach, maybe not.

how are you going to sand the fins, by hand or with a jig?
 

astronboy

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G Harry says that Elliptical fins are more efficient, but only by a few percentage points. These are much easier to cut and sand!!

Today I constructed the airframe including the motor mount/stuffer tube, made the boat-tail, and cut out the fins. I have also sanded the fin blanks thickness-wise from .25 at the root to .125 at the tips.

Tonight I will cut the fin slots, sand the fins to an airfoil, and mount them.

I should have some 'naked' pics tomorrow. My goal is to be ready to launch at the club launch on Saturday.

Phred
 

Stymye

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that looks like a good aerodynamic design!..and it appears ,the motor doesn't spike so hard off the pad to pose any problems.

yea the span looks kinda long to my eye as well ,, but it's not intended to be a machbuster ..good luck with it !

I have one of those motors in my box except it's the 6 sec delay
I also installed your .eng file phred ,thanks for sharing it
 

DynaSoar

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Originally posted by astronboy
OK, For those without rocsim:

18" BT-60
PNC-60AH (Mean Machine nc)
BT-50 heavyweight engine tube (od is .99)
Centering rings are .125" lite ply.
I doubled the engine block just in case.....
engine tube runs more than 1/2 the length of the rocket as a stuffer tube, in order to keep the recovery system up front, and to stiffen the airframe...

3g of noseweight brings the rocket up to oprtimum weight for this motor.

There is a 1.6" long paper boat tail from the rear of the BT-60 to the BT-50.

G Harry's fin rules are as follows:

root = 2 x Diameter of airframe
clipped tip is 1 x D
span of fin is 2D

with of root of fin is .1 root length (max)
with of fin material at fin tip is .1 tip length (max)

My fins have a 3.274 root, a 1.637 tip
Span is 3.5 (Harry says that you can add to span if needed)
I am now leaning towards .25 balsa fins sanded to .125 at the tip, and then doped with silkspan for strength.

Here is a jpeg of the design

Phred
I've been building several BT60 based higher power but Estes part birds similar to this design. It scales up in power well. I'm trying to break Mach with as little huigher powered material as possible.

Some suggestions:

1/8" basswood fins. You can get a better edge than balsa and it's easier to get a good flat finish. Glue a very thin strip of the same material along the root edge before connecting to the bird, to give it 3 times the body contact surface and way more for the fillets to grab.

Using a stuffer tube is a necessity since your engine is 40% of the body length. Very good for strength, but leaves little volume to be compressed by the ejection charge. It will be a powerful event in this bird.

If you think your upper body might need integrity, you could line it with a layer of BT60 cut with a slit down the side and slid in, or a piece of tube from Reynolds aluminum foil. The latter fits inside BT60 perfectly but isn't as heavy as BT60 coupler.

Put a shock absorber in your shock cord. Tie two loops in it a foot apart. Between them tie a piece of strong elastic that's 6" when slack. This will give a buffer zone of less "give" before the cord reaches maximum length, but won't cause "Estes Dents" due to its not being the full length of the cord. Alternatively, place a loop of elastic on the nose connection and attach the rest of the recovery stuff to that.

Keeping the recovery gear forward in the tube is good. Sometimes I use a 50/60 or 55/60 centering ring glue between the top of the MMT and the forward end to keep stuff from sliding down during boost. In 24mm birds I use a 20/50 centering ring with a piece of bamboo skewer glued across it, and also use that for shock cord mounting.

Consider cutting a PNC60 up to use as a tail cone. Only slightly better flight dynamics than a conical tail, but looks very sharp, and you can notch it easily if desired. It can also be notched for the exansion of an engine hook. And you CAN use a hook, or maybe 2 or 3, for motor retention. See my "cheap 29mm motor retainer" elsewhere for the idea. It can fit any MMT size. You just use an inch of the same motor tube slotted once to fit over the motor tube.

I don't know about the thrust curve of thre G37. Does this thing sim to Mach+? If it's close, take a look at a conical cone like PML's "1.5" urethane cone. That's always an option for later, if you put removeable connectors on all your recovery gear, or even just use a slip-loop to connect your shock cord. This also allows swapping in of a payload section later, a good idea since this is something you might want to get an altitude/speed measure on later.

And as mentioned elsewhere, a shiny mylar streamer. You can see the flash in the sun when everything else is still too small to see. Build it to be removeable, just like a chute, since mylar doesn't take heat well and you might want to replace it later.

I really like the combination of BT60 airframe and 24mm MMT for strength, internal volume and weight, as well as availability of various parts, including heavier style parts of very similar size if desired. Highly versitile, but excellent with plain LPR stock. I've built several birds on it (up to 7' long) and have more planned.

Build for the future! There's always more G37s. And others.
"The future is tomorrow!" -- Yoyodyne Propulsion Systems
 

astronboy

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Constuction is almost complete!!

I have soaked the inside of the upper BT (recovery components area) with CA for strength, cut the fin slots, and the fins have been sanded, and two are attached. I was not happy with the sanding job on one fin, so I am cutting a new one at break time this morning.

The shock chord will be two piece, ala Quest. There is a length of 1/8" Kevlar wrapped around the upper end of the stuffer tube, which comes out about 18" from the front of the rocket, I plan on adding a looong line of 1/4" elastic. remember: This thing only has an ESTES blow molded nosecone, not a cast or glassed cone.

The fins are 1/4" balsa stock, thinned to 1/8" at the tips. They are streamlined and will be coated with A couple of thin layers of yellow glue for strength. The reason I did not go with basswood are two reasons: 1) Sanding basswood is a b**ch, and 2) Weight. Even with two coats of glue, balsa is still lighter.

I thought about cutting a boat-tail from a PNC, but again, I am mostly concerned with wight in the rear. This MUST be a light rocket, and the looong motor makes it relatively tail heavy. The paper cone on there right now is soaked with CA and is plenty strong.

I will have pics this afternoon!!

Phred
 

Habu

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Originally posted by DynaSoar
snip
"The future is tomorrow!" -- Yoyodyne Propulsion Systems
Doctor Emilio Lizardo I presume...
:D
 

astronboy

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Ah Yes, one of my absolute fav Sci Fi movies:

Lizardo:
"Bigbootie, You are the , weakest alien I have ever met"

Bigbootay:

"Big Boo-tay!! Tay!!"

Ph
 

DynaSoar

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Originally posted by Habu

> Originally posted by DynaSoar
> snip
> "The future is tomorrow!" -- Yoyodyne Propulsion Systems

Doctor Emilio Lizardo I presume...
:D
Oh, sure, he made a pretty good mad scientist, but he made a very insightful psychological statement: "Home is where you wear your hat!"

Actually, I've requested copyright permission from the production company that owns the movie, so I can use the name for a business. I have plans for funding my hobby once I get moved back to Texas. I've already got the patch on my jacket.
 

astronboy

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OK, As promised, here is a pic of the 'Blitzen' before priming, with a G37-10 set next to the rocket to show the challenge.....

Fins are ttw yellow glue soaked, and sanded. Everything is installed except the streamer. With a dummy streamer, the CG comes in at 1/2" less than Rocsim!!

As for paint, I am going for visibility:

Dark blue body and fins, with a yellow cone and yellow 'Blitzen' decals.

Streamer will be silver mylar: 6" x 60" (!!) or 5" x 50" depending on prevailing winds.
 

GL-P

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Nice rocket!!! What is your current stability margin??? You might able to clip off a little of the fins.
 

cls

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nice job on the fins! trapezoids are a lot easier than ellipticals to cut out.
 

astronboy

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It is too close to clip some fin length....

CG is 19.156

CP is 21.082

The rocket should perform as planned, so I really do not see a pressing need to clip the fins.... Am I missing something here?

Phred
 

GL-P

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I know what made me tink youy could clip off the fins. I forgot that there is a tailcone that moves the motor back a little. Even that could throw off your stability. You might want to lengthen the rocket by maybe 5 inches or so. See what that does in rocksim. Should help your stability a little with minimal weight gain. Then you might be able to clip off the fins.
 

astronboy

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Well, I gave the rockt a single coat of primer, and found I had to fill a few spots. The fill n finish is almost dry, and I will go for primer coat two.

This rocket WILL be flying on Saturday's club launch!!

GL-P: I still do not understand the reasoning behinf clipping the fins? Adding to the tube is not an opprion at this time, due to the advanced stage of construction. If this rocket performs less than expected, I will build another, modified version....

Phred
 

GL-P

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You cut the drag by a lot and decrease the risk of a shred with clipping the fins a little. It was just something to ponder! There will always be another rocket! :D

Good luck and post pics!!!
 

astronboy

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Well, This baby was primed twice this morning, and sanded tonight. I painted one fin yellow, as well as the NC. I made them really thin coats, as I need to paint the body blue tomorrow night...
 

astronboy

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We have decals!!

The rocket is all set to go, I just received news that our launch field has been mown, but is muddy. Perfect for a high altitude streamer recovery!!

I am not happy with the finish however. It is very humid, so the blue is dull, even with two coats of Future. But launch day is tomorrow, so I can worry about that on Sunday.... if I get it back!!


Phred
 

GL-P

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That rocket is too pretty for mach busting.:D Might just never see it again.
Why'd you use blue??? It looks nice but is a pain to see in the sky. Too late but I'm curious. I love the paint job!!! Looks real cool!!!
 

astronboy

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Weeellll, I launched the Blizten today at the club launch......

I painted it dark blue so it could be seen against the fluffy clouds we get here in upstate NY.

Here is a pic of the rocket on the launch pad....
 
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