Approx. 1/4 =scale= Hawk Motor Test Vehicle

brianc · Dec 30, 2005

Sometimes you need something simple!

Starting with a Staples 3 inch mailing tube, I began calc'ing the scale numbers for this one
over the Thanksgiving weekend. I had Peter Alway's Scale Bash opened up because
everytime I turned a page in RoTW, I'd see something I wanted to build.

I just wanted
something quick and easy...

The OD of the tube is 3.125" so this works out to a 1:4.48 =scale=.

Stock Big Daddy shown for comparison.

brianc · Dec 30, 2005

I stuck in a 38mm MMT. The fins are 1/4" 5-ply birch.

I didn't bevel the scale airfoil, just the leading and trailing edges.

JB Weld was used at the MMT, with Elmers yellow wood glue elsewhere.

brianc · Dec 30, 2005

The nose is rolled posterboard with a sponge brush coat of Elmers yellow. Unlike
eugenefl and his <a href="https://rocketryforum.com/showthread.php?s=&threadid=19732">TLP Pershing</a>, I wasn't going for perfection.

A bit
of Elmers FNF took care of the crease and I was good to go.

The shoulder is a section of tube with a sliver removed. The bulkhead is more
1/4" ply. I used JB Weld here too, because the bulkhead was just a wee bit small
and JB fills gaps nicely. I wiped a little excess on the tip for added strength of the point.

The hole in the bulkhead is to add/remove clay ballast. Hey, this is a Motor Test Vehicle
and I plan on using a full range of motors!

brianc · Dec 30, 2005

The recovery system is anchored by a baffle made from another section of cutdown
tube and two plywood bulkheads. The bottom and inside of the baffle are coated with
JB Weld to hold up to the ejection charges.

brianc · Dec 30, 2005

Like I said, I was looking for quick and easy, so I didn't even fill and sand down
the mailing tube spirals. A bit of paint and 3/4" electrical tape and Ta-DA!

It looks pretty good from 15 feet away!

brianc · Dec 30, 2005

And here's a 'glamor' shot, poised for a twilight launch!

Art Upton · Jan 2, 2006

Originally posted by brianc
And here's a 'glamor' shot, poised for a twilight launch!

Wow, that is a very nice looking rocket !

Peter Alway · Jan 2, 2006

Oooh, pointy!

It's always fun to see my drawings put to good use.

mike_bar · Feb 19, 2006

Originally posted by brianc
I had Peter Alway's Scale Bash opened up because
everytime I turned a page in RoTW, I'd see something I wanted to build. I just wanted something quick and easy... [Snip]

Brian,

Wow, this is a elegant simple design. Nice build too!

38 mm motor mount?

Do you think this rocket would make a good level one certification flyer?

Thanks,
Mike

brianc · Feb 19, 2006

Originally posted by Mike_BAR
Do you think this rocket would make a good level one certification flyer?

I don't see why not! It's just about 9" shorter than my PML Ariel I used to cert. And without
any nose weight, it's just a bit lighter.

The fins are HUGE (but plenty sturdy), making it easy to establish a proper CG/CP relationship.
And the 38mm MMT inside the 3 inch BT makes it easy to add good internal epoxy fillets.

Cert Level 1 on a shoestring![tm] I love it!

mike_bar · Feb 19, 2006

Originally posted by brianc
I don't see why not! [Snip]

Cert Level 1 on a shoestring! [tm] I love it!

I love it too. It fits my style...

Thanks for the information.

I have ROTW; I need to get the Scale Bash and the Supplements.

brianc · Feb 19, 2006

Originally posted by brianc
I wasn't going for perfection.

Yikes! I just noticed there's a bit of an optical illusion happening here!
It looks like the point of the cone is off center- that's really not the case.
When I roll the shoulder along a table edge, the tip doesn't jump up and down.

When I said I wasn't going for perfection, I meant the surface/finish of the cone, not
the shape!

I just must not have had the NC inserted completely or something when I took the pix...

mccr3328 · Feb 19, 2006

How do you think it holds up compaired to epoxy ? I think I will try it on my next motor mount, or on the under side of a piston, is JB Weld more flexible than epoxy when dry ?

brianc · Feb 19, 2006

Originally posted by mccr3328
How do you think it holds up compaired to epoxy?

Due to it's heat resistance, JB Weld is the only thing I use on parts that touch a
(high power) MMT and baffles.

from https://jbweld.net/products/industro.php

Code:

Properties              (psi)
Tensile Strength: 	3960
Adhesion:               1800
Flex Strength: 	        7320
Tensile Lap Shear:      1040
Shrinkage: 	        0.0%
Resistant to: 	        500° F

I buy the economical 'Industro' packages at the Auto Parts stores. Be careful of JB Kwik,
that's only rated to 300 degrees.

The only downside is it takes 15-24 hours to cure.

I'll use general epoxy for fin fillets and such. But I'm of the opinion that you should use
the right glue for the right job. Usually that ends up being Elmers yellow glue for wood,
Elmers white for paper, and Gorilla glue for plastics (a la Crayon). Epoxy is reserved for
specialized applications.

mccr3328 · Feb 19, 2006

Thanks brianc I did not know about JB weld Kwik having diferent properties, I wouldent have even thought to look. ! Thanks for the link.

mike_bar · Feb 23, 2006

Originally posted by brianc
Sometimes you need something simple! [Snip]

Brian,

What's your plan for motor selections?

What is the expected altitude?

Recovery system?

Cool build...

PS- shouldn't this thread be in the scratch build forum? Just wondering... I'm glad I found it here.

I guess you are showing off your technique!

brianc · Feb 23, 2006

Originally posted by Mike_BAR

What's your plan for motor selections?
What is the expected altitude?
Recovery system?

I gotta go find the screen shot of the RockSIMs I did before Christmas. But- I have
AT 29mm (180 & 240) and CTI Pro38 (1, 2 and 4 grain

) cases. It's a pretty light
build, but I doubt if I'll try any loads for my 29/40-120 cases... The chute selection
will depend on the field conditions, and loaded weight after the motor and balast (if
any) is installed.

Cool build...
PS- shouldn't this thread be in the scratch build forum? Just wondering...
I'm glad I found it here. I guess you are showing off your technique!

THANX! You'd think the =scale= stuff would go in the Scratch section, but
someone decided Techniques....... I guess some =scale= could be kits.

mike_bar · Feb 23, 2006

Originally posted by brianc
You'd think the =scale= stuff would go in the Scratch section, but someone decided Techniques... I guess some =scale= could be kits.

Hmmmmm, that's interesting...
I would've never thought to look in the Techniques Forum to learn about scale modeling.

I do know I can learn something new every day.

Discuss and share your best modeling techniques with other builders. Also the main home for all Scale Built discussions. If you are creating a scale thread please use "=Scale=" in the title. It will help out with searches.

brianc · Feb 25, 2006

Originally posted by brianc
I gotta go find the screen shot of the RockSIMs I did

Hmmm... I must be too lazy to import the CTI motors into RockSIM...

Here's a shot of the sims using 29mm AT motors.

mike_bar · Feb 25, 2006

Originally posted by brianc
Here's a shot of the sims using 29mm AT motors.[Snip]

Good timing on your post!

I just received my copy of Peter Always Scale Bash in the mail today. (Also, I picked up the 1999 Supplement, and the Retro Rockets hardcopy.)

I worked out my scale conversions in Microsoft Excel for a 3.00-inch sustainer, so I can build a model similar to Brians.

I was reviewing the Aerotech catalog

I'm liking the RMS-29/180 H128W as a Level 1 certification flight.

Also, a long slow burning motor like the RMS-29/240 H97J looks like a fun flight too.

And then the RMS-29/240 H180W looks like a high flyer too.

mike_bar · Feb 27, 2006

Brian,

Do you have a photo of your 38-mm motor mount and centering rings?

I see a bit here:

Attachment: hawk_fincan_sm-trf.jpg

Thanks in advance.

brianc · Feb 27, 2006

Originally posted by Mike_BAR
Do you have a photo of your 38-mm motor mount and centering rings?

Unfortunately, no. But it's not anything special. Take a look at the RockSIM
screen capture. There's the MMT, the forward CR, the fins and the aft CR.

First I Dremeled the fin slots with a cutting disk. Notice these do not go all the
way to the end of the BT. There's a space there.

Then, I measured the motor tube for the forward ring, and JB'ed it into place.
The next day, I (yellow) glued the tube/ring inside the BT. I installed the aft ring
without glue to align the MMT. I also dry-fit the fins to ensure the CR was
tight against the leading edge of the fin TTW tabs.

After that assembly was dry, removed the aft ring and JB'ed the fins. The
next day I added (yellow) glue fillets on the inside and outside of the BT.
Finally, I JB'ed the aft ring.

That's really all there is to it!

brianc · Mar 11, 2006

Punched a hole in the sky with a H165 REDLINE today!

I ended up adding about a third of a stick of clay ballast (about 2 oz.) in the point
of the NC.

Jumped off the pad straight and true then coasted forever after burnout! Almost
outa sight as it arc'd over. Recovered nicely under a edwardw 24" T-Cup chute.

Can't wait to try a CTI Pro38 2 grain!

EDIT: fixed motor impulse typo. Who knew H168's existed?

Brian62 · Mar 13, 2006

any pic ?

brianc · Mar 13, 2006

Originally posted by Brian62
any pic ?

No. As I mentioned in the Arapahoe E thread, my camera freaked out. All I have
is white frames; not smoke-all white. After discovering this, I double-checked
to be sure I didn't burn out the CCD by accidentally aiming towards the sun at the
launch... Seems to be OK, so I'll try again next time.

brianc · May 13, 2006

Originally posted by Brian62
any pic ?

This time yes!

Flew at NEFAR on a Cessaroni 1-grain G69.

brianc · May 13, 2006

And lift-off!!

Love that flame!

brianc · May 13, 2006

Picture tells the story.

brianc · May 13, 2006

I'm not sure what happened here. I suspect the ejection charge was
too much for the baffle and it over pressurized the Staples mail tube.

It might also have happened upon landing, but it was coming down
nice an slow under a 24 inch T-cup. On to soft sod.

No biggie, I'll repair it.

Approx. 1/4 =scale= Hawk Motor Test Vehicle

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