Tiny Thor

[brianc]

Still have some masking and fin trim to finish, but here's a teaser pic
of my latest scratch build...

 

[brianc]

In a TRF thread long ago and far, far away, lalligood said

The BSD Thor in any proportion is definitely one of the coolest kits
available in our hobby There can't be such as thing as too many Thors!

Which is kinda ironic, because ever since I saw my first BSD Thor at an SRA
launch, I knew I had to have one... But I also knew the 4" (or even the 3")
versions were out of my reach for the short term.

So ever since that fateful day last summer, I'd been kicking around a smaller
Thor version in my head.

 

[brianc]

This is BT60 based which scales at 40% of the BSD 4" version. (OK, a factor
of 0.4038, but I can't measure that many significant digits! )
Besides, this is not just Stand-Off Scale, it's Stand-WAY-Off Scale.

I was originally thinking 29mm MMT, but when I looked in my scratch supplies,
I found I was out of 29mm tube. So it would have to be 24mm. Later, I figured
this is actually a Good Thing[tm]. I really didn't want to have to glass the fins
just to fly on a F25. F21 will probably be plenty.

The fins are 1/8" basswood. The NC is from an Estes multi-pak. The coupler is
a toilet paper tube cut to fit. The bulkheads are 1/16" plywood (there's one not
seen mounted in the upper tube). The four CR's are 1/4" foam board. And I have
1/4" launch lugs.

I used Elmers Yellow wood glue through-out.

 

[brianc]

Here's a dry fit of the parts. You can see the paper fin patterns I glued to
the wood while cutting.

The rocket stands just a bit over 34 inches. Without a chute, this stack
weighed in at 3 oz.

 

[brianc]

While researching the Thor for scaling, I discovered <a href="https://washingtonhighpower.com/THORS.htm"> this cool web page.</a> The Washington
High Power Rocketry group built just about every size Thor you could imagine!

Check it out!

 

[brianc]

As I mentioned, I still have to mask & paint the "Tiny THOR" on the upper BT,
and add the black trim above the fin can and on the fins.

The gold trim is DupliColor Metalcast paint (over the required ground coat primer).

The Black Gloss and Sun Yellow are WalMart $0.94 ColorPlace paints.

I'll finish it all off with a coat of Future...

I'm plannng to fly the Tiny Thor this week-end at the NEFAR Bunnell Blast!
Hopefully, the forecast will be wrong and the wind will remain calm and the rain
will hold off.

 

[lalligood]

Excellent work Brian! I'm very excited to see that you followed through with wanting to downscale the Thor--and that there's a good chance of me seeing it in person too!

(I cannot make it out there to Bunnell Blast on Saturday but will be there all day Sunday. If I don't see you, have a great time & enjoy!!)

 

[brianc]

Originally posted by lalligood
(I cannot make it out there to Bunnell Blast on Saturday but will be there all day Sunday. If I don't see you, have a great time & enjoy!!)

Had a great day at NEFAR (search for 'Bunnell' to find my various postings)!

Unfortunately, the Tiny Thor never left the pad... I picked up a roll of generic
masking tape last week, and the clips kept tearing thru it (even when doubled up)
causing the Copperheads to misfire... I guess I need to toss a roll of
electrical tape into the range box.


I doubt I'll be at NEFAR on Sunday (my son has some scout stuff to do). Hope
the weather holds out for you & have fun!

 

[Karl]

What a shame brianc! She looks awesome! What motor was she due to fly on?

Laligod, looks good, keep the pics rollin'
Karl

 

[brianc]

Originally posted by Karl
She looks awesome! What motor was she due to fly on?

Thanks. The paint, kevlar, chute and nose weight brought my 3oz dry fit
up to a flight ready 5oz.

I purposely didn't built a thust ring, so I could fly Estes D12's and E-9's
as well as AT E30's and F21's.

On the NEFAR pad, I had loaded an E30-7. wRASP shows a great profile
for that! See the attachment.

I was really disappointed I ran out of time to correct my masking tape ignitor
problem 'cause there was absolutely no wind when this was ready to fly!

My son's club has a launch this weekend, so hopefully I'll get another chance.

 

[powderburner]

brianc, you have a very nice looking rocket there.
It may be tiny to you but that looks pretty big compared to most of the stuff I fly.
Any chance that you could do a bit more documentation of the tube and fin dimensions? (Enough data for someone to copy your work?)
Thanks

 

[bsexton]

Love the Thor...in any size. Good job!

 

[brianc]

Originally posted by powderburner
brianc, you have a very nice looking rocket there.

Aw, shucks.... Thanks. But all the credit needs to go to Scott Binder. I simply
downsized his design...

Any chance that you could do a bit more documentation of the tube and fin dimensions?
(Enough data for someone to copy your work?)

Sure! I'll go thru the steps I did as well as give you the numbers. That way, you
can decide to calculate your own or just use mine.

I started by grabbing the gross dimensions from various locations on the 'Net,
but mostly BSD's data sheets and such. The fin dimensions came from the
<a href="https://www.rocketreviews.com/rocksim/bsd_thor.rkt">RockSIM file on EMRR.</a>

I then converted all the inches to millimeters 'cause that's easier to deal with when
downsizing.

Since I wasn't going for exact scale (remember I said this was Stand-WAY-off scale)
I used 1" == 26mm to allow for sanding and cutting tolerances. Yes, I know it's really
25.4mm - I can't measure that difference, much less cut it by hand. Close enough.

Next, I calculated the scaling factor to match the BT60 tubes and NC I had on hand.

The 4" BSD Thor body became 104mm. The BT60 is 42mm. 42/104 = 0.4038(mumble).
Yeah, I multiplied with 4 significant digits, but rounded to two (and cut with none).
Close enough.

With the scaling factor of 0.4038 in hand I then moved on to the other dimensions-

Length - 85.75" (2203.5mm) == 889.77 mm

This overall length was split into three parts. The NC and two sections of BT.
The NC is 120mm, a full 18" tube is ~457mm and I had a piece already cut at
just under 12" (~303mm). This totaled 880mm. close enough. Do you detect
a pattern here?

Fin span - 4.75" == 49.86mm
Forward root edge - 7.9" == 82.94mm
Aft root edge - 6.7" == 70.34

Forward sweep - 6.5" == 68.25mm
Aft sweep - 4.75" == 49.86mm

Note, the fin sweeps are measured from a line extending from the leading edge
of the root to the tip.

I also used the RockSIM file for the spacing of the fins- the rear fin is 2.6mm from
the tail and the trailing edge of the forward fin is 86.5mm from the tail of the BT.
This gives a 10mm spacing between the fins.











EDIT- One of these days I'll learn to spell dimension

 

[brianc]

The interior dimentions are fairly simple.

The 24mm MMT is 8.5" long. I left 1/4" exposed to tape the motors
in place. There is no thrust ring, so mask a lip on the motor, then
insert and put a wrap around the exposed MMT.

The coupler is a standard toilet paper tube. I left 1.5" exposed.

The bulkheads are 1/16" plywood. The coupler bulkhead is glued
1/8" back from the edge of the coupler and reinforced with
a good filet of glue. This one has a T-nut and swivel to anchor
75" kevlar shock cord. It has four 1/4" holes drilled around the T-nut
to allow ejection gasses to pass by.

The second bulkhead is mounted inside the upper body tube, splitting
it into parachute and payload bays. The bulkhead has a small hole
in the center to allow the shock cord to pass thru. The cord has a knot on
the NC/payload side leaving just enough slack to attach the NC.

 

[brianc]

Here's a closer view of the payload bulkhead.

I don't have an altimeter or flight computer now, but the Tiny THOR
would make a great candidate for one!

wRASP says about 0.5 mach for the E30 and F21. It'd be interesting
to see how accurate those calcs are...

 

[lalligood]

Your mini-Thor totally ROCKS!

I dig the zipperless airframe design too. It must scream on an F. Actually, does it whistle like the full-sze Thor from the split fin design?

Got any picture(s) of the business end?

Keep up the excellent work

 

[powderburner]

brianc,
Thanks for all the design info. It looks like your work is plenty 'close enough' to the original, it still looks great.
BTW, with that phot of the rocket reclining on red satin, are you by any chance trying to get us hot or something?

 

[brianc]

Originally posted by powderburner
...that phot of the rocket reclining on red satin....

LOL!!! Actually, that's an el-cheapo Bass Pro Shop sleeping bag.
I couldn't find the towel or blanket I usually use for a backdrop. It was
the first contrasting color I found...








Campouts will never be the same.

 

[brianc]

Originally posted by lalligood
I dig the zipperless airframe design too. It must scream on an F. Actually,
does it whistle like the full-sze Thor from the split fin design?

Don't know yet- I'm hoping it will. I'll let you know after the next launch attempt this weekend.

Got any picture(s) of the business end?

LOL! Well, OK. But there's nothing extrordinarily special about it... Just
your typical 24mm MMT tube.

 

[brianc]

Forgot to mention- when drawing up the fin patterns, don't forget
to add a TTW tab to the root edge!

Also, I aligned the grain on the forward fin with the leading edge, but
on the aft fin the grain lines up with the trailing edge.


If anyone does build a Tiny THOR, email, PM or post your results. I'd
be interested in seeing them.

 

[firemanup]

Looks great Brian, awesome job...

 

[Elapid]

Originally posted by brianc

Also, I aligned the grain on the forward fin with the leading edge, but
on the aft fin the grain lines up with the trailing edge.

hmmm...
how come?

BTW: great looking rocket!

 

[brianc]

Also, I aligned the grain on the forward fin with the leading edge, but
on the aft fin the grain lines up with the trailing edge.

Originally posted by Elapid
hmmm...
how come?

Fin strength. The leading edge of the aft fin is perpendicular to the BT.
You could probably get away with having the grain follow that edge too.
But I prefer to have the grain at an angle to the BT...

Refer to Section 8.2.13 of the RMR FAQ. https://www.ninfinger.org/~sven/rockets/rmrfaq.8.html
OR https://www.ibiblio.org/pub/archives/rec.models.rockets/RMRFAQ/rmrfaq.p08
(Yeah, that's the glider stuff, but it is a great wood and grain reference).

 

[Zack Lau]

The Estes PNC-55 assortment has a nose cone that looks awfully similar to the one on my BSD Diablo...

 

[Karl]

Cool, you have a Diablo too! That downscale is awesome! Would you happen to have some plans for it? I have another 'clone' of my Diablo that flys on 2x 24mm motors, same scale ect. I call it Evolution
Karl

 

[Zack Lau]

Here is the Rocksim 7 file.

 

[brianc]

Wow!!!

I loaded up an E9-6 at my son's launch today. I think the 1500+ feet
predicted by wRASP was a bit conservative. We didn't bust the 2000'
field waiver, but it sure was a bit higher than I expected for an E9.

And no Lance, the fins didn't whistle. I think the downsizing
just made the gap a bit too small.

 

[brianc]

This is still under power and it's already almost outta sight!

 

[brianc]

The flight was incredible even with the smaller motor (heh, an E9
smaller ). There was very little wind down on the field, but
there was a bit at altitude. This caused the Tiny THOR to arch over
while approaching apogee under power. The chute deployed just
past apogee, about 75 yards down range. The wind helped
push it back to within 50 yards (in the other direction) of the pad.

Here's a shot of the happy recovery team (my son ).

Can't wait to retry that F21! Maybe for that flight I forgo the pictures
and track with binoculars!

 

[Karl]

OMG! Those pics are awesme! You've got a impressive trigger finger
Congrats!
Karl