Questions on Home Made Launch Pad

Questions on Home Made Launch Pad

Post by Bob Sim » Tue, 11 Jan 2000 04:00:00



I ordered my very first rockets last week.  Since I haven't received
them yet, I thought I'd start by building my launch pad using Eric
Ohmit's modification of the Plumber's Delight, a PVC cross and 45
degree elbow design.  The business end of the pad specifies a threaded
coupler to hold the launch rods.

1) Where can I buy rods, what are they called, and what sizes do I
need for Big Daddy, Silver Comet, Fat Boy, Bull Pup, Skywinder, SR-71;
and AeroTech Barracuda, Strong Arm, and Initiator?

2) The coupler needs to be tapped for thumbscrews so I bought myself a
Hanson Home Threading Kit from Home Depot.  It comes with taps and
dies for five popular sizes but no drill bits.  The table of hole
sizes to drill lists some unusual (to me at least) bits:
#36  2.79mm
#29  3.50mm
#25  3.80mm
#21  4.10mm
#7    5.10mm
Where do you buy a set of these wierd size bits?  Is there any trick
involved in tapping a hole or do you just ream it out using a little
oil?

3) The design specifies a 2" coupler but Home Depot only has a 1.75"
coupler in the .5" size.  Is there any reason this is not suitable?

4) What do folks use for a blast deflector?  Would an upside down
aluminum pot pie pan (about 5" across, I think) work?  If this will
look ridiculous, what would be a better solution?

5) This pad is said to be suitable for rockets up to two pounds.  What
will be the launch weight of the heaviest model listed in 1), above?
---------------------------------------------------------------
Bob Simon (using wife's email account)
Please remove nospam. to reply by email.

 
 
 

Questions on Home Made Launch Pad

Post by Ted Mahle » Tue, 11 Jan 2000 04:00:00


Quote:

> I ordered my very first rockets last week.  Since I haven't received
> them yet, I thought I'd start by building my launch pad using Eric
> Ohmit's modification of the Plumber's Delight, a PVC cross and 45
> degree elbow design.  The business end of the pad specifies a threaded
> coupler to hold the launch rods.
> 1) Where can I buy rods, what are they called, and what sizes do I
> need for Big Daddy, Silver Comet, Fat Boy, Bull Pup, Skywinder, SR-71;
> and AeroTech Barracuda, Strong Arm, and Initiator?
> 4) What do folks use for a blast deflector?  Would an upside down
> aluminum pot pie pan (about 5" across, I think) work?  If this will
> look ridiculous, what would be a better solution?

  For my 4th grade class, each student builds a launch pad. We use 1/8
inch welding rods. I don't know about type but the kind I buy have a copper
coating on them that keeps them from rusting. I buy then by the pound
at the local welding supply store. You should be able to buy them in smaller
quantities. I always tell the folks why I am buying it. Sometimes they
come up with something I would not have thought about (like the copper
coating).

 I believe an inverted clay flower pot is the best deflector out there. They
are non-conductive (no shorted clips), come in many sizes, and, when
properly sized, actually deflect the blast away from the rocket. Don't
worry about looks!
 Pick a size that puts the rocket exhaust hitting the side of the pot.

--
        +----------__(')__----------------------------+
        |    (')-//__l|l__\\                          |
        |       \O_\/lol\/_O__  Ted Mahler  NAR 18184 |
        |       /O`. [ ]  ;O_L\             N5ZYO     |
        |      _\__\_[ ]_/__/_/                       |

        |    /_\l___|_H_|___|/_\                      |
        |   /       '-H-`       \                     |
        +-~~~--------~'~--------~~~-------------------+

 
 
 

Questions on Home Made Launch Pad

Post by Bruce Leviso » Tue, 11 Jan 2000 04:00:00


Quote:

> I ordered my very first rockets last week.  Since I haven't received
> them yet, I thought I'd start by building my launch pad using Eric
> Ohmit's modification of the Plumber's Delight, a PVC cross and 45
> degree elbow design.  The business end of the pad specifies a threaded
> coupler to hold the launch rods.

> 1) Where can I buy rods, what are they called, and what sizes do I
> need for Big Daddy, Silver Comet, Fat Boy, Bull Pup, Skywinder, SR-71;
> and AeroTech Barracuda, Strong Arm, and Initiator?

Try your local Ace hardware store as a source for purchasing material
for launch rods.

http://www.acehardware.com/

There is a locator at that site to help you find the nearest store.

For the small stuff, using up to 1/4 inch diameter rods three feet in
length, I find piano or music wire to be the best choice, it is harder
and more forgiving (less subject to bending) than plain steel or
stainless steel rod.  Since music wire is high carbon spring steel it
tends to corrode on storage.  As for the corrosion; I find a
synthetic scouring pad is useful for removing the rust that builds up
and the rod can be polished to almost mirror smooth with the same in
just minutes. After polishing I wipe the piano wire rods down with a
clean cloth an then rub them with powdered graphite to reduce
friction.  I also find that for long term storage wiping the rods down
with penetrating oil prevents the rust.
Some finer hobby stores also carry piano or music wire.  Should cost
you less than $1.00 per piece. I have yet
to find music wire in longer lengths (greater than 3 feet) and in
diameters wider than 1/4 inch.

You could probably find longer plain steel and stainless steel rod
stock is usually 4' by 1/8" diameter and 6' by 3/16" diameter pieces
of steel if you wanted. I have also seen galvanized steel rods at the
hardware store but have not tried using them for rocketry
applications.

Be careful with stainless steel rods they are not all the same stuff!
#316 stainless is too easy to bend, try a higher strength alloy such
as 303 (or 304).  Brass and aluminum rods are also too easy to bend.

For longer rods try using solid bar stock such as steel drill rod or
precision ground rounds available from McMaster-Carr at:

http://mcmaster.com

For a 48" long by 1/8 diameter launch rod try cutting up
something like a 6' long section of 303 Stainless Steel round, part
number 8984K21, cost 2.78 and for a 3/16 diameter rod, try part number
8984K93, cost $3.78.  The other alloys and rods with higher quality
finishes
(Machine polished) are available but at a much higher costs (2-4
times). Unfortunately as with music wire most plain steel (cheap)
drill rod less than 1/4" diameter is sold in 3' lengths.  McMaster
might be able to
obtain longer lengths for you; try contacting them.

Quote:

> 2) The coupler needs to be tapped for thumbscrews so I bought myself a
> Hanson Home Threading Kit from Home Depot.  It comes with taps and
> dies for five popular sizes but no drill bits.  The table of hole
> sizes to drill lists some unusual (to me at least) bits:
> #36  2.79mm
> #29  3.50mm
> #25  3.80mm
> #21  4.10mm
> #7    5.10mm
> Where do you buy a set of these wierd size bits?  Is there any trick
> involved in tapping a hole or do you just ream it out using a little
> oil?

McMaster also sells drill bits in wire gauge sizes.

Quote:
> 3) The design specifies a 2" coupler but Home Depot only has a 1.75"
> coupler in the .5" size.  Is there any reason this is not suitable?

> 4) What do folks use for a blast deflector?  Would an upside down
> aluminum pot pie pan (about 5" across, I think) work?  If this will
> look ridiculous, what would be a better solution?

As for a good blast shield, also in the same issue of "Sport Rocketry"
(p30) is my article on "Ablative Blast Shields". The 6 inch diameter
parabolic (bell/nose cone shaped!) or fluted deflectors I describe
cost only a few dollars to make (molded from floor leveler in the top
or bottom of a 3 liter pop bottle) and should work well on any pad
design.  Pictures and descriptions should still be available on the
NIRA web site at:
http://www.nira.chicago.il.us/Leading_Edge/jan_feb.pdf
Quote:

> 5) This pad is said to be suitable for rockets up to two pounds.  What
> will be the launch weight of the heaviest model listed in 1), above?
> ---------------------------------------------------------------
> Bob Simon (using wife's email account)
> Please remove nospam. to reply by email.

 
 
 

Questions on Home Made Launch Pad

Post by Mordecai Schmeeglefar » Tue, 11 Jan 2000 04:00:00


<snip)

Quote:
> The business end of the pad specifies a threaded
> coupler to hold the launch rods.

A complex design, though easy to use once fabricated.

Quote:
> 1) Where can I buy rods, what are they called, and what sizes do I
> need for

Home Depot, etc.  Carbon steel, you'll need to touch them up with fine
steel wool and wd-40 before each use.  You could go stainless (expense)
or music wire (length). I would go with 4' lengths on the 1/8 and 3/16
and 6' above that.  6' seems to make a big difference for the AT kits
when underpowered, as for a small field.  Using a heavier, longer rod
for the heavier estes kits will also help in a small field situation.

Big Daddy 1/8 - 3/16
Silver Comet 1/8 - 3/16
Fat Boy 1/8 - 3/16
Bull Pup ?
Skywinder 1/8
SR-71 ?
Barracuda 1/4
Strong Arm 1/4
Initiator 1/4

Quote:
> 4) What do folks use for a blast deflector?  Would an upside down
> aluminum pot pie pan (about 5" across, I think) work?  If this will
> look ridiculous, what would be a better solution?

Nothing looks ridiculous when covered with the soot of hundreds of
successful launches.

The clay pot and floor leveler suggestions are valid.  I use a cheapie
(<$10) 10 qt stainless mixing bowl from target but can really see the
advantage of a clay pot (insulator).  I thought the big clay pots were
alot more expensive.

Quote:
> 5) This pad is said to be suitable for rockets up to two pounds.  What
> will be the launch weight of the heaviest model listed in 1), above?

The initiator is a little over a pound, No direct experience, but I'd
guess the strong arm is less than 2.  You can always lay sandbags on
your legs to improve stability, if "tip-over" propensity is the limiter
of the pad.

Best of luck.  I found building the pad was as much fun as building the
rockets, and way more fun than painting!

Mordecai  (hotmail version)

 
 
 

Questions on Home Made Launch Pad

Post by Bob Sim » Wed, 12 Jan 2000 04:00:00


Quote:

>  For my 4th grade class, each student builds a launch pad. We use 1/8
>inch welding rods. I don't know about type but the kind I buy have a copper
>coating on them that keeps them from rusting. I buy then by the pound
>at the local welding supply store. You should be able to buy them in smaller
>quantities. I always tell the folks why I am buying it. Sometimes they
>come up with something I would not have thought about (like the copper
>coating).

Thanks for the welding rod tip.  I'm somewhat familiar with them
(PhosCop) from my youth because my Dad had an oxyacetylene rig in our
ba***t.  Do you happen to know if welding rods are available in 3/16
and 1/4 in addition to 1/8" that you buy?

Quote:
> I believe an inverted clay flower pot is the best deflector out there. They
>are non-conductive (no shorted clips), come in many sizes, and, when
>properly sized, actually deflect the blast away from the rocket. Don't
>worry about looks!
> Pick a size that puts the rocket exhaust hitting the side of the pot.

Do you mean the pot or the saucer?  The commercial pads all seem like
they have flat deflectors.  Would 5" be about right?

Bob
---------------------------------------------------------------
Bob Simon (using wife's email account)
Please remove nospam. to reply by email.

 
 
 

Questions on Home Made Launch Pad

Post by Bob Sim » Wed, 12 Jan 2000 04:00:00


Quote:

>For the small stuff, using up to 1/4 inch diameter rods three feet in
>length, I find piano or music wire to be the best choice, it is harder
>and more forgiving (less subject to bending) than plain steel or
>stainless steel rod.  

I'm pretty surprised that pianos have wires up to 1/4".  This seems
incredibly fat to me after seeing my son's bass guitar strings.

Quote:
>I have yet
>to find music wire in longer lengths (greater than 3 feet) and in
>diameters wider than 1/4 inch.

I've been told that 3' is long enough for the 1/8 and 3/16 rods, but
that for my 1/4" rod I should get 4' long because heavier birds take a
little more time to get up to a stable speed.  Do you agree?

Quote:
>> 4) What do folks use for a blast deflector?  Would an upside down
>> aluminum pot pie pan (about 5" across, I think) work?  If this will
>> look ridiculous, what would be a better solution?
>As for a good blast shield, also in the same issue of "Sport Rocketry"
>(p30) is my article on "Ablative Blast Shields". The 6 inch diameter
>parabolic (bell/nose cone shaped!) or fluted deflectors I describe
>cost only a few dollars to make (molded from floor leveler in the top
>or bottom of a 3 liter pop bottle) and should work well on any pad
>design.  Pictures and descriptions should still be available on the
>NIRA web site at:
>http://www.nira.chicago.il.us/Leading_Edge/jan_feb.pdf

Thanks for the pointer, Bruce.  What's floor leveler?  I don't suppose
your article has been uploaded somewhere, huh?

Bob
---------------------------------------------------------------
Bob Simon (using wife's email account)
Please remove nospam. to reply by email.

 
 
 

Questions on Home Made Launch Pad

Post by Bob Kapl » Wed, 12 Jan 2000 04:00:00


Quote:

>   For my 4th grade class, each student builds a launch pad. We use 1/8
> inch welding rods. I don't know about type but the kind I buy have a copper
> coating on them that keeps them from rusting. I buy then by the pound
> at the local welding supply store. You should be able to buy them in smaller
> quantities. I always tell the folks why I am buying it. Sometimes they
> come up with something I would not have thought about (like the copper
> coating).

When we ran NARAM, I did likewise, but got 1/8" stainless rods. Back then a
pound of rods cost something like $5 and got about 8 rods.

        Bob Kaplow      NAR # 18L       TRA # "Ctrl-Alt-Del"

Kaplow Klips:   http://members.aol.com/myhprcato/KaplowKlips.html (baffle too!)
NIRA:           http://www.nira.chicago.il.us  NAR:    http://www.nar.org

 
 
 

Questions on Home Made Launch Pad

Post by Ted Cochr » Wed, 12 Jan 2000 04:00:00



Quote:



>> The clay pot and floor leveler suggestions are valid.  I use a cheapie
>> (<$10) 10 qt stainless mixing bowl from target but can really see the
>> advantage of a clay pot (insulator).  I thought the big clay pots were
>> alot more expensive.

>The clay pots are cheaper at the end of the season when the garden stuff is
>being cleared out to make room for the snow blowers. The clay trays also
>work, and are even cheaper, but you're back to the flat surface.

>Some *** motors (Blue Thunder, Silver Streak) have a tendency to shatter
>the clay. but they are so cheap who cares.

Another idea is cast iron, stainless steel, and ceramic coated cookware at
garage sales.  It also helps to make garage sales more interesting if you
look at that stuff for its value as a blast deflector--Rounded stainless
steel frying pan covers (launch rod hole pre-drilled :-) for 50 cents;
Cast iron skillets for a buck, that sort of thing.

--tc

My opinions only.

 
 
 

Questions on Home Made Launch Pad

Post by Alex Merica » Wed, 12 Jan 2000 04:00:00


Quote:

> The clay pots are cheaper at the end of the season when the garden stuff is
> being cleared out to make room for the snow blowers.

                                         ^^^^^^^^^^^^

What's a "snow blower"? ;-}                                                          

--
Alex Mericas
NAR 62956 Level 2 Insured
President, Austin "This weekend's forecast is 72F" Area Rocketry Group

 
 
 

Questions on Home Made Launch Pad

Post by Ted Mahle » Wed, 12 Jan 2000 04:00:00


Quote:

> Do you mean the pot or the saucer?  The commercial pads all seem like
> they have flat deflectors.  Would 5" be about right?

 I use the pot. I don't like flat deflectors because they just bounce the
exhaust back to the rocket, they don't deflect it. By sizing I mean having
the nozzle*** over the slanting side of the inverted pot.

Quote:
> Bob
> ---------------------------------------------------------------
> Bob Simon (using wife's email account)
> Please remove nospam. to reply by email.

--
        +----------__(')__----------------------------+
        |    (')-//__l|l__\\                          |
        |       \O_\/lol\/_O__  Ted Mahler  NAR 18184 |
        |       /O`. [ ]  ;O_L\             N5ZYO     |
        |      _\__\_[ ]_/__/_/                       |

        |    /_\l___|_H_|___|/_\                      |
        |   /       '-H-`       \                     |
        +-~~~--------~'~--------~~~-------------------+
 
 
 

Questions on Home Made Launch Pad

Post by Dan Schneide » Wed, 12 Jan 2000 04:00:00


Quote:

>What's a "snow blower"? ;-}

Monica on Skis.

Dan (I couldn't help myself) Schneider

http://home.postnet.com/~poseidon

 
 
 

Questions on Home Made Launch Pad

Post by Dan Schneide » Wed, 12 Jan 2000 04:00:00


Quote:

> I use the pot. I don't like flat deflectors because they just bounce the
>exhaust back to the rocket, they don't deflect it. By sizing I mean having
>the nozzle*** over the slanting side of the inverted pot.

I've been using stainless steel soup bowls (about $1 each) on my 6 station
pad. They hold up nicely to the Estes motors (although I have a hole about
the size of a toothpick starting on one from composite motors). Throwing
another bowl on that rod should keep it good for quite a while.

Dan Schneider

http://www.FoundCollection.com/~poseidon

 
 
 

Questions on Home Made Launch Pad

Post by Rick Dickinso » Wed, 12 Jan 2000 04:00:00



[re: using clay flower pot as blast deflector]

Quote:
>Do you mean the pot or the saucer?  The commercial pads all seem like
>they have flat deflectors.  Would 5" be about right?

An angled deflector is even better.  The whole purpose of the deflector is
to prevent the hot exhaust gasses from melting the pad or hitting the
ground directly, causing a brushfire.  Unfortunately, a flat deflector acts
as more of a "reflector", reflecting the blast right back up at the tail
end of your rocket, which can leave some rather ugly char marks on your
fins, or melt them if they are plastic.

One simple yet effective blast deflector/rod mount system consists of a tin
can with both ends removed, split down the side, and opened up and folded
back and screwed to a board.  The launch rod passes through a hole you
drill in the fold of the can, and into the board.  There's a great picture
of this in Harry Stine's Handbook of Model Rocketry, which is an excellent
read for anyone getting into this hobby.

It looks something like this from the side (Bad ASCII art follows):

             !
             !
             !
            |!|
            |!|
           / ! \
    ____.-'  !  `-._____
=============!=============

The exclamation points are the launch rod, and the equals signs are the
board.  The rest of that mess up there is supposed to look like a circle
that's been cut and folded back open, making two 1/4 circles tangent at
their connection point.

Hope this helps,

 - Rick "Bad ASCII Artist"***inson

--
"For the purposes of this excercise, assume a spherical cow."