blast plate angle?

[radiO]

i'm scratch building a launch pad and was curious as to the blast plate. i see many with a rectangle piece of metal at an angle. is this the best thing to do?

 

[rocketsonly]

I believe the "Handbook to Model Rocketry" recommends the blast plate to be angled 45 degrees. If I remember correctly, it claims that a 45 degree blast plate will direct the flames from the motor in the safest fashion.

Hope that helps.

 

[radiO]

yes, thank you! i was just wondering why it was pointed down to the ground. as far as fire safety, the straight across would seem to make better sence.

 

[powderburner]

the purpose of the blast plate is to (1) prevent the motor exhaust from striking the ground and (2) from striking vulnerable parts of the launcher

if your launcher is going to sit directly on the ground like the little Estes portapads then you need a blast plate that will direct the exhaust horizontally--- the plate can be angled or configured in any way that works to accomplish this

if your launcher is going to be up off the ground (like on a tripod or work-horse-type stand) then you have a little more flexibility in your blast plate design, but you still need to break up the exhaust flow and redirect it away from the ground

 

[Bill]

Many pads position the blast deflector horizontally because that is the easiest and cheapest. But that has the unfortunate tendency to reflect the blast right back to the tail of the rocket.

A 45 degree angle deflects the exhaust to the side to avoid that problem.


Bill

 

[radiO]

roger that! thanks!

 

[radiO]

well this is what i have done so far. tyhnaks once again to this forum for letting a newbie get some cool stuff done. i spent a whole 5 bucks on these materials. i did already have the rod mount from an estes pad. just drilled a hole in the middle of that 4 way and a bunch of glue to mount it. i did NOT glue the legs on for easy moving. so, my next question is, do i just wrap tape around the rod to keep the rockets off the plate? oh, one more question, does the rocket HAVE to be clsoe to the blast plate for lift off, does it help? did that last question make sence?

 

[radiO]

next picture:

 

[radiO]

and last:

 

[powderburner]

You can use a tape tab to hold your rocket off the blast deflector (if the rocket is light enough).

Or, you could use a clothes pin clipped to the launch rod. Or you could use an old motor casing slipped over the rod, resting on the blast deflector. Or you could place a scrap block of wood between the blast deflector and the tips of the fins. Or you could invent your own device and report back here on how well it works.

You do not necessarily want the rocket (and nozzle) to be close to the blast deflector. If the deflector is made from an electrically conductive material, and if the rocket slides down to where the ignition clips make contact with the deflector, you will short-circuit the ignition system.

Also, if your rocket is configured with a fat, wide base, and that base is too close to a flat deflector, the motor exhaust will squirt out in all directions and cause a Bernoulli-effect between the rocket and the launcher----your rocket will be 'sucked down' onto the deflector. Don't worry, this hardly ever happens.

Mostly, you just want to have as much usable length of launch rod as possible sticking out in front of the rocket. If you launch the rocket from a spot halfway up the rod you will probably encounter an entirely new set of problems. (Can you say 'bunker?')

 

[radiO]

a little paint sure goes a long way....

 

[radiO]

used high heat silver and high heat red on the pad, love the way that stuff lays down. used good o' krylon gloss on the rocket:

 

[powderburner]

He PAINTS his launcher?

Radio, are you trying to make the rest of us look bad?

 

[radiO]

dont worry, i didn't sand and primer it. well, maybe i sanded it a little....

 

[JStarStar]

I've seen custom/homebuilt pads which use an elbow section of stove pipe to direct exhaust blast away from the tail of the rocket and at the same time, not directly on the ground. Obviously stove pipe would be pretty heat-resistant, as opposed to HVAC ducting which might not be.

I just ran a quick google, and found this:

stove pipe link

They list 6" elbow sections for $8, I am sure your local Lowe's and HD have something very similar.

 

[radiO]

what a great idea!