Custom Launch Pads

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cecil

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I have no financial arrangement with this guy. Just spotted him using Google, but he does what I was searching for. He'll make whatever you want...for a price.

https://www.knight-mfg.com/folding_launch_pads

custom launch pads.jpg

Now a question: is there a general rule for what percent of the launch rail (1010 American Al standard) should extend beyond the tip of the rocket being launched?
 
I have no financial arrangement with this guy. Just spotted him using Google, but he does what I was searching for. He'll make whatever you want...for a price.

https://www.knight-mfg.com/folding_launch_pads

View attachment 187626

Now a question: is there a general rule for what percent of the launch rail (1010 American Al standard) should extend beyond the tip of the rocket being launched?

They are indeed Good quality construction but they have one MAJOR Flaw! Because they are SO Low to the Ground the provided deflectors cause WAY to much Grass damage. bending the deflector up 60° at the lower end greatly eases the potential for a Grass fire. We have not had a fire but the charred and soot filled grass caused our park ranger to have pause.

I strongly recommend putting a bend in the plate about 3 or 4 inches from the lower end. This slight alteration in no way effects the use of the launcher while taking care of the damage potential. I bent our plates with a 30" Sheet metal brake on the field...tough but doable, it would be much easier at home with a good solid bench under the brake or better yet have Knight produce the deflector with the bend.

Another addition we used on our new Away pads was to replace the short 5/16-18 machine screws with longer 1-1/2" cap screws so the pad can be used with rails or round launch rods.
 

Attachments

  • Grass Condition-a2_Narhams AwayPad_Day's end No Grass Damage_08-16-14.jpg
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  • Narhams AwayPad #1a_8in x 11in Deflector Bend 60degrees_07-19-14.JPG
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I agree. I also prefer a higher pad for my 47 yr old knees.
 
They are indeed Good quality construction but they have one MAJOR Flaw! Because they are SO Low to the Ground the provided deflectors cause WAY to much Grass damage. bending the deflector up 60° at the lower end greatly eases the potential for a Grass fire. We have not had a fire but the charred and soot filled grass caused our park ranger to have pause.

I strongly recommend putting a bend in the plate about 3 or 4 inches from the lower end. This slight alteration in no way effects the use of the launcher while taking care of the damage potential. I bent our plates with a 30" Sheet metal brake on the field...tough but doable, it would be much easier at home with a good solid bench under the brake or better yet have Knight produce the deflector with the bend.

Another addition we used on our new Away pads was to replace the short 5/16-18 machine screws with longer 1-1/2" cap screws so the pad can be used with rails or round launch rods.

Very good observations: I'll pass them on to the manufacturer. Now could you guys take a second look at my question: Now a question: is there a general rule for what percent of the launch rail (1010 American Al standard) should extend beyond the tip of the rocket being launched?
 
Now a question: is there a general rule for what percent of the launch rail (1010 American Al standard) should extend beyond the tip of the rocket being launched?

Long enough that the rocket is going at least 30 mph when the first launch lug exits the rail (thus ending active guidance by the rail). This will depend on the rocket and the thrust to weight ratio involved. For most rockets you want a standard 6 foot rail. I use a an 8 foot rail with my 7.5 inch Pershing 1A to since it is long and heavy and needs to get up to speed for best stability.
 
Long enough that the rocket is going at least 30 mph when the first launch lug exits the rail (thus ending active guidance by the rail). This will depend on the rocket and the thrust to weight ratio involved. For most rockets you want a standard 6 foot rail. I use a an 8 foot rail with my 7.5 inch Pershing 1A to since it is long and heavy and needs to get up to speed for best stability.

A very useful answer. Thanks
 
NAR recommend "Safe practices" "Launching Safely in the 21st Century" from NAR report 10-29-2005
"Safe Liftoff
Current text:
4.12.1 A high power rocket shall be launched from a stable device that provides rigid
guidance until the rocket has attained a speed that ensures a predictable flight path.
Proposed text: Add 4.12.1.1 When the wind at launch exceeds 5 miles per hour, the launch
guidance device shall be of a length to ensure that the rocket reaches a speed of at least four
times the wind speed before its departure from the device.
Rationale:
The NAR Special Committee's analysis shows that the center of pressure of a rocket

moves forward (toward a potentially unstable condition) and the flight trajectory of a rocket rotates
significantly off of the vertical direction when the rocket is exposed to a crosswind while traveling at
low velocities. If the crosswind is greater than 1/4 of the velocity at which the rocket departs the
launch device, the rocket's trajectory will depart from vertical by as much as 15 degrees, and the
rocket's center of pressure will move forward approximately one caliber (body diameter) compared
to the position calculated by most commercial rocket design software. This non-vertical flight and
reduction in stability could lead to an otherwise-safe rocket becoming a flight safety hazard. It is
important to establish a requirement for safe launcher separation speed , in order to prevent the
hazards of unstable flight or of flight outside the range of 20 degrees of vertical that is the limit
established in paragraph 4.12.3 of this Code that could lead to impact outside the launch site."

 
NAR recommend "Safe practices" "Launching Safely in the 21st Century" from NAR report 10-29-2005
"Safe Liftoff
Current text:
4.12.1 A high power rocket shall be launched from a stable device that provides rigid
guidance until the rocket has attained a speed that ensures a predictable flight path.
Proposed text: Add 4.12.1.1 When the wind at launch exceeds 5 miles per hour, the launch
guidance device shall be of a length to ensure that the rocket reaches a speed of at least four
times the wind speed before its departure from the device.
Rationale:
The NAR Special Committee's analysis shows that the center of pressure of a rocket

moves forward (toward a potentially unstable condition) and the flight trajectory of a rocket rotates
significantly off of the vertical direction when the rocket is exposed to a crosswind while traveling at
low velocities. If the crosswind is greater than 1/4 of the velocity at which the rocket departs the
launch device, the rocket's trajectory will depart from vertical by as much as 15 degrees, and the
rocket's center of pressure will move forward approximately one caliber (body diameter) compared
to the position calculated by most commercial rocket design software. This non-vertical flight and
reduction in stability could lead to an otherwise-safe rocket becoming a flight safety hazard. It is
important to establish a requirement for safe launcher separation speed , in order to prevent the
hazards of unstable flight or of flight outside the range of 20 degrees of vertical that is the limit
established in paragraph 4.12.3 of this Code that could lead to impact outside the launch site."


Thanks, Ken.
 
Very good observations: I'll pass them on to the manufacturer. Now could you guys take a second look at my question: Now a question: is there a general rule for what percent of the launch rail (1010 American Al standard) should extend beyond the tip of the rocket being launched?

Our club uses 8' long 1010 rails. There is a stop to hold the rocket about 14" from the bottom. The rods pivot on the bottom and is pinned in a vertical position about 12" from the bottom. How much extends above the rocket is totally dependent on the rocket. We limit these pads to no more then 20 lb rockets although anything over 15 lbs will get a very close look. We have launched 15 lb rockets with small L motors from these pads where the nose cone was actually taller then the rail. The key is where the rail buttons are on the rocket and how much of the rail is used for guidance after launch. In this case the top button was 4.5 ft from the top of the rail and the rocket was doing over 55 ft/sec by the time the top button left the rail.
 
I use 50 ft/sec. I have used 1010 up to 20 lbs. I have never had an issue.
 
I use 50 ft/sec. I have used 1010 up to 20 lbs. I have never had an issue.

That certainly fits with what we use. It really does depend on how strong the pad is. I've seen some 1010 rail pads I wouldn't go over 6 or 7 lbs or larger then an I motor with. Others I'd feel comfortable with 20 lbs and mid L motors. The 1010 rail can certainly handle it. It's how the rail is mounted and supported that makes all the difference.
 
Our pads are pretty rough. I agree - some pads are a little rickety.
 
That certainly fits with what we use. It really does depend on how strong the pad is. I've seen some 1010 rail pads I wouldn't go over 6 or 7 lbs or larger then an I motor with. Others I'd feel comfortable with 20 lbs and mid L motors. The 1010 rail can certainly handle it. It's how the rail is mounted and supported that makes all the difference.

As you said, rail has almost nothing to do with it. My Balls project from this year was 80lb, 5" min dia O motor with 37lbs of propellant - shown here on a 1010 rail. All about the backing.IMG_2505.jpg
 
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Our club uses 8' long 1010 rails. There is a stop to hold the rocket about 14" from the bottom. The rods pivot on the bottom and is pinned in a vertical position about 12" from the bottom. How much extends above the rocket is totally dependent on the rocket. We limit these pads to no more then 20 lb rockets although anything over 15 lbs will get a very close look. We have launched 15 lb rockets with small L motors from these pads where the nose cone was actually taller then the rail. The key is where the rail buttons are on the rocket and how much of the rail is used for guidance after launch. In this case the top button was 4.5 ft from the top of the rail and the rocket was doing over 55 ft/sec by the time the top button left the rail.

Thanks, Handeman, you've given me a very clear perspective, given my uses.
 
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