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  #1  
Old 04-17-2009, 11:24 PM
James Pierson James Pierson is offline
Master Modeler
 
Join Date: Dec 2005
Location: Washington State
Posts: 654
Question Designing & Testing??

Hi Mike,
thanks for all of your wonderful work for so many years with Estes and for taking the time to answer some questions.

My first question has to do with R&D and general designing of rockets. What are your procedures for test flying a design and in particular how are you checking for chute deployment?

Also in the same lines, can you give us some (any) tips on how to correct a design that is already built that has deployment problems? Sometimes it would be nice to have a C6-4!

How many times have you had a design that looked great and had to completely re-design the thing or just start over?

Are you folks using RockSim or other rocket design programs or are you just doing the math?

PS.
If Shrox falls asleep on the job do this. Get one of the Ping Pong balls off his desk and cut a hole in it and then hold it under his nose. That smell would wake up the dead, trust me some thinks Ive learn the hard way .

Thanks for your time, JP.
James Pierson
NAR# 77907
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  #2  
Old 04-18-2009, 12:04 AM
MDorffler MDorffler is offline
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Join Date: Apr 2009
Location: Canon City, CO
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Quote:
Originally Posted by James Pierson
Hi Mike,
thanks for all of your wonderful work for so many years with Estes and for taking the time to answer some questions.

My first question has to do with R&D and general designing of rockets. What are your procedures for test flying a design and in particular how are you checking for chute deployment?

Also in the same lines, can you give us some (any) tips on how to correct a design that is already built that has deployment problems? Sometimes it would be nice to have a C6-4!

How many times have you had a design that looked great and had to completely re-design the thing or just start over?

Are you folks using RockSim or other rocket design programs or are you just doing the math?

PS.
If Shrox falls asleep on the job do this. Get one of the Ping Pong balls off his desk and cut a hole in it and then hold it under his nose. That smell would wake up the dead, trust me some thinks Ive learn the hard way .

Thanks for your time, JP.
James Pierson
NAR# 77907


James, nothing personal, but I have never had any need to use 'model rocket design software' to design my model rocket kits. Never. Ask yourself what software I would have used in 1968, or 1973, or even 1990? I have always designed all my models using my natural skills. Normally I conceive a design totally in my mind driving either to or from Estes. That's the truth. I can tell you whether a model will be stable by simply looking at it, or hefting it, or whether it needs a pinch of clay in the nose to correct any CP/CG imbalance.

I do use CAD to create all necesary parts in 3D. It is a real treat to see the first sample parts come to you that look precisely as you drew them. And I also use CAD to lay out the kit, also in 3D, for the sole purpose of matching up the fit tolerances.

I always build several flight test versions of any new design. The first test round is with parts from inventaory, then with parts from pre-productions. I build the first test model with all the parts in positions as if built by a serious and carefull modeler. The next are built as though the the modeler is clumsey. Any flight of any test model has to be arodynamically stable, even when parts are glued on crooked. Only when I am totally satisfied that all of these versions fly absolutely straight, do I release it for the next production steps.
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  #3  
Old 04-18-2009, 01:02 AM
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Royatl Royatl is offline
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Quote:
Originally Posted by MDorffler
James, nothing personal, but I have never had any need to use 'model rocket design software' to design my model rocket kits. Never. Ask yourself what software I would have used in 1968, or 1973, or even 1990? I have always designed all my models using my natural skills. Normally I conceive a design totally in my mind driving either to or from Estes. That's the truth. I can tell you whether a model will be stable by simply looking at it, or hefting it, or whether it needs a pinch of clay in the nose to correct any CP/CG imbalance.


I've noticed a trend that a lot of people trust RockSim implicitly. However, like you, I design the old fashioned way!

Quote:
I always build several flight test versions of any new design. The first test round is with parts from inventaory, then with parts from pre-productions. I build the first test model with all the parts in positions as if built by a serious and carefull modeler. The next are built as though the the modeler is clumsey. Any flight of any test model has to be arodynamically stable, even when parts are glued on crooked. Only when I am totally satisfied that all of these versions fly absolutely straight, do I release it for the next production steps.


In the past few years, however, I've seen a few kits that have ended up unstable as built. The well known example was the first shipment of SpaceShipOnes. Admittedly, that was probably a difficult design to deal with, but I was surprised when, after building mine as stock as possible, it immediately went unstable. Then we found that it needed an extra 1/2 ounce of nose weight, that later kits had. There was the E2X military kit -- can't think of the name -- but, built stock, it too was unstable on C6-5 and sometimes on B6-4. There was the SR-X, which I've only seen fly stably once out of five flights. I've heard of problems with the Solar Flare, though I haven't seen one fly yet (gotta get around to building mine).

Or how about the lower stage of the original Renegade, that was heavy and stable, and would spike into the ground (at one of our launches, a stock Renegade lower stage lawndarted within a couple of feet of a spectator. Later that day it flew again and spiked the tail lens of the rear door of a van. We banned the Renegade from our launches after that day). I guess you saw the problems with that rocket, since you redesigned it.
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  #4  
Old 04-18-2009, 07:40 PM
Rocket Doctor Rocket Doctor is offline
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Join Date: Jan 2007
Posts: 2,400
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Quote:
Originally Posted by MDorffler
James, nothing personal, but I have never had any need to use 'model rocket design software' to design my model rocket kits. Never. Ask yourself what software I would have used in 1968, or 1973, or even 1990? I have always designed all my models using my natural skills. Normally I conceive a design totally in my mind driving either to or from Estes. That's the truth. I can tell you whether a model will be stable by simply looking at it, or hefting it, or whether it needs a pinch of clay in the nose to correct any CP/CG imbalance.

I do use CAD to create all necesary parts in 3D. It is a real treat to see the first sample parts come to you that look precisely as you drew them. And I also use CAD to lay out the kit, also in 3D, for the sole purpose of matching up the fit tolerances.

I always build several flight test versions of any new design. The first test round is with parts from inventaory, then with parts from pre-productions. I build the first test model with all the parts in positions as if built by a serious and carefull modeler. The next are built as though the the modeler is clumsey. Any flight of any test model has to be arodynamically stable, even when parts are glued on crooked. Only when I am totally satisfied that all of these versions fly absolutely straight, do I release it for the next production steps.


Basically, that is how I design my rockets, grab some parts, with an idea, a name, a color shceme and test it.

I usually built one for me and one for Estes.
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  #5  
Old 05-03-2009, 11:13 AM
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shrox shrox is offline
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The way Mike described is how I do it too. It's not that hard to tell what will fly and what won't. Although the original SHX Star Shuttle glider seemed hit or miss. Some flew great, other were bricks. I think it might have been that the angle of the elerons had to be exactly right.
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