24mm Sorbitol motors: Drysophila Project: with construction idea
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About
This page is about the 24mm single use Sorbitol propellant motors that I make for flight and for testing propellant variations.
The standard motor static tests as a D16 and can be made with varying motor ejection delay times.
Numbers of grains can be varied yielding C's thru E's:
I have had good results with staging this system
Staying at 24 mm has several advantages over HPR Ex:
1. Increased Safety
2. Decreased cost
3. Can make static test equipment with minimum cost.
4. More locations are acceptable for this size static testing
5. Staying under 62.5 grams simplifies meeting legal requirements by not needing a LEUP
6. Can fly at more sites without the need for FAA notification or waivers.
7. Making, Testing, and Flying all can be accomplished faster, Don't have to wait for a few big remote launches per year to try things out.
That is why this page is called "Drysophila" Project. When biologists want to study generational genetics they often go with Drysophila. Fruit Flies are small, inexpensive to feed, and reproduce rapidly. There are not many scientists that study generational genetics with elephants.
There are disadvantages staying small:
1. Static data yields less info partly due to the short burn times.
2. There are issues in large motors that can't be reproduced in small short burn time motors
3. LPR Ex Doesn't get much respect from the Ex crowd that often sees E motors as just good for an ignitor pyrogen.
4. Can't lift as much payload nor large rockets
4. Not as much WOW factor
For safety I use an oil-bath/double boiler. The heat source must be shielded and cooler than the ignition temp of the propellant. Keep the oil (or paraffin) covered/contained so propellant can not fall into it. Some sites describe other heating methods but I feel safer with the double boiler method.
Legality
It is each persons responsibility to determine the legality of this hobby in their area and any needed permits and paperwork. In the U.S. staying under 62.5grams per motor removes the requirement for some permits and storage requirements. There are sites that can help with determining this. This site does not get into those details. One of the best sources is to visit a local Tripoli Section and talking to local members who have figured out the local requirements.
Construction
For sites that explain the KN03/Sorbitol propellant used in these motors see the links at the bottom of this page.
Construction uses paper casings and pressed clay nozzles.
To avoid problems with paper case bonding the propellant is poured into cylindrical autoclavable plastic caps (heat resistant).
The motors are assembled using concepts borrowed from reloadable motor systems. The end cap is made of Epoxy with a touch hole drilled through, for ejection.
Flight.
Have had many successful flights including a nice two stager flight. Lost a few minimum diameter rockets due to parachute drift out of the launch area, into the rocket eating blackberries
I only have video of the fatter rocket I use to keep altitude low. Unfortunately this one's ejection delay took too long and the rocket, with squealer, tangled 20 feet up an oak tree :-( YES the parachute did come out at the last second! sigh.
This is D16 motor construction #78 and had been stored a couple years before flight.
Not sure if that was the reason for the slow ignition startup and overlong delay?
Static Tests and other Projects 1. Static Test Stand Thrust vs Time Accuracy ??
.........So far my static tests have been by video capture frame analysis. .........I had a hydraulic scale and a spring scale available. .........I needed to know if they were accurate, so I tested both systems with Estes C6 motors .........and compared results to the Estes published thrust curve data: ......... Red curve is measured data. Black curve is Estes published curve. .........(Blue is a hydraulic system that didn't do well for low power). .........
For these small motors the spring scale was the way to go. .........It's disadvantage is if a motor starts up very fast one can get spring oscillations overlapping the actual data :-(
Richard Nakka's site A must read sugar site. Don't even start without reading this one.
I would add: buy McCreary's Experimental Composite Propellant It's focus is AP but it has essential motor theory info that is easy to read yet thorough.
Jimmy Yawn's page Recrystallized sucrose and many other great innovative ideas
Nakka's SRM.xls sim software. An Excel file that allows one to sim sorbitol or dextrose motors with Bates grains. (Excellent for sorbitol with it's varied "n" value.)
