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Experimental Rocketry
The Plan
Overview
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In the 1970's when I first got involved in experimental rocketry, the only
thing I really knew about was black powder. I knew that commercial
model rocket engines were basically black powder so I set about to make my
own versions of those. I had heard that sugar and potassium nitrate
could be used as a propellant and that it had been used with PVC pipe as a
casing but the idea of melting the mixture and getting that gooey mess into
a tube sounded like too much trouble and I never gave it much more thought.
This time, since I had already successfully made black powder rocket
motors, I wanted to try the sugar propellant. I found a lot of
material on internet, and bought John Wickman's book and David Sleeter's
book. The idea of being able to cast the propellant into short grains
and then put multiple grains into the motor casing seemed a lot easier than
the process of packing black powder into a paper casing. Rolling paper
engine casings was also something that I got good at and didn't mind 30
years ago but seemed especially uninviting now. PVC pipe is cheap and
easy to work with. So it was something new and even after reading
everything I could find on internet and in books and magazines about
building amateur rocket motors, I found that there were still a lot of holes
and a lot of areas that still had not been explored and documented. My
plan was to fill some of those holes. Below is an overview.
Detailed pages will also be following.
John Wickman has won awards for his book, How to Make Amateur
Rockets, and rightfully so. It is a great book and I am wearing out my
copy. John's business is commercial rocketry so he certainly has the
credentials for explaining any phase of rocketry including amateur
experimental rocketry. His book covers briefly a number of different
types of motors even including liquid and hybrid motors but the bulk of his
book covers how to make large (1" PVC pipe and up) using composite
propellant -- Ammonium Perchlorate and Aluminum powder or Ammonium Nitrate
and Magnesium Powder plus a binder and hardener. This is the same
propellant used in many large commercial rockets and missles. The
materials are available to the amateur through certain suppliers. The
advantage is this is a high energy propellant and is cast at room
temperature. The motor casings are PVC pipe and the nozzles are quick
setting concrete and can be made with carbon inserts.
David Sleeter took the same route that I did 30 years ago except he
took the development a lot further and made some excellent improvements in
the processes. David's processes require lathe work and welding which
a lot of people don't have access to. The basics are the same as my
free 1979 manual explain, however. Roll your casing with paper and
glue, mount it on a mold with a tapered piercer or coring rod, clamp
something around the casing so it doesn't split while loading, load in the
homemade black powder a little at a time, and compress it with hammer blows.
I have one method better than his. I used Sodium Silicate instead of
glue as an adhesive in rolling casings. That makes them rock hard and
semi-flame proof. When I started doing that, I no longer had to clamp
something around the casing to keep it from bursting but I also didn't
hammer it to death but moderated the amount of compression I used and still
had very consistent success with it. Anyway, the black powder, paper
casing motor has been pretty well developed now with the final frills being
added by David. David's motors range from 1/2" ID to 1-1/2" ID.
They can be built smaller but there are problems trying to get much larger
than that.
Richard Nakka is the guru here, and if I had an amateur experimental
rocketry (AER) hero, he (or Jimmy Yawn) would be it. His web site is phenomenal and
his research is the most detailed I have seen anywhere. On top of
that, he has documented an unbelievable amount of work on his website and
given explicit directions for anyone who wants to duplicate his successes,
all free of charge and readily available. Richard is also the most
diverse of all the people I have read about in AER. He not only has
done his work with metal motor casings but also documents his own and others
work with PVC pipe motors, all kinds of development work with various other
propellants and varieties of sugar propellants, recovery techniques, testing
methods, you name it, it is there.
Like everyone, and for good reason, Richard has spent most of his energy
with one type of motor -- metal casings and metal nozzles which require a
lathe. Metal casings and nozzles mean high pressure and so higher
efficiency. It also means that results can be more reliable. It
also eliminates his techniques for those that don't have a lathe.
Richard's motors are all larger than the Estes size motors and are in the
high power rocketry range, as are John Wickman's.
Scott Fintel has also done a tremendous
amount of experimenting and development. He started out using PVC then
went to metal casings and sugar
propellant, using sucrose, sorbitol, xylitol and erithrytol that I know of. He made and flew an "O"
motor with erithrytol and actually has done a lot of large sugar motor
development. He has a good video on
making potassium nitrate - sorbitol propellant as well as numerous other
videos and explanations of his work. His latest work has been with
large hybrids and his "O" class hybrid launch complete with onboard video
camera and gps.
Dan Pollino has done a lot of experimenting with large PVC motor
casings and Sugar Propellant. These are large motors and go in large
rockets. He has an excellent web site with lots of details, though a
little harder to find things on than Richard's. But then, there is no
web site that out does Richard's.
Chuck Knight is another person who has developed designs for large
(G, H & I class) PVC/sugar motors. You will find his detailed plans on
Richard's web site.
Jimmy Yawn's web site is a web site you don't want to pass up.
He also experiments with PVC pipe casings and sugar propellant but his
experimenting is a lot more along the line of what I'm interested in at the
moment. He builds large motors but has also got a method to make
motors the same size as Estes standard motors. He has made some
extremely small motors and everything in between along with some other
interesting and novel experiments. Jimmy is quite a character and I
really enjoy his web pages and humor as well as his various experiments.
If you have done much searching on the internet (and you probably have if
you found my web site), then you may wonder what is left undone. I
think anyone into AER will tell you that there is a ton that has yet to be
done. I doubt that there will ever be a lack of things to experiment
with that haven't been done yet. So here are the areas that I don't
believe there has been much development work done in yet and that I am
currently working on or plan to work on.
The smallest PVC pipe readily
available is 1/2" so I have started there, then 3/4". I plan to go on
up to large motors after I have mastered the small ones. I also want
to master using sucrose (table sugar) even though Richard Nakka and others
have already proven that Dextrose is better and Sorbitol is best in most
cases. Sugar is most readily available, cheapest, and has some
characteristics in certain circumstances that I think are actually better.
I'll develop the small sucrose motors, then move on to the other two sugars
and then will work on small versions of Richard's epoxy motors.
One of the big reasons I like
working with these small sizes is that you can build a ton of them really
cheap where the big sizes you'll notice in going through web sites, are
built in much smaller numbers. I find records of development where
maybe only two or three or at most maybe 8 or 10 of these large motors were
ever built and tested. Often a couple of static tests are all
that are done before flying them. I have already built scores of small
engines and tested them. As of 9-8-06, having just started a couple
months ago, I have built more than 50 and tested them. Just for one
type of test, I fired 20 motors.
I don't want to just build one at a
time. I want to build a dozen or two dozen at a time and I want to
develop a process for doing that quickly and easily. I have been
working on different ways to find the best and quickest way to cast a lot of
grains. How may can you cast at one time from the same spoon full?
What is the best method for coring the grains (a big question).
The most common method of retaining
quick setting cement nozzles is to use PVC caps. This is probably the
strongest and most reliable method but it has a number of draw backs: excess
outside diameter, uneven outside, not as convenient to load the concrete,
more difficult to retain in the rocket body, and actually relatively
expensive if you are building a lot of motors. There are a number of
other ways to anchor the nozzle that leave a nice smooth outside the same
diameter as that of the main case with no bumps: anchor holes drilled in the
side of the case, PVC ring on the inside of the case, pins, case squeezing,
and maybe other ways. Also, there are variations for the nozzles:
brands and types of quick setting cement, no inserts, steel inserts,
graphite inserts, with and without entry cones, with and without exit cones,
different lengths of exit cones, and so on.
Their is a number of methods for making sugar propellant: dry mix melted,
dissolved in water first, corn syrup added, glycerin added, direct on stove,
double boiler, deep fryer, oil bath, wax bath, kitchen oven, toaster oven,
electric skillet or wok, custom made heating unit. Which is best and
why? The traditional method is by grinding or milling the potassium
nitrate to a fine powder and then mixing it with powdered sugar thoroughly
and melting it directly in an oil bath. I found this to be slow,
requiring a lot of stirring, and for the batch process it has a head start
on caramelizing and shortens the overall pot life to as much as half of the
method using water. I didn't find any of the other methods to be any
better. Click here for the details.
The ratio of potassium nitrate to sugar can be varied and still be used as
propellant. The less the potassium nitrate percentage, the thinner the
heated mix, and the less tendency it has to caramelize. What is the
reduction in performance and how much thinner is the hot mix? Is the
difference in performance small enough to offset the difficulty in casting
the normal thick mix? Is it really easier? What sizes of motors
would be least affected by performance and most benefited by the thinner
mix? And how about corn syrup in propellant. It makes the fuel
flexible enough to not crack in larger motors which is why people have gone
to dextrose and lately sorbitol in place of sucrose. What are the
effects, best ratios, and best preparation and loading methods?
You won't find hardly anything
about end burning motors and if you do, you will mostly find that no one has
successfully made a practical one. The problem is that the propellant
burns to slow and so needs lots of surface area to create the mass flow rate
required to produce usable thrust. Richard did some experimenting with
burn rate modifiers and found that brown iron oxide mixed with dextrose had
an unusual characteristic and that is that it burns much faster at high
pressures (has a high burn rate exponent). He mentioned in passing
that it would be interesting to try an end burning motor with this
propellant, but apparently he never did. So I did. A single
grain produced 3.7 lbs of thrust for 1.5 seconds. That is enough to
launch a 12 oz rocket but that is a pretty small rocket, though not
unreasonable. When I did the strand burn test at atmospheric pressure
(I don't yet have a pressure vessel for testing at high pressures) the burn
rate seemed much slower than when I first made the batch a couple weeks
earlier (which is one reason to test the effects of time). This was
done with a 9/64" dia. nozzle throat which is pretty small. That was
with 1% Iron oxide. So more tests will be done with smaller dia.
nozzles, newer propellant, different iron oxides (red as opposed to brown)
and larger amounts of iron oxide.
What about other combination of
casings, propellant and nozzles that haven't been tried?
-
Compressed black powder in a pvc
case
-
Sugar propellant grains in a paper
case
-
Black powder grains rather than
compressed in a case
-
Compressed bentonite clay in a pvc
case
-
Quick setting cement nozzle in a
paper case
-
Steel nozzle in a pvc or paper case
Some questions I already had,
others have come up during my development work. Here are some of them:
Sucrose (and I think also Dextrose)
propellants caramelize (get darker) at the working temperature over time.
It is no problem when making a batch for one or two grains because as soon
as the propellant is ready, you cast it. If you are going to cast 15
or 20 or more grains with one batch, it is another story. One time I
cast about 30 grains of 3/4" (.803 dia, 1.375 long) grains with one batch of
propellant. That took me over an hour and in one hour, the propellant
is dark brown. Richard mentioned that caramelized propellant looses
power and you don't want it in that condition. Being the inquisitive
person that I am, I asked, why not -- how much power do you loose. So
one of my current areas of experimentation is to determine quantitatively
just exactly what the effects of various degrees of caramelization are.
Can you still use dark brown propellant? Do you loose power?
Does it burn slower? How much?
In my experiments, I have seen a
hint that propellant looses power after sitting for a few weeks. Is
this true? How much change is there? Is there a practical life
for sucrose propellant? How does shelf life compare to dextrose and
sorbitol propellant?
What is the actual shear strength
of the different quick setting cement types and brands and how do they
increase over time? How much pressure will a paper tube take before
rupturing. What is the difference between glue types and sodium
silicate in paper tubes. What about different grades and types of
paper? How thick should they be? There are some generalizations
to some of these questions but not much in real quantified numbers.
There are a number of types of test
fixtures and it seems everybody makes something different, some very
creative. I have built a test fixture to test a wide range of motor
sizes but need to do a lot of improving and fine tuning.
Doing strand tests to determine the
burn rate coefficient and exponent requires a pressure vessel and the
references I have all say to use nitrogen. What is the difference
between using nitrogen from a nitrogen tank and compressed air from a scuba
tank?
As soon as you think you have
thought of something no one else has, you can search the internet and you
will 99.9% of the time find you weren't the first to have that thought.
Having done a little skydiving and being an ultralight pilot, I have seen
lots of parachutes, powered and not, and they are all steerable. So
why not use R/C and make a steerable parachute for a rocket. I found
just one person who had attempted it and the web site mentioned just three
launches, the third one being totally successful, but very little
information. The standard recovery method for high power rocketry is a
dual system where a drogue chute is opened at apogee and allows a fairly
fast descent from a high altitude but slow enough to be able to open a main
chute closer to ground for a soft landing. Even with this, a high
flight can result in a landing quite a ways away even with no wind (rockets
rarely fly 100% vertical even though we would wish they would). This
conjures up all kinds of requirements as the thinking and imagining gets
more detailed. Rockets go out of sight at high altitudes. This
of course varies with the size of the rocket but a modest sized rocket can
be invisible over a mile high. There are all sorts of things that are
done to aid in recovery such as smoke trails during the coast phase, audible
beepers for locating on the ground, radio direction finders, and even gps
systems that conceivably could radio back the exact location (within a few
feet) of its landing place. If you can't see the rocket when the
steerable chute opened, then how could you control it to bring it home to
you? So imagine an onboard computer (not uncommon in high power
rocketry) that could sense what direction it was facing and even its
position with a gps and then be computer controlled to fly right back to the
point of launch (or any place programmed in). This would be quite a
feat and would be quite an achievement but why not? I will put my
money on it being done and eventually being the standard way of recovery.
It just hasn't been developed yet. I have trouble finding a place to
fly a small commercial rocket in my area, let alone a high power, high
altitude rocket.
This is nothing fancy and nothing
new. High power rockets have achieved several miles in altitude but
that is not common. There is a Mile High Club (or probably several)
and I just have a personal goal to be a member. There is a subset of
high power rocketeers that constantly try to beat the records for highest
altitude on specific sized motors and spend a lot of time fine tuning the
designs and lots of time building the smallest diameter, smoothest exterior,
most aerodynamic, most ideally balanced and weight and most efficient
rockets to beat the records. It is an interesting note that the
lightest is not always the best rocket for the highest altitude. The
lightest rocket will be propelled to the highest velocity but the rocket
needs a certain mass to coast the longest so there is a tradeoff.
Finding the ultimate balance there is just one of the goals. I would
like to build the smallest rocket with a homebuilt sugar motor to achieve a
mile altitude. There are a lot of people with a huge lead on me and I
have a long way to go to even try to catch up.
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