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1968 was the beginning of
the 3-man crew Apollo
era with the first manned space flight of the series,
Apollo 7, launching in
October of that year. Model rocketry was all the rage. Per this article from a
1968 issue of American Aircraft Modeler magazine, the average age of an American model
rocketeer was about 13.6 years. I was 10 years old at the time and had by that
time been building and flying model rockets for a year or two. Being a fan of
both airplanes and rockets - hence this website's name - I liked the rocket
boost gliders. The Estes Falcon,
Nighthawk, and
Space Plane models were available at the time. The Falcon was the simplest
with a pylon-mounted engine that ejected with the ejection charge. The Nighthawk
was more akin to the Polish boost-Glider in this article, where the power pod
separates from the airplane and comes down via streamer while the airplane
glides back to earth. The problem with that scheme is that the really takes two
observers to track both parts. A couple abbreviations used in the article that might not be familiar to readers
are B/G (boost−glider), AR (aspect radio), and then there's the word "prang,"
which means to crash.
Polish-Boost-Gliders
Jaronczyk shows three versions of his model for different weather
conditions. Unlike most American boost-glider designs, his models do not elect power-pod
at burn-out.
By Harry Stine
EASTERN Europe has been a hot-bed of model rocket activity for years. Although
the adoption of American techniques created a jump in interest, model rocketry in
Poland' has been a going thing probably as long as anywhere else in the world. The
Poles have been holding their meet at Krakow for more than five years, and Pawel
Elsztein of Warsaw has the distinction of authoring the first handbook of model
rocketry published anywhere.
As the American model rocket team learned in Dubnica, Czechoslovakia two years
ago, the Eastern European modelers are tough competitors in spite of the fact that
we Americans have more and better balsa, glues, and paint.
The Poles took up B/G with gusto along with the Czechs. The Poles seem ready,
willing, and able to try almost any configuration. In contrast to some of the wild
and woolly B/G design attempts seen in the USA, the Poles apparently have a stronger
background in model aerodynamics. This is probably because of the fact that Polish
rocket modelers tend to be much older than American modrockers. The average age
of an American model rocketeer is about 13.6 years, and most USA rocket types have
not had much experience in making and flying model aeroplanes and, in fact, tend
to look down their noses at flying machines when they should be eagerly trying to
find out how the airplane types do it. In Poland, because of the state-operation
of all modeling clubs, it young man doesn't get his hands on a model rocket engine
until he has proven himself to be a good aeromodeler. I don't know whether this
is good or bad, but I rather prefer our USA free-wheeling approach to modeling as
an individualistic hobby.
But the Polish B/G designs are good. Furthermore, they show some interesting
variations and departures from the usual American B/G design with its basic hand−launched
glider configuration.
Consider the subject of our plan this month, the FI 22 design by J. Jaronczyk
of Poland. This model was flown in competition at Dubnica, May, 1966, and was the
top-scoring Polish B/G with a flight time of 99 seconds, placing fifth in the category.
It aced-out the best USA B/G time of 90 seconds turned in by Gleda Estes.
The FI 22 design is interesting because of its very low aspect ratio (ratio of
span to average wing chord) of 2.94. Most B/G designs don't look like competition
types. at all unless they've got an AR of 5 or better, but the FI 22 with its stubby
little wings and a wing area exactly the same as an Astron Falcon is probably a
very good design for flying in windy, gusty weather. The Polish FI 22 did outperform
everything but Sky Slash types and Pavel Bares lowAR elliptical winger at Dubnica
under some of the worst flying weather ever encountered!
Another similar Polish rocket design uses even more wing sweep
and a lower span−chord ratio. They average nearly 90 seconds!
These two models by Furkai are quite out of the ordinary. One
is a swing−wing rocket and the other is a fork−tailed bat−bird.
Jaronczyk had four variations of the FI 22 at Dubnica with varying amounts of
sweep in the wing panels, as is evidenced from the photo. The FI 22 shown in the
plans is the one he flew at Dubnica; it appeared in plan form in the Czech magazine,
Modelar, in June, 1967.
The original FI 22 used simple engine ejection to shift the CG, but this is no
longer permitted under our new rule book, or FAI rules, either! So I have therefore
modified the FI 22 design for a streamer recovered powerpod. This makes it a longer,
skinnier model on the launcher, but cleans it up no end for gliding.
The drawing's dimensions are in millimeters. The millimeter is so much handier
to use because there are 25.4 of them in an inch. Anyway, model rocketry is now
in the metric system, and the original Modelar plans were in the metric system,
and Jaronczyk built the original model using metric system ... so why not metric?
The only concession to the English system is
in all of the balsa dimensions.
The fuselage should be made from hard, straight 1/8" x 3/8" balsa. Note that
it has its thinnest dimension in the pitch axis. A piece 383 millimeters long will
do fine - that's 15-5/64" long, so you see why millimeters are much easier to work
with.
The wing panels are cut from 1/16" sheet balsa, sanded to an airfoil section.
They are then glued to the side of the fuselage with 14 mm. of dihedral under each
tip. This didn't seem to me to be enough dihedral, but that's what Jaronczyk used
at Dubnica! Incidence should be carefully held at zero unless you want your hair
parted at launch.
The stab is cut from 1/16" sheet balsa to a symmetrical airfoil, then glued to
the bottom of the fuselage. Again, maintain a zero-degree incidence. In common with
most B/G designs, the FI 22 is a zero-zero decalage design. The long rudder is also
cut from 1/16" sheet and glued to the bottom of the fuselage.
The powerpod pylon height may seem to be too low, but again I matched the pylon
height used by Jaronczyk, allowing for the greater diameter of the Krywald 22 mm.-diameter
Polish engines he built his FI 22 for. The pod mounting arrangement is a refinement
of one I used on the original Uni-Jet Unicorn back in early 1965. A block of balsa
1/4" x 3/8" is cut 76 mm. long and a 45-degree angle cut on the back end of it is
shown. It is then glued to the top of the front fuselage ahead of the wings.
The powerpod is made in the usual way with nose cone (pick your favorite shape),
body tube, engine holder wire to keep the engine from blowing out at ejection, streamer
recovery assembly (be sure to use about 36 square-inches of streamer), and launch
lug. A piece of1/4 x 3/8" balsa cut to 45-degree angles as shown is glued to the
tube. Two side pieces cut from 1/16" sheet balsa are glued to the side of this and
to the tube.
The balsa side pieces slip down over the fuselage nose and hold the pod straight,
while the two pieces - one on the fuselage and the other on the pod - cut to 45-degrees
match up and lock the pod in place. The pod can come off the glider in an upward
and backward direction.
How does the pod part company with the glider? Hopefully, nice and clean when
the ejection charge goes off after the engine has lofted the FI 22 to a respectable
altitude. When the ejection charge fires, it kicks the wadding, streamer assembly,
and nose cone forward; the resulting reaction force shoves the pod to the rear,
unlocking the 45-degree angle pieces and allowing aerodynamic drag to separate the
pod from the glider.
Part of the problem of getting a powerpod like this to come off cleanly without
having the streamer tangle with the glider, resulting in a "Red Baron" spin, is
to pack wadding in tightly ... but not too tightly. If you pack it in too tightly,
the ejection charge will just gasp lightly and nothing will happen ... except that
your FI 22 will prang when it meets the ground.
The FI 22 should be trimmed-out like any other powerpod B/G. Trim for glide first
without the pod, using hand launches. I don't guarantee it with the FI 22, but some
of the other B/G designs will turn in better time with a hand-launch than they will
with a boosted launch! Once the glide trim is established, mount a loaded powerpod
and check to see that the boost CG is located at least at the leading edge of the
wing. With the FI 22 design, you should have no trouble in this regard.
M. I. T. papers available: For you buffs who really dig it, including integral
calculus, there are now available two of the erudite papers that were presented
by members of the M. 1. T. Model Rocket Society during their convention in late
March.
George Caporaso's paper, "Solutions of the Differential Equations of Ballistic
Flight Paths for Model Rockets," runs
pages and is loaded with mathematics. It takes up where Malewicki leaves off
and shows the results of some of the computer runs conducted by Caporaso at M. I.
T.
The second paper is a gem that will probably become a classic in model rocketry
and may also become a standard for full-scale professional rocketry as well. It's
Gordon Mandell's "The Linearized Rotational Dynamics of Streamlined Projectiles,"
50 pages worth of tightly reasoned analysis of the dynamic stability of finstabilized
rockets. It's the only work that I know of which takes the nasty math of dynamic
stability and puts it into a form usable by advanced model rocketeers. Note that
I said "advanced," and I meant just that. This is not a paper for beginners because
of the math involved and the concepts treated.
These papers can be obtained by sending a check for $1.25 to M. 1. T. Model Rocket
Society, M. 1. T. Branch, P. O. Box 110, Cambridge, Mass. 02139.
Thisa and Thata: New C6-x engines from Estes will literally put a B/G Bertha
out of sight! Both Estes and Centuri have scale model kits of the NASA Apollo Little
Joe II now available.
Willy Ley, NAR Trustee and one of the founders of NAR, has a newly revised edition
of his famous book on the history of rockets and space flight. This time it's called
"Rockets, Missiles and Man in Space." From Viking Press, 557 pages, $10.95 ... and
worth it! This is the definitive book on the history of what we're doing, and the
NAR is mentioned therein.
Polish Boost-Glider Plans (click for larger version)
Posted October 24, 2020
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