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| rec.models.rockets FAQ Part 08 - Boost and Rocket Gliders |
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of the desired turn, or tilting the stab in the OPPOSITE direction. Turn can
be increased by warping the trailing edge of the OPPOSITE wing down a bit. I
try to avoid warping the inner wing panel trailing edges up at all, as this
can lead to spiral dives. Turn can also be adjusted with the rudder.
For a left roll on boost, warp the left tip of the stab trailing edge up,
and the right tip down. This works at high speed, but has little effect at
glide speeds. Use wing warp, stab tilt, and a bit of rudder to increase or
decrease the turn as needed.
Try a few harder throws. The glider should quickly settle down into a flat
gentle circle. Continue adjusting the surfaces until you get this result.
Now you are ready for a serious hand launch. This is an art form in itself.
Throw the model up as hard as you can, at a 45 degree angle up and to
your right, and with the wing banked at the same 45 degree angle. The model
should slowly roll to the left, changing from a right turn to a left turn.
If you are lucky, the model will be gently circling 30 or more feet
overhead. If not, it probably smacked the ground, so pick it up and try
again. Go back and check the trim with a gentle toss, and if all is OK, try
again. You may want to vary the angles between 30-60 degrees each, until you
find what works best for you and your model.
Now you are ready for the first launch. Pick a reduced power motor, just
enough to get the glider to a reasonable altitude, and launch it. Use a
power tower as described previously. Carefully observe the boost,
transition, and glide. Watch out for a "death dive" where the glider never
transitions and comes straight down. This can be fixed with increased stab
incidence or warping the trailing edge of the stab up. Also watch for
"spiral dive" where the model turns very tightly and crashes into the
ground. This is caused by too much turn, or a wing that isn't producing
enough lift. Try reducing the turn or warping down the inside edge of the
inboard wing.
Continue to adjust the flying surfaces until you get the flight you want.
Now move up to the desired motor size, and fly again. Soon you'll need to
read the answer to the next question.
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8.2.16 My glider never came down and flew away. What is wrong?
If it went in a straight line, you need to re-trim the glider to circle as
it glides. Perhaps your field was too small. Find a larger place to fly.
If neither of these is the case, you probably just found a thermal. Air is
not static. It moves around due to uneven heating and cooling. A hawk
circling overhead, without flapping its wings is in a thermal. When air is
heated, it rises. Whatever is in that air goes up with it, be it bird,
rocket, or airplane. If the air is rising faster than the sink rate of your
model, the model will rise in the air. In general, this is good, as it
allows your model to fly much longer. It stops being good when you lose the
model!
This is a "good" problem. it means you've solved most of the problems you've
encountered, and have (had?) a pretty good glider. Picking thermals is an
art that is beyond this FAQ. Now we have to find a way to get the glider
back. These devices are called dethermalizers (DT) because they are designed
to get your model out of a thermal.
This is done by transforming a good glider into a bad glider. There are two
parts to this transformation. The first is some sort of timer, to cause the
action to occur when you choose. The second is an actuating device that
de-stabilizes the glide.
Timers come in several forms. Most common is dethermalizer fuse. This looks
more like cotton rope, and burns very slowly, typically 1/4" per minute. By
having this fuse burn a string or rubber band, we can actuate a device in
flight. Be sure to use a snuffer tube with the fuse, to prevent the fuse
from falling free and starting a grass file. Other more sophisticated timers
are built from small spring wound motors, or a viscous fluid like STP or
silly putty with a piston slowly moving thru the fluid.
There are many actuating devices used. The simplest is a drop weight. Since
we often need to add weight to the nose of a glider when trimming, this
weight can be dropped, with a string going either to the tail or INSIDE wing
(if you go to the outside wing, all you will do is change the glider from a
left turn to a right turn, or vice versa). By shifting the weight, the
glider will now severely stall (tail), or spiral (inside wing) into the
ground.
The "beer can" DT was popular at MIT because of its first step, empty a can
of beer! A piece of the aluminum can is deployed as a flap from the INSIDE
of the fuselage. This acts as a drag break, and causes the glider to slowly
spiral down.
Often a DT consists of a flap, either on the wing or stab, that pops up and
alters the trim of a glider, causing it to spiral dive or stall. One problem
with these is that if not set properly, they can mess up the trim of your
glider, eliminating the need for a DT in the first place.
Another problem with many DTs, especially those that produce a stall or
gentle spiral, is that in a strong thermal, they may be insufficient to
recover the model. Finally, the DT action may bring the glider down so hard
that it is damaged on landing.
I like the pop up wing DT used on the Gold Rush (Model Aviation May 1985
page 64). The entire wing is hinged, and pops up about 60 degrees. This
effectively turns the entire wing into a drag break, sending the fuselage
straight down. The model lands nose first, protecting the delicate tail from
damage. A variation of this totally cuts the wing loose, except for a string
that ties the wing to the tail. The fuselage falls like an arrow, nose
first, with the wing fluttering behind. Another nice feature for the serious
competitor is that the hinge pin can be removed, making the model very easy
to pack for shipping.
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8.2.17 References: (kits, books, publications, catalogs)
Kits:
Apogee Maxima A
Maxima B
Eclipse ???
Edmonds Deltie
Deltie-C
Deltie Thunder
Ivee
Ivee-C
Estes
#2075 ARV Condor
#2097 Manta
#1284 Space Shuttle
#2086 Tomcat
#2112 TransWing
MRC Thermal Hawk
QCR Auta Sight FWs
Easy Slide RGs
Edmonds Canard RGs
Folded Wing RGs
Never Loop BGs
Dethermalizer kit
Quest #3002 Aurora
#3006 Flat Cat
Plans:
Name Number Source
---- ------ ------
Athena NFFS plans
Bo Weevil NFFS 1973
Catharsis BH-151 Bill Hannah ???
Challenger MA August 1985 page 67
Flip SIG kit
Gold Rush MA May 1985 page 64
Pigeon SIG kit
Polly AMA #263 MA May 1979 page 50
Roll Out AMA #201 MA
Roscoe 18 AMA #509 MA May 1986 page 60
Semi Pro AMA #124 MA January 1976 page 22
Stomper AMA #510 MA May 1986 page 60
Supersweep 22 NFFS 1976, AAM December 1974
Sweepette 18 NFFS 1982
Thermic Jetco kit
Wasp VI AMA #343 MA August 1981 page 57, NFFS 85
Zenith AMA #705 MA December 1991 page 61
Books:
"Flying Hand Launched Gliders" John Kaufmann, William Morrow 1974
(out of print, often found in the children's section of libraries)
"Handbook of Model Rocketry", G Harry Stine, Wiley 1994,
"Hey, kid, ya wanna build and airplane?", Bill Hannan, Model
Builder
"Model Rocket Design and Construction", Tim Van Milligan, Kalmbach
1995 email: 102374.2533@compuserve.com
"Throw it out of sight" Lawrence Abrams
???, Bill Winter, 1951
Publications:
NARTREK, c/o Lew Proudfoot 310 Dover Court Allen, TX 75002 e-mail
lewis_proudfoot@comsys.rockwell.com or Dr40Lew@aol.com
NARTS, P.O. Box 1482, Saugus, MA 01906 e-mail
73320.1253@compuserve.com
NFFS digest, 19 Frederick Dr. Newport News, VA 23601 $15/year
NFFS plans, 10115 Newbold Dr. St. Louis, MO 63137
NFFS publications, 4858 Moorpark Ave. San Jose, CA 95129
Zaic yearbooks, Model Aero Publications, P O Box 135, Northridge, CA
91343
Catalogs:
Apogee Components Inc., 19828 North 43rd Drive, Glendale, AZ 85308
email: 71441.1111@compuserve.com
Eclipse Components, 570 Buckeye Dr, Colorado Springs, CO 80919
email: 102100.1566@compuserve.com
Edmonds Aerospace, 13326 Preuit Place, Herndon, VA 22070
email: RobEdmonds@aol.com
QCR, 7021 Forest View Drive, Springfield, VA 22150
SIG, 401 S Front St, Montezuma, IA 50171 (800)247-5008
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Copyright (c) 1996 Wolfram von Kiparski, editor.
Refer to Part 00 for the full copyright notice.
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