Here is a really unique twin-engined control line scale model jet.
The two 1/2A propeller engines are mounted on the wingtips where
they would be almost unnoticeable as integrated into the tip fuel
tanks. Interestingly, I could not find a single photograph of the
Douglas Skystreak with tip tanks. Oh well, if there ever was one
configured that way, surely this is how it would look! According
to designer and author Frank Beatty, his model flies just fine on
a single engine, regardless of whether it is the inboard or the
outboard. The wingspan is 43" and fuselage length is 40 inches.
How do you make a jet look like a jet in the air - and still
have a prop? Use two props and put the engines in the tip tanks,
says this designer. It can be a bit tricky to fly but offers surprising,
and unexplained, benefits!
Two hot .049's - old Holland Hornet .051's in
this case - are adequate for this 28 1/2" 26 oz. scale model.
This is the 'real' Douglas Skystreak
By Frank Beatty
The air powers of the world began developing experimental jet-powered
aircraft for possible military use during the early stages of World
War II. The vastly greater speeds of these radical new craft posed
innumerable design problems, so few of these ships actually became
operational or saw combat service.
Experimental work did not cease in this country at the war's
end and the Douglas Skystreak was developed for the United States
Navy to study these transonic speed problems. The Skystreak, truly
a flying laboratory, carried a fantastic maze of instrumentation.
For example, there were more than 400 pressure take-off points located
on the wings and control surfaces alone to accurately measure air
pressure distributions on these areas.
Few experimental efforts have been more crowned with success.
The Skystreak passed its Navy acceptance tests in record breaking
time, and priceless data were obtained during its flight test programs.
An added bonus was achieved when Major Marion Carl U.S.M.C., flying
the Skystreak, set a world speed record of 650.92 mph in August
What ship then could be more appropriate to use in our unusual
power plant arrangement experiment than the experimental Skystreak?
But hold on there, why power a scale jet model in this unorthodox
manner to begin with?
The jet age is upon us. We see and admire these sleek craft everyday.
Some of the most beautiful ships ever designed have been jet powered
and yet in many years of model building and flying I can count on
my fingers the number of scale jet models I have seen. Putting it
in the old nutshell, few model builders will power a scale model
that has required countless hours to build with a jet engine. The
heat insulation problems, brick-heavy wing loadings, fire hazards
and the jet engines' balky starting and running habits discourage
all but the most dedicated. So what is needed is a more reliable
method of powering scale jet models.
This configuration suggests why Frank's twin has proved such
Several approaches using conventional gasoline engines have already
been successfully demonstrated. Examples are the ducted fan jobs
and the Sabre Stunt. So here is one more way to fly a scale jet
aircraft using the old reliable gas engine. The engines positioned
in the dummy fuel tanks at the wing tips are hardly visible in flight.
And think of the many ships that used tip tanks or armament pods
that can be modeled using this idea. The Grumman Panther, Republic
F-84, and many of the Lockheed family including the F-104, to name
Our Skystreak was selected for its straight-forward lines which
would pose no unusual design or construction problems. The model
has been built to a scale of one inch equals one foot and it spans
28 1/2", is 35 1/2" long and the all up weight is some 26 ounces.
Coloring is bright red with the appropriate national markings and
two Holland Hornet .051's (use any comparable engines) power the
Skystreak. Construction is conventional except for the engine placement
- but do study the building and flight instructions; there might
be a helpful hint or two in them! Construction: Start the wings
by cutting out all the parts and making up the sub-assemblies. Cement
several widths of 1/16" sheet balsa together for the wing skins.
You will need four sheets approximately 8" wide by 13" long. While
these skins are drying, cut out all ribs, tip tank bulkheads, bell
crank mounting plate and plywood wing spar. Drill and groove wing
spar for the landing gear struts and bind these struts to wing spar
with thread and cement well. Attach the Hornet engine mounting brackets
(modify mounts according to your powerplants) to bulkheads NI. Drill
3/32" dia. holes through one of the fuel tanks as indicated. Slip
this fuel tank through bulkhead N2, which has the port wing-tip
fuel tank, cut-out and then solder the tubing line guides into position
through the tank. Attach the bellcrank/leadout wire assembly to
its mounting plate.
Cut the bottom wing skins to size and mark all rib, spar and tip
bulkhead locations on these skins with a soft lead pencil. Bevel
the trailing edges and drill a small hole for the landing gear strut
to pass through. Cement the spar, ribs, bellcrank assembly and tip
tank bulkheads to the port skin. When dry, cement the leading edge
and top skin into position. Next plank the tip tank area from NI
to N3 with 3/32" thick planking strips. The starboard wing panel
can be built in this same manner, with the exception of adding a
1/2 oz. weight to the tip as indicated. Bolt both engines into place
and shape the various cowling and rear fairings out of balsa blocks,
Sand the entire wing assembly smooth. Brush on two coats of clear
dope and fill all pin holes and dents with plastic balsa. Sand smooth
once more and cover with tissue or silk before setting wing aside
for final assembly.
Now for the tail assembly. Cement widths of the proper thickness
of balsa together so that the vertical and horizontal tail surfaces
can each be cut out in one piece. Plane and sand these parts to
shape. Cut the elevators separate from the stabilizer and add the
hinges and control horn. Before installing the control horn use
pliers to twist the wire horn ends to point away from the horn.
The vertical tail surfaces are going to look like a Chinese jigsaw
puzzle after we get through hacking on them. Separate the fin from
the rudder, then saw cut outs for the pushrod and stabilizer. Finally,
slice through the parting line so that the stabilizer-elevator assembly
can be cemented into slot, and then cement this rear portion of
fin back into position. Inset the 1/16" plywood bell crank brackets
into the lower portion of the fin and hook up the bellcrank-pushrod
assembly to the elevator horn. Fill in the pushrod slot with the
1/16" sheet fillers and add all fairings. Sand entire assembly well;
and then dope, fill and silk cover as you did the wing.
Cut out all the fuselage bulkheads and keel members. Pin the
top and bottom keel members to a smooth, even workboard surface,
and cement all port bulkhead halves and side keel members into position.
When dry, take assembly up from workboard and cement the starboard
bulkhead and keel members into position. Make up the forward landing
gear and plywood mount and cement this assembly into fuselage framework
especially well. Add the gussets to bulkheads #11 and #12 which
will help align the tail assembly later on.
The fuselage framework should be strong enough to plank from
the top down both sides without bending or twisting. When all but
1 1/2" of planking at the bottom has been installed, cement the
wing assembly into position. Cut an opening in the fuselage top
skin between bulkhead #11 and #12 and cement the tail assembly into
position. After the pushrod linkage has been hooked up, the remainder
of the fuselage can be planked. Sand the planking smooth and then
add the cabin and all fairings or fillets as well as the nose and
tail cone blocks. Sand the entire fuselage smooth and clear dope,
fill holes and dents and silk cover in preparation for finishing
If you plan to install the landing gear doors, cut holes in the
wing and fuselage skins behind where the tabs on the doors will
line up. Cement hardwood inserts in these areas so that wood screws
can be used to attach the doors after the model is painted.
The entire model should have been sanded, pin holes and dents
filled and sanded smooth and the entire model covered with silk
or tissue, Brush on an additional four coats of clear dope to seal
the silk down tight. Follow this with six or eight coats of balsa
filler coat which has had red dope added to it. Use a fine grade
of wet or dry sandpaper and wets and after every coat of paint throughout
the finishing process. When the model is smooth and the silk pores
are filled, spray six to ten coats of Stearman Red on the model.
Rub model down well with rubbing compound. Mask off the various
insignia, window and wheel well openings and spray each of these
four coats of dope. Rub these marking down with extra care as it
will spoil a nice finish if you chip the edges or rub through these
markings. Apply the aileron and flap outlines with a draftsman's
ruling pen and thinned out black dope.
Solder the wheels on, attach the landing gear doors with wood
screws and cement the rudder into position with 3/8" offset.
Before the model can be flown, it must be balanced properly.
Since there isn't an engine or other heavy components in the nose,
ballast will be required. By installing a sheet balsa plug and spacers
in the nose cone, we create a compartment large enough to hold the
four ounces of lead ballast that is required.
Flying: We naturally chose a calm, windless day for our test
flight in order to give our brainchild every opportunity to prove
itself. Light ships with 1/2 A engines like this are rather sensitive
to fly so we quickly discarded our U-Reely handle and switched to
a "half-A handle" and 40-ft. lines of 0.010 diameter cable. And
this baby has some weird flying characteristics, Sometimes when
I got a bit careless, I wondered who was flying whom. But the main
points are that a lack of prop blast over the elevator control surfaces
renders them inefficient at low speeds, so allow the Skystreak to
build up flying speed on the ground and haul her smoothly, oh-so
smoothly into the air. Maneuvers may be attempted when full speed
is attained in the air! But these are cautious, gentle maneuvers.
This model has no brute of an engine in its nose, so once that massive
nose or tail gets started going in one direction or the other, it
is reluctant to change directions again. But the model is a show
stopper. Spectators just don't believe it will fly at all until
they have seen it perform. It has taken off and flown a complete
flight on the port (inboard) engine alone when the outboard engine
quit on takeoff on more than one occasion (I don't understand it!).
And it doesn't turn in toward the flyer or go slack on the lines
even though the inboard engine has always quit half dozen laps before
the outboard engine quits. There is little perceptible difference
in the airspeed between operations with either one or both engines
running. (Amazing again.)
In retrospect - even though I have never found time for this
project - I've often wondered how a 36-in. Republic F-84 weighing
perhaps 2 lbs., similarly powered by two K&B .15's would perform.
Perhaps there will be a reader somewhere who will carry this experiment
a bit further. I'd relish hearing how his experiments turn out.
Douglas Skystreak Plans
The AMA Plans Service offers a full-size
version of many of the plans show here at a very reasonable cost. They will scale the plans any size for you. It is always
best to buy printed plans because my scanner versions often have distortions that can cause parts to fit poorly. Purchasing
plans also help to support the operation of the Academy of Model
Aeronautics - the #1 advocate for model aviation throughout the world. If the AMA no longer has this plan on file, I
will be glad to send you my higher resolution version.
Try my Scale Calculator for Model Airplane Plans.
Posted May 30, 2015