By John Worth (written in 2005):
What Ralph Bradley calls a “Cootie” I call a “Cutie”. To me it’s a very
cute little micro flighter which really flies well and has such a personal
connection to me that I had to build it. This is a basic design known by
many names: flexwing, parawing, sailwing, paraglider, parafoil, parasail,
Rogallo wing, etc. It was designed originally by Frank Rogallo of NASA and
it was a toy kite at first. Then it became a serious research project for
the military and for the space program.
I worked with Frank Rogallo on several of his flying wing projects and I
offer the following in connection with this subject. While not all of it
is related to models, a lot of it is and the background behind it is, I
think, interesting in regard to aviation, aerospace, and aeromodeling.
The Rogallo wing design is a very simple and provides a lot of wing area
for its weight. Though it started out as a kite, it became a glider when
it was ballasted properly and the tether was removed. In this
configuration it was conceived as the basis for replacing parachutes for
returning spacecraft to earth.
Stowed aboard a spacecraft like a 3 spoke umbrella it took up minimum
space and added little weight to the vehicle. The idea was to deploy the
wing when the vehicle got back into the atmosphere—the wing would pop out
of its tubular shield and would unfold then carry the spacecraft hanging
below like cargo on a parachute and would be steered by motors pulling in
or letting out the shroud lines.
When I worked in NASA’s special projects group at Langley Field, Virginia,
we actually tested this concept with a six foot long 30” diameter
fiberglass semi-scale model of the Saturn booster rocket that carried so
many capsules into space. Normally, at the end of a spacecraft launch the
empty booster rocket would separate and fall toward earth hanging from
parachutes until it splashed into ocean.
John Worth, right, and simulated
Saturn booster rocket with Rogallo wing. Dropped from a helicopter with
the wing folded like an umbrella, wing unfolded and was steered to ground
In our experimental concept, with
the parawing deployed instead of parachutes, the booster would be steered
from the ground by radio control and landed at an airport. Assuming a safe
landing, the booster could then be reworked for future launches, with much
less trouble, time, and cost that was involved in salvaging a booster that
had fallen into the ocean.
The concept worked well in model form and I still have movies that show
the model being dropped from a helicopter and then steered successfully
down to the ground. We also did something similar with a models of the
Mercury and Apollo spacecraft, to show how astronauts could fly their own
spacecraft while it was hanging from a parawing, and land on a runway
instead of being dunked in the ocean as was the case when parachutes were
Concept of Mercury capsule
with inflatable tubes on aluminized fabric Rogallo wing, for fold-up
stowage like that of a parachute. Drawings show sequence of deployment.
Note: a pressure canister was activated upon deployment to inflate the
tubes which would become rigid enough to support the wing shape for
But the concept died because the
parachute recovery system, despite its disadvantages compared to the
parawing, was already in use and served the purpose, whereas a switch to
the parawing concept would involve more expense and time lost in
perfecting the system in a full scale version. Time and money were scarce
in the space program so the model concept was discarded. Furthermore,
steerable parachutes were being developed that were simpler than the wing
Meanwhile, Rogallo was interested in developing a powered version of the
glider, to provide takeoff as well as landing capability. In our NASA
workshop, therefore, we took a relatively small powered military target
drone and replaced its conventional wing with a parawing. For the same
weight the parawing provided several times the wing area, with which it
could carry more payload than the conventional wing, and/or it could fly
slower and get in and out of small fields.
Here’s J. Worth working on the Fox 59
pusher powered model (with 8 channel reeds for RC) that was the basis for
a full scale Ryan Flying Jeep prototype.
We demonstrated a powered version
which weighed 15 pounds, powered by a Fox 59 gas engine. It flew very well
and attracted a lot of interest. It had very short takeoff and landing
performance. The military envisioned it as a flying Jeep that could serve
well in places like Viet Nam where regular aircraft runways were scarce.
It was seen as a possible replacement for many situations where only a
heavier and more expensive helicopter might be used. Also, enemy ground
fire shooting holes in a fabric parawing was less likely to down the craft
than holes in a rotor blade.
The full scale Ryan Aircraft
company’s Flying Jeep prototype, was intended to carry cargo on its
flatbed platform behind the pilot.
The Ryan company in California
actually built a full scale piloted prototype of the flying Jeep and
tested it extensively. But in one demonstration at Langley Field,
Virginia, the Ryan test pilot pulled it off the ground too sharply,
stalled it about a hundred feet off the ground, after which it crashed and
badly injured him.
This put a damper on the project and with the Viet Nam war ended there was
less urgency for the military to build a flying Jeep, so this NASA
project, too, died. But the parawing survived, finally, as an ultralight
hang glider which is still used by many who fly them for fun off of cliffs
or steep hills.
But the powered concept is still viable and Ralph Bradley’s Cootie is a
great example of its performance and flying qualities. It flies very
nicely and I was delighted to see it fly so well in a video. I had to,
therefore, revisit the concept after so many years being away from it.
Sidelight: In its simplest form the Rogallo wing has a negative feature
that can be scary, yet it need not be. The basic problem is that if the
airflow under the wing is lost, as might happen in a severe stall where
the wing pitches up very nose high and then drops the nose so that the
relative wind pushes down on the upper surface of the wing, all lift is
lost and the wing plunges down like a closed umbrella.
That’s what happened to the Ryan pilot with the Flying Jeep. Keep in mind
that with the wing collapsed conventional aerodynamic controls like
elevators are ineffective. A nose dive to the ground is the natural
result. But one of our modelers, the late and great Henry Struck, showed
how the nose of the stalled wing could be raised to allow airflow to get
under the wing again and restore normal lift.
Henry Struck (those of us who flew with him in New York called him Hank)
was a brilliant free flighter and radio control model designer. He really
knew how to adjust a model for best performance. It was said he could make
almost anything fly. Well, back in the 60’s Hank designed a Rogallo wing
type model that was sold by the A.C. Gilbert Co. It was a Ready-To-Fly
free flight model called the Wing Thing, powered by a small Gilbert glow
plug gas engine.
The Gilbert company provided a batch of them to AMA to be given away and
demonstrated at the 1963 National Championships at Los Alamitos Naval Air
Station in California. I was lucky enough to get two of them, one which I
flew regularly at the Nats, the other I brought home and flew many times
The one I flew at the Nats flew great, finally disappearing forever out of
sight—no dethermalizer was provided because the Wing Thing was not
expected to thermal. This type of wing is notorious for having high drag
and thus a poor glide, so it normally comes down quickly if power is not
available to ease the descent.
Hank’s solution to the fatal nose-dive problem was simple. He installed a
small dihedralled wing, very much like a V tail, in canard fashion just
below the wing’s nose, and with about a 30 degree angle of incidence
compared with the wing. Being small, the nose wing did not have much
affect on normal slow flight. But, if the main wing stalled and the nose
dropped below horizontal, with the loss of wing lift the model speeded up
in the beginning of a dive and the nose wing—being at a high angle of
attack to the airflow—pushed the main wing nose up so that the airflow
could get under the wing again.
This was Hank’s quick fix to complaints that too many Wing Things, in the
hands of novice fliers who launched the model at too steep a nose up
angle, had crashes from the resultant stall and nose dive. As those of who
flew Rogallo type wings learned, the nose wing was unnecessary with a
proper launch. But it might stage a comeback, applied to RC models, for
pilots who might try to climb at too steep an angle.
Elevator control on a Rogallo wing is typically not very powerful, acting
against the much larger wing mass, so it usually is more of a trim
control. Although the Rogallp wing is capable pof extreme maneuvers, if
flown gently the Rogallo wing flies very nicely and without the need for a
stall recovery device.
On the other hand, while a steep nose up launch is to be avoided, so too
is a level or even slightly nose down launch. What’s needed is a gentle
launch with just enough nose up to let the horizontal launch airflow get
under the wing and billow it out like a sail on a boat (although
horizontally rather than vertical).
Incidentally, I ‘wrote the book’ on Rogallo type wings for models, with an
8 page article in the 1964-65 Model Aeronautic Year Book by Frank
Zaic. The article is very detailed, with drawings, on the many aspects of
flexible wing design, stability, and control. Although 40 years old (!),
the book is still available, from the AMA through their store, for $15.
The book is chock full of articles, model plans, and data; a best buy, as
are all the Zaic Year Books.
One of several illustrations in the
Zaic Yearbook, showing proper c.g. location
In connection with all the above,
Ralph Bradley’s Cootie is a prime example of the microflighter art. I
tried it, I liked it, and I’m reliving the great flexible wing dreams and
years all over again. Even without this background, the Cootie is fun to
build and fly. I recommend you give it a try and also treat yourself to
the 1964-65 Year Book for a comparable kick.
RC Micro World
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