In the annals of aviation, few types of aircraft
have flown as both monoplane and biplane. The period between the
wars saw some experimentation with the monoplane configuration
using existing biplanes. A company developed an ejectable upper
wing for Hurricanes during the Second World War. The Pietenpol
folks developed a biplane version of the Air Camper called the
Aerial, STCs modded some high-wing utility aircraft with a lower
wing for crop-dusting.
But of all the designs, only one let a pilot stand by the
airplane and say, “Hmmm…shall I fly it as a monoplane or a
biplane today?” And that’s Pete Bowers’ “Fly Baby.”
Pete pretty much planned flying a set of biplane wings all
along. In the December 1962 issue of EAA’s SPORT AVIATION
magazine, he wrote, “…when it was decided to use three different
wing arrangements for versatility, the designation was expanded
to "Fly Baby 1A" for the low-wing design, "IB" for the same
fuselage with a new set of biplane wings, and "1C" for a
strut-braced parasol monoplane wing fitted to the biplane center
The “1C” never happened…but the Fly Baby biplane (sometimes
called the “Bi-Baby”) flew about six years later.
People often refer to the Fly Baby biplane as the result of
adding another wing to the monoplane. Not really the case: The
biplane configuration does not use the monoplane wings,
replacing them with four wing panels (each about 75% of the size
of the monoplane wings) and a center section. The lower wing has
the stock 3-degree dihedral, but the upper one has only 1
degree. The wings are built the same way as the monoplane ones,
with the exception of 1/16” plywood for the ribs instead of
Merely making the wings scale versions of the monoplane ones
would have put the top wing directly above the cockpit, making
access awkward. Instead, Pete set the center section forward,
and added about 11 degrees of wing-sweep to keep the CG in the
The same fuselage, tail, engine, etc are used, though the
fuselage needs some additional structure to hold the cabane
struts and attach the flying wires. A reinforcement bracket gets
added at the firewall for the center-section wire bracing,
attachment tangs are added for the flying wires, and the forward
strut of the cabanes bolts to a point on the forward longerons.
The modifications do increase the empty weight of
the aircraft. In a SPORT AVIATION article, Pete says the biplane
is about 70 pounds heavier. Yet when one compares the empty
weights listed in the plans, Pete shows only a 50 pound penalty.
In any case, the biplane has 25% more wing area than the
monoplane, so the wing loading is less.
The wing-sweep gives the Bi-Baby a bit of a chameleon look in
flight. It looks like different airplanes from different angles.
Many small biplanes sweep the top wing, but very few sweep the
bottom wing as well (the Marquart Charger is one). The
DeHavilland Tiger Moth is probably the best-known example, and
from some angles this American kittycat does look like a Tiger.
It also lends itself for “Faux Fighter” paint jobs…
The Biplane instructions became an extra-cost addendum to the
standard plans in the late ‘60s, with Pete charging $15
additional. The biplane addendum was merged into the full plans
set about ten years ago, and, in fact, is available as a free download
(you'll need to scroll
down a bit).
There is one problem with the biplane addendum: They aren’t
really finished. Pete was a bit of a prickly person, a
perfectionist, and the word is that he had a falling-out with
his draftsman about midway through the writing of the plans. So
the beautiful, clean diagrams that enhance the main plans and
the start of the biplane plans taper off to sketches; the
typewritten text tapers to notes written on the sketches. The
sketches aren’t bad, they do illustrate the points needed, but
they never get to some of the details of the rigging. In the
introduction, Pete apologies for the state of the plans and says
an improved version was on the way…but it never happened. That’s
part of the reason, after Pete’s death, that the person selling
the plans started including them for free.
I’ve never flown a Fly Baby biplane myself, but I’m told that
they climb better than the monoplane (better wing loading). All
the struts and the additional frontal area on the wings do tend
to slow the airplane. An A65 gives acceptable performance for a
monoplane, but a C85 or O200 might be a better pick for the
bipe. The man who originally checked me out in the (monoplane)
Fly Baby talked about the biplane for a bit. It flew fine, but,
compared to other biplanes he’d flown like the Starduster, it
didn’t really stand out.
So, why build a Fly Baby biplane? Well, it’s one the few
all-wood biplane designs out there...and unlike some, it's got a
decent amount of room for the pilot.
Wood is very pleasant media to work with, and doesn’t require
learning welding or setting up a workshop that sees burning slag
thrown about occasionally. Second, you can reduce the time
before completion of a Fly Baby by building the monoplane wings
first, then building the biplane wings while you have fun with
the airworthy airplane. Switchover from monoplane to biplane
configuration takes two people about an hour.
Downsides of the biplane? Well, as mentioned, its slower than
its single-wing counterpart. It *does* take longer to build, due
to two additional wing panels and the center section, and the
modifications required to the fuselage. The biplane wings don’t
On the plus side, the biplane configuration gets
rid of one of the least-liked features of the stock Fly Baby:
The stiff, unsprung, un-bungeed, landing gear. On the monoplane
Fly Baby, the landing gear is part of the wing-bracing system,
thus the only shock-absorbing feature of the landing gear is the
few PSI in the fat tires. The ‘Baby is hell-for-stout; it’s
almost impossible to damage the gear in all but a full-blown
crash, but it does lead to some horrific bounces.
In contrast, adding the biplane wing set frees the gear from
supporting the wings. Some builders have added spring-steel gear
legs, or Cub-type bungees. However, keep in mind that a switch
back to monoplane mode won’t work, then, unless the stock gear
is returned as well.
We don’t know how many Fly Baby Biplanes have flown. The FAA
registry, as one point, listed a dozen or so “Bi-Baby” or “Fly
Baby 1B” aircraft, but, of course, there are dozens listed as
merely “Fly Baby” and thus could go any way. The newest
one is Karl Grubert, which first flew in May 2015. His
plane shows how minor cosmetic changes can really make the
machine look like it's from World War I.
Keep in mind that *any* Fly Baby can be modified to biplane
configuration. Nothing wrong with buying a monoplane and
building your own biplane wings for it. Last Fly Baby sale I’m
aware of, the plane went for $6,000 and, after a couple of days
work, it was flown 300 miles to its own home. Biplane wings
could probably be added for less than $2,000 more.
I’m only aware of two Fly Babies that were built with both sets
of wings: Pete Bowers’ original airplane, and the late John
Day’s British Fly Baby. Day’s airplane was on the cover of
KITPLANES magazine, in both configurations, about 15 years ago.