Message #613

Date: Sep 23 2000 01:37:00 EDT
From: Ron Wanttaja <>
Subject: Re: Electrical system?

"" wrote:

> I am new to the list and planing on building a Fly Baby.

Hello again, Luis... :-)
> The electrical system comments interest me as I would like to have one in
> my plane. I've seen a lot of homebuilts with the battery mounted behind the
> seat/s. I have not received my Fly Baby plans yet so I really don't know if
> this is possible with this aircraft; but if so, it would certainly help
> distribute the weight a lot better.

When my Fly Baby was built, the battery was installed on a shelf behind
the seat.  The shelf doubles as an extra baggage compartment.

The guy I bought the plane from redid the CG, and moved the battery to
under the floorboards just in front of the instrument panel bulkhead. 
CG-wise, this is a better location, but that sucker is REAL tough to get
at.  It's flush on the floorboards with the avionics box (containing the
electrical gauges, switches, meters, radio, and transponder) mounted
directly above it.  The only thing saving it from being totally
unacceptable is the use of modern maintenance-free batteries.

I've got a CG spreadsheet I ginned up back when I bought the airplane. 
With the battery in the current location, my tubbish self in the
driver's seat, full fuel, and 25 pounds of baggage behind the seat, my
CG comes in at 13.1 inches aft of the datum, when the acceptable range
is 10 to 17 inches.  When I simulate returning a 25-pound battery to the
baggage compartment, the CG changes to 14.5 inches.  A bit aft, but
nowhere near the aft limit.

I think 'Babies tend to have a aft CG.  Both N500F and Moonraker have
spacers on the engine mounts to move the engine forward an inch or so. 
If I ever build my own Fly Baby, I'm going to lengthen the forward
fuselage by two inches or so to help counteract that.

Speaking of the "redone" CG for Moonraker, I suspect the original
builder had a mistake or two in his addition.  Not only was the battery
mounted behind the pilot seat, THERE WAS 12 POUNDS OF LEAD IN THE TAIL. 
I notice log entries specifying occasional reduction of the amount of
lead as time goes by.... 

> I weigh 160 lbs so I feel I'd be well within the plane tolerances. Do not
> like night flying so lights and all of that is not important. I would like
> to have a starter though.

One thing that occurred to me:  The modern gel and RG-type batteries can
be mounted in any attitude.  If I were building, I'd again do the
under-the-forward-floorboards mount, but I'd try to make battery
installation/removal from UNDERNEATH the airplane.  Have the battery on
its side, with the terminals toward the bottom, so you can just
disconnect the terminals, unbolt the battery tray, and drop the whole
thing out the bottom.

> Also, does anyone know the weight difference between the recommended
> Continental engine and the Rotax 912? I'd love to hang one of them babies
> on the nose of the plane.

I have a list of engine weights on my engine page:

I show the C-85 as 207 pounds, and the Rotax 912 at 165.  Often, though,
the certified engine manufacturers don't include accessories in their
weight statements.  The 912 would be a bitchin' Fly Baby engine, but
you'll of course need a longer engine mount.
> As a side comment, I usually rent a Piper Cub or an Aeronca L3 which, of
> course, I have to hand-prop. When I do this, I stand behind the prop (on
> the right side of the fuselage looking forward), with my left foot wedged
> under the right tire. I then prop the plane and, as soon as it starts, I
> reach inside the cockpit to adjust the throttle. Once that is done, I
> simply walk around the strut and get in. I think this is a lot safer than
> standing in front of a turning propeller. I have no idea if a similar
> approach would work with a Fly Baby.

I know a guy who uses that technique on his 'Baby, but I'm leary of it. 
It works well in Cubs and Aeroncas because the position gives good
access to the mag switches and the plane is *high wing*.  I find the
reacharound to get to the mag switches on the instrument panel a bit of
a reach, from in front of the wing.  Though, really, there's no reason
one couldn't mount the switches on the forward fuselage ala Tiger Moth,
and there's absolutely NO access to the switches from in front of the

The low-wing part is the thing that really worries me.  You're trapped
between the wing and the propeller if you hand-prop from behind.  If the
plane surges forward, the wing will hit you and try to knock you off
balance.  This isn't a problem on planes with very low-slung wings like
Volksplanes or Sonerais, as you can sit on the wing.  But the 'Baby's
wing hits me in the butt, and the landing wires don't let you sit down

Ron Wanttaja