Today was the day of judgement, the measure of my building
prowness- no, not the first flight, but the weight and
balance.  My plane weighs 1091 lbs, weighed as it should
be- no usable fuel, full oil and coolant.  I for one would
go with the aluminum housings if they cost me up to $1500
more than the cast iron ones.  If they saved 70 lbs total,
that would be around $21 for each pound saved, to get my
plane down to a more svelte 1021 lbs.  I'm sure I could
probably get another 15 lbs off if I did some weight
reduction on my Shertz beam front mount, along with other
things.  I also went a bit heavy on my engine mount- 1"
dia x .049 thick tubes on some of the mount.  I at least
have confidence that my mount should hold up.  The CGs all
work out OK- design range is between 6 8.7 -77.7 inches
aft of datum.  Here is how it works out:


Vans states that most RV-4s come in around 950 lbs.
Gross recommended is 1500 lbs.

Mine:
Empty 66.2, wt.1021 lbs  with 180 lb pilot, but no
fuel-68.51, just a bit out of CG by .2 inches, total wt.
1271 with 180 lb pilot and full fuel 68.8, total wt.  1465-
with 35 lbs baggage- cg-70.38 total 1500

If I want to take a passenger with full fuel and baggage,
they'd better not weigh a thing, or I'll be flying over
gross recommended weight.

Brian Trubee

Jeff's motor plate will help as it in effect
eliminates the 9 pound weight of
the Scheretz beam. It weighs about the same as Tracy's plate but
the motor mounts are built in. Not helpful for Brian as he is too far
gone for a new motor mount.

One inch .049" tubing weighs about .0462 pounds per inch. Four pieces
30 inches long therefore  weighs 5.5 pounds. 3/4 OD .049 4130 tubing
weighs .0346 pounds per inch  so if you replaced just the top two tubes
with 3/4 you would save 2 pounds. Careful design is important with
no tubes in bending.

I think 10 pounds can be gotten out of Tracy's gear box with out too much
trouble. See the attached PSRU parts weights.

Aluminum end housings are $1500 each. I am not sure about the TBO however.

If you are 100 pounds over gross your climb rate assuming the
same power will be down 1500/1600  or .9375%. Top speed will hardly
be affected. If the climb rate is given as 1500 FPM with a 150 HP
O-360 than a P-port rotary would be about 2500 FPM. I suspect a
few pounds would be saved in the intake manifold with a p-port
slide throttle setup.

--------------------------------------------------
Correction on the tube savings. 30 inch 1 inch OD tubes
weigh 1.375 pounds each for a total of 5.5 pounds.
So you would only save about a pound and not two pounds.

If a tube is in tension or real short use 3/4.

Also 2500 FPM P-port estimate is a bit high. More like 2000 FPM.

Paul Lamar


I was reading a reply to my posting "weighty matters" and saw
that I had mis stated the weight of the airplane. It is not
1021 lbs, its 1091 lbs, EMPTY. That's 140 lbs over what they
generally come in at. Not something that would sell a rotary
engine conversion. Obviousy, this is much more than I wanted
to end up with, but I'll fly it and then start a Jenny Craig
program for this airplane.

Brian Trubee

Brian, What does the aluminum cowl weigh and how does
that compare to the stock cowl?  How thick is it?

Mike Wills, What does your RV4 weigh?

Paul Lamar

The cowl weight is 28 Lbs., if I remember correctly. It's
.050 thick. Pretty much comparable to a fiberglass one,
maybe even a bit lighter. The Prop is wood.

My front motor mount is a massive piece of aluminum
extrusion, I could probably cut the weight down on that by
half. It's a 1/2 inch thick 4x4 aluminum angle. I do have
access to a very nice mill, so a future project for a rainy
winter day or three up here would be to lighten that. Same
with the redrive mount plate and one of the spacer pieces.
I don't know about the body of the redrive, I'll have to
see how thick that is. Maybe fluting the body of the
redrive would be an option, if there is enough thickness to
it.

My batteries are two powersonic PS 12180  batteries-
12.6 lbs each, 18 amp-hour. My water pump is a pretty heavy
hunk of metal, I should be able to lighten it up a bit. My
fuel filter/moisture separator is a big thing- it's the
size and weight of a larger oil filter, and the mount is a
remote mount, pretty chunky, and so is the adapter plate
that mounts on the oil filter mount point on the engine
block.

A peripheral port engine would
 be nice, since I'd have half the intake runners that I
have now, so there's about 7-10 lbs, plus a bit more power.
Not a bad trade off.  If I can fly this plane this summer
and get the hours flown off, I'll be happy. I'd be a lot
happier to have this plane somewhere under 1030 lbs. I
think it's kind of a deal killer to tell people about this
conversion being as heavy as it is.

How was Everett Hatch and Allan Tolle's Superlight engine
constructed? They made their own end plates, right?  How
did they hold up, and how did they deal with wear
considerations?


Brian Trubee


.050" aluminum weighs .72  of a pound per square foot. An RV cowl is
1/4 inch honeycomb fiberglass which is much lighter than that.

Two layers of ten oz cloth weighs .12 pounds per square foot.
Add or .26 pounds per square foot for hand layup resin.
The 1/4" honeycomb weighs next to nothing. Give it .05 pound
per square foot for a total 0f .39 pound. Near half the weight.
This is boat tech.

Way back in the late 1960's I did a study on vac bagged
1/4 inch thick PVC foam sandwich with 4 oz fiberglass cloth and
epoxy resin compared to the panel stiffness of .032 aluminum.
The foam sandwich was much stiffer and about 1/3 the weight.

Because of that study the body of this car was made
from that material. It was so light it became twice as
heavy when it was painted :) Of course you would have
to insulated it from the exhaust heat with .016" thick SS
sheet and fiberfrax.

A 4 by 4 by .5" thick Schertz beam 30 inches long
would be about 12 pounds. Jeff's adapter plate with MM
weighs about 8 pounds about the same as Tracy's adapter
plate so if the aluminum Scheretz beam is replaced
by Jeff's adapter plate you would save 12 pounds
there. No need of the Schertz beam.

Steve Beckham might be able to fill us in on the PS end plates.

With Racing Beat end plates, center housing and RX8 front
cover water pump the bare engine weighs 109 pounds.

Paul Lamar