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

Brian, I'm a huge fan of your skill with the wheel. I can't quite see it in
the photos, but where are your cooling inlets, and how big are they?

Craig