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

Steve Beckham sent a long reply so I converted it into
a pdf and included some photos.

Here it is.

Paul Lamar

OK, now I'm bummed all over again about the weight of my airplane. I'd
forgotten just how cool those Superlights were. I saw Alan and Everett at
the Copperstate fly-in in the mid 90s. They were there with Alan's RV-3.
That was an awesome airplane. Sure would be great to see that engine
technology applied to my airplane.

Mike Wills

Airplanes like the RV4 are marginal for a stock 13B weight wise. Where
the rotary really pays off is power to weight ratio in P-port
form with a 2.85:1 gear box. Then you are looking at 250 HP which takes
a heavier six cylinder to equal. If you have 250 HP in an RV4 you have a
good single place hot rod with baggage room :)

To get the speed however it takes a lot of work on the detail aerodynamics.
Dave Anders and Tracy Saylor used to hang out on our taxi way with
Klause Savier. Dave's RV4 airplane went over 250 MPH and Tracy Saylor's
RV6 238 MPH. Allan Tolle's rotary RV3 also went 235 MPH as I recall in
the Sun 100 with a Mazda based engine. Not the ultra light.

All three piston engines were souped up with reduced TBO to roughly 500
hours. Remember, top speed is the cube root of HP so it was mostly
reduced drag. I would say Dave's IO-360 engine was roughly 250 HP.
Tracy Saylors somewhat less. Both Dave and Tracy had special CS metal props.

The Nemesis Nxt fusleage mold was also built on our taxi way so we
arguably had the fastest light kit aircraft taxi way in the world
there for awhile :)

Paul Lamar


Paul,

I'm not sure what you mean when saying the RV-4 is marginal for a stock 13B?
My airplane is heavier than the typical RV-4, but my performance is slightly
better than what my old RV-6A would do with a 160HP Lyc. My overweight
issues (and I'm sure Brian's as well) are due entirely to engineering
issues. If there was any doubt, make it beefier. Cost was also a factor in
the weight. I have no doubt that with a careful weight loss program I could
remove 50 - 70 pounds. Which would make it comparable in weight to a
typical -4. Now if what you meant is that the RV-4 is a marginal 2 place
cross country airplane, I'd agree.

I've toyed with the idea of building a Harmon Rocket (Lyc powered) for
several years now. But you've got me thinking about going the same route as
Mark Steitle and building up a spare PP engine for my current plane while
flying the current engine. Building a PP engine with aluminum intermediate
housings is particularly appealing. Rocket performance in an airplane that
cost less than a new IO-540! Lots cheaper and less work than building a
whole new airplane. I'm looking forward to hearing from Mark on how much his
performance improves with the new engine.

Mike Wills

What I meant was weight of engine allowed.
An airplane with a higher empty weight or gross weight has a
little more margin of error on engine weight.

While you are at it I like the idea of air racing.
The Dayton to OSH 500 mile race requires more fuel than the
stock RV4 or RV3 can handle. Steve Beckham and I had a long
discussion on what to do about that and Steve is implementing
tip tanks on the RV3 racer.

The news letter Everett Hatch Memorial still has a $1000 prize for any rotary
powered airplane exceeding an average 220 MPH in that race.
A P-port PS 13B Velocity came close in 2007 at 214 MPH.


Paul Lamar

I have to agree with Mike- anytime there was doubt about strength, I over engineered. My
plane still has lower wing loading than the RV-8, even if I were to use 1700lbs as gross
weight. That's not to say that I am content with 1091 lbs as an empty weight. I'm not. I
just look at what Everett, Steve, and Allan have done - a rotary powered RV-4 at under 900
lbs- that's almost 200 lbs less than mine. Everything being equal, I'd prefer superior
lightness to superior power. I might have more power, but the airplane won't glide so well.

It cost about $6000 for my firewall forward installation- that includes the  redrive,
EC2 and EM2. Compare that with even a used lycoming 0-320. At that price, it's not
unreasonable to think about an extra $3000 for aluminum side and intermediate housings in
order to lose a goodly amount of weight.

I'm definitely going to think about building up an all-aluminum P-port engine in the
future. It's always good to have a spare, right?

Brian Trubee

Weight is unrelated to gliding performance. The airplane sinks faster, but it
also moves forward faster; the glide angles remain the same. If only the same
were true of climb!

Peter Garrison