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.

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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.

Paul Lamar