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