Idle speculation about airframe weight

[szicree]

Today, while trying to get my flaps rigged and straring at all those lightening holes, the thought occurred to me that much more weight could be shaved off. I'm no engineer and have no intention of modifying my ship, but I can't help but wonder just how light an RV could be without sacrificing strength. I mean, surely many more holes could be drilled all over the place. Also, I assume that during the design process one must choose between different readily available thicknesses of stock, erring on the side of too thick. For example, if .032 is too thin, but .040 is too thick, we go with .040. But perhaps .035 would be just right, yet unavailable. It's obvious that many parts on the RV are cut from .032 angle just to keep things simple and the materials list down, but I wonder just how light an RV could be if everything were optimized. I'm a cyclist old enough to remember 25 pound bicycles being considered light, when my current bike is about 15. Anybody think an 800 lb RV is possible?

[Robert M]

I'll bet the RV-12 will be close!

[David-aviator]

Originally Posted by szicree

Today, while trying to get my flaps rigged and straring at all those lightening holes, the thought occurred to me that much more weight could be shaved off. I'm no engineer and have no intention of modifying my ship, but I can't help but wonder just how light an RV could be without sacrificing strength. I mean, surely many more holes could be drilled all over the place. Also, I assume that during the design process one must choose between different readily available thicknesses of stock, erring on the side of too thick. For example, if .032 is too thin, but .040 is too thick, we go with .040. But perhaps .035 would be just right, yet unavailable. It's obvious that many parts on the RV are cut from .032 angle just to keep things simple and the materials list down, but I wonder just how light an RV could be if everything were optimized. I'm a cyclist old enough to remember 25 pound bicycles being considered light, when my current bike is about 15. Anybody think an 800 lb RV is possible?

Steve,

There are many ways to save an once here and there, but the quickest weight savings is in the engine/prop selection. IO vrs O and CS vrs FP can save 80 to 100 lbs if the IO inverted system is deleted.

For example - the dry weight of the IO-360-A1B6 is 333 lbs. The CS prop weighs at least 55 lbs. The inverted system, another 20 lbs. Total dry weght 408 lbs.

The dry weight of the 0-360-A1A is 290 lbs. A fine 3 blade wood prop with extension, bolts and spinner weighs 24 lbs. (I had one) Total dry weight 314 lbs. Of course the installed weight of each will be more but it is relative.

The question is, which airplane will be more satisfying in flight?

Actually, the market rules. Most builders want HP and top end performance so the IO/CS/INV set up is most popular and the weight penalty is accepted.

BUT, if one were really determined to build, for example, the lightest possible RV-8, 1000 lbs might not be unrealistic.

Eight hundred pounds would be difficult. Remove 200 lbs from the fuselage and it may be a 2 G airplane.

dd

[pierre smith]

If money were no object,
Consider a titanium stick and titanium brake pedal/pedals and instrument panel. Make it day VFR with no electrical system and no radios and definitely no paint and you could still fly into 90% of the airports around the country with a hand-held radio and cheap GPS. Not possible? I have flown a 235 Pawnee from Louisville, Ga to Wichita and then watched it go to Oregon-no radios and a lousy electrical system. It depends on how much sacrifice you're willing to accept but 800 Lbs in a 6/7/9 doesn't seem possible but maybe in a -4. How 'bout it Smokey?

You could probably bring a composite, fixed pitch prop/carburetted 0-320 6 or 7 close to 900 though with no upholstery except seats.

[flyboykelly]

I completely agree that saving weight starts with the "extras" especially the engine and prop. I am here to tell you that we installed an IO-360, inverted oil, and big three blade C/S prop and we are 10 kts slower that other RV's with smaller, simpler engines. I am seriously looking at the IO-340 stroker engine from ECI. They claim O-360 power with O-320 weight. All this with a fixed pitch cruise prop should result in a nice performing aircraft. Thoughts??? Brian

[pierre smith]

Hi Brian (and others),
When we were considering building an RV, a good friend who had built 6 or 7 of them (Ray Lawrence/Sandersville, Ga) said that he believed that the absolute best combo is an 0-360 powered airplane with a fixed pitch three bladed Catto prop. We took his advice and never looked back. We have the small Skytech starter and Van's alternator. The airplane is day/night VFR (only needs Nav for IFR) and weighed 1045 at first flight and has dual controls/brakes and the usual six-pack vacuum gauges. We did opt for the Classic Aero interior and it is beautiful and just 'finishes' the airplane.

The results.....204 MPH solo at 8000' and 2700 RPM (which a CS prop can't turn continually). It climbs at 1900 FPM solo at 135 MPH, 1100 FPM at 160 MPH, so we sacrifice some climb and takeoff distance but hey, we're nevertheless still smokin' and don't have but $55,000 in it.

Consider this. An engine turning 2700 RPM makes more horsepower than an engine turning 2400 or 2500 RPMs. If both a fixed pitch equipped airplane and a CS equipped airplane have full throttle while the FP is turning 2700 and the CS 2500, who makes more HP? Yes, the one turning more RPMs and one reason they can be faster. just look at the Nascar guys turning 358 cu. in. engines near 9000 RPMs! Horsepower.

The Lyc manual shows 2700 RPMs as 74 % power at 8000' so the engine is not being abused at all. We just have to depart from the old 2400 RPM mentality and go boogy if you don't mind the extra fuel burn.

[fl-mike]

I still feel the most overlooked area to save significant weight is....YOU! Doesn't make much sense to go titanium this and "no-paint" that if the guy in the seat is carrying an extra 50 pounds in his skin. (note: this is not usually an issue with competitive cyclist's for obvious reasons)

[pierre smith]

TOUCHE!! You said it!

[panhandler1956]

Originally Posted by fl-mike

I still feel the most overlooked area to save significant weight is....YOU! Doesn't make much sense to go titanium this and "no-paint" that if the guy in the seat is carrying an extra 50 pounds in his skin. (note: this is not usually an issue with competitive cyclist's for obvious reasons)

Mike,
I was thinking the same thing. I am on the lucky side of that equation (for now). I'll have to make sure I don't put on 50lbs in the next 5 yrs and I'll be golden. Hey, I have to bragg about something as I have no airplane or even parts at this point. - starting an -8 in the fall!!!

I remember reading about a guy with a beatiful RV-4 who the cafe race against the 6 cylinder guys a several years ago, I believe he went on a pretty extreme diet to safe every ounce......

This is a very interesting thread!

[pierre smith]

Hi Brent,
Here is the report on Dave Ander's record breaking RV4 in which he literally tromped a Rocket. Dave is a California dentist and RV owner.

http://cafefoundation.org/v2/research_aprs.php

Why can't you start the empennage on your -8 now?

Regards,