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szicree

Well Known Member
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?
 
szicree said:
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?
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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
 
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Weight

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.
 
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
 
Yes

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.
 
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)
 
lite flyer

fl-mike said:
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)
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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!
 
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fl-mike said:
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)
Click to expand...

BTW, I can spout off about that ONLY because by some freak of nature I'm genetically thin. (thanks granny). It certainly can't be attributed to my eating or exercise habits. (how many calories does pinhole-filler sanding consume?)
 
flyboykelly said:
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.
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If everything else is equal, adding a bit of weight has only a very tiny effect on speed. There is another reason for your 10 kt shortfall. It could be one or more of the following:

  • Prop with lower efficiency,
  • Engine that isn't making rated power,
  • Poor rigging leading to extra drag,
  • Inaccurate TAS measurement by you, or the other guys, and/or
  • Etc

Which prop do you have?
 
We have an MT three blade. Van's did a test on all of the popular props that they saw installed on rv's and found this prop to be the slowest and the fastest to be the two blade metal Hartzell. I would attribute most of the speed loss to the prop, but I do believe that the weight of the aircraft has alot to do with it to.
 
8-7-4-l-b-s

The lightest I have seen is a RV-4, O320, wood prop, 874lbs.**

Van list 905-913 lbs (strangely numbered) as spec RV-4 empty weight.

I think it's easier to get light weights today than just 10-15 years ago. Now we have lighter batteries, starters, alternators, lights and avionics. On the other hands we have more goodies and the "bar has been raised". Back in the day (15-20 years ago), a RV with 320/wood prop/day-night vfr/bare min inst (eng/inst) and basic interior was more common.

Now if you don't have deluxe everything: big engine, c/s prop, EFIS, dual battiers/alternator, 20 channel eng monitor, leather and gold plated control sticks you just are not cool. :confused: Can I coin a cliche', "Keep It Light"? ........... never mind, no one listens any more, go ahead just raise that gross again; I know you will. :D

** (min empties I've seen)
RV-6 980 lbs
RV-7 1011 lbs
RV-8 1035 lbs
RV-9A 1034 lbs

fattest: a RV-6 - 1244 lbs! :eek: (original max gross of 1,500 lbs, he he ha ha)
 
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My RV-4 weighs 874 lbs. That was weighed without the gear leg fairings and wheel pants but I don't see how they could add much weight. There is minimal instrumentation; MicroMonitor, airspeed, alt, vsi, turn coor, MicroAir radio and transponder. Very minimalist interior. I do have an O320 and a Catto prop too. Oh and no paint and very little primer, just primed where things touch and where things get rusty. I didn't completely coat the internal skins or anything.

I've had people flat out tell me my plane can't be that light. They may be right. I weighed my plane on those cheapie aircraft scales that look like bathroom scales with the reducing brackets that go on top. I've always been suspicious of those scales, the levers you park your tires on I think can magnify errors. Maybe someone who knows more about scales and weights than I do can... uh... weigh in. I did calibrate both scales with my body weight.

I'd really like to get hold of a set of digital scales and find out precisely how much the plane weighs.
 
Yes

Scott,
The digital scales are what we used. We borrowed them from a serious dirt track racer friend. Do you know any? Any hot rod or speed shops near you to rent them from maybe? They're so sensitive that even a slight breeze coming into my hangar made them vary a pound or two!
 
well then

szicree said:
Today, 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?
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you probally remember fat kids like me on specialized wanting a lite speed and saying why dont you just lose 10 lbs. :p
 
That's a thought too. It was pointed out to me that a local RV builder's group has them so I might try them out. I' rebuilding my elevators right now (using thicker skins, found trailing edge cracking) and when they are done I'd like to get a good accurate weight and CG. That way we'll all know for sure. :)
 
Saving weight

There is definately some weight to be saved in an RV! And for free as well! Has anybody looked at the Tank-skin screws? On my RV9, they stick out at least 6-7 mm out the back of the plate nuts. I calculated that I could have saved 100 gr. if they would have been 5 mm shorter (I have a total of 200 screws because of my long range tanks) and they would still be long enough, since they only have to protrude 2 threads. Shorter screws are not more expensive than longer ones, am I right? If you go in to detail you will find many more screws and bolts that could have been shorter, without compromising anything. Bolts are made of steel (7,85 kg/dm3) and may make a lot of weight difference, especially if there is a lot of them. To late now, all my tank screws are torqued, I am not going to replace them anymore. (might reconsidder if the empty weight turns out to high, thoug)

Regards, Tonny
 
svanarts said:
My RV-4 weighs 874 lbs.......I've had people flat out tell me my plane can't be that light. They may be right. I weighed my plane on those cheapie aircraft scales that look like bathroom scales with the reducing brackets that go on top. I've always been suspicious of those scales, the levers you park your tires on I think can magnify errors. Maybe someone who knows more about scales and weights than I do can... uh... weigh in. I did calibrate both scales with my body weight.

I'd really like to get hold of a set of digital scales and find out precisely how much the plane weighs.
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My 7 was weighed on certified scales from a local FBO for certification. It came in at 1174. Several months later it was weighed again with the bath room scale, lever arms you described. It came in almost 100 lbs heavier. The bath room scales, which are owned by the local EAA Chapter, are not of good quality and show a different weight every time you step on it. I sent them back to the company that supplied the kit to ACS where we bought it. They sent new scales but I have not used them since so I don't know if they are better or worse.

In any event, to find out what what an airplane really weighs, we probably should use scales other than the lever arm, bath room system. The weight could be way off in either direction. Who knows, your 4 might come in at 820. :)

dd
 
pierre smith said:
Why can't you start the empennage on your -8 now?

Regards,
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I am trying to pay cash and I just spent all my money on tools. I do have the tool box project and me and the son will be starting that soon. Also I promised the wife I would finish another project I owe her before starting on the airplane. My budget and "other" project should be perfect for a Oct/Nov tail kit delivery date.
 
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