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Super light RV-3?

BruceMe

Well Known Member
Looks like I have a line on a -3 airframe and it is likely my next project. From '97-'03 I owned an RV-3A (fuse tank) that was heavy at ~890lbs empty with an O-320. Has anyone flown a light one with a O-235 or 290 and want to compare vs? I'm contemplating going very light, no paint, hand prop target <700 lbs.

Btw, every time I do this... I keep realizing a simple O-320 is pretty hard to beat.

Thanks!
 
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I owned a Pietenpol... _HATED_ it! I'm hooked on total performance. RV is the crack of airplanes.
 
O-235 118hp dry weight... ~240 (models vary)
O-320 160hp dry weight... ~250 (same same)

Yeah... this is a really stupid question, I take it back.
 
A very light engine will introduce large center of gravity issues.

Andy Hill's RV-3B, with IO-320 and inverted system and electrical, came in at 733 pounds, if I remember. So it can be done. He paid rigorous attention to detail.

Dave
RV-3B, now skinning the fuselage
 
I had an RV-3A w/ 125HP O-290G, wood prop of course, no electrical, and J-3 simple panel. Builder listed it as 690 lbs. empty, which included a 15 lb. lead block bolted to the bottom of the engine case. I've flown a bunch of sport/acro planes and other RVs (but no other RV-3's), and IMO this one was the best all-around flying sport plane I've flown. I wouldn't mind having another one at some point, just as simple, but maybe with an O-320 for sustainability. At ~700 lbs, even 125 hp feels pretty sporty.

A no wind take off/landing video. Would comfortably fly a sub-70mph power off approach.

http://www.youtube.com/watch?v=5SEYsX0Bio4
 
Weight

RV3A with wing mods done.
O-235-F2B 125hp
Wood prop
Full inverted and electrical system.
Heavy original Lycoming starter
Primed inside and good paint on outside.
Heavy instruments including a remote compass
781 lb empty weight.

It is great to fly.

Rob
 
The RV line is designed around commonly available and standard materials. This means there is plenty of opportunity to shave ounces without a complete structural analysis. Many of the structurally insignificant subsystems that are installed on these airplanes are far heavier than required. Take the brakes on my Rocket for example:

I have rebuilt the rudder pedals to incorporate bushings in the pivots instead of snugged up bolts. While I was at it I decided the crude and heavy brake pedals had to go. Additionally, I tried something different with the brake line themselves and went with 1/8 OD stainless and compression fittings at both ends. I figured if Van used plastic tube and compression fittings, then this should be worth a look.

Heres a graphic illustration of just how small that 1/8 line is. Same size as the FI lines on a Lycoming. Very easy to work with.

2upfo0w.jpg



I machined a pair of firewall fittings which accept 1/8 NPT fittings. On the cockpit side they are AN nipples for the existing hose.

17s292.jpg



Nothing wrong with the existing brake pedals except they were not done very well and way heavier than required. The flat part is 1/8 plate riveted with #30 fasteners to that heavy extrusion.

The new parts start with a hoop of 1/8 X 3/4 strap with the web being a folded up piece of .032 sheet. The good news is that I reduced the weight by 50% with the new parts, but the tradeoff was about a day spent to save 6 oz for the pair.

mx10u0.jpg



Build the structure to plans, but be VERY careful with subsystem installation and I'll bet you will have featherweight.
 
My RV-3A with 0-320D1A, light weight starter and alternator, Sterba prop, steam gauges, wing tanks and fastback mod weighs 755#. Builder weighted it at 765# and I took 10# out going to smaller battery. Only RV I've flown but flys great!
 
Try to find a "Narrow case" O-320 and save some weight there.

Then replace the mags with P-mags, saving ~1.5 lbs each.

The other things people mentioned will help. If you avoid the electrical system (alternator), you won't have to put in a transponder or ADS-B, saving even more weight.

Check to see if ECi makes tapered cylinders for the O-320. On the O-360, they save about 1.5 lbs per cylinder. If they don't make them, have a machine shop turn your cylinders down.

DO NOT put an O-290 on it. While a great engine, the lack of parts and low TBO can make maintaining that engine a challenge.
 
Get a digital kitchen scale that you can set in grams. That'll help you track improvements. Lightening holes are your friends.

Keep the systems simple.

The Berringer red wheels are lighter, perhaps because they're tubeless. I understand that they save 7 pounds.

Watch the upholstery and cushioning. The RV-3 generally needs something to fill the butt well in the seat unless you're exceptionally tall. Keep that light.

Dave
 
I like all these suggestions.

Electrical - 5v - 5Ah LiFePO4 and a small 10W solar panel for X/C

Starter/Ring/Alternator - N/A
 
Sky Dynamics lightweight parts

Go to their website and check out their lightweight flywheel at 3lbs off stock, and oil sump at 9 lbs lighter, but they are not cheap....
 
RV-3 weight

Mine isn't light, with wood prop, O-320 with 6 pt engine mount, wood prop, B&C battery, PMag's, pretty packed panel, heavy Oregon Aero leather covered seat, I'm at 831 empty...:rolleyes:
 
I am working toward the same goal, a super-light -3, though toward a different end...I won't qualify for one of the 'new' 3rd class medicals, and have to find a way to make it qualify as an LSA. I don't want to abandon all the work I put into the thing, and can't afford to build from kits (my project is plans-only). So the -12 and the Panther are out (want single-seat and an Lyc anyway.)

I intend to use a J-3 style cowl, no wheel fairings, and an open cockpit with a detachable headrest to keep the top speed down. This won't get me all the way to the LSA max, so the rest will be done by prop-limiting it. All of the mods will be reversible. I have an O-235 for it.

VGs should get me to the stall requirement.

I think that Van built a very light -3 in the late 90s or early 2000s, and he had sheared wingtips on it for awhile. Does anyone have any more info?
 
You can't use vg's to reduce stall speed for LSA. But you can increase the wingspan 18" per tip to get there.

A 54" pitch prop will provide an amazing climb rate and keep your top speed under 120k

The RV 3 qualifies weight wise without any effort. You will not enjoy open cockpit above 80 mph.
 
snip... you can increase the wingspan 18" per tip

I like this idea... I have considered it for mine as well. As another "wild" idea; I've considering taping outboard of the flaps and extend the wing about a two feet a side. This would sacrifice a bit of stall speed and simplicity of construction for a larger aspect ratio and better high alt slow-cruise performance.

29kywyv.png


Quick spreadsheet, could improve wing performance by as much as 28%. That means it could make up to 28% less drag to lift the same weight. This is most pronounced at high alphas. High altitude slow cruise and landing/takeoff.

It would likely have little to no effect on maximum cruise speed a smaller but positive effect on climb rate (as that's prominently excess power).

Here's my sheet

There are structural implications to this alteration and the RV-3 center spar has it's own history. These modifications would have to be scrutinized structurally by an engineer. Bending/tapering the spar cap bars at the fuel tank, could prove difficult. I don't see any issue in making new outboard ribs and cutting the sheet to fit.
 
That's news to me. Please provide a source for this restriction.

It seems that if the plane is certified with VG's in Phase I, then it is good to go.

The regs require that the stall speed requirement be met "with no lift enhancing devices used".

This generally is considered to mean no flaps, retractable slats, etc
Would VG's fall under this? Seems so but it is probably another one of those things that is in a bit of a grey area and dependent on the rule interpretation by the person issuing the certificate.
Perhaps Mel has already dealt with this in the past and will comment......
 
I would have *expected* the rule to mean *deploy able* lift enhancing devices. But I should have learned by now to have low expectations, like the rest of society.

Otherwise, why didn't they just specify the airfoil?
 
....and extend the wing about a two feet a side....

This sort of modification would result in a non-RV-3, of course. It would not fly like an RV-3 and would not perform like one.

Plan on building your own spars, as the original ones would not be useful to you. Spar loads increase roughly as the square of the span

Expect to increase the size of the tail, as it is related to the chord, span and area of the wing.

Consider the Panther, as one version of it already has longer (straight) wings. It is available in an LSA version and other versions with different engines.

Dave
 
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