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RV-3 gross weight considerations

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
pierre smith said:
....a Lexus-3:)

Looking really good.
Click to expand...


But...not as heavy as you might think! Of course, the horsepower is quite a bit higher than the original design. Just following (very carefully) in the footsteps of Randy Lervold most of the way on this one (well - I don't think he had seat heaters, but they're light...), so we're in pretty good company.;)

Oh yeah, plural "seats"....hard habit to break....:p
 
I follow Junior's progress with anticipation. I am looking forward to seeing what your finished weight complete with paint is gonna be compared to Randy's which I think turned out a lot heavier than he wanted. I still have the 3 emp kit sitting in my workshop and I am seriously thinking of building it even though it will take a longer than the 4 because of Swiss bureaucracy
 
Weighty Matters

One thing that I have wanted to expand upon a bit is the issue of adding weight to what is generally considered (and what was designed to be) a lightweight sport machine. Especially with today?s awareness of modifications to kit designs, it is important to approach changes with an engineering eye and a clear intent on what you want the airplane to be ? as well as leaving the design margins alone!

In our case, we expect the airplane to possibly be a bit heavier than Randy?s by the weight of the Garmin 430W and the inverted oil tank. That will certainly eat in to useful load, because ? and this is important ? we are planning on observing Van?s design gross weight. I don?t have the resources to reverse engineer the structure to find the margin, and generally wouldn?t do that anyway.

So what about flying a ?heavy? RV-3 around? Well, there are two missions for this airplane ? a cross-country transportation machine, and a fun aerobatic mount. Since the tanks hold 32 gallons, it should be fine for as long as we want to sit in the seat for cross-country legs. And also since it has that much capacity, it is easy to leave fuel out ? and save 6 lbs per gallon ? when we want to fly local acro. Couple that with the fact that BOTH pilots are losing weight (to the tune of 60 lbs combined loss right now ? won?t tell you how it is distributed, no way!), that brings the actual operating weight into the ballpark.

Also to note is that we haven?t made any changes at all to any of the basic aircraft design features ? those are all built ?to plans? (despite the plans being just a little vague in places?), so what we have really done is simply equip the airplane for its cruising mission. Is this a lightweight, stripped-down local acro machine? Nope ? not at all. But that wasn?t our design goal. We wanted the handling and reputation for sound design that we got with the RV-3 kit, and didn?t want to change that (so long as we do our ?sporty? flying consciously light). And the fact that Randy reported cruise speeds close to redline tells me that the performance will probably be ?adequate?.

Paul
 
Weight & Fuel

Randy Lervold noted on his website (and I have confirmed through
discussion with Van) that you can ignore the weight of the fuel
in calculating the aerobatic weight limit in an RV-3 with wing tanks.

The original RV-3 was designed with a fuselage tank and the
limiting factor for aerobatic weight is the wing spar strength.
By moving the fuel outboard of the point of maximum bending
load (at the wing root), the fuel weight no longer contributes
to the peak spar bending load. Of course the fuel in the wing
tanks does change the distribution of load along the spar, but
Van believes that the limiting factor in the wing design is still
the bending load at the wing root.

Now this begs the question about the appropriate max gross
weight for an RV-3B. I believe that Van sets both the gross
and aerobatic weight limits to the same value of 1100# for RV-3's.
The argument above would suggest that you could increase the
gross weight by 180# (30 gallons of fuel) without exceeding the
aerobatic limit. Mabye so, but that extra weight might cause
trouble with the landing gear, engine mount, or other parts
of the structure that are only sufficient for an 1100#
airplane. It is notable that Van did not set a new gross
weight limit when he re-designed the wing for the RV-3B.

I don't mean to re-ignite the debate about setting gross weights
higher than Van's recommendation, but it is definitely something
to think about for the large majority of builders who end up with
higher empty weights than Van's prototypes. The two-place
builders can always tell themselves that they won't carry
passengers during aerobatics. But for us -3 builders, there isn't
much we can leave behind when we go flying. We either have
to build light, or follow Paul and Louise and go on a diet :).

- Dan Benua
RV-10 Flying,
RV-3B Almost...
 
Hi Dan...

What you say is frequently quoted, but never confirmed (re ignoring fuel).

I'll just add 2 factors:
<<The original RV-3 was designed with a fuselage tank and the limiting factor for aerobatic weight is the wing spar strength>> Agreed, but then the fuel tanks were moved to the wings, the spar was completely redesigned (to an RV-8 type spar) i.e. the original spar calcs are no longer valid.
<<the fuel weight no longer contributes to the peak spar bending load. Of course the fuel in the wing tanks does change the distribution of load along the spar, but Van believes that the limiting factor in the wing design is still the bending load at the wing root>> Maybe so... but then the RV-8 that was lost in an overload had the wing(s) spearate outboard of the Fuel Tanks.

So I am not too sure ignoring the fuel weight is appropriate?

Our RV-3B is aiming to comply with the 1050 Aeros weight (we have to over here), so target empty weight is 800lbs (which will be difficult I acknowledge).

Andy
 
More on Weight

Hi Andy,
You make a good point about the RV-8 wing failing at the outboard
end of the tank. So maybe the assumption that the wing root is
the critical point is not always correct. To make the structure light,
the designer strives to balance strength with predicted load along
the length of the spar. If he does the job perfectly, the wing could
fail at any location when overloaded.

The RV-3B wings are similar in design to the RV-8 wings, but of course
not identical. I'm not aware of anyone (including Van's) who as loaded
an RV-3B wing to the point of failure, so we don't really know where
it might fail.

Van's recent public commentary on a high-weight RV-10 is also
worth considering. He talked about designers "owning the margin" in
explaining why builders should not exceed recommended limits.
In the case of the original RV-3 design, the margin was not
sufficient and multiple pilots were lost in wing failure accidents
(including a good friend of Van's). In redesigning the wing for the
RV-3B I think Van was trying to reclaim the designer's margin. This
is probably why he did not change the weight limits even after moving
the fuel to the wings and substantially increasing strength in the wing
root area.

Like Paul and Louise, I'm using a lot of Randy Lervold's ideas in my
RV-3B. But instead of adding stuff, I'm trying to cut back by going
with a fixed pitch prop, lighter interior, etc. I'm not ready to predict my empty weight but my goal is to fly aerobatics without going on
a diet first :).

- Dan Benua
 
I've taken the liberty of splitting off some good posts from another thread on another topic that "crept" into RV-3 gross weight considerations. This is an important topic and should not be buried in another topic.

Info on my plane and my thoughts on it can be found here. Oh, and no, I didn't have a seat heater. ;-b
 
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It's great seeing a bit of resurgence in RV-3 interest. There have been some outstanding examples created in the last few years, and of course Paul's will be among them. I think the RV-3 is THE best all-around pure sport airplane available. I understand wanting to maximize the "perfection" in terms of performance and capability, and but there must be a tradeoff, and I'd imagine it would involve giving up a certain intangible light and unencumbered feel to the airplane.

I have only flown one RV-3, the one I owned for 5 yrs. It was built just like the prototype - original wing spar, fuselage tank, J-3 simple panel, no electrics, wood prop, and a 125 hp O-290G. Empty weight was 690 lbs. It had a climb prop, and was not as fast as most RV-3's, but it had such lightness to it, and was so much fun to throw around that it's still the airplane I have in my head as the holy grail of sportplane handling (this from a current Pitts owner). It was so light that I could fly a power off final in calm conditions (when I was light on fuel) at 60 mph and easily get in and out of 1000' backyard strips with little effort. It felt so light on the ground, during takeoff/landing, and in the air, that it reminded me of a J-3 flown solo...it just had that light feathery feel to it on the runway and in ground effect when taking off and landing.

I know that horsepower and a CS prop will compensate for a lot of added weight, but to imagine an airplane as small as the RV-3 carrying around an extra 200 lbs would make it a totally different feeling airplane...especially on and just above the ground - especially when slowing to a landing. That feathery lightness is why the feel of a J-3 is so prized, even though you can evolve this airframe into a 1200 lb. Super Cub with 180 hp. I guess I'm just a purist, don't need the "stuff", and truly enjoy flying the J-3 more than the 180 hp heavy Super Cub. I just wonder if a 900 lb. weight would significantly diminish the essence of the RV-3. I know Van is a purist as well, but he lists the min. empty weight of the RV-4 as 905 lbs. But I don't know, the light J-3 and 180 Super Cub are both fine airplanes, I'm sure...just very different - maybe just like various RV-3s.

But I totally get going in the opposite direction, and that there are pilots who use airplanes in more complex ways than I do. Except for light acro, my RV-3 pretty much had the same mission as a J-3. For those who like/need the added capability and "stuff", I applaud the ingenuity in the evolution of the design. No matter how you build it, you'll have a helluva plane. :)

I still have this image in my head of my version of a "modernized" RV-3...B wing, O-320, but still having a J-3 simple panel, no electrics, and maybe a Catto prop...with weight truly kept to an absolute minimum, just like the prototype. I think 725 lbs. would be attainable with the new engine and spar. That would be something.
 
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Good split randy!

I understand exactly where you are coming from Eric - one day, it would be interesting to build an "ultimate light" RV-3B - next-to-nothing radios, bare panel, no interior...keep the fuel at a minimum most of the time....it would be a lot of fun! This plane has a mixed mission, so it necessitates compromises which we consciously decided to live with, and we'll see how it turns out.

I think our next airplane might well be in the direction of a back-country Cub. Louise has been taking Steel-tube and fabric lessons from a neighbor.... ;)
 
Ironflight said:
Good split randy!

I think our next airplane might well be in the direction of a back-country Cub. Louise has been taking Steel-tube and fabric lessons from a neighbor.... ;)
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Randy L. can help you out! I really wanted to put the CC340 in the 3B I was building...nother story....
The 3B flew last month, 18 months after I sold it.
That airplane weighs in at #789. 0320 Sensenich Metal 81 cruise prop, no paint, no lights, basic analog VFR panel. Owner states that it does not climb out as well as his 8 but it goes like mad in cruise. He only has 2.1 hours on it so more data to come down the line.
Eric - that is a long way off from #725. I think the new wing adds some considerable weight over the old design.
 
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JonJay said:
Eric - that is a long way off from #725. I think the new wing adds some considerable weight over the old design.
Click to expand...

Does anyone have actual data on the weight of the Type 1 wing (with CN-1 and CN-2) vs. the B wing?

There are two light 3B's (with O-320) listed on Randy's registry - one at 755 lbs, another at 760. Both have batt/electrical systems. If these numbers are accurate, I would imagine removing the electrical components and a couple extra things in the panel would make 725 lbs. about right.
 
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Good Call

Hi Randy,

I agree with Paul, it was an excellent idea to split of the posts dealing with weight into a separate thread. Saving weight as most know is not just confined to the -3, it applies to all airplanes. Look at the new Boeing Dreamliner, composite materials applied in the construction of this beast means that Boeing will have a product that can out compete Airbus. I am certainly thinking of building in lightness into my -4. I am sitting on the fence at the moment as to whether or not to fit a VP prop. The field which I hope to use at 600 metres in length (1800ft) may be a bit tight and the field elevation is 1760 ft. The surface is grass reinforced with Perfo plastic tiles that may make any over enthusiastic braking interesting. The VP prop will be more than useful here. So I am slowly convincing myself to include an MT VP prop. I will go with MT and not a lighter american product as the MT factory is not far away in Germany and MT service over here is pretty good. I owned a Supercub for a number of years and have to agree that it was not the most responsive of types that I have flown, but boy it could sure get in and out of very short strips.

I suspect somehow Paul that the set heater will not be fitted when your using the parachute.
 
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sandifer said:
Does anyone have actual data on the weight of the Type 1 wing (with CN-1 and CN-2) vs. the B wing?

There are two light 3B's (with O-320) listed on Randy's registry - one at 755 lbs, another at 760. Both have batt/electrical systems. If these numbers are accurate, I would imagine removing the electrical components and a couple extra things in the panel would make 725 lbs. about right.
Click to expand...

I have asked the question before and nobody seems to know. Van's told me they did not know. Purely congecture on my part. I would love to see a 725 lbs 3B but not sure I want to hand prop the thing all the time. Good stuff....
 
Ironflight said:
[Stuff deleted...]

I think our next airplane might well be in the direction of a back-country Cub. Louise has been taking Steel-tube and fabric lessons from a neighbor.... ;)
Click to expand...

You might want to have a look at the Bearhawk (4 place) or Patrol (2 place). Super performance, tube and fabric fuselage, very RV like wings. Of course I'm biased, since I'm starting Bearhawk, but still... :D
 
sandifer said:
...the light J-3 and 180 Super Cub are both fine airplanes, I'm sure...just very different - maybe just like various RV-3s.
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Eric,

Wow, you just jumped into my current world!! Lightness in an airplane is something that just must be experienced to be understood and believed. In my current world I might fly a lightweight 900 lb Carbon Cub in the morning and a 1300 lb Top Cub in the afternoon. Big difference in the feel! It really makes you want to hold back on the option sheet once you've tasted it. There is nothing sweeter in the Cub world than slipping an especially light Carbon Cub down between some trees and putting on the runway exactly where you want it. As outstanding as that plane is in takeoff mode, which is what everyone is impressed with, it's the feel and the finese of a tight landing approach that to me is the greater achievement than the raw horsepower needed for short takeoffs.

It is hard to be light! We go to extrordinary lengths at CubCrafters to make our aircraft light, and it makes them more expensive in the process. Worth it though IMHO.

All that said, I remain very happy in restrospect with the decisions I made on my -3B and feel that it represented a reasonable compromise between the functionality that I was looking for and the compromise in weight. Paul & Louise's Junior will no doubt be heavier than my plane, but I suspect it will be the best equipped RV-3 on the planet. In the end, it's all about different mission profiles and priorities -- we all get to choose.
 
RV-Lite

My first RV flight was in a 1980 RV3 back in the early 90"s. my friend and F16 Sq mate RK kindly allowed me to jump in and slip the surlies. Wow, very impressive for an 0320, 725lb wood propped airplane. This 3 had the distinction of holding the time to climb world record to 3000 meters in 1983 and absolute altitude record at 20,500" for class C1A.
I later took my 920lb, 150HP wood prop RV4 to the same height.

Want great performance? Keep it light!
RV4 builders manual 1989"

Smokey
 
David Paule said:
Perhaps it's now time for a weight report update for Junior?

Thanks,
Dave
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887 - and at that weight, I am bumping the TAS redline during engine break-in, and rate of climb is exceeding the instrument display limits.....

We always new it would be closer to Randy's finished weight than it would be to one of the wood-prop lightweights, but that was becasue of our mission. I am looking into replacing the Odyssey battery (and lead-acid backup battery) with one of the ne LiFe lightweight batteries - they will save nearly the weight of the coming paint job!

Very happy with how the choices worked out for us. Who is it that says "build the plane you want...."
 
Ironflight said:
... I am looking into replacing the Odyssey battery (and lead-acid backup battery) with one of the ne LiFe lightweight batteries - they will save nearly the weight of the coming paint job! ...
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What are these, I have never heard of them.

Ironflight said:
... Very happy with how the choices worked out for us...
Click to expand...
That's all that matters!

Ironflight said:
... Who is it that says "build the plane you want...."
Click to expand...
I haven't a clue. ;)
 
N941WR said:
What are these, I have never heard of them.
)
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Lithium Iron batteries - they have been using them in motorcycles for about five years (as I understand it). A replacement for the Odyssey weighs less than 3 pounds. Very stable, apparently - not like the Lithiums that burst into flame if you look at your notebook computer wrong. I'm researching, they look promising.
 
Ironflight said:
Lithium Iron batteries - they have been using them in motorcycles for about five years (as I understand it). A replacement for the Odyssey weighs less than 3 pounds. Very stable, apparently - not like the Lithiums that burst into flame if you look at your notebook computer wrong. I'm researching, they look promising.
Click to expand...

Sounds promising. Please keep us updated.
 
What an interesting few days regarding the RV-3. Thanks for posting all the information.

I am becoming intrigued and challenged to take on a RV-3 build project.

To begin with, the challenge is to learn how to build an adequate jig, how to bend a piece of metal without spending a ton of money on equipment, to let Ken Scott know it can be done, and not least, to build an airplane as close to the original 750 pound prototype as possible.

It is a credit to Randy Lervold that he published data regarding gross weight. His airplane came in about 18% over weight. That has got to reflect in performance except maybe it does not with more HP and a CS prop. On the up side of not going that route, money can be saved by going light weight with a Catto prop, a stripped down 0320, minimal cockpit niceties, and little or no paint. Sure, such an airplane would never win an award at OSH - but it would fly well.

I am still on the fence with regard to a 3 or an 8, but am beginning to think it would be a very interesting build - the RV-3. And it might be just what my brain needs to keep it from becoming morphed with age. :)
 
David-aviator said:
It is a credit to Randy Lervold that he published data regarding gross weight. His airplane came in about 18% over weight. That has got to reflect in performance except maybe it does not with more HP and a CS prop. On the up side of not going that route, money can be saved by going light weight with a Catto prop, a stripped down 0320, minimal cockpit niceties, and little or no paint. Sure, such an airplane would never win an award at OSH - but it would fly well.

I am still on the fence with regard to a 3 or an 8, but am beginning to think it would be a very interesting build - the RV-3. And it might be just what my brain needs to keep it from becoming morphed with age. :)
Click to expand...

Wth your experience David, and from reading your posts over the last few years about the flying you do, I nominate you to build the perfect modern "Lightweigt -3". I can think of nothing better for you to use in your defense of the Missouri coastline.....and I want to see how light a -3B can be!

Paul
 
Thanks for posting the weight and the performance too. Sounds exciting!

Now we've got a rough idea of the weight difference between bare minimum and abundantly equipped, and know that the plane will perform very well at the heavier weight. That's good to know. Right there, that'll sell a few -3 kits.

Now - just what is the instrument max indicated rate of climb, and why should an EFIS have a display limitation like that? I'm missing something here.

Thanks!
Dave
 
David Paule said:
Now - just what is the instrument max indicated rate of climb, and why should an EFIS have a display limitation like that? I'm missing something here.
Click to expand...

Well, I probably just need to find the right page to change the scale to +/-3000 fpm....:p
 
Wow, this thread is interesting.

At OSH this year there was an RV-3 on the line at 903 lbs, a full 20% heavier than the designer's spec.
One half mile away was the prototype RV-4 at 870 lbs.
My -3B came in at 760lbs with inverted systems and shiny paint, no autopilot or leather seats.
Yes, build it the way you like it...but where do you draw the line ?
Mike
 
I think your empty weight impressive considering everything you have in the plane. I thought it would come in at 900+ easy. Fortunately these are sport aerobatic/cross country planes and not high alpha 3D aerobatic machines. In the giant scale rc world every gram counts, but that is only because theyre flown around fully stalled at 70 degrees aoa. When flying around at higher speeds weight really isn't an issue, which is why most smoke systems are removed before 3d flights.

Mike, 760 for a 3b is awesome. I wish there was a way to compare component weights so I could figure out how my relatively basic 3 came in at 845.
 
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Where do you draw the line?

My -3a weighs in at 742#, with an O320, wood prop. lights, paint, and a standard aircraft battery. Was built to plans, no changes. How far is too far when going for lightness? At what point do you sacrifice weight for safety? And how do we know when that line has been reached? I am building my -4 the same way, according to the plans. The only change that I made was to angle the instrument panel an additional 1/4" forward, because I am 6'2", and it makes it easier to see.
 
812

I weighed my -3B yesterday and was pleased that the empty weight
came in at 812#, with an empty C.G. of 57.3". This will allow me
to set my gross weight at 1250# and carry about 50# of baggage
without exceeding the aft C.G limit at minimum fuel. I will easily
make the aerobatic limit of 1050# excluding fuel.

For reference, I have an IO-320, Catto fixed pitch prop, AFS 5500
EFIS, 2-axis AFS/TruTrak autopilot, Odyssey PC680 battery just forward
of the spar, day/night VFR capability, and a sheep-skin on comfor-foam
seat, but otherwise simple interior. As you can see
in the photos from the weigh-in, the paint is complete.

Made for a nice X-mas. :)
- Dan Benua

111224_OnTheScales_7.jpg


111224_Panel.jpg


111224_OnTheScales_5.jpg
 
Very nice looking 3! Did you paint it yourself and what kind of paint? Is that a strip of felt or something I see around the edge of your canopy skirt?
 
Beautiful Dan! What's that, three new -3's in a month? We've practically got a production line going. Need to hook a few more of these old-timers who's tols are goign to rust if they don't et another project.... ;)
 
rph142 said:
Very nice looking 3! Did you paint it yourself and what kind of paint? Is that a strip of felt or something I see around the edge of your canopy skirt?
Click to expand...

The paint is PPG Concept single stage, color sanded, cut, and buffed. I thought it would take me three months to paint, but it took six! That's
why Paul and Louise beat me to the first flight :).

There is a felt strip around the canopy edge to reduce wear on the
fuselage paint. I copied that idea from Randy Lervold (along with
many other ideas!). Thanks Randy!

- Dan
 
That is a beautiful looking plane and the capacity-to-weight ratio appears outstanding! I hope you'll make Oshkosh and it can join The Show! Love to see it there.
 
Well done on that weight Dan... In the order of where we are aiming, although whether it can be achieved with a VP Prop who knows ;) And as for "when" :eek:

Re
I will easily make the aerobatic limit of 1050# excluding fuel.
Click to expand...
I have heard/seen this stated a few times, but never seen it formally quoted / justified?

Andy & Ellie Hill
RV-8 G-HILZ
RV-3B G-HILI "Very" Slow Build
RV8tors
 
Nicely done. I expect the visit to Parkside to be on your short list so we can all oogle over it!
 
Super nice!

Outstanding looking -3B Dan! Looking forward to seeing it in formation with the rest of the Homewing/West Coast Ravens.

For those that aren't familiar with Dan's work, this is his 3rd RV (that I know of). He built a -6A, a VERY nice award winning -10, and now the 3B. Dan is also an EAA Tech Counselor for EAA Chapter 105 and is an Instrument rated pilot. He doesn't mention it here, but the -3 also has a smoke system on it. :)

Nice checkerboard tail!
 
ALL I CAN SAY IS WOW!

You guys are sure making it rough on us few/now many that have always wanted a 3.
Absolutely a work of art! That 6 month's you spent painting that beauty will pay off with all the on lookers and compliments you'll receive.

Think the Factory phone went down when you posted that one! ;)

Best of Luck to You in Phase I.

Bruce Gray
RV8 Emp
(again)
 
Interior Paint?

It looks like a dark metallic grey/silver in the interior. Is that paint on the interior? If so, what color?

Very nice airplane - my 5 year-old son asked me to print him a picture so he could hang it on the wall in his room! "I want to make our plane red too!" I guess our RV-8 will be red too.
 
Ironflight said:
Beautiful Dan! What's that, three new -3's in a month? We've practically got a production line going. Need to hook a few more of these old-timers who's tools are going to rust if they don't get another project.... ;)
Click to expand...

Why is I feel that this comment is meant for me? Wish I had the time. Maybe 2012 will be the year for me to have more time in my life for things that I LOVE.

I guess if the shoe fits, wear it.
 
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Interior paint

Ogre said:
It looks like a dark metallic grey/silver in the interior. Is that paint on the interior? If so, what color?
Click to expand...

The interior is PPG DCC 35490 which they call "Stone Gray Metallic".
I have used this color on the interiors of all three of my projects.
The exterior colors are:
DCC 74179 (Red)
DCC 907522 (White)
DCC 9835 (Black)

- Dan
 
Aerobatic Weight Limit

Andy Hill said:
Well done on that weight Dan... In the order of where we are aiming, although whether it can be achieved with a VP Prop who knows ;) And as for "when" :eek:

Re I have heard/seen this stated a few times, but never seen it formally quoted / justified?

Andy & Ellie Hill
RV-8 G-HILZ
RV-3B G-HILI "Very" Slow Build
RV8tors
Click to expand...

Hi Andy,
Both Randy Lervold and I were told by Dick VanGrunsven in separate
conversations that we could exclude wing tank fuel from the aerobatic
weight limitation in the RV-3B. In the U.S. we can just put that in our
W&B report and claim it as fact. If you need something more "official" in
the U.K., you could ask Van's engineering department to put it
in writing. I don't know if they would do it, but it wouldn't hurt to ask.

Without that exclusion, most of the -3B's being built today cannot meet
1050# limitation unless they are flown by children carrying minimum
fuel :). (Mike Skoczen's incredibly light -3B is a notable exception.)

- Dan
 
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