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  #171  
Old 07-22-2015, 10:04 AM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
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Flaps. The stiffeners are made and drilled. I'm using the same sort of drill jig I used for the ailerons; I made a new one for the flaps since the length and hole spacing are different. Here, I'm using it to drill the flap skins.



Since I used the same drill jig for both the skin and the stiffeners, any stiffener fits any skin location.

Now for something that's harder.

Jim Bede died July 9th. For those of you that don't know who he was, take a look at www.bededcorp.com. I never met the man, but when I was a teenager, learning to fly, the BD-1 was announced and caught my attention. It was never produced as originally planned but later became the Yankee and the Grumman Tiger.

When I went to college, Bede was selling kits for the BD-5. At the time, Burt Rutan was his flight test director. Bede also was taking deposits for a certified BD-5, which he hadn't quite got certified yet - and never did. He'd sold over 4,000 kits and taken over 4,000 deposits for the certified version.

There were numerous issues with the planes. Two that I recollect were significant enough. He never found a reliable engine installation and thus never delivered that package - since the engine was buried in the fuselage behind the pilot, that was a significant lack. The other major issue was that the plane was available with short wings and long wings and it turned out that the short wings were really too short.

While I was in aerospace engineering school, I built a large portion of one of the short-wing kits for a local man. It was a great college job. In spite of the fact that all the riveted joints were bonded with Pro-Seal, it was fun.

Jim Bede's inability to produce production aircraft persisted throughout his career, the BD-4 being an important exception. Nonetheless, he was an innovative designer. There are enough kits out there that after-market developers did eventually provide some reasonably acceptable parts to complete the aircraft. Note that these two BD-5s use different engines, or at least different installations.



Thanks, Jim. You helped put me through college and gave me some great experiences. The BD-5 kit led directly to the current RV-3B that I'm now building, this time for myself.

Dave

Last edited by David Paule : 12-08-2019 at 06:07 PM.
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  #172  
Old 07-23-2015, 07:42 PM
David Paule David Paule is offline
 
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Location: Boulder, CO
Posts: 5,257
Default Saving Weight

The deal is, every gram counts. Seek it out wherever you can find it.

In this case, it was only 3 grams, achieved by rounding the corners of the flap's stiffeners, but I've been doing this all through the construction so far.

The photo shows the before and the after case.



I didn't draw or trace the curves. All I did was snip the corners off and rounded the ends with a coarse mill file, following up with a fine mill file.

The flap skins are mostly dimpled now and when that's complete I'll prime them. Ran out of those nails used for dimpling holes where I can't get a regular tool to.

Remember that cracked aileron nose rib? The new one arrived today, thanks Van's for excellent support even in Oshkosh week!

Dave

Last edited by David Paule : 12-08-2019 at 06:09 PM.
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  #173  
Old 07-23-2015, 08:17 PM
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longranger longranger is offline
 
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A 6-inch scotchbrite wheel on a bench grinder does a fair job of rounding those corners too.
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  #174  
Old 07-23-2015, 09:01 PM
Waterobert Waterobert is offline
 
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Location: Laguna Niguel, California
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Next year I will be building RV-3 and I've always wandered why some RV-3's weight 800+lbs. Van's site says 750 lbs. I guess rounding up all off the corners eventually will add up to some real weight loss, lol. Building RV-3 is hard by itself, building it under 750 lbs takes true dedication, thanks Dave.
Was 3 grams per stiffener or all off them? Do you keep track of weight all of the parts?

Last edited by Waterobert : 07-23-2015 at 09:04 PM.
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  #175  
Old 07-24-2015, 06:37 AM
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wirejock wirejock is offline
 
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Location: Estes Park, CO
Posts: 5,102
Default Rounding ends

I thought that was the way they were supposed to be done. I actually did something right.
Any time a hole is close, I draw a minimum edge line so I can't remove too much.
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  #176  
Old 07-24-2015, 07:49 AM
David Paule David Paule is offline
 
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Quote:
Originally Posted by Waterobert View Post
Next year I will be building RV-3 and I've always wandered why some RV-3's weight 800+lbs. Van's site says 750 lbs. I guess rounding up all off the corners eventually will add up to some real weight loss, lol. Building RV-3 is hard by itself, building it under 750 lbs takes true dedication, thanks Dave.
Was 3 grams per stiffener or all off them? Do you keep track of weight all of the parts?
Unfortunately that 3 grams was for the entire set of flap stiffeners. This isn't the quickest way to save weight. I tapered the tie-down fittings (see post #96) and saved more weight than this and it took less time. Still, I regard it as worth doing.

No, I don't track every part. But I go after weight savings where it appears feasible, and where I don't need to do a stress analysis of the part. One of the reasons I'm building a kit airplane is that after retiring from a career as an aerospace stress analyst, I didn't want to have to analyze a whole new-design plane. I have not done some things that I felt were feasible but which Van's said not to do or which I would have needed to stress analyze for.

The gold standard for weight savings is the RV-3B that Andy Hill just completed, at less than 750 pounds with an IO-320 and an electrical system. Most of his purchased parts were chosen for light weight, and he used a narrow-deck engine because it's lighter. He proved it can be done. He left out, as far as I know, some things that I'm including: an autopilot (see post #135) and lights (see post #95 and note that the homebuilt landing light mount I made saved over 100 grams compared to Duckwork's - but still, I added a light and wires and eventually a circuit breaker). He saved more weight by using Beringer's wheels and brakes.

Andy's example demonstrates that the major weight savings isn't in the airframe. It's in the parts that attach to it. They need to be chosen with great care and considerable discipline. In at least one case, he appears to have accepted a maintenance difficulty for the weight savings it brought.

I expect my plane to be heavier than his - but I'll do what I can.

Dave

Last edited by David Paule : 08-04-2015 at 08:00 PM. Reason: Andy's RV-3B is a LOT less than 750 pounds.
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  #177  
Old 08-04-2015, 08:24 PM
David Paule David Paule is offline
 
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Finished the new left aileron. I tracked the hours spent on this one. It took about 42.6 hours of my time and perhaps another 1.4 of a friend's who helped me buck the spar top flange rivets. I'd previously done that myself, using an L-shaped bucking bar, a shop light dropped inside the aileron and an inspection mirror. But that's how I damaged it, so this time I got help.

Working on the flaps now. The stiffeners are riveted on. I had a moment of considerable dismay when the retaining spring on the rivet gun unscrewed, the back-rivet set dropped on the floor and the spring propelled the plastic pusher to some mysterious place where it has not been found. You can read about it in this thread, which discusses the effect and its ramifications.

I found that a 7/16" box end wrench, pressed down around the rivet, makes a satisfactory substitute if you should find yourself in that position one day. Just put the end of the back-rivet set in the center of the box end and press the box end down on the parts, holding them and the set securely. It takes both hands but works okay.

I spent the evening figuring out where to put the doubler on the spars. If you do a search for flaps you'll eventually come across a recommendation that the inboard rib be moved inboard 7/8", and that the top flange of the spar be 49.5" long. The 49.5" comes from:

48" from the plans + 7/8" extra + 5/8" = 49.5".

The 5/8" is the flange width of the FL-303 rib and please be careful about where you're measuring, because the plans show 48" to the outboard side of the FL-303 rib, and doesn't actually mention the dimension to the inboard side of the rib.

I meant to follow the 7/8" advice and in fact confirmed it with David Howe, but somehow on my flaps I made it an even 1" instead, since that's where I put the inboard set of stiffeners. So on my plane, unless I can shave a bit from the FL-303 flange (unlikely) I'll use the 1" dimension instead.

The bottom flange of the flap spar is limited by the spar's length as received, 51". The plans say that it should be 51 3/8", I think, but the part itself is only 51".

Dave
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  #178  
Old 08-05-2015, 12:34 AM
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Andy Hill Andy Hill is offline
 
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Quote:
Next year I will be building RV-3 and I've always wandered why some RV-3's weight 800+lbs. Van's site says 750 lbs. I guess rounding up all off the corners eventually will add up to some real weight loss, lol. Building RV-3 is hard by itself, building it under 750 lbs takes true dedication, thanks Dave.
Was 3 grams per stiffener or all off them? Do you keep track of weight all of the parts?
Dave has commented above re our RV-3B: IO-320, VP Prop, Full Inverted, Basic Weight (unpainted) 733lbs.

In the basic parts from Vans there are weight savings to be made, but not dramatic. For instance, each Wing Rib I weighed before and after "hole cutting" and it saved 0.77lb total. I would guess almost every RV-3 has that weight saving applied? Aileron / Flap spars another 0.8lb, Flap / Aileron stiffeners 0.4lb.

The "state of mind" however is important - have spent all that time to save a few oz, you need to look at every nut, bolt, washer and decide if shorter / thinner hardware will suffice in that application?

But, as Dave says, the real "savings" come in not adding junk in the first place, or picking the lightest part you can. An example is a VHF radio. Now I cannot see why Brand X (or rather G ) is any better than Brand Z - you press a button and say "Hello Airport". It replies "Hello Plane". End of?

A Garmin SL-30 weighs 3.3lbs. A Dittel KRT2 weighs 0.8lbs. So the Garmin wipes out the entire Wing Lightning hole process in 1 go, for also I think a much higher price?

How far you want to go will depend on the "Mission" - we were fortunate enough to have a higher spec'd RV-8, so the 3 really could be "minimalist", and try some weight saving ideas.

If weight savings is your aim in a new RV-3, you need the version of the plans that shows the area forward of the pilot as "Fuselage Fuel Tank [option]" and leave that out. Not the version showing "Airbus Avionics Bay" There is a lot of room there, and very easy to (ab)use it if lightweight is the aim.

PS re
Quote:
In at least one case, he appears to have accepted a maintenance difficulty for the weight savings it brought.
not sure what this was? Maybe the Oil Filter? Having now done an Oil & Filter change, not a factor. The firewall cutout is "upside down" from most RVs i.e. the sloped part is the lower half. The aft facing Oil Filter (avoids an expensive and heavy B&C adapter) just extends into the cutout. But filter comes on / off no problem.

PPS CG needs to be a consideration, the RV-3 was designed for a 235 / wood FP prop at the front, so a 320 + VP prop is going to be nose heavy. See Randy's site (despite a light VP prop) for the fwd CG, and how he improved Basic CG (and handling) by moving the PC680 to the rear (57.08" to 57.56"). Ours is currently 57.46", and fine, but further aft (like Randy's) would be better, and no restriction on aft [with] or aeros [without] baggage. We could save 1.5lbs on the tailwheel parts, but would adversely affect CG. I think paint (10-15lbs) will bring CG back, so the tailwheel savings might click in then? So as Dave says, weight savings firewall forward are doubly important - not just saved weight, but where that weight is saved e.g. try to avoid a front mounted alternator - vacuum pad is not only lighter, but further aft...

Finally Randy's website is a gold mine of useful info, with little unnecessary waffle. He has a "weight" table that you can expand on, and now following through the LOP EGT balancing with AP - so if you're still reading VAF Randy - many thanks
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  #179  
Old 08-05-2015, 10:10 AM
David Paule David Paule is offline
 
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Andy, yeah, I had in mind the oil filter for that "maintenance difficulty" - and am glad to read that the oil change wasn't an issue. Might give that one a try myself, thanks.

Dave
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  #180  
Old 08-05-2015, 10:29 AM
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ijustwannafly ijustwannafly is offline
 
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Looking good dave
One of my favorite threads to read
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