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  #11  
Old 10-29-2014, 11:56 PM
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Doug Doug is offline
 
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Probably not an RV-4.
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RV-6 completed, flying since July 2010
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  #12  
Old 10-30-2014, 07:34 AM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by southtarnation View Post
If someone (a laymen) looked at it from the top where it meets (or would meet) in the cabin it might look like wood due to it looking similar to several thin(er) pieces of wood that have been laminated into a single "spar".
Best explanation yet. Maybe the current owner bought it used and doesn't really know how it was built. All those laminations coming together in the middle could be mistaken for wood grain, I guess. Especially if it was painted brown...
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1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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  #13  
Old 10-30-2014, 08:04 AM
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The RV-4 has had only one spar design for its entire life as far as I know. The only "options" where whether one tapered the laminated stiffeners in length.

The spar (similar to all RVs) has a large U Shaped channel (web) that is formed from bent aluminum. To both the front and aft sides of this piece 1/8" thick (going from memory here) stiffeners are riveted to the spar web using 3/16" rivets. The stiffeners strips are about 1 - 1.5" wide and are stacked on top of one another to make the complete thickness of the spar.

Since loads lessen the farther toward the wingtip you go the need for stiffeners to meet the designed load carrying ability decreases, hence the number of stiffeners decreases. Indeed for the last foot or two only one stiffener thickness (forward side) is needed.

Also, the stiffeners were made from 1/8" x 1.5" (I think) bar stock (a standard size. In order to save weight the builder could optionally taper the spar strips in width per the plans. Builders of later model RVs will see the same design feature in the machined dimensions of the one piece stiffener used in later models. Access to a CNC machine makes fabrication simpler than when you are doing things with a hacksaw.

Back in the day there used to be discussions and such in the early editions of the RVator as to techniques the builder without access to a machine shop could use to cut such tapers. The best answers usually involved a bandsaw but using a hollow-ground planer blade on a table saw produced the nicest finish IIRC.

All eventually came to naught as the availability of pre-made spars with machined cut tapers, anodized finished parts, and precise set rivets (in a brake press probably) made user fabricated spars as rare as humble tail-dragger pilots.

So, if that plane is an RV-4 it has a metal spar. Only question is was it pre-made by Phlogiston (a good thing) or made by the builder (something that just needs a bit more inspection but, in itself, no reason to run for the hills).

If, upon inspection you see anything that looks like wood, congratulate yourself on finding a rare, probably one-of-a-kind example of the homebuilt aircraft world. But just know that it ain't an RV-4 even if you can understand why someone might want to claim to be one of the best flying airplanes ever designed.
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RV-4 N144KT
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Last edited by rbibb : 10-30-2014 at 08:09 AM.
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  #14  
Old 10-30-2014, 08:22 AM
eisnerrv4 eisnerrv4 is offline
 
Join Date: Sep 2006
Location: Halifax, NS
Posts: 179
Thumbs up RV-4 Spar

No sense adding my two cents worth. It's all been covered.

Good luck in purchasing one. Fabulous aircraft.
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Brian Eisner
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Bedford Nova Scotia
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  #15  
Old 10-30-2014, 08:39 AM
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Mike S Mike S is offline
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Quote:
Originally Posted by rbibb View Post
as rare as humble tail-dragger pilots.
Gotta remember that one
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Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

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  #16  
Old 10-31-2014, 12:46 PM
Larryskydives Larryskydives is offline
 
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Location: Gautier, MS
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Thanks for all of the info. Knowledge is power. Talked with the owner again and asked if he was sure it was wood. Said it was, after I told him what I had found out, he said maybe it wasn't wood. I tend to think that the laminated look at a distance looked like a wood grain. But all for naught, I think he has sold it today.

On another note, I just can't understand a person buying an airplane. experimental or certified and not knowing it's construction. But such as it is, still in the hunt for an RV4, and again thanks for the info Never know when I might be back asking for more!!
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