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  #21  
Old 01-13-2016, 01:43 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,055
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Quote:
Originally Posted by czechsix View Post
As a side note, the empty weight of the proto -14A on the https://www.vansaircraft.com/pdf/RV-..._SampleW&B.pdf worksheet doesn't equal the sum of the three wheel weights. 436 + 364 + 435 = 1235 lb (not 1239 as shown). I'm not trying to nitpick, just wondering if the discrepancy indicates any errors in the original data (which might explain the CG differences as well?).

,
Errors in the posted document have been corrected.

Because the airplane has evolved a bit since new, there was some minor weight additions and subtractions that are part of the aircraft document that were deleted to reduce confusion. When the deletions were made, the weight and moment data wasn't listed correctly.

These are the official samples based on data from the two prototypes.
Still looking into why Mitch's computed C.G. is actually aft of the taildragger prototypes.
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Scott McDaniels
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RV-6A (aka "Junkyard Special ")
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  #22  
Old 01-15-2016, 04:28 AM
MLock MLock is offline
 
Join Date: Jan 2005
Location: Waldorf, Md.
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First of all, Mark, thanks for pointing the CG discrepancy out. It really got me thinking. Yesterday, I measured the moment arms for the landing gear again. Got different results than the first go around. Don't know why. Perhaps me or someone else bumped the airplane after it was set. Maybe it shifted somehow. Who knows. Anyway, with the new measurements, the empty CG is located 80.75" aft of datum. That is .17" further aft of the prototype 14A. Problem solved.
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President Van's Aircraft

Last edited by MLock : 01-15-2016 at 02:30 PM.
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  #23  
Old 01-15-2016, 08:18 AM
kaber56 kaber56 is offline
 
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Location: Fairview Park, OH
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Any chance of getting the actual W&B data from N144VA?
Thanks
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  #24  
Old 01-15-2016, 01:03 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by kaber56 View Post
Any chance of getting the actual W&B data from N144VA?
Thanks
It is at the first link in the first post of this thread.
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RV-6A (aka "Junkyard Special ")
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  #25  
Old 01-23-2016, 11:55 AM
kaber56 kaber56 is offline
 
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Any chance of getting the actual W&B data from N914VA?
Thanks
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  #26  
Old 01-23-2016, 12:55 PM
rvbuilder2002 rvbuilder2002 is offline
 
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I think the plan is for N214VA and N144VA to be the official examples.
Since N914VA is very close to matching N214VA, I am not sure what value it would have, but if that is what you wanted you can easily move a little bit of weight in the data set from the main wheels to the nose wheel until you get the C.G. position that Mitch quoted and that should be pretty close.
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  #27  
Old 04-10-2016, 06:53 AM
jswareiv jswareiv is offline
 
Join Date: Dec 2006
Location: New Orleans, LA
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Default W&B Done

Quote:
Originally Posted by rvbuilder2002 View Post
Errors in the posted document have been corrected.

These are the official samples based on data from the two prototypes.
Still looking into why Mitch's computed C.G. is actually aft of the taildragger prototypes.
Had a W&B done yesterday. Weight is 1229.5, CG is 80.54. Here's where it gets interesting. The arm on the tail for me is 255.5 and Van's lists N144VA as 230.38, a full 25 inches difference. They also show the weight on the tail is 75 and mine is 57, 18 lbs difference. So something is amiss there. We had 3 people double check the measurements, then totally redid it and still came up with the same number. We had the datum 72" in front of the leading edge of the wing, the plane level in flying attitude, per the instructions. Also, why would their tail be that much more weight? I do have the ELT back there like they do. Possibly the difference with the tail could be paint, mine has not been painted, but was drained of all gas. All work was done on professional digital scales by a very experienced A&P.
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First RV-14 Flight 04/17/2016
Serial #140087, N214SW
http://rvbuild214sw.com/
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  #28  
Old 04-11-2016, 10:07 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Stoney,

As explained in the response to your PM I sent to you over the weekend, the aft arm position on the sample form got inadvertently labeled tail wheel. The actual position used for weighing was the bolt that attaches the tail spring to the fuselage. A short threaded standoff can be made to thread onto the stub end of the bolt and then the tail supported with a jack stand set up on the scale pad. The tail has to be raised quite high and be carefully adjusted so that the airplane is exactly level. The hydr. jack stand makes this simple.

So, I think if you measure you will find that the distance between the tail spring attach bolt and the tail wheel axle bolt is probably the difference you see.
The sample form will be updated to reflect the difference.

The different CG position for your airplane when compared to N144VA is not really a surprise considering it is only 5 pounds lighter, and it is not painted. A paint job will add more than 5 pounds (8-15+ is common) so that means your airplane is already slightly heavier (at least will be once it is painted) than N144VA. Depending on where that extra weight is located, and then factoring in the shift aft that the C.G will make when it gets painted. As you mentioned, weight on the tail from paint or other objects like an ELT will have a strong influence because of the large moment as a result of the long moment arm.

Based on this information, I think your calculated CG position is probably about what would be expected.
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Any opinions expressed in this message are my own and not necessarily those of my employer.

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RV-6A (aka "Junkyard Special ")

Last edited by rvbuilder2002 : 04-11-2016 at 10:10 AM.
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  #29  
Old 04-11-2016, 10:26 AM
jswareiv jswareiv is offline
 
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Location: New Orleans, LA
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Quote:
Originally Posted by rvbuilder2002 View Post
Stoney,

As explained in the response to your PM I sent to you over the weekend, the aft arm position on the sample form got inadvertently labeled tail wheel. The actual position used for weighing was the bolt that attaches the tail spring to the fuselage. A short threaded standoff can be made to thread onto the stub end of the bolt and then the tail supported with a jack stand set up on the scale pad. The tail has to be raised quite high and be carefully adjusted so that the airplane is exactly level. The hydr. jack stand makes this simple.

So, I think if you measure you will find that the distance between the tail spring attach bolt and the tail wheel axle bolt is probably the difference you see.
The sample form will be updated to reflect the difference.

The different CG position for your airplane when compared to N144VA is not really a surprise considering it is only 5 pounds lighter, and it is not painted. A paint job will add more than 5 pounds (8-15+ is common) so that means your airplane is already slightly heavier (at least will be once it is painted) than N144VA. Depending on where that extra weight is located, and then factoring in the shift aft that the C.G will make when it gets painted. As you mentioned, weight on the tail from paint or other objects like an ELT will have a strong influence because of the large moment as a result of the long moment arm.

Based on this information, I think your calculated CG position is probably about what would be expected.
Scott,

I apologize, I didn't see the PM. Normally it notifies me, my bad. O.K., so I will go with what I have, then once I get it painted and redo the W&B, I'll see what it comes up with. Thanks for the response.
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Stoney
First RV-14 Flight 04/17/2016
Serial #140087, N214SW
http://rvbuild214sw.com/
Dues paid to 2018.
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  #30  
Old 04-11-2016, 12:18 PM
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czechsix czechsix is offline
 
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Location: Spring Hill, KS
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Default Update on Mitch's -14A W&B?

Mitch, now that you've got paint on N914VA, did you get a chance to redo the W&B? I'm very interested to see where the final numbers for empty weight and CG ended up with paint on it...

Thanks,
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RV-8A N2D #80583 - built/flew/sold
RV-14A #140017 - wings complete, empacone in progress...
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