VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #1  
Old 01-14-2021, 11:10 AM
bryanrene bryanrene is offline
 
Join Date: Apr 2005
Location: waco, texas
Posts: 67
Default variabilty in empty weight

I am not a builder but have a question about building in lightness. It would seem that all examples of a particular model would have a very similar empty weight of the basic airframe and then the difference in weight would be due to the add on items (engine, prop, avionics, interior, maybe even paint). If you had a baseline airframe weight, you would then be able to estimate weight based on the add on items, or the effect of removing/changing items.

Are there significant weight difference choices in the construction of the airframe?

Trying to wrap my head around the vastly different weights of planes. Is it maybe due to inaccurate initial weighing?
__________________
Crash Taylor

Pitts S2C purchased and flying
Pitts S1C bought and sold
Rv4-bought and sold x2
F-1 Rocket bought and sold
" live each day like it was your last,
One day you will be right"

2019
Reply With Quote
  #2  
Old 01-14-2021, 11:37 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,323
Default Too many variables

While nearly every certified airframe is built to a spec, and pretty much identical, our RV' are not. keep in mind also, an experimental is not required to be weighed on an accurately calibrated scale, and many have been weighed on bathroom scales..and may not reflect a totally accurate weight. Then there is the prime the inside, some, all ,none, varying layers of paint ect. Seemingly simple things like wiring weight (harbor freight wire vs zefftel aircraft wire) can be pounds of difference. The only baseline airframe weight I could see achievable accurately MAY be via VANs for a quickbuild kit, and that is meaningless. Even looking at the W/B data for 99% of experimentals, that data was put together and accepted by an individual using the best information he/she could obtain and seldom followed by the quality control of a certified aircraft. That why I often recomend to a "new owner" of a previously built RV to take the W/B as a baseline. Fortunately, the RV's built to or close to plans, with typical engines and equipment are a pretty safe bet of being in range even if the W/B data is sloppy. The data shared on this site between builders is a wonderful way to find a pretty fair target weight and C/G considerations to understand.
__________________
Bill E.
RV-4/N76WE
8A7 / Advance NC
Reply With Quote
  #3  
Old 01-14-2021, 11:50 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,213
Default

30# composite prop vs 65# Hartzell C/S prop
15# Odessey battery vs 3# EarthX lithium
7# cloth seat cushions vs 15# leather cushions
6# floor carpets vs no carpets
2 of everything on the panel vs basic instrumentation
40# ballistic parachute vs not
8# wheel pants vs not
320 vs 360 vs 390 vs whatever
interior panels vs not
plus 100 other builder choices, in the end they all add up
__________________
Ralph
built a few RVs, rebuilt a few more, hot rodded more, & maintained/updated a big bunch more
Reply With Quote
  #4  
Old 01-14-2021, 12:08 PM
wilddog wilddog is offline
 
Join Date: Feb 2008
Location: va.
Posts: 588
Default

Quote:
Originally Posted by Ralph Inkster View Post
30# composite prop vs 65# Hartzell C/S prop
15# Odessey battery vs 3# EarthX lithium
7# cloth seat cushions vs 15# leather cushions
6# floor carpets vs no carpets
2 of everything on the panel vs basic instrumentation
40# ballistic parachute vs not
8# wheel pants vs not
320 vs 360 vs 390 vs whatever
interior panels vs not
plus 100 other builder choices, in the end they all add up
Tires
Battery location, rear needs a couple of lbs cable
Glass v steam gauges
Type of foam in the seat cushions
Landing lights or not
EI is lighter than mags
Light starter and alternator

Last edited by wilddog : 01-15-2021 at 11:52 AM.
Reply With Quote
  #5  
Old 01-14-2021, 01:51 PM
bbsdad bbsdad is offline
 
Join Date: Oct 2018
Location: tx
Posts: 83
Default

Then there are the older planes which gave the builders the option of putting in lightning features. Ie.. lightning holes, trimming parts, removing exces material wherever possible. Well being seemingly minuscule, adds up. Consider the weight diferance between a standard washer and an L series washer. Tiny right but add up a couple hundred and you have a couple pounds. Same with lock nuts verses castle nuts, or fiber lock nuts compared to steel locknuts. It all adds up. Saving an ounce here letís you apply an extra ounce there kind of thing.
__________________
RV-6 o-360, WW ga200 prop. 90% to go
Reply With Quote
  #6  
Old 01-15-2021, 09:24 AM
FinnFlyer FinnFlyer is offline
 
Join Date: Aug 2018
Location: Bell, FL
Posts: 460
Default

In addition to primer/paint, there's also fiberglass work.

Finn
__________________
N214FL RV-4 Mazda 13B Renesis First flight 20 Feb 2021
N46AZ RV3-B Mazda 13B EFI -- Bought -- Flying
N993FL RV-3A Mazda 13B NA 575 hours
Reply With Quote
  #7  
Old 01-15-2021, 09:51 AM
David Z David Z is offline
 
Join Date: Aug 2010
Location: Thunder Bay Ontario
Posts: 485
Default Certified Aircraft

Certified aircraft vary quite a bit too. One fleet type at work weighs ~11000lbs empty, but varies 250lbs from plane to plane. This is identical avionics, engines, props, seats, everything. This aircraft type has most weights about 10x heavier than the RV-7/8s, so it's easy math to draw comparisons. Looking at two identical RV-8s and seeing a 25lb difference would make me wonder too.

Throw in all the variables in experimental, a 100lb difference isn't surprising. Metal prop, angle valve engine, dual lead-acid batteries, IFR panel with lots of redundancy, primer throughout, fancy multi-colour paint job, leather seats, bigger tires, steel gear (for those with aluminum gear options). That will be much heavier than a fixed pitch composite prop on the small engine, basic VFR panel, no priming, polished aluminum exterior, cloth seats, standard tires, and aluminum landing gear.

Just speaking of props, a heavy 3 blade constant speed prop can be upwards of 60lbs, where a 2 blade fixed pitch composite prop can be 10-15lbs. That's up to 50lbs difference in the prop alone when looking at extremes.
__________________
RV-8
Empennage Passed Pre-close Inspection
Wings mostly done
Fuselage started
83126
Dash 8 day job is financing the RV-8
Donation till September 2021
Reply With Quote
  #8  
Old 01-15-2021, 10:08 AM
Mel's Avatar
Mel Mel is offline
 
Join Date: Mar 2005
Location: Dallas area
Posts: 10,915
Default

Quote:
Originally Posted by Ralph Inkster View Post
7# cloth seat cushions vs 15# leather cushions
15 lbs for leather cushions. This made me smile as it is one of my "pet peeves" interior options. A complete, commonly used, leather interior for an RV-7 can easily weigh 55 lbs.

Another big weight variance is paint. A good paint job from a professional aircraft painter can weigh as little as 18 lbs. compared to an auto painter who is typically not concerned about weight can be up to 30-40 lbs.
__________________
Mel Asberry, DAR since the last century. Over 1,000 certifications accomplished.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>

Last edited by Mel : 01-15-2021 at 10:13 AM.
Reply With Quote
  #9  
Old 01-15-2021, 11:27 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,213
Default

Correction noted - cushions should have been cushion
I was totally floored recently after doing a W&B on a F-1, on how heavy the seat cushions were in that thing.
__________________
Ralph
built a few RVs, rebuilt a few more, hot rodded more, & maintained/updated a big bunch more
Reply With Quote
  #10  
Old 01-22-2021, 05:37 PM
Anon455 Anon455 is offline
 
Join Date: Dec 2020
Posts: 51
Default Weight and Stall

A few years ago I went for biennial. Afterwards the DPE, a far retired ATP through me a question:

Why is stall speed greater for an aircraft with a minimally weighted load compared with maximum?
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 03:52 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.