VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #41  
Old 11-04-2019, 10:07 AM
sailvi767 sailvi767 is online now
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,012
Default

When I owned my six it was set by the builder at 1800lbs. I was fine with it because the six probably has more actual flight hours than any other Vans model and as far as I can tell never experienced a inflight breakup. The same can’t be said of some other Vans models with fewer flight hours.
Reply With Quote
  #42  
Old 11-04-2019, 10:13 AM
Canadian_JOY Canadian_JOY is offline
 
Join Date: Aug 2007
Location: Ontario, Canada
Posts: 2,174
Default

I have no horse in this race, having built a Glasair Sportsman rather than an RV.

With that having been said, I've seen what Glasair did to boost gross weight in the Sportsman from 2350 to 2500. Just the increase in size of the wing strut and strut attachments and bolts is enough to pop one's eyes WIDE open. Increases in tubing diameter and thickness in the steel "roll cage" also give an observer the impression that design gross weight is indeed a maximum number.

There ain't no way in heck my airplane is flying over 2350 unless it's in a serious life-saving emergency mode of operations. And even then it would be done with extreme caution and with great respect for airspeeds and the need to adjust them to very conservative levels.

Again, I don't have a horse in this race, but provide the Sportsman as an example where one can see how much beefing up of structure had to be done to add 150lbs of gross weight capacity. It's not insignificant, not in the least.
Reply With Quote
  #43  
Old 11-08-2019, 03:38 PM
gmcjetpilot's Avatar
gmcjetpilot gmcjetpilot is online now
 
Join Date: Jan 2005
Posts: 4,065
Default

I do stress analysis and certification of aircraft structure. Not going to argue MGW (max gross wt.) but a few comments.

Gust load condition will produce higher G loads when operating an aircraft at *lighter weight*, for a given speed. The lighter AC weight the lower maneuvering speed (Va or Vo). Refresher, big fan of Rod Machado.
https://youtu.be/BAy4w3SYCTo

1800 lbs RV-6 is totally arbatray set by builder based on operational needs. Experimental airplane, end of story. [Question: Does every builder go through and evaluate all the performance and speed limits maticuliously during phase 1 at higher 1800 lbs gross weight?]

We don't know how Van designed/sized structure, set original MGW, determined limiting critical load cases and structure. Van is a degreed Engineer and sure he did "classical stress analysis" to size the structure (and was conservative). Van I also assume used certified aircraft 1.5 factor of safety [limit/design load x 1.5 = ultimate load] to size his structure.

I have not reviewed Van's stress analysis. From +40 years and thousands of RV's flown safely we can assume Van did a good job (including the few in-flight breakups which had causes other than deficits in design). With that said you can break an RV if you do something stupid.

RV-6 has an aerobatic [1375 lb] MGW at +6G. Normal category planes are 3.8G. You can fly your RV-6 at 1800 lbs or [30%] higher than published aerobatic Wt. and wings will not fold up, if you fly your RV like a normal category plane, straight & level. Regardless increase of MGW from 1600 to 1800 a 1.125 factor increases stress and reduces your margins in the air or on ground. [edit]

Exceeding MGW on GA planes is often an issue with low performance GA planes because they will have marginal performance. RV's have an abundance of performance. However at 1800 lb RV on hot day, high DA is not going to perform like a light RV. Also as mentioned aft CG makes it unstable as well.

There have been RV LOC (loss of control, stall) accidents where over gross Wt. and CG was a factor. In fact LOC is one of the biggest causes of accidents. Higher gross and stall speed is not helping.

Bottom line higher gross weight lowers performance and increases stress on the aircraft. Is it unsafe or critical?That's up to the builder and PIC? It's an experimental aircraft. Obviously at operations at 1800 lbs max gross weight one should limit the G loading on the aircraft and land smooth, while avoiding max performance T/O and Ldgs.

Last is Joy, I have flown very light RV6 with a wood prop and they was delight. I've flown really heavy RV6's and they lose a lot of the feel and enjoyment of a light RV6.
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767

2020 Dues Paid

Last edited by gmcjetpilot : 11-08-2019 at 07:28 PM.
Reply With Quote
  #44  
Old 11-08-2019, 04:10 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,445
Default

Quote:
Originally Posted by gmcjetpilot View Post
RV-6 has a 1600 lb MGW at +6G. Normal category planes are 3.8G.
RV-6 has a lower MGW for 6G / aerobatics, as well as a shorter aft CG. Maybe 1350 or 1375. I don't remember, as I don't fly aerobatics.

Larry
__________________
N64LR
RV-6A / IO-320, Flying as of 8/2015
RV-10 in Phase I
Reply With Quote
  #45  
Old 11-08-2019, 04:22 PM
RV8JD's Avatar
RV8JD RV8JD is offline
 
Join Date: Jan 2005
Posts: 531
Default

Quote:
Originally Posted by gmcjetpilot View Post
... RV-6 has a 1600 lb MGW at +6G. ...
This is incorrect. The RV-6/6A is stressed for +6g (Aerobatic Category limit) at 1375 pounds.

Note that the Max Gross Weight is 1600 pounds for the RV-6, and 1650 pounds for the RV-6A.

Refs:
RV-6: https://www.vansaircraft.com/wp-cont...9/01/RV6wb.pdf

RV-6A: https://www.vansaircraft.com/wp-cont.../01/RV6Awb.pdf
__________________
Carl N.
Arlington, WA (KAWO)
RV-8, 645 Tach Hours
(Pic 1),(Pic 2)
- Out with the Old, In with the New
(Pic)
RV-8, 1938 Tach Hours (Pic 1),(Pic 2) - Sold

Glasflügel Standard Libelle 201B - Sold
Rolladen-Schneider LS1-f - No longer owned
Reply With Quote
  #46  
Old 11-08-2019, 04:30 PM
gmcjetpilot's Avatar
gmcjetpilot gmcjetpilot is online now
 
Join Date: Jan 2005
Posts: 4,065
Default

Quote:
Originally Posted by lr172 View Post
RV-6 has a lower MGW for 6G / aerobatics, as well as a shorter aft CG. Maybe 1350 or 1375. I don't remember, as I don't fly aerobatics. Larry
Quote:
Originally Posted by RV8JD View Post
This is incorrect. The RV-6/6A is stressed for +6g (Aerobatic Category limit) at 1375 pounds.
Thanks, fair enough... forgot about lower aerobatic weight. So 1375 to 1800 is about 30%. So at 1800 lbs you would be around 3.8G limit of utility category plane.

To be clear I'm not condoning or recommending Flying at higher than 1600 lbs ever.
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767

2020 Dues Paid

Last edited by gmcjetpilot : 11-08-2019 at 05:00 PM.
Reply With Quote
  #47  
Old 11-10-2019, 10:48 AM
Snowflake's Avatar
Snowflake Snowflake is offline
 
Join Date: Oct 2009
Location: Victoria, BC, Canada
Posts: 3,593
Default

Quote:
Originally Posted by gmcjetpilot View Post
Thanks, fair enough... forgot about lower aerobatic weight. So 1375 to 1800 is about 30%. So at 1800 lbs you would be around 3.8G limit of utility category plane.
This only applies if the extra 200lb you're adding to the airframe is distributed evenly throughout the airframe. If you could "spread" 200lb of paint on the airplane, then yes, operating it at 1800lb and restricted to Normal category only would be no more dangerous than operating at 1600lb and restricting to Utility category.

When you take the extra 200lb and load it in *one place* in the airplane, say by carrying two "bubba" passengers (270lb) instead of two ICAO standard passengers (170lb), you "point load" the airframe, and the structure near that extra load isn't just carrying 1800/1600 or about 1.15x the load it saw before, it's now seeing 270/170 or about 1.6x the load it saw before.

As someone else said before: "It's not just the wing loading."
__________________
Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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 06:52 PM.


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.