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08-15-2015, 09:40 PM
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Join Date: Aug 2015
Location: Novi, MI
Posts: 107
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Quote:
Originally Posted by Ironflight
[...] In the risk management business, we call that relying on an Operational Control of risk - and while that might be a good approach if there is one additional backup to a pilot mistake, it certainly puts you way out there on the risk meter if a single (simple) failure can be fatal. Heavy AND aft CG is a good recipe for pilot overcontrol. [...]
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The effects of a changed gross weight on the stall speed are predictable, I could however indeed imagine that a stall develops differently at a significantly increased weight, even if the CG is within the originally defined limits.
In the case we are discussing here, an increase of the gross weight from 1,800 lbs to 1,900 lbs would raise the stall speed only from 58 to 59.6 mph: √(1,900 / 1,800) * old stall speed of 58 mph).
I consider a difference of 1.6 mph as pretty much negligible. Even in a 45° bank, the stall speed would increase by still only 1.9 mph. The difference between the stall speeds at solo and gross weight, Van's lists on their website, is 7 mph and should therefore be of much more concern if you are worried that pilots might forget these numbers and if you think that the exact value is important in an emergency situation.
The POH section of this website hosts the POH for N2447A. According to this POH, best glide with flaps down is 80 mph. Assuming the pilot sticks to this airspeed, despite of the of the aircraft's higher weight, the margin between his airspeed and a stall would be reduced from 22 mph to 20.4 mph - I would think that this is irrelevant in a real world scenario.
Btw.: I also opened a few other POHs. None contained any information in this regards at all. Even the latest Cessna 172SP POH only lists information for max. gross and at max. aft. CG.
Quote:
Originally Posted by BobTurner
[...] Have you and yours sat in a -7? in the -14? There is no question the -14 is more comfortable, but only you or, especially, your wife, can say how much more or if the -7 is too cramped to be tolerable.
As a long time 182 owner I will say it is a great airplane, and maybe that is what you want. [...]
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Neither of us sat in a 7A, I thought however that the cockpit of a 9A is almost identical!? The width is pretty much the same as in our 172, which is fine, even on longer flights.
I also spoke with my wife tonight, she was very specific: Either a half finished RV-7A project or a 182, with a strong preference for the RV-7A. We also agreed that building would be fun, but that our first project should be limited to 1 - 1.5 years. We therefore neither want a finished plane, nor start from scratch.
We will also consult the technical adviser at our EAA chapter about an increase of the gross weight from 1,800 to 1,850 or 1,900 lbs..
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08-16-2015, 07:11 AM
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Join Date: Jan 2011
Location: SoCal
Posts: 391
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Quote:
Originally Posted by Oliver
I am getting really unsettled, as I have received a number of messages, e-mails and responses in this thread, suggesting that I should never exceed the 1800 lbs, Van's mentions on their website...
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If I knew you personally, I would do as others have done via this site: sit down with you for a private, professional, pointed discussion to consider this (currently) four page discussion; I'm posting this publicly both for you and future readers:
-You have received advice from a number of separate sources, publicly and privately, recommending against exceeding the designer's gross weight.
-You have received a number of recommendations for alternate solutions.
-You are not qualified to assess the design, or the risk.
-Your actions have significant implications for you & your wife; your insurance carrier; future owners or operators of an airplane; and this community.
Please do not exceed designed gross weight.
__________________
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VAF dues paid though exempt
RV-9A sold (I miss that bird!)
RV10 sold (miss that one too!)
RV-14A build underway
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08-16-2015, 07:46 AM
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Join Date: Jun 2005
Posts: 375
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Previously Discussed - GW Thread
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08-16-2015, 07:56 AM
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Join Date: Oct 2005
Location: Estes Park, CO
Posts: 3,947
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Aerobatic
Something else to consider in the decision.
Aerobatic gross is 1,600 lbs.
You may want to do the math specific to your situation.
__________________
Larry Larson
Estes Park, CO
http://wirejockrv7a.blogspot.com
wirejock at yahoo dot com
Donated 12/03/2019, plus a little extra.
RV-7A #73391, N511RV reserved (2,000+ hours)
HS SB, empennage, tanks, wings, fuse, working finishing kit
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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08-16-2015, 08:29 AM
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Join Date: Oct 2009
Location: Victoria, BC, Canada
Posts: 3,932
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Quote:
Originally Posted by jrs14855
If you look at the history of most US light aircraft that had a long production run, in most cases you will find significant gross weight increases over the years. In many cases there were no structural changes for the weight increases.
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All of these increases would have been backed up with engineering calculations to show that they were valid... Not a group of people on the internet saying "i've done this lots of times and it was fine..."
__________________
Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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08-16-2015, 10:13 AM
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Join Date: Aug 2015
Location: Novi, MI
Posts: 107
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Quote:
Originally Posted by PaigeHoffart
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I am aware of this and other discussions, they pretty much all go along the same lines: The yaysayers come op with arguments and calculations why a certain weight will be OK.
The naysayer's sole argument is 'don't do this, you significantly increase the risk, stick with Van's numbers', without any reasoning behind this statement.
This is IMHO not very helpful.
In my case, we are talking about an increase of the gross weight from 1,800 to 1,850 (+2.8%) or 1,900 lbs (+5.6). Most of the time we would probably stay under 1,800 lbs., the increased gross weight would only be needed for longer trips.
I showed above that the increase of the stall speed is minimal, based on the aerobatic numbers it is also clear that the plane is strong enough to easily carry the additional weight, if it is operated within the limits of the standard category and if the CG also stays within them.
After another day of thinking and research, I still fail to see any other noteworthy risks, caused by such a relatively small increase of the gross weight, other than a possibly increased stress on the landing gear. The suggestion to define a max. landing weight of 1,800 lbs. would however also take care of this concern and document it for future buyers.
Please excuse my persistence, but I want to understand the pros and cons, as we really want a RV-7A, but also don't want to do anything stupid.
Let me therefore ask the question again: Which specific risks do you see and why?
I will also discuss this topic with our EAA chapter's technical adviser, I believe we also have at least one aeronautical engineer in our group.
Last edited by Oliver : 08-16-2015 at 10:15 AM.
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08-16-2015, 10:17 AM
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Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
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Rv7a
Why beat a dead horse , the 7 is not the plane for you and your mission , give it up ! Can't buy a corvette when you need a Suburban . Go look for a Rv10 or a 182 .
__________________
Rv8
N 666 TA
First Flight 2-3-2015 🚀
2017 donation paid
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08-16-2015, 10:57 AM
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Join Date: Mar 2014
Location: Alexandria VA
Posts: 305
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Oliver, Is acro flying "something you've always wanted to do" or is it something you've done lots of and like doing? If you're new to acro, might want to spend a few hours in a Citabria with a qualified acro instructor and fly the wings off it - only a figure of speech. You might also want to suugest to your wife that she too get some dual acro. This may help you and your wife assess if you need your next plane to be acro capable.
I like to travel and I like acro so my-7 is right for me. Still, I had my wife take a few hours of dual acro in a Citabria before deciding to buy the -7.
If she hadn't been comfortable with doing acro, or flying a tailwheel, then we would have bought a Mooney for travel and I would have satisfied my acro needs in a rented Citabria.
Robert
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08-16-2015, 11:05 AM
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Join Date: Feb 2015
Location: Fort Worth
Posts: 527
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Quote:
Originally Posted by wirejock
My 7a is not finished but I'm trying to keep her light. I carry around enough already. 
Sweetie and I used to travel a lot on our Goldwing. Pretty limited on baggage so we learned.
A few times we shipped stuff to the destination and shipped stuff back.
So basically we will learn to live within the limits of our airplane.
Just a suggestion.
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I agree with this. Every airport of intended landing will have an address and a phone number. Ship the gear and carry a gym bag or two if you plan an overnight. Much easier than weighing/loading etc.
__________________
Rob
RV-6A (Purchased)
2020 Dues Paid, of course
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08-16-2015, 12:23 PM
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Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,393
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Phase 1
Quote:
Originally Posted by Mel
Gonna have to jump in here. You must test the aircraft "throughout the aircraft's normal range of speeds and throughout all maneuvers to be executed."
Vso, Vx, Vy, and the weight and CG location at which they were obtained are the only numbers required to be listed. That does NOT mean that these are the only numbers that require testing.
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The new ops specs only address aerobatic maneuvers. My airplane is non aerobatic. So the only maneuvers I tested were power on/power off stalls. flaps up and down.
I agree with your normal range of speed statement, I tested the airplane to slightly over Vne, which most people on this forum appear to be adamantly opposed to.
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