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10-11-2016, 01:59 PM
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Join Date: Oct 2013
Location: Boerne, TX
Posts: 53
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RV-8 Weight n Balance question
I am finishing my 8, my weight is 1084lbs. I have a 200hp with CS prop. My W&B puts my Datum at 73.67. That makes me pretty nose heavy. I ran the numbers solo and my W&B stays so far fwd that it looks really ugly once I burn the fuel out. I ran numbers with 45lbs in aft cargo floor, the numbers look better but....
My tail weighed in at 29lbs. Any thoughts on weight mods to the tail?
Thanks
Bones
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10-11-2016, 02:34 PM
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Join Date: Mar 2008
Location: houston, texas
Posts: 900
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common problem with the angle valved set up.
Yep this is seen a lot with the angle valved engine and heavy prop set up.
The first thing is that the battery or batteries need to go in the back. You can ballast by putting some lead in the tail. I would only add as much as it take to get you 3/4 to an inch and a 1/4 behind the forward most CG though as you want to keep the weight down as much as you can. Always remember the most aft CG moves forward and you gross weight goes down if you want to do aerobatics later on. Other than that try to sift as much of your weight aft of the fuel tank moment that you can. I am glad you are seeing this as it is something that has gotten a few in bad situations before. If you can get the CG as close to the front of the box as you can with the 8 you are doing the right thing as other than the front baggage most every thing you will load for a trip makes the CG move back not forward. Hope this help. Yours, R.E.A. III #80888
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10-11-2016, 03:05 PM
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Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
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W&b
I have the same set up and a prop spacer ( James Cowl )
My battery is behind the panel , 4.5 gallon smoke tank (and ballast ) where the plans call for the battery and made a new tail wheel that weighs 16 oz more than stock . Mines 1094 with 42 on the tail .
29 sounds pretty light , have you verified the weights ?
I can email you pics of the tailwheel .
__________________
Rv8
N 666 TA
First Flight 2-3-2015 🚀
2017 donation paid
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10-11-2016, 03:24 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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If you do not have your battery mounted aft of the baggage compartment, move it there. If it is already mounted there, add a second battery in the same spot. If you are going to add weight you may as well get some benefit from it. A second battery, even if you don't optimize the power distribution design, will add electrical reserve.
Carl
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10-11-2016, 03:43 PM
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Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
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W&B
I wouldn't move the battery , especially considering the weight is almost nothing now days , consider adding weight under the vertical fin on the rear deck and making a heavy tail.
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Rv8
N 666 TA
First Flight 2-3-2015 🚀
2017 donation paid
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10-11-2016, 03:47 PM
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Join Date: Mar 2008
Location: Seattle
Posts: 1,412
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Also try to remove some weight from the front.
Install a lighter starter and alternator, that's as close to the front as you can get (except the prop) Get a light weight flywheel (Ouch $!)
Install a light weight sump, like a Superior or Sky Dynamics.
When you move the battery to the back, you get unwanted additional weight, like more than 3 pounds of battery cable!
I went the opposite direction when I removed my powerful but weighty Mazda Turbo Rotary and installed a Parallel valve conical mount IO-360 with Catto prop and light starter & sump.
I move the battery forward. The removed cable alone was 3.2 pounds!
My son Peter had a rear mount alternator on his Pitts, so he machined the alternator pulley off the flywheel to save weight. He also switched to an AeroVoltz LiFPo4 battery. It all counts!
G Zero has a good point, add a little weight very far aft.
__________________
Scott Emery
http://gallery.eaa326.org/v/members/semery/
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is nothing-absolute nothing-half so much worth doing as simply messing around with Aeroplanes
(with apologies to Ratty)
2019
Last edited by SHIPCHIEF : 10-11-2016 at 05:12 PM.
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10-11-2016, 04:25 PM
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Join Date: Mar 2006
Location: Gilbert, AZ
Posts: 1,628
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Quote:
Originally Posted by g zero
I wouldn't move the battery , especially considering the weight is almost nothing now days , consider adding weight under the vertical fin on the rear deck and making a heavy tail.
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OK, I really don't know what you mean by "weight is almost nothing". But if you are considering adding weight under the vertical fin read this:
http://www.vansairforce.com/communit...d.php?t=133740
Disregard the negative comments. The mod works!
__________________
Ron Schreck
IAC National Judge
RV-8, "Miss Izzy", 2250 Hours - Sold
VAF 2021 Donor
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10-11-2016, 04:54 PM
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Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
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[quote=ronschreck;1118035]OK, I really don't know what you mean by "weight is almost nothing".
I meant today's batteries, my Battery Tender brand battery weighs 3 lbs
I like your "ballast tank " , I'll add that to my list of future upgrades.
__________________
Rv8
N 666 TA
First Flight 2-3-2015 🚀
2017 donation paid
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10-11-2016, 05:51 PM
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Join Date: Nov 2010
Location: Okanagan Valley BC, Canada
Posts: 483
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Is it painted yet? Can make a significant difference as most of the paint is behind the c/g...
If it is, a little weight added to the tail = a whole bunch taken off the nose if it's already equipped as you want it...
__________________
Ron Townson
Okanagan Valley BC, Canada
RV-8 Completed Dec 2013
Membership renewed Sept 8, 2019
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10-11-2016, 06:00 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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If you care, a PC925 on its side fits the stock rear battery tray. And it will blow up a lot of air mattresses.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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