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  #1  
Old 09-01-2021, 12:17 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,180
Default RV-14 rear mounted battery

Yank, my neighbor here a Dogwood is well into his RV-14 build. Thanks to some good W&B data from other RV-14 builders he now has a strawman W&B to makes decisions on such things as where/how to mount a second battery.

Assuming a IO-390 EXP119 engine, Hartzell BA prop and the standard battery on the firewall, CG for most conditions is a little more forward of what you would want. Adding a 13.2 pound PC-625 battery aft of the baggage compartment provides for a nice W&B, even at gross and with 100 pounds of baggage.

Note: Calculations assumed battery install at 15 pounds to account for mounting and such.

Looking at the RV-14 rear bell crank mount I noted that the setup is identical to my current RV-10 build (I took my RV-10 bell crank and battery mount over to verify - exact fit).

So - using the Vans RV-10 parts in the RV-14 makes for a perfect aft battery mount. Here are the needed parts:
(1) F-1035
(1) F-1036
(2) 1/4x28x8 bolts
(4) 3/16 nutplates
(2) 1/4 nutplates

As a side note, this modification supports, and he may move the ELT forward to just behind the baggage compartment bulkhead.

Carl
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  #2  
Old 09-10-2021, 09:57 AM
bk1bennett's Avatar
bk1bennett bk1bennett is offline
 
Join Date: Nov 2015
Location: Sachse, TX
Posts: 81
Default Thanks

Carl,

This is a great post and a perfect example of what makes this forum uniquely valuable. A spare battery is good insurance.

thank you.

Quote:
Originally Posted by Carl Froehlich View Post
Yank, my neighbor here a Dogwood is well into his RV-14 build. Thanks to some good W&B data from other RV-14 builders he now has a strawman W&B to makes decisions on such things as where/how to mount a second battery.

Assuming a IO-390 EXP119 engine, Hartzell BA prop and the standard battery on the firewall, CG for most conditions is a little more forward of what you would want. Adding a 13.2 pound PC-625 battery aft of the baggage compartment provides for a nice W&B, even at gross and with 100 pounds of baggage.

Note: Calculations assumed battery install at 15 pounds to account for mounting and such.

Looking at the RV-14 rear bell crank mount I noted that the setup is identical to my current RV-10 build (I took my RV-10 bell crank and battery mount over to verify - exact fit).

So - using the Vans RV-10 parts in the RV-14 makes for a perfect aft battery mount. Here are the needed parts:
(1) F-1035
(1) F-1036
(2) 1/4x28x8 bolts
(4) 3/16 nutplates
(2) 1/4 nutplates

As a side note, this modification supports, and he may move the ELT forward to just behind the baggage compartment bulkhead.

Carl
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  #3  
Old 09-10-2021, 10:43 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,180
Default

No problem Brian.

I suggest however adding a second battery should not be considered a spare. The second battery is the enabler to a more robust power distribution design.

Carl
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  #4  
Old 09-10-2021, 11:27 AM
Nova RV Nova RV is offline
 
Join Date: Aug 2015
Location: Leesburg, VA
Posts: 573
Default

I did some rough calculating using the W/B info from Vans demo -14 taildragger and the issue is not at max gross, but when the fuel gets lower the C/G moves aft. With a 200lb pilot, 200lb passenger, and 10 gallons of fuel, even with 90 lbs of baggage you are almost .25in aft of the rear limit of 88.24 in. This is with a 15pound battery at approximately station 150 which is 20in from the center of the baggage compartment measurement used by the factory.
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RV-14A kit # 140243 (flying as of 11/18)

www.mykitlog.com/chrismoon/
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  #5  
Old 09-10-2021, 08:37 PM
dmattmul dmattmul is offline
 
Join Date: Dec 2015
Location: Spring Hill, FL
Posts: 183
Default 2nd battery

I put both my batteries on the firewall (Earth X). With 200 hours and 14 months so far going well. Id be careful putting that much weight so far aft but we are experimental builders and need to understand the risk/reward.
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RV-14A QB building, Lycoming 390 Thunderbolt arrived July 2019, Garmin avionics, Vertical Power, EFII-32 Ignition and Fuel, Whirlwind 300-72, Parts became a real airplane 8/15/2020.
Started RV-10 Nov 2020. Empennage arrived (Built) Working on QB kits. Garmin avionics, Vertical Power, EFII-32 Ignition and Fuel, Whirlwind 3 blade, real airplane hopefully early 2023.
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  #6  
Old 09-11-2021, 12:57 PM
ben barron ben barron is offline
 
Join Date: Sep 2013
Location: Fall City, WA
Posts: 161
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what prop do you have?
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  #7  
Old 09-11-2021, 05:24 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,180
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Id be interested in what W&B people are using. I did an average of W&B from other RV-14 builders to come up with the below tables when I did the math to add the PC-625 battery aft.

I suspect that moving the ELT up forward will move the CG up slightly as well.

Flying the RV-8 I find that a CG more aft than forward is helpful - and I load the plane to support (as in ballast when I have no passenger). Translating to the RV-14 it would seem that having this second battery aft would also be helpful and will eliminate the need for ballast when not fully loaded.

Carl

Situation 1 - Full baggage, full fuel, at Gross
Weight Arm Moment
Aircraft 1252 79.21 99167
Fuel 50 gal. 300 81.97 24591
Pilot 230 99.83 22961
Front Seat Passenger 153 99.83 15274
Mod (one battery aft) 15 150 2250
Baggage 100 129.48 12948
Gross Weight 2050 Total Moment 177191

CG inches aft of Datum: 86.43
Inside of CG limit.

Situation 2 - Full baggage, min fuel, at Gross (when starting at full fuel)
Weight Arm Moment
Aircraft 1252 79.21 99167
Fuel 50 gal. 30 81.97 2459
Pilot 230 99.83 22961
Front Seat Passenger 153 99.83 15274
Mod (one battery aft) 15 150 2250
Baggage 100 129.48 12948

Gross Weight 1780 Total Moment 115059

CG inches aft of Datum: 87.11
Inside of CG limit.
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  #8  
Old 09-12-2021, 05:00 AM
Nova RV Nova RV is offline
 
Join Date: Aug 2015
Location: Leesburg, VA
Posts: 573
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Carl, is Yank building a taildragger or -A model, I don't remember? I used Vans taildragger demo plane empty weight and C/G which is 81.33 or 2" aft of the empty C/G you are using which would put both of your examples beyond aft limit. I have not sampled other people's empty C/G so perhaps your numbers more represent the actual flying fleet.
Your comment about the aft C/G flying better I would definitely agree with on the -14, the pitch feeling is heavy especially at landing with the typical forward C/G. I have an -A model with a light Whirlwind prop and now an Earth X battery on the firewall and I love the way it flies much more than with the Odyssey PC680.
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Leesburg, VA

CFI-I ASMEL, ATP

RV-14A kit # 140243 (flying as of 11/18)

www.mykitlog.com/chrismoon/
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  #9  
Old 09-12-2021, 08:16 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
Posts: 3,180
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Yep, Yank is building a 14 tail dragger.

Carl
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  #10  
Old 09-12-2021, 08:15 PM
Yank Yank is offline
 
Join Date: Feb 2013
Location: Spotsylvania
Posts: 55
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I believe the taildragger demo has a IO360 with a basic VFR panel (less weight). Not sure if this is the reason the CG is 2” aft of what Carl is using.
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