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RV8 CofG question…

Rich Pulman

Rich Pulman

Well Known Member
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I fly my RV8 solo 99% of the time. It has an IO-360-A1A in the nose which makes it nose heavy. The obvious (and easy) way to move the CG aft is to strap a bunch of weight into the back seat. However, I would rather add 10 pounds further back instead of 100 pounds in the back seat. Has anyone devised a simple solution to easily add/remove a small weight way back on the fuselage? I was thinking of something like a small tube running through the fuselage just in front of the horizontal stabilizer (kind of like the handle on the RV15 in a similar location) with removable end caps (recessed) and into which a small lead weight could be inserted as/when needed. Have any clever people out there built anything like this? Are there any other simple solutions?

Thanks in advance for your ideas!

Richard
 
Rich Pulman said:
I fly my RV8 solo 99% of the time. It has an IO-360-A1A in the nose which makes it nose heavy. The obvious (and easy) way to move the CG aft is to strap a bunch of weight into the back seat. However, I would rather add 10 pounds further back instead of 100 pounds in the back seat. Has anyone devised a simple solution to easily add/remove a small weight way back on the fuselage? I was thinking of something like a small tube running through the fuselage just in front of the horizontal stabilizer (kind of like the handle on the RV15 in a similar location) with removable end caps (recessed) and into which a small lead weight could be inserted as/when needed. Have any clever people out there built anything like this? Are there any other simple solutions?

Thanks in advance for your ideas!

Richard
Click to expand...

Composite or metal prop?
Battery in aft location already?
 
I can’t find them now but I’ve seen a couple of methods to add counterweight to the tail. One was a tube that went through the fuselage that you put a lead rod in.

The coolest one was an aluminum tank under the empennage fairing where you poured lead shot in cap at the top and emptied it at the bottom. I think it was VAFer ronschreck.

I wish I would have known about it when I started. I want to do it too but it’s too invasive for me at this point.
I have a parallel valve IO360 with a composite CS prop with an empty CG of 78.5 so it’s pretty good as is.
 
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This is of interest to me because I’ll be in the same situation. O-360 A1A and all
I’ve done and plan on things to mitigate. Superior cold air sump to reduce ~3lbs up front. SDS flywheel that takes 1lbs of nose. Grove gear takes 15lbs off but not out front. Composite prop if I need and finally to place battery in the most effective location. I want it up front for shortest cables. Finally a weight placed in the most rear location. Maybe a fishing pole tube placed down tail and lead secured at aft most portion.
 
Thanks for the link to that CAFE article, PhatRV, interesting stuff I didn’t remember.
I’m „only“ 71kg (157lbs) and usually make sure to stow at least 10kg (22 pounds) of tooling in the rear most compartment of the -8, same config as the OP.

Having a quick, and safe, solution to add weight at the rearmost possible location would be neat.
 
A 2 gallon plastic flat SUV water tank mounted to the side of the baggage compartment will give you up to about 17 pounds of ballast and won’t take up much room.
 
RV-8 CG

Richard,

I’m sure you have a traveling tool kit bag. Add tools/weight to get your desired CG and keep it tied down in the aft baggage compartment. You can put a lot of weight back there and easy to remove when you have a passenger.
 
olyolson said:
Richard,

I’m sure you have a traveling tool kit bag. Add tools/weight to get your desired CG and keep it tied down in the aft baggage compartment. You can put a lot of weight back there and easy to remove when you have a passenger.
Click to expand...

That's what I do - and I move the tool bag to the front when traveling with someone in the back. With nothing in the baggage compartments, two 80kg (175 lb) people, half tanks, it's still in the aerobatic range of CG and weight.

Flying solo in my 8, it's just barely possible to be out of CG if you put the max weight in the front baggage area. Solo, loading up the rear baggage area, it's not possible to be out of CG.

Without a doubt, landings are different depending on the CG, so it's a very good idea to test this during the test flight period. You don't want to get a surprise the first time you take your buddy Bubba for a flight. :D
 
It’s the moment arm

I and the OP fly almost exclusively solo. If you want the total performance RV8 experience it happens in the middle of the CG range. Around 82”. The plane stays in trim over a wide range of speed and the stick force in 4G pulls goes way down.

I have a light 180 HP composite prop setup. At 1400# me and half tanks the CG is 80.4 inches which is pretty nice as is.

If I put 50# in the the back seat it moves to 81.8” which is magic.

Or I could make a 33 pound tool bag and put it on the baggage floor and get the same thing.
A 26# bag on the shelf if I could figure out how to hold it
Or 13# back in front of the VS under the fairing.
 
Aft baggage floor ballast

There is 25# of lead shot in the bag. I was thinking this would be a good place to carry a tool bag anyway with nylon straps holding it with angle across the longerons. would the floor support the 150# of a 6G load?
 

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FWIW, Van's states that for the RV-8/8A the weight limit of the aft baggage floor is 50 pounds, and the weight limit of the aft baggage shelf is 25 pounds.
 
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Don't add weight

I urge you not to add weight.
Reasonably cheap solution is EarthX battery. Big difference. Especially if battery is firewall forward.
Expensive solution is Whirlwind prop. Or other composite.
A nose heavy RV8 is not ideal but is not unusual. If mostly solo, live with it. Remember if you balance the RV8 for solo flying, it will get really pitch sensitive when you have a passenger.
 
Read the thread Jim. We understand the ramifications of adding ballast. It’s worth it to us. I have a rear mounted battery and a lightweight prop. I still use 60 pounds of sand in a backpack in the back seat now. By moving the weight to the aft baggage shelf I get the same CG with 25 pounds.

The difference in the moment on a -8 using a firewall mounted EarthX versus SLA battery is negligible.
 
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Mikeyb said:
There is 25# of lead shot in the bag. I was thinking this would be a good place to carry a tool bag anyway with nylon straps holding it with angle across the longerons. would the floor support the 150# of a 6G load?
Click to expand...

My rear baggage "hat shelf" would buckle at the load you are describing. I put my tools on the rear baggage floor where there is more structure. The rear hat shelf is for my canopy cover, sleeping bag, spare headset, and other light camping stuff. Also, I have tailgate webbing holding it in not so much for negative Gs, but in case I have an off-field landing. Whatever is back there will fly forward to try to kill you, so tie it down well. Obviously you also want to keep the empty rear seatbelts latched as well.
 
If you need to mount the ballast on the semi-permanent basis, maybe you can build a shelf next to the rear bulkhead frame and bolt the lead ballast there. Since you fly solo most of the time so unbolting it won't be an issue. Plus it can handle the load with connected structural arrangement. Also due to the moment arm behind this rear shelf bulkhead, you may not have to use as much ballast mass.
 
Ballast

I have just posted a couple of photos of my solution to ballast. A well sealed 43 lb bag of sand well secured on the aft baggage floor. I also have a standby emergency battery behind the baggage.
IO 360 with a Hartzell prop, firewall mounted battery.

Brent
 
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