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RV-6 CG

H

houndsfour

Active Member
A short time ago on this forum, there was a question on the CG for the RV6 with wood props.
I have the same problem. Wood prop and aft CG. I changed to a light weight tail wheel(saved 15 oz.) Added the old styled Delco heavy starter adding 17 pounds to the nose. I have the vibration "ring" behind the prop.
I have moved the CG forward 2" but it still isn't in the mid range yet.
Anyone have any suggestions. No I won't give up the best woop prop I've ever had.:)
Rich
RV6 N712ET
 
Ti Tailspring?

houndsfour said:
A short time ago on this forum, there was a question on the CG for the RV6 with wood props.
I have the same problem. Wood prop and aft CG. I changed to a light weight tail wheel(saved 15 oz.) Added the old styled Delco heavy starter adding 17 pounds to the nose. I have the vibration "ring" behind the prop.
I have moved the CG forward 2" but it still isn't in the mid range yet.
Anyone have any suggestions. No I won't give up the best woop prop I've ever had.:)
Rich
RV6 N712ET
Click to expand...

Hi Rich, I'm in the same boat. On the previous thread, someone mentioned a titanium tailspring, but I haven't been able to locate any prefab resources. Seems like there might be a market if someone wanted to build them. As you know, a few ounces at the tail goes a long way.

-jon
 
Examples?

RV-6, 0-360, lt wt alt, wood prop, minimal interior. I also have an aft CG but still within range for reasonable utilization. It doesn't have to be in the middle of the range as long as it doesn't go aft of CG when flying. With two 200 lb pilots and 1/4 fuel I can still get 60 lbs of baggage. This works for weekend trips with the wife. What are you trying to achieve? What pilot weights, what baggage weight at what fuel level? At these condition were are you at with your CG?
 
RV6 CG

I planned on moving my battery forward of the fire wall to help. Others have done this. Don't remeber how much it helped.

You have done the main things.

Remember: One pound at the tail = Fifteen pounds forward.
 
I still building mie, but aft CG is a big concern of mine. I have a 6A so the tailwheen isn't a problem, but I have a RV-7 tail with the 0.020 skins and the counterbalanced rudder. To counter the aft CG I have the battery on the firewall plus I am keeping the old prestolite starter for now. I am also trying to keep equipment forward whenever possible. I have a Catto prop so that dosn't help with the aft CG problem. We'll see how it all works out when I'm done...
 
Too bad we can't mount the battery way up front somewhere.?!? Hmmmmm, why didn't I think of that before??

Would it be feasible to mount the battery forward, say near the alternator, or on the other side?

Or, ......... did I have one too many Dr. Beam's this evening??? :rolleyes:
 
Frank Smidler said:
RV-6, 0-360, lt wt alt, wood prop, minimal interior. I also have an aft CG but still within range for reasonable utilization. It doesn't have to be in the middle of the range as long as it doesn't go aft of CG when flying. With two 200 lb pilots and 1/4 fuel I can still get 60 lbs of baggage. This works for weekend trips with the wife. What are you trying to achieve? What pilot weights, what baggage weight at what fuel level? At these condition were are you at with your CG?
Click to expand...

This is very similar to my RV-6.

One thing I do to allow the use of more fuel is plan ahead so there is an easy to reach bag in the back which a passenger can place in his/her lap for landing. Moving 10-15 pounds ~3' makes difference. In reality, I'm not that concerned about slightly exceeding the CG limits in cruise flight, but in the pattern, I'd rather have a more forward CG.
 
PCHunt said:
Too bad we can't mount the battery way up front somewhere.?!? Hmmmmm, why didn't I think of that before??

Would it be feasible to mount the battery forward, say near the alternator, or on the other side?

Or, ......... did I have one too many Dr. Beam's this evening??? :rolleyes:
Click to expand...

Just think how much structure you will need to add to support the weight of the forward mounted battery at the same G-load the airplane is designed for. Airplane structure is designed at safety factor of 1.5 so to get a 6-G structure, you design to support 9-G. In other words, a 10-pound battery mounted at the alternator station would need a structure that can support supports 90-pounds.

Maybe you should not type while or after drinking Dr. Beam. I prefer 100-proof Jeremiah Weed. You can read the True Story of Jeremiah Weed at this link.
 
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RV6 CG

Rich, I had much the same CG issues on my 6A, here are the things I did:

1) Moved the battery to the firewall (like the 7(A) battery design).
2) Mounted the ELT in the center of the floor up aginst the firewall.
(where the battery in the 6(A) is designed to go).
3) Used the heavy Delco starter (17 lbs).
4) Used the ballance ring on the flywheel (12 lb).
5) Used a 1/2" thick SS crush plate (9 lb) on the prop.

.................and finally got the CG where I wanted it!!!

Hope this helps!
 
Tommy,
You may have hit on something didn't thing of. My crush plate is aluminum Bet it can't weight 3 lb.
My reson for moving the CG forward. I've flown the airplane for over 7 years with the aft cg. I learned to live with it. My landing were always a sight to behold. Then I flew a 6 with a metal prop and a cg in the center of the range and wow it was a different plane. I'm at the age were I don't need the excitement of landing with an aft cg any more. My son will be flying my 6 now that he has his ticket and I just want the cg were it should be.
I have never had a 200 lb passenger but with one that was 180 lb and full tanks with a tent and other camping stuff (less that 60 lb.) we were aft cg.
One guy suggested I add a second battery on top of the battery case.
Thanks for the help guys.
Rich
RV6 N721ET
 
RV-6(A) CG

Rich, I got a buddy in the Tool & Die business, I gave him my aluminum crush plate and he made the SS plate for me. He actually made 2........... one 5 lb (about 7" in dia.) and the 9 lb (about 9" in dia.) both made from 1/2" SS plate. You can do a little math work and figure weight by thickness and diameter etc. A cubic foot of SS weighs about 490 lbs.

I didn't mention that I also have an aux. battery mounted on the inside of the firewall (powers my emergency bus) that probably weighs 8-9 lbs which, of course, helps the CG also.
 
Move the baggage

Try putting your heavier baggage items into smaller duffel bags, like gym bag size, and putting them forward of the seat under your knees.

Make sure the bags can't move forward, use some nylon webbing or perhaps whip up something out of the bungee netting they make those doo hickies for pick 'em up truck tail gates out of.
 
19 pound crush plate

My RV6A with a wooden prop had a one pound aluminum crush plate. Changing to a 19 pound crush plate put it right at center CG. Added benefit is it flies like it has an autopilot. Well worth the $400 expense.
 
Empennage tips

Out of interest I weighed the fibreglass tips, they came out at about 1.5 pounds. Has anybody experimented with carbonfibre tips? Half a pound saved at the rear is worth about 7 pounds added to the front on the fifteen to one theory.
 
My RV-6 has a Landoll inertia ring on the flywheel. I also swapped the stock Van's tailwheel for a lighter weight composite one with sealed bearings from Flyboy Accessories, which surely helped as it reduced tailwheel weight by about 6 ounces.
 
walkman said:
Try putting your heavier baggage items into smaller duffel bags, like gym bag size, and putting them forward of the seat under your knees.

Make sure the bags can't move forward, use some nylon webbing or perhaps whip up something out of the bungee netting they make those doo hickies for pick 'em up truck tail gates out of.
Click to expand...

http://www.vansairforce.com/community/showpost.php?p=551483&postcount=3

I did the same thing. Even going so far as putting in straps on the center floor between the rudder pedals to strap the tent bag (with tie down, hammer and flashlight). This moved 15 pounds forward. Note: my RV-6 has the battery forward of the firewall which allows me to do this.
 
Another good option for bringing weight forward is a set of Bison Mountain bags for behind your seats. They straddle the flap tube, and snug up to he back of your seats. I put the heavy stuff in them, and then the lighter stuff like sleeping bags at the back of the baggage compartment.

Putting small duffles with heavy stuff just ahead of the spar works too. Water bottles, your wife's purse, etc. :) I keep meaning to draw up a design for a custom bag to fit that space, that you could attach with velcro straps that went under the seat... I keep forgetting to do it though.
 
Way back in the mid-80's, there was a standard cowl and a Constant Speed cowl. The standard cowl was used with a prop extension and wood prop. Not sure how much that helped with CG but my guess is that it would help move the CG closer to the range that exists with the CS prop on an RV-6. I know a friend that had an RV-4 with the standard cowl that had an extended hub CS prop like the Sam James cowl uses.

This may be more work than one wants to do on a flying RV-6 but if someone is building, it could be an option. I am sure that Van no longer has the old cowl but the Sam James cowl with a longer prop extension should help without bolting Lead ballast to the engine.
 
What about using the RV-9 "long" engine mount? The one they intended for the O-235.

And how about changing out those .025" baggage compartment sides to .016". I guess that isn't going to make much difference, but I thought I'd toss that idea in. I can't see why those panels are that heavy.

It is a pitty the RV-6 doesn't have a forward baggage compartment like the RV-8.....

Andrew.
 
Kiwi said:
It is a pitty the RV-6 doesn't have a forward baggage compartment like the RV-8.....
Click to expand...

No kidding. My RV-6 has a good portion of empty space just between the firewall and the first bulkhead, above the rudder pedals, that possibly could have been turned into a skinny, but still useful storage area. Cutting a baggage door in the top skin like on an RV-8, might have weakened the structure too much, though.
 
Luggage CG

Neal@F14 said:
No kidding. My RV-6 has a good portion of empty space just between the firewall and the first bulkhead, above the rudder pedals, that possibly could have been turned into a skinny, but still useful storage area. Cutting a baggage door in the top skin like on an RV-8, might have weakened the structure too much, though.
Click to expand...

Good point Neil. RV's are experimental although the engineering of the basic structure is there for a reason. In some areas, a modification may compromise the strength. I have seen hatches installed ahead of the windscreen for avionic access.
 
NickAir said:
Good point Neil. RV's are experimental although the engineering of the basic structure is there for a reason. In some areas, a modification may compromise the strength. I have seen hatches installed ahead of the windscreen for avionic access.
Click to expand...

Yep, and a significant portion of what Van engineered into these planes isn't there just for in-flight strength either, it's also there for crashworthiness protective measures too.
 
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