So this is more of a theory but I’m prepared to be shot down or for someone to tell me this isn’t permitted.

In doing some research to move CG i was reading about how the side panels and foam on the extended baggage weigh an extra 12 lbs. I believe the floor is the limiting factor of the Selkirk baggage mod, so adding more panels and structure wouldn’t take away from your permissible 50 lbs in the baggage.

So this got me thinking one step farther. The Selkirk foam isn’t necessary special foam or a specific part of a stc right? I’ve heard people sourcing foam from other places so I’m thinking it is a basic product. What would keep someone from using a product like Dynamat on an airplane for foam? A little more research revealed they make a product now called Dynapad. If your not familiar these products are used for noise reduction in cars and homes. The Dynapad material weighs 1 pound per sq foot. Instead of foam, why couldn’t you Dynapad? With side panels and foam, it looks like a way one could add 20 pounds at station 123 while still legally being able to load 50 lbs of baggage.

A total of 70 lb would move cg 2.2”. A big help for most people with cg issues. Anyway, just a thought.. what do people think?

https://www.dynamat.com/products/dynapa ... automotive

I also have to say that as far as CG is concerned, firewall battery mod seems pretty stupid. Moves CG approximately 1.7 in the wrong direction to save weight… so you can just add at least 50 lbs back to balance it. Yes your weight scorecard looks good before you add ballast and Yes there are other benefits like flat extended baggage but I’m not sure I would do it again. Who cares about flat baggage when the whole compartment is just stuffed with survival kits and tool boxes anyway.

I don't have a opinion on the concept for the use of a different product other than any "burn cert" requirements.

On the battery discussion and as someone who is constantly searching for weight reduction the battery move is a win, EarthX even better. A empty forward CG issue is really only a concern if your operating, empty and how often does that happen. Too your point adding "installed" ballast seems a bit counter-intuitive and I agree whole hearty. I have an empty forward CG, I resolve it with "loading planning" and its never been a limiting factor for me. On a related theme, why go to the trouble of installing an extended baggage area only to loose the gains by adding "fixed" weight. Just carry something useful back there in the newly created space, adult beverages of your preference etc.

For most planes in the fleet burn certs arnt really a factor, and if you want them easy to get, and most quality automotive stuff you’ll find will pass anyways

https://www.avweb.com/features_old/inte ... -aircraft/

I’m not sure how much the Selkirk foam weighs but dynamat is not exactly a featherweight ether

In real life a forward CG is not so bad. When I am empty two big guys and full tanks I am outside the envelope. Add tools and emmergency kit in the extended baggage and I am fine.

But 99% of my flying is about going places with a load and it is never a problem. I thought it would really bug me but it just never does.

If you want to compete in STOL competition it is probably not for you, but I think in the real world it is not a problem.

Is you CG that far forward that you need 70 lbs in the extended baggage to fix it?? I would recheck the math. How is your trim set in level flight? I would say if you agree if you need extra weight in the back make it something useful. DENNY

Yeah it flies very nose heavy even with MT prop. I hit the trim stop on every landing. For instance, Me and full fuel and I’m required to add 20 lbs in the extended baggage just to stay legal.

Right now, my survival and tool kit and case of oil will always be back there which will help. But it’s still not really optimal. Maybe for most people it doesn’t really matter, but I just enjoy hypothesizing and working to make the plane fly better. So that’s why I thought of the dynamat product.

I have a similar CG problem with my 170B. I need 25lbs at the back of my extended baggage when flying solo to stay inside the envelope. Currently I keep tools, covers, and a folding bike tucked into my extended baggage which keeps me and a passenger inside the envelope.

That said. I'd rather avoid hauling weight around for no reason. I have plans for a baby bushwheel + T3 for the added weight in the tail. Isn't there a 10" tailwheel option on the 185?

I have heard rumors of people filling the tailwheel with antifreeze....

In my amphib 185 the last thing I need is to push the CG forward as well

The ABW big fork is a great mode for cg, adding some extra weight about as far back as possible.

DENNY wrote:Is you CG that far forward that you need 70 lbs in the extended baggage to fix it?? I would recheck the math. How is your trim set in level flight? I would say if you agree if you need extra weight in the back make it something useful. DENNY

Mine is, when I put another person in the front seat. 60# is enough when I’m solo…



I’m 6’8” and 310#.

DENNY wrote:Is you CG that far forward that you need 70 lbs in the extended baggage to fix it?? I would recheck the math....

I'm curious what your empty weight & CG is?
And what is the CG envelope for your airplane?
FWIW the empty CG on my early C180 is 34.9"-- just about at the forward edge of the CG envelope (35" > 45.8")
Everything that goes in is aft of that empty CG-- front seaters at 36",
fuel at 48", back seaters at 70", baggage at 95", extended baggage at 124".
When light the CG is pretty far forward....but that does give me a lot of flexibility when loading up..

I'd second the suggestion that you balance the airplane as required with something useful as well as removable--
tools, survival kit, etc-- instead of heavy insulation or other permanent-ish ballast.

I bet 8.50x6s in place of those bush wheels would move the CG a fair amount

AEROPOD wrote:I bet 8.50x6s in place of those bush wheels would move the CG a fair amount

Dunno about the OP's plane, but I just did the math on my own airplane--
If I remove the 850 airtracs (32 pounds at 18"),
and add a pair of standard 29" BW's (62#),
the CG only moves about 3/10 of an inch forward.

Yeah the BW really don’t move it much. I saw the same move on my WB. Pretty minimal. Firewall battery moves it 2 inches in comparison. I used to think “an extra 16 lbs at -2 isn’t so much” but I wasn’t fully grasping that the important distance isn’t from the firewall but from the current CG. So the odyssey is actually about 36-37” from cg and definitely makes cg move the wrong way in combination with weight loss in the back.

Another issue Hot Rod, is that even though everything you add to the back is behind the cg, it doesn’t mean it won’t be too far forward. The graph has an angle on the upper portion of weights, so if you just add two heavy people and gas, you will move too far vertically on the WB graph and out of the envelope. On the picture below, the orange dot is with 2 x 200lb people. The next dot is with full fuel. I’m wayyyyy out there. My cg is 34.8 empty. So it’s not that crazy far forward and I imagine lots of people with modified wagons, especially 182s, are pretty similar.

You're right.
My airplane is 1652 empty at 34.6" CG.
Two pilots at 170# each & 40 gallons fuel adds up to 2232# & 36.2" CG--
just barely within (or maybe just forward of) the envelope.
Except my usual 20# or so of stuff in the extended baggage at 124"
makes it 2252# & 37.0" CG....in the envelope.
And plenty of room farther aft in the envelope to carry my anvil collection in back.

I don't recall if you said you have a firewall battery or not.
If you do, your easiest CG solution would be to relocate it to the back again.
Otherwise, just carry a big survival kit in back, as others have suggested.

Yup I do. Firewall battery moved it 2” forward. Pretty big move.. My new ballast includes all the goodies and weighs 50 lbs, tent, rations, backcountry tie downs, alight air compressor, tools, everything one would need. Moves cg 2.4”. It might be a little overkill but it’s all really nice to have. I could stack them and keep it 10” behind the center of extended baggage. I like it but wondering if the hard cases are maybe a bad idea. At least they are tied down well.