Wa180 wrote:I am working a W&B problem for my SkyWagon and wondering how others look at this... f I add Wing-X STOL it looks to help a lot, the 300# upgross allows more ballast with fuel. How are others overcoming this problem?

Rod, I forget what model 180 you have, but the Kenmore GW STC is a great STC. It requires a doubler on the horiz stab and running the bigger 185 V stab. This will get you to 3190 with the added benefit of a couple more lbs way back in the tail. The only rub is the cost of the Stabs as they are getting really rare. Also, you will most likely need the 3 bolt stab rather than the more common 4 bolt. They were $6-$8k the last time I priced one for a customer.

DENNY wrote:If I was going exp and needed to fix CG I would make tool bag and emergency gear part of required equipment and put it in the tail, or as far back as possible to solve CG.
DENNY

DENNY, this was pretty much exactly what my thoughts were about at the onset... The fact is that a toolbag, no matter how heavy wont make much of a difference at all, at least that is what I was trying to show.

I think we all have this idea that these gutting these birds aft of the datum is ok because somehow we will then have the ability to load it up in the back... and Hotrod's post proves my point. This is a fairly common misconception. The fact is that if you have a CG right up against it empty, than there is pretty much NO WAY you can legally move it past say the middle of the box.

Don't get me wrong, Im not saying that we shouldn't take weight out... we should. Just so happens that the weight that we can take out is pretty much all aft of the datum. Just go in eyes open knowing that everything is a compromise. If you gut your bird like a mad man and make it really light, it will have a FWD CG and you will most likely pay for it in other places... but for what we like to do, playing in the short stuff, these are usually worth while.

Actually Im not sure exactly what my point is, other than just an observation.

NET NET, I believe that taking as much weight out of these birds as we can is a good thing. If we can afford to pay someone to do it or can do it ourselves, go for it. Ounces equals pounds, and pounds equal performance. No one can argue this point... It comes down to how much it matters to you. After swallowing this, its important to then remember that the bird will carry it and perform regardless. It's a testament to the engineers. Lots of guys out there doing amazing things with bone stock birds for sure... but with an even lighter and capable machine, those same guys could do even more amazing things.

Double

Wa180 wrote:I am working a W&B problem for my SkyWagon and wondering how others look at this.

I have done a few mods; firewall battery, airglas extended baggage, removed dead avionics and wiring, and I sit at 1749#. This should be pretty accurate as it was scale weighed shortly before I purchased it.

I put the two fatties, my flying buddy and I, up front, ~220# each, then my daughter, ~120#, in the back seat, and 100# of ballast in the baggage areas, leaves me only room for 35 gallons. Any more than that and my COG is out the front. Looking at it my 172 works out better, except for time, to fly than the SkyWagon.

If I add Wing-X STOL it looks to help a lot, the 300# upgross allows more ballast with fuel.

How are others overcoming this problem?

Rod

Why does it only leave you so much for fuel? Are you at max gross then? Adding fuel should move th CG back, not forward... doesn't help if your already at GW though.

Well with Greg's observations it got me wondering what the empty weight CG numbers were on all our airplanes back in the day when they were light and hadn't started "eating/gaining weight yet. Just wondering....

Kurt

BigRenna, the Kenmore STC starts at G models, and mines an E. ;-(

I believe the actual weighing was a valid one, and I have double checked their numbers and it works out. I might do a “test” weigh-in in the hangar to see if I can get the same thing.

Here’s weight, COG, and arm from the last change we did; 1748.68 32.64 57,072.21

I do run out of UL before I can get much fuel in, especially with 3 people.

I hope someone can find an error in my calcs because that would be really helpful!

R

Wa180 wrote:….Here’s weight, COG, and arm from the last change we did; 1748.68 32.64 57,072.21 ....

I did some math using your figures.
350# of front seaters and 240
# of fuel outs you at 2338# and 34.7" CG-- still out of the envelope forward.
However, add 100# of gear at station 95" and now you're 2438# and 37.2" CG--
well within the envelope.
So an aft-ish load can make a notable difference.
That same 100# of gear in an extended baggage back at around 124" would make even more of a differnce.

That 32.64" CG still seems off to me though--
maybe some other slywagon owners could post their empty weight and CG for comparison.
Like I said before, mine's 1652# and 34.62" CG.

Wa180 wrote:BigRenna, the Kenmore STC starts at G models, and mines an E. ;-(

I believe the actual weighing was a valid one, and I have double checked their numbers and it works out. I might do a “test” weigh-in in the hangar to see if I can get the same thing.

Here’s weight, COG, and arm from the last change we did; 1748.68 32.64 57,072.21

I do run out of UL before I can get much fuel in, especially with 3 people.

I hope someone can find an error in my calcs because that would be really helpful!

R

That seems very far ahead. My 62 E model with a 3 blade hartzell and FW mounted battery was 1750 and in the 34" range...

Wa180 wrote:...Here’s weight, COG, and arm from the last change we did; 1748.68 32.64 57,072.21... I hope someone can find an error in my calcs because that would be really helpful!

It's hard to say w/out seeing the bird in person and looking it all over. But one easy upgrade that helps with C.G. is to go with the ABI wide fork and run the 400x4 tire/tube. This is about 3 lbs heavier than stock and gives you about 1 more inch of total arm aft.

With respect to your question, I would say:

1) anytime I see a W&B where the mech lists the weight out two decimal points causes me to scratch my head. First that degree of accuracy wont make a lick of difference, and second it tends to induce all kinds errors downstream. That alone would make me want to weigh the bird again.

2) I have seen all kinds of errors in all knids of places... not just with math. I just weighed a Skywgaon where the numbers added up, but didnt make any sense. The last mech didnt apply a "common sense" test to his figures. Turns out he had used a measurement of 22" aft of the datum for the tires rather than 18", and a TW measurement 5 ish" shorter than it measured out when I plumbed the bird on the floor. This caused a 4" aft error in the C.G. If it seems weird, it usually is.

3) W/out looking at the bird, my gut says that such a FWD C.G. seems wrong. The envelope for your bird is 34.5" - 45.8". At 32.64, you are not legal at all. Lets say you are 200 lbs sitting at Sta. 36... With only unusable, you are illegal at 32.97. Now add 20 gal... 33.13 (still out.) You get where Im going. If the numbers are right, you would not get legal until you had at least 37 gal of fuel in the wings.

Here is a common sense test:

For reference, I have a 1966 180H. The orig WB sheet from Cessna (below) weighed in at 1632 with a C.G. of 35.9. You report the C.G. at 32.64. In order to get the C.G. of my orig. airplane to shift that far forward, I would have to gut 80 lbs out of Sta. 100. (roughly the standard rear baggage.) Impossible right?

I did some pretty heavy dieting on my bird. On 8.5x6 tires, she is 1744 lbs. This is my "utility" weight w/ no rear seats etc... The bird has fwd battery, no interior, wingX, Sprotsman, etc etc etc... I consider it very light for an H model considering its got most of the "bush" mods a fool could waste his money on. The C.G. is 36.01, which is 0.1" away from Cessna's orig calculation.

I guess what I am saying is that the numbers dont "seem" to be right... but that doesnt mean they arent. Certainly grounds for a closer look.

Again, Im not yapping about all of this for any particular reason other than to bring awareness to what these mods may or may not do. Im in the middle of an engine swap which is going to add much more weight in the wrong direction. SPW engine mt, back to orig starter, 2-3 blade MT, air/oil sep, heavier mags (Shower of Spks,) etc... which will move the C.G. a bit more FWD.

If all else fails and you dont want to bother with any of this... you can always just pick up one of my T's (Below.) I hear it makes everything work out fine. https://www.avthreads.com/products/if-it-fits-itll-fly-mens-t?variant=18788707845



This is the Scale Sheet I made that I use when I weigh birds. It lays out how Cessna wants you to do it.




https://www.avthreads.com/products/if-it-fits-itll-fly-mens-t?variant=18788707845

Greg, wouldn't having the gear further back and a shorter tailwheel length move the C.G. fwd? So when fixed it would move it rearward? Not sure why it would cause him to be flying out the fwd side of his CG, but on reasonably new to this. Love learning these math problems.
What is the arm of the gear on the early 180s? I think it's pretty close to 22".

A1Skinner wrote:Greg, wouldn't having the gear further back and a shorter tailwheel length move the C.G. fwd?

If you do out the math, the CG would move aft. Using the scale sheet (which is just hypothetical and not the bird I was speaking of) it reads 36.72. Now if you use a 22" MGL and then 237.5 for the balance to the TW. You get 150 lbs x 237.5 = 35625. Then divide by weight (1975) to get 18.04. Then add the distance from datum to MGL (incorrect of 22) and you get 40.04. CG moves aft.

The point that I think is important is that the numbers worked out, but the C.G. was wrong because someone used the wrong data as a baseline. This stuff happens all the time and important to keep an eye out for.

I forget about 170's and early 180's (someone here will know,) but I believe there were some that had a further aft MGL, but this was then moved to 18" to prevent nosing over.

I might mention that the folks at Seaplanes North (lake hood) sell a small tire that's the same dimensions as a baby bushwheel (actually they were selling it before the bushwheel came out), and being a tube/tire it might be a tad heavier, and it wears WAY better, and it's about 1/4 the price. Here is what it looks like:

Thread drift:
From a STOL competition standpoint adding a big tailwheel will stall hurt AOA. If you look around you can usually find a tire that will fit the wide fork but not sit as high. For play/work off field I prefer a big tire.
DENNY

Bigrenna wrote:

A1Skinner wrote:Greg, wouldn't having the gear further back and a shorter tailwheel length move the C.G. fwd?

If you do out the math, the CG would move aft. Using the scale sheet (which is just hypothetical and not the bird I was speaking of) it reads 36.72. Now if you use a 22" MGL and then 237.5 for the balance to the TW. You get 150 lbs x 237.5 = 35625. Then divide by weight (1975) to get 18.04. Then add the distance from datum to MGL (incorrect of 22) and you get 40.04. CG moves aft.

The point that I think is important is that the numbers worked out, but the C.G. was wrong because someone used the wrong data as a baseline. This stuff happens all the time and important to keep an eye out for.

I forget about 170's and early 180's (someone here will know,) but I believe there were some that had a further aft MGL, but this was then moved to 18" to prevent nosing over.

Thanks. Ya it's very easy to make mistakes. Doesn't help that a lot of schools dont teach how to plumb bob and actually measure. I did it with a few of my class mates because I've done it before. But everyone else just went off the numbers on th old W&B, which were wrong. It was an early model that had later gear on it. The only reason that as found out was because I actually did the measurements.
Great topic you are bringing up here.

I am pleased to say that we did several weighting’s on shop planes using plumb bob and the maint manual process in school. Won’t say we always got the maths correct afterwards, but I do believe we got the process correct. I have mine in a spreadsheet to help cut down on mathematical errors, that’s why things go to 2 places, but garbage in garbage out of the recent weigh-in of my plane was boogered up.

I haven’t had a chance to go back through all the W&B for a sanity check on my 180, but will this afternoon.

For reference, I have Gar-Aero adapters and 8.5x10 mains, and baby bushwheel on the back. I am going to get a hold of that ribbed tire AKSchu showed.

R

Wa180 wrote:I haven’t had a chance to go back through all the W&B for a sanity check on my 180, but will this afternoon.

I would strongly recommend you get her on the scales again. Only way to really know for sure.

Wa180 wrote:...I am going to get a hold of that ribbed tire AKSchu showed.

FWIW... the ABI TW fork I am talking about allows for both the Babybushwheel or a 400x4 tire. This is what I run most of the time because it wears like iron. Same idea but its STC'd.

Bigrenna wrote:FWIW... the ABI TW fork I am talking about allows for both the Babybushwheel or a 400x4 tire. This is what I run most of the time because it wears like iron. Same idea but its STC'd.

I have the ABI fork with a baby bushwheel, and purchased the 4.00x4 tire / tube from them, but it seemed like it would be stretched to much by putting it on the wheel. I talked to ABI and they said it would work, but I never got back to it.

R

Has anyone tried foam filling their tailwheel tire? Definitely adds weight and makes the tire flat proof. Possible legal issues but adding weight to an area that is more designed for stress.

Wa180 wrote:

Bigrenna wrote:FWIW... the ABI TW fork I am talking about allows for both the Babybushwheel or a 400x4 tire. This is what I run most of the time because it wears like iron. Same idea but its STC'd.

I have the ABI fork with a baby bushwheel, and purchased the 4.00x4 tire / tube from them, but it seemed like it would be stretched to much by putting it on the wheel. I talked to ABI and they said it would work, but I never got back to it.

R

We've put them in a few planes. Use lots of talc powder and it'll mount up on the bead. Without it wont.

Original factory W&B



Sept 21, 2015 Wegh-In



The biggest movement was replacing the battery with the firewall battery. That alone moved my COG almost 2" forward.

List of changes to W&B ( I just put weights and arms )

1788.0 34.5 61632.4
-5.0 44.0 -220.0
-3.2 44.0 -138.6
2.4 44.0 105.6
2.4 44.0 103.4
-3.9 17.0 -66.3
-1.4 17.0 -23.8
-4.1 17.0 -68.9
-1.2 17.0 -20.4
-18.7 26.0 -484.9
-1.3 20.0 -25.0
-0.2 20.0 -4.0
3.4 17.0 57.5
0.3 20.0 5.0
2.3 17.0 38.3
0.8 17.0 12.8
2.0 17.0 34.0
-2.8 114.0 -313.5
-29.2 114.0 -3323.1
-1.7 114.0 -193.8
3.0 -3.0 -9.0
14.5 -3.0 -43.5
0.7 183.0 125.8
-15.0 -2.0 30.0
-1.3 -2.0 2.6
-1.1 -1.0 1.1
10.0 -2.0 -20.0
2.6 -2.0 -5.2
1.0 -1.0 -1.0
1.0 17.0 17.0
1.0 -8.0 -8.0
1.5 17.0 25.5
2.0 -24.0 -48.0
1748.9 32.7 57173.9

Rod