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Weight & Balance

L

LarryT

Well Known Member
Preface:
After reviewing "as built" weight & balance info on Dan C.'s website, I am trying to do some advance planning.

It does not appear to be possible to build a -7 at the forward end of the CG envelope. The most forward empty CG listed is 77.65. For a 160 lb. pilot and 20 gallons, I calculated the CG as 80.16, which is aft of the forward aerobatic CG.

My problem is the opposite. At 6'4" and 240Lbs. I won't have any trouble w/ W&B falling in the aero CG envelope solo. However, since the pilot and passenger sit 20" aft of the empty CG, my concern is X-C flying with baggage. At the end of a trip with my average weight spouse, with minimum fuel and 100Lbs. baggage, it seems that we will be right at the aft CG limit. Were I to travel with a heavier passenger (e.g., my 6'8" 240 lb. son) we would absolutely be behind the aft CG limit.

Question:
The other day there was a thread about consideration of using a "long" Vans cowl and 320 engine mount with the 360 engine. This would appear to have the potential of addressing this issue. Rough calculations suggest that moving the engine/propeller combination 2" forward would move the empty aircraft CG forward about 2/3". Could the individual who made this suggestion please comment on both the degree of difficulty and the plausibility of doing this. Is it reasonable that the engine mount could handle the extra torque and weight of the 180 hp engine? I gather from another thread that there are not any SJ cowls that would accommodate this suggestion?

Larry Tompkins

currently constructing wings
 
I don't know how to answer your question about whether or not you can do it...but I wouldn't even consider it without some engineering knowledge being applied to the problem. I can foresee lots of problems with your arrangement...custom fitting the cowl, FAB, and plenum (or baffles) would suck. Not to mention that you'd have a heavy engine hanging on a mount that's built for a slightly lighter engine.

A simple solution to your problem would be to add a weighted spacer between the prop and flange. I'm going with a Catto prop and if I have CG issues I will put the 20 lb. spacer on. I've heard it can move your Aft CG forward more than an inch.
 
The most forward empty CG listed is 77.65. For a 160 lb. pilot and 20 gallons, I calculated the CG as 80.16, which is aft of the forward aerobatic CG.
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Larry,

I think you made an error in you calculation. You will be with-in acro limits in that senerio, I get (actualy Dan's calulator got) 79.17.

Click on the 'N' number of the aircraft in question. You can do 'what-if' weight senerios. Good luck.
 
I'm the one that was questioning the 360 on the 320/7 mount (it is 2" longer than the standard 360/7 mount)...I've talked to Gus about it, and there is no problem with the mount and engine as far as engineering goes. The problem appears to be with the FAB or the fuel injector servo interferring with the bottom Van's cowl.

I've done more research on the James cowl with this combo, and it appears that the 360 on the long mount will work...there's a lot of room in the bottom SJ carb cowl. Gus did tell me that the Van's cowl will flat out not work with the 360, either O or IO. He said that the 320 with a carb is the only engine that will fit the Van's cowl with the long mount. The IO-320 uses the same FI servo as the 360, and is too tall.

The long SJ carb cowl will for sure work for the O/IO-320. jconard on here has the long SJ cowl with an O-320. He says the FI servo will fit as well with no issues for the 320...so, in theory, so should the 360. Will James told me that the 360 FAB won't fit, but it appears that it would seeing the amount of space in the bottom half.

The engines are within several (8-10 on average) pounds of each other, bare, parallel valve.
 
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Thanks Chad...I guess my point was that adding a weighted spacer to the prop flange would be way easier than all the modifications you mentioned. It can be done, as you pointed out, but it doesn't appear to be the easiest route to take if all you're doing is addressing a CG issue.
 
Just to be clear for others....the Vans FAB will NOT fit the normal James cowl with the long mount, but the cowl comes with the james FAB setup, and it will fit.

Actually we looked and poked at mine over the weekend to measure clearances on my 320...particularly at the front corners because the 360 is wider than the 320, though the length is the same. I have an easy inch of clearance at the front of both valve covers on the forward cylinders...so I am pretty sure there is plenty of clearance for the 360 which is a little less than 1/2 inch wider on each side.

I love the free space behind the engine!
 
lostpilot28 said:
Thanks Chad...I guess my point was that adding a weighted spacer to the prop flange would be way easier than all the modifications you mentioned. It can be done, as you pointed out, but it doesn't appear to be the easiest route to take if all you're doing is addressing a CG issue.
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Totally agree Sonny. I plan to use a weighted spacer as well up front to aid CG.:cool:

The mods are just a "could be necessary" issue for fitting the SJ cowl. John (jconard) has been a tremendous help in helping me (us) figure this long mount thing out with the SJ cowl. Make it fit!:D
 
I used the wrong fuel moment arm.

You are correct. I had the wrong moment arm for fuel CG.

In my case, I will hang a CS prop on the front if I have to. At least I will get some take-off and climp advantage from the weight.

If there were drawings with good section data at various stations, we could figure the clearance issues out a lot easier.

Larry
 
Developing stations/sections

If there is soomeone close to Vancouver, WA. with a 320 or 360 installation, I would be willing to measure and develop section drawings with stations referenced to the firewall. And make them available to listers.

Larry
 
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