Cg & all

[HansLab]

All, I have a question:
Now that the PH-FOX has flown some 10 hours, it is time for me to solve this queeste. The CG is pretty forward. The plane is build per manual. Trim with the flapperons.
Now when I fly on my own, the flapperons are some 8+ degrees UP.....And she's in perfect harmony: she flies hands-off. But there is much drag from the flapperons that way. I lowered the elevator one hole (one to go), and it made some difference (not much). Flying two pob I trim more aft, and the flapperrons are almost 0- degrees, hands-off.
Now I wonder: shouldn't it make difference to move weight aft? And if so, what to choose.....the plane is build per manual, you guys don't have the same, have you? And there's added weight in the back: rudderhorns and elevator and stabilo all have profiles, the ACL techniques are in the back - what can I do?

[Av8r3400]

Hans, is your plane a tail dragger or tricycle gear?

[Danzer1]

His photo album shows taildragger, model IV, speedster wings and with Grove gear and a 912 UL - assuming we are talking about that aircraft.

Hans - please clarifly. And it would also be helpful if you posted your empty weight and balance numbers.

[HighWing]

Hans,

Lots of thoughts here. Where is your battery? This might not be the simplest solution, but if your battery is forward of the forewall, moving it aft would help some. You can check the results by manipulating the CG spreadsheet.

When I built my recently completed Model IV, I moved the engine forward 2-1/2 inches to help compensate for the fully ribbed and faired empennage with ruddder and elevator trim - I did the math. My final CG calculations put me pretty much where you are and like you I wasn't quite comfortable with it for a number of reasons. My battery was already behind the firewall and I didn't want to mess with a new mounting tray and the run of the wire so left it there. What I did is prepare some lead that I could bolt to the tailwheel spring bolt. With an arm of 11 feet, it was the best location to put the least amount of "dead" weight. Future plans call for a pneumatic tailwheel which should eliminate most of that weight.

A friend who built a Series V with O235 decided to fix a tool box to the aft edge of his baggage floor and filled it with tools he thought he might need. It was placarded as mandatory when not carrying baggage. Then when he was on a cross country with significant weight back there, he felt free to lighten that according to his CG needs. Just some ideas.

[HansLab]

Thank you for thinking ahead!
The FOX is a taildragger, the battery is behind the FW: cockpit-side. Enclosed the drawing we made during W&B, before I attached the wheel pants...(behind CG).
Measures in millimeters and kilograms (!)
Adding lead is an option - but I consider it as one of the last: firstly this bird isn't one of the most light-build, and secondly I can't stand having build an airplane that isn't balanced whilst building per manual.

[t j]

Hans, am I correct that your Empty weight is 327 kg and empty CG is 285 mm? For us that is 719 pounds and 11.2 inches.

For a reference point, My Classic four is 547 (249 Kg) empty and empty CG is 12.5 inches (317 mm). First flight with horizontal stab in top hole required slight forward stick pressure for level flight. I have no + (up) flaperon rigged. Moved horizontal down one hole and level flight was hands off.

Everything that is put in the airplane (passenger or baggage or fuel) moves the CG back. I have no need for trim solo up and only slight down flaperon trim for level flight at all combinations of loading weight.

I would do some test flights with increasing weight in the baggage sack to get an idea of how much weight you need and where. When you find the weight needed in the baggage to fly hands off compute the CG arm with only that weight in the airplane. That will give you a new target empty CG arm to shoot for.

For what its worth. A friend built an RV 7 with same problem you have. His solution was a 5 gallon collapsible plastic water jug behind the back seat for solo. When he picked up a passenger or cargo he dumped the water out of the jug.

[jtpitkin06]

Hans,

Let's say you decide to move a 13 kg battery from above your knees to behind the seat... about one meter. That will shift the empty weight CG 40 mm aft. It will also add weight to the aircraft because you will need longer battery cables and other wiring. It's a lot of work.

Adding weight to the tail spring bolt is 13 times more effective. So if moving the battery added only 1 kg of new cables you could accomplish the same CG shift without moving the battery and adding the same one kg to the tail.

Adding weight to the tail is simple and you can easily change the weight after a flight test to fine tune the amount needed.

John Pitkin
Greenville, Texas

[HansLab]

Thank you all for thinking with me.
Adding weight was something I simply did not think about..;-(
Looking at the CG drawing I calculate that there should be some 2,5 - 3 KG's added on the tailwheel......;-( to get the flapperons more or less 0 degrees per manual.

Does that much sound familiar to you? And some practical question: how do I get it there - and hold it there...?

And another one: how did the nose-weight get there? There's a quite common 912 with oil cooler and Grove gear in the front, but that's about it. No IFA stuff, no thermostats (yet), battery behind the FW....

[t j]

In need to change my post (#6) from First flight with horizontal stab in top hole required slight forward stick pressure for level flight. To required slight back stick pressure for level flight.

[t j]

I calculate 3kg on the tail wheel will bring the empty CG back to 319 mm (12.5 in.). That sounds good to me.

When people were putting Subaru engines in model 4's I remember some reports of empty CG arms in front of the forward CG limit. Of course they would sweep wings forward and install the battery on the tail to get the loaded plane within CG limits.