1deg. Forward sweep vs. straight wing.

[ghillifox]

can someone please shed some light on how the straight wing kitfox has the same forward cg. Limit as the 1deg.forward swept wing.
Why would you sweep the wing for heavier engines if it all stayes the same.
i have a model 5 with an o-290 d2. Ready for first flight with new engine.
it weighed 919 empty. But the cg. Is out the front.
my manual says .9.96 most forward, which is back from a straight wing series 7. (9.5).
allready have a 25 lb battery in the tail.
maybe you IO240. Guys can straighten me out.

[GuppyWN]

Heavier up front. Forward sweep to counter it. Same same. It's just math.

[PapuaPilot]

It appears a swept wing model 5 has a different CG range than the model 7. I can't find the information for the straight wing model 5, but you have the correct number of 9.96" for the forward CG with the 1 degree sweep.

What EWCG did you end up with, you only mention the EW?

My original EWCG was 8.11" @ 887 lbs, which put the plane exactly at 9.96" for the max forward CG calculation. Remember that you still need to put some fuel and a pilot in the plane, which will move the CG aft. It looks like you need an EWCG of 8.10" or more. It may require some ballast in the tail.

[ghillifox]

431. -2.0
441. -2.0
47. 168.0
—————————
919.0. Ewcg 6.69
These are my numbers .
Do the arms look correct.


What at is it about the series 7 that allows it to have a more forward cg. Limit, than the series5.
thanks Jared hatch.
Kitfox5 o-290d2.

[PapuaPilot]

Your stations are right and the calculation is correct. I think I would have ended up in the same boat if I hadn't aggressively worked at lightening anything I could firewall forward and putting anything possible as far aft as I could. As it stands you need about 10# of ballast way back in the tail.

What can you lighten up, change or eliminate at the front end? Alternator, mags, vacuum pump, instruments? What does your prop weigh? If you have a metal prop, replace it with a wood or composite one. Otherwise you are going to be ballasting the tail. Do you have a T3 tailwheel spring? That could add about 4# to the tail and be useful.

Now that you have the EW and EWCG you can crunch the numbers and see how any change affects the EWCG.

Best of luck.

[jrevens]

[QUOTE=ghillifox ...
What at is it about the series 7 that allows it to have a more forward cg. Limit, than the series5.
thanks Jared hatch.
Kitfox5 o-290d2.[/QUOTE]

larger tail surfaces?

[jiott]

FWIW, wing sweep affects center-of-lift maybe more than CG. The relationship between center-of-lift and CG affects how the plane flies and its stability. I don't pretend to know how this interrelates, but do believe that wing sweep with heavier engines may involve more than just CG location.

[ghillifox]

Thanks all, I guess lead in the ass it is.
at least it’s not the stealing moonshine kind of lead in the ass.

[PapuaPilot]

larger tail surfaces?

It would be good to know if this is true. I upgraded to the larger elevator and am wondering if my plane has a different CG envelope than a standard model 5 with a negative 1 degree sweep.

Yo, Brandon . . .

[alexM]

I just had my series 5 manual open last night and was reading way ahead (I like to know how the story ends). It has the CG information in the very back in the section for getting the plane ready for test flying.
CG is different (relative to the theoretical datum) with the forward wing sweep because it is shifting the center of lift forward (wing sweep) and center of gravity of course because the heavier mass up front.
For the CG limits to be the same the datum would have to move also, but the datum is arbitrary. For example with the products produced by my employer the datum is about 20' ahead of the airplane. For others it's the firewall or the leading edge of the wing (thankfully not in our case with the swept wing because that would be messy). Makes no difference if the datum is down the street at Dairy Queen - you just do the math and get a max forward and aft CG location and you keep your actual CG between those numbers. Inches, angstroms, furlongs - makes no difference.

The distance between the forward and aft locations will be the same regardless of sweep, and of course the maximum gross weight will be unchanged.