Longer spar for wider fuselage?

[Steve Innova]

I have modified my fuselage to be 3" wider in the center. Should I also add 3" to the spar, or should I leave it as is?

 

- If I widen the spar, the strake and wings will be the plans size, but the overall wingspan will increase by 3"

 

- If I leave the spar plans length, the strakes will be 1.5" narrower on each side, at the root of the strake, but the overall wingspan will be per-plans.

 

What are the possible aerodymanic consequences of either course of action?

[Kent Ashton]

Long-EZ or Cozy? If you use a wider spar, you're basically building a bigger, longer-wingspan EZ. You are already adding surface area to the fuselage thus increasing skin-friction and form drag. If you extend the wings with a wider spar you'd add more of the same sort of drag. I imagine I'd cost you a few knots at the top end where that sort of parasite drag is predominant. You'd be moving the wing's center of pressure slight aft, too. Who knows if you could tell any difference there.

 

However, if you extend the spar the strakes could be normal-sized which would simplify building them and give you standard fuel capacity. A longer spar would see a little more bending moment, though.

 

I think keeping the spar the plans length makes for the fewest aerodynamic changes. . . but I'm a Poli. Sci major.

-Kent

[TMann]

Yes ..... widen the spar. Take into account that by not widening the spar you will shorten the clearance available for your retracts, decrease your fuel capacity, etc.

[dirtdox]

Is 1.5 inches on each side going to make that much of a difference? The Aerocanard firewall is 3 inches wider per plans.

[Steve Innova]

Is 1.5 inches on each side going to make that much of a difference? The Aerocanard firewall is 3 inches wider per plans.

Sure, but is the Aerocanard spar [and wingspan] 3" wider as well?

[Jon Matcho]

Sure, but is the Aerocanard spar [and wingspan] 3" wider as well?

No, same spar and wing design as the Cozy Mark IV.

[michaelj]

You would not necessarily loose fuel capacity. You would loose baggage space in the strake. If you lengthened the spar and the resulting increase in wing span, you would definitely be altering the flying characteristics. You would most likely have to tweak the span on the canard as well by testing. Nat originally had too much span on the canard and all of the early builders had to trim our canard span. My Cozy MkIV was the 15th to fly so the canard span modification was completed just prior to the first flight.

[TMann]

I would talk to JD about this.

Because the retracts you are using swing inward, a wider fuselage will make a difference.

[Waiter]

I assume this is a LongEZ:

 

ADDING 3 INCHES -

 

Yes, add 3 inches to the middle of the center spar. Don't forget to calculate the new positions for the engine mount extrusion hard point in the center spar. Also make sure the dimensions for the wing attach point are also moved outboard by 1 1/2 inches

 

As you've noted your wings and strakes will be per plans.

 

This should have very little impact on flight charastics, slightly more drag from the wider fuselage, slightly slower roll rate because of the wider wing span.

 

Possible slightly better slow speed stability becuase more of the wing is now exposed to clean air, vs turbulance from the canard.

 

Minimal impact on CG calculations.

 

NOT ADDING 3 INCHES -

 

If you DO NOT make the center spar wider, your strakes will be 1 1/2 narrower. You WILL NOT have enough room to install the Infinity gear, as your strakes will not be wide enough.

 

 

CLARIFICATION:

 

Your making the fuselage 3 inches wider and this will include the rear seat and aft bulkhead (firewall). If this three inches also goes all the way forward, you may want to make the canard three inches wider also, don't forget to move all the hardware outboard by 1 1/2 inches.

 

On the centerspar, The engine mount extrusions will now be 3 inches farther apart. You will need a custom engine mount. The extrusion attach points are moved farther outboard 1 1/2 inches from the center

 

The Cowling will be 3 inches wider where it attaches to the wings, Custom Cowling needs to be made.

 

The center spar will be 3 inches wider. This effectively moves each wing outboard by 1 1/2 inches. The wings themselves will be per plans (SEE NOTE BELOW)

 

If you do the above, there will be no impact on the per-plans dimensions of the Strakes, as the dimensions from the outboard end of the centerspar to the fuselage side will be per plans.

 

The Strakes will be per plans, with the same fuel capacity, bulkheads, etc etc. Same for the Infinity gear, they will be per plans, except each gear leg is now 1 1/2 inches farther outboard.

 

 

 

NOTE- BUILDING THE WING - The trailing edge of a per-plans LongEZ wing does a little joggle forward. (When Burt Originally designed the LongEZ, he intended on using the VariEZ cowl, so he had to bring the trailing edge of the wing forward so the shorter cowl would fit)

 

If your going to be building a custom cowl, You might want to just make the wings trailing edge straight. This will move the TE aft about 2 inches where it intersects the cowl.

 

 

Good Luck

 

Waiter

[Lynn Erickson]

NOTE- BUILDING THE WING - The trailing edge of a per-plans LongEZ wing does a little joggle forward. (When Burt Originally designed the LongEZ, he intended on using the VariEZ cowl, so he had to bring the trailing edge of the wing forward so the shorter cowl would fit)

 

If your going to be building a custom cowl, You might want to just make the wings trailing edge straight. This will move the TE aft about 2 inches where it intersects the cowl.

 

 

Good Luck

 

Waiter

One my long eze plans the trailing edge is straight in the fore and aft direction but bends up 1 inch on the inboard section of foam block. the bend makes it look as if it bends forward. on the plans for the long eze, cozy, cozy IV there is the upward bend on the trailing edge. on the berkut, E racer and aero canard they took the trailing edge bend out.

[Steve Innova]

I assume this is a LongEZ:

No, it's a modified Cozy MkIV.

[Waiter]

No, it's a modified Cozy MkIV

OK, Everything I said is still OK, (I think; Take the Cozy folks word over mine )

 

EXCEPT - On the Cozy IV, you don't need to compress the strut like you do on a LongEZ. So, even if you didn't have the original clearence, you could always compress the strut.

 

 

Lynn, If I were building today, I'd make the trailing edge straight. Do you know of anyone who did this??

 

 

Waiter

[Lynn Erickson]

OK, Everything I said is still OK, (I think; Take the Cozy folks word over mine )

 

 

 

 

Lynn, If I were building today, I'd make the trailing edge straight. Do you know of anyone who did this??

 

 

Waiter

yes , my wings are that way . the trailing edge is straight

[Lynn Erickson]

No, it's a modified Cozy MkIV.

if it is a cozy IV with a 3 inch wider fuselage then it is the same as an aero canard. the infinity gear will fit in an aero canard if you compress the strut before retracting the gear

[Jack Morrison]

Waiter

 

The trailing edges on my E Racer are straight also.

 

Jack

E Racer 113