This is a follow-up to a thread I posted earlier today, but I'd rather broaden the discussion and have folks chip in ideas. I'm trying to figure out how to build my trailing edges. What would you do?

Given (tentatively):

Trailing edge angle 16.8°

Skin thickness (each) 0.020"

Target bend radius (6061-T6) 0.040"

Rivet diameter (-4) 0.125"

Minimum rivet edge spacing 0.219"

Target rivet edge spacing 0.250"

Maximum rivet edge spacing 0.500"

Rivet blind clearance (-4-01) 0.355"

Aluminum density 2.7 g/cm^3

Delrin density (glass filled) 1.6 g/cm^3

Minimum TE thickness 0.060"

Target TE thickness 0.125"

Maximum TE thickness 0.250"

Skin thicknesses, rivet sizes, etc are all straw-men to allow comparison, and its possible that tweaking these numbers could lead to a much better approach. I'm interested in finding that tweak!

A note about area and weight numbers… these arbitrarily look at the weight of the portion of the wing that would be the last two inches, given an infinitely sharp trailing edge, ignoring rivets if applicable. Perhaps the best way to think about them is in comparison with Approach 1. The aircraft has about 20 ft of total trailing edge.

This last-two-inch portion of the trailing edge is what's illustrated… I should have shown more scale, sorry. Rivet thickness is a good marker for scaling.

Finally, all of this is conceptual. I'm deliberately ignoring some real-world factors like machining precision on the wedge, under the theory that it doesn't effect the comparison too much.

Cross-sectional area: 66600 mil^2

Weight per linear foot: 0.0780 lbs/ft (0 lbs/ft vs. Approach 1)

TE thickness: ~0.119"

Pros: Simple, light

Cons: Sheet size limitations, rounded TE aerodynamics

Cross-sectional area: 73800 mil^2

Weight per linear foot: 0.0864 lbs/ft (0.0084 lbs/ft vs. Approach 1)

TE thickness: ~0.138"

Pros: Light

Cons: Bad aerodynamics, cannot use blind rivets

Note: By shifting the lap joint forward, we gain enough clearance to use blind fasteners

Cross-sectional area: 73800 mil^2

Weight per linear foot: 0.0864 lbs/ft (0.0084 lbs/ft vs. Approach 1)

TE thickness: ~0.119", with weirdness

Pros: Light, simple, constructible

Cons: Even worse aerodynamics?

Note: The max rivet edge spacing means that we can't use blind rivets and take the sheet to the end… this might be fixable

Cross-sectional area: 97000 mil^2

Weight per linear foot: 0.1136 lbs/ft (0.0356 lbs/ft vs. Approach 1)

TE thickness: ~0.119", with weirdness

Pros: Easiest construction, might be able to get a clean trailing edge with different size or BK rivets

Cons: A bit weird ith the current trailing edge, hard to bend a TE sheet and get good straightness

Note: I've arbitrarily chosen a constructible, nice TE thickness here; very tweakable

Cross-sectional area: 111400 mil^2

Weight per linear foot (aluminum): 0.1304 lbs/ft (0.0524 lbs/ft vs. Approach 1)

Weight per linear foot (Delrin): 0.1025 lbs/ft (0.0245 lbs/ft vs. Approach 1)

TE thickness: ~0.070", selectedpr

Pros: Best trailing edge quality and thickness control, easily formed with good straightness

Cons: Strange angle for squeezing rivets, heavy

A machined/extruded trailing edge in the style of Approach 4 could be used, giving potentially better straightness, TE quality, etc...

The weight penalty for a machined wedge really isn't as bad as I thought, IF that trailing edge is built to near-minimum dimensions based on rivet spacing (and assuming rivet size). At only a half inch chord, there's just not a lot of material there… going to even a bit bigger (one inch, say) makes the situation MUCH worse. So Approach 4 is very sensitive to changes in rivet size. It also remains to be answered how feasible squeezing rivets on a 17° slope is… the RV guys do have difficulty at 9°.

Given (tentatively):

Trailing edge angle 16.8°

Skin thickness (each) 0.020"

Target bend radius (6061-T6) 0.040"

Rivet diameter (-4) 0.125"

Minimum rivet edge spacing 0.219"

Target rivet edge spacing 0.250"

Maximum rivet edge spacing 0.500"

Rivet blind clearance (-4-01) 0.355"

Aluminum density 2.7 g/cm^3

Delrin density (glass filled) 1.6 g/cm^3

Minimum TE thickness 0.060"

Target TE thickness 0.125"

Maximum TE thickness 0.250"

Skin thicknesses, rivet sizes, etc are all straw-men to allow comparison, and its possible that tweaking these numbers could lead to a much better approach. I'm interested in finding that tweak!

A note about area and weight numbers… these arbitrarily look at the weight of the portion of the wing that would be the last two inches, given an infinitely sharp trailing edge, ignoring rivets if applicable. Perhaps the best way to think about them is in comparison with Approach 1. The aircraft has about 20 ft of total trailing edge.

This last-two-inch portion of the trailing edge is what's illustrated… I should have shown more scale, sorry. Rivet thickness is a good marker for scaling.

Finally, all of this is conceptual. I'm deliberately ignoring some real-world factors like machining precision on the wedge, under the theory that it doesn't effect the comparison too much.

**Approach 1**: Bent trailing edgeCross-sectional area: 66600 mil^2

Weight per linear foot: 0.0780 lbs/ft (0 lbs/ft vs. Approach 1)

TE thickness: ~0.119"

Pros: Simple, light

Cons: Sheet size limitations, rounded TE aerodynamics

**Approach 2**: Bent-and-magically-riveted trailing edgeCross-sectional area: 73800 mil^2

Weight per linear foot: 0.0864 lbs/ft (0.0084 lbs/ft vs. Approach 1)

TE thickness: ~0.138"

Pros: Light

Cons: Bad aerodynamics, cannot use blind rivets

**Approach 3**: Bent-and-blind-riveted trailing edgeNote: By shifting the lap joint forward, we gain enough clearance to use blind fasteners

Cross-sectional area: 73800 mil^2

Weight per linear foot: 0.0864 lbs/ft (0.0084 lbs/ft vs. Approach 1)

TE thickness: ~0.119", with weirdness

Pros: Light, simple, constructible

Cons: Even worse aerodynamics?

**Approach 4:**Formed trailing edge insertNote: The max rivet edge spacing means that we can't use blind rivets and take the sheet to the end… this might be fixable

Cross-sectional area: 97000 mil^2

Weight per linear foot: 0.1136 lbs/ft (0.0356 lbs/ft vs. Approach 1)

TE thickness: ~0.119", with weirdness

Pros: Easiest construction, might be able to get a clean trailing edge with different size or BK rivets

Cons: A bit weird ith the current trailing edge, hard to bend a TE sheet and get good straightness

**Approach 5:**Machined trailing edge wedgeNote: I've arbitrarily chosen a constructible, nice TE thickness here; very tweakable

Cross-sectional area: 111400 mil^2

Weight per linear foot (aluminum): 0.1304 lbs/ft (0.0524 lbs/ft vs. Approach 1)

Weight per linear foot (Delrin): 0.1025 lbs/ft (0.0245 lbs/ft vs. Approach 1)

TE thickness: ~0.070", selectedpr

Pros: Best trailing edge quality and thickness control, easily formed with good straightness

Cons: Strange angle for squeezing rivets, heavy

**Other approaches…**A machined/extruded trailing edge in the style of Approach 4 could be used, giving potentially better straightness, TE quality, etc...

**Thoughts…**The weight penalty for a machined wedge really isn't as bad as I thought, IF that trailing edge is built to near-minimum dimensions based on rivet spacing (and assuming rivet size). At only a half inch chord, there's just not a lot of material there… going to even a bit bigger (one inch, say) makes the situation MUCH worse. So Approach 4 is very sensitive to changes in rivet size. It also remains to be answered how feasible squeezing rivets on a 17° slope is… the RV guys do have difficulty at 9°.

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