Project Expedition: A 3500-pound Metal Wing, Tube and Fabric Utility Plane

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Chris In Marshfield

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Hi all,

Since I've been speaking of it recently, I'll start logging progress on the plane here. This plane is an adaptation of the Barrows Bearhawk that meets my "wants" in an aircraft of the type. It is not endorsed by "The Bob" in any way, but he and I had a long discussion about it at #OSH15, and he encouraged me to use his ideas and made suggestions of how he would improve it based on his experiences with the Bearhawk design. He said there is nothing as satisfying as designing, building, and flying your own aircraft, and was very supportive of this project.

The aircraft is essentially 15% larger than the original Bearhawk 4-place in every dimension, and adapts the Patrol (2-place) Riblett GA30-413.5 airfoil to the 4-place airframe (per Bob's recommendation).

Mission:


  • Utility Plane
  • Taildragger
  • 3500 pounds targeted gross weight
  • Metal Wing (38 feet in span, 210 ft^2 area)
  • Rag and Tube Fuselage
  • 4-6 places capable (but mainly 4 plus "stuff")
  • Wide body and comfortable (48 inches in the front seats)
  • Rigged for 8.5+ tires, skis, floats
  • 260-300+hp engine

I was originally targeting the Jake 275 as the engine of choice for this design, but given the "short" posture of the cabin compared to a C-195 and similar, I wasn't terribly satisfied with the potential loss of visibility over the nose. The M-14P is a better choice, as it's 10 inches smaller in diameter, 360hp, and it can be configured to minimize loss of visibility. The AutoPSRUs LS-3 isn't out of the question, either. It just depends on what's available and what mood I'm in when the time comes to purchase an engine. If all else fails, the trusty 300hp Lyc (I)O-540 from a Cherokee Six/Lance/Saratoga will be the answer.

I'm looking forward to sharing progress with you all!

Best regards,
Chris
 
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Chris In Marshfield

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The wing I'll be building.

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As described previously,


  • Riblett GA30-413.5 airfoil
  • 75 inches chord
  • Overall 38 feet in span
  • 210 square feet wing area
  • Integral tanks hold ~80 gallons total (not a wet wing, it's a strap-in aluminum tank)
 
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Chris In Marshfield

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Routed my first collection of nose ribs. I have a really tall laminate bit, so can do a lot at once. This round I did 12. No problems at all.

Bolted them all together:

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Drill the pilot holes for the lighteners:

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Cut off the excess on the bandsaw:

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Put up a tent to contain the flak (learned my lesson before):

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Got myself sealed up, lest I find metal in unfriendly places:

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Then got busy with the router. Make sure you've got a climbing cut going, else it's going to chatter all over the place:

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Success!:

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Clean as a whistle, no deburring really needed:

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Round one complete. Two more to go on nose ribs:

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And, as bonus, you come out of it all sparkly for Christmas spirit. Or I'm a vampire. Not sure which.

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Chris In Marshfield

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Well, shoot. Suffered a setback at the airplane factory tonight. My trusty router of 15 years gave up the ghost while cutting a batch of aluminum. Looks like I'll be asking Santa for a new router. :cry:

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Chris In Marshfield

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Sad moments don't last long (with the best of luck), and my sad moment is over with the arrival of my new router! And, of course, the whatever-you-do-to-kill-it-we'll-replace-it plan! :)

Back to the adventure (and with fewer sheets of metal stacked up this time).

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Old Freud will be sadly missed.
 

Chris In Marshfield

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Back at it again. Replaced my old dead Freud router with a new Bosch, and of course the old router plate didn't fit. So needed a new one of those, too! Figures. Now the rig is back in place and ready to work.

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Finished the false ribs (the ones that took the life of my beloved Freud), and decided to take it easy on this one. I only cut half as many blanks this time around. Also finished the blanks for the aileron and flap noses as well. Not a bad night, all around.

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Next round, aileron pocket ribs, and then centers.
 

Chris In Marshfield

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Cut out the flap ribs last night. Things are starting to move along again after traveling for work last week.

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Had some friends over helping last night. One wanted to give the router a go, and he did a good job. But, he got in a hurry on the last batch of ribs (six or so), and the router got away from him and started to chatter. Another reason to make sure you're using a climbing cut, moving slowly, and keeping a firm hand on the routing jig!

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I was able to clean it up with a sanding drum in my drill press, but with it being only six ribs, it's easy enough to make new ones. So I think I'll do that and keep these for backups, just in case.

Also added a new friend to the building team, and he's very excited to learn about the process. He recently finished university, earned his commercial ticket this past fall, and is working in the flight department of a local business. He's never seen this end of aircraft, so I'm happy to help build his experience on this side of the community!
 

Chris In Marshfield

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Rebuilt the few damaged flap ribs, and they turned out great. Time to move on to the center ribs.

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One thing that was a problem in the middle of this event, was that I had a problem with metal shavings getting into the router. This particular router has a contact strip that runs up and down the motor body that connects to the handle switch when the motor slides up and own the base. Well, they got in there and shorted out the switch and it wouldn't turn on. The startup circuits are all electronic, so no worries, but still an inconvenience.

I removed the motor from the base, blew it out, and life was good again. A friend suggested that I create a filler plate to go between the base plate and the bit (I imagine I could use one of my guide collets from a trim kit I have) to minimize the shavings going down the opening. I'll also see if I can find a vacuum fitting for the base to help keep chips out of innards of the beast.
 

Chris In Marshfield

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Finished the aft ribs and started pre-drilling the center ribs for routing.

New band saw blade made for easy trimming of the excess aluminum. Although using a narrow blade is a stinker because it tends to wander. Perhaps some more tension is in order.

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Got them on the router table, and life is good.

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Had some more helpers in the shop tonight, doing a fine job with the drill press, as well as general supervision of events (guess which ones are the supervisors).

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Now all the centers are drilled and ready for routing:

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Have to be mindful, though. The .032" ribs have different aft lightening holes than the .025" ones. There's a separate jig/pattern for that hole. Don't screw up!
 

Chris In Marshfield

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Finished routing the .025" center ribs today, and got about half of the .032" ribs preliminarily routed. The aft hole is different, so when I finish the forward ones, I'll have to jig up for the aft one.

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First half of the .032" ribs:

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Once I finish the second collection of ribs, I'll jig them up to do the aft (oval) hole. The holes on the .032" ribs are the same as the false ribs (behind the fuel tank) in post #8 above.

Almost done cutting ribs!
 

Chris In Marshfield

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With the exception of the two full-length ribs (I ran out of MDF for the routing forms), the rib cutting adventure has concluded! I jigged up the aft holes in the .032" center ribs and got them all cut out.

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And then I drilled the flap torque tube holes and aileron cable holes one at a time with the Unibit.

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I went back and drilled the same two holes for the false ribs behind the fuel tanks as well.

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Now, they're all stacked up and ready for deburring. My Scothbrite wheels should be arriving from ACS any day now.

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Chris In Marshfield

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I trimmed the ribs to length Saturday, which required a bit of massaging of the routing jigs. The nose, center, false, and long aft ribs were all shortened by 1/4". The centers on both ends.

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When I first started going down this path, I knew how big the wing cross section was going to be, but I hadn't yet calculated the spar sizes. So to avoid analysis paralysis (you techie types know what I'm talking about), I created the forms "to the line" where the spar web line was on the master wing panel. I finished the spar calculations this week, and trimmed the ribs back to accommodate.

Interestingly, the spars for the Expedition, aside from being longer, use the same size and collection of spar caps that the regular 4-place Bearhawk does (.125" x 1.25"). References tell me that the stiffness of an I-beam increases with the cube of its height. And the Expedition spar is 2" taller than the regular 4-place spar. So it all makes sense. The aft spar caps will be double-stacked, unlike the 4-place which has only one layer. Because there is an extra 10 inches of chord to deal with, the chord-wise moments are going to increase substantially, especially with larger flaps and ailerons.
 

Chris In Marshfield

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Routed out the rib routing jigs for flanging the lightening holes today. Getting ready to start bending ribs. My favorite thing!

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Also created the hardwood bending form for the edge flanges. Made from solid oak, they'll last a long, long time. I bent a lot of ribs on the last set I created.

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The circles you see traced into the top will be routed out on both sides so the lightening hole flanges will have a place to go since they'll be done first. I'll be routing notches in the edge of the bending form for the flutes, which I'll pound in with a hammer and the edge of a screwdriver. More to come there.
 
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