Sethhunter

There has been some renewed interest in Pfalz airplanes during the past few years with a few DIII's, DIIIa's and a new DXII. I finished a fairly detailed DIIIa last year and have been looking around for a new project (I squeezed a quick build of a Junker J10 designed by Dick Allen in between - a great flying plane and crowd pleaser!). The DXV jumped off the pages as a great airplane to model - nice proportions, fairly uncommon, thick tapered wing (DVII like) and a really cool lower wing - passing below the fuse - to add interest and a bit of challenge! So I got started and thought I'd post a few pictures here from time to time if there's interest. I've designed this DXV to be easier to assemble at the field and quicker to build. So I welcome any and all comments, suggestions, documentation references, etc.
First image is from the plans I drew up based on outlines in "Pfalz Aircraft of World War I" by Jack Herris (must have for any Pfalz afficianato!). I'm hoping to power this with a FUJI 43, or alternatively, a DA-50. Construction is straight forward ply and balsa. The full set of plans is about 9 pages. I'll make the CAD plans available (for free) on request after the plane proves itself flight worthy, probably early next year. (PS - I started this thread on RCSB but decided to move it here for a few reasons. Sorry for any confusion to those who visit both forums.)

Sethhunter

A few pictures of the sides being laminated from balsa and ply under some cawls, then assembled with bulkheads:

Sethhunter

Bottom sheeting going on:

Sethhunter

Stab/elevator:

Sethhunter

One set of walking beam parts. The walking beams (as well as control horns) are 3/32 fiberglass. The beams have bearings in them and ride on aluminum stub shafts that are glued into plywood. The big plywood disk spans the bearing and will hold the walking beam approximately in position if for some reason the bearing retainers break free, loosening the beam.

Sethhunter

Walking beams and fairleads installed in the fuselage before buttoning up the top. The walking beam assembly is secured with 2 bolts so it can be removed through the cockpit. 1/32 fiberglass reinforces the slot in the stab where the cable passes through, since the sheeting carries the load.

Sethhunter

Top sheeting going on. Some strips run from side to side on 45 degree angle, some meet in the middle in a herring bone pattern. One of the cool shapes on this airplane, inherited from the DXII, is the relief behind the radiator for outlet air; the fuselage cuts in around the engine, opening up space behind the nose mounted rad.

caribefoto

My Feedback: (2)

Very nice project and top notch workmanship Seth. The control horn hookup looks like you used Proctor turnbuckles. Did you fabricate the "clevis" that connects the turnbuckle to the control horn from brass sheet, or is it available commercially? Thanks ........ John Olson

Sethhunter

Top sheeting done. Since neither wing intersects the fuselage, there's no "natural hatch". So access will be entirely through the forward engine compartment and cockpit. My Dick Allen design the J10 that way and it works well. You can see the lines drawn where the hatch will be cut. I'm planning on somewhat permanently mounting the wing center sections, and plugging the outter panels in with aluminum tubes. I like the cockpit set way back on the fuselage. Kind of a racer look. I suppose it was to improve visibility. The little holes are for the upper and lower (?) cabane struts and LG struts. They will plug into hardwood blocks and secure inside with collars. Anyone know if the lower cabanes have a different name? This plane will need a tricky fairing where the LG strut passes through the lower wing. Something that slides so the strut can move without ripping out the wing!

Sethhunter

Hi John - For the moment, I bent some brass sheet to form the clevis, and soldered it onto a standard proctor TB eyelet end. I may try making some thing smaller/cleaner before the end (and loose the bulky locking nut). If anyone has good ideas here, please let me know. I didn't want to use cable between the TB and the horn, and the standard clevis strikes me as a bit small for a primary control surface. On my Pfalz DIIIa I made made a much more scale ball style end that nestled into a pocket on the horn but the construction was complex and the horns were pretty heavy by the time I fab'ed brass pockets, reinforced with glass and ply. Seems someone could make some money with vintage 1/4 scale fittings - maybe they already have?

Prop Nut

My Feedback: (3)

Sethhunter, thanks for posting it here. I look forward to following your progress. You last build was fantastic.

chashint

Every time I browse this forum I just sit here in awe of the building skills on display.

caribefoto

My Feedback: (2)

I'm considering something similar for my Proctor Albatross by using a standard Sullivan (or DuBro etc.) solder clevis sldered to a Proctor turnbuckle which avoids the necessity for a nut/bolt attachment on the control horn..........John

Sethhunter

Hey thanks for the comments!

I looked at using a standard metal clevis too - I think its a good idea and plan to get back and take a second look. It's worth noting that soldering on those TB ends is tricky because the solder tends to wick up the thread and bugger the thread. Any ideas how to mask the thread? It would also be nice to have more thread to work with (i.e., buy some threaded rod and maybe a clearing die. By my estimation, the thread is a 1-64; .072" major diameter, 64 tpi. If I stick with the brass "add-on" clevis, I would probably grind down the bolt head, and dispense with the nut by soldering a brass doubler on the opposite side (say three threads thick), tap it and secure with thread locker. I like the idea of having a nice beefy case hardened machine screw running all the way through the clevis.

caribefoto

My Feedback: (2)

A little oil protects any metal surface from solder. The clevis may need to be sleeved down to a diameter closer to the 1-64 TB bolt diameter. I would think left hand threaded rod might be a bit hard to come by so the use of a section of allthread would apply only to the right hand threaded side of the TB, not a problem unless I'm overlooking something.............John

Sethhunter

No I think you're right John. After 20 minutes of googling, I think 1-64 rod may be hard to find even right handed. I'll look into this a bit more but here's a link to a source for miniature taps and dies...http://www.gismosindustrial.com/Prod...MCT-1190-31102 Disclaimer - before buying, count the threads youself (or call Proctor) - Don't trust my old eyes[:-]

caribefoto

My Feedback: (2)

I don't know how "unscale" they are but DuBro makes nice and sturdy 1/4 scale (4-40) turnbuckles. DuBro and Great Planes offer pull-pull systems in both 2-56 and 4-40 sizes but these don't have true turnbuckles. They do terminate with threaded clevis' however. I have several of the DuBro large TB's but I think they might be too heavy for the empenage hookups on my Albatross..........John

cocobear

My Feedback: (2)

Hi Seth. If you use the Dubro 1/4 scale TB, You can cut off a piece of all thread screw it into the clevis, solder it and then screw it into the turn buckle. I have switched to the Dubro's exclusivly on my big projects for a couple of reasons.
1) I have had judges point out that brass looks wrong on the model.
2) The strength of the Dubro is vastly superior. I have seen failures of the Proctor.
3) If you use gun bluing on the Dubro, It looks awesome. A bit tarnishy and weathered!

DJ

caribefoto

My Feedback: (2)

www.smallparts.com is a super source for hard to find goodies. They have 12" and 24" lengths os SS 4-40 allthread. ..........John

Sethhunter

I like the clevis/DB idea - will give it a try. Thanks!

Erich_Prinz

I feel a little like Rumpelstiltskin missing out on all this content. I had no idea you were this far along with the project Seth!

Erich_Prinz

The rigging is impressive.

How did you arrive at this configuration?

Sethhunter

Hi Erich,
Well, I tried to avoid the pitfalls of my DIII; installing permanent hardware inside the shell after it was built. Never again! I wanted the control hardware to be reachable (fairleads near the cockpit rather than near the cable entry points), walking beams to be removable (rudder and elevator on same mount, bolted in), lightweight (same walking beam used for both elevator sides, fiberglass), don't obstruct the cockpit (pushrods and rudder walking beam low and behind/under seat and below floor boards), low friction (bearings), strong (fiberglass). From there, entry points and control horns need to be at scale locations (passing through stab, etc.) which determined the fairlead positions and angles. Most important, reliable: That means fairlead mounts need to be rigid (u-channel construction) and tied securely into side stringers and doublers. Walking beams secured to bulkhead. Bulkhead is balsa core with ply front and back for low weight and stiffness. Also made very close fitting "cheeks" around the pulleys so the cables wont ride off (also need to get the angles right, so the pulley is in the right plane of cable). What else? ball links for low backlash. Cable passes through the walking beam in a figure 8 path, passing around the back to reduce wear on hole. And bitter end of cable loops back and through the swage again to prevent pull-out. Then mostly a lot head scratching!! However, it should be easy to run replacement cables by reaching the fairleads from the cockpit (only have to remove the seat).

Sethhunter

Over the last week or two I've filled and fiberglassed the fuselage. The plane is now about as UUUUGLLLY as it'l ever look! Pictures below show the hatch detail, and the tail skid mount. The wooden part is laminated 1/16 ply over hard balsa. The whole fuselage, stab and rudder is fiberglassed with .73 oz cloth:

Sethhunter

Here's some pictures of the fixture that will help with building the struts; "M" struts for the top wing, and odd 4 strut arrangement for the lower wing (kind of an "N" strut with an additional strut to tie the N to the landing gear hardpoint). The fixture picks up 2 datums; the back of the firewall and the top of the fuselage doubler (accessible in the hatch area). The 10-32 bolts show where the struts will enter the wings. The holes in the fuselage are where the struts will enter the fuse. The fixture is basically a pair of plywood "E's". The center of the E rests on the doubler. The back of the E is clamped to the firewall. The top and bottom of the E carries sheets with blocks that represent the surface of the wing (top of the bottom wing, bottom of the top wing). Now the strut fun begins!!