Building D VII bits

[Maxim08]

A few pieces under way so I thought tha a few photos would be of interest. Hopefully it will goad me into accelerated action. Consider this content as alternative and/or supplemental to the information previously posted by Brooks and Engels.

First up is the frame for the seat.

I have made 5 or 6 seats so far for different projects but this is only the second seat frame, first for a D VII. Jeff hit several challenges in making his frame and before I weld in the primary cross tube I will be travelling to Ottawa to double check the frame on their Fokker built D VII.

The D VII seat is unlike most homebuilt aircraft seats that are fixed into position. The Fokker seat is easily adjusted vertically utilisng a sliding seat frame locked into position by the use of two pinch clamps that use 'wing nuts' to adjust tension.

So far.



A few things going on in this photo.

The jig is made from MDF scraps. I like mdf because of its unwillingness to burst into flame as I weld. The vertical piece locates the forward tube that runs transversely under the front of the seat. The top of the frame is closest to the camera so the orientation of the jig is with the seat lying on its back.

There are two short lengths of tube located on the base to represent the vertical tubes that the seat frame slides on. The narrow dimension of the jig base equals the distance between the bottom of the top seat clamp and the top of the bottom clamp.

The clamps were made first. They are of 0.060" mild steel sheet that I cold formed around a steel bar. The extended tubes will sleeve the clamping bolt that pinches the clamp shut. This was made from bushing stock and, after welding, only requires final reaming for the bolt.

The tubes are 0.035" 4130 of various diameters which most closely equate to the original metric dimensions.

The forward trasverse tube is cut to length +10mm to ease welding, and clamped to the jig. It is then a simple matter to cut and file the side bracing tubes to length.

Here is the apex of the two port side tubes at the transverse.



When finish welded, I will trim the transverse ends down to the correct OAL, approximately where the silver mark is.

The long tube lying on the jig is the primary transverse that runs between the port and starboard upper clamps. This is the piece that I need more information on: exactly how it mates to the clamps and whether there is a slight bow in the middle of the tube.


FYI, there are 15 parts in the seat frame not including the hardware.

Regards,
John

[Maxim08]

So, while I am waiting to get the info required to finish the seat frame, I am working on the stabiliser lower struts.

The struts are quite simple consisting of a streamline strut located outboard with a single bolt and inboard to the lower longeron with an adjustable fitting.

Like any of these exercises, planning first, draught anything that doesn't have an accurate drawing, make whatevere templates are required and then make the bits.



The two upper left pieces that look like armless stick people, are fittings to go into the stab end of the strut. The outer width of the legs is the width of the sreamline tube and the offset in the body is so that the bolt hole, when drilled, will be aligned with the minor axis (thickest part) of the tube.

These were cut from 0.125" 4130. Note that the grain runs along the length. They will be bent just before the flare to create the angle bewteen the horizontal plane of the stabiliser and the angle of the strut. You want thegrain to run at right angles to the bend. The legs have been milled towards the pointy ends giving a similar appearance and function as the forged legs used in the D VII landing gear. The tube will be cut and shaped to conform to the outline of the end fitting. As the tube narrows, the fitting gets thicker providing more strength.

The parts on the lower left are the fuselage end fittings. These were turned from 4130 bar but the female end, which is welded into the strut, is mild steel. If the threaded female end distorts during welding, weld hardened 4130 is a bu**er to re tap.

The parts above are the fuselage attach box and an aluminum template that I used to fit this piece.

Regards,
John

[franzkait]

the Fokker D7 seat frame is OK , if you are able to lift the frame in the fuselage with one hand . If not , it is not a Fokker seat frame .

[Maxim08]

franzkait,
I will let you know when it's finished.
Regards,
John

[franzkait]

I hope you know , the seat frame is not weldet in the fuselage . You put the weldet parts in the fuselage and press the tubes together . Most people make the mistake and weld in the fuselage . All Fokker seats are made this way .

[Maxim08]

Last post failed to upload so I will try again.

The finicky part for the struts is the fuselage attach bracket. While simple in concept, alignment is important to ensure that all the parts look and work properly.



Above is the bracket that captures the strut adjusters. This piece is welded to the lower longerons just aft of the tailskid pivot post. In the photo it is upside down. Other threads have indicated that this was originally made from a lengthof metric rectangular tube, sectioned in the middle, bent to the correct angle and welded in place.

Not having a tube 18mm x 12mm, I have used a section of 0.75" mild steel tube with a 0.06" wall cut to create a 'U' channel. This is welded to a strip of 4130 to create the correct shape. In this metric conversion, the box is about 0.05" off in dimension. The strip is first bent to the corect shape which allows for the divergence of the lower longerons and the angle upwards required to align with the strut. When everything checks out, the boxes will be seam welded, the ends trimmed and the pilot bolt hole drilled.



Here it is mocked up to check alignment. Note the string. After mounting the stabiliser and ensuring that it is square to the fuselage, I ran a length of string from the upper strut mount on the port side, down under the longerons and up to the starboard mount. This alignment string was used to check the angle on the bracket bottom strip prior to tacking and in the mockup shown.

Here's what the basic setup looks like.



The strut was borrowed from another airframe and is not the correct length, being about 20mm short.

For D VII afficinados, note that the lift handles are coming off and being corrected.

Regards,
John

[Maxim08]

franzkait,

Thanks for the information. Each of the four clamps will be spread to fit around the tubes. The frame will be free to slide when the thumbscrews are released. Using the Knowlton aircraft as an example, I intend to use cable and turnbuckles looped over the upper transverse tube as a 'safety' retainer to prevent the seat from collapsing down under severe load, ie one of my not-so-good landings.

Were the seat frames installed prior to welding up the fuselage and therefore no seam in the lower sliders or where they installed after final welding the fuselage?

Regards,
John

[franzkait]

first you weld the 2 triangle ready . Slide over the fuselage tubing , and weld the fuselage . Press the top pipe in to the welded bushes and weld the front pipe in . All fittings and clamps have to be in place bevor you weld the fuselage .

[Jeff Brooks]

Originally Posted by Maxim08

John

John,
I know the original didn't have a drain hole on the bottom of this part, but I put one on mine ...

[Maxim08]

A little progress today on the stabiliser strut pieces.

The streamline is marked with the outline of the fitting and is then trimmed in a bandsaw.



The fittings need to be bent to allow for the angle between the strut and the stabiliser. This was done on a hydraulic press using a homemade pressing nose piece made from some scrap 1/4" plate with a rounded nose. I made a cardboard template of the angle and checked to ensure that both sides of the stab were the same. Fortunately, they are. FYI the angle is about 25 degrees.

Here are the pieces after drilling the pilot holes for the bolt and bending.



The first piece took about 6 setups in the press. Mostly caused by concern over bending the piece too far. The second one was correct first time. Lucky I guess.

Here they are trial fitted into the tapered streamline.





Welded up the fuselage bracket and trimmed the ends with a hacksaw. In this photo only the right side has been trimmed.



Tomorrow is July first which is Canada Day and a national holiday. Normally we sit around, drink beer and talk about Canadian things like Henderson's winning goal aginst the Russians; why the Canadian C8 is a better carbine than the Colt M4; why does it always rain on holiday weekends etc but perhaps I will do something productive and finish the darn struts!

Regards,
John