DR-1 (Sands): Builders Group - Page 104

AchimEngels · 18 February 2006, 02:08 PM

Hi Baldeagle,

Well, what is simpler, lighter and more stiff than a simple bent sheet of aluminum?

I think it is a matter of practice.

If you are not used to shape metal and rivet, I would agree, that welding is more practicle than the authentic way.

Just my two cent.

Cheers!

Achim

baldeagle · 18 February 2006, 03:08 PM

I would say that two steel tubes would be simpler and stronger than the aluminum box, and probably not enough weight difference to make a difference. Just the savings in time welding in two tubes instead of cutting, forming, rivetting, and installing the aluminum box would seem to be worth it. And I suppose that in the long term, after some hard landings, the steel tubes would be less likely to come loose than the aluminum box. Now if I was doing a rotary engined authentic aircraft I would do it as original just on the principle, but if I'm already compromising with a modern engine, brakes, etc, why not make the rest simpler where it would be hidden? The Triplane that I flew to Dayton in 2003 had diagonal tubing in the fuselage instead of wires and turnbuckles, imagine how much time (and money!) the builder saved that way, and nobody who saw the 'plane noticed. Plus it flew great (for a Triplane...) was not tail heavy, and climbed well. My view is pretty much to either go all authentic, or to compromise as much as possible to make it quicker and easier to build, as long as it looks right from the outside and is as strong as before.
By the way Achim, I love the D.VII thread, and all that you are accomplishing and trying to accomplish, this certainly isn't anything against that, just looking at simpler ways of getting to a flying replica. I've worked on very authentic aircraft, and loved doing it, especially when it was on somebody else's dime (mark), but for my own projects I don't mind simplifying structures if it will get me in the air sooner and won't make a difference in strength and flying qualities.

Fritz Kempf · 18 February 2006, 06:13 PM

Baldeagle
The box is not structural at all, the two rods that go across the air foil for the shock cords is what holds it together, and of course the wires above it. The air foil needs a spar to hold the ribs that make it up and that is my understanding as to why its there. To replace it with tubes wouldn’t work. As for the Sopwith I believe it has wood on the front and back just to make it stream lined, where as this little puppy actually creates lift.

What I would like to know is, why were there two aluminum tubes going through the ribs in front and behind the box spar on the air foil? Was this just a stiffener?

Ed

Fokker210 · 18 February 2006, 07:05 PM

Fritz,
Aluminum tubes ?

My sheet #7 lists these as being .049 wall 4130 tubing... Also states they are there to "prevent separation of steel box ends from aluminum housing" and that this was an original Fokker 1917 field fix.
Can anyone shed any light on this "field fix" ??

gipsymoth236k · 18 February 2006, 07:09 PM

Yes, the Dr.I had two 70mm (1mm wall) diameter aluminum tubes running through the ribs for alignment and reinforcement. They were simply peened over outside the outer end ribs for attachment. These aluminum tubes, as well as the ply ribs and ply covering had nothing to do with landing gear shock loads. They only carried air loads of the landing gear's airfoil wing assembly.

Regards, Gary

baldeagle · 18 February 2006, 10:09 PM

I guess I assumed that the Triplane was like the D.VII where the aluminum axle box is the structural member between the steel Vees, so it isn't? I only have D.VII plans here. In any event the axle wing could easily be attached to steel tube spreader bars without the box.

Also, no cross tubes on this one, from the Canadian guys, only the aluminum box: http://www.greatwarflyingmuseum.com/dri/tri156.jpg ???

And the photos on Achim's web site don't show any cross tubes, just the aluminum axle box, which must then be structural, correct? Perhaps Ron Sands added cross tubes to strengthen the unit. Maybe Achim can comment on this "1917 field fix".

AchimEngels · 19 February 2006, 12:54 AM

I am not sure what you all are talking about here.

The original design was made from two streamlined tubings that served as legs. These terminated in a steel box assembly (it was called "knee") which had the axle passing through. The design of this box was altered from the original simple square box type used on early triplanes and the previous V-types ( as seen in FritzKempf posting on page 101 of this thread). The two rods that hold the axle shock chords are welded to the sides of this box. on later Dr.I´s and subsequent Fokker D.VI, D.VII and E.V/D.VIII these rods have been placed further apart. This was achiveved by welding the side "ears" to the square box. You can see these on the current posts of the FTS Thread. The rods did not run through from one leg to the other side, but are parts of the bottom "knee" only to which the undercarriage legs are welded.

The aluminum box does only serve two proposes: It joins both, left and right, leg assembly. These can not seperate since the steel "knee" is riveted to the alu box and because of the cross bracing of the undercarriage. This way the aluminum box serves as a kind of compression member.

The other propose of the axle box is to provide a kind of spar and attachment point for the two part undercarriage wing-like fairing.

The aluminum box itself (considered as standing alone) does not provide a structurall member. For this reason Baldeagle is of course correct with his question whether the box could be replaced with steel tubes welded to the "knees".

The lift and drag produced by the fairing is not only taken by the box. The entire original design of the "wing" which is made up from two pieces slided over the box from front and rear is what make the "wing strong", since the ribs are carried on small stringers in the corners of the square center cutout which are attached tightly to each flank of the aluminium box. This provides the transfer of forces from the ribs to the entire lenght of the box. You have to judge it as a clever design in the whole. the pieces play all together.

Baldeagle would have to design something around his steel tubes to not only attach the fairing to, but also make it strong enough as a whole unit when under load.

As a mater of fact there are Aluminum spars of round cross section running through the ribs of the front and the rear piece. These are sheets of aluminium rolled to tubes and riveted at the joint.

The only factory drawingrefference I have for those tubes comes of the undercarraige wing fairing drawing made by the Fokker staff on 22. of June 1917, drwg. No. 28008 which was for the early V types, most probably the "D.VII" V.2 and V.3. This source gives them with a sheet thickness of 0,3mm.

The interesting part is that it is light in weight and strong. There have ben pretty impressive load tests on the wing that have been carried out after some officers in the field complained about fears concerning probable weakness of the design. Actually those load tests revealed quite the contrary and prooved the design was sufficient.

I know of course that these things do not apply to some of the heavily modified undercarrriages I see here.

Just to make it clear! I absolutely agree with the point of view Baldeagle mentioned in his post and see his reasons, but on the other hand I am pretty impressed by the simplicity of the original design which in a whole indeed is pretty reliable and reasonable.

Enjoy!

Achim

Fritz Kempf · 19 February 2006, 05:50 AM

Fokker210
Ron doesn’t show this on his plans. If you look at your ribs from the side there would be no lightning holes, just one hole in front of the spar, and one hole in back of the spar in which the aluminum tubes ran through. I had always thought that the steel tubes that connected the shock tubes together where part of the change that happened after the prototype gear. Also the shock tubes should not go through the last rib like Ron shows; the last rib was opened up in a triangular shape to access the shock cord.

Achim & Baldeagel
While you could change the box to tubes what would be the advantage? The time you would save, would be lost reengineering something to hold the ribs.

Ed

Fokker210 · 19 February 2006, 06:24 AM

Fritz,
Ahhhhhhh......now I see !
Very nice !

baldeagle · 19 February 2006, 07:09 AM

Wouldn't take much engineering to weld a few tabs on the tubes to hold the ribs. Heck, if you've got steel tube spreader bars the box, as you say, isn't structural and could be made a simple plywood box, would still do the same job. The point is, there are ways to simplify the structure of parts of the airframe and save time and money without changing the strength or looks of the finished product.
So do the Sands plans show steel tubes as spreader bars? Are they continuations of the tubes that the bungees wrap to?