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1/3 Scale Halberstadt D.III

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Old 03-10-2010, 03:39 PM
  #51  
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Default RE: 1/3 Scale Halberstadt D.III

ORIGINAL: Sethhunter
I'll move it if I think the benefits outweigh the asthetics, which I did here.
But I don't see this as an issue of aesthetics, particularly on a model this large. Features like the Wing span, cord width, elevator and rudder size, and that "droop" were all part of the original aerodynamic design solution. And it was these characteristics that made the Halbi fly the way it did (good or bad). In short, I don't want to "improve" on the original.
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Old 03-10-2010, 06:54 PM
  #52  
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Default RE: 1/3 Scale Halberstadt D.III

Don, I don't think we disagree. Perhaps my word choice was poor. I didn't mean the aesthetics of the design, but rather the aesthetics of the hobby - our faithfulness to the elusory goals we set ourselves to replicate the perfect miniature (now I'm sure I'm bashing words). So we all set the height of our hurdles based on how much we're willing to put in (time, money, time, time), what our capabilities are and what our expectations are for the result (win contests, win bragging rights, chase others around the sky, nail a landing with a "flying death trap", or just do lazy circles in the sunset). I think we all respect those who set them higher.

On this particular model, my goals were not high fidelity, but rather an interesting project that meets my timeline to fly this year, flies well, is readily servicable, presents some challenge, teaches me something, assembles quickly at the field, fills some holes in my fleet, is a fair representation of the original, and engenders good conversation about planes with friends. Will I change the design to meet those goals? YOU BET! I like to think I make good tradeoffs that balance all that out. The line in the sand is hard to see. Some people leave their trailing edges big and fat. Others use dowels for machine guns. That's their choice. I wouldn't. But I would move a stab pivot point, and make flying surfaces thicker. I absolutely respect that you wouldn't. I guess I draw the fidelity line, for me on this project, is where people walking down the flight line will stop, look, look closer, maybe take a picture and ask what kind of plane that is. If they do, it's worth the effort. I know those who set the hurdle higher might not stop and look. That's ok. If someone gets inspired by something on these pages to take crack at the H.DIII and do one better - all the better!

PS - Although scale appearance on the ground gets the most talk, we all watch these airplanes fly. And I understand those who feel planes in the air, that get a bunch of RC "outsiders" to visit the field and turn their heads up and enjoy a show, cause a kid to point, are doing a good thing. This plane is a little more like that. Maybe the next one will belong in a museum!
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Old 03-10-2010, 08:44 PM
  #53  
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Default RE: 1/3 Scale Halberstadt D.III

Don't get me wrong, I'm loving your build here and your design and construction skills are way beyond mine. And I certainly haven't yet built anything more scale than your models. Perhaps it's exactly because I don't understand the technical design issues that I feel I need to stick with the original. I guess I trust the original because I really can't do better myself.

There are lots of different approaches to scale modeling...and there's no reason that we have to stick to just one.
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Old 03-10-2010, 09:09 PM
  #54  
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Default RE: 1/3 Scale Halberstadt D.III

Here is my 2 cents worth........

The original didn't have any kind of power assist on the flying stab, did it? No, I don't think so. The air loads didn't over power the pilot and the slip stream didn't cause any undo osilations or flutter of the flying stab........so isn't it reasonable to assume that the model will respond in a similar fashion? Consequently, the servo requirements would be similar to those requirements for a conventional stab/elevator set up of a similar size. Right?

I flew a 1/3 scale Fokker E1 for 7 years without problems.......the tail was full flying and scale in outline and function.

I am enjoying the build and all the discussion.

Cheers,
Art
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Old 03-10-2010, 09:45 PM
  #55  
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Default RE: 1/3 Scale Halberstadt D.III

Art's 2 cents sums up my perspective perfectly. I really do trust the original designers. Still, I'm definitely enjoying all of the clever design work you're doing Seth and am mentally filing away each technique for possible future use.
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Old 03-11-2010, 07:38 AM
  #56  
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Default RE: 1/3 Scale Halberstadt D.III

All good! One curvy spar done. Looks odd pics soon!
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Old 03-14-2010, 02:01 PM
  #57  
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Default RE: 1/3 Scale Halberstadt D.III

The lower wing is coming along. The photos show the sequence. The wing is constant chord but drooped at the trailing edge. The leading edge is straight. So the main spar has some droop, and the TE has the most. The shape of the TE also factors in some washout.

I built the wing in reverse order, starting with the shear webs! I glued together a strip of webs (cross grain), and using a pine board as a guide (cut to the shape of the curved spar), cut the strip of webs to the right height (curved). Then placed the webs between two pine formers and glued the top and bottom spars to the webs, clamping them to the pine. After the glue dried, I put the webs on the top side of the spars and removed the spar from between the pine formers. I originally planned on using one-piece spars top and bottom (3/8 thick) but I was afraid they would spring back to shape (webs would not hold the curve). So I resawed the spars to 3/16 thick, and glued them together (two-piece lamination for both top and bottom). I only used one strip from each resawed piece since I lost too much material from the bandsaw blade kerf. Fortunately I had extra stock.

Next I built some pine supports to hold the trailing edge and main spar in position while I glued ribs in place.
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Old 03-14-2010, 02:02 PM
  #58  
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Default RE: 1/3 Scale Halberstadt D.III

I installed the secondary spar and front spars in the usual fashion.
The TE is made from two sheets (top and bottom). The bottom sheet is tapered to match the curve of the top of the rib. The top sheet is glued to the ribs and bottom sheet. Before gluing the top TE sheet in place, I CA’d a strip of 1.4OZ fiberglass to the underside, to give the TE a little more “hanger rash resistance.” Because of the droop, and angle between the top and bottom TE sheeting, they don’t line up (looking down). You can see the mismatch that looks like the top piece is warped. I added some filler strips to even them up before putting the cap strips on.

I put an aluminum square tube “sleeve” around the main spar at the root. This reinforces the spar, and will handle the stress of a bolt that will hold the wing on (passing through the sleeve, and an aluminum dihedral brace that slips inside the spar. I also made an aluminum root rib, to handle the stress of transferring all the loads to the main spar/dihedral brace, and serve as a strong attachment point for the rigging wires.

Next steps are to put the strut anchor blocks into this structure. Although the ailerons are on top, I planning on having scale pull-pull wires that drop down to and run back through the bottom wing. To avoid the hassle of connecting cables to servos in the fuselage (which I did with the Pfalz DIII), I plan on putting the servos in the bottom wing near the fuselage, terminating the cables at a bellcrank, with a short pushrod to the servo. This means a door or two on the underside but easier to assemble at the field.
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Old 03-14-2010, 05:52 PM
  #59  
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Default RE: 1/3 Scale Halberstadt D.III

Very clever engineering! The true mark of a modeling guru is when you can build a "twisted" wing on purpose!
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Old 03-14-2010, 06:03 PM
  #60  
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Default RE: 1/3 Scale Halberstadt D.III

Thanks Don - I'm really banking on your theory - if it looks like the original, it'll fly like the original. Hey - how did these fly, anyway?!![sm=what_smile.gif]
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Old 03-15-2010, 09:04 AM
  #61  
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Default RE: 1/3 Scale Halberstadt D.III

Hi Seth, Don't know how I missed this build but now that I have found it I will follow to the end. It is a great subject. BTW, wish you could have made it to the Blue Max. Your Pfalz would have had a great chance at the static contest. I am not going to go into a lot of detail here on the event since I am sure Ron will be posting something but if you have never been to the Fantasy Of Flight Museum you are really missing something. Kermit Weeks even gave us a private tour of the "behind the scenes" collection which is just incredible. The photo I am posting sums up the flying situation.
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Old 03-15-2010, 03:50 PM
  #62  
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Default RE: 1/3 Scale Halberstadt D.III

Hi John - welcome to the thread! Yeah, I need to get out more. This plane will force me to build a trailor, so I'll have fewer excuses for staying home! Those flags look like it was blowing at least 15 knots. Was it steady? I died for days like that when I was racing sailboats, but it sure makes flying RC "powered kites" a challenge!!
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Old 03-15-2010, 04:08 PM
  #63  
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Default RE: 1/3 Scale Halberstadt D.III

Hi Seth, It was a constant and increasing blow. In fact, it blew over the GTM 1/3 Fokker D VII that was on display on the field even though it was just in the bones! Everyone had a great time anyway and I didn't hear one negative thing from anyone even though we were all disappointed. Got lots of good feed back and the necessary changes will be made to make the Blue Max the ultimate WW1 event next year. You should really put it on your calendar. Can't say enough about how great the FoF staff were and the private tour given by Kermit Weeks just put them over the top. The Aviatik is ready to fly with the exception of a few details that will not keep it out of the air. BTW, do you have a source for lithoplate?
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Old 03-28-2010, 09:35 AM
  #64  
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Default RE: 1/3 Scale Halberstadt D.III

Details on the lower wing are coming together. First pics show the supports for the interplane struts. Basic ply box construction that tie into the spars in six places (4 struts and 2 lifting wires at the root). Locking nut on the backside will take the bolt that will hold U shaped strut fittings. Next are the turning block assemblies out at the tips to receive the cables coming down from the top wing. Pretty straight forward with a nylon sheeve, metal pin and ply box. Then balsa framing.
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Old 03-28-2010, 09:37 AM
  #65  
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Default RE: 1/3 Scale Halberstadt D.III

Next a few pictures of the tip being laminated from balsa with a 1/64 ply core. Lastly, the servo tray, belcrank and servo installed. The compartment is accessed through a hatch on the bottom. The servo is mounted at an angle to accommodate the length of the arm, and so it's easy to access the mounting screws with a straight tool.

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Old 03-28-2010, 12:59 PM
  #66  
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Default RE: 1/3 Scale Halberstadt D.III

Seth:

Just a word of caution when it comes to the placement of those aileron pullies! I built mine per the "Sunderland" prints, where he showed the pullies on the wing top view, and where the aileron bellcrank was located, without checking things out, covered the wing panels and all. Well guess what? The cables coming up from the bottom wing run right smack dab into the rear outboard strut to get to the aileron bellcrank! At this point all I can do is open up the wingtip and move the pullies , but then I have internal tubes that route the cables right to the pullies, what a mess, huh? It is all on the back burner for now as I'm finishing my DH-84 "Dragon".

Keep up the excellent work, your a real inspiration to us all!

Dan
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Old 03-28-2010, 02:46 PM
  #67  
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Hey Dan - oh that sounds painful!! Kind'a how I felt when the LG on my DXV didn't intersect the lower wing LE like it was supposed to. I never had the umph to go back and fix it. Thanks for the warning though - I just double checked and fortunately the aileron horns and pulleys are both just outboard of the struts. Have you considered moving the horn on the aileron? Might be easier. I actually spent a lot of time on the cable arrangement here, since the hinge line on the aileron is in the wrong position relative to the cable attachment points on the horns (hinge line should be on the cable side, not opposite, for the pull-pull to tension correctly. But I did make up for it with the geometry of the bellcrank in the lower wing. Figuring that out, and the servo attachment point that gives equal throw, seemed to take a lot of time.

Oh BTW I should also point out, I put a washer on the outboard side of the ball-links. I've been told by "the guys" that the plastic can wear enough for the body to slip off the ball. Putting a washer under the head of the bolt keeps the link roughly in place should that happen. I've never seen it, but figured it's worth a washer.
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Old 03-29-2010, 08:51 PM
  #68  
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Default RE: 1/3 Scale Halberstadt D.III

Seth:

Hey man, that sounds like a good fix to me just moving the bellcrank over a bit, obviously I hadn't thought of that! Thats why I appreciate this thread, and especially your engineering skills which are evident! I'm an aircraft mechanic by trade and that is a common practice to put a washer under the bolt head going through a rod-end, this keeps the linkage on if the end was to let loose, kind of important when its hooked up to your carburetor!

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Old 03-29-2010, 09:24 PM
  #69  
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Default RE: 1/3 Scale Halberstadt D.III

I've heard of that washer trick before, but somehow I just can't visualize it, despite having read and reread the text. Can someone post a photo?
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Old 03-30-2010, 05:39 AM
  #70  
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Default RE: 1/3 Scale Halberstadt D.III

Don, look closely at the last photo in the set, of the aileron servo. There's a washer on each end of the connecting link. On the servo end, you can see the washer between the head of the bolt (that mounts the ball to the end of the servo arm), and the ball itself. That washer doesn't come with the set. If somehow the black plastic popped off the ball, the washer would keep if from completely separating - i.e., slipping right over the head of the bolt. The washer on the bellcrank end is also visible under the bolt head. I'll post a picture of what the link looks like without a washer - it might make more sense.

Funny thing about those aileron cables, I put them of the outside of the struts without thinking about the interference. The 3 views weren't really clear. But the color plates seem to show one cable passing inboard and the other passing outboard of the strut, which doesn't make sense to me unless the pulleys are staggered. Anyway. I kept it simple, if not exactly scale. Hopefully that works out well for you Dan. I thought about using tubes to run the cables, but worried about the cables rubbing against the end of the tubes near the servo, as the arm sweeps through it's arc. Did you use some kind of eyelet or fair-lead? Instead, I framed the blocks (pulleys) with balsa on the underside of the wing tip so the covering would have something to attach to near the block, so if I need to run cables after the wing is covered, I only need to strip the covering in the little framed-out spot, rather than the whole tip. I suppose I could put a little hatch cover there too.
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Old 03-30-2010, 07:49 AM
  #71  
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Default RE: 1/3 Scale Halberstadt D.III

Ah, now I see it! I guess the problem is that I've never used that sort of ball and socket with the bolt through the ball. I was thinking of the small ball and plastic cup type and had somehow imagined the washer wrapped around the whole thing.
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Old 03-30-2010, 08:49 PM
  #72  
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Default RE: 1/3 Scale Halberstadt D.III

Seth:

That doesn't make much sense to run the cables on each side of the strut? I have tried looking at old photo's with an eye loupe to see if I can get some small detail figured out but no luck so far on this one. I have used the nylon tubes quit a few times with no problems. The tubes stop at the root rib, then enter the fuse on their own without any other tube. The angular difference with the servo arm swinging through its arc is not enough to make any problem, and the balance cable is just a straight shot across the fuse.
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Old 03-31-2010, 07:57 AM
  #73  
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Default RE: 1/3 Scale Halberstadt D.III

Seth, another amazing build. Just came across it and did a catch up read this AM. I really like the Halbie D fighters, unususal and interesting. A friend of mine with an Eindecker had some oscillation problems with his full flying stab, that after removal of all slop and tightening the pull pull wires to the scary zone, was cured by static balancing the stab adding weight (sorry to use the w word) to the LE.
Doc
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Old 03-31-2010, 12:48 PM
  #74  
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Default RE: 1/3 Scale Halberstadt D.III

Hi Dan, I live in Aurora Or. Where do you fly? Don.
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Old 03-31-2010, 05:21 PM
  #75  
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Default RE: 1/3 Scale Halberstadt D.III

Hi Doc - welcome and thanks. I hope I don't have issues with the stab. Hopefully your friend had the pull-pull set up correctly - tight on center, loose when deflected. If it's the other way around, that could cause big trouble. I'd be worried about flying with cables super tight - it's begging for something to break. Assuming the pull-pull is set up correctly, I'd make sure the aircraft cg is not near the neutral point. Even if the plane is flying well, I'd add nose weight before static balancing the stab. Nose weight would shift the stab trim - moving the stab angle of attack to a position where it generates a bit more lift (negative), a "biasing" load that might move it away from it's (sloppy?) fluttering point. I really don't see static load as a major factor. Adding the weight tends to lower the stab's natural frequency, but I doubt that helped much. Mostly, I'd bet the high tension in the cables caused enough friction damping to settle it down. In addition to stressing the airframe, it wears servos and draws more current. I can't argue too much with success, though!
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