Sethhunter

Fuselage is coming along. Some detailed photos of the tail struts (for rudder and skid). I cut the struts from a plate of AL 6061-T6. The main landing gear is 3/16 music wire in poplar fairings (the poplar was left over from some drawers I built). I didn't have a long enough drill to true-up the holes in the mounting blocks for the main gear so I made a quick ream with a length of music wire and a dremel cut-off wheel to cut the flutes. This is the first plane that spanned the benches in my shop - opens different possibilities for working on the bottom! Dubro wheels are for testing. I will probably put some covers on them.

Lucky Dog

My Feedback: (1)

Very nice Seth! Except for your shop...much too neat.

R/C Art

My Feedback: (38)

Seth....how are you anchoring the landing gear into the fuselage?
Your work is very nice indeed.
You must have an abundance of patience!
And I might add, I rather unique subject, too.

Sethhunter

Thanks for the comments/question! (this has been a pretty quiet thread - I think the project is not "scale enough" for this forum - oh well, quintessential democracy at work)

Here are a few pictures from earlier - all the struts are attached to the fuselage by slipping into holes in hardwood blocks which are bolted to the bulkheads. To keep the weight down, I use two short blocks per strut versus one long one. Also, to give the blocks a bit more strength across the grain, they're capped with fiberglass (ooh there's that word again - I can hear the mice clicking on close [sm=wink_smile.gif]). I bolted the blocks so they're removable. I originally thought about using aluminum channel, but the wood is actually about half the weight. The block-pairs are aligned with the side-to-side angle of the struts so all the bends in the strut wires are front-to-back, flat in one plane, so they'll slip in and out easily. I'll grind flats on the wires adjacent to the blocks for collars.

I don't know about the shop being clean - I've seen some pretty impressive/clean shops on RCU. I actually have two adjacent shops - one for modeling stuff, and the other for woodworking. The woodworking shop is much harder to keep clean. It's certainly true with me that the quality of work plummets as the surroundings get cluttered so I try to keep it organized. This room, and the counters in particular, are not really big enough for projects this size. Maybe the next project will be a smaller, high scale project (teaser). Or maybe a model ship....

abufletcher

You;re getting almost the same "view per post" as my CI thread. I know I'm always over here pouring over the details of every photo you post. You have building skills I could only dream of.

Oh, and that fiberglass, I don't have any problem with it as long as it stays on the inside!

udet1918

Seth I was just told about this thread. I guess you'll do the Ansaldo another day, the Halberstadt is an excellent choice however. I briefly went through the thread and noticed the discussion about the wings and the droop. It so happens the droop was indeed built into the wing "on purpose" have a look at Halberstadt wings being built...... Subscribed!

Ron

abufletcher

Ron, what book is that from? I notice the text is in German.

udet1918

Here you go Don.....
Ron

jtisch

Seth,
Your workmanship is fabulous! I am in awe. Keep up the good work! As for the number of "hits"on your thread, I think it is just the obscurity of the subject rather than the "scaleness"(new word?) that has the count low.

J

caribefoto

My Feedback: (2)

Some of us just lurk in the background and look on with awe. Superb modelling skill on display here, thanks for posting..............John

ARUP

I agree! Once folks see this airplane... they'll remember what 'Halberstadt' is!

Henner Trabandt

Hi Ron and Abu,
I see some old pix comeing up again. And I still got the book mentioned in my workshop. But, you know, the book describes the story of three Halbi CL IV, not the D III, this thread is about.

They found three Halbies in Krakow, Poland, took them to Berlin, Germany where they restored them. Two of them are now exhibited in the USA, in the U.S Airforce Museum Daiton/Ohio and the National Air And Space Museum in Washington D.C. In the book they describe the full story of the restoration and in addition al lot of information about the Halberstadt Flugzeug Werke from the beginning to the end. In many colour pictures they show lots and lots of details ans fine drawings complete the book. A must-have for every Halbi-fan, I think.

Too bad, the book is no longer available. If someone should be interested, I could scan some of the fotographs.

And there is another CL IV exhibited in Germany. It is the plane, the owner Paul Straehle flew after the war as a civil passenger plane. It is the D 71. Could be an interesting thing to build.

And the Halbi is a very nice plane. I´m sure, she will fly as she looks like!

Yours
Henner

Sethhunter

Great Stuff! I appreciate the comments and glad to know there are a few Halbi admirers out there! I admit I'm new to the plane, but the more I look at the details, the more I appreciate the design. I spent most of this weekend working on the cabane strut wires. I also added some ply to the edges of the engine opening and "chine" to the sides of the top-fuse - to get a finer edge for the metal and plywood panels, and started the blunt nose block. The tops of the cabane struts are capped with 10-32 threads (clipped bolts) borrowing the technique from Dan Schmidt that worked so well on my Pfalz DXV. The tops of the struts bolt onto an aluminum plate (partial rib) that carries the load to the square opening for the dihedral brace (which will also be aluminum). About now I really wish I had a mini mill. But I got my exercise for the weekend filing these parts! There are two of these plate-ribs, separated by wooden spacers and tied together with 10-24 CS machine screws. to produce the gap between the wing panels (really no center section). Lots of time spent here (about 5 hours of tweaking) getting the alignment right - to the stab pivot tube and lower wing alignment dowels, should make life easier later. I went this route (aluminum root ribs) so the panels could plug on as a box-kite set, and since there's no center section to speak of (and there's that gap), there really didn't seem to be enough volume there to make a decent structure out of wood.

Sethhunter

Finished up the fairings for the cabanes and built the stab this past week. The lower end of some of the cabanes will be covered with cowl panels later. Some will be exposed (cuts in the panels) and need some scale bracket detail at the bottom. The starboard side will be pretty cluttered with a huge scale muffler and pair of guns hung on one side.

The switches and fuel fillers will be hidden behind doors on the fuselage side. Halberstadt very conveniently placed some big barn door hatches on the sides, I'm sure to make RC modelers a century later happy! The stab is pretty straight forward. I tried to make the flying stabs as stiff as possible to keep the natural frequency much higher than the aerodynamic loading to reduce the chance of flutter. The whole pivot design seems to work pretty well. It has a tiny bit of play in the tube bushings which I may try to coax out with some shims but it's pretty small - maybe 1/16" measured at the stab tip. I'll be putting some big servos in to drive the stab, in part because the forward pivot location hangs a fair amount of the stab weight on the servo. But also while the pivot works freely with no load, aerodynamic loads will increase friction in the pivot. All very manageable I think. Before flying, I'll hang a load on it to simulate drag load and measure the servo current. I originally designed the stabs to be coupled to each other through the tube, but changed that to independent movement so I could use separate servos for each side.

Sethhunter

A few more. The stabs have an alignment dowel and a single 4-40 SH Mach screw to hold them on, plus of course, the tube. I suppose it's worth mentioning I believe the scale stab is much thinner, but I scaled thickness up to accommodate the smallest diameter tube I was comfortable using. This makes for some artistic judgment how to shape the bulging root section right behind the pivot - where the stab essentially "grows" a new leading edge projecting inward (towards the centerline) from the thickest portion of the main stab structure. I didn't think it would look right to make the leading edge of this protrusion fat, so I created a break parallel to the slipstream and drafted the bulging section down to a thin edge. Same applies to the rudder, where the bottom section behind the fuselage essentially creates a new leading edge coming off the thick main section near the pivot. I suppose on the original, generally thinner sections and a little bit of tube welding made these transitions straight forward.


PS - the arched cut-out on the stab root is clearance for the surface-mounted tailskid strut, and bolt head. I thought about burying these struts but it would have required more structure/weight in the tail.

destrat

Seth:

Your Halbi looks great, love to see your work in the photo's. Thanks for the mention on the "cabane struts", I think that technique solves a lot of wasted piano wire, seems you can never bend two pieces the same! I haven't been doing much in the way of modeling since last August after losing my job, hope that changes soon. Keep up the good work.

Dan

TKFOKKER

Seth, I can't tell you how much I am enjoying this build. You have really set the bar high with such a well built and fabulous craftsmanship work on this model. I like it because it's something different from the norm. Fokker s, Albatross, Sopwith's, you know what I mean. Keep up with your posts. We all enjoy them!
D-8 build, Tom

abufletcher

Each post is like a lesson in woodworking/mechanical engineering. I just have one question: Is there going to be a test at the end? [8D]

Sethhunter

Hey thanks for the support. Keeps me goin'! Dan I hope things turn around for you soon - we need you building and flying and setting the bar ever higher!

This week I dive into the wings and take on that droopy lower. Also started thinking about the pilot - since I have all the paints left over from painting the Aces of Iron pilots I put in my Junkers (and those AoI painting instructions are a real confidence builder), I figure all I need to due is figure out how to make a 1/3 head (the body part is easy). Thinking 3 views from digital pictures, sculpted clay, resin cast. My wife thinks I'm crazy. Never sculpted in my life. Digital camera in hand. Who will be the subject...

Nieuport nut

My Feedback: (10)

Perhaps it would be unnecessary, but you could put some weight along the stab LE to statically balance it and reduce the servo load.

Martin

Sethhunter

Thats a good suggestion Martin. Hopefully it wont be necessary. I did move the pivot location back from the scale location, which is really close to the LE. That helped. Each stab is only 2.7 oz - not too bad. Putting weight in the back of such a long fuselage is not the most desirable option. If I need to add some balance, I'd also think seriously about adding an arm to the walking beam (bellcrank) on the front end of the cables, where the push rod attaches just behind the cockpit. Weight added to an arm on the walking beam would also balance the stab without the long moment arm penalty of putting it in the tail. We'll see how she goes!

Thanks.

abufletcher

I say that any of us scale modelers who can create these spectacular scale models can probably also manage a simple head sculpt! I thought of doing this myself and had found these to get my head around the basics...so to speak.

http://www.cdhm.org/tutorials/learn-...-and-head.html

http://www.youtube.com/watch?v=RZTm5miRiGY

Seriously, I always thought it was odd that the same builders who spend weeks perfecting the subtle weathering on their scale creation, will nevertheless make some comment like "but I left the painting of the pilot figure to my wife." As if it were somehow unmanly to paint a face.

Nieuport nut

My Feedback: (10)

Sudden recollection - it seems to me that flying stabs should pivot at the 25% point. IIRC that is the aerodynamic neutral position of symmetric sections. I'll have to dig up some theory to be sure.

Martin

abufletcher

I know I'm old-fashioned and unrealistic, but the way I see scale modeling it's a not about where the pivot SHOULD be, but rather where it WAS.

Sethhunter

Martin I think you're right, and Don - I agree! But as Johny Depp said in Pirates of the Carib - It's really more of a guideline. Well, I look at it this way. First, where is the scale pivot and can I make it work. I'll move it if I think the benefits outweigh the asthetics, which I did here. Then there are the inertial loads (represented by weight times the g load) which can be very significant during maneuvers. I worry about this the most, because the loading will tend to pull the stab in a direction opposite to where you're trying to go (a.k.a. "the pullout aint happening!"). So pivot location (compared to the stab CG) and overall weight are important. Lastly the aerodynamic loads - static and transient. On a stab, I worry the least about the static aerodynamic loads, like neutral point (or point where the moment coefficient is zero). Although a flying stab is much bigger than an elevator, throw is less (I base the throw on the ratio of areas) and so the net lift is about the same and should be within the range of a servo that drives a comparably effective front-hinged elevator. Then there's the transient aero loads ( that cause flutter). In the venacular, blunt airfoils shed a Karman vortex that oscillates between the top and bottom side at a frequency that's about 20% of the ratio of air speed (say feet per second) to chord (feet), which gives you the units of hertz (cycles per second), for low Reynolds numbers. In this case, that's down in the tens of hertz. Hence a good stiff structure is important too. [reference, strouhal number].