Erich_Prinz

Seth,

Makes sense now - designing medical devices certainly gives a great skill set to draw from when working out a scale build out from scratch!

The flange accents are a great visual add with little weight penalty.

On the air scoops, I've seen a trend from past projects that these seem to be in various places on the original aircraft from that period. I half suspect the scoops were either more after thought or left up to interpretation from the crew building out the aircraft. Purely supposition on my part, but the evidence seems to lean in that direction.

A friend of mine is a world class model rocketeer (has won one world competition against the Russians on their home turf) and they have modeling software for their body tubes, cones, and shoots; that's the reason I had to ask about the scoops!

How are the CAD drawings coming along for this project? I haven't forgotten your offer ;-)

Sethhunter

Seems like a reasonable supposition, Erich. The CAD drawings are coming along fine. I update them regularly as the build progresses. Of course the offer still stands: If the 'crate' flies, I'll be happy to send a copy to anyone interested (for personal use).

Cheers!

Erich_Prinz

I have no doubt of its airworthiness, and at this pace, you'll be waiting on the weather to break and not on the plane being ready to fly.

E~

1bruno

Seth I would love to have them as I am itching to build this plane. If at all possible I would like to get a copy of the plans or CAD drawings. I can send you my email or [email protected]. Let me know if this is possible, I will pay you for them too if you would like. This is for my personal build as I would never sell them in any way for profit.

1bruno

Seth why did you choose to fiberglass the fuse?

Sethhunter

The plane certainly can be built without glassing the fuselage, I'd just use thicker balsa for a little more strength on the fuselage and stab. Here's a general note I posted a few days ago on the topic of glass versus other finishes:

I think it's important to decide what role the finish plays in (how much you need it to) strengthening the structure. Even a light cloth and resin adds significantly to the strength of the fuselage, etc. (I glassed the fuse, stab and fin on my Pfalz DIII and DXV, which were plywood on the originals). I factor the finish into deciding the weight/strength of the structure underneath - lighter/thinner balsa under glass, than say, fabric finishes. That helps offset some of the weight. I especially build light in the tail when I plan to glass. That is, I think of the finish as more than a seal, but part of the structure. I concur with comments above that the cloth weight is minimal, and even the resin weight can be kept pretty low. I think I used about 1.5 oz of resin on the fuse/tail of my Pfalz DXV (1/4 scale) and .7 oz cloth. I thin the resin about 10% with alchohol, and squeegee it on with a stiff plastic card, then put the glass down and let the cloth wick-up the resin from the balsa. After sanding etc. I squeegee another coat of resin, putting down another 1 oz or so. The tail was sheeted with 1/16 balsa, and the fuse with 3/32. 1/4 sq balsa stringers underneath. On fabric covered planes, I generally up the balsa thickness by a 32nd. Obviously flat versus round fuse sections make a difference in the strength /finish tradeoffs.

No problem getting the plans when the build is complete.

Sethhunter

Just a little progress to report..... did a bit of design work on the wing attachment details and updated the CAD drawing. I think I've put around 150 hours into designing and drawing (I mention it because I always like to know how long it takes other people to do stuff).

Took 2 days off from work, and made a pile of ribs. (I never tell work associates what I do with my vacation - I always get kind of a blank stare!)[sm=what_smile.gif]

In the meantime, I'm waiting for the aluminum tubes to arrive. Since the wing is thin, the tubes are thin (7/8 and 3/4" OD) so I ordered tubing with thicker walls than usual; .065 thick rather than the "model standard" .035 or .049. This yields a safety factor >2 over a design load of 10 G's with a weight penalty of 6 oz (23oz versus 17 oz, .065 versus .049 wall thickness). It's perhaps noteworthy that I also need 4' tubes, since the wing center sections are very wide (24" span on the top centersection). This leaves 12" penetration into each panel to transfer the load from the tube to the panel spars.

To hold the panels on, I was going to put dowels in the centersection that I could fish a few rubber bands around, and attach them to hooks on the panel. Anyone have any other favorite semi-invisible method for holding wing panels on?

Erich_Prinz

"Anyone have any other favorite semi-invisible method for holding wing panels on? "

Really, really, really strong magnets! ;-)


Rare earths actually works very well on the small models with low wing loading - I'd be afraid to see the weight penalty for what would be needed on your application though.

Erich

Sethhunter

I like out of the box thinking! Great idea. I don't want to be the first to try it on this size ship[sm=47_47.gif]

geezeraviation

My Feedback: (3)

Seth, are there flying wires on this airplane? They would hold the panels on. As an added safety measure anchor the end of your tube socket in a block of hard wood and put a bolt up through the bottom of the wing through the block and the tube into a nut plate. The wing joiner tubes on my 1/3 scale N 28 are square alum and I'm doing something similar. The top wing has been modified to be two piece and has joiner straps at the center as on the full scale and the cabane strut bolts but the lower wing panels are held on pretty much just by the landing wires so I'm doing the block and bolt thing to make it easier to sleep at night.Doc

Sethhunter

Hi Doc - thanks for the idea. No, there are no wires on this airplane
I had a plane, with rubber bands holding the panels on, catch a wingtip on a passing tree. The tube bent and the wingtip was damaged, but that was all. The only concern I'd have about putting a bolt through the end of the tube in the middle of the panel, is the possibility of much more severe damage in a similar accident. If the panel is secured at the root, you might get away with minimal damage at the root. I'll certainly give it a bit more thought.

In the meantime, I cut the spars today from Sitka spruce. I made an extra and destructively tested it to calculate the failure stress in bending, etc. For those interested in numbers, here's what I learned:

I measured/calculated the weight density of the wood as 520kg/cubic meter; medium density for soft structural timber. I loaded a 20" cantilever sample (1/4 x 1/2) until it broke and calculated the failure stress at just under 9,000 psi. This is a bit low for Sitka, which I've read is typically around 12,000psi. The elastic modulus average was 1.5 million psi, a little low. I cut the spars "back sawn", with growth bands vertical (stronger that quarter sawn with bands horizontal). Overall, I thought the stuff worked pretty well - very light, very straight grained, nice to work with. And given the small cross section, it held its properties pretty well.

abufletcher

You can't get more "invisible" than the way it was done on the full-scale. My philosophy is "when in doubt, just doing it scale."

Sethhunter

Fair enough - although details on this plane are sketchy. As far as I can tell, the DXV was the only cantilever, wireless, design the Eversbusch brothers produced. The Herris drawings do not even show any access ports on the wings.

foodstick

When I look at this plane the thing that strikes me is that the original designer decided to do everything the hardest way possible ! Nothing about it looks simple. Then Seth comes along and makes every endless detail look so good! Maybe the original idea was to allow future modelers to have a challenging project to spend unlimited head scratching on, needless to say I doubt I would have had the nerve to start it, I am glad its being done, and done so well for the rest of us to enjoy...

Great effort Seth...

geezeraviation

My Feedback: (3)

I've caught a wing tip on a tree before, twice to be exact. The first was a VK Cheroke back in 1975, the second was a Tanzer Cabin wing two years ago, the Cheroke was totaled, it contacted the ground upside down and backward, the Tanzer damaged the tip that hit the tree and shortened the other tip about a foot when it slammed into the ground after being spun sideways after the "brush" with the very small scrawny leafless nearly invisible sapling that had volunteered at the boundry fence of the field, I never saw it, it's gone now, ( can you imagine ). Doc

geezeraviation

My Feedback: (3)

Seth, as a reply to your 12-14 post about securing the panel at the root. The Block/bolt scheme would work there as well, it doesn't have to be at the end of the tube to work, I may do mine at the inboard end of the panel, thanks, Doc.

Sethhunter

Hope everyone is having a nice holiday season. Here's a few pictures of my progress on the upper wing center section. I decided to retain the outter panels with rubber bands. You can see a paper and phenolic/cardboard tube. The paper tube is for the rubber bands, the other obviously for the structural aluminum tube. I'll use either a rigid wire or cable to extend the rubber bands to the full span of the center section (24 inches). Outter panels will have screw eyes to hook the cable onto. The hole just behind the middle spar is where the connector will be for aileron servo cables, and the hole near the TE is for an alignment dowel. 2nd photo shows the detail of the ply plates that mount to the cabanes. The struts are threaded on top, so the wings will have hatches to access the internal nuts. Lots of gusseting ties the plates to the spars. Note for strength, I cross-cut the gussets so the grain runs perpendicular to the joints, not parallel. Detail pics of the cabane struts show the entry and exit points for the aileron servo cables. Not completely concealed, but pretty close. The aluminum tube sits high in the root section because the outter panels are heavily tapered (in thickness) on the bottom surface. The tube show here is pretty long - I'll will be shorter but here it was handy to have the extra length to check perpendicularity of the wing center to the fuselage. I had to slot the holes in the mounting plate slightly to true it up. For those counting, the center section added about 20 oz. On to the bottom wing!

Erich_Prinz

Seth,

It's looking great.

So your query for attach points were for the wing panels then? It makes sense seeing the current progress photos.

The rare earth magnets would actually work in that scenario with the tube providing structural support. Regardless, I would add some sort of safety capture wire/cable in the event of a materials failure of the retainer mechanism just to keep the wing panel from sliding and dorking up the control surfaces while in-flight.

Two things I'm curious about:

1. How will you hide the seam where the panels connect (presuming the wing panels are in fact removable for transport?)
2. Do you have the skis for take-off and landing in the snow? You're almost done!

E~

geezeraviation

My Feedback: (3)

Excellent work as always Seth. The ail cables going up through the struts blows me away. I've cut gussets that way for years just makes sense. I make em out of ply cut the same also. Doc

Sethhunter

I knew there was something funny about that wing section - I forgot to install the false ribs (riblets!) The scale spacing is so tight, it looked ok without them - figures I spend all this time on the plans, then don't look at them! Fortunately easy to fix.

Hey that's a great seam question Erich. I'm afraid I don't know of any way to hide it. I went back to the Herris drawings to see if there's any indication if and where the panels connected on the full scale. I assumed they joined at the cabanes, where the taper starts. That's clearly the case with the DIII. But on second look, I'm not so sure about the DXV. It probably makes more sense that cantilever wings were joined at the centerline. The illustration shows "stacking pads" on the leading edge (I guess for standing the unrigged wings up on their leading edge). The pad locations suggest the wings were split down the middle. Does anyone know where the Fokker DVII wings joined? Or were they one piece? The DXV supposedly borrows much from the DVII.

I don't think I would have designed this model any differently (if I knew the full scale wings joined in the center or were one piece); my goal was still to have a model that assembles quickly at the field. While I'm pointing out other departures from scale, I also installed flush sheeting on the outboard ribs to reinforce the ends and make for secure fabric attachment. I did think about recessing the sheeting, but again, opted for simplicity.

Skii's sound like fun but I don't think I'll need them. These projects have a way of bogging down on the details. This is my third model with the ol' straight six power plant (Mercedes/BMW). It seems that detail draws the most aclaim at the field so I'll probably put the time into making a nice one. (I can't bring myself to strip details off earlier projects).

Thanks guys for the comments.

Erich_Prinz

Well, the skis idea was completely tongue-in-check - more a reference to how fast this build is going for you compared to the DIII.

On the seam, I was thinking of some sort of faux finish layer that is for static presentation and removes for flight. Not sure how that would be pulled off - just the idea that came to me so I figured I'b better pass it on.

It doesn't matter much if it isn't being entered into competitions.

Agreed - cannibalism is just wrong.

Erich

cocobear

My Feedback: (2)

Hi Seth, Beautiful build!!!!!!!!!!!!! As to the seam question, I have used a very small overlap (1/16th) of 1/64th plywood on the outboard panel over the inboard. I then stitched and taped it and it is not noticable as a seam unless you are looking fairly close. Just an idea.

Dave

Sethhunter

Oh that's a great idea - thanks!

Sethhunter

Anyone have a favorite idea for a nice, neat, scale-like mounting for N-interplane struts? On my DIIIa, I embedded a nylock nut in the strut, and had a small access hole on the opposite side of the wing to insert a bolt thru the wing and into the strut. Have also used U brackets & bolts, clevis & plate, dowel pin & tension wires, horizontal tubes & hooks.... they all have draw backs. Has anyone tried, for example, a keyhole (or track) & T-slot bolt? How about struts that fold in the middle with a sleeve to lock them? Other (less wild) ideas?

Erich_Prinz

That's a great solution!!