curtrc

Got the gear done and decided to mount the tail stabs before covering. The filling in and around them is poorly thought-out and Ineed them mounted to carve the balsa fill correctly. Trying to think of a better way to do this in the next design. Luckily my color scheme calls for a flat-color base on the tail with decal-ish highlights so this should not pose much of an issue. Always a nail-biter for me, measure 10-times 30-min epoxy ONCE.

I like how the gear came out, its a bit springier than I'd prefer but I can fix that with a length of piano wire as a stiffener if Ineed to, we'll see when it's at its full-up weight.

rgunder

Curt,

The build looks great! Keep it up!

Rich

curtrc

Sheeted the turtle deck today and it came out nice, very smooth. Got some parts in today and a whole passle of them come in tomorrow.. maiden is probably 3-4 weeks away.

curtrc

Got a BUNCHof parts in today from my "big order" including the servos, smoke pump, BEC, reciever, fuel tank and misc hardware. Theoretically I have everything in-house that I need to maiden it! now to get the build finished..

Ordered a canopy, Horizon Hobby 89" Yak 54 part.

$25 shipped and figured it had to be big enough that I could cut it down to what I needed. boy was I right.. this thing was huge, initial test-fit confirmed it

Later that evening I think it came out rather nice. Also finishing the magnets on the canopy hatch and some sheeting, should have the hatch feature-complete in a few days.

curtrc

The hatch has been a slog since every joint needs to be clamped and let dry. no "wick in the CA and go" for all the form-fitting balsa. blech.

Just about one with it, and turning my attention to the front of the plane, plan to sheet it and "commit" to some internal structure that will be difficult to get at once I'm done.

QUESTION: I have been pondering this for some time now and still do not have a good answer. What is a clean way to route the upper-wing servo wires down S12-style cabanes? Right now I'm sort of setting on a separate, small-diameter non-load-bearing tube that will drop down between them. I'll paint it black or use thin carbon-fiber and hope it goes mostly unnoticed, but I would love to hear a better idea.

pimmnz

Curtrc,
I have been watching this build for a bit and I thought that it would end up way heavier than your original projections...a 1/4 Pitts is a tiny plane and the structure would only need to be minimal. The trouble with computers, cad and laser cutters is that they encourage complexity. You need to get a drawing of the full size structure of the airplane, figure out the load paths, and reproduce it in 1/4 scale. Then remove all that is not required. Your fuselage should be just a box of 1/4 squ balsa or 3/16 squ spruce longerons triangulated to carry wing and u/c loads. The tailplane and fin are wire braced, make the wire work and then the outline can be laminated 1/16 balsa with 1/16 'ribs'. Those fuselage stringers need be nothing more than 1/16 x 1/8 bass on edge, the fuselage is already carrying the loads, so the stringers are just for looks, and should therefore weigh nothing. Treat the wings the same way, the spars and struts, with the rigging wires, make a braced box, the ribs and covering merely streamline the spars, if the spar is a nice 'box then the rest should weigh just enough to support itself, design the thing to fly. Your current weight is already heavier than my 1/4 (84") Pfalz 12 and SSW D3, and they are complete and flying. A good place to start, structurally, is with reference to the old Free Flight jobs, they needed the lightest airframe combined with the strength to survive the landings while coping with minimal power. They were, despite their looks, efficient airframes, structurally.
Evan, WB #12.

curtrc

Yeah the stringers are way oversize. I've been making lots of modifications to my design. I didn't know if they were going to be structural or not, or how much stiffness the sheeting would provide, as I had hoped the answer is "quite a bit". The thing is the weight isn't in the fuse. Even with that extra stringer mass it's barely 30oz; the problem isthe second wing + 2 extra servos.

However I've reduced the weight by about a pound and a half now, I had weighed the cowling and canopy without making cutouts and that reduced their contribution by 8oz. The gear is all aluminum and weighs 10oz, I think I could cut that in half with carbon-fiber but I'm not going to bother. I had allowed 16oz for the smoke pump but hadn't actually recieved it yet and when I did it was only 5oz so *whew*. I'll be using a 16oz tank for the smoke fluid but can always partially fill it if I need to.

I'm also using a 16oz fuel tank which is a bit oversized for a DLE30 and I will likely only 2/3 fill it if weight is "going to matter".

All of which puts me down around 12lb take-off weight, sans smoke fluid. Which is only 1.5lb over my target, so I'm okay for this first pass. the Dash-B will be shaving more weight, to be sure, especially in the front where it will have full-length 1/4" birch rails with cutouts rather than the over-heavy (by 2oz) ad-hoc rails I have there now, along with other redundant sructure.

I was also pretty unsure of what the laser-cutter was capable of and now think I have a much better feel for where I can shave weight on parts that I knew wouldn't be load-bearing but wanted to make sure wouldn't be too fragile to assemble either. I have learned so much from doing this, I actually can't wait to make another one and apply it!

Nergall

This Dash-B is sounding better and better.

Can't wait to see how the Dash-A flies though!

curtrc

YIPEE!! So I am going over this weight thing with a heavy heart and carefully re-measure everything and record it on a spreadsheet (instead of keeping a running tally on my calculator)to see where I really am and where I might be able to save some weight. I was still confused because Ihad been so careful in the design to do volume-calculations against reasonable ply/balsa densities to get in the ballpark on weight, and to weigh incoming parts and be careful with glue and all..


<colgroup><col width="209" /><col width="86" /></colgroup>

hatch	4
cowl	4
tail surfaces	1.9
struts	2.5
fuse	35.6
Engine + ignition + muffler	44
lower wing	14.6
upper wing	14.6
prop/spinner	6.2
Fuel tanks + plumbing	6
Electrical + 2200 LiFE	13.4
smoke pump	3.7
covering (estimate)	18
Total oz	168.5
Total lbs	10.53

10.53 lbs! On the nose! I don't know how I screwed it up the first time but I went over this three times to be sure.

NOTES:
- I know the upper and lower wing are identical to the 10th of an ounce. I can't explain it, but thats what the scale said no matter how I arranged them.
- The wing weights DOinclude servo +ailerons but do NOT include covering
- Both tanks are 16oz so technically this would result in 12.5lb take-off but I am fine with that since Ican easily do less
- This is the weight with a 2200 LiFe battery, the flight pack will actually be a 2-cell nanotech LiPo, I expect it to be a smidge lighter.

So I am thrilled again! I was quite surprised at how heavy the Ultracote was so added a generous 18oz for covering weight, but I think that's conservative and expect it to be less, possibly half that, since I measured an entire roll to be 5oz with the backing attached (took the cardboard tube out)

I have finished sheeting the left side and most of the cowl, one more build session (likely tomorrow)and I'll be ready for some final sanding on the fuse! Itook these shots before gluing the canopy on, that came out pretty good I'm pleased with it, not that it's a good job, but its the best I've ever done on a canopy I fully expect it to be blown off on the first full-up engine test.

Also notice the re-enforcing rails I added to the front which were part of the weigh-in. I cam trying to think of anything I forgot to weigh that I got around to the first time and there just isn't anything so the Dash is back on track to be a 3D floater, or at least impersonate one until It actually flies.

curtrc

More progress. Sheeting is complete and the fuse is now ready for radio installation and some final finishing sanding. Still debating covering color schemes.

I haven't cut the cowling out yet since I don't know how far forward the engine is going to need to be mounted to get the CG in the right ballpark.

Here are a couple shot showing a wing-servo mount and the bottom of the Dash, designed for easy access, with the rudder and throttle servo installed. There will be some removable baffling in place to direct air downward away from the firewall, but there is no structural need for it right now so its left open for ease of work-on-ability.

Nergall

Looks good!

Make sure those servo wires don't flop around too much though. They can chafe in some cases and cause a failure.

curtrc

Been busy, just didn't want to post any pictures until the covering was somewhat complete on the tail section (without the white stripe to break up the two colors.. it looked pretty bad).

Not that it looks good the way it is now, covering has always been my designated "you suck at this" area, I'm not proud of it, but its the best I can do.

Hinged and attached the tail feathers, added a steerable tail-dragger, set up a pull-pull on the rudder and traditional servo horn for the elevator, servos are installed and hardware in somewhat-close-to-flight configuration, still under my 10.5lb weight goal! 10.43lb after measuring this assembly. (my 1lb weight allocation for covering seems to have been way overblown, but made up for with the little things/screws/extension wires)

curtrc

Indexed, measured, indexed, measured AGAIN.. sanded.. .. you know the drill (pun intended) mounting the lower wing. Finally got everything square and straight and then mounted the dowels/nylon screws. holds like a charm although how strong it really is Idunno.

Built up some lower-wing structure to make nice with the fuse when its covered. Added a bit of weight, 1/4 of a pound actually in epoxy and hardware.. more than Iam comfortable with the dry weight is up to 10.76lb and likely will be climbing when Imount the upper wing.

Fitted the top wing and it looks nice!

Nailed the incedence its 0-degrees all around, with the size of the ailerons this sucker is sporting it probably won't matter much, I will be able to trim out just about anything, but I'd still rather have everything straight

AA5BY

The last picture offers a view of a concern that I've felt since the beginning of the design, that being the gear strut mounting. I might be (hope I am) wrong in my perspective that it is a good thing when gear stress cancels in a common mount and without a common mount there is no canceling so the supporting structure needs to be quite strong. I think the way the struts are mounted is fine but I'd like to have seen a box structure between the two with all thread screws traversing both mounts.

As is... gear stress might/will lever the mounts away from the former and failure with a difficult surgery to repair.

With the covering not yet on... not too late to think about that.

One plan might be to simply add two all thread rods (one up and one down) with both interior and exterior washers/nuts traversing between the two mounts and gear struts. Doing so, there would be no need to change any of the existing mounting screws and the result would offer stress canceling.

The reason for the interior washers/nuts is that the upper rod would see compression loads whereas the lower would experience extension loads.

curtrc

I am concerned about that as well, in fact using a threaded rod as you detailed was the original plan (I think further up I mentioned it) I even have a few lengths of #8 rod in the bin that I purchased for that purpose.

That was before I decided to add a 4th wall to the box structure, it's not in yet so I can access the underside and mount ignition/battery/smoke pump or whatever else to move the CG around. But I do plan to add one. At that poitn I figured the rod would be overkill and am cutting every piece of weight I can.

Also the gear is not very stout, I expect it to bend long before the structure fails in the "crushing" direction. which would require quite a bit of side force anyway and I'd be more worried about where the wings went

If the gear were made of sterner stuff I'd be more worried and probably add the threaded rod at that point, I plan to drill the holes in the sheeting before I cover it so I can do that. With any luck, though, the gear will survive moderate landing with a bit of spring (this is my hope) and I won't need to spend the extra 7-10 ounces in aluminum it would take to reinforce it.

AA5BY

Much depends upon the field condition and I'm coming from a pretty rough field where few ARF gear supports are adequate and the additional weight of gear reinforcing is needed and in fact welcomed to avoid headaches of ripped out gear on landings that weren't that hard.

Sounds like you have thought the issue well and that was my primary concern.

curtrc

Mounted the top wing! The struts still need some balsa to sandwitch them (and sand to shape) but the design is coming together.

I should be able to spend some time tomarrow hinging ailerons and finishing servo installation and then its covering time for the wings. I COULD mount the engine (I have all the parts) but that seems like it would make the fuse needlessly bulky and difficult to handle while I'm still building parts of it so that's going to wait until the wings are finalized.

Nergall

It's a plane!

Scottgir

Hey Curt,

I've been following this since we spoke about the center rod. This looks great. I wish I could contribute more to this but you know while you took off into the air...I stayed on the ground LOL.

Good luck!

Scott

curtrc

Scott! damn Ididn't know you were still following along. Getcherbutt down to Atlanta and join me for the maiden, one thing's for sure Iknow its going to be fun one way or another

I'll take video though.

Anyways got the lower wing 98%complete now. Ailerons hinged and wired up (deflection is stupendous, one thing I'll have is gobs of authority) just needs a few touch-ups and maybe some bottom detail.

Next up will be the top wing, which needs a few pieces of back sheeting and some odds/ends (figure an evening or two before its ready to be covered)

I am liking the way the color scheme is coming together, but I am not quite sure what to do with the front. IWASplanning some red/dark blue striping but my wife is dubious about those colors going with the white/purple theme. Iconfess Iagree. She understands that it's largely about visibility and orientation in the air (thus contrasting colors and different top/bottom) but red and dark blue stripes? against purple? yech. I guess I'll think of something.

curtrc

Top wing mostly covered and all surfaces hinged. Starting to see the light at the end of this project

curtrc

Mounted the engine in it's semi-final (pending final weight/balance) position, which turned out to be around 1/4" further forward than the plan called for. I am frankly stunned I got it that close.

Nergall

I use 2-3 degrees of both right and down. I stack two washers in the top left, and one each in the adjacent corners and everything usually works about right. Bigger engines use bigger bolts and bigger washers.

I've never noticed this to be too much either. Usually, it is not enough. All my planes still pull a little left in the up line and climb a little on power.

Also, DEFINITELY remove the idle stop screw.

curtrc

Big milestone, took the Dash out to the field today and fired it up for the first time for a full-power test.

Snafu of the day: forgot to tighten the rubber stopper on the fuel tank. oops. Good news is once that was sorted it fired right up with only a little fidgeting, nothing unexpected for a new engine. The airframe took full power without incedent, everything held and remained rock solid so yay for that.

Big shout-out to Nergall for lending his experience, aid, and big leather glove at the field

I realize most reading this are familiar with engines of this class but it's my first experience with them and boy howdy I was not prepared for the power. I tried to pull it away from the test-stand at full throttle and actually had to put my back into it! 17-ish pounds of thrust may not sound like a lot but wow.

There will be a maiden shortly. As soon as the weather cooperates.

curtrc

She's ready!! Still need some vinyl on the cowling to break up that white, but all the parts are there, the engine has been run up and nothing shook loose (okay nothing important

Maiden will most likely be next weekend, or maybe tomarrow if there is a minor miracle in family scheduling.