RE: Mystery Project - Will it fly
I'd feed VERY uncomfortable with the thrust-line up that high, consider moving the engine to the lower wing. With that kind of top-heavy moment you will nose-over very easily on any kind of landing, and take-off's will similairly be frightening until the elevator gains authority. On that note I would suggest much larger control surfaces on the elevator. A flat airfoil like you have detailed would be quite unstable, I'd add some dihedral, maybe even some sweep if you need to maximize wing chord while minimizing wingspan, as your design suggests. I presume you have some very interesting design constraints, I'm going to assume it has to have a very short wingspan (fit within a 1-meter box or some such) and probably carry an odd-shaped load. Rather than comment on your soultion, perhaps you could present us with the problem? -Curt
Posted on: 9/18/2012 7:56 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11232330

RE: Scratch Building 1/4-Scale Pitts Model-12
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.
Posted on: 9/12/2012 8:41 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11226835

RE: Scratch Building 1/4-Scale Pitts Model-12
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.
Posted on: 9/9/2012 6:54 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11222630

RE: Scratch Building 1/4-Scale Pitts Model-12
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 I dunno. 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 I am comfortable with the dry weight is up to 10.76lb and likely will be climbing when I mount 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 :)
Posted on: 9/8/2012 9:47 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11222417

RE: Scratch Building 1/4-Scale Pitts Model-12
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)
Posted on: 9/3/2012 4:07 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11216125

RE: Scratch Building 1/4-Scale Pitts Model-12
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.
Posted on: 8/19/2012 12:16 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11198798

RE: Scratch Building 1/4-Scale Pitts Model-12
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 I had 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.. 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 DO include 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 I can 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! I took 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.
Posted on: 8/13/2012 9:31 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11192539

RE: Scratch Building 1/4-Scale Pitts Model-12
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 is the 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!
Posted on: 8/13/2012 5:35 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11191407

RE: Newbie looking for 1st Build
A field is only partially about finding an open area to fly, it's more about the helpful folks you'll find at one who can give a new pilot crucial advice and It's pretty easy to locate one. For something small like the Super Cub of course you don't need much more than a parking lot, but it would be good to familiarize yourself with the local culture, pick a weekend and you should be able to see some aircraft out there and maybe get a feel for what you want to build and how they fly. I have yet to bring someone to a field who ended up saying "yeah thats about what I thought they looked like flying" its usually more along the lines of "you can do WHAT with these things?!"
Posted on: 8/13/2012 5:19 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11191391

RE: Newbie looking for 1st Build
Building from plans is a very dicey affair. The big obvious stuff is easy, anyone with decent skills and a few basic tecniques should have no trouble, laying out ribs or building up the fuse. The problem is, in my experience, plans are at *best* 75% complete and 10% wrong. They assume deep knowledge on your part. Imagine instructions for building a car that show a 3-view drawing of the front and then an arrow with a line that says "put the engine here". Vague? Welcome to plan building. Imagine further that they put the hinges for the door on the wrong side. It would be obvious to an experienced car builder that this was an overisght/error and simply correct it in his build. But imagine the error was more subtle, without an obvious cure, like the wing dihedral is called out in 2 different places in 2 different ways with 2 diffeerent values! (it calls out a 7-degree angle, but according to the plans it's 4 degrees..) which is right? which should you choose? what should you do? Sure you can see how it's supposed to look, but what adhesive should you use to assemble it? thin CA? wood glue? epoxy? does it need to be clamped? pinned? should you build a jig or can it be sanded to fit? "Sheet this"? really? how!? The plan-builder makes decisions like that almost every build-session. Then there is hardware installation, where to put the reciever? how to mount it vibration-free? Planning to fill this model with fuel? how? Covering a model is a whole adventure in and of itself, lets talk hinges :) Be prepared to buy a lot of "little things" that add up to big $$. There is just no way to sugar-coat it. My only advice is that when you buy any piece of smallish hardware (screws, clevisis, pushrods, washers etc...) that you buy more than you need. need 2? buy 5. need 10? buy 50. Never throw away anything that your servo comes with (not that I know anyone who does..) keep it all and organize it somehow, your collection of hardware will grow [rapidly] to the point where when it comes time to build from plans, you'll have "something that kinda works here" for most occasions. That's the bad news, the good news is that kits (especially trainer kits) have almost NONE of those problems. The instructions walk you along a well-trod path through the tecniques and steps for success. After a good kit-build or two you'll have most of the experience you need to take a whack at a [good] plan build. Order a short-kit that someone at your field has built (ideally.. don't have a 'field' yet? find one! go there and talk to the pilots!) Or something popular so when you do have a question, there will be a good chance that someone can answer it for you. A piece of advice I would offer is that when the instructions tell you to do something a certain way that doesn't make sense, trust that it does, and there is a good reason for it. Definitly ask why, but be sure you understand all the reasons a certain thing is a certain way before changing it to a way that makes more sense to you. Usually there is a tradeoff, and if you fall on the other side of a compromise, by all means have at it! Just be sure to understand what that compromise was. There is nothing like the feeling of flying a model that was uncut balsa only a few short months ago. Except maybe crashing it. But on that point I will sing you a song you are likely to here many times before your first 'solo' (hum along if you know the tune): Get a Simulator! They are expensive but worth every penny, balanced against the time and wrecks they will save you.
Posted on: 8/9/2012 7:36 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11186874

RE: Scratch Building 1/4-Scale Pitts Model-12
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.
Posted on: 8/8/2012 8:20 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11186390

RE: Scratch Building 1/4-Scale Pitts Model-12
Got a BUNCH of 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.
Posted on: 8/6/2012 9:04 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11183744

RE: Scratch Building 1/4-Scale Pitts Model-12
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. A rather disappointing turn today, I weighed all the components I have now and came up with 11.5 pounds. That's minus covering and some odds and ends, so call it 12 pounds dry, call it 13 with the smoke system. Add gas and smoke fluid and its minimum 14 lbs My original target weight was 10.5 pounds dry so I'm way over. I've used ~4 ounces of wood glue and 2 ounces of CA so that's not it, I guess I just misunderestimated what the structure was going to be. I expect it to still fly well, the wing chord is very long (10.75") and the wing loading is still quite light even at 14 lbs, but I am really looking for ways to cut that down to where the K factor says I need to be.
Posted on: 8/5/2012 6:33 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11182259

RE: 24% Pitts S2B converted to S12 build
moved to scratch-build forum: http://www.rcuniverse.com/forum/m_11096359/tm.htm
Posted on: 7/29/2012 7:22 AM by Author "curtrc" in the forum "Kit Building"
http://www.rcuniverse.com/forum/fb.asp?m=11173193

RE: Scratch Building 1/4-Scale Pitts Model-12
Got the gear done and decided to mount the tail stabs before covering. The filling in and around them is poorly thought-out and I need 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 I need to, we'll see when it's at its full-up weight.
Posted on: 7/28/2012 8:11 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11172815

RE: Landing gear bracing
True as that may be, that isn't really a helpful response. I am interested in this too for my Pitts scratch-build. The gear is too springy and I am considering some wires.
Posted on: 7/28/2012 2:38 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11172461

RE: Scratch Building 1/4-Scale Pitts Model-12
Important step today- the first full-sized mock-up. I guess not everyone does this but once I have enough pieces I like to just do a gratuitous layout to say "hey.. THIS is what you are building.." it makes all the minute details-on-bizzare-looking-parts seem worth it. Took me a solid two hours to get those cabanes right. had to use a makeshift bending brake and lay them out on the plans to check for correctness.. lot of iterations. As I said in an earlier post the cowling came in, fits perfectly, and I couldn't be happier with it, has a very nice NON-beercan shape. next step is to finish sheeting. had to install the cabanes and ... oh sanskrit.. I forgot the gear. how am I gonna bend THAT slab of aluminum. Okay guess I'll tackle that tomarrow so I can finish sheetnig. I am also uncomfortable with how well butressed the firewall is, I plan to run those 1/4-inch plywood rails all the way forward (wigh some lightening cutouts in the next lasercut) and I think that will lock the model together solid as a tank.
Posted on: 7/27/2012 9:01 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11171888

RE: Scratch Building 1/4-Scale Pitts Model-12
After much thought and consideration I've decided to go with the DLE-30. I know I know I was bouncing around from 33GT to DLE-35 but common sense won out, namely: there are many folks at the field running them so lots of help/experience, it's relatively cheap, and 17-ish pounds is plenty of static thrust. Got it in today along with the prop and wow, this is the biggest engine I've ever installed in anything. Being a biplane the Dash doesn't quite seem as big a scale as it is. A 62" wingspan is not that large, and while the body is stout, it's not that long. I just got a sense of the size and power of the model I'm building with the king-sized 18x8 egg-beater It will be swinging. Measured 3-times, drilled once and had it mounted in the plane as a fit check, so far so good. Need some hardware to complete the installation but there are still plenty of steps between here and firing it up for the first time. Also completed the surfaces buildup. I am leaving the holes in the ailerons since I am planning to cover it with transparant blue, but I may sheet it with 1/32 if I change my mind, they are relatively large and I'm not sure I'm fully confident in their robustness, even though those ribs are 3/8 stock, that trailing edge is just not attached with much surface area. lower wing is complete except for rib caps, hinges, servos and covering. liekwise the top wing. Still saving up money for servos (the next big buy) but I have ordered a sample of this little guy: http://www.servocity.com/html/hs-225bb_mighty_mini.html and for only $18 it seems like it might be okay for the ailerons. Bear in mind there will be 4 of them and this is a biplane so the surfaces are not as large as a traditional 1/4 scale (although they are oversized) I am not trying to pinch pennies on the important parts, but the next servos up for consideration are in the $35-$50 range and having to buy 4 of them, well that's worth the savings if it will comfortably do the job. Will report on findings, unless someone has a strong 'no and here is why' answer for me.
Posted on: 7/25/2012 8:29 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11169550

RE: Scratch Building 1/4-Scale Pitts Model-12
To the person who PMed me offering to plot the plans: thank you! But in the future please turn on your PMs so people can respond to you :) I created some PDFs of the views I needed to build up the wings & tail and brought them to Kinkos, was a very pleasant experience! The one near me (don't know if its standard equipment) had a 36"-wide laser printer that printed onto continuous spool, so 36" by "whatever" is easy to do, they charged $0.15 per square foot, I spent like $8. I was careful to put on an X and Y scaling box and they were both spot on. Started laying down color schemes for the Dash as I finish off the sheeting. Sorry no pics for this update.
Posted on: 7/17/2012 7:00 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11158502

RE: Scratch Building 1/4-Scale Pitts Model-12
Seems my attachments didn't make it in my last post.. odd.
Posted on: 7/12/2012 10:24 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11153446

RE: Scratch Building 1/4-Scale Pitts Model-12
So I have been busy, added a lot of filler to the fuse, and most of the stringers. The lower wing is structurally complete, waiting on some balsa to finish the aileron buildups, then some sheeting and covering and it'll be done. Worked on the upper wing most of today, ran into some issues in the center joint I had not anticipated. Mainly.. I did not include one at all. As designed the wing would just fold in half. oops. After some noodle-time I have a solution I really like and have amended the plans to reflect it. I'm making zillions of little improvements to the plans as I go, the Dash-B will be so much easier to build, and a superior design in a lot of ways, including lighter. I have identified at least 4oz of weight I can shave off this design with no compromise in strength, doesn't sound like much I know but it adds up, I am a miser. purchased the aluminum I'll need to make the cabanes today, installation will be straightforward but I need to complete the upper wing first. Also got the cowling in from Fiberglass Specialties: http://www.fiberglassspecialtiesinc.com/catalog.htm Ordered an off-the shelf model 8 1/2" x 8 1/4" and couldn't be more pleased with it! Looking forward to acquiring the engine so I can make some cutouts and install it. Speaking of which I am starting to consider the DLE-35 for this. the OS GT33 looks like a great choice but its a bit spendy, I think I can get more bang-for-the-buck with the 35
Posted on: 7/12/2012 10:22 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11153445

RE: Scratch Building 1/4-Scale Pitts Model-12
Tell you the truth I hadn't thought about it. I researched conventional gear design (not more than X degrees from CG, not less than Y, track at least Z.. etc etc.. ) and then computed those values for a volume representing where the CG location might ever be (all the way forward and a lot aft) and then put the gear right in the middle (which turned out to be an area about half an inch wide) I figured this location will "work" for any CG but will obviously not be optimal for every one. The gear is split, and I had envisioned mounting them with 3 #8 threaded rods (to act as supports between them) . They will be accessible from the underside, but not the outside through the sheeting. I guess I could slot the top screw a bit and allow some (maybe 1" either way?) adjustability, but hadn't planned on it. Frankly with the powerplant I'm planning to use I was not expecting this plane would be "reluctant" to take off :) and as for landing, I just want it to be ground-loop resistant. If it flies well but the ground-handling is poor I'll work up a bracket to move the wheels around (will be ugly but just a testbed) and fine-tune the location, then redesign the landing-gear struts to reflect my findings.
Posted on: 6/30/2012 1:36 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11137860

RE: Scratch Building 1/4-Scale Pitts Model-12
Got the odds and ends I needed to start building. Most importantly a pair of 4-foot 1/2" steel tubes to act as the build-jig ($7 apiece from online metals, sure wish I could build airplanes out of steel). The idea was to design-in a pair of removeable hole-carriers running the long -axis of the fuse so it could be easily built guaranteed-straight without needing a plan or pins or anything. Worked perfecly! build this up in all of 3 hours :) Next up will be the stringers, some sheeting, and then the wings and tail-feathers. I re-worked the landing gear a bit and am quite happy with the new swept-forward design bolting directly to the cabane-ribs, it's also lighter and simpler as it no longer requires it's own 1/4" ply mounting plate.
Posted on: 6/30/2012 6:31 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11137512

RE: Scratch Building 1/4-Scale Pitts Model-12
So I fit checked the parts and so far so good! Some very minor issues not worth mentioning, did not need to do very much sanding at all to get it to fit perfectly. The pictures you see here are held together with friction only :) Just makign notes and figuring out an assembly order when I whip out the epoxy and CA, I expect this plane to go together very quickly. The wings are another matter but their design is fairly conventional so no real biggie. So far the full-up weight of the fuse plus wing ribs is just over 1.5 pounds. figure weight of glue plus the balsa I need to finish it (sheeting/stringers/tail) should have me well under my 6lb structural weight budget.
Posted on: 6/23/2012 5:15 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11128987

RE: Scratch Building 1/4-Scale Pitts Model-12
They parts came today! Surreal that just a week ago this was a drawing in a computer, and now I am holding the actual physical piece cut out of wood exactly as I drew it. I know this is old-hat to most of you but I am just in awe of how relatively easy it was to go from screen to real-world! Gotta shout out to http://www.laseredgecutters.com for holding the hand of a newbie, they did an excellent job and the price was more than reasonable, I do not hesitate to reccomend them. So time to.. get to work? Wait.. how do I cut these pieces out of the plywood? My hobby knife is too thick as is my keyhole saw. I was about to drill them out but thought I'd ask first if the vets had any tips on the best way to get laser-cut parts out of their 'tree'.
Posted on: 6/21/2012 6:59 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11125999

RE: Scratch Building 1/4-Scale Pitts Model-12
Got a few laser-cut quotes and went with one in the low $200's which I think is a pretty darn good deal. Have ordered the rest of the balsa I know I'll need and am keeping careful track of materials and sources. Don't know if I will make this a 1-place or 2-place aircraft. I think the 2-place looks cooler but don't know what kind of canopy I'll be able to make. Pretty sure the ol' Soda-bottle trick will get me a small one, but the top hatch was designed to accept either. Maybe I can source a cooler one. Planning on a single 5/8" carbon wing-tube on the bottom wing, pretty sure the top wing will be okay with the wide cabane butressing combined with the outter struts. I will probably add flying/landing wires on the first iteration but I don't think they will be required. Speaking of which I don't know if I'll go with traditional Pitts anti-flutter cables on the tail, I'm pretty sure they'd just be for show, but not sure how I'll know for sure unless I mount a rear-facing camera or the tail is ripped off in flight. I'm hoping to affect plan 'A' there. I added the sheeting and stringers to see how it was going to look and I couldn't be happier with the rear profile, that says "Pitts" to me. but the front? well that kin of says "beer can" to me and I'm hoping it doesn't look that way in the final equation. I may change that profile a bit if I don't like how it ends up turning out. Can do wonders with color-blocking :) In addition I'm working up a "plan" view which is basically a piece of cake! I just project the 3D model, delete a few non-visible objects and viola, done! Trick is going to be printing it out on large-format. I was going to try Kinkos or some other McDonalds-of-printing but I think I read where the largest they'll do is like 24" or something. I'll research other options, but if anyone knows where I can print out 24" (ish) by 65" (ish) from PDF's or something, send me a PM please.
Posted on: 6/9/2012 8:34 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11112852

RE: Scratch Building 1/4-Scale Pitts Model-12
Thats a really nice looking plane. I sure hope the Dash ends up being viable. I really only planned on building this one for myself but I would be over the moon to see others :) Laid the Dash out for lasercut and it was an interesting feeling looking at all the parts splayed out like a boned fish.. it seems a little less initimidating now, that big 3D mass just seems so impossible to actually build outside of a computer but looking at the individual components now I think it seems a lot more approachable. Just have to find a kit cutter willing to do it.
Posted on: 6/5/2012 11:17 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11107469

RE: Pitts M12 26% plans available soon
I wasn't going to resurrect this thread but since someone else already did.. I referred to these plans while designing my own S12 (1/4-ish scale, 62" wingspan/length, 30cc) and In case the original designer still checks I want to thank you for your hard work, it made my hard work somewhat less hard :) You are right this is an incredible level of effort. I'll be sending it out for laser-cutter quote this week.. no idea who I'm going to use or how much it's going to cost, this is the first time I've attempted a project this large and involved and there is just no way I can scroll-saw it. If the design flies anything like stable I'll be happy to provide plans/details/drawings to anyone who wants them. And if not.. well I'll still let anyone have them as an example of what NOT to do. Scratch-build thread: http://www.rcuniverse.com/forum/m_11096359/tm.htm -Curt the attached photo is the current state after some simplification passes and moving the wings 1" back. Questions/comments/wtfyoufailed appreciated.
Posted on: 6/4/2012 10:38 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11106013

RE: Scratch Building 1/4-Scale Pitts Model-12
Have been sanity-checking the design, just could not shake the feeling that the wings were set too far forward and I think I was right. I checked the ratio of as many photos as I could find of similair aircraft (Beast, Ultimate) and the ratio of the measurement from the front of the cowl to the front of the top wing to the back of the top wing to the tail was around .23:1 quite consistently, whereas the Dash (working title of this Pitts) had a ratio closer to .2:1 Meaning what my gut was telling me was right, the wings were set too far forward. So I'm moving them back by the requisite 1" to bring it in line with other 3D biplane ratios. There is sincere flattery and there is NOT flushing $500 down the commode. I'm doing this by extending the cowl forward by 1" and shortening the tail by 1" rather than re-do.. well.. everything. -Curt
Posted on: 6/1/2012 2:15 PM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11102909

RE: Scratch Building 1/4-Scale Pitts Model-12
I've finished the wing design, which was quite an excercise in wetware stress analysis. Trying to make sure the wings are securely anchored for positive and negative G's. I have read where aerobatic models routinely undergo 12g's and on up to 20 g's. I've seen that figure quoted a few places and it does pass the sniff test, which leads to an interesting calculation. Lets assume the weight of the fuselage is 8 pounds at 1G (yes I know I should talk slugs or grams, but easier to think about) then at 20Gs it impart a 160lb force acting about its center of mass. Assuming uniform wing loading (a bad assumption, but probably not terrible) then that force will need to be reacted by 4 cabane connections and a wing saddle in positive Gs (not so bad) but in negative Gs it will be reacted by the same 4 cabanes and... two dowels and two nylon screws. hmm.. so.. 160 lbs / 2 wings = 80lbs per wing == 20lbs per cabane or dowel/nylon screw. That's not.. terrible.. but that force is going to then be transmitted through the frame, and while it's cliche it remains true: a chain is only as strong as its weakest link. Want to lose a week? Download this game: http://www.bridgebuilder-game.com/bbg-info.php It teaches you how to construct bridges and results in some surprising stress concentrations. So anyways I have that on my mind (inverted alien wall, anyone? :) I think I'm finnaly ready to collect all the parts and send them out for a cutting quote. I have tried to reduce partcount but there are still a lot of intricate parts here, like how much is this bulkhead going to run me cut from 1/8" lite ply.. ? $5? $10? $50? I doubt I could cut it myself to the precision required. Guess I'll see. I've attached some shots that include the built-up wing, but I think at some point this just becomes noise so I'm not going to post gratuitous pics anymore probably until I actually get some parts in.
Posted on: 6/1/2012 8:21 AM by Author "curtrc" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=11102446