Curtiss America

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Re: Curtiss America

Postby BillG » Wed Aug 18, 2010 5:20 am

Unlike plan and kit builds, the wing tube mounts were located and drilled after building up the fuse. Not everything is planned ahead of time. I remembered to fit reinforcements for every strut that will mount on the fuse, but forgot to add inset sheeting, at the areas where the wing tubes enter the fuse. I did manage to install ply plates inside the sheeting, for the front wing tube socket supports. Drilling for the aluminum tube sockets included drilling through the center fuse keel, which is 1/32" ply laminated. This was one of those "eyeball up" the drill straight and true, as close as you can jobs. I managed to drop bomb the rear socket with CA, where it passes through the center keel, without hitting the cables. This solid joint is needed, as the rear socket fuse support is only CA coated balsa sheeting. Sure enough, the rear aluminum tube was directly in the path of the tail control cables, which were then routed above the tube. This should actually be a good thing though, as it will make the change in direction less severe, where the cables exit the fuse. The cables will slide easily against the smooth tubing.

Drilled and installed aluminum tubing wing tube sockets. Alignment turned out well, but was not a job I was looking forward to.
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Aluminum wing tube sockets, supported by fuse center keel and ply inserts inside the sheeting.
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First time using this method of wing construction, which builds up easily, after fabricating all the formers, that is.
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Re: Curtiss America

Postby TASSE » Wed Aug 18, 2010 2:31 pm

Hi Will, its nice to see larger photos.

Roy.
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Re: Curtiss America

Postby BillG » Wed Aug 18, 2010 7:43 pm

TASSE wrote:Hi Will, its nice to see larger photos.

Roy.
Sure is.
Took me a bit to realize that the photos appear larger here, when they are enlarged at the donor site, before cutting and pasting the link. :lol:
What was not immediately obvious is that the photos actually have a different link, after I click on them to enlarge them at the donor site.

Finished one of the lower wing panel frames last night, at 18 gms. Not terribly heavy for a 16" panel, which could have been lighter if it was not for my use of a wooden dowel LE. The strength of hardwood, along with not having to shape the LE, easily convinced me to use it. The CF rods selected are more than amply strong/rigid, for a cable braced plane, along with using relatively heavy 1/16" sheet for the airfoil formers. This type of wing design could be built very light, with lighter rods and balsa stock. The completed spans will be 36" and 52".

May as well add recent accomplishments to this post, so as to not make a 1 million post thread:

Finished the bottom wing panels. This was likely the most critical part of the build, as there is more to it than there appears to be. I wanted to have fewer than scale formers, but not so much fewer that it would kill the looks. At the same time, I wanted to find a consistent spacing that would put all the strut and engine strut mount formers exactly where I wanted them. This spacing turned out to be 1-1/4", which worked out perfectly. There's more than that though. The lower wings had to be joined such that the exact spacing had to be held from the center of the fuse, or they will not align with the strut mounts on the top wing. It would not look good to have crooked struts. Adjusting the plan spacing for errors would not be fun either. After assembling and measuring the wings, all looks good. I'm almost thinking that if I keep up at this pace, I may actually be able to fly it before the season is over. Pretty optimistic though, as the assembly, with all the struts, fittings, and cables will be quite the job.

Weight so far is looking good also. The completed fuse with the wing, 2 tail servos and cables, is 7oz.
Everything so far is 20oz which includes:
Fuse/2 tail servos-cables
2 motor assemblies
2 rad assemblies with 30A (plenty ample) Pentium ESCs
2 tip floats
3s-1345 EVO lipo

I had figured a 40oz worst case scenario, based on the power system and wing loading, but if I can come in a good bit under that, it would be good. This is especially true considering that I am not a seaplane expert, and they obviously need more power than a hand tossed or ROG'd land based plane. I'm a bit limited in that the motors will not reach full potential, being limited to 7" props. Using 4s lipo, even with conservative throttle management, would be risky.

Image
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Re: Curtiss America

Postby BillG » Sun Aug 22, 2010 2:21 am

History:
I received historical Curtiss America info from Roy today. I found it interesting to read about performance, that the pilot of the replica may have not had the opportunity to read. The pilot, Jim Poel, had stated that the plane unintentionally took off during low speed taxi runs, before ever reaching a plane. The historical info states that with a light loading 3/4 ton short of the fully fueled maximum, the plane would fly at 800 of the 1300 rpm possible. This is probably similar to the loading that the replica took off with.

In the info, there is also a small print of a drawing with cross sections drawn by a man man named Weberspacher, circa 1972. With my insane building practices, I would likely have enlarged the 5"x3" print for 52" span and used it. 1/4" thick line widths, no problem! :lol: It appears to be considerably more accurate than the print I had worked from, and would be a good starting point for anyone else who may take on the project. Don't all volunteer at once now.

Progress:
Finished the top wing and aileron fabrication. I'm now thinking about how the servos/cables will mount, along with a second dummy pull-pull setup for each aileron, as they have two per aileron, on the full scale plane. There is still a good bit of work remaining to be completed on the top wing, before starting that less than exiting task known as covering.

Figured I'd better take a few bare bones shots, after all this work. Pardon the taped in place test interplane struts. They've proven their value in determining the correct lengths, to set proper incidences. It's relatively easy to make mistakes/inaccuracies on the drawing, where the assembled parts never lie.

Image

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Re: Curtiss America

Postby TASSE » Sun Aug 22, 2010 3:35 pm

HI Will. Its amazing how long that top wing is when its seen from above. It looks a very flyable model.
Glad that you got the historical write - up and it was of some help.
You will have your model in the air well before i have
completed the Dornier as i only spend a couple of hours per day on it and some of those days are taken up with correcting yesterdays mistakes. I forsee the wing being a winters job as its nearly time for a holiday which i usually take in the fall.

Keep up the good work. Cheers Roy.
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Re: Curtiss America

Postby BillG » Mon Aug 23, 2010 3:27 am

TASSE wrote:HI Will. Its amazing how long that top wing is when its seen from above. It looks a very flyable model.
Glad that you got the historical write - up and it was of some help.
You will have your model in the air well before i have
completed the Dornier as i only spend a couple of hours per day on it and some of those days are taken up with correcting yesterdays mistakes. I forsee the wing being a winters job as its nearly time for a holiday which i usually take in the fall.

Keep up the good work. Cheers Roy.

Thanks Roy
The top wing is the largest I've ever built. It's now at 52.5", and is still actually a bit undersized. The added 1/2" came as a "correction factor" by enlarging the wingtips, as every bit helps with scale looks. I'm expecting it to be flyable, at least in the sense of reasonable wing loading. I will also have to take a measuring tape, and try to determine if there is a possibility to angle the plane into a 1994 Toyota Camry, to actually get it to the water. It will be close.

I spend a good bit of time on the "yesterday's mistakes" also, as well as dabbling with how to make all the small parts. I formed some of the aileron horns with wire, and am not sure if I'm happy with them or not. Decisions, decisions. It's quite possible that they will be scrapped, and made with thin tubing, as they are a bit thin, in appearance. I could overlap them with tubing, but that's added weight. For the tail, they need to be as light as possible.

It's also a good thing to start determining how a model will go together. Sometimes we find some interesting dilemmas. I don't want servo harness plugs out in the open, so I can either snake the wires and add plugs afterwards (sounds too much like work) or cover the wings with the harnessing all in place. This would entail having the motors and ESCs hanging off of the bottom wing, while the aileron harness would string both wings together, while I cover the innermost portion of the bottom wing, from the motor going inwards. Since we can't have large wire access holes in a seaplane wing, the wires will need to be enclosed with a plate while going into the wing, where the entry point will be sealed, and covering can attach to. Picture all that mess going together on the bench. :shock:
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Re: Curtiss America

Postby BillG » Sun Aug 29, 2010 4:48 am

It sure is good to have the forum back. Maintaining 2 forums is a bit of work, and I want to post here also, as the site deserves the contribution for providing the excellent reference pics. Fortunately I haven't taken many pics lately, so we're all caught up with posting recent progress.

The most difficult part of the covering is behind me now, as well as completing the aileron linkage. The aileron linkage is setup as a pull-pull, where the only non-scale feature is the servo arm hidden underneath the top wing. From the top view, the two cables enter the wing in a scale fashion, where the second cable on each aileron is simply a dummy that will appear to be functional.


The aileron cables enter the top wing and route through heat bent tubing, exiting through the bottom wing, and then through the aileron servo E-Z link which provides adjustment. The aileron horns on the bottom aileron surface are not shown in the picture below. There will be 4 horns per aileron.
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The servo arm geometry works smoothly in conjunction with the path that the cable enters the wing, through the nylon tubing.
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Added covering sections to corners and other areas, where I want to ensure fully overlapped seals.
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Fuse and floats covered with Econokote, where the tail and wings will be Coverite Microlite. The final finish will be a different red than the fire engine red seen here, and will also be flatter, to simulate painted fabric.
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Starting to look more like this, every day now:
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Re: Curtiss America

Postby Cameraman » Sun Aug 29, 2010 9:35 am

Hi BillG

I have to say that's beautiful work.

Regards

Reggie
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Re: Curtiss America

Postby BillG » Sun Aug 29, 2010 4:58 pm

Thank You Cameraman.
I'm also a bit more optimistic about the project, as of last night. At 2am, I couldn't resist the urge to see how well the motor/ESC combos would perform, so I setup a test. After looking at known specs of similar successful models, and watching some underpowered rc seaplane videos on YouTube that couldn't get off the water, I would have lost sleep anyways. The 370 class outrunners ran at a bit over 100W on 3s lipo, with the inefficient 7x6 wooden props to boot, which is better than I expected. The plane can fit up to 7.5" props, and I've also found molded props to far outperform wooden props, as an option for more power. Given the wing area and less than perfectly ideal motor cooling, 200W should be ample for takeoff at around 2lbs, and the wooden props look better than painted props.
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Re: Curtiss America

Postby TASSE » Sun Aug 29, 2010 7:58 pm

Hi Will, the spray ruins a wooden prop.

Cheers Roy.
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