Decided I would post the tail and fuse parts of my build as I'm not following the plan here. I am not an experienced builder and this may turn out to be a lesson in HNTDIY (How Not To Do It Yourself!) Add the fact that once again my life is in a state of turmoil, with happy and sad stuff going on and the outcome is anything but assured...
The plan tail feathers seem overbuilt and overweight and are at least partly responsible for the model's tendency to be tail heavy...ergo my tail feathers were built to plan outline but not with plan materials. Borrowing from Polaris building and indoor building, I built the tail feathers out of depron covered with Econokote...gives a light build...flying will tell if they're strong enough...there is a carbon strip embedded in the h. stab to stiffen it.
Sorry if the thumbnail presents upside down...it pops right side up when expanded.
Fuselage
I like the look of some of the big American radial powered biplanes...Super Stearmans and Wacos coming to mind...I wasn't as enthusiastic about the nose of the Skywriter...so...time to start figuring out if I could put a radial cowling on my Skywriter...sounded...challenging and intimidating at the same time
Started looking at radial engine noses and settled on the cowling of a P-47 because, unlike most radial engine cowlings, the P-47's is oval, not round. This shape would allow me to employ Frank's Norseman battery mounting system and get the battery under the motor...almost as far forward as the back of the prop, again battling tail heaviness without adding ballast.
I bought a Parkzone P-47 cowling which looked great but didn't appear to want to match up with the Skywriter fuse. Ordered two more P-47 cowlings from Park Flyer plastics and one of them looked doable.
Head scratching ensued over how to retain the character of the Skywriter fuse from the cockpit area back with a P-47 cowling up front...hmmm
Stole fuse construction ideas from Rob Pike's build but re- designed the nose so that top and bottom run parallel and the sides taper in to accomodate the P-47 cowling...
Used my magnetic building table to try to keep things square and plumb...
Looks great Bill.
We're going to have 6 or 7 different Skywriters! How exciting.
While I was surprised, honoured(?) and amused to be awarded the Crash of the Year trophy last night, I'm not anxious to repeat, so hopefully this all comes together well.
Unlike some of the other builds, I have not lengthened the nose.
The white firewall is actually a sheet of depron which I'm using to create a template before I cut a ply firewall. Firewall and motor are stuck in place with two-sided tape, so I can see where everything's likely to end up. I've angled the firewall to create down and right thrust but still have to locate the motor accurately to compensate.
The battery is a 3300 4S which will sit on a piece of ply between F1 and F2 and be anchored with a battery velcro strap which can be strapped/unstrapped through the cowling. It's Frank's idea from the Norseman build.
I think the thrust line will be approx 3/4" lower than the original Skywriter's...less downthrust? Suggestions, opinions appreciated...before I start gluing
That looks great! Good work.
About down thrust. Hmmm.... I'm wondering if we even need any. I put in the 2 degrees that the plans called for but I'm now second guessing that... now that you ask.
My understanding of down or up thrust is that it's used to counteract the pitching effect caused by the separation between the thrust line of the motor and the drag line of the aircraft. With a high wing aircraft the line of average drag is above the thrust line, so application of power with tend to swing the nose up. With a low wing aircraft we provide UP thrust for the same reason but in the opposite direction. For an aircraft where the wing and tail are inline with the motor (or at least very close) there's no significant pitching effect with application of power, so no need for up or down thrust. In the case of the biplane, with one wing above the thrust line and the other below, I would assume the average drag line is closer to the thrust line causing very little pitch effect. I bet we don't even need down thrust on the Skywriter.
However, if you're going lower with the motor, and therefore further below the average drag line, you may be introducing the need for a little down thrust. Still, based on the above pile of bull... I certainly wouldn't add more than the recommended 2 degrees. :)
What do YOU think?
Go without for a start and if you need it just use washers to achieve it.
Jack.
Thanks guys. I like the washer solution. Rob, I think you're right about compensating for a lowered thrustline with downthrust...how much? I dunno...
Added some gussets (I think they're called scab gussets) to the rear part of the fuse. Hopefully the gain in stiffness and strength outweighs the gain in weight! More gussets to go but they can be done after the firewall and front formers go on.
Bill, IMHO that will be a weak fuselage. While it will save on weight it won't stand up to a robust landing. I think you are over compensating for weight. To strengthen the fuselage you should add trusses to distribute the stress loads. If you do a single truss top left to bottom right corners on each side you will get an "X" shape when viewed through the side. This will add great strength for only a slight gain in weight.
Jack.
I will add some trusses...good idea... Thanks
Added diagonal bracing to create Warren bracing style trusses out of each fuse side. Scab gussets helped to provide gluing surface area. Will add similar to top and bottom later.
Nice!
Hi Bill, it has always been my understanding that the strongest truss structure has the opposite side trusses go to opposite corners. This includes sides and top. You have both sides going to the same corners. I have seen it done both ways but I believe the opposite structure divides and distributes the stress more efficiently. Jack.
(http://www.homebuiltairplanes.com/forums/attachments/hangar-flying/5666d1264318931-cheap-aircraft-simply-impossible-truss-compare-sml.jpg)
Hi Jack,
Your suggestion and the photo make sense. Followed the bracing from the Norseman fuselage and what I've seen in other models in deciding to do the two fuse sides the same. Will alternate the top and bottom bracing.
In the midst of Christmas chaos, found a little time to work on my Skywriter. Built a 3/32 ply plate between F3 and F4 to stiffen the fuse, mount the cabane struts and the tail feather servos. Figured out a way to make the cabanes removable so they can be out of the way for covering. Struts are not bent yet as I won't be sure where to bend them until the fuse is completely framed.
Plates for mounting the lower wing, to support the battery and to mount the L.G. are next and then the nose job can proceed. Took a look at what I've done on the fuse so far and realized I haven't used anything from the short kit or even cut as per the plan.
Maybe that's why I'm so slow...every step on the fuse has involved lots of head scratching!
Top photo is from the top, bottom from the bottom.
Plugged away at my Skywriter fuse over the holidays. Lots of head scratching as I try to solve a custom designed fuselage...but some slow progress. Wanted yo solve the problems of wire routing and power train component location before I started sheeting.
Motor, battery and ESC are located and pretty much mounted...photos below.
One problem has me still scratching my head. Battery is plugged and unplugged through the prop arc. This system requires a way to plug in with no chance of the motor starting...or removing the prop every time and re-installing after the battery is plugged...a nuisance I' m living with on my Norseman.
Suggestions?
Suggestion - use a smaller lipo and build a hatch! ;D
Lookin' great, Bill!
Hmmm... I was going to suggest the good, ol', arming switch (or jumper) in the motor leads, but I'm not sure how "we" now do that with those new, fangled, brushless, motors. Switch two of the three leads?
Besides, an arming switch is a requirement of the MAAC safety code :)
Hi Bill. I have always been dubious of Frank's method on the Norseman for that very reason. That is why I elected to do the complete motor unit removal.
Looking at your pictures you might have space on the left side if you cut through the former with the triangle braces and put the battery on it's side. Access would be through a hatch on top.
Jack.
Have poked away at my Skywriter fuse and looking back at where it was last post, there's been some progress. Re-oriented (not repositioned) the battery so plugging and unplugging takes place away from the prop.
Mounted the landing gear, and upper wing ( a bit of a challenge until I found the three level trick in the manual...went much better when I got the wing saddle level with the lateral datum line... Not sure that's the right term)
Sheeted the fuse sides and sheeted the forward part of the fuse top...think it looks more like a stretched Pitts Python than any other plane I can think of...gonna look for or make a bubble canopy to capture a little more of the Python's look...still lots to do...
Turtle deck framed, interplane strut brackets bent...looking more like an airplane! Trying to use my iphone as an inclinometer...works fairly well except you need three hands to hold the phone against the bottom of the wing and take a picture!
Looking good Bill.
Bruce
Thanks Bruce...how's the Savoia coming?
Question for other Skywriter builders..."What are the arrowed slots cut in R2s of the lower wing? Pictures are from the manual...photo blog thing.
Our best guess is that he intended to fix the under carriage to the wing but changed his mind and placed it on the fuselage. These slots were where the under carriage would have been.
Jack.
I'm thinking servo wire routing. Look at the exit hole in the sheeting. ????
Gonna go with Jack's reply and use the wing to secure the rear strut(s) of a bent wire LG. Rear strut will rest on the diahedral brace and be held there with plywood locating strips and nylon straps as per the big Norseman. Hoping this results in sturdy LG
Looking more like an airplane...have put a hatch in the top for the battery but it's still located with its front just behind the prop. With standard length nose, and battery in place, it's pretty close to balancing...no ballast.
Have to paint the LG white, add wheel pants, bubble canopy and graphics...
Callie's done the graphics which are a somewhat whimsical grab at Canadian history...what else would I put on a red and white aircraft?
Looks amazing!
The battery hatch is excellent!
Great looking Bill and you can still see the Sky Writer in there somewhere.
Jack.
Jack, sometimes l'enfant terrible in the SB class listens and does what the instructors suggest...I put the Warren truss bracing in as per your suggestion and before I close up the bottom, I'll add diagonals opposed to the ones in the top of the fuse.
Graphics are almost done...kind of a nostalgic look at the Miss Supertest unlimited racing hydroplane from the 50's and 60's...
With almost everything attached and a 3300 mah 4S battery on board, model is balancing on top wing main spar...no ballast...4lb, 7oz AUW
I love those graphics. Looks great.
Jack.
Cool! ;D
Looking great Billy. The sky will a mass of beautiful multi-winged planes this summer. Each of the skywriters have their own character.
That looks fantastic Bill. Congratulations! What a unique build. It looks awesome.
A final footnote to my Skywriter build
1. The model survived a complete radio failure and ensuing crash. Happened at another club field where I now refuse to fly DSM2.
After losing radio control, my Skywriter went into a freshly plowed field and inspite of some earlier posts about the fragility of my fuselage construction, tail feathers built out of sheet depron and AUW a half pound lighter than some build class Skywriters, fuse, wings and empennage survived struturally intact. Nine of the ten hard points connecting the wings to the fuse tore away and some of the covering tore...
2. The model was re-built for TEMAC's Fun Fly and with a new DSMx rx flew reliably at the Fun Fly, renewing its builder's faith in a build, fly, crash cycle rather than a buy, fly, crash cycle. :)
I'd really like to finish the Pitts Python look with wheel pants but can't find suitable off the shelf wheel pants...suggestions?