|Nov 10, 2013, 01:44 PM|
SB2C Helldiver 100" ws from Jerry Bates plans
This may be a bit premature but I thought I would start this build thread. I have received the plans from Jerry and the canopy. Still waiting for some other accessory parts that I ordered, they are slowly trickling in.
I read that the flaps had 2504 holes in them. No way I was going to do those but found out that Bob Holman had a laser cut set. Called Bob and talked him into doing a set for me. He wasn't crazy about it, said they were areal PITA. I've bought from Bob for many years and he is a really great guy. And excellent service too. I ordered them on a Monday, received them on Friday! At least they are here in plenty of time.
I'm out of foam but found a supplier in Nashville and turned in an order last week, should have it this week.
I shipped the wing plan off to a core supplier and it will be about 3 weeks before I get the cores. I would have had to build a bigger bow in order to cut them myself so just went the easy route. So this isn't going to be a quick build and will be slow starting off.
The Bates plan is a balsa build type but I'm planning on a FG fuse with integral vertical fin.
And the stab I plan to hot wire and sheet.
Since it will be slow starting this build, I decided to start it with a smaller version, 49" ws. It doesn't qualify for this forum but I really didn't think it deserved a full thread in Foamies either. It sort of half qualifies here. I wanted another "beater" plane like my F2A Buffalo and P-40. I call these my simple series park flyers. Quick, easy, and the way they fly are a plus. Just throw in your car, get to the field, load a batt and chuck in the air.
It's all foam and came out at 2 lbs AUW with a 3s-2200 battery.
Took about 4 days to frame up and alot of that time was waiting on glue and poly to dry. I glassed it with 3/4 oz glass and poly.
Another few days installing the power system and electronics and tossed her in the air. Didn't fly as well as the Buff does but it will once it is trimmed out. At least it flew better than what was said of the real one.
I normally start these by putting a 3 view on my overhead projector and tracing the outlines. Just as I was about to start, the bulb burned out. So I had to go old school and just scale it up by hand.
These are super simple type "plans" but who needs plans, right? All you need are the wing, stab, and vertical fin planforms and a side view of the fuse.
Once I had the drawings, I cut the fuse side view in three pieces. One is a small rectangular section through the middle of the fuse side view leaving all the curves on the top and bottom pieces. I just used a comfortable width for the box to accommodate the electronics.
Made a rectangular box from fanfold and use the tracings of the top and bottom to band saw pink foam pieces to fit the basic box. You could hot wire them if you prefer.
Then just a matter of gluing the top and bottom pieces to the box and you have your basic shape. After the glue dries, it's ready for shaping.
|Nov 10, 2013, 07:43 PM|
Only Surviving Helldiver in EAA Sport Aviation magazine
Looking forward to this build with great anticipation!
Below is a link to a great article on the world's only flying SB2C Helldiver belonging to the CAF (Commemorative Air Force).
Be patient while it loads. It may take a minute or two .
|Nov 10, 2013, 07:57 PM|
Nice, John, should be a kick in the pants! Nobody has one. They shouldn't fly too bad, they made a few thousand of them until Curtiss-Wright got caught up in the scandal, check it out. Lack of quality control. Take care,
|Nov 10, 2013, 08:50 PM|
Don't know about magic Bruce but it might take magic to get it done. Looks to be a complicated build, we'll see.
Thanks Brad, I'll check that out.
Good to hear from you. Hope you had a good trip back to CO.
I did take the little Diver out for a couple short flights today. Beautiful fall weather and just had to get out. I added a little down and right thrust but not enough. It needs more. Plus I taped on 2 oz weight up front to move the CG up a tad. Flight characteristics improved but they still aren't where I want them to be. She does a little better under power but still requires some right trim and some down as well. But the hand launch was easy, it tracked out just right under half power. I'll keep working on it. Smooth rolls can be accomplished but you need to feed down into it as its goes inverted.
I did make a spinner for the 3 blade prop today and it gives more of a Helldiver look to it. The spinner is simple to make too with magnets. I'll show the method when I get to that part of the build.
I tried the 4 blade prop and it flies it well too. Problem is, it will over amp my 25A esc if you go much over 1/2 throttle. But it doesn't need much throttle with the 4 blader.
OK, where were we? After the glue dried on the fuse, I shaped the top and bottom blocks to a sort of Helldiver shape. I got a bit over zealous on the cockpit and had to add some spackle to fill it back in. This was rough shaped, I then finished it but a little more rounding here and there and then gave it a coat of thinned spackle to dry overnight. Next morning it was sanded smooth and the glassing process was commenced with 3/4 cloth and WBPU.
That's it for tonight( gotta stretch this part out a little), tomorrow we'll do the wing and tail feathers.
|Nov 11, 2013, 01:38 AM|
Joined Jan 2005
Looking forward to watching progress on this one, looks great already.
I really don't know how you can carve out a shape freehand the way you do, I need all sorts of guides to get a shape
|Nov 11, 2013, 08:25 AM|
Thanks Ken, but like I said this is a quick, simple stand way off scale. The big one will be whole different animal.
So let's build the wing, won't take long. A semi-symmetrical wing would be a better flier but much more complicated to build. This one is flat bottomed for convenience and goes together quick.
I start by taking the wing planform, take 1/2' off the LE( that will be balsa) and cut a bottom panel out of 6 mm depron. Sand a taper on the TE so when you glue the top sheeting on, it will make the TE thinner. It doesn't need to be razor sharp, we're not building any speed ship here. Mark the aileron on both sides so you will know where to place pieces and where to cut it out once the wing is done. Pin that to your board with wax paper under the LE and then cut a tapered depron wedge about 2/3 the length of the TE. Make the wedge 3/16" at one end and taper down to nothing. This is the washout. Pin that under the TE wingtip. This allows us to build in the washout. Cut a length of 1/2" balsa for the LE and glue it to the front edge. I like Titebond for this but that's up to you. Make the LE tall enough so that you can glue the top sheeting to it and trim the remaining off later when you shape the LE.
Next I hand draw a simple airfoil with the high point about 30% from the LE of it. Make sure the airfoil tapers short of the TE so the top sheeting will glue to the TE and the airfoil won't hold it up off of it. I only make a root rib and a wingtip rib. The root rib is only about 1/2" tall at it's highest point so these are not thick wings. Glue those in their place at each end on the bottom panel.
I measure the airfoils height at the 30% mark and cut a tapered spar out of 6 mm depron and glue it. Next do the same for the rear spar. You want the spars flush with the ribs so the top sheeting will lay flat when applied. I make sure the rear spar runs just in front of the aileron with a space to glue in a balsa piece so there will be some meat for the CA hinges. Glue the short balsa piece in for the aileron and then a depron scrap behind the balsa piece, sand it to a taper so the sheeting will lay flat when you glue it on. A small depron piece for the aileron inner edge completes the aileron.
The wing is almost ready for top sheeting now. But you want something to glue the front of the top sheeting against the LE. So measure the front of both airfoils and cut another tapered sparlike strip and glue that to the inside of the LE.
Now it's ready for sheeting. I used 3 mm for the top. Cut a slightly oversize piece and trim it after the glue has dried.
Using white gorilla glue, I ran a bead all along the spars, airfoil ribs, aileron pieces, TE and the strip against the LE. Place the sheeting snug against the LE, pin it well, and pin or weight it all down. I like magazines for this, they will conform to the curve and hold the sheeting down. Use sanding blocks, pins, taper, whatever it takes.
Once the top sheeting is dry, remove the wing panel and shape the LE, sand a dihedral taper on the root and clean up all the edges with a sanding block. I glued a chunk of foam on the wingtip and sanded it to shape.
The aileron needs to be cut out, LE on it shaped and it's ready for hinging or glass, your choice.
I prefer to glass almost everything for a decent finish and some ding resistance.
I used spackle on all the rough sanded depron places and once sanded smooth I glassed with 3/4 cloth and WBPU.
Once that's done, I glued the panels together and used a strip of 3 oz cloth on the middle to reinforce it.
I like to do both panels at the same time, it speeds things up when you are cutting parts out on the fly and you make sure you have a right and left. Don't ask how many times I have made two of the same side.
Hope I haven't forgotten anything, doing this from memory and we all know how that is.
I added down and right thrust this morning and checked the wing incidence (again). It has about 1.5 degrees of positive in the stab so that isn't a big problem. I'm hoping the down thrust helps that ballooning of the flat airfoil when power is increased.
May get another trimming flight today but have a doc appt so we'll see. It's still not flying as well as I would like it to but has improved so hopefully the D & R thrust will help it some more.
Next up is the tail feathers. They can be built in about 30 minutes or less.
|Nov 11, 2013, 08:39 AM|
Wanted to add one thing on the fuse build. When I position the templates on the foam blanks, I mark where the wing and stab LE and TE are. Poke a hole through the template at those points, both sides. Then when you remove the template, check the incidence between the wing and stab. I like the stab at 1 degree positive, makes the plane fly on the right attitude. I then take a bamboo skewer and deepen the holes so I don't lose them in the sanding process. This makes locating the wing and stab a snap later on when you're ready to cut them in.
|Nov 11, 2013, 04:08 PM|
The tail feathers are "easy peesy". Stab was cut out from some black 6 mm that I had laying around. I trimmed 1/4" off the LE and added balsa. Cut 1/2" out for the elevator balsa inserts. Once dry, trim up and sand the LE and edges. Spackle where you sand. Once it is final sanded I used a wire "U" to connect the elevators.
After that it was glassed.
Vertical only needs the balsa insert for the LE. Sand edges, spackle sanded areas and the it was glassed too.
That's it they're done.
The glassing and waiting on the poly to dry took as much time as anything else on this build.
I took it out just awhile ago for another trimming flight. The right and downthrust helped it quite a bit. I still think it might need the CG moved a little more forward. I'll try that next. These straight LE wings seem to like a more forward CG, just like the Tigercat.
Foam suppler called and said my order would be ready Friday. That will let me start the big Beast.
|Nov 12, 2013, 06:18 AM|
After glassing all the assemblies, I cut the wing, stab and vertical in. Align and glue, make sure you check wing/stab incidence before gluing. Once that was done I primered it all to check the finish. Spackled all the joints and after sanding them, gave them a coat of poly to seal the surface. I also cut the cowl off at the first former and used magnets to mount it back on. I left the belly pan under the wing off, it will be installed after the electronics are done.
All that is left before maiden is equipment installation. That's next.
|Nov 12, 2013, 10:03 AM|
I have a few quick questions before you get deep in to that big 'Diver...
Do you use depron for the wings instead of fanfold because it's consistent in thickness? (fanfold not being so)
You mentioned that you use titebond for the LE balsa. Do you use titebond as well for all the spars and other balsa before you glue the top wing skin with GG?
As for incidence, I think I read on one of your other builds that you do 2 deg pos at wing root. Is the 1 deg pos you mentioned for the stab 1 deg pos of the wing, making it 3 deg from datum?
I ask all this because I'm excited about a mass launch for "Ace" next year. I'm gonna have to get busy and do a pusher jet of some kind for that as well as wrap up my other birds...
And like others say, great work and effin' FAST on the first Helldiver. I look forward to the big one.
I thank you too for your generosity in the sharing of your techniques.
|Nov 12, 2013, 10:07 AM|
Joined May 2009
If I recall correctly J uses titebond in any location where sanding will be required as gorilla glue does not sand. I've started using this tip and it works great. Wood to foam or foam to foam. It works.
|Nov 12, 2013, 02:33 PM|
I use the depron so I don't have to sand the waves out of the fanfold. I really like fanfold better, it's easier to work with on curves but this thing doesn't have that many. I don't like the way depron sands, you must spackle it to have any chance at a smooth finish.
WM is right. I like Titebond anywhere I will have to sand through the glue. It sands much like the old Ambroid( yep, I have some of that too, I still love the smell of it, guess I'm an old glue sniffer). But I think I used GG on the spars, Titebond needs plenty of time to cure esp if in a place where it doesn't get much air.
It probably is about 3 degrees from the datum as the 3 view had a positive angle on the wing.
I like a 1 degree difference in the wing/ stab incidence( stab an overall negative of course i.e. the LE of it down ). It always seems to make it fly at the right attitude.
But this little bugger has had me scratching my head. I moved the CG up a little yesterday and tried it, had it at 20% of MAC. It still seems to be dragging its tail around a little. I got the Bates plans out and he has the wing at 2.5 degrees positive and the stab at 3 degrees positive! That got me thinking( always a danger) that since it is so short coupled, the plane may fly better with the stab at a slight positive instead of the wing. I'm at 1.5 degrees negative and there is no way I'm cutting that stab back out. I plan on moving the CG up to 17% MAC and flying her again. I think that might solve my problem. We'll see , but it's blowing gusts up to 35 mph today so nothing going on with that.
I meant for it to be faster than it is. 5 trimming flights have yet to get it sorted out.
I don't have it flying as well as the BUFF but getting closer.
OK, back to the build. I installed the electronics. The ailerons have their own 9 gram HXT servos. Another for the elevator. I just ran a pushrod through the fuse for the elevator and mounted the servo at an angle to match the rod.
Once that was done, I cut the middle out of the belly pan and glued it in, sanded it flush and then glassed it.
At this point I took it out and maidened it. Didn't take any pics of the motor install but I used a BC-3548-6 790kv. Just a wonderful and very versatile motor. It will handle 3-5 lipos, 13" prop and put out 700 watts. I just threw a 25A esc in that I had lying around and with the PZ 3 bladed prop on a 3s-2200 batt this motor just loafs. The plane cruises around at just over 1/4 throttle.
Then it was time to paint. And the plane really needed a spinner so I made one for it. I'll show how I do that for these low powered setups, simple, quick, easy and works great.
Callies decals came in today, she is finished, just needs a sealer coat. I think I will go with a satin coat, you can wipe dust off a lot easer than the flat coat.
Finished pics coming soon.
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