Giant scale B-24J Scratchbuilt

[frednjess]

Always wanted a big bomber and the "24" is pretty rare. Can't seem to find a reasonably priced kit that builds light. I build my own flying wings that are clearing the 100 mph mark, so I figure a nice slow 4 engine plane shouldn't be a big deal.
Here's the goals:
Functional bomb bay
Retracts
4 Brushless outrunners
Flaps
Possible working gun turrets
IMAA legal
Under 6 lbs
Under $200 RTF.

Those last two ought to be interesting...
I'm going to make a foam subframe with a balsa laminate over the whole thing. Not sure on a final coating, but I'm leaning towards paint. I've got the wings figured out and have the foam cores cut. The foam needs a little sanding but is essentially ready to be covered. I'll be laminating the wings with 3/32" balsa, 1/2" leading edge, and a capped trailing edge. I'll cut out the ailerons after the wing is laminated. Wingspan is going to be 82.5". Now I've got to figure out how to mount the motors.

Also, if anyone needs wing cores for a B-24 let me know. They're not too bad to cut and I don't like to charge too much.

[frednjess]

I glued the wing sections together and got the carbon fiber arrow shafts installed in the wing halves. I'll be putting in another piece of arrow closer to the wing root for some extra strength.

[wartoy]

I love bombers!!!

I will be watching this for sure!

[R/C_Addict]

Looks good. Keep up updated. :)

[frednjess]

Forgot to put up the plans picture, so here she is. I'm going to work on the top and bottom panels of the fuselage today. Should be fun!

[minitelemaster]

How are you going to fit retracts into your "under $200 RTF" goal?

[frednjess]

I'm planning on using some low cost 40-60 size retracts from Tower. Here's the link:
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXL406&P=0
This should work well, as I'm working on keeping the weight down. $6.95 metal gear servos to accuate the gear. Foam wheels should round out the package. Sound good?

[minitelemaster]

Retracts look good, and so cheap! You're using Hobbycity servos I presume? Do you need three of them?

[frednjess]

Yeah, I'll be going the Hobbycity route. Just can't beat 'em. Also, yes, I think I'll need 3 servos. The wings are going to have one for the mains. The nose gets one for retraction and one for steering. I'm going to have the wings and the wing saddle Plug-N-Play ready, i.e. all one unit. Should make the wing root joint very strong and make it very easy to disassemble. 7' of wing has to make it into my car somehow!
I'm toying with the idea of leaving the steering servo out and using vectored thrust for ground steering. Might make for some cool aerobatics too!
Right now the biggest question is what to do about foam covering. I was originally going to sheet the foam with balsa, fill the voids and give it a nice paint job. Now I'm leaning towards using fiberglass cloth and water-based poly, then painting. I did a test piece and got some good results with bond strength. It also makes the plane quite a bit less expensive. Any thoughts on covering with fiberglass?

[frednjess]

I also wanted to apologize for the delay in posting new building. I took the family to Disneyworld for a couple of days. And yes, the Disney princesses are pretty hot in person! :cool:
Now back to work. I've got a Tiger 2 to recover today, but I'm hoping to pick up the 1/2" foam for the fuselage tonight. I'm also going to work on the motor mounts and engine cowls this afternoon. Yay!

[minitelemaster]

Do you need special equipment to cut foam wing cores? Foam seems a much more economical route than balsa when scratch building large airplanes, and is also lighter, allowing more "goodies" like bomb drop, retracts.

[ScaleBrad]

Here is a B-24 build with foam wings..Maybe it will give you some ideas.

http://www.rcuniverse.com/forum/m_1433853/anchors_1433853/mpage_1/key_Bomber%252CBoys/anchor/tm.htm#1433853

Good luck on this !!

[frednjess]

Do you need special equipment to cut foam wing cores? Foam seems a much more economical route than balsa when scratch building large airplanes, and is also lighter, allowing more "goodies" like bomb drop, retracts.
Yes, I do need special equipment to cut the foam wing. Fortunately, it's rather cheap and easy to build the piece of equipment. I made a "bow-saw" stye hotwire cutter using fishing leader line for the wire. It's great! I use the cutter to cut all sorts of wing cores. I'm going to laminate the wing with balsa for some extra strength, while keeping things light. I'm still planning on the "goodies" like the retracts and bomb bay.

[frednjess]

Here's the latest build news. I've got the fuselage top and bottom pieces ready to cut as well as the fuselage side template. Here's a shot of the plans for the top and bottom, plus the tail group. I'm having a little issue with the engine cowls and how they join the wing. I'll figure it out.
I still haven't found a consensus on balsa sheeting or fiberglass. I kind of like the idea of the balsa to help conceal any minor imperfections. I'm hoping to get the fuselage cut and glued this weekend.

[appleflyer]

ooooo, i love scratch build threads! keep it coming!!

[flyrobert]

Very Nice

[appleflyer]

are you still building it?

[frednjess]

Yes, I'm still building it. I've just been working on some woodworking projects to bring in some cash. I'm planning on cutting out the fuselage this week. Then it's lots of sanding to get that nice round shape! I've also been toying with ways to make the engine nacelles. Built up would be nice, but time consuming. Also, I don't have plans for them. I'm working on foam nacelles with lite ply firewalls glued to the front. Should be plenty strong after some glassing. Then I just need to vacuum form some cowls...

[frednjess]

Alright, I've finally gotten something done on this ol' bird. I cut out the fuselage pieces; top, bottom, and two identical sides. I've used this building technique with two other planes and it seems to work well, making a very strong fuselage. It allows me to build a pretty accurate plane from a 3-view. My previous planes were a Fokker Dr-1 and a 30" B-24. Both have flown beautifully. A bunch of the old guys that I fly with have said that the Dr-1 is the best flying version they have ever seen, as most are tough to fly. The B-24 gets cool points for being only 30" and having four counter rotating props.
If anyone ever wants to build a micro multi engine plane, get the props off of an Air Hogs Storm Launcher. They are only about 3" long and push right onto the motor shaft.
Here's the picture of my progress. I'm hoping to glue this monstrosity up either today or tomorrow.

[frednjess]

Well, got the fuselage glued up last night. This thing's going to be huge! I've got to cut out the wing saddle and fit the wings, as well as the bomb bay. I'm also trying to figure out the bomb drop mechanics. I saw one here on RCGroups that should work. I'm also cutting out the tail pieces. I had originally thought of using 1/4" balsa, but now I'm leaning towards a built up structure. I may still do the vertical stabs out of 1/4", but the horizontal stab will be built up so I can hide the rudder servo wiring.
Here's the fuse pic.

[frednjess]

Thought I'd see how big this monster will really be. There is a silver 4 foot straight edge in both pictures. It's centered on the wing in the width picture. I'm going to have trouble keeping this one from the wife!

[appleflyer]

nice.

[minitelemaster]

Lookin good. Do you have a link for the bomb drop mechanism you are planning on using?

[frednjess]

I can't find the link for the bomb bay mechanism, but I'll take a picture when I get it built. :)

[F-86FLIER4LIFE]

hurry up and get this done so we can see it fly! :D

[frednjess]

Hey, I'm doing what I can. I've got to get some fiberglass cloth ordered. I saw an ad for .75 oz cloth, 10 yards for $25, in AMA last month. Got to check that out since the local HS on carries the little packages. :( I'm still fiddling with the engine cowls, hope to get them done tomorrow. Anyway, what's the hurry? >:) I like to fly when it's cold!

[F-86FLIER4LIFE]

i love to fly when it is cold! that seems like the best since all the grass goes dormant and you don't have to worry about the runway growing to tall. :D

[catman529]

Looks good...I love scratchbuilds.

[frednjess]

Well, I may have hit a little snag in my grandios plans...The retracts I was planning on using are a little thick. I think the actuator arm will stick through the wing. This may end up being a hand/trolley launched giant plane! I'm going to do some more research, but it's not looking good. Those darn air retracts just cost too much!

[F-86FLIER4LIFE]

do fixed gear, it won't look to bad on a B-24 since the nose wheel is barely out of the fusalage in the first place, and the mains will blend in with the wing. :D

[frednjess]

Worked on the horizontal stab yesterday. Still need to put some lite ply on top and bottom for some extra strength. I think it's needed due to cutting out a pretty good sized servo wire channel. That and I don't want the vertical stabs wiggling!
I've made another change on the covering. I think the box fuselage and the carbon in the wings, as well as balsa LE and TE, should make a strong plane. I don't think I'll need the extra strength (and weight) of fiberglass, so I'm going with Doculam. A little 3M for some extra bonding power should do the trick. I already did a couple of test pieces and got a good bond with no foam distortion.

[frednjess]

Yeah, I know. I take awhile to get things done. Here's what I've been working on. Got the tail group made. The verticals are 1/4" balsa with cross grained top and bottom. The rudder servos are inset 1/2 way. The horizontal stabilizer is made of 1/4"x1/4" balsa sticks with 1/4"x1/4" oak end caps(to screw in the verticals). The top and bottom are sheeted with 1/16" balsa. It's all very strong and still pretty light. Going to cover it then attach to the fuselage.
I'm still messing around with the engine mounts. I had to build a jig to cut them with the hotwire. Should cut them this weekend. I've got the cowls all figured out. I'm using the plastic containers from frozen juice concentrate. I know they're round and not oval, but after all, this is flying housing insulation! :D I should be able to cut out the engine vent flaps into the plastic to cool the motor and ESC.
I did get my RDS8000 2.4 Ghz and the two receivers the other day. I've got one set aside for this bird, while the other is in my 1/3rd scale Pitts. It works great!

[Ercoupe Ed]

Thought I'd see how big this monster will really be. There is a silver 4 foot straight edge in both pictures. It's centered on the wing in the width picture. I'm going to have trouble keeping this one from the wife!
Hmmm, trouble keeping from the wife?
You have the same problem my buddy Tim has! LOL! :D
Bring it over and keep it at my house, I'll let you come over and look at it every now and then, and I'll fly it for you in the meantime!!LOL!!! :D :D :D
Ohhh the joys of being single, nobody tells me how many airplanes I can have! :)

Ed

[RyanPSU21]

I built a similar sized B24 last winter. The build thread is here: http://www.rcgroups.com/forums/showthread.php?t=662830
It was 82inch span. Flying weight was 7 lbs using HC cheapo motors. If I was doing it again I would use speed400's. It would be much cheaper and probably still similar power. Any weight saved going for lighter brushless motors was more then lost with extra wiring and weight for the ESC's. 6lbs might be doable if you do everything really really really light.

The Hobbico mains seemed to work okay. If you are mounting a servo at each one, the main servo actually needs quite a bit of torque as the main gear legs are quite long. The Hitech HS85's I used were just barely enough. The nosegear is probably the worst one to try and fit a linkage up to.

[frednjess]

Hi Ryan,
Thanks for checking out my build blog. I actually looked at yours when I was planning mine. Is she still flying since the ESC cooked? I too had the MA issue sitting around tempting me to build.
As for the retracts, I'm hoping a standard size, metal gear will work for both mains. I'm going to use a micro, metal gear for the nose. There's also the slight chance that I'll omit the gear entirely, for weight and simplicity. I like the idea of hand launching a giant scale plane! :D I'm definately keeping the bomb bay, though.
For the power system, I'm hoping the HC outrunners with 3 blade 8x4.3 props will pull enough air. I'd also like to use a 3S2P 2200mAh pack for power. There's something endearing about a $40 flight pack for an electric, 4 engine, giant scale plane.
I'm hoping to get some more done this week. I've had to take a little break to build a couple of for-profit flying wings. Gotta pay for this thing somehow!

[RyanPSU21]

She is still flying but was sold a month or so after the last flight to someone else who has a paved runway. The nosegear had about a 4 flight limit before it broke and I couldn't see a good way to get a larger nosegear into the space I had available and if there was any tall grass at all at the field it couldn't get off the ground. It had a record of about 2 and 6 for the number of times it flew verse the number of times it went to the flying field and couldn't get off the ground. I will do another 4 engine bomber again and start building next year. If I do another B24 I will enlarge it up to more around 100inch wingspan which will put it at a wheel size that is more suitable to grass field flying.

[frednjess]

Sorry to hear she's been moved to a new hanger. Your problems with the gear make a pretty strong argument for skipping the wheels. I fly at a couple of sites and 2 of the 3 are paved, but the unpaved one is really close to my house. Maybe I could build a trolley for takeoffs.

[RyanPSU21]

The nose gear is particularly challenging on this. The nose gear position in scale position is not that far in front of the CG. The main gears are a big rearward of the CG so the nosegear carries a disproportionately large amount of the weight when it's on the ground. I used a retract for a 4 to 6lb plane which is where I thought weight would be and came out 7 lbs. The nose gear did not last long. To dig the mounting rails out and make a new mount for a different retract servo to fit in front of a larger retract would have been a major tearing apart of the nose for mine that I didn't feel was worth the effort to do. A lot was learned on that plane for future builds so it was still worthwhile to do.

[frednjess]

Sorry that there's been no progress as of late. I've been building some other projects and I'm still waiting for my landing gear to come in from Tower. They've been on back order for over 4 months!!!!! Wankers. I'm hoping to get back to work in the coming weeks before the weather starts keeping me outside... :)~

[Rengine]

fred - cant' wait to this beauty flying. Looking good so far.

I recently built my own huge lightweight foamie P-39. I flew it with fixed gear for 2 months and it worked good. Then I wanted to see it fly without gear and tried a hand-launch (that almost hit my truck). I don't recommend that unless you have a friend handy to do it.

After that I decided I needed to build a launch cart / trolley. It works great - so I can certainly recommend it for your plane too.

Here's a short video of my first couple launches/take-offs from the cart. I built it all from blue foam (except the pool noodle wheels and arrow-shaft axles :) )

http://vimeo.com/3677842

[frednjess]

Hi Rengine,
That's a pretty cool "little" plane. What's the WS and AUW? I'm leaning towards the hand launch/dolly just to keep things simple. I'll definately keep the bomb bay though.

[Rengine]

fred,

Thanks! I agree - I was keeping it simple with this build too - no retracts or flaps. It flys so docile that flaps, while cool - are not needed. It's an 84" span - AUW 6 lbs. (my little postage scale only goes to 5lbs - and this is over that - but doesn't peg the meter needle - so i know it's very close to 6lbs)

Yeah - keep the bomb bay - those so cool! :)

Anyway if you want to see the build log it's here:

http://www.rcgroups.com/forums/showthread.php?t=935622