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1:9 Scale B-17G - 'Sweet Pea'

wilmracer

I build things that fly (sometimes)
Mentor
#41
Prepping to start the horizontal stabilizer. For comparison the horizontal stabilizer on this one will be about 1/2" larger in span than the FT Simple Storch (about 58"). I've decided I want to cut my teeth on a "new" method of wing building that I haven't used before. Here on the FT Forums we've seen Rockyboy use this method with great success on his Monster sized Fock-Wulf FW-42 build. I've watched a few other fantastic builders use this method too and it seems like a quick and easy way to build a really solid and light weight structure. If it works for the stab I'll use it for the wing.

I'm going to build the stab as 3 pieces. There will be a center section that will be permanently mounted in the fuse and then removable outer panels with the stabs and elevators. Elevators will be balsa and covered in solartex, and a servo will be built into each panel to drive each elevator half independently. I would have preferred to keep the servo weight out of the tail but for simplicity and reliability I want to keep the linkages short.

I am using this website to calculate torque estimates on the control surfaces. http://www.mnbigbirds.com/Servo Torque Caculator.htm
It is a nice tool to give you an idea of whether or not your servos are up to the task. I'm going to go with a pair of Hitec HS-5645 Digital Metal Gear servos for the elevators. They have more than the necessary torque and I have NEVER stripped gears or had a Hitec servo fail on me in flight. I know there are loads of less expensive options that have proven themselves reliable, but I will sleep better with these servos on the most important control surface.

On to construction... I've got the base of the box built and will be adding panels similar to wing ribs and will then hotwire and sheet them.
 

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wilmracer

I build things that fly (sometimes)
Mentor
#43
This will rival the Mac Hodges B-29 (1:7) if you finish this the way you plan to.
Mac's B-29 was larger for sure (about 20' span I think). I certainly hope it is anywhere near that impressive. I can promise that you'll never see this one do a low inverted pass though :)
 

JTarmstr

Elite member
#44
Mac's B-29 was larger for sure (about 20' span I think). I certainly hope it is anywhere near that impressive. I can promise that you'll never see this one do a low inverted pass though :)
yes, the B-29 was larger than the B-17 though, and his was 1:7, I just meant for scale looks, besides 11 and a half feet isn't all that small. If it has the sound and bomb drop, i wouldn't be surprised if it looked better than the B-29. Any chance this will be at flite fest 2019 or 2020?
 

wilmracer

I build things that fly (sometimes)
Mentor
#46
yes, the B-29 was larger than the B-17 though, and his was 1:7, I just meant for scale looks, besides 11 and a half feet isn't all that small. If it has the sound and bomb drop, i wouldn't be surprised if it looked better than the B-29. Any chance this will be at flite fest 2019 or 2020?
2020 is a possibility. I'm confident it won't be done in time for 2019, and TBH as much as I LOVE Furey field and Flite Fest Ohio I can't realistically see flying this off of the event runway. It is perfect for smaller models but not wide enough for larger stuff and the temporary geo-textile runway can bind up under heavier models.

We'll have to see how Edgewater looks in 2020. I will definitely be flying her in the Ohio/Indiana area so I can share her with my family.
 

JTarmstr

Elite member
#48
2020 is a possibility. I'm confident it won't be done in time for 2019, and TBH as much as I LOVE Furey field and Flite Fest Ohio I can't realistically see flying this off of the event runway. It is perfect for smaller models but not wide enough for larger stuff and the temporary geo-textile runway can bind up under heavier models.

We'll have to see how Edgewater looks in 2020. I will definitely be flying her in the Ohio/Indiana area so I can share her with my family.
Supposedly Edgewater will have a full scale field. Will this be able to take off of grass like its big brother?
 

wilmracer

I build things that fly (sometimes)
Mentor
#49
Supposedly Edgewater will have a full scale field. Will this be able to take off of grass like its big brother?
She will be perfectly happy on grass. Mains are 6" wheels and the tailwheel is 2.75". She should track quite nicely on roll-out too. Even though the full scale didn't have it I'll be doing counter-rotating props so P-factor shouldn't be an issue.

I'm not sure the full scale runway at Edgewater will be open in 2020, or if we will be flying from it during Flite Fest events, but we'll see :). I would likely bring her out even if I couldn't fly her there just so I could share her with folks.
 

wilmracer

I build things that fly (sometimes)
Mentor
#50
Stabilizer panels cut. In hindsight I probably could have skipped the 2" foam and done the whole box with the 1" stuff and the 6mm MAF, but I think it will work just fine. The CF tube and sleeve shown are 36" and will be installed as a wing tube. I'll have to build in anti-rotation pins, a tab with a bind nut to retain the panels, some paper tubes for servo wiring, and obviously servo hatches and mounts. I'll also be adding hard points for the hinges. Lots left to do with these but this box method worked quite well and I'm pretty confident I can make it work for the wings. At that size the panels will be harder to cut, but I'll figure it out.
 

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rockyboy

Skill Collector
Mentor
#51
The panels came out great! I agree that the 2" foam spar is a little overkill but it's not that big of a weight penalty and you'll have one heck of a strong stabilizer.
 

wilmracer

I build things that fly (sometimes)
Mentor
#53
The panels came out great! I agree that the 2" foam spar is a little overkill but it's not that big of a weight penalty and you'll have one heck of a strong stabilizer.
So... thinking about the anti-rotation pins and the retention bolts. What did you do for those on your big wings? I think you have a second smaller CF spar that will double as anti-rotation but I don't recall how you are holding them in place. Could even be as easy as tape but I'm not sure what you're planning.

I'm leaning toward a small dowel for anti-rotation and a 4-40 bolt through a thin ply tab for retention.

No building last night as we were taking the kid trick-or-treating. Might get some work done tonight as I have to be on an 11:00PM call for work and I'll be up anyway.
 

rockyboy

Skill Collector
Mentor
#54
So... thinking about the anti-rotation pins and the retention bolts. What did you do for those on your big wings? I think you have a second smaller CF spar that will double as anti-rotation but I don't recall how you are holding them in place. Could even be as easy as tape but I'm not sure what you're planning.

I'm leaning toward a small dowel for anti-rotation and a 4-40 bolt through a thin ply tab for retention.

No building last night as we were taking the kid trick-or-treating. Might get some work done tonight as I have to be on an 11:00PM call for work and I'll be up anyway.
Yes, anti-rotation is provided by those CF arrow shaft spars, but I'm still looking for the right idea for wing retention. A small plywood tab / slot just a little bit behind the main spar with a recessed screw down from the top seems like a good solution... but I probably should have put all that in place before getting crazy with the fiberglass and painting.

So tape is an option I haven't taken off the table yet :p
 

wilmracer

I build things that fly (sometimes)
Mentor
#55
A small plywood tab / slot just a little bit behind the main spar with a recessed screw down from the top seems like a good solution... but I probably should have put all that in place before getting crazy with the fiberglass and painting.
That is the direction I'm leaning, although I'll put screw in from the bottom so I can hide it as best I can. I'm thinking I'll need a custom assembly stand at the field anyway so I don't have to flip it upside down to assemble. That is a long way off for now.
 

rockyboy

Skill Collector
Mentor
#56
That is the direction I'm leaning, although I'll put screw in from the bottom so I can hide it as best I can. I'm thinking I'll need a custom assembly stand at the field anyway so I don't have to flip it upside down to assemble. That is a long way off for now.
Yeah, I don't want to try and flip these over at the field once the wings are on.

Not having a fancy RC trailer to bring my own custom designed field lift and creeper I think I'll go with the topside approach :p
 

wilmracer

I build things that fly (sometimes)
Mentor
#57
Yeah, I don't want to try and flip these over at the field once the wings are on.

Not having a fancy RC trailer to bring my own custom designed field lift and creeper I think I'll go with the topside approach :p
I don't want to think about my wing loading if I needed that lift. It would be up there with Ben's angry bee and the space shuttle ;-)

There was a company selling nice stands at FF OHIO that I'm thinking about.
 
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wilmracer

I build things that fly (sometimes)
Mentor
#58
More progress. Got the lower sheeting in place and started prepping to secure the wing tube. To make sure everything is true I went ahead and installed the anti-rotation pins. For retention I'm going to do a small tab that will slot into the panel and be held in place with a 4-40 bolt. I'll work out the servo tray and access hatch before sheeting the upper surface.
 

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wilmracer

I build things that fly (sometimes)
Mentor
#60
Looking good!

Also, on the wing retention - I just saw on J Morgan's current build where he used a brilliant steel pin and magnet method that leaves a very small visible hole on the top! https://www.rcgroups.com/forums/showpost.php?p=40435420&postcount=258

I'll be doing this for sure :D
Yeah. That is a really good idea and I have no doubt it will work. That being said I went ahead and added retention tabs last night that use a 4-40 bolt :p. I think the weight is comparable or perhaps even a touch less when you consider the weight of the magnet. Just need to work out servo placement, hatch access, and internal linkages before sheeting the topside.