P40 Warhawk SBK: My thoughts after Maiden flight.

PaulBlack71

New member
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The build: Mine is quite ugly, has too much glue, is heavy but functional.
The build was fantastic fun and pretty easy. There's a few tricky bits, but overall it's a great plane to build. There are however a couple of little gotchas though: There is no access hatch other than the lower front end, so installing and reaching electronics after the build can be tricky. I added FPV gear into mine and it was a little annoying trying to fiddle everything through the body. Not a huge problem, just an annoyance. I have placed a runcam2 and an All in One fpv cam and transmitter in the canopy area, so mine has no canopy, I may try to build a clear plastic one later. Pay no attention to the horrid green removable vinyl strips, I threw them on there for orientation during testing. If it survives a few good flights, I'll give it a proper shark mouth detailing. My plane has entirely too much hot glue and some rough hackjob cuts around the prop to get spinner clearance, but it flies great so far despite is ugliness and in the air has a great war-bird silhouette.

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The design:
I quickly found a few perceived weaknesses in the design: The wingtips where the under-camber starts out to the tips are VERY weak. Only really one thickness of foam out the the wingtips. One botched crooked landing and they will fold or tear off. I bolstered them up with some long skewers on the underside in one of the creases for the airfoil folds and extending into the wing a few inches. Some have used Popsicle sticks etc. Whatever works, it is now quite a bit more rigid out there although I don't know what difference it will really make other than adding weight.


The landing gear if you use them are prone to fail if you don't make sure you glue them only to the wooden hard-point and not the paper under the wing. My first landing sheared one off and peeled off some paper and foam from under the wing. I've since fixed it by cutting the paper and foam back a little more than the instructions show and making sure the gear are glued ONLY to the wood hard-point inside. Seems much better now but who knows.

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There doesn't seem to be any thrust angle built into the firewall plans at all. This plane, if taking off from the ground seriously pulls to the left to a point where it's almost uncontrollable. I tossed the small self tapping screws for the motor connection and used longer bolts with washers/nuts at the back instead. This allowed me to place some washers between the motor and firewall to give it some right and very slight down thrust angle. I will post after testing to state if this makes the plane better or not. It's easy enough to undo if it doesn't.

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My additions:
Since it's a warplane, I wanted a spinner. The dubro one recommended for this plane in the FT store works fine, but the Cpack motor has no real back mounting surface for it. It's a tapered surface and very small. I've managed to make it work with some fiddling, but getting it to spin true has been a bit fussy. A properly sized washer to act as a real pressure plate for the spinner to rest on is needed and does not come with any of the kits. It adds some weight up front too. I also had to cut some of the front of the fuselage back to fit the spinner up there without rubbing as it's quite wide. Fills in the ugly open front end nicely though.

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I also added a telemetry receiver with vario and the frsky battery telemetry sensor as well so have a screen full of juicy data while flying. I also glued some scrap foam cross-members in places where the body looked like it had a little too much flex here and there especially up front.

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Overall, these simple tweaks and strengthening additions will make the model a bit heavier, but since it is not short on power at all, I think it should be fine. Just have to fly it slightly faster I guess. This model has been great fun to build and fly thus far. I've tried to toughen it up a bit to see if it will last some abuse, but I don't think these things are meant to last. Expendable and cheap. It's still a low wing fighter shape though and therefore maybe not for beginners as it is quite quick compared to a trainer and does gain a lot of speed in turns when rolled sideways too far it just wants to keep rolling and of course falling. Some tip stall also seems to appear so watch that altitude.

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Note: these little micro all in one fpv cameras get HOT! hot enough to melt glue. I had to use zip ties rather than glue to hold it on or it would just melt and fall off after about 30 seconds powered up to 200mw. I wired both cams to a hobbywing 5v 3A ubec attached to the spare 12v (direct to battery voltage) lead on the esc.

I have balanced it to around 3/4 inch from the leading edge. I think the spinner and extra motor mounting hardware I used have put more weight up front because it seems quite nose heavy at that CG. I've moved it back to about 1 inch and will test that on the next flight. (It seems anywhere from 1/2 inch to 2 inch is working for many people building this model.)

Will post an update when I get to fly it again in current trim and with all the fpv junk running. If it goes ill, I already have 4 sheets of foam board staged up to make new parts as needed :)
Cheers all.
 
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Flyingshark

Master member
I quickly found a few weaknesses in the design: The wingtips where the under-camber starts out to the tips are VERY weak. One botched landing and they will fold or tear off. I bolstered them up with some long skewers on the underside in each of the creases for the airfoil folds and extending into the wing a few inches. Some have used Popsicle sticks etc. Whatever works, it is now quite a bit stronger out there.

I've just started building the FT Spitfire, and I've had some difficulties with the wingtips. Reinforcing them with BBQ skewers (which I have) rather than popsicle sticks (which I don't have) is a lot easier. Did you glue the skewers inside the score cuts when you folded the wing, or glue them on top of the seam afterwards?
 

PaulBlack71

New member
I've just started building the FT Spitfire, and I've had some difficulties with the wingtips. Reinforcing them with BBQ skewers (which I have) rather than popsicle sticks (which I don't have) is a lot easier. Did you glue the skewers inside the score cuts when you folded the wing, or glue them on top of the seam afterwards?


I glued them afterwards on the underside of the wing allowing them to extend into the main portion of the wing a ways. Seems a little more rigid but not sure how much stronger it is. I didnt realize this until after I landed on a wingtip and nearly sheared it right off at the point where the under camber starts. It's literally only 1 thickness of foam from that point on to the end. Flies fine with the mod, but luckily I havent put the repair to the test (yet).
 

BATTLEAXE

Legendary member
I found the same concern you guys are having with this weak under cambered wing tips, however like you I have reinforced them before with mixed results. If the landing is hard enough to rip the tip off then it will do it whether it is reinforced or not. The thing is the more reinforcement you put in the more damage it does and the harder it is to fix. The skewers or pop sticks will tend to cause more inevitable damage where it could have been easier to replace the immediate damage area then try to fix everything else the reinforcing skewer tears out as well. Just my experience with this stuff.
 

PaulBlack71

New member
I found the same concern you guys are having with this weak under cambered wing tips, however like you I have reinforced them before with mixed results. If the landing is hard enough to rip the tip off then it will do it whether it is reinforced or not. The thing is the more reinforcement you put in the more damage it does and the harder it is to fix. The skewers or pop sticks will tend to cause more inevitable damage where it could have been easier to replace the immediate damage area then try to fix everything else the reinforcing skewer tears out as well. Just my experience with this stuff.

You are probably right. More glue, more weight, more inertia and more wreckage if things go wrong. I think the instinct for every builder is to try to make it stronger on each needed repair. That of course may not be a solution as with many approaches there are diminishing returns. Mine is already feeling too heavy and will still be pulverized in any crash. I think Flite Test's main design approach here is that the foam board is expendable after all therefore you just replace the parts you break rather than strengthen them adding weight and complexity. My biggest problem is that on days when I can't fly, I tinker. When I tinker, something else usually gets glued to the plane lol.
Cheers.
 
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BATTLEAXE

Legendary member
I am the same way, I get bored and start brainstorming and usually ends up a failure on some aspect. Every once in a while there is a glimmer of brilliance but it is better to replace then to start gluing everything stronger. I had a crash with the P-47 and the undercambered wing tip did get crushed, first point of contact. It was a simple cut off and replace, as opposed to digging out an embedded skewer, only to cut that out now. Then the rebuild is more involved, having replace more FB in an odd shape. Been there and have the T shirt to prove it.

I have made multiple versions of one build back to back to get it dialed in, full builds from scratch. If i know i will be bored at some point and I like building, i will crash more planes pushing the skills at the sticks and do full rebuilds if the crash was good enough. Some people like to fix what they have, but like you said it adds more weight. I like a fresh build on the next try up in the air with the mods I like that pertains to my style of flying.
 

Rhaps

Elite member
I read this thread and kept nodding all the way and now my neck is sore.

I do wonder about the complaints on the Dubro spinner, @Moke had same problem. I just set the spinnr against the motor and I've yet to have any problems. The spinner do require moving the powerpod bit forward or removing some nose foam though.

As for landing gears - don't use them, they don't work for takeoff, they ruin the good looks of the plane in the air and then they rip off in the landing. (Altough problems on takeoff and landing may be related to my field. Or my flying skills)
 

PaulBlack71

New member
I read this thread and kept nodding all the way and now my neck is sore.

I do wonder about the complaints on the Dubro spinner, @Moke had same problem. I just set the spinnr against the motor and I've yet to have any problems. The spinner do require moving the powerpod bit forward or removing some nose foam though.

As for landing gears - don't use them, they don't work for takeoff, they ruin the good looks of the plane in the air and then they rip off in the landing. (Altough problems on takeoff and landing may be related to my field. Or my flying skills)
I agree. The landing gear may have to go.

I wanted them because I'm left handed and hand tossing is just awkward for me. If they fail again I'll just rip them off. I also have my spinner working fine but the c pack radial has very little flat surface at the base of the shaft so that only the adapter shim inside the spinner back plate really touches it. Seems to work though so I'm rolling with it.
Cheers