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MiniacRC Mighty Mini P47 Thunderbolt

CapnBry

Well-known member
#21
@CapnBry That’s wonderful man!!! Glad the instructions are sufficient so far and thanks for posting the stl, this community is awesome!
Yeah! I have only had one "Wait... what am I doing?" moment which is where you said that the slightly larger of the two hatch formers goes to the front but I didn't know which end was the front. I skipped forward in the video real quick to see. If that's the only question I'm going to have on this whole build and I've never done this before, then the instructions must be top notch. One minor issue in the plans: in the tiled plans you have Fuselage Mold F twice, but the one on page A6 (Mold E) is labeled correctly on the full size page.

Lunch break! I also quickly messed around with creating 3D printed versions of the formers, since cutting curves on small parts can be a little perilous for me.
DSC06547.JPG

It would definitely save a lot of time but the tradeoff is weight. All the DTFB formers are 0.4-0.7g each. Printed in ABS with 10% hex infill and 1x 0.6mm perimeter they weigh up to 2.3g. That would add 12-16g of weight to the plane which would be OK for a larger build but this whole thing only weighs 137g so far with 2 of the servos so that's a significant increase.

I was able to remove the cowl from my build with a little denatured alcohol and an eyedropper to break down the glue. Heck yeah, right side up!
DSC06538.JPG

I had a little bit of a rough time with the larger mold pieces. A tip I would give to new people is to jump forward and do the hatch first, since the smaller size makes the molds easier to form and give you some practice before getting to the fuselage. It didn't come out too bad though.
DSC06542.JPG

To smooth them out, I considered getting some body filler or super-light spackle but it seemed easier to just coat the seams with paper and some spray glue. I think I'll be able to sand out some of the wrinkles that came from me being overzealous on the curve in the front too. I should have just done like I did near the tail where I just cut strips from the scrap mold paper.
DSC06546.JPG
 

CapnBry

Well-known member
#23
I can't believe it is already Tuesday and I thought I'd be done with this on Saturday! My elevator has a bit too much glue in the hinge or something even after taking a second go at cleaning it out, so the little bamboo skewer wasn't cutting it for linking the two halves. I 3D printed some little torque transfer bars. It is 2.5mm thick and about 0.45g. I printed 4 in different infill amounts and patterns and perimeters to see which would be strongest. They were all about the same apart from the gyroid fill one, which was only slightly worse than the rest, but also the lightest. I think gyroid just needs a slightly higher percentage of infill or more area for the pattern to gain full strength. I used the one with 50% grid infill and it is more more strongly connected to the driven side of the elevator than with the skewer.
DSC06552.JPG

I really got lucky with the placement of everything inside, since the CG is juuust slight back from where it should be and there's not a chance I can move anything apart from the battery, which can only move 2-3mm. It is a 1300mA 3S so it is pretty big for a mini. I used some scrap foam to center the servos since the elevator pushrod would run into the center bit running down to the tail. For the rudder, I didn't use the hole in the side of the fuselage, I just ran it directly out the back of the fuselage, so I'd wait until you build the thing before you cut the slots to put pushrods.
DSC06562.JPG

The razorback canopy just did not want to stay glued on. The paint is krylon colormaxx satin Italian olive and the glue would just come off like I tried to glue to plastic wrap. A combination of perseverance, CA, hot glue and white glue and I think it is going to blow right off when I punch the throttle. It looks eh, OK I guess but I am really pleased with the way covering the seams between the molds came out.
DSC06556.JPG

So there we go, 393g all up weight which is way way way more than the 290g in the plans, although my battery is 120g and I have the rudder servo so that's an extra 11-15g too. The 5x3.5 prop on the 2205 2300KV motor only puts out 410g of thrust on 3S so that's probably not going to be enough for Maximum Fun. FlySky FS-iA6B receiver and 4x SG90 knockoff servos round out the build.
 

mayan

Well-known member
#24
I can't believe it is already Tuesday and I thought I'd be done with this on Saturday! My elevator has a bit too much glue in the hinge or something even after taking a second go at cleaning it out, so the little bamboo skewer wasn't cutting it for linking the two halves. I 3D printed some little torque transfer bars. It is 2.5mm thick and about 0.45g. I printed 4 in different infill amounts and patterns and perimeters to see which would be strongest. They were all about the same apart from the gyroid fill one, which was only slightly worse than the rest, but also the lightest. I think gyroid just needs a slightly higher percentage of infill or more area for the pattern to gain full strength. I used the one with 50% grid infill and it is more more strongly connected to the driven side of the elevator than with the skewer.
View attachment 136304

I really got lucky with the placement of everything inside, since the CG is juuust slight back from where it should be and there's not a chance I can move anything apart from the battery, which can only move 2-3mm. It is a 1300mA 3S so it is pretty big for a mini. I used some scrap foam to center the servos since the elevator pushrod would run into the center bit running down to the tail. For the rudder, I didn't use the hole in the side of the fuselage, I just ran it directly out the back of the fuselage, so I'd wait until you build the thing before you cut the slots to put pushrods.
View attachment 136306

The razorback canopy just did not want to stay glued on. The paint is krylon colormaxx satin Italian olive and the glue would just come off like I tried to glue to plastic wrap. A combination of perseverance, CA, hot glue and white glue and I think it is going to blow right off when I punch the throttle. It looks eh, OK I guess but I am really pleased with the way covering the seams between the molds came out.
View attachment 136305

So there we go, 393g all up weight which is way way way more than the 290g in the plans, although my battery is 120g and I have the rudder servo so that's an extra 11-15g too. The 5x3.5 prop on the 2205 2300KV motor only puts out 410g of thrust on 3S so that's probably not going to be enough for Maximum Fun. FlySky FS-iA6B receiver and 4x SG90 knockoff servos round out the build.
That looks pretty :).
 

CapnBry

Well-known member
#25
Maiden went PERFECTLY... if the goal was to crash it into the ground and break apart on launch.

I gave it a toss and it rolled left and I couldn't recover. I did a frame-by-frame analysis to verify that the control surfaces were moving and in the proper direction and it looked fine. The throws on the ailerons are ~24 degrees on the left ~22 degrees on the right so maybe this isn't enough for launch, or I didn't give it a hard enough toss. One wing broke off and ripped off all the paper on the side molds to halfway back to the tail. Prop was broken and the cowl got a chunk broken out, some minor damage everywhere else.

I'll fire up the hot glue gun at lunchtime and get it all back together again, up the throws a bit, and try again. EDIT: Added 5g of weight to the nose to bring the CG to 30mm, upped all the throws to 27 degrees. Added some right roll trim for good measure. No joy. It almost survived the second toss so I taped everything back together in the field and launched with full power and more right trim. It almost flew but did not and took the wing off again. The power pod has also gone soft. The foam on the top has crushed in a bit so the motor can tilt up and down, and the skewer holes are getting elongated so there's a mm or two of slop back and forth. I'll glue it all back together again this evening and try with a 6x4.5 prop (the only 6" I have) and hope it isn't too much for the ESC, although with flights this short I think it will be fine. ;)

EDIT2: And with a 6x4.5 prop, it rolled all the way to inverted as soon as it left my hand and smashed into the ground at even a greater rate of speed, smashed the nose off, broke the prop, and the power pod skewer ripped a good 10mm gash in the nose. Looking at the film it was upside down 0.6 seconds from when my fingers were still on it. Looks like with full aileron I was able to stop the roll but at that point I was upside down and pulling back on the stick so we know what happens there. Flight terminated at T+0.966seconds.
 
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#26
Sorry you are having so much trouble CapnBry, but I do admire your perseverance. I have been having a similar issue with my P-40 that I just built but not as extreme, I was just getting stalls shortly after takeoff, most likely because I misread the specs on the motor I had grabbed out of my spare parts box. It is only able to put out 50-60% of the plane's AUW in thrust... no wonder it was hard to hand launch while also holding the transmitter :) Since 0.5:1 TWR wouldn't be super fun anyway I went ahead and ordered a new motor, but I now have to decide whether to just glue up my smashed up wing and cowl as best I can or rebuilt from scratch, so I feel your pain. Hopefully you find your issue and get it sorted out, that P-47 looks like it would be a blast to fly and I want to build one also!