1/18 Scale P-51B 3D Print Build

[Maxim61]

16 hours ago, JayW said:

I needed to do a reality check on this ambitious dream I have here.  To get a better idea what I am up against.  How well did I model the engine cowl surfaces, including the "smiley face", that I have created so far?  How well is the printer set up (exposure times, etc), and how well have I designed my supports and is my part orientation for printing acceptable.

 

So I designed and created some test parts.  Already I had a part defined for the cuffed propeller, done a couple years ago just for kicks:

 

       

 

I could go on and on with this effort.  It was a ton of fun.  To make a long story short, Airscale Library has some Hamilton Standard data on prop blades including the one used for P-51's. Data is available for cross-section shapes at various prop stations from root to tip, and their twist angles.  Create curves in Rhino of all these shapes, at the right angles, loft between them, do some tweaking, and you get what you see. 

 

Then I had to define other test parts using the cowl surfaces I created over the last few days, which I described last post.  And also the spinner surface.  Here:

 

 

And after many hours of 3D printing I got these parts:

 

 

 

Except for possibly the prop blades (they are practically perfect), these are merely test parts.  Parts I make for the model will be much more detailed. 

 

So this was a test.  What did I find?

 

The printer is probably set up about as well as I can do it.  No print failures, and part quality looks good.  I certainly expected no less; I have already produced some parts for the Corsair.

 

The "smiley face" part has excellent surface smoothness.  no lumps, no ripples.  What a victory!  But it didn't print that great.  More work to do on that score....

 

The cowl surface is actually pretty good.  There is one seam between patches where I didn't do a good job of getting it smooth (I can fix that), and some edges are a bit ragged as can be seen on the smiley face part below.  I hope I can fix that with a locally more dense array of supports on the 3D print file.  I am a bit concerned about that.  It could possibly be addressed with some putty though.  Here:

 

 

 

Fit between the two parts is pretty good, but I was expecting perfection.  The 3D printing process is not yielding theoretically perfect results.  Any imperfections will show up when trying to mate two parts together.  And I do not like those ragged edges.  Hope I can get that taken care of.  I should say now that I intend to skin this model in aluminum litho sheet.  So the final fuselage parts (wing too) will be under the defined surface by .005 inch to allow for the thickness of the litho sheet.  And that will cover up some imperfections in the 3D printed parts.

 

And speaking of imperfections:

 

 

The spinner halves didn't fit together worth a sh_t.  And edges are ragged similar to the cowl parts.  The spinner will not be skinned so it has to be right on.  Again - more supports locally should help with most of the shape problems.  Also, the prop blades didn't fit in their holes at all.  The holes need to be a few thousands of an inch larger, just like holes for a bolt need to be slightly larger than the bolt diameter.  Instead of being exactly the same diameter.  I am a dummy.  Also, I am finding that 3D print parts might be just a tad expanded - so the prop blade roots might be a tad oversized, and the holes a tad undersized.  On the bright side, these parts look very cool, and have the potential to be transformed into excellent ready-for-primetime parts.  I will be doing some substantial redesign, and will probably make the prop blades and spinner my first effort at production parts.  A stand-alone unit that will gather dust for a long time waiting to be installed on a complete fuselage.

 

I combined test parts to see how it looks:

 

 

 

I am both encouraged, and discouraged.  It sure looks like a Mustang - that's great.  But fit-up is going to be a challenge.  This is not going to be as easy as I envisioned.   But we all experience learning curves, and I hope to experience that here.  Stay tuned - I will post progress on a greatly improved prop before long.  Meanwhile I have alot of surfacing work to do on the computer. 

 

I had similar problems printing my 1/24 LEM. You really have to think about how you will support the piece you want to print and the orientation of it. If not set up correctly you get slightly out of round issues and non straight edges due to the weight of the part and gravity as it's hanging of the build-plate.Don't know how you printed the spinner but i would print straight onto the build-plate with no supports, Run some IPA under it and it'll come off the build-plate without having to scrape it off and damage it. Your printed parts look good though.

[JayW]

23 hours ago, airscale said:

as you have found out you think you have won when you have designed it, then a whole new world of pain opens up printing it 

 

True Peter.  Looking for you to break trail for me with the P-39!  I'll thank you in advance.

 

15 hours ago, Citadelgrad said:

i am eyeing the Elegoo Saturn 3 as we speak,

 

Oh I think you would like that unit!  I like my 2.  

 

13 hours ago, MikeMaben said:

Alistair may be able to help with the canopy .

 

 

Thanks Mike.  Small world - Tim Perry helped him with this - the very person who provided so many of the 3D print parts for the Corsair.  Yup, I will add this to my growing collection of all things Malcolm.  And I will contact Alistair.

 

21 hours ago, geedubelyer said:

Don't forget to factor in the ability to create kits or sell files of this. I can't believe you'll be the only one to desire a 1/18th scale Mustang and you might be able to recoup some material costs along the way.  

Thinking outloud and along those lines, do the two marques (B/C) differ greatly? Would it be possible to design in the ability to offer either version by producing modular and interchangeable components?

 

Hi Guy!  

 

Yes I will keep that in mind.  However this is not going to be a complete 3D print kit.  I don't have a good plan yet, but I am pretty sure that some of this build is not going to directly involve 3D printed parts.  For instance it could very well be that the sidewalls around the canopy will have scratch built skins over 3D printed frames.  As opposed to the engine cowl, which is probably going to be fully 3D printed.  And the wings - I have no idea at the moment how I am going to address the long wing spans, the gear bays, etc.  There will be scratch building as well as 3D print.  Anyone who would be interested in parts I create would have alot of work to do to integrate them into his/her own build.  Yeah - at this point I just don't have a plan.  I want to create as much CAD surface as I can, then go from there.

 

As for B/C differences, as Mike stated they are essentially the same, only built in two different factories.  Did you perhaps mean B/D differences?  If so, they do share a good bit of geometry, but from the windshield back, they diverge alot.  Except the radiator scoop area which again is the same for both.  The tails are about the same too except the fin root which has to match with different fuselage contours.  The B/C wing is same basic wing, but the extended leading edge is completely different leading to different landing gear doors and alot of other stuff in the leading edge.  Also there is four guns versus six guns.  Yeah, a modular approach would be pretty extensive. 

 

B/C/D/K aside, within each variant is a dizzying amount of change, just like all these vintage WW2 aircraft production runs saw.  A P-51D-5 has many differences compared to a P-51D-20, for instance.  But pretty sure you know that...  Once I decide on a B or a D, then I must pick a subject, with its serial number, and once again strive to give it the right parts.  It isn't very hard - the NAA drawings are not shy about specifying serial number blocks in which parts are effective on.

 

6 hours ago, Maxim61 said:

I had similar problems printing my 1/24 LEM. You really have to think about how you will support the piece you want to print and the orientation of it. If not set up correctly you get slightly out of round issues and non straight edges due to the weight of the part and gravity as it's hanging of the build-plate.Don't know how you printed the spinner but i would print straight onto the build-plate with no supports, Run some IPA under it and it'll come off the build-plate without having to scrape it off and damage it. Your printed parts look good though.

 

Goodie goodie!!  I need 3D print experts watching this build.  Stick around!  I am going to substantially redesign the spinner parts, where each will probably have internal "roofs"  which would not have the benefit of lying directly on the build plate; thus would require supports, and would spoil any plans to print straight off the build plate.  To date, with the exception of the "rook" chitubox file that came with my printer, I have never made a part that is directly on the build plate.   However it's an option worth considering.  Another person suggested printing the forward spinner part upside down, with supports.  That would give me a much more accurate interfacing surface to the aft part, which would be done right side up either directly on the build plate, or at an angle.  My flat surface on the test part of the forward half of the spinner was, like you said, affected by gravity during build-up, and was not flat at all.   It was however minimally supported.  Whereas the flat surface of the aft half part seemed just fine.  It was not affected by gravity.  Next post you will see my next try (or tries). 

 

Thank you all for your interest in this - there are challenges to come.  I hope to be successful.  

Edited September 1, 2023 by JayW

[brahman104]

Another incredible journey has just begun! I definitely admire the exacting tolerances you set for yourself Jay, which is just one reason why you're on a very tall pillar way above most of us!!!!!  Always inspiring.

 

I know you've had some fit/print issues and given the level of accuracy you're going for there's room for improvement, but when I think back to my first forays with the ABS UpMini and what's inside the my B-17's rear fuselage, it's like Wright Brothers versus walking on the moon!

 

Very excited to watch this one unfold!

 

Craig

[TAG]

On 8/31/2023 at 2:36 PM, JayW said:

P.S. - if any of you Mustang experts out there have any information on the Malcolm hood - like shapes and cross sections, well that would probably clear the way for me to do the B-model!

 

Hi, Jay

 

Stoked to embark on another epic journey with you, here's a few photos I have in my archives of the Malcolm hood. Personally, I've never been a huge fan of the look of B/C's without the birdcage canopy but there are certainly some interesting Malcolm hood schemes to choose from. It was quite a labor intensive process, something north of 300 man-hours to install, mainly because the original birdcage didn't slide back so the entire mechanism had to be built for a Malcolm hood to work. Also, the blown canopy had no framework, having instead a clear, heavy duty bead on each end. Here's some pics, starting with period photos.

 

Here's some modern photos from P-51B-10-NA 42-106638 "Impatient Virgin", a 361st FG WW2 vet with over 700 hours in combat and several aerial victories that's been faithfully restored to flying condition.

 

Here's the actuating mechanism which included chains to operate the Malcolm hood.

 

There's a lot more info out there, just gotta do a little digging is all.

 

Cheers!

- Thomaz

[JayW]

1 hour ago, TAG said:

here's a few photos I have in my archives of the Malcolm hood. Personally, I've never been a huge fan of the look of B/C's without the birdcage canopy but there are certainly some interesting Malcolm hood schemes to choose from. It was quite a labor intensive process, something north of 300 man-hours to install, mainly because the original birdcage didn't slide back so the entire mechanism had to be built for a Malcolm hood to work. Also, the blown canopy had no framework, having instead a clear, heavy duty bead on each end.

 

Thanks Thomaz - Great pics (I have some of them already).  Can I assume that hood is newly made (somehow)?  If so, do you think the "Impatient Virgin" hood is "overblown"?  The side bulging is more severe than scale models I have seen with the Malcolm hood - looks just like a fishbowl.  And I have found no period pictures where the side profile is in evidence.  I inquired at Aircorps Library to see if they had anything, as their sister company Aircorp Aviation does restorations (Lope's Hope being one of them - a greenhouse canopy C-model), and of course have a giant documents library, but they don't have anything on the Malcolm.  I was told however that modern restorations, if the item is usable, will refurb it.  And if it is unusable, reverse engineer what they have to work with - suggesting some of the old hoods actually exist but are unsuitable for repair.  I'll bet you can count them on one hand and divide by two.  Either way that suggests what we see on "impatient Virgin" might be correct, whether restored or remade.  Thoughts?

 

The mechanism.  Yes.  What a mod that must have been.  And somehow the LH chain must be slaved to the RH chain (the RH has the handle crank).  I don't know how they did that, but I would guess there is a torque shaft behind the seat armor with a sprocket on either end, fixed to the bearing brackets on the airframe, and those sprockets engage both chains.  ????  Wish I knew, I would attempt to model it because it might be in sight.  Also, I'd like to know what the means of attachment to the chains is, or at least how hidden (or not) it is.

 

Personal preference as to the look.  I personally like the look of the Malcolm hood better.  Should I go with the B-model (have not decided yet), one of my goals is now to convince you.  It does have the look of a mod I will concede.          

Edited September 1, 2023 by JayW

[Maxim61]

5 hours ago, JayW said:

 

True Peter.  Looking for you to break trail for me with the P-39!  I'll thank you in advance.

 

 

Oh I think you would like that unit!  I like my 2.  

 

 

Thanks Mike.  Small world - Tim Perry helped him with this - the very person who provided so many of the 3D print parts for the Corsair.  Yup, I will add this to my growing collection of all things Malcolm.  And I will contact Alistair.

 

 

Hi Guy!  

 

Yes I will keep that in mind.  However this is not going to be a complete 3D print kit.  I don't have a good plan yet, but I am pretty sure that some of this build is not going to directly involve 3D printed parts.  For instance it could very well be that the sidewalls around the canopy will have scratch built skins over 3D printed frames.  As opposed to the engine cowl, which is probably going to be fully 3D printed.  And the wings - I have no idea at the moment how I am going to address the long wing spans, the gear bays, etc.  There will be scratch building as well as 3D print.  Anyone who would be interested in parts I create would have alot of work to do to integrate them into his/her own build.  Yeah - at this point I just don't have a plan.  I want to create as much CAD surface as I can, then go from there.

 

As for B/C differences, as Mike stated they are essentially the same, only built in two different factories.  Did you perhaps mean B/D differences?  If so, they do share a good bit of geometry, but from the windshield back, they diverge alot.  Except the radiator scoop area which again is the same for both.  The tails are about the same too except the fin root which has to match with different fuselage contours.  The B/C wing is same basic wing, but the extended leading edge is completely different leading to different landing gear doors and alot of other stuff in the leading edge.  Also there is four guns versus six guns.  Yeah, a modular approach would be pretty extensive. 

 

B/C/D/K aside, within each variant is a dizzying amount of change, just like all these vintage WW2 aircraft production runs saw.  A P-51D-5 has many differences compared to a P-51D-20, for instance.  But pretty sure you know that...  Once I decide on a B or a D, then I must pick a subject, with its serial number, and once again strive to give it the right parts.  It isn't very hard - the NAA drawings are not shy about specifying serial number blocks in which parts are effective on.

 

 

Goodie goodie!!  I need 3D print experts watching this build.  Stick around!  I am going to substantially redesign the spinner parts, where each will probably have internal "roofs"  which would not have the benefit of lying directly on the build plate; thus would require supports, and would spoil any plans to print straight off the build plate.  To date, with the exception of the "rook" chitubox file that came with my printer, I have never made a part that is directly on the build plate.   However it's an option worth considering.  Another person suggested printing the forward spinner part upside down, with supports.  That would give me a much more accurate interfacing surface to the aft part, which would be done right side up either directly on the build plate, or at an angle.  My flat surface on the test part of the forward half of the spinner was, like you said, affected by gravity during build-up, and was not flat at all.   It was however minimally supported.  Whereas the flat surface of the aft half part seemed just fine.  It was not affected by gravity.  Next post you will see my next try (or tries). 

 

Thank you all for your interest in this - there are challenges to come.  I hope to be successful.  

Happy to help out. 3D printing is all trail and error. I went through probably 2 litres of wasted resin to get my LEM done.  Many people don't realise that it's all in the planning and you don't always get it right first go. It's a bit like scratch building where you basically end up with three kits, two of them in the waste bin. I use Lychee for my setup and use only Siraya resin which I have had really good luck with.

[TAG]

1 hour ago, JayW said:

 

Thanks Thomaz - Great pics (I have some of them already).  Do you think the "Impatient Virgin" hood is "overblown"?  The side bulging is more severe than scale models I have seen with the Malcolm hood - looks just like a fishbowl.  And I have found no period pictures where the side profile is in evidence.  I inquired at Aircorps Library to see if they had anything, as their sister company Aircorp Aviation does restorations (Lope's Hope being one of them - a greenhouse canopy C-model), and of course have a giant documents library, but they don't have anything on the Malcolm.  I was told however that modern restorations, if the item is unusable, reverse engineer what they have to work with - suggesting some of the old hoods actually exist but are unsuitable for repair.  I'll bet you can count them on one hand and divide by two.  That also suggests what we see on "impatient Virgin" might be correct, whether restored or remade.  Thoughts?

Dollars to donuts that Impatient Virgin's hood is spot on. Here's some more photos that show how bulged out the Malcolm bubble really got, including what I could find from period pics. Starting with a couple of RAF Ponies, you can see how far the canopies bulged.

Let's zoom in. Flight leader's kite.

Wingman's bird. Uncanny resemblance to an actual fishbowl.

 

Not a side profile, but look how huge the bubble looks!

 

Some more examples.

 

Here's Kid Hofer in Salem Representative, note how bulged out the canopy looks.

 

Here's a B/C cutting daisies, you can see in the second shot the 'fishbowled' sides of the Malcolm hood.

 

1 hour ago, JayW said:

The mechanism.  Yes.  What a mod that must have been.  And somehow the LH chain must be slaved to the RH chain (the RH has the handle crank).  I don't know how they did that, but I would guess there is a torque shaft behind the seat armor with a sprocket on either end, fixed to the airframe, and those sprockets engage both chains.  ????  Wish I knew, I would attempt to model it because it might be in sight.  Also, I'd like to know what the means of attachment to the chains is, or at least how hidden (or not) it is.

This thread on ww2aircraft.com is chock full of good info, including a few key contributions from the sadly missed Edgar Brooks regarding the 'drape molding' process used to manufacture the hoods.

1 hour ago, JayW said:

Personal preference as to the look.  I personally like the look of the Malcolm hood better.  Should I go with the B-model (have not decided yet), one of my goals is now to convince you.  It does have the look of a mod I will concede.          

Hmm, you have your work cut out for ya, I just never liked the slapdash look of the Malcolm bubble but who knows, I may come around eventually. 

Edited September 2, 2023 by TAG

[Rainer Hoffmann]

With all this 3D-printig stuff going on here I feel like a dinosaur (I still build my models with frames and stringers, spars and ribs and so on ... ), but this is looking very good already and I'll follow this one for sure.

 

Cheers

Rainer

 

 

[JayW]

 

If that is not one of the most awesome period pictures of a mustang, well I'm a monkey's uncle!  Cutting daisies indeed!  

 

Thomaz, once again you have provided me with a treasure trove of pictures and information.  Great to have you on my team!

 

I think by now I have a pretty good idea of the basic shape of this Malcolm hood.   Soon I will do one up in Rhino, but first I need to do the fuselage and windshield surfaces that surround it (you know - using all that point data I described in my first post).   

[JayW]

11 hours ago, Maxim61 said:

I use Lychee for my setup and use only Siraya resin which I have had really good luck with.

 

So not to belabor the point, as many who are following are not conversant in 3D printing, but not knowing any better, I am using plain old Elegoo 8K standard space grey resin.  It seems like great stuff, but what do I know....  And for transparencies I am using Nova3D High Transparency resin.  I am having trouble with it, even after various tweaks to exposure time, lift speeds, and some other parameters.  And, varying ways of supporting and orienting the part.  And have yet to get a really good exposure test part (I've used several types). 

 

Have you done transparencies?  If so, how are they and what have you used?  

[airscale]

awesome thread already

 

Jay, I have been messing about making a 109 spinner and am trying a sacrificial edge

 

 

it's kind of perforated and the idea is all the rageddy bits where it's hard to get a clean edge are absorbed by the edge which should either break away or be easily sanded off. I am trying straight on the bed and one with supports... thought seeing yours it might be worth a try, will let you know how it goes

 

on another note - I strongly recommend printing test parts in 1/32 or something or you will burn huge amounts of time & resin - any problems will be apparent at a smaller scale and when experimenting is done, whack out the real one

 

Peter

[patricksparks]

39 minutes ago, airscale said:

awesome thread already

 

Jay, I have been messing about making a 109 spinner and am trying a sacrificial edge

 

 

it's kind of perforated and the idea is all the rageddy bits where it's hard to get a clean edge are absorbed by the edge which should either break away or be easily sanded off. I am trying straight on the bed and one with supports... thought seeing yours it might be worth a try, will let you know how it goes

 

on another note - I strongly recommend printing test parts in 1/32 or something or you will burn huge amounts of time & resin - any problems will be apparent at a smaller scale and when experimenting is done, whack out the real one

 

Peter

I actually did the same thing a couple years ago on an early B-17C cowling, it worked well, I made it fairly tall with round holes through the collar that were fairly big to cut down on resin use.

Pat

[patricksparks]

25 minutes ago, patricksparks said:

I actually did the same thing a couple years ago on an early B-17C cowling, it worked well, I made it fairly tall with round holes through the collar that were fairly big to cut down on resin use.

Pat

[JayW]

4 hours ago, airscale said:

Jay, I have been messing about making a 109 spinner and am trying a sacrificial edge

 

 

it's kind of perforated and the idea is all the rageddy bits where it's hard to get a clean edge are absorbed by the edge which should either break away or be easily sanded off. I am trying straight on the bed and one with supports... thought seeing yours it might be worth a try, will let you know how it goes

 

Literally minutes ago, I began printing off my "production" nose cones!  And yes, I thought about some sort of sacrificial edge as well.  But this time at least, I left the parts at an angle without any augmented edge, and just doubled or tripled the supports down on the bottom where the print layers have a severe angle.   Report out probably tomorrow.  

 

I see you have included depressions for rivet heads.  Boy Peter - you set a very high bar.  I'll think about that.....

Edited September 2, 2023 by JayW

[JayW]

4 hours ago, patricksparks said:

I actually did the same thing a couple years ago on an early B-17C cowling, it worked well,

 

Well shoot!   So this B-17C - is it done?  What does it look like?