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

[cmayer]

Ermergerd! That looks magnificent! Congratulations!

 

[easixpedro]

OhFFS. (I literally got nothing else)

This is good Jay, really, really good

[Landrotten Highlander]

1 hour ago, JayW said:

It was quite a ride, but I have a Malcolm Hood mechanism to show you.  This is what I am trying to represent:

 

 

The chains, the emergency release pushrods, the sprocket support fittings, the crank handle, the emergency release handle, and the black cover plates.  Not the cross-tube.  That comes later.

 

First, just as what happened so many times back in the 1940's when -B's and -C's were getting their hoods, I had to relocate the recognition light switch box on the windshield frame.  From here:

 

 

 

To here:

 

 

Had to be done to clear the new crank handle.

 

All the parts printed up pretty well.  There is alot of small detail, especially the chain itself, so I went with the 3 micron thickness setting on the printer (I normally use 5 micron).   After careful removal of supports, and carefully painting, I got this collection of details:

 

 

 

The black plates are not 3D printed - just old fashion scratch build.

 

Ok that was the easy part.  Installing these details into the airplane was hard - a most stressful and "stimulating" experience, trying to pry into a small space all these parts without breaking anything.  I broke one of the chains, but had a spare and used it.   Everything else worked out OK.  Pictures:

 

 

 

 

 

The 3D printed chains are a success, I am happy to announce.

 

Let's see the finished mechanism in the fuselage jig:

 

 

 

 

 

I need to do a better job painting up the rollers - I know.  But that comes later.  Glad to put this sub-project in the rear view mirror!

 

Next I believe is the lower radio floor and the fuselage tank.  I've been waiting forever to get started on that.  Hope you like the chain drive!  Later.

I think I shall be taking up knitting (throws toys out of pram...)

 

seriously though, amazing work

Edited April 23 by Landrotten Highlander

[Azgaron]

Very nice progress!

 

Håkan

 

[Rocat]

Amazing work, bravo.

[JayW]

While toiling away with the Malcolm Hood operating mechanism (so glad I am basically done with it), I tried and failed to figure out how the emergency egress system works.  I just know one exists - it consists of a red pull handle on the RH side under the windshield, about the same place as the production version of same for either the greenhouse canopy (B/C) or the bubble top (D/K), connecting to a tube that runs along the inside of the RH upper longeron parallel with the chain.  From there the tube attaches to a weird crooked bar which is part of the aft sprocket bracket.  From there is a cross tube that connects it to the LH side of the airplane. 

 

Pictures:

 

      

 

 

 

The last picture, showing the aft bracket with the crooked bar and the cross tube - the hole for the cross tube is slotted aft and down but you can't see it from that view.  That suggests the tube can be pushed aft and down to free itself from the bracket.  Also, when the red handle is pulled, it acts to push the long tube aft which will push the cross tube, or something attached to it, aft.  So if that is so, what goes with the cross tube?  The aft sprocket and aft portion of the chain?   ???

 

One thing is for sure - the hood itself is not going to jettison itself from the airplane, as is the case with many other airplanes.  Not with those permanent roller bars on either side of the fuselage, and permanently attached roller guides on the hood.  The greenhouse canopy on the B/C, however, looks jettisonable to me.  Pretty sure all the Malcolm hood can do, however, is slide aft for emergency egress.  The hand crank is going to take several rotations to get it open; could it be that when the red handle is pulled, the chain somehow disengages itself from the hood, or at least the crank handle, allowing it to blow back or be pushed back very quickly?

 

Inquiring minds want to know.     

Edited Tuesday at 07:32 PM by JayW

[wingman777]

[Oldbaldguy]

What stops the canopy from going all the way aft and falling off the guides if you keep cranking?  Is there a stop?  If the chain is driven by the sprocket, how does the chain connect to and drive the canopy?

[JayW]

14 hours ago, Oldbaldguy said:

What stops the canopy from going all the way aft and falling off the guides if you keep cranking?  Is there a stop?  If the chain is driven by the sprocket, how does the chain connect to and drive the canopy?

 

OBG asks good questions.  At the risk of boring some of my followers on this project, I will pontificate a bit further on this (to me) most interesting major B/C model modification - the Malcolm Hood.  This is all just purely analysis of pictures I have.  

 

First - "how does the chain connect to and drive the canopy?"

 

The canopy has a bracket on either side at its forward edge, whos function is to attach the canopy to the chain (brackets circled in red):

 

 

 

Note the studs protruding downward from the brackets.  Those studs engage a special link in each chain - circled in red:

 

 

"What stops the canopy from going all the way aft and falling off the guides if you keep cranking?  Is there a stop?"  There are two stops, one on either side, which make contact with those brackets described above:

 

 

This next picture shows the canopy cranked back fully open - I circled in red the chain-attach brackets and stops:

 

 

You can see pretty clearly the brackets are either engaging the stops, or there is a small gap between the two.

 

All this picture evidence suggests to me that for emergency egress, the canopy simply slides aft into the stops, and does not jettison itself from the airplane.  The red handle somehow (I don't know how exactly) disconnects the hand crank from the chain allowing a rapid aft movement of the canopy.   That is all it can do, apparently.

 

Stand by - soon I will post progress on the fuselage tank and radio rack, and preparations for joining the LH and RH forward fuselage panels, always a milestone for any airplane build.  

 

 

[Pete Fleischmann]

Well that is pretty damn impressive!

 

super cool Jay!!

P

[Paulpk]

Jay, I don’t understand why the warning label was needed if the canopy just went back. Label states drop seat and lower head? I guess the wind could or would rip the canopy off. Could the hood be opened in flight?

[Timmy!]

5 hours ago, Paulpk said:

Jay, I don’t understand why the warning label was needed if the canopy just went back. Label states drop seat and lower head? I guess the wind could or would rip the canopy off. Could the hood be opened in flight?

So the front frame doesn’t rip the top of the pilot’s head off…as the canopy slides aft.  The frame is somewhere around forehead level.  

[Oldbaldguy]

You know what?  I’d get in touch with either the folks who own the airplane in your pix or the guys who restored it and ask them how the damn canopy release works ‘cause I don’t think any of us are going to figure it out.  If I understand this whole thing correctly, we ended up in this hole because somebody decided they could improve on a perfectly good airplane by swapping a canopy that employed a couple of piano hinges and a cabinet lock with a fish bowl, two gutted bicycles, the crank from a well and several pounds of water pipes and unspecified hardware; all in order to see better.  Did not the Germans solve the same problem by simply removing the extra frame pieces from their 109 canopies later in the war so that they had three big plexi windows to look through instead of several small ones?

[JayW]

10 hours ago, Paulpk said:

Jay, I don’t understand why the warning label was needed if the canopy just went back. Label states drop seat and lower head? I guess the wind could or would rip the canopy off. Could the hood be opened in flight?

 

Ah yes the warning label:

 

 

As we continue to speculate, it makes perfect sense to me for that warning, if as the canopy is de-coupled from the crank handle and subjected to a several hundred miles per hour wind, that the canopy would indeed blow back - fast and forceful.

 

2 hours ago, Oldbaldguy said:

If I understand this whole thing correctly, we ended up in this hole because somebody decided they could improve on a perfectly good airplane by swapping a canopy that employed a couple of piano hinges and a cabinet lock with a fish bowl

 

OBG - I have heard from so many sources including testimoney from the actual pilots that seeing was everything.  The pilot who spots the other guy first almost invariably had the advantage.  Looking for our fighter pilots who are following this build to comment.....   As I continue to incorporate this mod to my P-51, it is more clear that it was very involved.  The British modified nearly if not entirely all their fleet of Mustang III's (the B/C models).   So it must have been worth it, and then some.  Either that or the vis from the greenhouse canopy was so poor they felt something ought to be done.  Oodles of cash was spent by governments and manufacturers modifying practically all fighter types as the war progressed to a bubble or Malcolm arrangement.   All for seeing.

[Pete Fleischmann]

5 hours ago, JayW said:

 

Ah yes the warning label:

 

 

 

 

The pilot who spots the other guy first almost invariably had the advantage.  Looking for our fighter pilots who are following this build to comment..... 

I was pretty spoiled in the F-16 with virtually unlimited visibility..in a visual fight it was a real factor.

 

The pilot who spots the other guy first BVR with a superior radar is also similarly advantaged.

 

P