P/F-82 Project

[foiler]

I have been gathering information for a project for the the last year after suffering from haunting mental images of "Betty Jo", the F-82 Twin Mustang in the Air Force museum. Many thanks to those of you who have helped me locate information and for the ominous warnings about the differences between the P/F-82's and P-51's. What I have learned from a myriad of sources is very interesting and has provided a game plan for me to work with. This will be a long WIP with some pregnant pauses, direction changes, and severe mental lapses, but I'm going to give it a try. Just to establish a fundamental understanding: this build will not be for rivet counters. This is simply another way to get a model of something that does not exist in 1/32 scale injection molded kits. My stash is empty, and I am approaching 70. Since the days ahead of me are fewer than those behind, I figured I had better try something I have wanted to do for a long time. I also think I am drawn to the subject because my Dad worked for Aeroproducts for 20 years, and had a hand in the development and testing of several propellers including those used on F-82's.

 

So, which version should I build? I decided to leave the mainstream of consensus here and do one of the versions that is typically not the first choice; the "B" model. Why? The first reason was that the "B" has quite a few similarities to a P-51. It also has dual cockpits that are similar to the P-51, and there are 1/32 P-51 kits I could use as a foundation if the similarities are close enough. I also wanted to build the "hot rod" Merlin powered version. So, now I need to find out what differences I will encounter.

 

I started with several good profile pictures of various P-51 and P/F-82 variants. I brought the P-51D into my CAD system, sized it properly, then created an accurate outline of the profile.

 

 

Knowing that the outline was now an accurate representation of the real thing, I pulled in a picture of my Dragon 1/32 scale P-51D EP for comparison. Not bad......

 

 

Depending on the reference material you read about the P/F-82's most think the 82's were derived directly from the P-51H. That's not the case, but I wanted to see what differences there were between the "D" and the "H". Significant......

 

 

In the same scale I brought in images of two F-82 versions for comparison. First the "B", and next the "E". Since the spinners are the same for 51's and 82's, I used them for alignment.

 

 

I gathered the line drawings I had acquired and started searching for profiles that most closely resembled the profile outline I had created from the real plane. Fortunately, the one that most closely matched also had cross sections. This gave me a little more confidence that I could trust the whole drawing to be accurate. I learned very quickly that just because a drawing has dimensions, it doesn't mean it is accurate.

 

 

Following the same procedure of the 51, I made an accurate outline tracing of the F-82B. I found there is a 4 inch height difference in the vertical stabilizer between the "B" and the "E"......

 

 

Using the most accurate drawings of both the P-51 and the F-82, I made outline tracings from the top views.

 

 

The traced outlines were then "extruded" to create intersecting solid bodies at 90 degrees to one another.

 

 

(See continued discussion that follows......)

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When the two bodies were intersected they formed a simple model based on the profile outlines.

 

 

The two models could now be superimposed on one another to see any obvious differences.

 

 

And just to get fancy, I changed the F-82 material to "glass"......

 

 

Using this technique to compare the differences between the P-51D and the F-82B have given me enough information to feel comfortable with using the nose sections off 1/32 scale P-51's as a foundation for the rest of the fuselage(s) of the F-82. I also feel comfortable using the section drawings I have to create a more accurate fuselage, wings, and tailplane. That means I will also have a lot of cockpit components and other (as Brian puts it) fiddly bits to work with. Don't be too hard on me about all the details guys. I know the path I have chosen isn't perfect, but it is one that won't be terribly costly, and should be a lot of fun. My biggest fear is that I will get 3/4 of the way done, and a kit will be released. Others have said that they don't think that will happen, but There are a lot of models that I never thought would even be considered for production.......

 

Thanks for lookin'. It might be a while before I add more, but it will come.......

 

Ken Friend

[LSP_Kevin]

Ken, this has to be one of the more ambitious projects I've seen on LSP to date! I admire your courage to take it on, and your attitude in realising that you need to build what you want, while you can. Your CAD techniques are great, but I'm not sure I'd trust completely the outlines you get from photos. That said, I don't think it matters that much if you produce a result that looks right, and have a blast doing so.

 

Kev

[foiler]

Ken, this has to be one of the more ambitious projects I've seen on LSP to date! I admire your courage to take it on, and your attitude in realising that you need to build what you want, while you can. Your CAD techniques are great, but I'm not sure I'd trust completely the outlines you get from photos. That said, I don't think it matters that much if you produce a result that looks right, and have a blast doing so.

 

Kev

 

I fully understand Kev, and am willing to take the risk. Using not only the photos, but the drawings as well, helps me validate the information I have. I could get the 8000 production drawings for the F-82B from the Smithsonian Air & Space archives, but they are pricy and on microfilm. I have been very cautious with what I am copying, and have made some real time measurements on actual aircraft before committing to scale factors. I feel pretty good about the info I have and have gotten rid of the bad stuff. It has taken a long time just to get to this point.

 

Thanks for the vote of confidence!

 

Ken

[LSP_Kevin]

Thanks for the vote of confidence!

 

Hey, no problem Ken! I'm quite looking forward to this one.

 

Kev

[Jim A.]

Ken,

I am really looking forward to your progress and think you are off to a great start. I hope more info comes to light to help you.

 

 

Best,

Jim

[JRutman]

This is really something. Very impressive. I must admit though,it's making my head hurt trying to follow all of the cad stuff. LOL I am really getting to be a dinosaur.

J

[foiler]

Well, I got through the initial post without getting beat up too bad, so I thought I would try to add a little credibility to the CAD model(s) before all the other CAD folks started to log in.

 

I have seen other projects on the forum that start with a CAD model, but thought there might be those who would like to see how the CAD model ws originally created as well. Please keep in mind that my objective is to create basic 3D models of the P-51D and the F-82B in order to find what differences and similarities exist. The initial CAD images I posted were just a quick "draft" to see if I was even close to having a viable solution for the project. As Kev points out, the photos may present a distorted view. But, I had to start somewhere, and the images I got are high quality Air Force Museum images for the most important planes I would be working with. The comparison(s) gave me enough info to start the more detailed work.

 

The block-shaped models indicated that the nose sections of the P-51D and the F-82B were virtually the same from about mid cockpit to the tip of the spinner. If they are not the same, they are close enough for what I want to do. The next step is to utilize the most accurate cross sections I have to create more defined 3D models. This will help show any gross contour variations. In this first stage I have used the P-51D cross sections to create a more contoured model.

 

The sections are first created on a 2D plane then moved to the appropriate "station" along the length of the fuselage:

 

 

 

A process called "lofting" is used to generate a solid model that flows through the individual sections.

 

 

It is only necessary to work with one half of a symmetrical model since the other half can be "mirrored" from the original parts. Mirroring the wing and fuselage half required selecting the parts to be mirrored, identifying the mirroring plane, and pressing the "enter" key.

 

 

The next step will be the same for the F-82B. Once both models are defined I can start cutting them apart and designing the new parts that will be required. Once those are created, I will be able to generate accurate sections to use for making the real plastic conversion parts.

 

Ken Friend

[Out2gtcha]

AWESOME. Your CAD/CAM skills have always amazed me Ken. Honestly. This is a huge undertaking and I know you can pull it off.

 

I think you have the EXACT right attitude and knowledge going into this that is needed to make a great build without getting caught up in all the rivet counting that sometimes prevents people from actually BUILDING the project.

 

Cant wait to see more.......

 

Brian

[Derek B]

Brilliant 3D CAD/CAM work Ken...Kinda reminds me of my master pattern making process!

 

Derek

[foiler]

I actually decided to post this project after watching and admiring the detail work that Pete and Timmy! are putting into the AT-38B, and some of the other projects that have a CAD foundation. The techniques are all similar, but have a different look simply because of the graphic capabilities of different software packages.

 

If anyone happens to know where I can get a couple inexpensive Dragon 1/32 P-51D's, I would really appreciate some feedback. Funds are limited, and I would hate to pay full retail for a couple kits that will ultimately be cut up........

 

Thanks for the comments and interest!

 

Ken Friend

[foiler]

One of the fun parts of using CAD to model things is that you can do things in a virtual world that are phisically impossible in the real world; just like superimosing the P-51D and the F-82B on one another. I knew the F-82 was stretched relative to the P-51, so tried stretching the P-51D 3D model just to see how close the resulting model would come to the F-82B. I selected the P-51 model, grabbed the tail end, and stretched the model to the F-82 outline. I thought it was interesting to see the new model come so close to the F-82.

 

 

 

Now, where did I put that rubber Dragon kit????

 

Ken Friend

[foiler]

Got some more done with the virtual F-82 model. I decided to use the gold colored (picture) section of a Dragon P-51D as the foundation. No need to 3D model the complete nose since it already exists. This will give me good contours to match up to as well as the engine and cockpit detail bits. The silver section is the rest of the F-82B body work that will be required for the conversion. Before the 3D model I was limited to a small number of sections to use as patterns for the new components. Now that the 3D model exists, I can cut sections wherever I want.

 

 

Creating the second fuselage was simply a matter of copying the first one to the 172 inch centerline distance.

 

 

Applying an extruded NACA 66-2-215 airfoil provided the center wing section. The horizontal stabilizer is a symmetrical airfoil. The outer wings are not constant, so will require a little more design work.

 

 

Here is what the model looks like in wireframe.....

 

 

Thanks for lookin' in on me!

 

Ken

[Tallyho]

Hello Ken,

 

I have a NIB Dragon F-6D which I think will serve your purpose, if so, it's yours for the asking as I'd like very much to see this project come together.

 

Fred

[foiler]

Brilliant 3D CAD/CAM work Ken...Kinda reminds me of my master pattern making process!

 

Derek

 

I was fortunate enough to have worked around pattern makers for experimental engines years ago. You are right, the techniques are very similar, but the "virtual" world lets you do/make things that are impossible in the real world. Not real sure how I would have gone about this 20 years ago: oh yes, T-Squares, triangles, rules, and pencils! ------ NOT!

 

Ken