Hellcat Build with 250cc Radial
 

This is a scratch build project for a 21% scale Grumman F6F Navy Hellcat.

Specifications:
Wing span: 108”
Weight: Estimated at 50 lbs
Engine: Moke 250 cc 5 Cylinder Radial:
Fuel Tank: 50 oz
Retractable Landing Gear: Custom Made by Sierra Giant Scale:
Wheels: 7” Main Wheels by Sierra Giant Scale
Plans: Zirloi Plans enlarged by 12%
Cowl: home made fiberglass plug
Canopy: home made from vacuum form mold.
Construction: Built up using balsa, light and aircraft ply and maple and poplar hard wood. The skin will be 1/8” and 3/32” balsa skin covered with 1 oz glass cloth and fabric covered control surfaces.
Paint to be used: KlassKote epoxy paint.

I took the photos below at the Air and Space Museum in Washington DC

RE: Hellcat Build with 250cc Radial
 

First I would like to apologize for not responding to the many messages posted for me on RC Universe when I first anounced this build. Some date back about a year ago. I just noticed them today. Hopefully this post will answer most of your questions. Please feel free to ask about any details that I did not describe well.

I started to build this plane back in December of 07 approximately a year ago. About that time I ordered the landing gear from Darrel at Sierra Precision. I proceeded up to the late summer and since I didn’t receive the gear yet I decided to put the project on hold. I was at the point were I needed to start working on the wing and did not feel comfortable proceeding with out having the gear in hand. From the late summer until last month I built a Skymaster F-15 starting with a basic white airframe and doing it up in the blue aggressor flanker scheme. Anyway about the time I started the jet Darrell came though with the gear. I have to tell you it is truly a work of art. It was modeled after the gear he made for Phil Clarks 30% Skyraider that was commissioned by Ali Machinchy of Al’s Hobbies in the UK. I am sure if you ordered a set now it would not take as long. Darrel said he made it three times before he was good with it. See photos below

RE: Hellcat Build with 250cc Radial
 

The gear and plans are available now. The cowl and canopy will be available as soon as I finish building the mold for it.


I just received my engine last week. While I was building I used my 215 cc radial from my Balsa USA Stearman for size. It is actually exactly the same phyical size but the 250 has no piston sleeves to give it a larger displacement. It is also slightly lighter as well.

RE: Hellcat Build with 250cc Radial
 

I will be following the plans for the most part but I did alter the way the control surfaces are hinged for scale appearance. You will see that I had to greatly alter the main wing so that the new landing gear was nice and secure. I am currently working on the main wing and almost have it framed out now but I will do this build project in the sequence that I actually built it. So here goes.

It took a bit of effort to enlarge the plans. The print shop I used had only 36” roll size paper. The Ziroli Hellcat which is actually 18.75% scale is provided on four 36” wide sheets. I had the print shop scan in the sheets and then I blew it up in Photoshop program and rearranged views so it fit back on 36” wide sheets. It went from 4 to 6 sheets. Below is the layout. The blown up 21% plans are going to be available from Nick Ziroli Plans.

RE: Hellcat Build with 250cc Radial
 

I see that the plans got posted at a very low resolution but you can get the idea of the layout. Nick Ziroli Jr. is a friend of mine and also a fellow club member. I will make the full size plans available for him to sell. Check out his web site at: http://www.ziroliplans.com/

These are the 3 views that I am using

RE: Hellcat Build with 250cc Radial
 

this should be a great project to watch. The engine alone is amazing seen a few of these and boy they look and sound the buisness.
good luck with it all

RE: Hellcat Build with 250cc Radial
 

I have posted high res images of the 3 views in ZIP file format at:
http://www.liskyhawks.org/images/hel...s_Drawings.zip (3.3mb file)

Here are lots of Hellcat photos I took at the Air and Space Museum in Washington DC
http://www.liskyhawks.org/images/hel...ace_Museum.zip (128mb file)

Other photos I found on the web that show some of the close up detail of the Hellcat:
http://www.liskyhawks.org/images/hellcat/Hellcat_Full_ Size_Photos.zip (15 mb file)

Below are the books I purchased that I found very helpful. They are listed with my favorites first

1. F6F Hellcat by Adam Jarski, Waldemar Pajdosz. It is an Aircraft Monograph 20 book by AJ Press. ISBN 83-7237-176-8

2. Walkaround F6F Hellcat by Richard Sl Dann. This is a Squadron/Signal Publication. ISBN 0-89747-079-6.

3 Hellcat Aces of World War 2 by Barrett Tillman. This is an Osprey Aircraft of the Aces #10 publication. ISBN-10: 1-85532-596-9 and ISBN-13: 978-1-85532-596-8

4. The Maru Mechanic No. 40. All of the text is in Japanese which I can not read but the fold out 3 view, illustrations and photos are really great. I ordered it on the web from the Japan. I do not see the link to the book any longer but I sent an email to [email protected] (in English) and asked for the THE MARU MECHANIC book for the F6F Hellcat. I paid with PayPal. The cost including postage was $25.00.

A very good plastic model I also got for reference was by Hasegawa titled the F6F-3/5 Hellcat. It is 1:32 scale. It is very detailed. I do not plan to build it but it is great to be able to see the detail you are duplicating in 3D.

RE: Hellcat Build with 250cc Radial
 

Thanks Sir C.

-

I started with the horizontal stab, mostly because it was the easiest to do. I wanted to change the method of hinging so that it would have a scale type hinge and so that the control horn would be inside the fuselage. Below is a sketch of what I wanted to do.

RE: Hellcat Build with 250cc Radial
 

I used brass tubing and 1/16” dia music wire for the hinge pin. The hinge arms are 1/8” aircraft ply the rest is balsa. Attached are some photos of the stab framed out and then sheeted.

Note the 4 foot scale to see the size. By the way this is the widest part of the plane (including the center section of the main wing) and it is just under 4 feet so it will fit in my mini van.

RE: Hellcat Build with 250cc Radial
 

Next comes the rudder and fin. In a effort to keep it light I used some pink foam for the leading edge of the rudder. So much was sanded away that if I did it again solid balsa would be just fine.

RE: Hellcat Build with 250cc Radial
 

wish i had money and space to build somthing as big and as dedicated as this, i supose on the good side i could afford to buy 1 prop for it after saving up for a year:):)

RE: Hellcat Build with 250cc Radial
 

This is fantastic Lou, I am really enjoying the build so far. And am really looking forward to the flight video some day!

RE: Hellcat Build with 250cc Radial
 

I set the stab and fin aside and started on the fuselage. All of the formers are of 1/8” light ply. They can be cut from a 2” x 4” sheet but I had a nice large piece to work from that was donated by my friend Sal Calvagna.

With regards to my shop I have a large band saw and a scroll saw. I cut out the patterns from the plans and sprayed the back side with 3M77 adhesive then applied it to the wood. It is just a matter of cutting out on the lines. I cut out for the stringers but kept the slot small so I could shave it to fit later on.

The photos show formers on the crutch with out glue and the paper still attached. I wanted to get a feel for where I could add some lighting holes.

RE: Hellcat Build with 250cc Radial
 

Yes I love woring on this kind of stuff and it keeps me out of trouble. I will be sure to post a video when it is flying. No pressure but maybe this fall.


The formers are quite warped before stringers are attached. I used scrap sticks to make a brace on the top and bottom and clamped them in place.

RE: Hellcat Build with 250cc Radial
 

With regards to the stringers when you scale it up it should be a bit larger then the 1/8x1/4 that is called for. It is 12% larger or 0.14” x 0.28”. I cut my own with my bandsaw using a fence. I used clear pine that is available at home depot. Balsa would work but the extra stiffness of the pine is nice to have when sheeting the skin. I am allergic to CA glue and I am forced to use alternatives. I found that Elmer’s ProBond works very well for most joints. The only exception is when you are laminating balsa. The water base in the glue will warp the wood. In this case I will use epoxy or CA with a respirator.

RE: Hellcat Build with 250cc Radial
 

I need to hold up on the fuselage here so that I don’t box myself in when I am ready to install my servos and control linkages.


In my shop I have a small CNC milling machine that I taught my self how to use. It is not big enough to do this size landing gear but for small parts it is great. I planed to make the linkages for the elevators and rudder using ¼” od brass tubing and large servo arms. The ID of the servo arms needed to be drilled out to fit the tubing. I doubled the wall of the tubing by sliding in the next smaller size and using epoxy to glue it in place. I plan to use the Sullivan Composite Flex Rod 4-40 to connect each half of the elevators and the ruder to a servo. The servo will be located forward near the CG. I made the bearing blocks on the CNC from aluminum but you can use aircraft ply just as well if you plan it out when you build the stab and rudder.

There are two 1/8” music wire pins that are right angles to the ¼” brass tube. This is what drives the elivators.

I made the elevators removable by using the next size brass tubing on the elevator to accept the pin. You slide it on the 1/8” pin and then slide the 1/16” music wire hinge in place.

The last 3 photos are showing the bottom of the stab were the control linkage will go.

RE: Hellcat Build with 250cc Radial
 

For the rudder I will be using pull-pull cables. See the bottom view of the rudder which is also removable by sliding out the 1/16 hinge pin and disconnecting the pull-pull cables.

RE: Hellcat Build with 250cc Radial
 

Here I am covering the fin and horizontal stab with 1 oz glass cloth and Z-poxy finishing resin.

RE: Hellcat Build with 250cc Radial
 

Nice neat work Lou!

Keep the pics coming!

RE: Hellcat Build with 250cc Radial
 

Still waiting for my landing gear and trying to avoid working on the wing at this point. After looking over the fuse I figured I could add the stringers to the belly pan with out causing an access problem later. The belly pan would be cut out when I fit the wing and I would still have lots of room to get inside. I stopped the stringers at angled former F7A and used 1/16” spacers between this and the main former F7. I used a thin sheet of polyethylene between the two formers with clamps so that it will come apart easily. This is from past experience as I found it is very difficult to cut through the sheeting and glued spacers as the plans call for.

I noticed that the inner wing saddle FS1 appeared on the plans to but up to former F1. It did not fit correctly though. I think the intention was for it to fit in a slot in F1 although it is not shown on the F1 pattern.

RE: Hellcat Build with 250cc Radial
 

Since it was already mounted I used a neat tool, for the first time, that I had for my Dremel. It is a miniature circular saw. It cut a nice clean slot while the former was in place.

RE: Hellcat Build with 250cc Radial
 

More photos of the fuse progress.

RE: Hellcat Build with 250cc Radial
 

About this time I am seriously wondering were my landing gear is. I am ready to start on the main wing but have no idea what the gear will look like. I didn’t want to keep bugging Darrel as I knew he was working on it so I took on doing the plug for the cowl mold.

As I mentioned earlier, I did not have my 250 cc engine yet but I do have a Balsa USA Stearman with the 215 cc 5 cylinder radial that I built a few years ago. I pulled the engine out and used it to make sure the cowl plug would fit properly. My plan is to end up with a good quality, light weight fiberglass cowl. I need to have a female mold to do that. There are a few ways to go about this but I also wanted to be able to provide cowl to anyone wishing to build a big Hellcat like this. Darrel felt that there were builders out there that would be interested in this size model. We had an agreement that he would make the custom gear and I would provide the cowl, canopy and make the plans accessible.

My plan for the cowl, briefly, was to make an exact replica of the cowl that could be waxed and covered with fiberglass and epoxy resin. This is called a plug. Once the epoxy hardened the plug would pop out and I would have a female mold. Okay that is a bit over simplifying the process but that’s the general idea.

Since the hellcat has an interesting air scoop at the bottom I decided to make my female mold in three pieces. One piece would be the leading edge part with the air scoop and then the right and left sides.

Using the 3 views and the plans I made a cowl plug former for the rear center and front. Then I check clearances with the engine on a dummy mount with 2 ½ degrees of right thrust.

RE: Hellcat Build with 250cc Radial
 

Wow, a lot of nice details. But that CNC linkage is sweet! :D

RE: Hellcat Build with 250cc Radial
 

Here I am adding the rest of the stringers to the belly pan and I had to put a removable offset in the forward crutch stand as the original one I made had the stringers passing through the support.