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Hellcat Build with 250cc Radial

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Hellcat Build with 250cc Radial

Old 01-15-2009, 03:57 PM
  #26  
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Default RE: Hellcat Build with 250cc Radial

Thanks Knot. Every shop needs a CNC ha ha. You can do really cool stuff on it. Later I will show you a photo of it.


Here is another view of the dummy engine mount sitting on the rear cowl former.
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Old 01-15-2009, 03:58 PM
  #27  
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Default RE: Hellcat Build with 250cc Radial

I made up a ¼” ply wood frame to support the next to formers. Remember that weight is not an issue for the plug
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Old 01-15-2009, 04:00 PM
  #28  
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Default RE: Hellcat Build with 250cc Radial

Now to add the stringers. As I said I used the side view outline of the 3 view to size the formers. This later proved to be incorrect.
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Old 01-15-2009, 04:01 PM
  #29  
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Default RE: Hellcat Build with 250cc Radial

Here I am checking for fit on the fuse. Looks good so far.
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Old 01-15-2009, 04:02 PM
  #30  
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Default RE: Hellcat Build with 250cc Radial

Now to sheet it and check it again.
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Old 01-15-2009, 04:04 PM
  #31  
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Default RE: Hellcat Build with 250cc Radial

By the way I made a nice sanding tool with 60 grit paper attached to a foam packing pad with 3M77 spray adhesive. It does a quick job of sanding the balsa sheeting.
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Old 01-15-2009, 04:06 PM
  #32  
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Default RE: Hellcat Build with 250cc Radial

Now on to the leading edge of the cowl. Here I am using scrap balsa blocks. Balsa USA bag of blocks is great for this. I arranged them like a jig saw puzzle until I had enough coverage. Then I glued them in place and attached a second copy of the forward former from the cowl plug base.
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Old 01-15-2009, 04:08 PM
  #33  
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Default RE: Hellcat Build with 250cc Radial

Now to cut the od on the band saw and the ID on the scroll saw and check for fit
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Old 01-15-2009, 04:11 PM
  #34  
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Default RE: Hellcat Build with 250cc Radial

After lots of sanding and elbow grease I discovered something wrong. There was not enough room left in the leading edge for the air scoop feature. It turned out that the 3 View was incorrect. I was short by ¾ of an inch on the bottom of the leading edge of the cowl.
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Old 01-15-2009, 04:12 PM
  #35  
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Default RE: Hellcat Build with 250cc Radial

Oh well it is easy to fix with body filler and more balsa. The following photos show the extra solid balsa that I added to the leading edge ring and a web guide on the cowl base. I would use this guide to build it up with autobody filler
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Old 01-15-2009, 04:19 PM
  #36  
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Default RE: Hellcat Build with 250cc Radial

After filling I checked again on the clearances to the engine. Actually the outline drawing for this engine that are on-line do not take into account that the valve lifters move up and down. This makes it effectively larger. I needed to add more material to my cowl to allow the lifters to clear. I was using a sheet of polyethylene between the front and base of the cowl so the body filler would not fuse the two together when it hardened. In the process you can see that I added a pink foam base with clamping pads. This was so that I could clamp it down and sand with two hands.
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Old 01-15-2009, 04:22 PM
  #37  
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Default RE: Hellcat Build with 250cc Radial

Ahh that is about right . . .

Now to shape the leading edge lower scoop I needed to cut away the lower section and then glue it back.
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Old 01-15-2009, 04:23 PM
  #38  
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Default RE: Hellcat Build with 250cc Radial

More shaping and checking.
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Old 01-15-2009, 04:25 PM
  #39  
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Default RE: Hellcat Build with 250cc Radial

I added the vanes in the air scoop and primed it. I used several coats of laquer based automotive primer surfacer.
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Old 01-15-2009, 04:26 PM
  #40  
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Default RE: Hellcat Build with 250cc Radial

I added the panel lines and the larger fastener impressions on the surface. Then I used what ever color lacquer that I had handy. I then rubbed it out with compound and it should be ready to build my mold now.
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Old 01-15-2009, 04:46 PM
  #41  
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Default RE: Hellcat Build with 250cc Radial

This was around the end of April and I decided to put the project on hold until my gear came. Jets were becoming popular in my club and after much research on what would be scale but not too difficult to fly I got a Skymaster F-15. Shortly after the jet arrived my gear came but I was committed to the Jet at this point. I don’t want to get too off track here but I included a few photos of the rocket ship. I used Klasskote and did the division of colors with an air brush. The decals were homemade using Decal Pro FX and enlarged and cleaned up 1:32 plastic model decals. First flight nest spring.

On my next post we will fast forward to last month were I focused on the main wing.
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Old 01-16-2009, 02:24 AM
  #42  
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Default RE: Hellcat Build with 250cc Radial

Beautiful work, and great job catching us up to the present! I'll be watching along and learning!

Tom
Old 01-16-2009, 11:54 AM
  #43  
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Default RE: Hellcat Build with 250cc Radial

Thanks Tom. I am nearly caught up to present day.

-

I can’t say enough good things about the landing gear. They are incredibly tough. However, due to the large air cylinder and the massive strut diameter the wing can not be built according to the plans. Below is a photo of the gear in place on the side view of the fuselage. When you look at the photo that has the gear retracted it is clear that the wing spar must be moved. It is possible to place it between the rear of the air cylinder and the front of the tire. However, using an aluminum tube to join the center section to the wing tip is not going to fly. There is not enough room for both.
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Old 01-16-2009, 11:58 AM
  #44  
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Default RE: Hellcat Build with 250cc Radial

I recalled reading about a very large Ziroli Skyrader with a 400 cc radial on an RD forum. In this case the spar was also used as the wing joiner. After finding it and reading it over I sent the builder, Phil Clark, an email to get his opinion on my problem. Actually Darrel with Sierra Giant Scale also made his landing gear which is a very similar design to mine. Phil is from the UK but he replied in a few hours with diagrams photos and a lot of encouragement. Thanks Phil!

Attached are some of Phil Clark’s diagrams and photos. You can see the Skyraider here at: http://www.rcuniverse.com/forum/m_6028566/tm.htm
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Old 01-16-2009, 12:04 PM
  #45  
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Default RE: Hellcat Build with 250cc Radial

My new wing design will have one, in-line spar for the center section and the wing tip. The spar also moves to the rear by 2.26” This is measured from the trailing edge of the original spar to the leading edge of the new spar. This places the spar right in the center of the space between the end of the air cylinder and the tire. I am using a spar that is 5/8” wide x 3/8 thick. This was cut on my band saw from Maple. Poplar is also a good choice as it is very close to the properties of Sitka Spruce for weight and strength. I chose maple because it is stronger and only a little heavier. It also holds screws very well and my local Home Depot has both in stock. Attached is a view cross-section of changes to the wing spar.
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Old 01-16-2009, 12:14 PM
  #46  
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Default RE: Hellcat Build with 250cc Radial

To join the wings I am using a 7/16” wide x 1/16” thick type 304 stainless steel strap on the top and bottom of my wing spar. I will have a single long bolt going through joining the wings with a locking nut on the bottom. Attached are the drawings for the straps I made. I use SolidWorks as the drawing program and then use the image to make the part on my little CNC milling machine. If anyone is interested in the 3D version let me know. By the way stainless steel is extremely tough to work with. I suppose plain steel would work nearly as well and you can cut it with hand tools.
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Old 01-16-2009, 12:31 PM
  #47  
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Default RE: Hellcat Build with 250cc Radial

The other major change to the wing is where the wing break is located. The plans show the wing break at the dihedral line. If you do this there is only about two inches for the strap on the bottom of the center section. This is because of the notch that is needed for the landing gear strut. I decided to move the wing break out one rib and it gave me a longer spar work with. This is located at rib #7.

Please see the attached photos for the construction of the center section spar.
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Old 01-16-2009, 12:50 PM
  #48  
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Default RE: Hellcat Build with 250cc Radial

What I did is reinforce the spar in the center section and two ribs past the wing joint with 1/8” aircraft ply. The space between the spars is solid aircraft ply going back one rib from the wing joint and also solid where the notch is for the gear strut.
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Old 01-16-2009, 12:55 PM
  #49  
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Default RE: Hellcat Build with 250cc Radial

I am sure I got a bit carried away with too much strength and weight here. If I needed to build it again I would go with a ½ x 5/16” spar. With the 3/32” aircraft ply on each side it would still be super strong. The key is making it solid between the spars where the strut notch is and at the wing joints. The lightning holes I added are 1 3/8” diameter.

One note is that it is important to align the angle rib #7 at each end of the centersection and the wing tips. This much be perfectly square so that the wing is straight. I used a nice heavy flat plywood board. Mine had Formica on each side. I used some 3M77 adhesive and sprayed a light coat on a sheet of polyethylene. Then I stretched it over one side of the board and took out any wrinkles. Epoxy will not stick to the polyethylene sheet. Before hand I used my belt sander to square up the ends of my center spar. Then I used the flat board to position rib #7 and make sure it was a flat as possible while the epoxy dried.
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Old 01-16-2009, 01:30 PM
  #50  
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Default RE: Hellcat Build with 250cc Radial

Now for the wing tips
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