Newbie Questions: 402 P-51

[leonhsu]

Hi, new builder (and pretty new to the forum) with a few questions. Building a 400-series laser cut P-51D, having only ever built one model before -- a 500 series Bf109 before (and that was done without much research, so had a lot of trouble).

1. Some of the bottom stringers (that go from the underbelly intake towards the tail of the plane have to be curved pretty significantly. Is there any trick to that, or after soaking the stringers will they take the right shape pretty easily?
2. This model has a 1/4" square length of balsa for the leading edge that you are supposed to carve/sand into shape. I've never done any kind of carving/shaping like that (in any medium) and I'm worried about doing a good job. Any suggestions on tools and/or techniques to use?
3. The wingtips seem hard to cover well in tissue (that was definitely my experience with the Bf109) and somewhere i saw someone talking about making them out of a solid piece of balsa (this isn't going to fly, so I'm not concerned about weight). Am I crazy to try to do that (given my limited carving/shaping experience)?
4. Any advice about getting the dihedral right? I think for this model, the middle section should be square (i.e. outside ribs at 90%) so that it fits snugly under the fuselage, but the wings need to be sanded a little so that the pieces sit flush against the middle section. Is that right? Or do I angle in the outside ribs of the middle section and keep the wings square?

I'm sure I'll have more questions as I progress further, but those are the ones that are in my head right now.

Thanks in advance to anyone who can help.

[leonhsu]

Oh, another question. Just saw something about scalloped formers in the fuselage. Is it too late to do that if the fuselage is already assembled? Or is that the best time? Do I just wrap some sandpaper around a piece of dowelling and go at it?

[paul]

2. This model has a 1/4" square length of balsa for the leading edge that you are supposed to carve/sand into shape. I've never done any kind of carving/shaping like that (in any medium) and I'm worried about doing a good job. Any suggestions on tools and/or techniques to use?

Hi leohsu and welcome

If you are worried about sanding and shaping the leading edge and spoiling your build, may I suggest that you purchase pre-shaped 1/4" leading edge from your LHS.
Doesn't cost a lot of pennies, but saves on the heartache and time if you get it wrong.
Advice in shaping would be helpful for me too

Paul

[leonhsu]

Hi Paul,

Does LHS stand for local hobby shop? If so, it just closed, so I have to go in search of a somewhat less local one.

But more importantly, you can buy pre-shaped leading edges!? I wish I had known that before glueing the wing frame together!!

Maybe I'll try that for the right side wing.

[Wildpig]

Hi Leonhsu,

1. The stringers can be soaked in water for a few hours and will curve better than dry stringers. You might search this forum for a build on the 402 P-51 to see how it's done. Forum member Mitch built one.

2. If you can't find pre-made leading edge, I would carve the stock wood. It's not too difficult. Takes time and care.
The Laser cut kits tend to have good quality wood. I would make a sanding block using #220 grit sandpaper and then finish with #400 grit. You cannot get aggressive with the sander. You risk damaging the ribs. But, I don't think you will have much trouble sanding the leading edge yourself.
3. Try carving your own wingtips. The key is to get some soft balsa. It will be much easier to sand.
4. For dihedral. There should be enough information on the plans to explain that. Look carefully at the plans, it's there somewhere, what to do. I didn't think the non-flying P-51 had any dihedral?? or maybe it does, slightly.
Most of these kits, you angle the rib.

One other piece of advice; your model won't be perfect. You'll have all kinds of errors or see things that you can do better, next time. That's just the learning part of this hobby.

[Mitch]

Welcome... Mitch here from Kodiak AK (on my ship)

For the curved stringers I look for some soft (weak) strips and use those. If they are all pretty hard I squirt Windex on them(The ammonia works well to soften the wood)
For the wing tips... I cover the top wing in 5 sections. Center, Port, Stbd then the wing tips separately. From the last rib to the wingtip cut a piece slightly oversized, then as is goes over the wingtip make several cuts from the outside towards the wingtip to relieve the stress, and get the paper to lay down.

I have built this model at least 4 times and I know it will fly if you build it straight and not too heavy. I have built it as per Guillow plans and flown with guillow prop and rubber. It weighed about 100 grams. I have built my last P51 with some modifications and got the weight down to 80 grams and flown in competition.

PS The 400 series is my favorite, I have built and flown every model (with rubber) Some more than once! Good Luck and Good Flying, Mitch

[leonhsu]

Thanks for all the advice.

Tonight I tried test carving some wingtips and it didn't turn out too badly. the first one i over-sanded, but i think I'll just glue it to the wing-tip piece from the kit and take another shot at sanding it down.

Given how that went, I'm less apprehensive about shaping the leading edge, except for the fact that i don't want to break the wings while doing it.

Will report progress and add more questions.

btw ... when I said that "this is not going to fly" i only meant that i'm not planning on trying to fly it -- afraid of crashing it and losing all my hard work. but, whatever i build after this one, i think i'll try to get it to fly.

[davidchoate]

we got something in common. My first model was also a 500 ME109, and my second was a 400 P-51. its not as hard as you think to sand the leading edge,just TAKE YOUR TIME,and dont over sand the stringers, or you will have thin spots between the ribs. For me the toughest part was the covering. there are alot of compound curves around the radiator scoop, and I would use small pieces, and eqally switcch sides, as the scoop under the wing is not as strong as the fuselage. I had some warping go on there cause I got impatient, and covered too large an area at once. the silk shrinks quite a bit,and I now use the "wet" method when I use silk because I have had too many warpages when spraying it ,and then let it shrink.I was surprised at how light the P-51 was for its size, and I know Mitch has had some very good Flight Times with his.