Finishing Those Foam ARF RC Scale Airplanes – P-51 Flight Report (and some corrections)

Finishing Those Foam ARF RC Scale Airplanes – P-51 Flight Report
Last time around, in my initial blog/article on modifying the Atomik RC/J-Power P-51 ARF for improved appearance, I explained that all the stuff I tried worked and I was able to report that “It does fly.” In this installment I’m here to let you know how well the “enhanced foam” model performs and share some photos my friend (and fellow FLY RC Magazine columnist) Gary Ritchie shot during one of those clear blue sky flying days that are so unusual in the Pacific Northwest at this time of year.

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 First, however, I need to address an issue with “my” fiberglassing-and-refinishing process (Let’s call it “foam enhancement”) that has been brought to my attention since I first posted the material on-line. My bad…! Problems with foam compatibility with various finishing materials have been reported to me regarding attempts to work on foam ARF airplanes other than the J-Power P-51 I used as a demo model. Sorry, guys … I thought I had explained this detail properly and it appears that I did not. The J-Power P-51 is made from EPO (Expanded Poly Olefin) foam which tolerates contact with the solvents used in those model-building products such as dope/lacquer thinner, acetone, etc. that have always been classified as non foam-friendly. I intended to emphasize that NOT ALL of the foam ARF’s on the market are made of EPO … there are plenty of styrene-based-foam models around and they MELT when you get them close to the “bad stuff”. I chose to use several of these non-foam-friendly products such as cellulose-based body putty and the various Stits finishing products to emphasize how easy it is to use the various Deluxe Materials right alongside them…but…this only counts when the foam structure beneath the finish you’re working on is EPO or a similarly tolerant material. NOTE: A carefully applied EzeKote/fiberglass cloth base MAY protect the more sensitive foam types from aggressive solvents used over it, but there’s no guarantee. That’s one I’d suggest you might want to experiment with on your own.

There’s one other issue I want to discuss while we’re talking about difficulties that have been reported to me. I may not have been clear enough in explaining that all your major surfacing work (filling servo wire cut-outs along with smaller voids, smoothing bumps, etc.) needs to be done before you are ready to begin to apply the new EzeKote/fiberglass skin. The proper place for any “filler” on your model is under the glass cloth where it will be locked/bonded in place. Filler/primer on the surface of EzeKote/glass should be limited to whatever small amounts may be necessary to correct pinholes and whatever other tiny imperfections might appear in the hardened EzeKote surface. Your new glass skin after two coats of EzeKote should already be smooth and require nothing more intrusive than wet block sanding with 200-grit silicon carbide (black automotive) paper. After that, if you are working over non-EPO structure and don’t want to risk that the EzeKote/glass skin might not work as a solvent barrier, I’ll suggest that you use Deluxe Materials Sand’n’Seal as a foam-friendly, wet-sandable base for your color coats. At that point (when you have a base finish of sanded primer that is as good as it’s going to get) you’re ready to choose and apply your color coats (“paint”). No matter how good a new skin you have created so far using EzeKote/glass, you should not assume that your shiny new surface will serve as a barrier to foam-eating solvents. (It might, but that’s not what these Deluxe Materials products are intended for). If there’s any question, use ONLY paint products that are labeled “FOAM SAFE”. Choosing from the many water based/acrylic products on the store shelves is a safe way to go.

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With all that said, let’s have a look at what a winner this enhanced foam conversion of the J-Power P-51 turned out to be where it counts…at the flying field!

Before getting my head into “test flight checkout mode”, I moved the P-51 around to different places on the field so photographer Gary Ritchie could get some detailed static shots under varying light conditions. This one turned out to be excellent for showing off the overall high quality of the finish I was able to achieve. With an “ordinary” foamie up this close you would already have noticed plenty of surface details you didn’t really want to see at all. Not so with this airplane!

 

It looks just as good from the other side, too. If you get really close to this P-51 and look for them, you might discover a few spots that betray the foam underneath…but you’re not gonna’ find them at this distance. There’s one “scale error” evident in this shot that has nothing to do with foam…the prop/spinner assembly should be about ¼” “back” (closer to the cowl). Fixing that was not strictly part of the finish conversion, so I left it “stock” (for now).

 

There are no inner landing gear (flipper)doors, and the four-bladed prop that comes in the box is clearly way too small for scale accuracy, but there’s no mistaking the “I mean business” attitude of the P-51 seen from this angle. OK…here’s the info I know everyone has been waiting for. “How much does it weigh?” The answer, with all the stuff I’ve added, is 6.5 pounds. The call-out weight in the instruction manual is 4.85 pounds. Simple math says I have increased the weight by a factor of 1.3, or 130%. What difference does that make? This P-51 still flies well, but it’s not as “floaty” as the stock ARF model would be. It will use more runway both on takeoff and on landing…more weight =higher wing loading=higher stall speed…but performance is still way better than “scale”. In short it flies just about the way you’d expect a traditional built up model of the same dimensions would.

 

Same deal here. This model has real presence…character that the out-of-the-box foamie just couldn’t pull off. As I mentioned in the first article, you must always consider the question “Where do I stop?” The old “law of diminishing returns” applies here. At some point, adding ever more time and effort to what will always be an “enhanced foam” model stops making sense. What you see here is about as far as I’m comfortable going.

 

This looks like a different airplane because it is. I went through the entire “enhanced foam” conversion process on another “Brand X” ARF to work out the details so I could be sure of getting them right when I presented the larger J-Power model.  In other words, I used this model to make my mistakes on, which is why I’m not going to tell you any more about it.

 

Now it’s time to get serious. Back in the pits I confirmed that everything on the airplane worked RIGHT and that the 4000 mAh 4S VENOM LiPo pack I installed was indeed fully charged. Out on the “ready pad” it’s time for one final control check with the airplane fully assembled and “buttoned up” for flight.

 

And … I went on making a last check of the RLG (retract landing gear) system before I depend on it for real.

 

Taxi-out. This is slightly wet, winter-browned flying field grass, which the enhanced J-Power P-51 handles OK … but…I ALWAYS taxi any tailwheel airplane with “full-back-stick” (up elevator) as you can see here.

 

Power for takeoff is not an issue! I had still not gotten all the way to full throttle when the P-51 leaped off the grass. The “scale guy” part of me said “Get a more realistic takeoff angle!”, but the engineer side of me says “It’s clear we don’t have to worry about takeoff performance.”

 

I flew a couple circuits of the field with some extra “safety margin” altitude, then brought the P-51 “down close and personal” so Gary could get some good close-up photos. By the time he took this shot I had run through several trim adjustments, some steep turns and a stall test with the result that at this point the airplane was “hands-off” stable.

 

Same thing going the other way. The landing gear door detail and fit aren’t perfect, but for a sport scale job like this it’s just fine…and it’s reliable.

 

“Now turn the other way.” From the top, all cleaned up and ready for business, there’s no doubt this is a Mustang. So…is it worth the trouble? I say yes. I set out to show that a nice scale foam ARF could be “enhanced” as I have described for improved appearance and still be fun to fly. It will carry the weight. How far you might want to go with enhanced foam models is up to you.

 

“Let’s beat up the field and grab their attention.”

 

Landing gear coming down… The offset/stepped operation of the main struts is pretty close to scale.

 

This is a final pre-landing inspection pass…

 

…and a real “wheel landing” with the tail up and the airplane still just flying. Right now, as the wheels touch, you pull off any remaining throttle, let the tail come down, and then apply and hold full up elevator all the way back to the pits.