allanflowers

This is a report on my build of the Nexa P-47 from Motion RC. It is a balsa & ply ARF, formerly sold as the VK product.
It has just been finished today, flying may happen on Sunday if the weather holds up and I can get down to the field (the road is rather muddy at the moment). The box arrived a week and a half ago so I have been busy with it. I don't think I have ever actually built an ARF before - plenty of kits and scratch builds however. I will say that, with this product at least, It takes an experienced person to expect any success. Instructions are bad, same as when the model was from VK.
The look of the model is very nice with a few notable problems. The decals (peel and stick), though generally very nice, do not have good opaque colors on the red and yellow. The numbers on the tail almost completely disappear on the gray fin which is disappointing. The black letters are great and most of the markings are on the printed covering already applied.
Another problem is the landing gear doors which stand so far off the wing as to be unusable in my opinon. I elected to make new gear doors out of .05 aluminum. The struts seem kind of flimsy but I won't know until I get it to the field.
Another issue is the fact that the nylon wing bolts seem to be too short so I had to replace them with longer (metal) ones.
The model can be done as electric or glow. I am using an old Saito 72 and servos from a previous project.

capt1597

nice work. thanks for sharing

allanflowers

One of the first things I did was to reconsider the throttle servo location which is called out to be in the area above the wing with the rudder and elevator servos. The model from which I took the engine and servos from had the throttle servo in the engine bay, above the engine. I made a mount to do that on this plane and was able to utilize the linkage without modification. More importantly, this opened up the main tank area since there was no linkage passing through it.
With more models than I have easy storage for, I have to hang my planes from the ceiling. This means placing a tube through the fuselage at the balance point for hanging up the model.
Since I also reclaimed an on-board glow system from the old project, I needed a place to put it - along with the Rx and the charge plugs. A plywood shelf covers the batteries (Rx and on-board glow) and provides the surface for the other functions.

allanflowers

You may note the invasion stripes on the wing (first post). They only appear on the bottom of the right wing. Apparently this is historically correct since the real aircraft had a wing replaced at some point. Probably the camo work was done later (and only on the wing tops).

allanflowers

Another issue was using full size servos on the ailerons rather than the minis which were called for. These are digital and should be very accurate as well as more powerful. They fit in without significant modification to the wing. I did use minis for flaps, full size for elevator and rudder. All the provided linkages on the model seemed okay so that is what I used. There is no slop anywhere so it should be all good.

allanflowers

After getting everything ready for a trip to the field on Sunday I decided I better start the engine to make sure it would still run. It ran great last time I started it but that was five years ago or so.

Of course it did not start so I struggled for a two days with little success. Sunday, instead of going to the field, I ended up at the Discount Hobby Warehouse, our local hobby store (a great one by the way), and bought some new 15% fuel. It started right up – but ran terrible. I could not get it to idle down and it spit oil all over the place. Today, I undertook a broad overview of the engine setup, beginning with the valve adjustment. One was way too loose and the other had no gap at all. I also went over all the other aspects and found the culprit to the lousy running. The exhaust unit, a flex pipe with a muffler tap, had broken almost through, right up by the engine. This part is now on backorder so I don’t know when I may get it. I used my Dremel with a wire brush wheel to clean up the break area, got some high temp solder (1200F) and took a shot at it. I don’t know if it will hold up or not but I added some JB Weld to reinforce the repair. I will try it again today at home. The field is closed on weekdays until we get out LOA from the FAA & Navy so no trip to the field until the weekend. If it rains before then, the road will probably be impassable however.

allanflowers

Here is the repair on the muffler pipe. Keeping my fingers crossed...
Also a shot of the throttle servo installation.

HiCurrent

Some caveat: the ailerons and elevator are sensitive. I have D/R set at 50% for elevator and 70% on ailerons. The plane is a little unstable due to a straight wing (almost no dihedral). Right turn is normal, left turn a little unstable.
Overall performance, it flies OK, not a great performer

allanflowers

Hicurrent, I take it you have this model and are referring to it?
I have added a little dihedral so that may help. Thanks for the heads up on the settings. If I can get it running this could be helpful.

allanflowers

The muffler repair seems to be holding up. I finally found that the low speed needle was way to lean which was preventing it from starting. Now it seems to run fine and I have dialed it in a bit more.
Ready for the maiden.

allanflowers

The landing gear doors were flat wood and stood off the surface about 3/8” which looked terrible as well as being bad aerodynamically. My workout uses aluminum and, with a bit of crown to the surface, fits better to the wing. I made U-shaped brackets to hold the door to the strut. I left them in metal finish which is actually what I have seen on photos of the real aircraft.

allanflowers

Here is more on the lateral tube on the fuselage which serves a dual purpose, hanging the plane from the ceiling and checking the CG. Like many people, space in my workshop is very limited so hanging is a great way to store models. On electric planes, the hanging system is placed at the storage CG (no battery) so it can't serve to check the flying balance point.

jwalk2c

My Feedback: (47)

Interesting that you added a dihedral.
That encourages me to start on one of the 2 P47's I have inbox. (TarHeal Hal, and a Razorback version) and would like to know how you added dihedral.

Impressive door brackets. I have studied your picture, but cannot figure out how you attached the alum tube to the mounting surface?
Could you elaborate?
Thank you

John

allanflowers

Hi John,
I cut the one side of the dihedral brace to give a bit more angle. I could have made a whole new one with the new angle on both top and bottom but thought this would work okay since the stress point on the brace is still as large. Then, when epoxying it all together, I used plenty of glue to make up for the angle on the root rib fit, which is now not so good.
I did add tape to the joint on both sides (just packing tape, didn't have any fiberglass tape). To get more angle, one could also make
a wedge shaped shim but that would be more work than I wanted to do. Today (hopefully) is the maiden so I may soon know if the change is good or not.
This modification is NOT recommended for high stress flying but I don't do that anyway. The drawing exaggerates the angle change by the way - it really is fairly small.

The bracket was made by bending aluminum sheet around a drill bit of the right size in a vise. This needed a spacer to fit right so I attached that to the hat shaped part, marked,
drilled and bolted it all together - before slicing off the individual parts like baloney. With a little fitting, it did the job.

allanflowers

The maiden was today. All told, it could have been a better day. Weather was great, sunny with a light wind down the runway from the west. The engine started easily and everything seemed fine. I taxied around a little to verify that it could turn either way easily. The take off roll was good although power seemed a little off from what I expected. Still, it flew pretty well and I was able to trim it out, although it took a number of circuits to do so. It took a little down elevator, some right rudder and quite a bit of right aileron. I think the wing has a little warp in it so wasn't too surprised at that.
I am running a 8.5 oz tank which is minimal. I should have topped it off after my initial start up while waiting for the wind to swing around to the west. At one point, the engine coughed and it was time to land. The engine then quit completely. After getting the gear down and the plane turned around, I barely made to the runway. Unfortunately it had run out of steam and dropped pretty fast in the last few feet. I got some damage on the cowl, one wingtip and both gear got a bit bent. The dummy engine, which turns out to be very fragile, was broken up and in a couple of pieces.
The muffler repair I had done did not hold up, breaking off completely right at the engine end. From all the oil inside the cowl, this must have happened well before the tank ran dry.
It is all repairable although I will have to wait for the new muffler parts to come in. I don't think my soldering is good enough to trust, obviously. I will have to start using my Tx timer also, since there isn't room, with my workout, for a bigger tank.
I am relatively happy with the model and, after it is repaired, should be able to get a few years of flying with this model. The tank is large enough for my typical flights, just not enough for multiple circuits while trimming extensively.

allanflowers

My muffler from RC Specialties came and I am installing it. I also ordered a new bendy pipe on back-order but will cancel that.
The cowl may have to be modified a little to work with the new muffler but not too much. The pix is from their website.
The other issues for the repair are the landing gear which was bent pretty bad and the cowl with some local damage on the bottom front. It will be glued back, reinforced with some fiberglass, patched up with bondo and repainted.

jwalk2c

My Feedback: (47)

Thank you allanflowers for sharing that knowledge.
I apologize for the late acknowledgment..
I look forward to trying this on my VQ P47 Tarheel Hal
I was disappointed when I realized this model did not have the correct dihedral but is a non-issue with your modification.
Johnny Walker

jwalk2c

My Feedback: (47)

Please let us know how you like that header/muffler.
I have heard they produce a great sound.
Thanks
Johnny walker

allanflowers

Here is a pix of my new muffler installation, the repaired cowl and landing gear. It is now ready, with some additional adjustments, for the second flight. Unfortunately, the winds are bad for the next few days, especially for a high stress flight like a second maiden. Maybe by Tuesday.

allanflowers

Between bad winds at my club field and rains, which have currently mucked up the roadway going down to the field, it has not been feasible to get in the second flight. The aviation weather report ( https://www.wunderground.com/forecas...idro/KCASANYS3 ) does look good for Monday (hopefully).

allanflowers

No report
The winds were rather high and my tail wheel kept getting loose, tracking badly. I did run up the engine (first time with the new exhaust) and refine the needle setting. Also did some taxi tests when I discovered the tail wheel issue but did not attempt a takeoff in those gusty winds.
Today and the next week the weather doesn't look good for a maiden flight. I have fixed the tail wheel and am watching the weather.

allanflowers

Progress report:
Maybe I should put quote marks around the term "progress" since the day was not very good. The weather was okay but a little hard to see without good sunshine (which of course came out a little later). The engine ran up fine on the bench and my prelim flights with a little electric plane went good. Takeoff roll was fine and the plane lifted off, first turn as expected, gear went up okay. My trims were very close (after the earlier flight a few weeks back) and I took about four turns around the oval before deciding to land. Unfortunately the engine, which has been VERY reliable on other planes, sagged and died - at relatively low altitude on the final upwind leg. The model was too far up wind to make the landing strip, which left me with few choices, none good. I tried to at least yank it around and find a good place to crash land but it went into a death spiral. I should have dropped what little altitude I had before the turn. Luckily it leveled out just before impact and I was able to flare it a little before it went into the weeds about two hundred feet out.
The weeds at this field are HIGH and dense, for which I must be very thankful. Since the landing gear was still up it wasn't hurt and the plane survived relatively unscathed, other than losing the bomb and having the cowl dislocated an inch back at the top.
You can see from the photo that there isn't significant damage. It is wearing some of those weeds. I have taken it down and will be working on better cowl attachments (much needed). I ran it up on the bench before leaving the field and think I have the needle adjusted much better now, now about 2-1/2 turns out.
As far as the ARF product is concerned, today's problems were mine (and the Saito 72). I will say that the landing gear on this model is terrible, especially the tail wheel which is impossible to tighten down sufficiently. The main gear struts are also crap and can not be expected to keep alignment no matter what you do. It is a beautiful model and, if I can solve the engine settings, should give me a long service life but I will have to re-engineer the cowl attachments completely and the LG will be a continuing pain in the ###. My initial choice to go glow, with a small tank, was not good - electric reliability is hard to beat and with that small tank my flight times are very limited. The plane flies good and looks great but, even in electric mode would still be cursed with the landing gear issues.

allanflowers

I suspect that part of the engine-out issue on my first two flights might be overheating, in addition to a somewhat out of tune engine. Therefore, in repairing the cowl, I made a new baffle to better direct the air past the engine cooling fins and added a large extractor scoop on the bottom - to enhance the exit air situation.
The weather doesn't look good for the next few days but maybe then I can try it out again.

allanflowers

I have come to the conclusion that my propeller is too small. It is in the middle of the recommended range but this model has a very large blunt face which seems to be stalling out the center part of the prop (a 13-6). The main clue was the fact that, at most any needle setting, the rpms were over 10K, which is too high. I have now installed a 14-6 APC for the next flight but will have to see what my tach is telling me.

allanflowers

The other conclusion (after a frustrating session at the field today) is that the Nexa landing gear on this ARF is not only terrible but unusable. I guess I will be spending the next few day trying to find alternative gear. The main gear is s### and the tail wheel is double s###. I had beautiful weather and good running engine but couldn't get a takeoff run that was acceptable. The gear shifts around no matter how you try to tighten down.
Don't buy this plane unless you are willing to change the landing gear completely. Sad to say...