The big thread that exists on this bird has a lot of info, and there is a lot of really good stuff in Ken Isaac's excellent review, so I'm going to only put up the stuff that I personally notice, and the things that I'll do that might be different.

First of all, the covering on this bird is about as good as it gets in the ARF world. Some wrinkles and bubbles in the corners, and a lot of shrinkage needed on the elevators, and that was about it. I ran the iron over every inch so as to tease up any loose spots, and there weren't very many.

Here's the equipment I'll be using, along with the reasoning on some of it:

Engines: OS 55 AX. Inexpensive, reliable, powerful, and fuel efficient. Probably end up using 12x6 or 12x7 APC props, depending on what the tach says. 13x6 if possible, but not likely. I'm running both engines on my Lanier Mariner 40 as kind of a flying break in stand. I intend to get both of them set perfectly (in flight) before they go on the Mitchell.

Fuel tanks: 10oz Great Planes. The 14oz tanks supplied with this airplane are too big for any of the recommended engines. I see this a lot on ARFs. No clue as to why, but a tank that is too big reduces the available exhaust pressure so much that fuel delivery suffers, particularly as the tank empties, and the engine can become erratic at lower rpms. Examples: the OS recommended tank for the 55AX is 12oz; 46AX 10oz; the 70FS 10oz; and so on. I've run both of my 55s on 10 oz tanks, and never came close to using all the fuel during a flight.

The recommended Robart retracts, along with the Robart tuff tread 4" 10 spoke wheels with brakes. A lot of airshows and flyins take place on paved runways. A 20 pound twin without brakes, in my estimation, is an accident looking for a place to happen on a paved runway.

Futaba 6EX 2.4 system with a Smart Fly Power Expander. With 13 servos on board, I'm concerned that there will be a time when too much current will go through that itty bitty receiver. The expander supplies an individual connection for each servo, and the power to the servos does not go through the Rx, it comes directly from the packs. The unit impedance matches the servo wiring, so that ringing circuits don't occur. (Current ringing is why old style ignition points needed condensers, or capacitors.) There's some other nice features, too: the expander accepts two batteries, isolates them from each other and keeps them at the same voltage as they discharge. If one shorts or dies, it is taken off line by the expander. The Rx is supplied with a regulated, filtered 5V. There are two charge connections on the expander circuit board, and a switch connection. Purchasing smart fly's fail safe switch gets you two external charge jacks that connect to the expander, and a switch that uses a pin with a "remove before flight" flag to turn it OFF, so it's impossible to turn it off accidentally. The batteries will be a pair of Hydrimax 2000 NiMh.

I'm going to mechanically synch the engines. Not as elegant as having two channels, but about $600 cheaper. I always use a lot of expo on the rudder (75%), so nose steering sensitivity should not be a problem. For brake activation, I'll have a micro servo on the elevator channel that will push on a Robart gear door valve under full down. I've used this before, and it works well.

I'll be using four Futaba S-3001s for the flaps; and Hi Tec HS325s for the throttles, ailerons, retract valve, and nose steering. I'm going with the recommended Futaba S9001 for the elevator, but not with the recommended plastic gear micro servos for the rudder. Futaba says they are "Ideal for electric planes and small electric helis. Nylon gears." That speaks volumes. I learned my lesson about plastic gear micros on glow powered airplanes. NoNoNoNoNo.....unless one likes expensive holes in the ground. I'll be using a pair of Hitec HS-125 ball bearing metal gear thin wing servos. They operate the ailerons on my Mustang, and are superb, if a bit pricey.

Using all the recommended servo extensions and Y cords can cost a lot, especially if one gets the HD ones with the heavier 20g wire.
I noted Ken's difficulty with getting the various leads with their connectors through the wire tube in the fuse, so I'm going to do something I've not attempted before: I'm getting 13 of the 6" heavy duty extensions and 50 feet of the heavy duty servo wire and a bunch of the 1/32 shrink tubing. I'm going to run the wires through the fuse tube, and then cut the extensions in half and solder them to the ends, using heat shrink on the individual solder joints. Not as elegant as soldering on pins and loading them into the connectors, but my old fingers aren't very good at that kind of fine work. (Deans connectors are about as elegant as I get, and those, I think, are a real pain in the ****, but they work well.)

Oh, yeah. The large air tank. Absolutely. Top Flite claims two complete cycles of the landing gear are possible at 120 psi with the small tank. Huh? What were they thinking?

More later.

I have the large air tank in by B25, and I can get al least 10 complete cycle, but never have tried that many in flight.

CCF:

That's good info. I didn't realize there is that much difference between the small and large tanks. How do you like the way yours flies, and which engines did you use?

I've decided to dump the brakes. Guess I'll just run off into the grass if need be. I'm thinking to keep the weight and the complexity down on this one, and retracts are complex enough.

I'm using two OS 70FS. It flies great. I have the Robart wheels, with foam inserts, so with my 21 lb plane the wheels are kind of flat, which makes brakes unnecessary. Our asphalt runway is 500 ft, which is plenty of length for take-off and landing.

Kind of off subject but what size mustang are you using the hitec servos in? I have a couple of planes tha I would like to try those servos in.

metaldriver: the 1/7 Gold Edition kit, same design as the 60 size ARF. Two of them provide more total torque (83oz) then one standard size HS 475 servo (61oz)

Made another decision today- I won't be using the opening and closing landing gear doors. First reason is, although they look great in the air with the gear up, they look wrong when the airplane is on the ground. It would be like a Mustang having the center doors hanging open when the engine is running, it just wouldn't look right. Second reason is, hanging down like that whenever the gear is down, they're likely to hit things and get all banged up.

I'm going to use the hinges to mount the doors, cut a hole for the wheel and strut during retract/extend, and then use some flat gray covering to tape them closed.

I will be converting my doors to the correct cycle effect this winter. Not all that hard to do. Will need 3 more servos, two minis, one for each set of main doors and one micro for the nose gear door and a little electronic sequencer module.

There is a link to someone that has already done it over in the big thread. He used a Futaba 14Z and the tx programming, though, instead of a module...

Easy to make little tabs that are sprng loaded for the tiny doors that stay open for the gear legs.

I have some data on the OS 55 AX, now. Got a chance to tach it in the Mariner tonite.

12x7 APC: peaked 12,300. Backed off to 11,800 or so for flight. That's good for close to 80 mph and around 10 pounds of static thrust.

Thomas: I like the idea of the scale door operation, but I think I'll pass. I have one of those electronic sequencer modules if you'd like to buy it cheap.

Had some fun bolting all the big pieces together. I went ahead and drilled/tapped the inner wing panel tubes, and bolted the entire tail section together. Also stuck all the hinge points in so I could hang the control surfaces. This momma is big!

When I went to do the outer wing panels, BooBoo #1 popped up: the 2" nylon, 1/4-20 screws that are supposed to secure the leading edge of the outer panel to the inner panel should have been about 2.5". They are not long enough to reach the blind nut in the inner panels. Called support, and they are sending me 4 of the Dubro 3" nylon screws.

2" was the correct length for the TF B25 I assembled in January. I did find it helps to sharpen the 1/4-20 bolts slightly in a pencil sharpener to get them started.

CCFPILOT

CCF:

Thanks for the tip on nylon bolts. I'll use that in the future, as they can be a bummer to get started.

This one I'm sure of, though. I stuck the screw all the way through the hole in the outer panels (till it bottomed), and compared the length sticking out to the length required to reach the blind nut in the inner panels, and they are identical. Needs another 1/4 to 1/2 inch to do the job.

Back again.

I couldn't work on it for awhile as I was broke. Destroyed my P-51 yesterday, which freed up a bunch of equipment. That combined with a loan from my wife makes it possible to now finish the B-25 and get it flying before the snow does around here. I really want to take this aircraft to Warbirds Over Paradise in Cape Coral this January.

I made some decisions to reduce the cost and the weight, as it was weight that got me into trouble with my Mustang.
1. The retracts go. I'm using the fixed gear that comes with the kit.
2. The power expander and the dual batteries go. I'm going to use two 7 ch futaba 2.4 receivers, powered from separate switches off one 2000 mAh pack. I'll divide the rudders, ailerons, and flaps between them. (flaps will be split inboard/outboard)

Going downstairs to start gluing hinges right now

The stuff that I need has been ordered from Tower and should be here Saturday.

Finished all the hinging today, wing and tail feathers, and took the nacelles off the wing so I can start the engine installation tomorrow. I noticed another "short screw" problem- the forward 1/4-20 nylon bolts that hold the nacelles on are not long enough. There is barely 1/8" thread engagement in the blind nuts. The rear bolts are OK. Basic rule on bolts is thread engagement should equal the diameter of the bolt.

I think Top Flite really should have stated that this airplane is intended for four stroke engines, and that us two stroke fans will have to do some engineering. There's no way in hell the factory throttle servo mounts (either one) can be used to do a two stroke throttle linkage unless one switches to cable assemblies instead of the included pushrods, and that looks doubtful.

Here's how I did it. I traced the outline of the opening on the right side of the nacelle assembly, and cut a ply piece that can be epoxied in there. The servo is only stuck on to it with sticky tape right now- I'll make some nice mounts later. It all fits inside the nacelle nicely, and gives a short, straight pushrod.

Also, the included spinner nuts are for 5/16" prop shafts. I'll have to get a pair of 1/4" ones to fit the OS 55AXs.

Some more progress to report- the things that I've done differently than what the instructions recommend, mostly.

First, something that can bite. The aft fin 4-40 screw can hit the rearmost servo mount screw and break the mount off if it's not shorten to about 1/2" or less.

I like all my airplanes to have access to the fuel line behind the needle valve so I can "pinch" test during initial run up. This is especially critical for a twin, I believe, so I cut a hole in the cowl so I can get in there with a pair of needle nose pliers for pinching, and to remove the line for fueling/defueling. My tank is a three hose Great Planes, the hose shown hanging out the bottom of the cowl is the uppermost (vent), and I've used the secondary fitting on the tank for the exhaust pressure hose. During fueling I'll remove the plug from the vent line so I can see the fuel running out when it's full. When I'm defueling, I'll turn the bird upside down so I can use the vent line, as it is a better way to get all the fuel out of the tank.

I used the fixed gear, and used button head screws to secure the factory doors in place. They look real nice and fit real good.

I went with twin receivers, twin switches and twin 2000 mAh batteries. Having two receivers gives lots more places to hook stuff up without using Y cables. I used them only to connect the inboard flap servos together (to channel 5 on Rx #1), outboard flap servos together (to channel 5 on Rx #2), and rudder servos together (channel 4 on one Rx, while the nose steer servo is channel 4 on the other.) I went with separate channels (1 & 6) on the aileron servos so as to be able to have some differential, with a lot more "up" aileron than down. The 2.4 gig receivers require that the antennas be routed at 90 degrees to each other. All the little pieces of yellow plastic tubing accomplish this- they are glued to the cockpit floor and the antennas are slid into them.

The nose gear steering I made pull-pull rod, instead of cable, because I have an awful time with cable.

This thing fills up the back of a Chevy Traverse. Got the airplane kit in June. Got the Traverse a month ago. That was close

She's been ready to fly for almost three weeks, now, and it looks good for the maiden tomorrow at the Interlochen Field of the TRAMPS club. One day of 63 degrees, little wind and no rain, and then it's back to winter when the storm moves in Friday.

Dry weight as shown is 18.3 pounds. It took 8 oz of lead and two 2000 Hydrimax packs in the nose to get the CG, which is set at about 4-5/8" back from the LE, as close as I could get my CG machine pads to the fuse. Using the accepted methods of calculating CG, this equals 36.8% of mean aerodynamic chord. I don't mind saying that scares the hell out of me. All my other conventional aircraft fall between 25 and 30%. I've seen a half dozen videos of this B-25 flying OK with the CG at 5", and generally they look pretty good, except there is a noticeable tendency for everyone to "over flare" on landing. I think this is due to pitch sensitivity, caused by being tail heavy. MHO. That's why I went with the CG I did. (Top Flite says 4.5 is ok) I also took some hints from various reviews and forum posts, and put in about half the down trim that has typically been used, and some right aileron trim. I also made the flap/elevator coupling give me a total of 1/4" down trim, instead of adding 1/4" to the existing trim, as one reviewer said that the recommended down coupling was way too much.

I'm leaving the turret, gun packs and decals off until she's had some time in the sun to see if the covering wants to bubble up anymore.
If I can get three good flights tomorrow, I'll feel comfortable taking it to Warbirds Over Paradise in January.

From watching the various videos, I get the impression that this bird is a wonderful flyer. Being 2 pounds lighter than most of them and with more power (55AXs) I'm thinking takeoff should be pretty easy. The Interlochen field has a long runway, and even if the grass is a bit tall, I shouldn't need flaps. I also used some "real" wheels instead of the foam ones, which should help.

I set mine up for high rate travels only, and rely on expo to keep it from being too twitchy. Seems to work- the maiden today was flawless. No excessive pitch up on landing, just a nice, nose up scale touchdown. Take off was a non issue, too. I used full flaps as the grass was a bit long. As I was turning around at the very end of the runway I started bringing the throttle up and by the time it was headed into the wind it was at full power. When it was about opposite me, I pulled a little bit of back stick and held it. She rotated real pretty and climbed out at a nice angle.

Like has been said elsewhere, tho, it's important to keep the speed up. I only go back to idle on final approach while she's in a nose low glide to the end of the runway. When she's near the end, I level off and bring the power back up some to get her settled down at about 3-4 feet altitude. Then I start gradually reducing to idle and pulling back stick to get the nose up.

Never ran my two 55AXs together until today. Adjusted each separately for a good max rpm "pinch" test. Under those conditions, they both tached between 96 and 9800 RPM with the 12x7s. Idle speeds were considerably different, but at all other points on the throttle curve they were together, as I could just discern a slight harmonic. They did both have a very nice transition from idle to wide open, though, which is characteristic of the 55AX. What the hey, I don't fly at idle, so away I went.

I ended up with the following elevator trims (bear in mind the 4and 5/8 CG and fixed landing gear):

Flaps up: 1/4" down, measured at the widest point
Flaps down: 3/8" down, same technique.

This resulted in hands off level flight. With flaps down, she pitches down just a touch, and that's fine with me as I prefer not to have to hold down stick to maintain a glide.

This is a superbly designed and very easy to fly airplane. Top Flite and the entire design team are to be commended.

The nose gear didn't do too well at the bumpy grass field- there was a lot of the strut hanging down beneath the plastic mounting block, and it bent in that area. So......I played around with the tiller bar, and ended up putting it in there upside down, with a thin spacer, so as the get the spring coil as close to the mounting block as possible. Should minimize the bending.

The airplane has had a slight nose down angle at rest from the start, and between that and recombobulating the strut, it was way nose down, so I epoxied in some 3/4" thick maple rails on top of the original mounts. She now sits level.

It was a little hard to see, given the overcast skies, especially when on the opposite side of the field. It was almost impossible to tell whether it was banking towards or away from the flight line. Thus the yellow flashing on the wing LE and the fin LE. Ultracote Cub Yellow.

The top turret and the teardrop antenna would be just too vulnerable during transport and setup, so they're staying off for now. Turns out my switches are exactly where the gun packs would go, so those are still in the box as well.[8D]

Been a long time! [8D]

No flights since the maiden last October. The weather here started to get nice in March, all the ice melted off the lake and I've put almost a gallon of fuel through my Arrow, flying off the water, but the wind has been so bad in the afternoon that I've been unable to do much land bird flying at all. Maybe 3 times, with various sport birds.

Maybe this weekend things will be better and the flyin at BARCS (Thompsonville, Mich) will be the place for the bomber to do her thing again.

I ran the engines up this afternoon, using 12x6 APCs on the 55AXs instead of the original 12x7s. Better, but still more airspeed than I need and not the thrust I'd like to have. Tried a pair of 12x5 MAS S2s, and they are the item- both engines are turning 12,100 on the ground, which is good for a little under 60mph and around 18 pounds of thrust total. That should make her quite peppy on takeoff, and stall turns should be fun.

More later

It seems to me that my engines are running a little on the warm side. (Nose test.) It wasn't a problem during the maiden last fall, as the temp was in the high 40s, but it's a problem now, with temps 70-80F during the day. Not enough air being forced past the mills to cool them.

For starters, the plastic, pretend radial engine is too scale- Top Flite went to the trouble of cutting all the plastic out from between the cylinders so that it would look right. I filled those in with a piece of balsa from the back side, so that air can only enter through the hole I made for the carb, directly in front of the cylinder.

Secondly, any air that does come in can exit any way it wants, instead of going past the engine, as the "cowl flaps" opening is about 360 degrees around the back. Took some more balsa, and blocked off the half of the cowl flaps opening opposite the engine. The pieces are semi circular, and fit behind the cowl mounting ears, with another piece glued to the front between the mounting ears to close up the gap between them and the cowl mounting ring.

Finally, I enlarged the hole on top of the engine so that lots of air can flow around and out.

Wish me luck. I have an infrared therm coming from Tower. I plan to measure my cowled in Magnum 91 that's in my Camel, and has never shown any signs of running hot. If I can get the 55s down to its cylinder head temp, or even near it, I'll be happy.

I had to laugh at the Top Flight "scale" engine when I got my ARF. The full size B25 has a 14 cylinder engine, but not like the one Top Flight modeled. It has two rows of 7 cylinders each, not a single row of 14.

Back to your temperature problem, in my opinion, it looks like the air won't exit at the hole above the cylinder head, but it will try to enter there, with no place to exit. I'm no expert on cooling, so I have the OS FS70's in mine, and the standard cowling setup as designed by Top Flight with only the rocker cover sticking out of the cowling, and there seems to be no temperature problems.

I would try unblocking around the cowl flaps so the air can exit more freely.

Good luck.<br type="_moz" />

Jeez, I never looked that closely at those engines before. That's a hoot. Maybe they were trying to do 14 pushrod tubes and got confused about what they should look like.

The air flowing past the cylinder head hole in the cowl should create a low pressure area, but your theory could also be correct, due to the angle on the cowl at that point. If so, they'll run hotter than before, no question, now that I've close off half of the flaps. If that happens, I think I'll put a reverse scoop over the hole, with just a small hole in the center for the glow driver.

Four strokes seem to have completely different cooling needs. The muffler gets hotter than anything else on them, just the opposite of 2 strokes. I have a friend with an SE-5 that has an OS 91FS, and he has it completely boxed in with NO cooling air, just the muffler hanging out the bottom, if I remember right, and it does just fine. Backfires every now and then, but he likes that. Go figure.

I'll run her up as soon as I get my therm, and post the results.

The rule of thumb for the full scale stuff in the exit is 3X larger than the inlet, thus helping pull the air across the engine. That also holds true for the little stuff!!! Make sure the outlet is larger than the inlet.

Enjoy

L.

The engines are cooling ok. I was just not letting them cool off at idle before shutdown after a WOT run.

As far as cylinder head temp, I don't know what's best. I ran them up this time about 1200 rpm off peak, and they're holding at 275F with 88F ambient temp. They use a lot of gas at that setting, though, and rapidly drop below 200 at idle.

I've read one place that says don't go over 350F head temp, and at least one other that says 225. Anyone have any ideas?

honestly that prop is too big for the ax55 when its breaking in, i would use a 11x5 or 12x4 (both apc), you want your engine turning about 13500 on the ground, this will help with your cooling problem a lot and it will give you more power.
my temp reading is very simply, put a wad of spit on your finger and rub the drops over the cylinder head, if they sizzle off imediately your to hot. if they sizzle off after 5+ seconds your fine.
if it does sizzle off instantly your prop is to big or your cowling is messed up.