B25 Guillow's r/c w/Flight video pg6

[dirk gently]

Mitch,

how about - find what the wingspan ratio of the fullscale aircraft to the wingspan of your model is. Let's call it R.
Now, look up in wikipedia what was the wing area of the fullscale plane.
Divide that by R times R.
viola, the wing area of the model.

[Bill Gaylord]

As for lightening with thinner stringers, there are some issues there with this model. First, the wing has no main spar, and depends on the stringers for both strength, and conforming to/holding shape during construction. The bare wing panels are also fairly light, given the trade-off of not having a heavy main spar. The fuse has relatively long former spans for thinner stringers, unless one doesn't mind a scalloped fuse appearance, after shrinking covering. My philosophy is that the best way to lighten is to use lighter wood. I've easily lightened this model by over 1/2oz, by substituting lighter wood, including the kit stringers. Removing that much weight from the design through modification would require some effort. With really good quality contest wood, it's amazing how light a build can be, even with a LOT of wood. I would imagine that it's not terribly difficult to find wood 50% lighter, than the average wood that comes with most kits. I built a built up 34" ME 109, fully sheeted and using 3/32" fuse construction, including the outer slabs. The model finished at something like 12oz AUW, after spending some time collecting contest grade wood for everything, right down to the tri-stock for the inside fuse corners. That was a model that would commonly have an AUW of 20+ oz.

Thanks for the kind words Woundedbear. As for flying this model, I would definitely video it, hopefully being a first. I wouldn't advise anyone to hold their breath however, as it will be a while for tall grass at the park field. I've had at least a few second chances, thanks to tall grass/weeds.

As for the C47, I wish I did have a video for it. The wing is very efficient. Although it has a slight wing span cheat, I've never tossed a 19+ oz model that lightly, on such low power, and land as slowly as it did. It may have not flown, if it didn't initially almost stay airborne trying to rog. The park road is narrow and bumpy, making it difficult to track straight, with or without the tail wheel on the ground. That pushed me to attempt rotating earlier than I should have. When it finally got airborne, I was amazed that it was flying at such a low speed. Literally almost got going, if it didn't clip tall weeds 100 feet away, fortunately with no damage. That was all I needed to see however, knowing a hand toss would easily get it going.

Finished covering the fuse. One nacelle is assembled, with one to go. The parts fit is actually pretty good, considering the difficulty of fabricating molded parts like the nacelles. The motor mounts will need about 1/16" added to the mounting surface, to give the props a bit of clearance, making the initial mount height dimension about as good as I could ask for.

It does not make sense to me, but I have been told you count the fuselage portion and any nacelles. so just look at the wing on the plan. For a rough measurement I just take the wingspan, and look at the cord, I choose what I believe is the average. Then it is just Length x Width, or Wingspan x Average Cord.

Ditto. Guaranteed reasonable accuracy, without messing around with scale factors and chance of error, let alone the model not being perfect scale.

[Chris A.]

Bill, that plane is really looking good! Nice work on a well thought out project! Yes, tall grass and contest wood are necessities for success. But most hobby shops don't carry real contest grade wood. I'm curious regarding the weight of the RC components, What percentage are they of the weight?

[Bill Gaylord]

Bill, that plane is really looking good! Nice work on a well thought out project! Yes, tall grass and contest wood are necessities for success. But most hobby shops don't carry real contest grade wood. I'm curious regarding the weight of the RC components, What percentage are they of the weight?

I've weighed components as the build has progressed, but haven't weighed everything together yet. Most of the gear comes with specs, such as the 10 gram outrunners, 2.5 gram servos, and Eflite 2s-430 lipo, although they tend to be understated, sometimes not considering the lead weight. The wiring is a killer. For this build, I've eliminated connectors and unnecessary harness length, keeping it at a minimal. The motor wires are soldered to the ESC leads, eliminating 3 grams of gold pin connectors. The ESCs come with standard 26 gauge leads, which is heavy. Any extensions needed were made using 32 gauge servo wire. They ESC to receiver leads have been trimmed to leave about 1" of service length if ever needed, and will be directly soldered. S-connectors really add weight and should be eliminated wherever possible.

The motors are now mounted. The 10gm "Hextronik" motor leads with stiff insulation require flexing about as much as I care for, to fit in the nacelles. It's not difficult to break the leads at the motor base, if they're horsed around too much. After installation, I tested both motors to make sure everything is in order, along with rotation direction. With the ESCs powered together, I would have to cut the battery y-harness if I ever wanted to reverse program a single ESC, so best to check the rotation directions for the counter rotating propellers. The engine cowlings are attached with screws, with balsa blocks laminated to the nacelles for the screw attachment. The thin plastic cowlings are laminated with CA around the screw holes, for reinforcement around the holes. The motors have narrow mounting bases, probably a bit smaller in diameter than the actual bell. The mounting screws should be installed first, with the motors installed in the bases afterward, unless the screws are angled a bit while screwing in place. This could be a bit of an issue, with a narrow, non removable engine cowling. The prop adapters use set screws, but are worth using, being a good bit lighter than collet type. I was tempted to drill and tap new set screw threads further rearward on the adapters, as the screws are inline with the dummy engine bank. Small holes were drilled into the bottom of the engine cowlings for allen wrench access, with a small portion of the dummy engine hub cut away also, between the dummy cylinders.

I hear you on the wood quality at hobby shops. What I've done is collected light grade sheets whether I need them or not, whenever I'm there. The LHS has stocked Bud Nosen, Sig, and Midwest, and, with Midwest being known for ironwood. Generally about 10% is within contest weight range however, so you just have to buy it when it's there. Fortunately it seems that a people don't always want the lightest grades, so over time you can usually find decent wood. For that reason it's probably good to promote build to crash, instead of build to fly, so the light wood will be there when you need it.

[davidchoate]

Bill, could You show me a simple wiriung diagram of a multi engine plane the way You set it up? I am an expert at wiring diagram readind ,nomenclature, ets, so you do not have to "dumb it down" fore Me like Aerodynamics.

[Bill Gaylord]

The multiple ESCs are simply wired in parallel. Of course there are Castle ESCs that are the only brand I've found that will run 2 motors on 1 ESC (inrunners only), but that's an entirely different story. The only difference is that linear BECs are not recommended to be wired in parallel, without a crowbar circuit or diode on each output lead (small red wire) with the cathode band closest to the receiver end of the wire, after soldering the diodes in place. Some people say there's no problem wiring them in parallel without the diodes. Generally I would only wire one BEC lead and leave the other disconnected, but I have a bit of reservation with as single low rated 0.8A BECs, which is the reason for the second one. I've seen multi-page discussions on this topic, while I believe this is most likely how it works in the real world, without actually measuring the circuit: The BEC with the higher output voltage (unless somehow they're perfectly matched) will latch it's diode first. The second BEC will now not have the voltage potential across it's output diode to latch it, and will remain idle with a small "leakage" current due to being near it's full turn on voltage. If the first BEC (higher voltage) shuts down, then the second (lower voltage) BEC will take over.

I've had some thoughts that it just could end up where I might want to use a 3s lipo on the model, although hopefully 2s should be ample. At this size I'm really not interested in Motocalc results, as OTOH is probably just as close when you've flown enough similar sized, not feather light models. The problem here is that a small amount of weight can make the difference between flying well and not flying. I've ran these motors and ESCs on 3s without issue, although it may be wise to use 2-blade props, but it really stresses the linear BECs. I probably should wire this model to allow for the external switching BEC that I showed earlier, but again it would add weight. At least in this case, the ESCs are in the nacelles with some cooling. The only BEC I ever shut down was mounted in a fuse, with poor cooling and ran near it's max continuous rating. It was after a good 4 minutes when it shut down, due to heat buildup and reducing throttle to land, which raised the battery voltage and stressed the BEC even more. That said, even though the BECs on this model do not seem to be heating up now with heavy servo cycling, they can heat up when the entire board is heated, due to running the motor.


The ailerons are now added, using Dubro flat pin hinges. The slots are first cut with an exacto, where the hinges will initially fit a bit tight. Now you can decide which side of each slots can be enlarged a bit to perfectly center the ailerons, removing a small slice from the slot with an exacto knife. My method for gluing them is to pack 5 minute epoxy in the slot, then wiping it down to remove any excess. Both sides of the flat hinge bodies are given a thin wipe of epoxy before insertion. Too much will build up as the hinge is installed, and will lock up the hinge.

I was reading the B25 Facebook page and came across information about the front turret vents on the fuselage, needed to clear the potentially lethal gun smoke from the cabin. I fabricated the parts from sheet plastic, and will probably add them. For more trivia, I also came across what appears to be the full scale aircraft of the box art scheme, going by the tail number:
http://www.ww2wings.com/wings/heroes/al ... webb.shtml
The "Mom and Pop" graphics cannot be seen, but it's quite possible that the camo is more of a motting scheme, versus the clearly bordered camo patches seen on the box art. No offense to the model of the month, which I can finally see, after discovering a trick to open the photos. For the past few months, I've only been able to view previous months in the Guillow's Picasa album, and not the most current month posted on the website.
This color photo shows a B25 that was probably painted with similar colors and camo scheme:
http://worldwar2headquarters.com/HTML/a ... t/b25.html

[woundedbear]

Hey! Bill that build is looking great! Where did you get those three blade props?

[Bill Gaylord]

The props are GWS, painted black with yellow tips. I'll need to order more from Heads Up RC, as the counter rotating are more difficult to find. They actually fit the prop adapters without drilling, for once, with the prop adapter supplied aluminum washer placed behind the prop, versus in front.

[davidchoate]

I predict in the next 2 yrs BUS systems will be quite affordable. it would help greatly with these small (every gram matters) Kits in AUW.It, will be the programming software thats gonna be the cost. On Cars today there is 80% less wiring on a car from 20 yrs ago, but if You have to replace say a dooir lock switch it must be programmed. the switch is not a lot of $, but I have to buy the program for it, or send it to a manufacturer for programming. Also I (*not for any pourpose or intent was just wondering if two seoerate Rx's could be bound in the same plane to run different things. Like if You had an 8CH Tx and used two 4 CH Rx's say in a P-38 that has a double fuselage? Bus systems are the way though. I have checked into it and the cost lies in the servos (because they're now a little Rx kinda and the main Rx uses logic gates to make sewse of it all). Try and rewire a tail light on a late cat to a trailer without proper programming and see what happens. I have been using this Bus network stuff since the 90's on cars, and it is weird at 1st, but once You get used to it; it is soo much better. We have gone from a hundred fuses to 5 or 6 total in Cars. *0% lkess copper in a car is a lot of weight.

[woundedbear]

Hello davidchoate, I have been a North Carolina Lug Nut for almost as long as I have been Planecrazy. I was a late 60s' early 70s' car guy. While building plastic model airplane kits was my mainstay, building 2 dollar model car kits was the other thing I spent all of my money and time on back then. Before the arthritis in my back sidelined me I use to help out a guy who restored British Sports Cars. He had bought an old Pontiac dealership. If I had only met this guy before he got so old. If you had ever worked on an old jagwire or MGB you know why they use to call Lucus the lord of darkness. Just when you think it's time to call the owner you turn on the radio or headlights and the windscreen wipers start! But when you got one running right they were a blast to drive!

[davidchoate]

The 1st Car I had was 1980MGB. It was 1986 and I was 16, and wondered why an almost new car was so cheap. Yes Lucas wiring, and I just ended a two year tour at a Land/Range Rover Shop! The Old Defenders are OK, but those newer ones. A Range Rover Chassis with a BMW drivetrain.Imagine that. Well I am 1 of a handful of Guys with MG and late model Land Rover Experience. That little MG was fun though. And I liked to work on cars, so I was O.K. And Land Rovers They kinda grow on You after a while I guess.

[davidchoate]

I managed to find the plans free for a Guillows Mosquito. I understand it flew well. Control Line though I think, but it is'nt a Bomber, and it has two Glow Engines turning at 15,000 to 20,000 RPM's.I read an interesting Post on RC Group Forum about 3 or 4 blade props. This Guy had made a twin RC convert of some Guillows kind, and was told that 2 bladed props, though not scale in appearance perform better on a small scale. Something about "dirty air" or something, but Dude decided to try the scale looking 3 bladed props after He maiden and trimmed, and to his surprise, and even in further controlled tests. Yhe multi props made better power and less noise, and except for drawing a small amount more of battery juice performede better overall on multi engine planes. Oh, Every maiden of every type of multi- engine Guillows planes that took off ROG almost went down in the first application of full power.Yeah real white knuckling take offs til they get set right. Apparently it seemed that almost all of them had to have 3/4 min on the gas to want to Fly reasonably. And one guy with the C-47 would do Left Rudder and Right aileron to turn and it looked really level and realistic. But on ROG takeoffs once about 6 ft up its like a wing stall. One side just drops away . I think ( But i'm the most novice pilot around) They got a bit steep on the climb angle and a forward stall happened and the power is not there to pull up out of it on those detail laiden Guillows Twin engines. The 4 engine ones have the wing Area and power to (from what I saw) Fly extremely timid for a scale bomber. Some used two engines and had the outer ones freewheelin a prop even!

[Bill Gaylord]

David you should look at some of the equipment the drone flyers have these days. They probably have much of that stuff you mentioned. I haven't kept up with it, but it's really moved ahead. I was just talking with a guy at a swap meet today, about how I thought AS3X was cheating.

Moving along, with mostly masking/painting and a bit of assembly remaining. The model uses the Naval tri-color scheme, with dark blue on the top (MM blue angel blue), lighter grey blue (MM intermediate blue) for the sides, and a very light grey blue on the bottom surfaces (MM pale blue grey). The short throw rudder linkage was even a bit less than expected, so the micro E-Z link was moved in to the most inner hole on the servo horn. The clear sheet plastic control horns make the rudder linkage assembly fairly simple, and can be made to any size necessary. With the linkage centered and rudders parallel, they horns are then sized based on the distance from the pushrod ends to the rudder. Once the first horn is installed, the second is adjusted in it's mounting slot to make the rudders parallel, and then locked in place with a drop of thin CA.

[davidchoate]

I miss My Hobby Store. I can not find 1/32

' sheet balsa anywhere. I built up a nice inventory though. like Bill, for a few years I would hoard all the best pieces of wood. People used to give me some odd looks when they saw Me get out My scale to weigh a sheet of wood, I hope someone reopens that place soon.

[davidchoate]

Oh, I set My DVR to record "Warplanes" on AHC, and some kids at a Engineering school were wind tunnel testing 1/4 scale WW 1 planes, and the Eindecker Wing would stall at 8degree climb. It took guts to Fly back then. More casualties from unknown aerodynamic effects and under powered Engines of the time.