1/19 Scale Martin 4-0-4 - RC Groups
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Dec 20, 2012, 10:24 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
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1/19 Scale Martin 4-0-4


OK guys, time to dive in. I'm long-past due kicking this one off!

I'm building a Martin 4-0-4. This is my first airliner. My goal is to have her on her wheels and "blacked in" by the first week in April. I have plenty of time to get this right, and can go away for awhile and ponder on things during the build. I have some ideas, but I will need some feedback by the excellent group of builders that frequent the Airliners forum. I'm so impressed by the workmanship and attention to detail; I really don't venture out of the Airliners forum very much; it's that good!

I haven't decided on the livery yet, but the Eastern Airlines scheme is really cool. I may give Callie Graphics a shot for the decals, as I'm really sloppy with that kind of stuff.

Built in the early 1950s as a short-haul airliner, used by TWA and Eastern. They flew them about 12 years, then sold them off to regional carriers. None are airworthy that I'm aware of, I believe the last one was ferried to AZ in 2009.

As the build title indicates I'll be going with an approximate 1/19 scale size. This will primarily be fan fold foam along with some spruce and possibly carbon fiber. Control surfaces may end up being balsa. I will be figuring out some things as I progress through the build. This airplane will be a nice fit for the AMA field I fly at, which happens to be a full-size private airstrip. We have plenty of overrun on runway 1/19 - 2300 feet!

Here are the specs:
Wingspan: 62 inches
Length: 49 inches
Height: 18.1 inches
Target AUW: 4 pounds

Propulsion:
2 180 watt 1150kv motors spinning 8040x3 props
2 20 amp ESCs
2 1800-2200 mah 3S batteries in parallel
With the above gear, if I get in target weight, I will be at 90 watts per pound. Pretty aggressive for a propliner, but that will give me some wiggle room if I build heavy. I think I could get away with 6 pounds (60 watts/pound).

Don't knows...
Haven't decided on retracts.
Maybe flaps inboard of nacelles, KISS...
Haven't decided on nav and landing lights yet - this bird has a light on the front of the fuselage right in the center of the radome, that would be cool.

I will start with the fuselage. Things may be slow at times, and I may not post at break-neck pace like DemonDriver! Feel free to bump this thread if you want to know what is going on. I'll try my best to keep this a build thread instead of a "here is my new completed airplane" - I think that takes the fun and enjoyment out of watching something come together. Be prepared for questions from me on this thread for advice and how to do something.

Wish me luck, subscribers welcome!

Best,
Kevin
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Dec 20, 2012, 10:44 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Here is the correct size fuselage over a piece of 2x4 FFF. At a 45 degree angle, the fuselage fits nicely.

I have an idea to cut out a complete profile, including the vertical fin as one piece. I would like to use this profile to apply stations on each side of the fuselage, and build up the vertical fin as well with thinner foam like Cellfoam 88. I'm planning on using FFF as the skin, so this should be strong.

Any comments on reinforcement needed?
Dec 20, 2012, 10:48 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Regarding propeller size, I might have jumped the gun, but it turns out very nicely. I laid an 8040 prop in front of the wing half in line with the engine shaft, and I have about 3/4 of an inch between the fuselage side and the edge of the propeller. That is very close to scale!
Dec 20, 2012, 11:02 PM
Airliner Builder
WAGliderGuy's Avatar
Count me in, I'm subscribed

With the skin and and backbone, I don't think any reinforcement is needed for the fuse except some wood on the wing mount for the bolts to have something solid to hang on too and the nose gear.

I recommend either flaps or retracts (or both) to give that nice scale and slow nose-down approach (flaps) and fast outline during cruise (retracts). Because the two mains are out in the nacelles, use servo-less electric retracts such as the E-Flite 10-15 size or RCAerodyne .25 size tricycle sets. The less servos, the better!

Also, I highly recommend an external UBEC with at least a 5A capacity like this one: http://www.headsuprc.com/servlet/the...Battery/Detail

Splice the UBEC input connectors in to the ESC input connecters (with the red ESC receiver wires disconnected) and wallah, you have a steady and safe power source for your electronics!

Another suggestion, with all the wires coming from the wing I would mount the RX on the wing because all you have to do is plug in the tail servos and nose retract However if you use plug in wings, it would be a bit trickier because you would have to built a hatch somewhere in the fuselage, taking away from the scale lines.

Good luck I can already feel another great airliner builder is among us

Ethan
Dec 20, 2012, 11:12 PM
Registered User
LuvEvolution7's Avatar
subbed.
Dec 20, 2012, 11:27 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Ethan,

Thanks for your comments and assistance! I admire your skill, and you definitely rank up there with the great builders of this forum.

You have already answered some of the questions I certainly would have asked later. I will have a look at the retracts, as some I have seen are a reasonable cost.

I agree on less servos; my plan on flaps is one metal gear servo to drive both flaps mounted in the wing box. I think I'll just go inboard of the nacelles for simplicity.

Agreed on the UBEC. I had a 5 amper I bought from Heads Up, but sold if off to a flying buddy who needed one for a large DC-3 he is building. That is a no-brainer for a bird this size; too close for comfort to skimp on a $10 component. I really like Heads Up; they have the props, ESCs and motors I'll be using.

My plan was to place the RX in the wing as you suggested. Still pondering over battery location though. Gotta be thinking about airflow for the batteries, and making sure I don't spoil the appearance too much. The ESCs will pull 12-14 amps with the prop / motor combination, and since they are 20s, we should be good on temperature and loading. There is an inlet in front of the wing on the left side, but I don't know if I can get enough airflow through that.

My thought on wing attachment is to place stations adjacent fore and aft of the leading and trailing edge and reinforce with thin ply. Stations over the wing would be trimmed from the bottom to provide clearance for the wing box. Use some gussets in the corners inside a spruce frame off the thin ply fore and aft, positioned at the right location for mounting the wing box. I used four nylon bolts on another airplane I built and that worked out well.

Off to bed now, gotta work tomorrow!
Dec 20, 2012, 11:37 PM
Up-Out-&-Gone
demondriver's Avatar
I'm Very happy to see your Martin 404 Build has started, I'm happy to Sub-Up for this one!

Take your time Kevin, Your gonna build a legend!
Latest blog entry: Three RC 737 Progress Report!
Dec 21, 2012, 01:57 AM
Official Boat Bum
Eddie P's Avatar
Glad to see you will be cutting and gluing soon on the 4-0-4
Dec 21, 2012, 05:02 AM
Registered User
Zephyr41's Avatar
Quote:
Originally Posted by ruff1

Wish me luck, subscribers welcome!

Best,
Kevin
Hi Kevin,

Good luck! With the amount of thought you're putting into this I doubt luck will be needed though.

Flaps and retracts are a good way to add some weight but if flaps give you the typical 4-0-4 nose-down approach attitude I reckon it will be worth it!

Watching with interest.

Cheers
Rich
Dec 21, 2012, 07:08 AM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Thanks Rich, for the drawings and the advice. I do want the nose-down approach, so the flaps will probably be included. I saw something on the plans about a 3 degree incidence angle on the wing, could you have a look at them and explain? I think this has the trailing edge of the wing 3 degrees below the front.
I'm not sure how that measures up with other airplanes. All of the others I have built are zero incidence.
Kevin
Dec 21, 2012, 09:34 AM
Registered User
Doushiyou12's Avatar
Subbed. This will be great
Keep us posted
Dec 21, 2012, 12:08 PM
Official Boat Bum
Eddie P's Avatar
Quote:
Originally Posted by ruff1
Thanks Rich, for the drawings and the advice. I do want the nose-down approach, so the flaps will probably be included. I saw something on the plans about a 3 degree incidence angle on the wing, could you have a look at them and explain? I think this has the trailing edge of the wing 3 degrees below the front.
I'm not sure how that measures up with other airplanes. All of the others I have built are zero incidence.
Kevin
The angle of incidence (AOI) is the difference in angle between the leading edge and the trailing edge of the wing "root" airfoil as compared to the longitudinal axis of the airplane (nose to tail). It would likely be shown based on the wing root AOI. Most transport aircraft are built to be most efficient in cruise flight. That means designing the least amount of drag at long range cruise speeds based on the compromises of power plant, design range, payload, etc - from that model they choose an airfoil and a power plant that compliment each other at the speed and altitude and give the most bang for the buck. The least amount of drag tends to be with the fuselage relatively flat so... if the wing airfoil chosen is such that it makes efficient lift at certain angles of attack, they place the wing in a geometric angle of incidence that gives that quality to the wing at the design cruise speed and altitude while keeping the fuselage relatively flat. You tend to see positive angles of incidence on these types of airplanes (the difference in degrees between the airfoil angle of attack and the aircraft longitudinal axis). Also, since washout is commonly used to tame slow flight threats / control ability and stall recovery, the wing root needs to have a little more AIO to account for the washout at the tips and the overall "span wise" lift distribution. I'm getting a little technical calling back to my college courses here but that's the reason for positive AIO at the wing root in a nut shell on this type of airplane.

In model airplanes, you can sometimes use relatively no AOI if you are using a Clark Y and still fly at level attitude. The reason for this is you can't really tell much from a remote position in RC that the fuselage is maintaining a 3 degree body angle in the first place and secondly, the Clark Y has a natural AOI built into it by the geometry of it compared to a semi or full symmetrical airfoil. So you can measure with a micrometer but you'll likely not be able to view the model in flight with such keen distinguish-ability anyway. But, for me, I like to design them accurately for the sake of it.

Sorry for the segue.
Dec 21, 2012, 01:41 PM
was geht , müssen unten kommen
Keenan smith's Avatar
Subscribed
Dec 21, 2012, 02:42 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Quote:
Originally Posted by Eddie P
Sorry for the segue.
No problem, the more-technical the better in this thread! Whoever doesn't like it can go away!

I'll be doing some thinking on the fuselage build and may post some drawings on my ideas for wing attachment.

Mounting retracts will be a first... Question. Do retracts come with extra-length landing gear wire to account for differing placement depths in the fuselage and wing? I hope they give you something to work with, as I know the nose gear will be a lot different than the engine nacelles. I better do some measuring here too, gotta make sure I have enough room to place the forward retracting gear. I need to get the nose gear setup down pretty-quick.
Dec 21, 2012, 02:50 PM
was geht , müssen unten kommen
Keenan smith's Avatar
gimme your measuremennts for the leg and pplane size and ill cad it up to find the Geometry for you


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