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Apr 30, 2012, 07:52 PM
Newtron's Avatar
Build Log

Peter Rake's 60" Martin MO-1

About the full scale:
From Wikipedia - The Martin MO was an American observation monoplane built by the Glenn L. Martin Company of Cleveland, Ohio for the United States Navy.
In the early 1920s the United States Navy became interested in a thick aerofoil section cantilever wing United States military observation aircraft developed by the Dutch company Fokker. The Navy's Bureau of Aeronautics designed a three-seat observation monoplane to use a similar wing. Production of the aircraft, designated the MO-1, was contracted to the Glenn L. Martin Company with an order for 36 aircraft. The MO-1 was a shoulder-wing cantilever monoplane with a slab-sided fuselage and a fixed tailwheel landing gear. It had an all-metal structure with a fabric covering and was powered by a Curtiss D-12 engine. In 1924 one aircraft was fitted with a float landing gear for evaluation.

Specifications (MO-1)
Data from The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985), 1985, Orbis Publishing, Page 2419
General characteristics
Crew: Three
Wingspan: 53 ft 1 in (16.18 m)
Powerplant: 1 Curtiss D-12, 435 hp (324 kW)
Maximum speed: 105 mph (169 km/h)

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Apr 30, 2012, 08:52 PM
Newtron's Avatar
About the Model:
Back in 2009, I was glancing about for a plane to build and enter into the FunBuild 2 contest. I came upon Peter Rake's 30" version of the Martin MO-1 as a free plan in RC Model World "Plans & Construction Special". It was exactly what I was looking for, with that thick Fokker-like wing. Plus it was built right here in Cleveland Ohio and for the USN (I'm ex-USN). The only problem was it was too small. Following a quick trip to CopyMax I had plans for a 50" wingspan one so problem solved. I built it and flew it and thought, "This is awesome but I should have went bigger."
Now, thanks to Peter (and Manzano Laser Works) I have plans and short kit for a bigger one.
Since I don't use much foam anymore, this version will be built mostly with balsa and ply. I plan on covering with Mod Podge, SIG Koverall, WBPU and Acrylics.
Since I have a smallish car, Peter's design includes removable wings. Brass straps and screws hold the wings on in flight.

Here's the Build Thread from the FunBuild 2 (for anyone looking for a bit of nostalgia):

Apr 30, 2012, 09:07 PM
Newtron's Avatar
First question for Pete.
It looks to me like the wing tips need to be raised about 3/8" (or 1 mm) for the quasi-polyhedral. Was that your thinking?
As an explanation, the wing is level across the top but has polyhedral on the bottom.Does anyone know if this particular wing feature has a name.

Last edited by Newtron; Apr 30, 2012 at 09:13 PM.
Apr 30, 2012, 10:05 PM
Registered User
kdahlhaus's Avatar
And we're off! Did you fix the Eindecker fixed already?
May 01, 2012, 03:32 AM
Registered User
No mate, if you mean the actual tip itself. From what I can see, there is only one break in the line of the wing undeside, where I show it on the spar drawings. From there the line appears straight to the extreme tip and that is how I set up the spars.
Building procedure would be to join the spar parts (although one-piece spars might be better, Charlie only has 24" bass), build the root section of the wing and then lower the spar over the plan to build the outer 'panel'. Once plugged onto the fuselage, the wings should (if I got it right) have more or less flat top surface, sloping down at the tip and a single dihedral break on the lower surface.

The attached photo seems to show a totally straight line to the tip, with a quite sharply defined tip profile.

May 01, 2012, 08:06 AM
Newtron's Avatar
I knew I should have included a line drawing. And I shouldn't have referred to it as quasi polyhedral.
I'm talking about where the spar pieces join. As you explained much better than me, when the outer spar is joined to the root spar, the outer spar is angled upward. I was asking what that angle is. I just wanted to insure that I assembled the spars correctly.

Last edited by Newtron; May 08, 2012 at 06:20 PM.
May 01, 2012, 11:43 AM
Registered User
They're shown on the plan. Assemble over that and you won't go too far wrong.

Quasi-polyhedral, otherwise known as the hunchfront of notthisplane.

May 08, 2012, 07:19 PM
Newtron's Avatar
"the hunchfront of notthisplane"
Now after that bit of humor, the build progresses...
And quickly jerks to a halt. On my prior builds, I have always started with the wing. As mentioned before the MO-1's wing is removable. The 3 wing sections have 12mm carbon fiber tubes running in parallel with the spars. The wing sections slide onto longer 10mm cf tubes. Everything is held together with brass straps. I forgot to buy the cf a few weeks back at the Weak Signals show and I have found out that the LHSs don't carry cf tubes that large. It took a few days of internet searching before I found what I was looking for. They have been ordered and are on their way.
I went ahead and joined the 3/16" bass main spar sections together over the plan using the provided 1/16" ply braces and epoxy.
I then assembled the tailfeathers. Although there are a few rudder and elevator laser cut parts in the short kit, they're mostly built from 3/16" balsa sticks.
Next up is the fuselage. Like a typical PRake kit, the MO-1 fuselage consists of a forward box section and aft stick section. (Typical for me anyway - I haven't built any of his round fuselage types yet. I'm watching the HE-51 come together and think maybe it might be my first. ) First the 3/16" balsa forward fuselage sides pieces are joined and then the 3/16" balsa doubler D2 is glued. I assume D2 is there to strengthen the lower section of the fuselage where the landing gear attaches.
And that's where I'm at.

May 08, 2012, 10:18 PM
Newtron's Avatar
Pete -
I've run into a issue while assembling the front half of the fuselage.
Regarding the plywood formers, none of the tabs slide into their intended slots. I'm talking about the slots on F2 and F4 and the tabs on BT, MR and ML. The open sided slots, like the ones on M, MR and ML are ok.
I think you (and Charlie) have mentioned before that this may have more to do with the wood swelling and shrinking than with design or cutting. I thought you would want to know, just in case.

May 08, 2012, 11:35 PM
Registered User
portablevcb's Avatar
So you mean the slots are too narrow?

If slots too narrow, then yes, that is a wood problem. The wood source for our plywood considered 3.8mm the same as 3mm. We are finally about to solve that problem as suppliers are changing. Going from Finnish plywood to Russian plywood.

So for your build you'll have to open up the slots a little to fit the wider 1/8" ply.

May 09, 2012, 03:24 AM
Registered User
Yes I did expect the slots to be snug, but I have to draw them for the size wood that's SUPPOSED to fit into them - 1/8 ply. Theoretically, if what's actually used is oversize 3 mm ply it should still fit, but it depends on how much oversize it is..

The u/c doubler just means there's plenty of gluing area and positive locations for the UC parts.
Hopefully the ply doublers at the wing area will mean you don't pull a loop and rip off the top of the fuselage still attached to the wing.

May 13, 2012, 12:21 AM
Newtron's Avatar
I've run into an issue with the forward fuselage. When assembled the fuse is 3 7/8" wide instead of the 3 5/8" shown on the plans. This means that WMs and UCs are too short. At this time I have one side epoxied on. It may be my fault (wouldn't be the first right? ) but to me it appears F2 and F4 are too wide. Hopefully the pics show what I'm talking about.

May 13, 2012, 04:47 AM
Registered User
Oh B****R!!! I wonder how that happened, the numbers make no sense at all.

I would have suggested trimming the formers, but since you have a side epoxied on that complicates matters somewhat. It won't matter that BT is a little narrow because it rests on the doubler anyway . F3 is also too wide by the same amount and, for some mysterious reason, there are no H parts at all (not even on the plan). Obviously I wasn't concentrating.
Easier than trying to take things apart to trim formers, it would be best to cut new WM, UC and H parts to suit the fuselage width you have. The ply parts are simple rectangles and there should be enough room on the 3/16 balsa for H3.
In the meantime, I'll modify the formers and add the missing parts.

May 13, 2012, 06:55 AM
Registered User
Right, that's the updating done. Correct size formers and H parts added to both plan and cut file. All the extra parts fit into gaps on the original sheets, so no extra wood is needed apart from possibly for the WM and UC parts.

Sorry about that,
May 30, 2012, 10:33 PM
Newtron's Avatar


Wings... words to be added later. I promise Pete.
Last edited by Newtron; May 30, 2012 at 10:41 PM.

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