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Old Dec 13, 2014, 07:19 AM
CH Spring
Canada, ON, Osgoode
Joined Mar 2008
422 Posts
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Dumas Northrop Alpha 4A

I have no idea whether there is any interest in this kit. In fact, from what I can gather the kit itself can be perhaps a little difficult to find. It is however the project I currently have on the bench. As kitted it is intended for rubber band, free flight.

This is my first laser kit, and my second complete build in about 50 years. Thanks to jhspring, I have been re-introduced to the hobby. I was never any good at it first time around. This time, I am hooked.

If there is interest, I can describe the project so far, which is probably 60% complete. What I did think might be of interest is the method I used to tackle the powerplant, electronics and the aileron installation. You be the judge.

Last time out I built a Guillows Sopwith Camel. Short nosed, notorious for being difficult to get the C of G right. I think I managed, but like everyone else I had to add nose weight. It came in at under 12 oz.

The next two kits that caught my eye were the Dumas F9C2 Sparrowhawk, and this one. Both posed a similar problem, WRT C of G.

I bought the kits dirt cheap. Before doing so I pondered the short nosed, powerplant installation thing. I came up with an idea so I decided to buy the kits with no clue as to whether it would actually work. I decided to build the Alpha 4A first. I have no idea whether my powerplant concept is original, but it certainly is new to me.

Power is a GWS 7x6 prop, Hobbyking motor, 850 mah 2S battery, and a 10 amp esc.

The original design would be modified to 4 channel RC using a Spektrum AR400, two Hitek HS45HBs, and I have no clue what the aileron servo is. Its is something out of my spare parts drawer. It looks skookum enough.

Who knows whether I will finish the Alpha? I work pretty slowly and have the attention span of a goldfish. But for now I'm having fun.

WRT powerplant, I wanted to avoid hatches etc. Since the original aeroplane was radial engine powered, the model had lots of frontal area. If I could just shoehorn everything in through the nose, that'd be cool. So I went to work.

What you see here is a 1/32 ply firewall. The motormount itself stared life as a 35 mm film cannister which was then cut down. Once I had he alignment right, I went about mounting it in place and adding a ply battery box to the back of it. The BB has the esc mounted on its base.

To install a battery, I simply grasp the nose bowl, rotate it about 10 degrees, then tilt the top portion outward. That provides enough clearance for everything to be removed. The lead from the esc is long enough to give me room to install the battery. Installation of the battery is the reverse. Friction fit and motor torque will hold the motor in place.

Locating the receiver was also key. To do that I built a removable plate which holds the receiver, elevator, and rudder servos. It is locked in place as the wing is installed. All the mass is as far forward as I could get it.

The esc is easily connected, as is the aileron servo. The aileron servo is part of the wing. If the wing needs to be removed, it can be easily done. The aileron servo lead is long enough to allow me access to the receiver/servo plate which can be easily removed, yet as I said previously, is locked in place with wing installation.

The wing posed its own challenge since it has a flat centre section with dihedral on the outer wing panels. The simplest solution would be to locate a servo in each wing but that would be cheating. I understand that this model doesn't fly worth a darn as a 3 channel.

Running an wire directly to each aileron from a central servo was not an option due to the wing geometry, and the landing gear location. What you see is my solution. Simple, and not much of a weight penalty. Adjustment is accomplished at the servo itself, which is likewise located as far forward as possible. It has been tested. It works.

So far, I am pleased with the results. I threw everything I have so far on the scale. Battery included I am at 6.9 oz.

I have some additional stuff to do WRT wing and wing mounting, then its on to the tailfeathers. I'm thinking fishing line for hinges, and perhaps pull/ pull. We'll see.

As they say in the newscast. Film at 11.

Cheers!
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Last edited by Spring; Dec 13, 2014 at 07:26 AM.
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Old Dec 13, 2014, 07:32 AM
Registered User
United States, KY, Taylorsville
Joined Mar 2010
2,131 Posts
Northrup, as was Luscombe, were way ahead of the curve back in the day! Hope you end up with a nice flier!
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Old Dec 13, 2014, 08:10 AM
Or current resident
glewis's Avatar
USA, FL, Tampa
Joined Jul 2002
5,041 Posts
Looks good. You can't get the equipment any further forward than that!
Don't know how tight your cowl friction fit is, but I would turn the ESC brake off. If the motor slams on the brakes, it might work your cowl loose.
Glenn
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Old Dec 13, 2014, 08:16 AM
Oh no, not again!
jhspring's Avatar
United States, LA, Carencro
Joined Dec 2005
5,780 Posts
We've been talking along the way, brother. Glad you started a build thread. You do very neat work. I think the Alpha will be a gem. Keep plugging.

J
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Old Dec 13, 2014, 04:39 PM
CH Spring
Canada, ON, Osgoode
Joined Mar 2008
422 Posts
If my understanding of aviation history is correct, the Alpha was the first aircraft to be equipped with Goodyear de-icer boots. The aircraft itself was produced in limited numbers because it came out about the same time Donald Douglas was offering the DC 2 and DC 3, twin engined aeroplanes that were far more capable and became far more popular.

glewis. The friction fit of the mount is adjustable. The motor brake will be off. If I decide to take a 'belts and braces' approach I can always add a small magnet to the mount that would be attraced to one of the screws to ensure there is no rotational movement.
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Old Dec 13, 2014, 04:59 PM
Or current resident
glewis's Avatar
USA, FL, Tampa
Joined Jul 2002
5,041 Posts
Cool. I was thinking a magnet too.
I always liked the early Lockheeds. I built a Gamma from the Pres Bruning rubber model plans. Flies good but the landing gear was a bear to build and limits the model to a smooth landing strip.
Glenn
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Old Dec 14, 2014, 08:42 PM
Registered User
Joined Feb 2013
701 Posts
Always like to see the lesser converted kits built and converted. Haven't seen this one done very often. I've looked at it a number of times on Ebay and your build definitely increases the interest.
Quote:
Originally Posted by glewis View Post
Looks good. You can't get the equipment any further forward than that!
Don't know how tight your cowl friction fit is, but I would turn the ESC brake off. If the motor slams on the brakes, it might work your cowl loose.
Glenn
That's what I was thinking too. There's no reason these long tail moment subjects need to end up with any ballast, with the gear properly positioned. Recently finished a P26 and ended up adding a pilot, since I needed a hair of rearward ballast once it was said and done.
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Old Dec 15, 2014, 02:01 AM
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P_J_Glor's Avatar
Valencia, CA
Joined Oct 2002
3,847 Posts
There is a Dumas Alpha in my "stash," so I will be following with interest.

Pete G
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Old Dec 15, 2014, 04:45 PM
CH Spring
Canada, ON, Osgoode
Joined Mar 2008
422 Posts
P-_J_Glor.

I hope to convince you to put the Alpha into the queue.

If, and when you decide to build you will find that these are great kits.

I recommend that among the first things you do when you start is to write the number of each part on it before you remove it from its sheet.

I have included several pics taken as I built. I started with the tailfeathers. I substituted spruce for the horizontal stabiliser rear spar. I used balsa for the elevator leading edge. I cut the elevators from the stabiliser after it was built.

WRT the fuselage, there were a couple of parts, I believe they were labelled B1 which fare around the wing at the fuse. I could not visualise how they fit, so I simply set them aside til I had the wing finished. Their fit then became apparent.

Aileron construction is straightforward. For an aileron horn I went to my old standby. I always keep my hotel room keys. They provide great stock to cut parts from. I usedDduBro higes for the ailerons. I'll cut them down a bit before I am finished.

When it came to the wing I did similar in that I substituted spruce for the aileron spar.

What should be my last pic is of my byzantine wing attachment method. I should have done better but this will suffice. The tongue is made from a piece of popsicle stick. It fits into the fuse at I believe 4A. To do that I beefed that piece up with a layer of 1/32 ply.

Cheers!
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Old Dec 15, 2014, 04:53 PM
CH Spring
Canada, ON, Osgoode
Joined Mar 2008
422 Posts
I managed to duplicate a couple of pics. Sorry. One pic shows the whole on the scale at 6.8 oz, battery included. The other shows me using a sheet of glass with a pices of sandpaper on top to smooth the flat underside of the outer wing panels.

Cheers!
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Old Dec 20, 2014, 07:14 AM
CH Spring
Canada, ON, Osgoode
Joined Mar 2008
422 Posts
Not too much progress to report. When it came to tailfeathers, my priorities were light, and concealed control horns. On that front I am having some success with the elevators, but anticipate problems with the rudder.

From the pics you can see how I have cut the aft bulkhead to allow the stab to be inserted in one piece. You can also see I infilled an area where the fin will mount, then cut out the original stringer.

A small hole was drilled in the next bulkhead to support the sheath for the control wire. that said, I have scrapped the pull/pull idea, it being, as my brother would say, too much sugar for a donut.

The sheath got a drop of CA on the forward side of the bulkhead.

A short wire with a z bend was connected at the servo end. The elevator wire was then connected to the servo wire via a DuBro connector. I did this for three reasons. The first was to ease final assembly. The second was to permit easy removal of the servo tray. And the third was to permit adjustment of the system without using servo trimming.

The elevator will receive a spruce spar centre section. A credit card material control horn will be attached to it. Elevator, stab, fin, and rudder spars all got matching holes drilled in them. The elevator will have four small fibreglass hinges in slots yet to be drilled. The fin and rudder will have two. Because the elevator is relatively long, it needs additional support along its length. To do that, short lengths of 30 lb monofiament fishing line will be installed and secured on the elevator side of the pre-drilled holes. During assembly the lines will be installed in their matching holes. The idea is that the monofilament will be permitted to move through the stab, yet it will provide proper alignment and support of the elevator.

I extended the base of the fin such that it now meets with the stab. That allows proper alignment and good security.

The rudder will receive similar treatment to the elevators. Once the stab is installed I can continue the vertical cut to allow the rudder to be installed the same way.

The problem with the rudder is that there will not be enough room for the horn to clear. I'll have to sort that. I am thinking that I might have to make a small, non- scale blister on the side of the fuse to fare over the horn.

In any event, this is what I have so far.

Cheers!
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Old Dec 20, 2014, 07:22 AM
Oh no, not again!
jhspring's Avatar
United States, LA, Carencro
Joined Dec 2005
5,780 Posts
Fuse looks nice and straight, brother. Got a couple of pics of you ele/rud horns and linkages? I'm having trouble visualizing them.

The Alpha is coming together great!

regards,
J
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Old Dec 20, 2014, 10:22 AM
Registered User
United States, WI, Hudson
Joined Aug 2012
117 Posts
Nice job. B.F. Goodrich deice boots, not Goodyear.
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Old Dec 20, 2014, 02:57 PM
Registered User
United Kingdom, Scotland, Killearn
Joined Aug 2014
211 Posts
This is coming together very nicely. A quite demanding build, even without the conversion you are working through. Can you imagine tackling those lightened wing ribs without laser cutting!

Alec
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Old Dec 21, 2014, 04:57 AM
Branjo
Joined Sep 2013
323 Posts
Very nice job. I have this kit on shelf so will be watching your build. I really dig the way you did the cowl with the motor and battery and the slotted attachment. Also, really like the aileron controls you did. I have never seen it done that way. Good luck with the build!
Branden
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