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Twin Otter 125inch wingspan

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Twin Otter 125inch wingspan

Old 02-25-2009, 09:15 PM
  #76  
SteveD-RCU
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Default RE: Twin Otter 125inch wingspan

Nice jig setup Tom,keep the pics comin to pump us up to get going on ours.
Steve
Old 02-27-2009, 05:00 AM
  #77  
John La Belle
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Default RE: Twin Otter 125inch wingspan

Great job Tom on the fixtures. at this point I found it helpful to assemble but not glue all the pieces in this area, the floor plate F12the wing saddles F13spacer blocks F15 and the formers. line up former F5b in correct location and glue then glue both formers at the end of wing saddles F13 to the crutch and F13's. then square up and glue F5A and F5C's in place. Locate floor plate F12 in place using F15's under the crutch and on top of F12 glue in place and add triangle stock braces as required hope this helps in this area. John
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Old 02-28-2009, 07:54 AM
  #78  
John La Belle
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Default RE: Twin Otter 125inch wingspan

Hi Guys; Please note:: the above sequence puts F5A 1/8 farther back than is shown on the top view but all will be in the correct location only in the top view F5A was shown 1/8 too far frontward and this has been updated as of today . All the part prints and locations on the side view including F5A are fine and only the F5A location on the top view is to far frontward Pencil in F5A one eight back on the top view plan if desired

Hope I am not confusing people with these posts John
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Old 04-17-2009, 10:27 PM
  #79  
GoNavy
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Default RE: Twin Otter 125inch wingspan

Progress report: I opted for a slightly different mounting system for the stabilizer. I tried my darndest to align the stab carefully, using the aluminum brackets called for by the plans, but I was not able to achieve the accuracy I wanted by that method.
Thus, (1)I filled in with an additional piece of plywood glued to S5 in the stabilizer, and (2) a mating piece of plywood where the stab mounted in the fin. I also used triangle bracing under R3, and added balsa in front of and under the stab, in the saddle, to increase the gluing surface.

I found this a workable method to achieve what I believe is a properly aligned stabilizer. After the epoxy dried, (3) I filed in balsa above the stab, leveled that, and installed R3A.
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Old 04-18-2009, 12:09 PM
  #80  
John La Belle
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Default RE: Twin Otter 125inch wingspan

Hi Guys; I have been filling in under the stab with epoxy and microballoons but the balsa blocks are lighter therefore better- good idea Tom
Old 06-07-2009, 02:25 PM
  #81  
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Default RE: Twin Otter 125inch wingspan

Update

I am making progress.

For anyone who hasn't started yet, I include a photo of a new a[img]file:///C:/Documents%20and%20Settings/All%20Users/Documents/My%20Pictures/Kodak%20Pictures/twnOtrconstrt/100_0318.jpg[/img]nd I think better building jig. GoNavy

Edit: Trouble getting upload photo correct.

Old 06-07-2009, 06:54 PM
  #82  
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Default RE: Twin Otter 125inch wingspan

That would be interesting Tom,hope you can get some pics uploaded...
Old 06-07-2009, 07:05 PM
  #83  
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Default RE: Twin Otter 125inch wingspan

Let me try those pics again.
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Old 06-08-2009, 05:32 AM
  #84  
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Default RE: Twin Otter 125inch wingspan



Nice jig Tom,keep up the good work.,plane looks great also.Looks like your pics need reducing to email size before uploading.Some camaras have that setting built in,or your computor can do it also.

Old 06-08-2009, 01:13 PM
  #85  
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Default RE: Twin Otter 125inch wingspan

Steve: Agree on the pic size; never had a problem before. Trying to fix it. My computer literacy is limited. Sorry.
Old 06-08-2009, 04:31 PM
  #86  
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Default RE: Twin Otter 125inch wingspan

Steve:
RCU support indicates there is a glitch in the pix link and they are fixing it.
Old 06-09-2009, 04:38 PM
  #87  
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Default RE: Twin Otter 125inch wingspan

4th time is a charmer.

This jig is easier to instal and remove, and can be used on initial construction and when turning the fuselage to instal lower longerons. (6/16; I must clarify the latter statement; They will not support the fuselage inverted if you have sheeted to the lower side longeron. (Sob, sob....)
Old 06-16-2009, 07:18 PM
  #88  
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Default RE: Twin Otter 125inch wingspan

Is anyone else in the construction phase? I have some issues with the main gear I would like to discuss.
Old 06-16-2009, 08:03 PM
  #89  
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Default RE: Twin Otter 125inch wingspan

Im not  starting till this winter but would still be interested to hear your concerns Bill..
Old 06-16-2009, 08:53 PM
  #90  
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Default RE: Twin Otter 125inch wingspan

Bill:
1. Is it necessary/desirable/better to remove the two longerons beneath the main gear (per construction pixs), or can they be left in place? (I know the five bolt holes can be located to allow the longerons to remain uncut.)

2. Why one rod 1/4 inch (a real bear to bend) and the other 3/16 inch? Why not two 7/32 inch?

3. If there are two 1/4 inch ply bolting blocks per construction pix, is the one sandwiched between the gear backer, i.e., is it a spacer to help align the landing gear rods?

4. Is the aluminum backer to be 1/4 inch or 3/16 inch thick? Both thicknesses show on the plans.
Old 06-17-2009, 06:50 AM
  #91  
John La Belle
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Default RE: Twin Otter 125inch wingspan

Hi Guys;  The planes have been built both ways, the only reason to cut the bottom  stringers is to allow the gear to be removed. it's a personnel choice, I made mine removable but the gear could be built  enclosed. I believe that 2 pcs 7/32 would be strong enough I used 1/4 and 3/16 as those sizes are easier to get.. The smaller block is an alignment spacer between the wire rods ( this could be eliminated if the 5 bolts were located to keep the wires in location. but this requires very  precise  locations when drilling)  3/16 aluminun is fine but 1/4 gives a  choice to the builder of the gear if desired. 
Old 06-17-2009, 06:59 AM
  #92  
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Default RE: Twin Otter 125inch wingspan



I was just thinking the same thing John about personal choice and weight considerations John.I 'm thinking of going with 1/4" rod and 3/16" plate.Should be plenty strong.One could also add a faring over the landing gear that you bolt in place.

Old 06-17-2009, 07:07 AM
  #93  
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Default RE: Twin Otter 125inch wingspan

Perhaps a removable section similar to the section of the fuselage above the wing?

My thinking was to maximise the strength in this area, to leave the 2 longerons intact; With the fancy fairing work for the landing gear, removing the gear for any reason would require major restoration.
Old 06-17-2009, 08:40 AM
  #94  
John La Belle
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Default RE: Twin Otter 125inch wingspan

Hi Tom;, I just used a thin alum. cover over the landing gear but I will build the gear in place next time. ( as you say any removal is a major repair and you  might just as well  have the full stringer strength) I am still in Anchorage Alaska  and will catch the boat now down to Vancouver, will be back in New England next week. Everybody in Alaska must have a float plane many Twin Otters on floats here, got some good info on Twin Otter floats   cheers  John
Old 06-17-2009, 10:14 AM
  #95  
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Default RE: Twin Otter 125inch wingspan

Ahah, a working vacation.

Could you sleep at night, er, excuse me, night doesn't exist there now.

Did you catch a 600 pound halibut?
Old 06-24-2009, 08:09 PM
  #96  
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Default RE: Twin Otter 125inch wingspan

Good evening to all,

Just ordered a set of everything from John for 130" version. Keep those pictures coming guys, they're a great inspiration for the rest of us to try a twin for the first time! Thanks to John for shipping everything so quickly, much appreciated!

Jeff
Old 06-25-2009, 09:15 PM
  #97  
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Default RE: Twin Otter 125inch wingspan

This is the current setup for the front gear. I assume nose weight will be needed. The servo and linkage etc., will be accessible via a semi scale hatch between formers F2 and F3, and between the longerons one above and one below the side longeron.
Batteries for the landing lights and tail beacon will also be located in this area.

I did not cut the robostrut length. I tested the strut; it takes between 18 and 28 pounds to compress the oleo spring. I suspect that a milder spring may be better, but in all events, the longer the spring the better. I will use Dubro inflatable tires. We fly off grass.
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Old 06-25-2009, 09:33 PM
  #98  
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Default RE: Twin Otter 125inch wingspan

Good evening "GoNavy",

I talked to Robart yesterday, and they told me they don't make a tiller arm assembly to fit the 5/8"Robstrut, that it was originally designed as a main gear. By chance, did you talk with Darrell at Sierra as a possible option for the nose gear in lieu of Robart? Have you decided on a choice of powerplant for you build? Appreciate you taking the time to document your build with pictures, they will help a ton with my build this Fall!

Jeff
Old 06-25-2009, 10:53 PM
  #99  
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Default RE: Twin Otter 125inch wingspan

Alexzach: I did not talk to Sierra.

I purchased a second "clamp" ($15!) for the Robart, and using the brass shown made it into an arm. You need something above and below the gear block to keep it in place and the clamp fills the bill.

I used an abrasive foam pad to remove the primer from the upper portion of the strut and to achieve a nice slip fit of the strut thru the aluminum block. Those are thrust washers (i.e., oil impregnated), and the gear turns smoothly and easily.

Re power plant; The final decision has not yet been made, but the criteria are: 1. engine and muffler must be fully concealed within the cowl 2. Pumped for reliability 3. Ignition to ensure reliability because engine will be inverted. 4. Ability to swing a 17 inch (exact scale) or at least 16 inch three blade prop. In most cases, the cheaper 2 stroke gas engines have the walbro carb on the side, so they will not fit in the cowl. The MVVS/Evolution engines have the carb in front and mufflers are available to fit within the cowl, but the 26ccs can't swing the 17 inch 3 blades. The evo 35 is no longer made. I see DL engines announced a 30 cc. Stuart Mackay has an engine that would meet these criteria if you don't mind getting your engines over the pond. Moki has brought out ignition engines that should do the trick.

I suspect that Saito 150s, certainly 180s, would swing a 16/6 three blade, but that of course is glow, and no pump; I would then use a Cline regulator. The OS 200 would fit, is pumped, tho glow; I think John LaBelle is installing a pair of those in his most recent build.

An RCV 120 would swing the 17inch three blade, but I wonder if it would be sufficient power.

I am open to suggestions and would be interested in what others favor for power.
Old 06-27-2009, 03:52 PM
  #100  
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Default RE: Twin Otter 125inch wingspan

Hatch construction.

I decided to include the side and upper and lower longerons in the hatch itself. I added extra longerons above and below the hatch, spaced 1/32" to allow for cutting after sheeting and glassing. I have added three 1/8" thick light ply hatch "formers" to help ensure that the hatch will keep its shape after cutting. I am installing 1/4" balsa along side these formers for additional sheeting gluing surface.

It is not exactly scale (the scale hatch is shown on the fuselage side view), but this is close and avoids having the hatch cross a fuselage former.
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