Twin Otter - Electric Twin from Anton Eisele Plan

[Wasaforumite]

I am currently building from this plan that I bought from AirAgeStore.com in the USA. The plan arrived quite quickly, about 10 days and post cost was $14. There was no Duty or VAT. The plan is on 2 large sheets and is nicely printed and I rate it at good value at $19.95.

It wasn't easy to find a suitable plan. The ones I found on the web are too big or too lightly constructed for my purposes. This one is semi scale which doesn't bother me as I want the plane for everyday flying. At 65 inch span it is about the same size as a traditional trainer.There is a huge range of liveries available to disguise its appearance!

Hangar 9 did an artf slightly bigger than this a few years ago and currently there is another quite costly artf availble from Europe. I believe they are all good fliers - the Twin Otter makes a good prototype to turn into a flying model. The good ole Twinstar is a great flying plane and I believe the Hobbyking twins go well too. But it is nice to have a balsa model that's been build the trad way.

There is a youtube video of the plane I am building at **LINK**

I have spent some time time studying the plan and there are only a couple of minor errors found so far. The AirAge web site has links to some building instructions. Originally the plan was for geared 480 brushed motors and Nicads. Standard sized servos were used with long rods to the tail and bell cranks to the ailerons.

I am not going to change the plane extensively apart from up dating the servos and motors/batteries.The large fin looks rather fragile so a few strips of carbon will be used. I think adding flaps will only increase weight and complication without any real benefit. The plane evidently takes off in a few metres and has plenty of drag to slow it down.

I hope this will be of interest. Given the advantages of electric for twins it is rather surprising that they are still quite a rarity. Some photos of the build will follow in later posts.

[Denis Watkins]

Very interested in all aspects of this build, a good size twin, manageable by most of us, and not so far out of reach

Of club flyers. This build holds loads of problem solving and set ups for all to enjoy.

[Biggles' Elder Brother - Moderator]

Very interesting - I sahll be following.

I have the Hangar 9 Twin Otter ARTF and I can cinfirm that it is indeed a very good fyyer. It is electric powered and runs off two 4s 5000 mAh Lipos very well.The high aspect ratio wing, with large high deployment flaps, make slow speed flying a dream and making final aproaches into a slight breeze is great fun - and totally safe down to ridiculously low airspeeds.

One small issue with the model - and I have heard others say this about the Otter - it can come out a bit tail heavy. Mine has about 6 oz of lead shot epoxied into the nose cone to give a good solid CoG position - maybe just one to think about whilst you are building?

I have adapted the working side door on mine so it can be opened with a servo and drop 4 "paracutists" - great fun and always pleases spectators - through a I did have a dog run off with one of my "little men" on one occassion!

BEB

[Former Member]

[This posting has been removed]

[Wasaforumite]

Regarding the Hangar 9 version, I think it's quite a bit bigger than this one - it weighs about 10/11lbs whereas I'm hoping for 5/6lbs for this. H9 TO has its batteries behind the engines which saves wiring length and a little weight but against this there is the possibility of battery voltage imbalance and the fixed position prevents the batteries being used to balance of the plane. Not a criticism, the designs are just different. H9 version is a lovely plane, a triumph of production, lets hope I can get somewhere near it!

Apart from a Twinstar, I have built a Eurotwin and a Short Scion. In all of these having a single battery worked out fine. I didn't experience any motor problems having fairly long power supply wires to the ESCs mounted behind the motors. Perhaps with bigger motors it can be a problem.

I looked at the Ivan's TO as well. It was too big for me and looked rather fragile. Unless laser cut parts are available it looked a challenging build and I would be too frightened to fly it having spent that amount of time and effort.

Parachutists eh! Sounds great. I think I will use mine for carrying a camera.

Edited By Wasaforumite on 08/10/2017 13:07:45

[Wasaforumite]

Here's some pictures of the early stages of the build.

The fuselage is in two main sections. The main section at the front has parallel sides. I cut a sheet of 1/4 balsa accross the grain the exact width between the frames and then slice it for the sticks in between the sides. I set it up using 4 set squares.

The rear section is just a straight taper built out of two frames and again 1/4 square sticks in between. I ruled a line on a fresh sheet of plasterboard and marked the centre of the front cross beam and pinned the tail triangle down to line. It seems to work. Underneath both sections there will be notched formers to take stringers.

There is an article on the web giving the designers notes on the build found here:

**LINK**

I will try not to duplicate this too much and only give some comments that add to that article. The plane dates back to about 2004 and since then digital photographs have vastly improved on the old grainy images. Hopefully my pictures will make it easier to visualise how the plane is built.

I am leaving the frames to dry thoroughly before fettling the joining surfaces so that when glued I get a straight fuselage.(Hopefully!) I don't use cyano because the Modellers White Glue gives more time to adjust components and sands better.

I seem to remember Peter Rake has used this system of two module fuselages in his WW1 biplanes. The result is a rather boxy fuselage but there is no stress during construction and it is comparatively easy to get it straight.

[Biggles' Elder Brother - Moderator]

Nice neat work, good start!

BEB

[Wasaforumite]

The front and rear components of the fuselage are now joined. Tomorrow I'll start on the stringers.

Pictures from my phone often post here upside down.

[Wasaforumite]

Sooner or later I am going to have start on the wings. There are in set ailerons and I am showing the catch-all cross section here. The wing is easy enough, looks like Clark Y but I have some fear about building the ailerons. I really prefer to build them as part of the wing and cut the out but it doesn't look like that is possible here. The idea of getting an accurate chamfer on the 1/4 sheet aileron leading edge of the aileron looks very challenging as well as building using fiddly little triangles. I going to have to think of a another way.

I will be using separate aileron servos and no bellcranks.Servos are one of the few things that are cheaper than in 2004!

[Wasaforumite]

I've started on the wings now. I have decided to build the wings entirely as normal and then cut the ailerons out. Similarly the engine 'gap' will be cut out later. The ribs have holes in them for the wiring. I never seem to be able to make a good trailing edge by camfering the top sheet and sticking it down along the edge to the bottom sheet. Instead i have planed the edge of the wing and glued on a 3/16 by 3/16 strip. This is then planed and sanded to an edge about 3/32 thick.This is a similar idea to when trailing edges are put on foam cored wings.

There are two relatively inexpensive tools I use all the time. One is a plastic ruler with notches to gauge balsa sheet thicknesses. The second is a Great Planes sanding bar about 2ft long. Both seen in the picture below.

The fuselage has had some stringers added and part of the nose. So far it is entirely as per plan. I'm not quite happy with nose in the original design, it looks too 'beaky'. This is probably because the designer wanted to make construction simple avoiding compond curves. I'm not about to make it more complicated. I just think by shortening it a couple of cms it will look better even though it will be less to scale.

Edited By Wasaforumite on 20/10/2017 22:30:21

Edited By Wasaforumite on 20/10/2017 22:30:54

[Wasaforumite]

This is the stage where progress seems to slow. Work becomes more to do with details that creating structures.

I am trying to keep to the original plan as far as possible because it was the basis for a commercial kit many years ago so it was basically well sorted and also modifications usually mean more weight. However the photo below shows a depature from the plan which had a standard servo in the middle of the plane operating the front wheel and the rudder via long control rods.

I have used a sprung noseleg, I believe it is a Dubro part but i've had it so long I could be wrong. Also a small metal geared servo is used for steering with control wire bent in a elongated 's' shape (not visible in pictures). This should have some shock absorbing properties as a result. The servo is just under the cockpit of the plane.

[Wasaforumite]

This time there is a photo of the tail mocked up. Others who have made this plane have said that although the tail seems to work OK it is rather prone to damage when the plane is handled. The main problem is weakness of the fin. I have doubled up some of the frame and used 1/64 veneer each side of it under where the stabiliser or tailplane is fitted. It is much stronger as a result. I am going to use two Savox 225mgs to operate the rudder and elevator, deleting the two heavy standard servos in the middle of the plane under the trailing edge of the wing.

[Wasaforumite]

My final posting today just shows the splitting of the ailerons from one of the wings. This is not a job I have been looking forward to as it is difficult to measure where the cuts go. The new trailing edge can be see (oversized before planing and sanding).

I have had some graphics arrive from Callie in the USA. I will be dressing the plane as a WinAir Twin Otter, mostly white, with stripes, blue tail and wing centre panels and red rudder. I decided against the yellow Canadian military strip as it has been done before. Similarly, I avoided the US para team. The former was available as a VMAR ARTF, the latter a Hangar 9 ARTF. For those impatient to haqve a new Twin Otter, I saw on Ebay that a German ARTF manufacturer is doing a Swiss survey liveried version (very nice it is too). It's rather expensive and with the power trains it will cost about £400 to get into the air plus battery and radio. Mine will cost about half that even after buying Oracover.

[Wasaforumite]

Building has been slow recently, held up by the holidays and the time consuming work of constructing the engine nacelles and ensuring that the ailerons matched the wings properly. I have now nearly finished the construction work and have made a start installing the motors and wiring.

The nacelles are built by planking over formers so with a top and bottom it is like building 4 little rowing boats!

The motors, are Emax GT2218/10 (about 1000 rpm/v) obtained from Totem Hobbies, Plymouth. I found it quite difficult to source motors of the right size. Most places only had 1 in stock!. Using 9 by 6 props they should draw about 15 amps each on 3 cells. If this isn't enough thrust I can go up to 10 by 5. Motor tests will take place when I can be bothered to go out in the horrible weather! I am using two 30 amp opto ESCs. Power for the Rx will come from a LiFe battery and voltage regulator.

Roughly balancing the model on my fingers, the c of g seems about right and the correct balance should be possible by moving the batteries around. I intend using 2 3 cell 2200s as these are a popular size. Each motor will have its own battery so I will get new batteries and keep them in pairs.

Here are a couple of pictures of the airframe so far. The control surfaces remain to be attached.

[Dwain Dibley.]

Very Neat and Tidy. Will you be adding a pilot/s ?

D.D.

[Wasaforumite]

Would be nice. I'd need to source a couple of 1/12th scale head and shoulders pilots - any ideas?

Readers may have noticed that I changed my original plan of having one battery powering both motors. I realised I'd need some 4000 3s lipos and none of my other planes would use them. Two 2200 will give the same result for less outlay. Hopefully these common lipos will be reliable as they are so popular these days.

[chris larkins]

Following your build with interest as I have a soft spot for the Twin Otter, in fact I have an ARTF in a box in the loft which is getting nearer to the top of the build list (ESM, 65" span).

With regard to the covering have you ever tried the Hobbyking film? It is far cheaper than Oracover or Profilm and in my opinion is equal in quality and is easy to apply, I believe most of the Far East ARTF's use this film, only £8.13 for a 5m roll.

**LINK**

[Wasaforumite]

I've heard some good reports about Hobbyking film. I may try it on my next build. For this one its going to be Solarfilm white and blue on the wings and Oracover white for the fuselage. I wanted some extra strength in the fuz. I wasn't aware that the HK stuff was as strong.

The ESM Ottter must be a rarity now. It looks a lovely kit and I have to say the fuselage particularly is a lot more realistic than this plan because the moulding allows for all the curved surfaces of the original. Hoperfully, the all balsa build has some virtues. It will probably turn out a bit lighter and at least I can build another one if the worst happens!

[Wasaforumite]

Had a chance to test one of the motors today. On a rather tired 3s lipo that I had hanging around, the motor used 155 watts. This is about 15 amps. The propellor used was a 9x6 APC E series. From postings on a US forum this should be enough to give a lively performance with a short take off run. Flight times should be around 15 to 20 minutes. This assumes the total weight of the plane is around 4 to 4.25lbs. Fingers crossed!

I've sorted out the wing servos. Next jobs are the rudder and aileron servos. After that it's covering, a job I never look forward to.