GoNavy

My Feedback: (15)

Thailazer: What was the design source of your 100 inch version? Did you do your own plans? Why did you power with the .28s if you thought them insufficient?

Did you ever have a single engine incident, and how did that turn out?

Given your experience with that aircraft, what power would you judge appropriate for John's 1/6 version, assuming, let's say, a flying weight of 38 pounds?

thailazer

GoNavy, My Twin Otter was scratch built from 3 view drawings out of the DHC-6 maintenance manuals. Wing was built up balsa D-Tube covered with monokote, and the fuse was a solid dock billet with very light glass. There were cut-outs for the radio/servos and a bulkhead for the nose gear. 1/8 ply was used as a box inside the fuse for wing mounting and strength.

I really didn’t intend it to get as heavy as it did, but since the .28 OS Max engines put out almost 4 lbs of static thrust, I need not have worried. The aircraft would do great aerobatics and take-offs were very scale. It took 2nd place in NW Scalemasters Sport Scale the first year, and 1st place the second. It was an awesome flying aircraft which I flew for four years before the nacelles (balsa and glass) developed cracks and I retired the aircraft. I used to do about a dozen hammerheads in a row with roll-out three feet or so above the runway until the next vertical climb. (Not in scale competition of course!) It was awesome to see a big twin like that flying close in.

My first 18 flights (yes, 18!) were flame-outs at various altitudes up to 100 feet. I had a very difficult to diagnose (only flying) throttle cable vibration problem that I finally sorted out. (The carb barrel would rotate at high frequency, pumping air back into the fuel line, leaning and killing one engine.) In almost every case, I just throttled all the way back and landed straight ahead or wherever I could. It was a rather frustrating time, but after that, never a flameout in any later flight. The few times I did fly it single engine, I found the big rudder to have no problem in keeping it going straight. To keep complexity and weight down, I used a single throttle servo and synced the engines by design and adjustment on the ground.

I am not familiar with building or flying aircraft in the 38 lb category. I would take a look at what heavy aircraft you fly now and measure static thrust on the ground. Most models are way over powered (1:1 static thrust-to-weight is normal!) but that 10:1 aspect ratio wing should allow you to fly at ratios much lower than that. I always recorded wing loading, A/C weight, and static thrust on all my aircraft to get a feel for what would and would not work well. One thing to really watch out for is engine weight, as some of the ignition engines are quite heavy. If you could find some old single cylinder glo Tartans, those might make dandy powerplants for the Twin Otter, but check the static thrust of what you would get out of those engines. As I remember, they were very strong engines for the weight, and would swing a 16-18 inch prop.

By the way, I used 3 blade props on my Twin Otter to keep it scale, so my static thrust to weight ratio was actually about 6/13.5. That additional 25 inches of wing on John’s design should allow you to go even lower. As with any model, keeping weight down during the building process has to be a high priority. I’m looking forward to getting one of John’s kits in the future. I hope all that helps.

thailazer

If this doesn't make you tingle, nothing will! Check out the flaperons deployed, as well as the good practice of full back stick during taxi.

http://www.youtube.com/watch?v=782JR...feature=rec-rn

Lins

That's one of the paint jobs I was debating. I think I'm going for a paint job that's on some of our helicopters, that is somewhat similar to the Viking Air paint job. That twin is owned by Air Tindi, which is based out of my town. They are owned by the same company (Discovery Air) that owns the company I work for (Great Slave Helicopters).

thailazer

I was thinking that would be a nice paint scheme! Sounds like you have plenty of examples to use up there.

Lins

There are 3 companies up here that operate twin otters. Not including Max Ward's personal plane when he comes up to visit the North

thailazer

I like your thinking! Someone will end up doing it I am sure. Looks to to me like they would fit quite well. Small problem with two exhaust ports but a minor scale infraction.

http://wrenturbines.co.uk/usa/engine...op/44turboprop

Didg

I agree [8D]

Lins

I am wanting an aircraft to put a turboprop in. There are turbo porters people have put a little turboprop in. I think it's the 54 though. I'm not sure the 44's are small enough for this plane!

Didg

I've yet to find a scale aircraft for a / 2 turboprops that takes my fancy, a twotter on the other hand.........hmmm.

Not sure of turbine size, would need to be pretty small I would guess, but the sound would be amazing.

thailazer

Some outstanding photos of Twin Otters in the YouTube link below.

http://www.youtube.com/watch?v=PDIx6...=rec-fresh+div

John La Belle

My Feedback: (52)

flew latest 130" Twin Otter today 2 flights great at the 36# weight using 2 OS200 four stroke engines plenty of power very rock solid and stable will check if anyone got in flight pictures and post. John

Lins

Damn that looks nice! I'm still waiting for wood to show up from the hobby shop.

Syssa Aircraft

Did you see the short landing in Saba? The pilot is coming in for a landing...and it is a nice landing with the Otter...but did anyone see the X over the end of the runway on the side he was landing in?

GoNavy

My Feedback: (15)

John: I think it looks great!

Are those 16/8s on the OS 200? Do you think that is about the right amount of power?

I don't recall if your first had the lower landing gear fairings installed. Do they tend to get damaged easily?

John La Belle

My Feedback: (52)

Hi Tom Those are Master 16x8on the OS200's. This combination provides plenty of power at 32 lbs static thrust on the 36# plane. I never have been able to get them to run as well as all my other OS engines have run. Both change speed and mixture during flight and gave me fits landing with engine speed changing on final and during flight and always did even in the Decathlon test plane. If one can fix this, they would make ideal size and power set up for the plane at least up to 45# but for me I will replace them this winter with 26CC gas engines probably Evolution which I get along with well. I just didn't get to the lower fairings and other finish details yet . I make the lower fairings upper and lower 2 piece and bolt together over the wire landing gear with no problems just do not attach lower and upper fairings together as per the full size plane

GoNavy

My Feedback: (15)

John: Great pics. Nice cabin detail. Glad to see it will fit in a pickup.

We are still studying the engine issue.

Have you found a muffler for the Evo 26 that will fit inside the cowl? What prop do you intend to run with those? The Syssa 30 cc while bigger, has a nice rear exhaust muffler that appears as tho it would fit. The price is around $450 with muffler, and he told me he could provide a counter rotating version! I am awaiting three views of that set up.

Saito advertises that their 125 gas four stroke will turn a 15/7 three blade. Do you think that would get the TO off grass in 300 feet?

John La Belle

My Feedback: (52)

Hi Tom. I have been following the Syssa engine but until very recently he had not been shipping them. They appear to be able to fit entirely inside the cowl and only weigh 40 oz complete with muffler and ignition They claim to provide 18# static thrust on 18x6 props at 8800 rpm which is equal if not better than the OS200's which have plenty power so they would make an excellent choice if they are good reliable engines and can be purchased. They would be my engine of choice if they prove to be good running engines. if the reports prove good will test one in the spring and may use them instead of the Evolutions. Right now Smooth runningtransitionreliability is now my main concern . I think the Saito 125 would underpower the plane but that is only my guess as I have never run one cheers John
PS there are 3 views of the engine in the gas engine forum under syssa thread

Lins

Has anybody looked at the 37cc Mintor engine?

http://www.dietrichaircraft.com/stor...829v3gqsch6kc4

John La Belle

My Feedback: (52)

Hi Lins; looks like the carb would have to stick up thru the top of the cowl or am I looking at the picture wrong. This is an even larger engine than The evolution 35cc which way overpowered the Twin Otter as did the OS200's , I believe the best engines to use are smaller if the model weight is 40# or less. I will be using 30cc gas or smaller in the spring. That Syssa looks real promissing and will try to do some testing on even smaller engines in the spring

Lins

Yeah I was wondering about the carb, but I'm wondering if you can rotate it, it almost looks that way. I'd love to hear of your review of the Syssa's!

GoNavy

My Feedback: (15)

This thread has been quiet for awhile, and to keep John up to date on changes, let me comment on the photos:

I made removable hatches for the landing gear on both sides which will permit access to the landing gear bolts to tighten or to remove the gear; the center bolt will be accessible by a hole in the fuselage skin; all landing gear bolts will be held with t nuts.

I am using a servo on each flap and placing them in the wings. The latch will provide access

GoNavy

My Feedback: (15)

OOPs, I goofed on the one photo.

pinky_d_brain

Zup guys nice work was just looking around I happen to live in Yellowknife as well and can watch these plains land out my window. was actually looking for info on where to get building material in Yellowknife or find someone that would know I’m not actually building a plain hope to someday but will be starting with something small and cheep I have no Experian’s with flying RC plains and expect to crash vary often. I actually build airboats but building is building still need the same stuff

Lins where do you get you’re building material from??

Lins

Great Hobbies out of Edmonton/PEI, they just finally shipped what I ordered a couple months ago. I could have split the order and pay extra shipping between the two stores, but I opted to wait. Hiflight RC also sells stuff to the public now. Roy at Roy's Audiotronics would probably order what you need as well, he's big into R/C