Let410/420 vs Twin Otter

[Tango24]

Looking for any info on pros and cons of Let 410 and Twin Otters. Anybody who has flown/operated either or preferably both and has an opinion would be greatly appreciated. Specifically looking for short, soft field performance, reliability and operating cost comparisons.

Also opinions on Let 410 and 420 differences.

Thanks

Thanks

[Shrike200]

This topic has actually come up before in a fair amount of detail in this forum - some searching of the archives should yield something useful.

[MungoP]

If you put the two of them to the test you'd find that the twotter is the better tool.. no doubt , BUT.. very much more expensive.. becoming few and far between in the right condition... watch out there are some dogs out there. What you need to ask yourself is just how important is that marginally improved short field performance to your operation... just how short and uncomfortable are the strips you'll be operating into.. if only the twotter can do it with the load demanded then there's no decision to make , but if the Let can do it effectively then why spend the extra money ... a lot of extra money .

[Goffel]

T24.
I fly both the Twotter and the LET.......the LET, to me, wins hands down.

For comfort, (both pax, plus pilots), it is definitely much more comfortable than the Twotter.

Performance, both the same...only time to test the two is if you are going in to really marginal strips with pax, and normally most people are not doing that...but then again, I have found them to be much of a muchness anyway.

From what I gather, the LET is cheaper to run and to buy.

I am sure there are going to be guys that differ from me, but I still say the LET.

Goffel..(by the sea, and my boss knows).

[Solid Rust Twotter]

http://www.youtube.com/watch?v=_8wmZ6hhpg8

http://www.youtube.com/watch?v=PS0-5...eature=related

http://www.youtube.com/watch?v=2pk2y...eature=related


I believe Viking has begun assembling the new -400 series with the PT6A-34 engines.

[Tango24]

Thanks for the input so far. I have been looking through old posts and it appears to be that those who fly the Let say its the best and those who fly the Otter swear it can't be beaten. Reading between the lines I have to say that performance wise they are much of a muchness and simply because of the price I am swaying towards the Let. I can get a factory reconditioned Let with zero time on all components,or even a new one for less than a 10-15thousand hour Twotter.

Now, apologies for more questions, but I currently fly C208s. Would it be safe to assume that if a Caravan can get in and out of an airstrip with pilot plus 13, could a Let do the same with 19 pax?

To be more specific, I am looking for a commuter aircraft that can carry more than a C208 and operate off 800-1000m soft dirt airstrips in 40+C. Am I asking too much perhaps?

[V1... Ooops]

I believe Viking has begun assembling the new -400 series with the PT6A-34 engines.

That is correct. The first Series 400 - the pre-production prototype - is almost fully complete and will be removed from the fuselage jig before Christmas. The wings have already been completed. The goal is to fly it in April or May of 2007. Delivery of the next aircraft, which will be the first production Series 400 (serial number 845) is scheduled for the first quarter of 2009.

The Series 400 will be an evolution of the 300. No substantial changes are planned (other than avionics), but there will be a number of small incremental changes that will improve reliability, reduce maintenance cost, and reduce aircraft weight. Expect the basic empty weight of a Series 400 fully kitted out for commercial IFR (TCAS I, TAWS A, CVR/FDR, weather radar, satphone, Mode S EHS, and dual everything) to be well under 7,000 lbs.

[Ejector]

Maybe the twotter cost so much is due to supply and demand. Big demand for a machine that can do alot.

[Woof etc]

Flew a couple of thousand hrs on the Let (ZS reg) and I found it to be a very Robust and reliable aircraft. Unfortunately there are a number of operators in Africa who buy old former soviet union UVPs with timex components at a snip and then operate them illegally until they break, giving the aircraft an undeserved bad name.

re. loads - you will have to check the graphs. Depends. 40 degree plus, 19 pax, soft field, 1000 m - you will be borderline and probably illegal with full mains - it depends on the amount of clearway, stopway etc. How much baggage? How much more than 40? How soft? Slope etc etc. will make a big difference. Remember the Let is a part 121 aircraft and has to meet the min climb gradient and accelerate stop / go requirements to be legal, the Twin Otter does not. Typically the aircraft weigh between 4000 and 4300 kgs depending on equipment. MTOW is 6600 and full mains give 1000 kg of fuel.

The undercarriage is moereva tough on the Let - it soaks up bad landings and if you manage to break it you deserve some sort of award! Big takkies are good for unprepared surfaces.

The Twin Otter is a better STOL performer due to that big fat draggy Clark Y wing and lower stall speed. You can land the Let in a couple of hundred meters with the correct technique, helped by a combination of big double slotted fowler flaps, ground spoilers, antiskid and fat tekkies. However, you probably want to land in a field you can take off from again (personal preference of course).

Any aircraft is a compromise - the Twin Otter sacrifices comfort and cruise speed for better STOL performance. If runway length is not limiting then I would go for the LET simply for the increased comfort and cruise speed and lower operating costs. Having spoken to a number of pax who have flown in both, they stated a definite preference to flying in the LET from a comfort point of view. Having never flown in a Twin Otter, I can't comment.

[Solid Rust Twotter]

Howdy Mike. Need any test pilots for the new Twotters, mate?

Looking forward to seeing them around.

[Turbolet410]

Hi

I have got over 4000 hours on a LET 410 I think it has more future than the Twin Otter.
Performance is the same I have been told.
Regards,

[Turbolet410]

I think you are asking to much

[V1... Ooops]

I'm really not that familiar with the LET. I saw a particularly good looking one on the ramp in Abache a few weeks ago (ZS registered, ICRC livery). The cabin and avionics fitment were certainly up to Western standards.

I think weight is going to be the big issue here. If, as Woof mentioned, "the aircraft weigh between 4000 and 4300 kgs depending on equipment. MTOW is 6600 ..." that gives a 2,450 kg useful load. A Series 400 Twin Otter will weigh about 3,100 kg with a MTOW of 5,670, thus providing pretty much the same useful load but with a significantly lower all up weight. I am sure that there are some single engine performance issues that need to be considered when working in hot environments with short runways (what we're all up against in humanitarian aviation), and I kind of suspect that the Twin Otter will have the safety advantage there due to its lighter weight. On the other hand, if runway length and surface condition is such that you don't have to worry about what happens if you lose an engine at rotation, then the LET does have a bit of a cabin size advantage.

Horses for courses, I think. However, to be honest with all of you, I also have to disclose an obvious conflict of interest here - I'm the Engineering Test Pilot and Manager of Flight Safety for Viking, who manufacture the DHC-6 Series 400.

[mrwebs]

To be more specific, I am looking for a commuter aircraft that can carry more than a C208 and operate off 800-1000m soft dirt airstrips in 40+C. Am I asking too much perhaps?

Hi, i fly twotters out of the tropics, our hottest days are max 34 degrees C, and the strips are asphalt and grass
the mtow we use is 12500lbs with a mlw of 12300lbs

according to my graphs;
t/o- a sea level field at 40 deg C and mtow requires 730 meters with normal takeoff config in nil wind

ldg- a sea level field at 40 deg C and mlw requires about 700 meters, thats brakes only without beta or reverse, and at 20 flap setting in nil wind.

i use 400m with mlw, 30flap and beta in 34deg C.

cant vouch for the LET, hope this helps.

[kijety]

Let410 vs Twotter

I have flown left seat both the let410 and the twotter.. few thousand hours..
YOU CANNOT COMPARE a twotter to that other one.. the let is a flying landrover. it could probably do a good job in a safari rally.. on a hot and high situation and full board it will take you 25 minutes to get from 5000ft to FL115... from sealevel to FL105 you will level out when 45 miles out.
TWINN OTTER perfomance is double that of a let410...
choose wisely..

[Soap Box Cowboy]

Search for this thread in African avaition, it's one I started ages ago with the same questions. "Let410 V. Dhc-6 "

There is a lot of usefull info on it for you though the thread has been closed now.

[V1... Ooops]

TWIN OTTER performance is double that of a let 410...

And it will improve with the new 400 Series, which are being fitted with PT6A-34 engines (or, optionally, -35). The flat rating will remain the same at 620 HP (50 lbs torque), but full horsepower will now be available during climb all the way up to ISA +31°, which is a significant increase over the ISA +6° full horsepower flat rating limitation for climb power on the legacy Series 300 Twin Otters.

The final selection of the avionics suite for the new Series 400 will be announced before the end of the year. I think everyone will be quite pleased with it. It will be a fully integrated system, not a federated system.

[chuks]

Twotter pilot, me. Ugh!

All I know about the Let I got from just watching Air Express doing engine-out training at DAUH on hot days (Hassi Messaoud, Algeria and by hot we mean 50° C). The only reason the Let climbs, seemingly, is that the Earth is a sphere! Give me a Twotter any day.

That said, the Let is a bit faster and it has air-conditioning. The Twotter designers did not pay much attention to comfort issues so that it is a pig in that regard, but I will take climb performance over comfort and speed any day.

[maxpwr]

DHC6

Isnt there a max temp. for the Twotter to be operated in STOL config ? AFM ?

On the L410 you have max contingency power ( 10 Min ) in case of engine failiure , same as max Take off on Twotter. Obviously you dont use max contingency for training purposes.

Aircraft Industries has new L410 in 2008 fitted with UNIVERSAL EFIS and is working on PT6A-42 powered version.

[V1... Ooops]

Isn't there a max temp. for the Twotter to be operated in STOL config ? AFM ?

There are no airframe (OAT) operating temperature limitations published in the Twin Otter AFM - at the time the aircraft was certified, the certification requirements did not include temperature limitations.

Having said that, be aware that available engine takeoff power in a standard Twin Otter (an aircraft equipped with -27 engines) will begin to decline at ISA + 17°, which is the point where the crossover from the flat rating limit to the thermodynamic limit takes place. For climb and cruise power, the crossover is ISA +6°.

You mentioned "STOL config". I am going to guess that you mean 20° flap takeoffs. Be aware that you need a letter of permission from your regulatory authority (state of registration) before you can do that - flaps 10° is the only approved takeoff configuration in the AFM. If you are making takeoffs at flaps 20°, you might want to check and see if you are actually setting full takeoff power (as determined from the takeoff power graph, figure 4-3 in the AFM) for your maximum performance takeoffs. If you are making flaps 20° takeoffs with reduced power (45 lbs takeoff torque), there is an awful contradiction there - you might find that you would get better overall performance (a faster, shorter takeoff) and significant safety benefits if you tried a full power takeoff with flaps 10° instead.