• Aerosoft DHC-6 Twin Otter

    Aerosoft Twin Otter For FSX

    By Andrew Herd (2 March 2008)

    The success of the de Havilland Beaver led to customers asking if they did the same thing in a larger size, so the designers went back to the drawing board and came up with the DHC-3 Otter. This single-engined plane was powered by a Pratt & Whitney R-1340 and 465 were built, with the US Army being a major purchaser. The DHC-6 took the concept further, the result being a twin-engined, high wing monoplane powered by a pair of 550 hp P&W PT6A turboprops which went into production in 1965. DHC originally had their eye on the STOL civilian passenger market, but they sold a fair few for utility purposes, for example to the British Antarctic Expedition (largely because the plane is rated for operation in temperatures down to minus 75 centigrade) and quite a few to the military, production eventually ending in 1988. The initial model was the short-nosed series 100, available on wheels, skis or floats; then came the 200, which had a longer nose, improved baggage capacity and uprated engines; and finally in '69 came the 300, which had 625 shp PT6A27s. Just to confuse matters, the floatplane version of the 200 series retained the short nose. Overall, 844 hulls of all types were built and the majority remain in service, the type having found a niche that few other planes are available to fill, thanks to its rugged construction and its ability to haul 19 passengers out of small spaces. From a flight sim point of view, the great attraction of the Twin Otter is that high lift wing with its double slotted trailing edge flaps and drooping ailerons, which give it a great STOL performance.

    The Aerosoft Twin Otter is available as a 180 Mb download from the Pilot Shop. For this, you get four different versions of the plane: wheeled, on floats and on skis; and fifteen different liveries, including the Royal Norwegian Air Force, British Airways, Yeti Airlines, Air Moorea and a slew of others. I did the review using a 2.66 Core2Duo with 4 Gb of RAM and a 768 Mb GeForce 8800GTX running Windows Vista and FSX SP2. Frame rates were very good throughout and although there was a performance hit compared to the default planes, it was never large enough to be problematic.

    The download and installation went fine, creating the usual program group, which contains a 114 page manual, the first 31 pages of which are about the general operation of the plane, the remainder covering the avionics, the bulk of which is about the Bendix King KLN-90B GPS. For all that anyone who is familiar with the Caravan ought to be able to get it in the air, it is worth reading the documentation, not least because the Twin Otter has a relatively complicated panel compared to the default planes. But don't let that put you off, because this addon is as fun as all got out.

    The visual model is excellent, with some very fine detailing indeed and the developers have somehow managed the neat trick of making the interior visible without killing the frames rates dead. I do not know how the developers have managed to do it, but this is one of the few planes I have loaded in Flight Simulator that looks as big as it does in real life. Just about all the panel line detailing is there and the doors, wheels and control surfaces are particularly well done - if you drop the flaps, the selection of ironmongery under the wing is a sight to behold. The liveries are very good, none of the textures show blurring and the reflective shine isn't particularly overdone. All the usual animations are there, together with opening doors, the ailerons droop with the flaps and the interiors differ from plane to plane, where appropriate; the gear flexes and the nose wheel oleo compresses. One place where the animation departs from reality is that the flaps can only be lowered in stages, this being a limitation of Flight Simulator that has never been attended to by Microsoft - many aircraft, the Twin Otter included, allow you put the flaps wherever you want them and being limited to four stages isn't quite as real as it gets. The flap lever is up there on the overhead, together with the throttles.

    The last Twin Otter to grace Flight Simulator was published by Lago and it made its name as one of the most patched addons in FS history, with a flight model that took many attempts to get right, but by contrast, the Aerosoft package gets it right first time and flies just as you would expect a 6000 pound plane with a 65 foot wingspan and a high-lift wing to do. The real DHC-6 is an interesting plane to pilot, because for all its size, it combines seriously good short field performance with approach speeds comparable to those of a light aircraft and the sim correctly flies like a small twin. One thing to beware of is the temptation to dive-bomb on the approach, throttled right back with full flaps, because when you pull out, all that kinetic energy will translate into airspeed which takes a long while to bleed off, the result being an overshoot or a balloon and bounce. The other error the Twotter positively encourages you to make is to do the reverse - holding the nose up and mushing in with no reserve of airspeed left over the stall; this tactic results in a thrilling rate of sink and is liable to result in an undershoot. Either method is safe enough if you have to dump height early during the approach, just make sure that you have enough power on to keep the wing flying on short final and don't forget that hitting F2 will put you into beta (reverse) thrust, so you can stop on a sixpence. For what it is worth, the approach in a real Twotter is generally flown at 85 knots/flaps 20, going to full flap on short final if needed and touching down at 70 knots, but the sim gives a very convincing demonstration of what can happen when you get on the wrong side of the drag curve and the developers are to be congratulated on the flight model. While I am on the subject, there is nothing to stop you using beta thrust in the air, which can make for some nearly vertical approaches, but isn't exactly encouraged in the POH - and if you are very clever and remember that the pedals work in reverse when you are going the wrong way, you can even back the plane up.

    Aside from the beta range, the entire secret of the Twin Otter lies in the low loading of its advanced wing and those big flaps. At sea-level, the takeoff run is only 700 feet and the ground run is a paltry 515 - virtually the same as a Cessna 172, which is nearly four times lighter. Performance takeoffs in these planes are done by dropping twenty degrees of flap, applying full power and holding the yoke fully aft until the wheels come off, before pushing the yoke briskly forwards to gain flying speed. With a bit of practice, you will be surprised at the places you can get in and out of, particularly since the aircraft can climb out at an incredible angle.

    The sim has an excellent virtual cockpit, though it is slow to skin and lacks a 2D panel other that the 'strip' view gauges that all FSX planes seem to inherit. For once, the developers have set up the A key properly so that you can use it to cycle the view around the cockpit, the sequence being left hand seat, right hand seat, engine gauges and radios, throttles and flaps on the overhead, lighting and electrical panel, interior looking aft, interior looking forward, and a 'clean' view, which is where the 2D panel would show up, if there was one. Hitting W here will bring up enough gauges to keep you flying. As usual, the point of view (POV) feels as if it has been set a little too far forward, although this is more a limitation of the shape of computer monitors than anything to do with FSX; I have the left hand rocker on my CH Products yoke set up to move the POV backwards and forwards and it is the fastest way I know of solving this problem.

    The panel has gauges everywhere, but apparently Otters are famous for never having any two cockpits alike. In addition to the standard barometric version, there is a radar altimeter, an airspeed indicator, an HSI, a DI, transponder and an ADF, but no DME in the 200 series planes, and even though the Nav radios appear to have a DME setting it doesn't work in the sim. The function of the radios has been limited to tuning them using the mouse wheel - so if you don't have a mouse with a wheel, you won't be able to use them. The radios can't be tuned when the sim is paused and the click zones on the ADF are rather fiddly, but unless you insist on absolute realism, the units are fine - just a shame about the lack of DME. The 300 series planes retain the original ADFs, but have more advanced KX 165A radios, which are complex enough to merit their own appendix and they do have DME and just about every other function a 165A should have, including an on/off switch. The one big plus about the lack of a 2D panel and a properly set up A key is that the developers have had to think about panel operation and with the exclusion of the radios they have done well with the ergonomics; this is a sim designed for flying, not for book learning and it doesn't take long to get the hang of how everything works.

    The 300 series Twotters are fitted with a KLN-90B GPS which clocks up eighty pages of explanation in the manual - I haven't checked it against the functions of the real unit, but Dun Kuhn, who developed it, seems to have left no stone unturned and there isn't much that you could wish for it to do except make toast. The section in the manual does a very good job of describing the facilities offered by this unassuming little box and by the time you get to VNAV advisories on page 51, you will be beginning to get an idea of how much power it has on tap. I am sure that many simmers would wish for a more modern unit, but Twotters are ladies of a certain age and there are certain things they don't do, one of them being have ultramodern glass panels. Anyway, you are going to be using this sim to bang around out of bush strips and beaches and off grass and snow and you will be flying half the time with only the need to preserve your ass to guide you.

    The one area where the documentation could be improved is in illuminating the way the GPS, the KAS 297C control unit and the autopilot work together, because if you are used to the simplified FS default autopilot, the rather complicated relationship between these three will take a while to unpick. Most of the information is there, it just needs pulling together in one place so that it is possible to leave the plane to fly itself while you figure out how you are going to get down on a thirty foot strip with a forty five degree slope in a snowstorm. The KAS 297C is hidden away behind the right hand yoke, where many users will fail to spot it.

    The sound set is very neat and captures the bass howl of the PT6As very well, the overall effect being very atmospheric, especially when the weather is bad. One thing worth mentioning is that the float plane doesn't possess water rudders, which means that you will need to have a couple of levers allocated to the throttles on your yoke, or you won't have any steering worth mentioning while you are afloat.

    Verdict? Very good indeed, just about the only things which could be improved are the section of the manual describing the autopilot, the speed that the VC skins at, and if Aerosoft ever contemplate a patch, they might consider building in an 'expert' mode of operation, similar to the one in their Dornier 27. However, these are minor beefs when it comes down to it and I can recommend the Twotter to anyone - it makes a great pair with the Aerosoft Beaver and every bush simmer needs one.

    Andrew Herd
    andy@flightsim.com

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