Twin Otter gross weight rationale?

bodyflyer · Post by **bodyflyer** » Thu Sep 27, 2007 6:49 am

Anyone know why the gross weight for the Twin Otter goes from
11,579 lbs for the -200
to
12,500 lbs for the -300?

The simple answer is the bigger engines.
But specifically, what allowed the increased gross? Is the structure still the same? (Eg, I vaguely heard that the life limit on the -300 wings is lower.)

Otherwise, is there some specific performance standard, which the -300 was able to attain at higher weight?

So, for example, if a -200 were being flown a little heavy, would the consequences be only the more obvious ones like lower fatigue life, climb rate, and single engine performance? Or is there something else involved?

I'm not trying to get into issues about the the 12,500 lb certification limit, or higher gross weights used for ferry permits or the military. Although details of those might shed light on what the critical aspects of Twin Otter performance are at high weights.

CAL · Post by **CAL** » Thu Sep 27, 2007 9:43 am

How does Borek get approval for them up to what is it 17k?

oldtimer · Post by **oldtimer** » Thu Sep 27, 2007 7:59 pm

I am not an expert by any streach but if I remember, when the DHC-6 was first built and certified, it was done in Canada which did not have as sophisticated a certification process as we now have and the 19 seat airliner industry was just being developed. With the advent of the market and new rules, the -300 was developed to fill a need. Most Twin Otter's were not built solely for the bush market but rather as a commuter airliner because there was nothig else available that was turbine powered and could be bought new. Then along came airplanes like the Beech 99 and early Merlins which pushed the Twin Otter into history because it was slow and non pressurised and who needs STOL when you have a long runway. 12,500 lbs is the max allowed MTOW for a normal category or small airplane. After that it is a transport category. At least this is what I remember.

NWONT · Post by **NWONT** » Thu Sep 27, 2007 8:21 pm

You are right on oldtimer. A Twin otter was equipped with 20 seats but, at the time, if you filled more than 19, I believe you must use a flight attendant. Also, an aircraft must pass certification testing at 1.5 times the desired TOW. So if you wanted an aircraft to be certified at 10,000 Lbs GTOW, it must be tested and pass at 15,000 Lbs.

twotter · Post by **twotter** » Fri Sep 28, 2007 4:59 am

CAL wrote:How does Borek get approval for them up to what is it 17k?

I believe it's 17.5K and it's only for ferry flights. There are a couple ferry kit's you can put in to do this. It brings you up to 9000#'s of fuel so @ say 600#/hr you can do the math..

Way longer than my ass could stand to sit in that seat!!

Sure shows what the airplane is really capable of.

CID · Post by **CID** » Fri Sep 28, 2007 6:41 am

12,500 lbs is the max allowed MTOW for a normal category or small airplane. After that it is a transport category. At least this is what I remember.

There's also the commuter category that allows for over 12,500 pounds.

bodyflyer · Post by **bodyflyer** » Fri Sep 28, 2007 7:01 am

oldtimer wrote:when the DHC-6 was first built and certified, it was done in Canada which did not have as sophisticated a certification process as we now have

For what it is worth, a US type certificate data sheet on the web shows that it was certified under the old CAR 3 rules (before FAR 23 etc). But some newer rules may apply - the sheet shows that certain newer rules supplements are required to be followed if used for FAR part 135 flying.

Daart · Post by **Daart** » Fri Sep 28, 2007 8:27 am

I once asked a good friend of mine, who is an A.M.E., and owns Otters the same question. His answer was that 200's and 300's are completely different animals. Skins are thicker, basically the whole structure is beefier on the -300 allowing the higher gross weight.

oldtimer · Post by **oldtimer** » Fri Sep 28, 2007 8:56 pm

Commuter Category came into being in 1992, before that there was US sFAR 41, which came into being in 1985, long after the Twin Otter was certified.
After 19 paying passengers, a flight attendent is required.
CAR 3 was the US certification standard before the FAA, which came into being shortly after the Twin Otter was first built.
I think the -300 is done as a STC, in other words, a factory modified airplane. A very common procedure.
I understand Viking is doing the -400 as an STC for the new engine and glass panels, but otherwise, same old, same old.
Sell a bunch and make hockey socks full of money and maybe they will consider recertification. I think that would be a very big (read expensive) undertaking.

twotter · Post by **twotter** » Sat Sep 29, 2007 12:47 am

Daart wrote:I once asked a good friend of mine, who is an A.M.E., and owns Otters the same question. His answer was that 200's and 300's are completely different animals. Skins are thicker, basically the whole structure is beefier on the -300 allowing the higher gross weight.

Bullshit.. There are minor structural differences but the main one is the wings..

CID · Post by **CID** » Sun Sep 30, 2007 7:58 am

oldtimer,

Yes, I understand the history of the commuter category. Just throwing in what is available now.

As far as the -300 being an "STC", unlike the CV-580, the -300 is a type certificated variant.

Bullshit.. There are minor structural differences but the main one is the wings..

Yes. And everyone knows that the wings are just minor structures.

twotter · Post by **twotter** » Sun Sep 30, 2007 5:29 pm

In the fuselage..

sarg · Post by **sarg** » Mon Oct 01, 2007 8:05 am

If memory serves the -300's designed for a higher structral weight, thence the military operating at a higher gross. Under the reg's of the time though any aircraft certified to a gross wieght higher than 12,500 lbs. required 2 crew at all times which most civilian operators didn't want to deal with.

bigpinky · Post by **bigpinky** » Tue Oct 16, 2007 12:59 pm

So whats the actual GWT if all this mumbo jumbo about certification was to be discarded? Or in other words-how heavy have you flown it?

North Shore · Post by **North Shore** » Tue Oct 16, 2007 1:05 pm

Well, if you can get ferry permits up to 17,500lb, then that's your answer..

just curious · Post by **just curious** » Tue Oct 16, 2007 2:52 pm

Having said that, at ferry weight, it doesn't quite fly like a twin otter.

It's more like geting up in the morning, walking over to your bedroom window, and trying to fly your house.

It'll fly, but if you ever try this while doing stuff a twin otter was designed to do- take off on a 500 foot strip fer instance, you're gonna die.

Rowdy · Post by **Rowdy** » Tue Oct 16, 2007 4:29 pm

just curious wrote: It's more like geting up in the morning, walking over to your bedroom window, and trying to fly your house.
.

Ohh man.. Classic! Thanks JC

Blakey · Post by **Blakey** » Tue Oct 16, 2007 5:04 pm

just curious wrote:It'll fly, but if you ever try this while doing stuff a twin otter was designed to do- take off on a 500 foot strip fer instance, you're gonna die.

What, you mean like trying to take off over a 100' iceberg grounded right at the end of the strip?

Like this: http://aviation-safety.net/database/rec ... -2&lang=fr

just curious · Post by **just curious** » Tue Oct 16, 2007 7:43 pm

Harsh, but, yes.

sprucemonkey · Post by **sprucemonkey** » Wed Oct 17, 2007 3:47 am

twotter wrote:
CAL wrote:How does Borek get approval for them up to what is it 17k?
I believe it's 17.5K and it's only for ferry flights. There are a couple ferry kit's you can put in to do this. It brings you up to 9000#'s of fuel so @ say 600#/hr you can do the math..

Way longer than my ass could stand to sit in that seat!!

Sure shows what the airplane is really capable of.

Well, from the report, we can determine that it will SINK at 18,500 lbs after takeoff so......18,000lbs max???