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Confusion with Twin Otter Max Cruise Perf Tables

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This refers to the following two tables in the "Vol 4 - Data.pdf" document.

Here is a link to the two tables in question....

 

Twin Otter Max Cruise Performance


Can someone explain the difference between these two tables for 7,400 lb weight.

The only difference between the two tables at that weight is 1 psi torque, but the air speed and fuel flow are very different in each table.

If Np, temperature, pressure altitude and torque are the same... why the two tables & why the big difference in speed?

 

What am I missing?

Many thanks.

 

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Based solely on your attached copy of a portion of the manual, it's likely one is for the -100 and the other for the -300 (550 compared to 650 SHP). The labels may be missing in the manual included with the product. My computer with the entire manual is in storage during a move until early August, so I can't say for sure if there are missing labels.

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That would seem to make sense.

What makes me wonder is there is only one set of take-off, climb & landing data, but there are three tables for Max Cruise @ 2000 RPM. Strange.

Unfortunately they aren't labeled distinctly so it's all very confusing.

 

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In reviewing open questions on the Twin Otter, I returned to this one and suddenly remembered the manuals are on-line on the shop page. On quick review and as I suggested, one set of tables is for the 100 and the other for the 300. The "tell" is torque at max cruise thrust. At max continuous, the -100 engines are limited to 42.5 psi on the torgue gauge, while the -300 engines are limited to 50 psi (page 4-1-1). You can see the difference at the sea level settings. Floats and skis likely explain the other variances, with floats producing the slowest cruise TAS.

 

So I'd say what happened is the labels were somehow excluded during formatting. I'm not sure what it would take to get them updated. Without Adobe Acrobat, I can't directly edit the tables, but maybe I can figure out another way. Meanwhile, I'll try to come up with a performance chart supplement that tells users what condition applies to what page.

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Thanks Herman - That would be super helpful.

As they are at the moment, the tables are really confusing.

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