Tora Zeros, why the geared 1340?

[famvburg]

I've been watching re-runs of "Black Sheep Squadron" on RTV on the weekends. I remember reading in the past that the Harvards had geared 1340s installed as part of their Zero mods. I did a search or two here but didn't find anything. So, why did they put geared 1340s on the Tora Zeros? What did it improve over a straight 1340?

Last edited by famvburg on Sun Mar 27, 2011 8:12 am, edited 1 time in total.

[Warbird Kid]

I guess my question to add to this is: what's the differences between a regular 1830 and a geared 1830?

My only thought is that maybe they needed the extra power to tangle with the P-40s when filming Tora?

[snj-5]

Probably done for looks more than anything else (so they could use a 3-bladed prop, that would make it look more like a real Zero).

Bela P. Havasreti

[Matt Gunsch]

The geared nose case is longer and gets the prop out further from the cowl so it has more of a Zero look to it, a added benefit is allowing the use of a 3 bladed counterweight prop that increases speed a bit, but really helps in formation and acro.
The snarl you hear from a T-6 on take off is the blade tips going supersonic, and the prop is not pulling thru the air, as much as beating the air. The geared engines are much more efficient at take off since they have more blade area, and are turning the prop at a lower RPM, where the prop can bite the air.

[Jerry O'Neill]

I don't think all the Tora Birds had Geared engines. I know some did, including some Kates & Vals, but there are many photos of the two bladed set up on all three types during the filming.
I think it was a mixed bag.
Jerry

[Invader26]

No such thing as an un-geared 1830.

The R-1340 geared engine was used in numerous Tora Zeros to give a closer look to the real thing which was fitted with a geared 14 cyl Sakae radial driving a three bladed prop.

Others were fitted with R-1340-AN1 engine prop combo same as T-6. In the flight scenes look OK. Some geared Tora Zeros were retrofitted sometime in their lives with -AN1 I guess as a simplification when engine popped or was due overhaul. My old Tora Zero A-110 in the movie has the geared engine. Runs sweet as a nut and much smoother than two blader.

[famvburg]

I see. I didn't know you couldn't run a 3 blader on a straight 1340, I guess that's why we don't see more then. I always figured if you could run a 2 or 3 blader on a 985, the same would be true for a 1340. This brings up another question. Why can't you run a 3 blader on a straight 1340?

[51fixer]

I see. I didn't know you couldn't run a 3 blader on a straight 1340, I guess that's why we don't see more then. I always figured if you could run a 2 or 3 blader on a 985, the same would be true for a 1340. This brings up another question. Why can't you run a 3 blader on a straight 1340?

The 3 blade props on the 985s are Hartzell made for the 985s 30 spline prop shaft. Originally they used the Hamilton Standard 2 blade props in either 2 speed or constant speed set ups.
The 1340 has 2 different nose case set ups. The non geared engines use a crankshaft in which the 40 spline prop shaft portion is a part of the crank.
The AN2 versions of the engine feature a set of gears in the nosecase and separate the prop shaft from the crank. I believe it is still a 40 spline shaft and I've seen 3 blade counterweighted and oil driven hydromatic Hamilton Standard Props used.
The props are all engineered for the application. The blade areas, airfoil design as well as the diameter are all parts of designing a prop that will allow the engine to make its rated horsepower and turn that power into thrust in a way that is safe and will last a long time.

[Invader26]

you can run a three blade prop on an AN-1.

T-6 here in Brisbane has one.

[AvroAvian]

you can run a three blade prop on an AN-1.

T-6 here in Brisbane has one.

That's right. See http://jetphotos.net/viewphoto.php?id=6861396&showexif=1 and http://www.sandoraaviation.com/The blades are considerably shorter and as a result, don't go supersonic.