Single vs twin row

[rogerwilko]

Was there any particular durability difference between the Pratt and Whitney twin wasp 1830 and the wright cyclone 1820. Seems the 1830 would be much more expensive to manufacture considering the same horsepower output?

 

[gjs238]

Could the 1830 manage more RPM?

 

[Shortround6]

Depends on the year/model.

The early R-1830s were rated at 2400rpm (a few prototypes may have been run at 2300rpm?) then they went to 2550rpm and then to 2700rpm for take-off and 2550rpm for max continuous. Last models were good for 1350hp at 2800rpm for take-off.

The R-1820 started at 1900rpm of direct drive and 1950rpm for the geared engines in 1930, went to 2100rpm take-off and 1950rpm M.C. (max Continuous) then 2200rpm T.O. and 2100rpm M.C. After going through the E,F,and G models you get to the G100 series which was good for 2350rp for take-off (mostly), the G200s were good for 2500rpm (again, mostly) and the "H" series engines went 2600rpm for 1300-1350hp, 2700rpm for 1350-1425hp, 2800rpm for 1425-1525hp (post war engines and using up to 115/145 fuel) most of these last engines went about 1400lbs, the 1900rpm engines could be as light as 850lbs with direct drive.

The R-1830 was supposed to be smoother and transmit less vibration to the airframe. It was smaller in diameter and had less frontal area.

Since each type was built in dozens of different models with different crankcases, cylinders, bearings and what not it gets very hard to generalize about the series as a whole.

 

[GregP]

The R-1820 generally had a takeoff RPM pf 2,200 while the R-1830 generally had a takeoff RPM of 2,700. This varied a bit with dash number.

If you check the USAAF Statistical Digest of WWII, the average man hours expended on an overhauil for the R-1820 was 129 hours while the average for the R-1830 was 188 hours. These are averages for the entire war.

The TBOs were set by the USAAF, not by condition of the engines. When they reached recommended TBO they were replaced and the engines were rotated back through depot for overhaul.

Most of the people I know who fly both prefer the Pratt for flying and the Wright for overhaul costs ... fewer cylidners means fewer parts and less time. I don't see a LOT of difference between them, performance-wise. The Pratt was smoother. Dry weight was within a stone's throw of each other with the Wright at 1,184 pounds and the Pratt at 1,250 pounds.

Looks like they delivered about 121,000 R-1820s and about 160,000 R-1830s during the war years.

All in all they seem like pretty good engines.

 

[kool kitty89]

From the engines I've seen actual performance details on, the single stage R-1820s tended to have somewhat better altitude performance than similar 1830s (plus 2-speed models were in production earlier and more common). The 1820 never got a 2-stage supercharger AFIK, but did get models with further increases in power from RPM and boost pressure increases with or without water injection. The existence of the R-2000 may be one reason such wasn't pursued on the 1830, but I'm not sure.

On aircraft where the smaller diameter of the 1830 was of little benefit, the advantages of the 1820 may have outweighed any small benefit of the smaller cowling and smoother operation of the 1830. (the Dauntless and Wildcat both come to mind, more so the latter with its barrel shaped fuselage significantly bulkier than the F2A's at its widest -the Buffalo didn't bulge out much more than the engine cowling, while even the R-1820 powered Wildcats showed a good bit of curves around the mid-section of the fuselage -cockpits aside in both cases) I do wonder if the Buffalo might have benefited more from the R-1830 than the Wildcat did. (even the single-stage ones, which were after all lighter, and that smaller plane never did cope well with weight gains)

 

[Shortround6]

The Wright Cyclone was about the longest lived large piston engine going production wise.

See; http://www.enginehistory.org/Wright/Cyclone9Facts.pdf

Including the predecessor P-1 (R-1634) the Cyclone was built for 39 years. Counting just the R-1820 it went 33 years. Of course nothing remained of the early engines on the late ones except the bore and stroke. Please note weight went from 850lbs to 1484lbs.

We really have to be careful to compare particular models.

 

[kool kitty89]

The Wright Cyclone was about the longest lived large piston engine going production wise.
...

We really have to be careful to compare particular models.

Indeed, with such a long evolution, a great deal changes and only relatively similar aged models will share much in common. (even then some older models may remain in production for extended periods so long as the lower weight/power is marketable) I'd expect some of the mounts and peripheral connectivity would be more universally compatible, though shifting weights would obviously be a concern.

 

[GregP]

At the museum, our 1820s and 1830s are both reliable and we can get parts for either when required. They are very good engines. All radials last a LOT longer if you treat then gently. They do NOT like to change rpm, so taxi with the brakes, not throttles. Make rpm changes gradually except for takeoff and watch the mixture, as on any engine. Radials do NOT like low-power, high-speed descents. It cracks cylinders from shock cooling.

Both have decided ways to achieve a good starting process and they aren't quite the same.

I'd fly behind either one and have behind both. Great engines, both, if treated with respect, and long-lasting.

 

[rogerwilko]

What was the unit cost difference?

 

[Shortround6]

What was the unit cost difference?

Again it varies by year and model of engine. One would guess that the Cyclone was always cheaper as making fewer but larger parts is generally easier than making more but smaller parts. However different tooling and manufacturing methods can change things, at least until the other company catches up or thinks up something new.
Castings vs forgings or how many machining operations were needed on certain parts. Very large production runs are cheaper than small ones.