How to estimate performance difference of R2800-41/43 equipped B-26B compared to R2800-5

[Greg Boeser]

I have several Martin B-26 manuals, but none has data for the short winged models equipped with the R-2800-41/43.
I see looking at the engine charts that the -41/43 uses much more fuel than the -5, but how would performance be different.
Climb rates, max speed, etc? Comparing the later long wing models won't work, because they were larger and heavier.
I'm trying to determine the performance curves of the B-26B to B-26B-4 as used in North Africa. Any help would be appreciated.

 

[wells]

T.O. 01-35EA-1 RB-26 26A and B-26B Airplanes Pilot's flight operating instructions

Charts for both engines

 

[Greg Boeser]

Yes, I've seen that. That is useful for the performance of the B-26 and early B-26B aircraft used in the Pacific, but does not give me information on how the upgrade to the more powerful R2800-41 and -43 engines in the later blocks of B-26B (through block -4), as used in North Africa, affected performance. The manual I have for the post-July 1942 modified B-26B, which includes the armament upgrades, only contains flight performance data for the R2800-5 engine.

 

[wells]

Hmm, I'm confused. You want performance data for short wing version with upgraded engines. The charts are in the manual I posted the link to. Climb performance with -5 engines is on page 38. Climb performance with -41/43 engines is on page 39. Speed performance with -5 engines is in the flight operation instruction charts ( pg 41-43 ) and with the -41/43 engines ( pg 44-47 ). If the airplane had -41 or 43 engine, it was a B-2 or B-3, so I'm not sure why you think those charts don't apply. The manual also describes the 4 blister guns ( B-4 model ), so the block numbers you are interested in are inclusive. You will need to determine the weight of the airplane, depending on armament configuration. That's the only factor affecting performance, besides engine power.

 

[Shortround6]

It might have affected take-off to some extent. after that any increase in power was probably used up by weight (drag) increases.

While take off power went from 1850hp to 2000hp (at an increase of 100rpm) the power at altitude didn't quite follow suit.

Military power went from 1850hp at 2700ft to 2000hp at 1500ft and since you loose about 2% of power per 1000ft you are down to around 1950 at 2700ft ???
High gear went from 1500hp at 14,000ft to 1600hp at 13,500ft.

These are the 5 minute ratings. the more important max continuous rating (used for climb)
went from 1500hp at 7500ft to 1600hp at 5700ft both at 2400rpm in low gear and slowly decreasing (2% per 1000ft?) as the plane climbed higher.

In high gear the early engine was good for 1450hp at 2400rpm at 13,000ft and the later engine was rated the same.

SO unless you are at low level (under 5-6000ft) and pushing the engines at or beyond max continuous I doubt you are going to see much change in performance.

edit, I would also note that that in the hot dessert conditions the extra power probably evaporated like spilled gasoline and the higher rated power engines would be lucky to offer the same performance as the older engines would in a cooler climate. Granted the older 1850hp engines wouldn't give full power in hot conditions either.

 

[Greg Boeser]

Oops. Sorry, Wells. My eyes saw, but my brain failed to register. I thought you posted an older manual.
Thanks.

 

[Greg Boeser]

Shortrounds, thanks for the commentary. The earlier planes were used in the Pacific, mostly New Guinea and the Solomons, so temp-wise it was pretty close. The Aleutian boys of the 28th Group may have experienced a bit better performance then?

 

[Greg Boeser]

T.O. 01-35EA-1 RB-26 26A and B-26B Airplanes Pilot's flight operating instructions

Charts for both engines

This is exactly what I was looking for. Thanks again.