B-17 and B-24: plausible upgrades?

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I guess Griffons would've made performers of any plane. The quirk was that it would take two stage versions, and even the UK was not exactly awash with those.
 
Indeed. One might contemplate 2 stage Packard Merlins on heavies, yet the turbo V-1710s seem like only engine that would provide both extra HP and numbers produced, for 1943-45.
 
While the trubo V-1710 B-17 was a viable option, it would have required two supply chains ... one for the radial engines and one for the V-12's. That is probably what doomed the XB-38. It WAS a better mousetrap in my opinion, but was it worth the expense of mechanic training and the spares / tools supply chain? My guess is "no," but I have no magic spyglass into the decision-making process.
 
There may not have been enough difference between them in everyday operations to make much difference.

http://www.zenoswarbirdvideos.com/Images/P-38/38SEFC.gif

http://www.zenoswarbirdvideos.com/Images/B-17/17SEFC.pdf

At MAX cruise (lean condition) the Allison is good for 795hp at 63 gallons an hour. The Cyclone is good for 750hp at 62.5 gallons and hour.

At MAX continuous (rich) the Allison is good for 1100hp at 113 gallons and hour and the Cyclone is good for 1000hp at 103 gallons an hour.

Is the reduction in drag good enough to increase the cruise speeds? The increase in power is marginal at best and power per gallon of fuel burned seems to be of no practical difference.
 

I would say that much of the aerodynamic drag advantage was lost because the V-1710 nacelle fitted onto the standard firewall. That is, the nacelle was actually larger than needed for the V-1710.

The problem with the XB-38 project is that it used radiators mounted in the wing leading edge between the inner and outer nacelles. This required modifications, and would have caused delays in production to implement. If the V-1710 was designed with the coolers all within the nacelle, and designed as a bolt up replacement the concept could have been explored further.

Also, regarding power numbers, one would think that even in 1942 it could be recognised that the the V-1710 had more potential for performance improvements.
 
That can't be the case.

The standard B-17G had top speed of 287 mph (up to 300 mph depending on who you believe) and a cruise speed of 180 mph.

The XB-38 had a top speed of 327 mph and cruise speed of 226 mph.

Speaks volumes to me of reduced drag with near equivalent power. The Allison engined version would have been better for penetration speed and carried an equivalent payload. The range was 3,300 miles which was better than the 2,000 miles for a standard B-17G.
 
The XB-38 was based on the B-17E which was being used as a pattern aircraft for the B-17F, neither of which had the chin turret. It is those to which the XB-38 should be compared, not the B-17G, which suffered an increase in drag due to the chin turret.
 
I like Bill's idea of fitting low drag remote turrets in place of the manned turrets/flexible gun positions of the historic B-17. I would ask if the system was reliable enough for an earlier introduction?

Perhpas something based around the P-61's turret? Or was that the same family as the B-29's turrets?
 
Cruise speeds without altitudes or power settings are near useless for comparison.

http://www.zenoswarbirdvideos.com/Images/B-17/17FOIC.pdf

Please note that the B-17F could fly at 149mph Indicated at 15,000ft ( 193mph true?) while burning 52.5 gallons and hour per engine.

OR 151mph Ind. at 20,000ft burning 71 gallons an engine per hour. Isn't that about 211mph true?

OR at max continuous (not really practical) 172mph Ind. at 25,000ft ( 258mph true) while sucking up 104 gallons an hour per engine.

The 300mph for a B-17G may be the speed when using WEP which for some "G"s gave them 1380hp at 25,000ft according to some sources.

The engines used in the XB-38 were supposed to be good for 1425hp at 25,000ft. They were the -89 model as used in the G H P-38s.

We should also compare apples to apples. One source (Joe Baugher"s website) gives the following performance for a B-17E and since the XB-38 was the 9th B-17E airframe (no chin turret and perhaps some other drag producing additions of the "G") it seems a fairer comparison.

"Maximum speed 318 mph at 25,000 feet. cruising speed 195-223 mph."

The XB-38 also crashed on the 9th test flight with about 12 hours of flying which may not have allowed for a full exploration of performance. Numbers given may have been estimates or may have been able to be tweaked (improved) with more time. I don't know either way.

I am not seeing a huge improvement here though.

True airspeeds are a rough calculation using about 2% per 1,000ft as in 20,000ft Indicated airspeed would be multiplied by 1.4, those of you who are pilots are welcome to correct the figures.
 
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The XB-38 with the Allisons was at least 25 mph faster than any other B-17. The cruise speed was at least 40+ mph faster, whatever the circumstance.

Ergo, it would have been a better penetrator by speed alone. Equivlent armament and bomb load. Better aircraft unless proven more vulnerable by combat, and it wasn't since they didn't produce it.

A lot of better aircraft also weren't produced, not just the XB-38. Personaly, I like the Beechcraft XA-38 Grizzly, but they only built two. Wildly capable but not proceeded with. Too bad.
 
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B-17's cruised at 180 mph. The XB-38 cruised at 226 mph. That's about 46 mph in my book, if not yours. No B-17 was much faster than about 300 mph in actual combat trim.

Facts speak well, and the Allison engined version was faster and carried the same or greater load, depending on whom you believe. I beleve it was. It was better but not produced ... like the He 277.

You are free to disagree ... in good humor, hopefully.
 
Looking at the numbers on Wiki the R-2000 gained about 150hp over the R-1830, and around 300lbs. Is changing the B-24 from R-1830s to R-2000s going to be worth it?
 
From what I can gather, non-turbo R-2000 offered about 10% more power at max continuous setting vs. non-turbo V-1830.

The (Allison's?) proposal, B-24 with V-1710s. Too little cooling capacity for my taste, but worth a look:



Wuzak, do you know anything about speeds of Halifaxes with different turrets, and/or any other aerodynamic improvements?
 
There is another aspect to bear in mind.

RAF Halifax crews found that, once later models had improved speed and lighter weight with the removal of the front turret etc, Bomber Command said, excellent, so they can carry a greater bomb load at the original speed and height. The RAF calculated in terms of tons of bombs not in numbers of aeroplanes.

Would the USAAF not go down the same road if the improvements let them? They were already embarrassed by the 'teeny weeny' bomb loads compared to RAF night bombers over the same target.

There is a story (almost certainly apocryphal) that, when the first Flying Fortresses were being delivered to the RAF, a company representative was extolling their virtues at a FAA mess on an RAF station. He boasted that they could carry 4,000lb of bombs to Berlin or 8,000lb to the Netherlands on their 4x1,000 bhp engines. The FAA crews gently pointed out that their 4 1,000 bhp engines, on 4 Swordfishes, already flew 8,000lb to the Netherlands so it didn't seem that much of a step forward.
 
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How about lifting power?
The whole object is too get as many bombs dropped on the enemy so, while speed is good, you need to maximise the ability to get bombs in the air.
Four Merlins could lift a larger bomb load than the B17's, and yes I know the Lancaster was not as heavily armed so there was more bomb weight capacity.
Does anyone know if Boeing experimented with Merlins on B17's? I cannot find any evidence to suggest they did....
Cheers
John
 
The turbo V-1710s were offering 1325 HP for take off from mid 1942 on, and 1425 from mid 1943 on. That would be some 10 and 20% more than historic B-17s and B-24s have had on tap.

No Merlin Fortresses were ever tested, I'm afraid.
 
The B-17 started at 26,520 pounds empty, 37,000 pounds gross, 45,650 pounds (Y1B-17A)

Went to: 29,021 pounds empty, 39,320 pounds gross, 49,650 pounds maximum. (B-17C)

Jumped to: 32,350 pounds empty, 40,260 pounds gross, 53,000 pounds maximum (B-17E)

And finished at: 32,720 pounds empty, 55,000 pounds normal loaded, 72,000 pounds maximum. (B-17G)

A few structural modifications and beefed up landing gear along the way. Bomb Bay fit between wing spars so it was limited in length.

On lot of these big bombers (especially ones that grew in weight) you cannot stick what ever you want, where ever you want.

From the B-17 Manual:

A) B-17F airplanes, with modified landing gear
and added chord-wise wing tip tanks, can be flown up to
and including a gross weight of 64,500 pounds, with
the following restrictions:

(B) At 64,500 pounds,the extra wing tip tanks
must be full to obtain the effect of a relieving load on
the wings in flight. Care must be exercised in taxying
avoiding rough ground. Take-offs, above a gross
weight of 56,000 pounds may be made only on smooth
fields or prepared runways. All pivot turns on one
wheel, while taxying, will be avoided.
(C) All B-17 type airplanes, equipped with extra wing tip
chord-wise tanks, must be operated in accordance
with (B) preceding, whenever the wing tip
tanks are more than half full. Maximum permissible
indicated air speed of B-17F airplanes, with extra
wing tip tanks full, must be limited to 230 mph, when
loaded to 64,500 pounds. Maximum maneuver permissible
at 64,500 pounds; positive, 2.056; negative,
1.22; landing gear, 2.1.

A B-17 running light (40-45,000lbs) could hit 226mph at sea level (true and indicated speeds the same?) using max continuous power. A B-17 at 53,000lb could probably pull a 2.5 G maneuver and in the low 40s it could pull 3 "G"s.

Even if you increase the power you are starting to run in "placard" limits that restrict the actual performance increase.
 
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