High Altitude Heavy Bomber for RAF (1 Viewer)

[Alan Stevens]

The standard B-36 in typical war dress could cruise at 40,000 feet.

But for how long? Featherweighting greatly increased the range at that altitude.

 

[RCAFson]

If you put in more powerful engines but don't increase the fuel load you get shorter range.

A lot of these bombers had operational ceilings thousands of feet lower than their 'service ceiling'. A lot depended on weight and some times the "book' weight was way under what they actually operated at. Some B-29s were taking off 13-15,000lbs heavier (overload) than gross weight. They were not burning off all the extra fuel just taking off and getting to cruise altitude.
Same goes for the British 4 engine bombes just not quite as extreme.

Another factor is when did they discover they needed a pressurized crew compartment at around 30,000ft? They developed the pressure cabin in the Wellingtons with a goal of 40,000ft.
The B-17 was supposed to operate above 30,000ft but................they couldn't. The Plane would, with some difficulties, but the crews could not. Oxygen masks and heated suits worked for a few hours, not 5-8 hours at the high 20s and low 30s. They needed pressure cabins, just not quite as much as flying at 40,000ft but you have to know that at the design stage or early development stage, and you have to be OK with dropping the big bomb at a lower altitude and having a lower impact speed (less penetration) or.................you need the heavier pressure cabin and the fancier engine installations to not just reach 40,000ft but actually operate at 40,000ft.

Pressure suits would have allowed very high altitudes in unpressurised cabins.

 

[Thumpalumpacus]

Could they use a Vulture for an auxiliary blower engine? With Merlins or Griffons for the main power.

The Vulture was used to drive the experimental 2-stage superchargers for the Merlin, IIRC.

Would you want an engine prone to overheating to be buried in the center of your fuselage?

 

[GrauGeist]

But for how long? Featherweighting greatly increased the range at that altitude.

The Featherweights came about around 1953 or so.
Prior to that, very few fighters of any nation were capable of reaching 40,000 feet and remaining stable enough to conduct an intercept.

As jet fighters improved.in performance, the decision was made to strip the B-36 of all defensive positions (and their crew) save for the tail turret as well as removing armor (as mentioned earlier) which allowed the Featherweight variant to operate above any known (at the time) interceptor.

The advantage that the B-36 had (in any form), was that it's wingspan and area made it very adapted to extreme altitudes.

 

[ThomasP]

B-36A and B models with a 10,000 lb bomb load could barely reach 40,000 ft at about half fuel and maximum power. Normal power Service Ceiling was about 35,000 ft at the same weight. ROA was about 4000 miles with a 10,000 lb bomb load and full fuel, so you might be able to trade some fuel and range for a higher drop altitude over target.

I think the B-36D-III were the first of the 'Featherweight' variants. Note that the D models had the additional 4x jet engines fitted and IIUC these were used over target to gain drop height.

The above info is from tha B-36A and B SACs dated 1949-1950 and B-36D-III from 1955.

 

[Shortround6]

Douglas did get the XB-19A close to 40,000ft (39,000ft) using four Allison W-3420-11 engines with turbos, maybe somebody has got the weight?

2600hp from each engine and with the turbos it could make 2100hp per engine at max continuous at 25,000ft.
Max speed was 265mph at not listed height. It could carry the weight and carried an awful amount of fuel for long range. A European bomber could be smaller/lighter.
It did not have pressurization. It had an enormous wing (4285sq ft) of late 30s airfoil and flaps. Around 2 1/2 times the size of a B-29 wing.
It was used somewhat for engine testing for the XB-39 program.

Interestingly while the XB-39 was a lot faster (405mph) it's service ceiling is listed as being 4,000ft lower (35,000ft)

Again a smaller/lighter plane (fewer guns and less fuel) could do better. But you need a propulsion system in the same area as the turbo V-3420s.
Eight Merlins (coupled in 4 power units if you wish) or 6 two stage Griffons or 6 Vultures or 6 Centaurus engines?

 

[SaparotRob]

Douglas did get the XB-19A close to 40,000ft (39,000ft) using four Allison W-3420-11 engines with turbos, maybe somebody has got the weight?
View attachment 836746
2600hp from each engine and with the turbos it could make 2100hp per engine at max continuous at 25,000ft.
Max speed was 265mph at not listed height. It could carry the weight and carried an awful amount of fuel for long range. A European bomber could be smaller/lighter.
It did not have pressurization. It had an enormous wing (4285sq ft) of late 30s airfoil and flaps. Around 2 1/2 times the size of a B-29 wing.
It was used somewhat for engine testing for the XB-39 program.
View attachment 836747
Interestingly while the XB-39 was a lot faster (405mph) it's service ceiling is listed as being 4,000ft lower (35,000ft)

Again a smaller/lighter plane (fewer guns and less fuel) could do better. But you need a propulsion system in the same area as the turbo V-3420s.
Eight Merlins (coupled in 4 power units if you wish) or 6 two stage Griffons or 6 Vultures or 6 Centaurus engines?

When were the W-3420's trialed in the B-19?
The coupled power units made me think about other planes. Besides the He-177, the Bristol Brabizon came to mind. How was its performance compared to these high altitude/long range military aircraft? I'm not suggesting a military role for this plane. Just curious how this civilian super prop's performance would compare.

 

[MikeMeech]

When were the W-3420's trialed in the B-19?
The coupled power units made me think about other planes. Besides the He-177, the Bristol Brabizon came to mind. How was its performance compared to these high altitude/long range military aircraft? I'm not suggesting a military role for this plane. Just curious how this civilian super prop's performance would compare.

Hi
Data for the Brabazon, from 'Bristol Aircraft since 1910' by C H Barnes:

Design of this aircraft took account of Bristol's work on the 100-ton Bomber project of 1942, engine choices being six Centaurus, eight Griffons or eight Centaurus, with various airframe layouts with engines inside the wings. Comparison with Brabazon below:

Another option below:

Mike

 

[Shortround6]

When were the W-3420's trialed in the B-19?

Some time in 1943.

The coupled power units made me think about other planes

The Allison 'coupling' was a lot simpler than the DB 606/610. The DB coupled engines could shut down one side and decouple it from the prop. The Allison kept both crankshafts geared together at all times. Allison also used one big supercharger at the back and not one on each 12 cylinder engine.

I will note that the Brabazon I (radials) weighed more empty than a B-29 did overloaded or about twice as much loaded or around 4 times what a Lancaster/Halifax/Stirling did.
You better make sure your sums (math) is correct

 

[wuzak]

Some time in 1943.

The Allison 'coupling' was a lot simpler than the DB 606/610. The DB coupled engines could shut down one side and decouple it from the prop. The Allison kept both crankshafts geared together at all times. Allison also used one big supercharger at the back and not one on each 12 cylinder engine.

The Allison was a single engine, whereas the DB 606/610 were separate engines joined at the gearbox.

The DB 606/610 was complicated a bit by the DB series having side mounted superchargers, which meant for the coupled units they had to mirror the supercharger, and maybe other accessories, on one half of the engine unit.

 

[wuzak]

To be clear, the 40,000ft requirement is something that would be asked for by MAP, but it might not have been achievable.

Many (most?) performance requirments for aircraft in the WW2 period were not met.

 

[don4331]

The Allison was a single engine, whereas the DB 606/610 were separate engines joined at the gearbox.

The DB 606/610 was complicated a bit by the DB series having side mounted superchargers, which meant for the coupled units they had to mirror the supercharger, and maybe other accessories, on one half of the engine unit.

There are advantages advantage and disadvantages for both the Allison and DB solution to the issue. And the Allison is still very much 2 - V-1710s connected than a single engine.

Allison had issues with the distribution of the intake charge split from the single supercharger to the individual manifolds.​

Let's not forget that 40% of the P-75 DV-3420s failed in flight (OK, 2 of 5 aircraft is a small sample, but it doesn't indicate Allison had the solution completely under control)

 

[special ed]

The Featherweights came about around 1953 or so.
Prior to that, very few fighters of any nation were capable of reaching 40,000 feet and remaining stable enough to conduct an intercept.

As jet fighters improved.in performance, the decision was made to strip the B-36 of all defensive positions (and their crew) save for the tail turret as well as removing armor (as mentioned earlier) which allowed the Featherweight variant to operate above any known (at the time) interceptor.

The advantage that the B-36 had (in any form), was that it's wingspan and area made it very adapted to extreme altitudes.

Your observation about an interceptor being stable at that altitude, reminds me of one of many briefings given cadets as motivation building. I may have mentioned this in another thread, so be forgiving. The time was summer 1960.
A USAF Major was telling of an encounter over the pole into Siberia. Routine missions in an RB-47E to check the USSR inventory and reactions of northern bases. He said all previous trips they could see below, MiG-15s taking off but they never reached any where near the B-47 altitude. We didn't ask how high, as this was within our Top Secret classes. The particular event in question, which eliminated further flights of this sort, three MiG-15s continued climbing while the others had reached their limits. Eventually two stalled out, spun down, while the third finally made to the altitude of the B-47. The pilot was described as wearing leather WW2 style helmet and mask. The Russian formated along side, the Major describing rapid considerable aileron deflections to keep from stalling, and pointed at the B-47 and using his thumb motioned for them to go back.
As a dumbassed 19 yearold who KNEW about aviation, I asked, "What did you do?"
The Major said, "We got the hell out of there."
I said, "But Sir, he flew along side because our wake turbulence would have caused him to stall, and if he had guns, if he fired them, the recoil would have slowed him, he would have stalled, so there was little danger."
"We didn't give a damn about all that, we got the hell out. Nobody had ever got that high before."
That's why he was a Major and I wasn't.

 

[Alan Stevens]

Douglas did get the XB-19A close to 40,000ft (39,000ft) using four Allison W-3420-11 engines with turbos, maybe somebody has got the weight?

2600hp from each engine and with the turbos it could make 2100hp per engine at max continuous at 25,000ft.
Max speed was 265mph at not listed height. It could carry the weight and carried an awful amount of fuel for long range. A European bomber could be smaller/lighter.
It did not have pressurization. It had an enormous wing (4285sq ft) of late 30s airfoil and flaps. Around 2 1/2 times the size of a B-29 wing.
It was used somewhat for engine testing for the XB-39 program.

Given its massive size, weight (over 160,000 lbs at takeoff), and relatively modest climb rate for the era, it likely took well over an hour—possibly 90 minutes or more—to reach that altitude under ideal conditions. And that's assuming it was lightly loaded and flying in a test configuration, not a combat one.

This wasn't a nimble climber—it was a flying laboratory, and getting to 40,000 feet was more about pushing the limits of engine performance and airframe endurance than speed.

 

[Alan Stevens]

.Your observation about an interceptor being stable at that altitude, reminds me of one of many briefings given cadets as motivation building. I may have mentioned this in another thread, so be forgiving. The time was summer 1960.
A USAF Major was telling of an encounter over the pole into Siberia. Routine missions in an RB-47E to check the USSR inventory and reactions of northern bases. He said all previous trips they could see below, MiG-15s taking off but they never reached any where near the B-47 altitude. We didn't ask how high, as this was within our Top Secret classes. The particular event in question, which eliminated further flights of this sort, three MiG-15s continued climbing while the others had reached their limits. Eventually two stalled out, spun down, while the third finally made to the altitude of the B-47. The pilot was described as wearing leather WW2 style helmet and mask. The Russian formated along side, the Major describing rapid considerable aileron deflections to keep from stalling, and pointed at the B-47 and using his thumb motioned for them to go back.
As a dumbassed 19 yearold who KNEW about aviation, I asked, "What did you do?"
The Major said, "We got the hell out of there."
I said, "But Sir, he flew along side because our wake turbulence would have caused him to stall, and if he had guns, if he fired them, the recoil would have slowed him, he would have stalled, so there was little danger."
"We didn't give a damn about all that, we got the hell out. Nobody had ever got that high before."
That's why he was a Major and I wasn't.

The MiG-15's official service ceiling was around 50,800 feet (15,500 meters), but that was under ideal conditions and with a lightly loaded aircraft. In reality, most MiG-15s operated well below that, especially when armed or carrying fuel for combat patrols. But in a stripped-down, high-performance intercept configuration—minimal fuel, no external stores, and a pilot willing to flirt with a stall—it's plausible that one could claw its way up to the high 40s or even touch 50,000 feet.

What makes your story so compelling is the detail: the MiG pilot barely hanging on, using rapid aileron deflections to stay aloft, and signaling with a thumb instead of engaging. That paints a picture of a jet pushed to its absolute limit—likely on the edge of aerodynamic stall, where even a small disturbance could send it tumbling.

So how did he get that high? Probably-- minimal fuel and weight - perfect atmospheric conditions -- a gutsy pilot with nerves of steel -- and maybe a little Cold War bravado.

 

[Frog]

The MiG-15's official service ceiling was around 50,800 feet (15,500 meters), but that was under ideal conditions and with a lightly loaded aircraft. In reality, most MiG-15s operated well below that, especially when armed or carrying fuel for combat patrols. But in a stripped-down, high-performance intercept configuration—minimal fuel, no external stores, and a pilot willing to flirt with a stall—it's plausible that one could claw its way up to the high 40s or even touch 50,000 feet.

What makes your story so compelling is the detail: the MiG pilot barely hanging on, using rapid aileron deflections to stay aloft, and signaling with a thumb instead of engaging. That paints a picture of a jet pushed to its absolute limit—likely on the edge of aerodynamic stall, where even a small disturbance could send it tumbling.

So how did he get that high? Probably-- minimal fuel and weight - perfect atmospheric conditions -- a gutsy pilot with nerves of steel -- and maybe a little Cold War bravado.

And possibly no ammo to save more weight.

 

[bf109xxl]

MiG-15s taking off but they never reached any where near the B-47 altitude.

MiGs reached the altitude of the RB-47 at least twice - on April 18, 1955 near the Bering Islands off Kamchatka (the RB-47 was shot down) and on November 7, 1958 over the Baltic Sea off Ventspils (the recon aircraft was damaged).
On May 6, 1954, a pair of MiG-17s from the 1619th IAP of the Northern Fleet tried to intercept a pair of B-47s over the Kola Peninsula. Long-range fire proved ineffective. The repeated attack of another MiG-17 from the 614th IAP was also unsuccessful. Three days later a MiG-17PF tried to intercept an RB-47 near Arkhangelsk without success, but the MiG still reached the altitude of the recon aircraft. For these failures, Lieutenant General of Aviation Borzov, commander of the Northern Fleet aviation, was removed from his post.

 

[Alan Stevens]

MiGs reached the altitude of the RB-47 at least twice - on April 18, 1955 near the Bering Islands off Kamchatka (the RB-47 was shot down) and on November 7, 1958 over the Baltic Sea off Ventspils (the recon aircraft was damaged).
On May 6, 1954, a pair of MiG-17s from the 1619th IAP of the Northern Fleet tried to intercept a pair of B-47s over the Kola Peninsula. Long-range fire proved ineffective. The repeated attack of another MiG-17 from the 614th IAP was also unsuccessful. Three days later a MiG-17PF tried to intercept an RB-47 near Arkhangelsk without success, but the MiG still reached the altitude of the recon aircraft. For these failures, Lieutenant General of Aviation Borzov, commander of the Northern Fleet aviation, was removed from his post.

But what were the altitudes of those B-47s?

 

[bf109xxl]

But what were the altitudes of those B-47s?

About 40k feet (12-13 km). The MiGs had time to climb to this altitude and attack the RB-47s, but were afraid to approach directly from the tail for fear of fire from the tail guns, which, as it turned out later, failed at this altitude. I've seen no mention of missions at altitudes above 40k feet - except for ejection experiments over the Gulf of Mexico (ha ha, we still call it that the old fashioned way), but I haven't interested in B-47 history too much

 

[yulzari]

At extreme height I recall an Avro Vulcan pilot telling me he had out manoeuvred an F14. A simple matter of wing area. Not operationally relevant for the time as the F14 would be launching missiles at the Vulcan not closing for a gun attack but it was a genuine example of the issues of extreme height interception. He responded to any closing attempts by merely making turns which the F14 could not match without the risk of stalling. This was at @60,000ft. He found the same with RAF Lightnings despite them being able to zoom climb to nearly 88,000ft. But at even approaching those heights they were one direction missiles. Any manoeuvring would stall them out.