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DrPaul
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B-36 Question

Wed Jun 26, 2019 5:31 pm

Something that has long puzzled me is why Convair designed the B-36 with pusher engines. Considering the disadvantages of pusher engines, which were soon apparent when the B-36 entered service, designing it in this way seems rather odd. Does anyone know what Convair's rationale was, and why the USAF accepted it and didn't ask Convair to reconfigure it to a more conventional and less problematic design?
 
aumaverick
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Re: B-36 Question

Wed Jun 26, 2019 5:58 pm

Try the response from JoeB posted in this outside forum: https://ww2aircraft.net/forum/threads/b ... her.32590/

Quote: "...The B-36 specification heavily emphasized long range and thus cruise performance. As a rule a pusher configuration will be more efficient in cruise, subject to considerations like rotation on take off, which might force the pusher prop to be smaller diameter to clear the ground on rotation. However in B-36 case they found that pusher was definitely more efficient in cruise. Some early concepts leading to the B-36, and some wind tunnel models even, had push-pull nacelles or conventional tractor nacelles. but the designers believed pusher would win, and at least at the state of the art in wind tunnel testing at the time the tests proved them right.

The disadvantage of pusher is not so much that wing down wash will actually make it less efficient net, but the vibration considerations of uneven flow, not only wing down wash in cruise, but also the engine exhaust stream flowing through the prop. These were issues with the B-36 which had flight restrictions related to prop vibration. Also, besides the cruise configuration, the wing interaction issues become more serious with flaps down. Note in photo's of B-36's even fully extended flaps are continued right in front of the props. And also in low speed flight, the tractor prop helps generate lift which the pusher doens't to the same degree. And then there's more potential for FOD from stuff thrown into the props by the main gear; again see B-36 photo's: the main gear legs are within the radius of the inboard props."
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DrPaul
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Re: B-36 Question

Wed Jun 26, 2019 8:47 pm

Thanks for that!
 
Armadillo1
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Re: B-36 Question

Thu Jun 27, 2019 10:11 am

Also italian piaggi flying boats have pusher props for same reason
 
Armadillo1
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Re: B-36 Question

Thu Jun 27, 2019 10:19 am

C-133 could be pusher, but they did it in common way. May be because of commonality and more texh expirience in tractor props
 
LightningZ71
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Re: B-36 Question

Thu Jun 27, 2019 1:24 pm

It all boils down to range. The US wanted a VERY long range bomber that could practically live at high altitudes, far in excess of what almost every contemporary interceptor could reach. That pusher configuration gave it a non-trivial boost in cruise efficiency over a conventional puller arrangement, at the expense of higher maintenance costs. The problems with pushers were well known at the time. They just decided that they could afford to throw money at the problem (as in, afford the higher maintenance costs and lower availability rate) as they could afford to have far more bombers than any of their potential adversaries of the era.

The end result was a bomber that was never quite right. Maintenance costs were well in excess of predictions. It had problem after problem, was effectively underpowered in its first revision, and was generally a headache to keep in the air. Granted, if it was working right, it was a fantastic bomb delivery platform for the early atomic era.
 
sandbender
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Re: B-36 Question

Thu Jun 27, 2019 7:04 pm

LightningZ71 wrote:
It all boils down to range. The US wanted a VERY long range bomber that could practically live at high altitudes, far in excess of what almost every contemporary interceptor could reach. That pusher configuration gave it a non-trivial boost in cruise efficiency over a conventional puller arrangement, at the expense of higher maintenance costs.


The fact that it was designed during WWII also had an impact on the decision making process. When it was initially proposed, it was a contingency for loosing the airbases in Britain. Trade-offs that wouldn't have been considered during peace-time were accepted because they thought they might need the capabilities it did offer, no matter the cost. After WWII there were a few years of draw down and substantial cost cutting before the Cold War started in earnest and they had to just deal with what they had.
 
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scbriml
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Re: B-36 Question

Sat Jun 29, 2019 7:57 am

I love the B-36, it's such a beast.

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frmrCapCadet
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Re: B-36 Question

Sat Jun 29, 2019 2:16 pm

I loved the sound, it is so distinctive that even with an unexpected fly over I think I could still identify it by sound alone. If there are there any flying models left! Alas, per avgeekery, none flying.
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DL_Mech
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Re: B-36 Question

Mon Jul 01, 2019 12:14 am

Last B-36 flight: February 12, 1959
This plane is built to withstand anything... except a bad pilot.
 
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Phosphorus
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Re: B-36 Question

Mon Jul 01, 2019 10:22 am

A reference to the origins of B-36 pusher design: as early as 1942, it was already shown as a future of air power.
For example, this Walt Disney movie, featuring Alexander de Seversky as proponent of air power, has bombers in six-engine pusher configuration on a mission
https://archive.org/details/VictoryThroughAirPower1942
for example, at 56.04 there is a flock of these, and at 1.03.49 as well
There are other visuals of those, surely.
Just to show that six-engine pusher for long-range was fairly widely accepted as the proper solution for long-range bombers, especially if Britain was unavailable for bombing Germany, and if Alaska was the nearest stepping stone for bombing Japan.
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SuperGee
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Re: B-36 Question

Sat Jul 06, 2019 7:06 am

frmrCapCadet wrote:
I loved the sound, it is so distinctive that even with an unexpected fly over I think I could still identify it by sound alone. If there are there any flying models left! Alas, per avgeekery, none flying.


The “D” model also had 4 jet engines, 2 on each wing which I understand were used primarily to get the plane off the ground and occasionally for extra power when in the air. They were shut down when not in use. I would imagine they had to be careful when fueling it since they had to keep track of both jet fuel and avgas. Getting them mixed up would be disastrous.

I can remember as a kid outside my house in upstate NY one day, I heard a horrendous noise, a rumbling like nothing I had ever heard before and the ground was shaking terribly. It kept getting louder and louder and I had no idea what it could be. Suddenly a B-36 appeared what seemed like barely over the rooftops of the buildings across the street. I don’t know what altitude it was actually at but it darned sure wasn’t very high. I didn’t know that it was a B-36 at that age but it was absolutely massive, the largest plane I had ever seen or imagined at that time and it dwarfed some of the buildings it was flying over. I counted 6 prop engines and 4 jets on it.

There was also a small, single engine plane (I think it was a prop) flying just off the bomber’s starboard wingtip, as if it were escorting it. I’ve never figured out why it was flying so low or why the small plane was with it. The nearest airport was Hancock field, about 2 miles east in Syracuse I certainly doubt any B-36 could ever have landed and/or taken off from there.

Also, the nearest AF base was Griffiss AF base near Rome, NY which was about another 75 miles or so east of Hancock field and which I decided must have been where it was headed. It didn’t seem to me that it should have needed to be so low since I was still that far from Griffiss but I could only figure that they had to get those things down lower for their approach even at that distance from the runway.

There is a good movie that contains lots of action with the B-36 staring Jimmy Stewart (who was a General and pilot in the USAF reserves in addition to being an actor) and June Allison. It is still available on DVD or blu ray wherever you get your movies.
 
mxaxai
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Re: B-36 Question

Sat Jul 06, 2019 1:31 pm

SuperGee wrote:
There is a good movie that contains lots of action with the B-36 staring Jimmy Stewart (who was a General and pilot in the USAF reserves in addition to being an actor) and June Allison. It is still available on DVD or blu ray wherever you get your movies.

Wow. Great footage there. This one scene really shows the different contrail formation behind the props and the jet engines. https://youtu.be/YWEyvBkFkBY?t=86
Also you can see several scenes where the jets are turned off - only six contrails visible.

Thanks for recommending the movie.
 
frmrCapCadet
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Re: B-36 Question

Sat Jul 06, 2019 3:44 pm

SuperG - good post!
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SuperGee
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Re: B-36 Question

Sat Jul 06, 2019 9:52 pm

Here is a photo of the FE station. Talk about the amount of stuff you have to keep an eye on. I believe they had to have 2 FE's:

http://www.nmusafvirtualtour.com/cockpi ... /CW-7.html

Here is a 360 degree view of the cockpit. You can use the up/down, right/left arrows to move around the cockpit.

http://www.nmusafvirtualtour.com/cockpi ... /CW-5.html
 
Max Q
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Re: B-36 Question

Sun Jul 07, 2019 5:26 am

SuperGee wrote:
frmrCapCadet wrote:
I loved the sound, it is so distinctive that even with an unexpected fly over I think I could still identify it by sound alone. If there are there any flying models left! Alas, per avgeekery, none flying.


The “D” model also had 4 jet engines, 2 on each wing which I understand were used primarily to get the plane off the ground and occasionally for extra power when in the air. They were shut down when not in use. I would imagine they had to be careful when fueling it since they had to keep track of both jet fuel and avgas. Getting them mixed up would be disastrous.

I can remember as a kid outside my house in upstate NY one day, I heard a horrendous noise, a rumbling like nothing I had ever heard before and the ground was shaking terribly. It kept getting louder and louder and I had no idea what it could be. Suddenly a B-36 appeared what seemed like barely over the rooftops of the buildings across the street. I don’t know what altitude it was actually at but it darned sure wasn’t very high. I didn’t know that it was a B-36 at that age but it was absolutely massive, the largest plane I had ever seen or imagined at that time and it dwarfed some of the buildings it was flying over. I counted 6 prop engines and 4 jets on it.

There was also a small, single engine plane (I think it was a prop) flying just off the bomber’s starboard wingtip, as if it were escorting it. I’ve never figured out why it was flying so low or why the small plane was with it. The nearest airport was Hancock field, about 2 miles east in Syracuse I certainly doubt any B-36 could ever have landed and/or taken off from there.

Also, the nearest AF base was Griffiss AF base near Rome, NY which was about another 75 miles or so east of Hancock field and which I decided must have been where it was headed. It didn’t seem to me that it should have needed to be so low since I was still that far from Griffiss but I could only figure that they had to get those things down lower for their approach even at that distance from the runway.

There is a good movie that contains lots of action with the B-36 staring Jimmy Stewart (who was a General and pilot in the USAF reserves in addition to being an actor) and June Allison. It is still available on DVD or blu ray wherever you get your movies.



Great stuff


Pretty sure the B36 didn’t carry separate
avgas and jet fuel


I believe the Jets ran on the avgas, they
just ran hotter and had a shorter life
The best contribution to safety is a competent Pilot.


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Phosphorus
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Re: B-36 Question

Sun Jul 07, 2019 9:09 am

SuperGee wrote:
frmrCapCadet wrote:
I loved the sound, it is so distinctive that even with an unexpected fly over I think I could still identify it by sound alone. If there are there any flying models left! Alas, per avgeekery, none flying.


The “D” model also had 4 jet engines, 2 on each wing which I understand were used primarily to get the plane off the ground and occasionally for extra power when in the air. They were shut down when not in use. I would imagine they had to be careful when fueling it since they had to keep track of both jet fuel and avgas. Getting them mixed up would be disastrous.
...


The story of 10-engined B-36 variants is somewhat more complicated -- B-36D indeed had 6 piston and 4 jet engines, but it was not the only model. All subsequent variants -- B-36F, B-36H, B-36J -- had similar layout. Moreover, earlier B-36B models were also converted to 10-engine configuration. At some point, it appears, all B-36 still flying (maybe with exception of prototype, that was also converted from XB-36 to an YB-36 variant, used for training) were converted to 10-engine setup.
Fuels -- it appears it was avgas only, period. That avgas is a curiosity in itself -- it was ridiculously high-octane, and lead on spark plugs was a common occurrence. According to Wiki (I know, I know...), maintenance at a certain interval called for wholesale replacement of all spark plugs on all 6 engines, 28 cylinders each. Such fun... Especially if you consider that hangars to fit B-36 were non-existent, and planes had to be fixed outdoors, in Alaska or Fort Worth weather...

SuperGee wrote:
...

There is a good movie that contains lots of action with the B-36 staring Jimmy Stewart (who was a General and pilot in the USAF reserves in addition to being an actor) and June Allison. It is still available on DVD or blu ray wherever you get your movies.


"Strategic Air Command" is the movie you refer to. Indeed, probably the only film to feature B-36 so prominently.
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SuperGee
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Re: B-36 Question

Sun Jul 07, 2019 4:44 pm

Phosphorus wrote:
SuperGee wrote:

There is a good movie that contains lots of action with the B-36 staring Jimmy Stewart (who was a General and pilot in the USAF reserves in addition to being an actor) and June Allison. It is still available on DVD or blu ray wherever you get your movies.

"Strategic Air Command" is the movie you refer to. Indeed, probably the only film to feature B-36 so prominently.


Yes, "Strategic Air Command" is the movie. I inadvertently left the title out of that post. It was late at night and I also made a few typos in that post that I didn't find until it was too late to edit it. :sorry:
 
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scbriml
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Re: B-36 Question

Sun Jul 07, 2019 6:13 pm

frmrCapCadet wrote:
I loved the sound, it is so distinctive that even with an unexpected fly over I think I could still identify it by sound alone. If there are there any flying models left! Alas, per avgeekery, none flying.


Wow, I wish I could have seen one flying. :crying:

There are only four complete examples left from the 384 built (a sadly small number). I've seen three of these - USAF Museum, Pima Air & Space Museum & Castle Air Museum. I'm going to have to work out how I'm going to see the last one at the SAC & Aerospace Museum as I don't see myself visiting Nebraska any time soon.
Time flies like an arrow. Fruit flies like a banana!
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aumaverick
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Re: B-36 Question

Mon Jul 08, 2019 12:45 pm

scbriml wrote:
frmrCapCadet wrote:
I loved the sound, it is so distinctive that even with an unexpected fly over I think I could still identify it by sound alone. If there are there any flying models left! Alas, per avgeekery, none flying.


Wow, I wish I could have seen one flying. :crying:

There are only four complete examples left from the 384 built (a sadly small number). I've seen three of these - USAF Museum, Pima Air & Space Museum & Castle Air Museum. I'm going to have to work out how I'm going to see the last one at the SAC & Aerospace Museum as I don't see myself visiting Nebraska any time soon.


If you're a baseball fan, there's always the annual College World Series in Omaha as an excuse.
I'm just here so I won't get fined. - Marshawn Lynch
 
nycbjr
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Re: B-36 Question

Mon Jul 08, 2019 3:10 pm

SuperGee wrote:
Here is a photo of the FE station. Talk about the amount of stuff you have to keep an eye on. I believe they had to have 2 FE's:

http://www.nmusafvirtualtour.com/cockpi ... /CW-7.html

Here is a 360 degree view of the cockpit. You can use the up/down, right/left arrows to move around the cockpit.

http://www.nmusafvirtualtour.com/cockpi ... /CW-5.html


Good lordy! Thats a crazy amt of dials and switches!!
 
GalaxyFlyer
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Re: B-36 Question

Mon Jul 08, 2019 4:10 pm

Then, there’s the one-off cargo version, the XC-99 which flew on for a number of years. Used to be parked at Kelly AFB looking rather sad. Carted off somewhere.


GF
 
Buckeyetech
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Re: B-36 Question

Mon Jul 08, 2019 7:39 pm

GalaxyFlyer wrote:
Then, there’s the one-off cargo version, the XC-99 which flew on for a number of years. Used to be parked at Kelly AFB looking rather sad. Carted off somewhere.


GF


It was at KFFO for a long time, before the museum curator finally pulled the plug on any future restoration, and has since shipped it by air to KDMA.
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ssteve
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Re: B-36 Question

Tue Jul 09, 2019 4:20 am

Relevant Anet topic:
viewtopic.php?t=769743
 
Newark727
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Re: B-36 Question

Tue Jul 09, 2019 11:02 pm

Max Q wrote:
Great stuff


Pretty sure the B36 didn’t carry separate
avgas and jet fuel


I believe the Jets ran on the avgas, they
just ran hotter and had a shorter life


This was also how two other mixed-power airplanes, the Ryan FR-1 Fireball and the North American AJ-1 Savage, did it. Seems keeping them separate would add quite a bit of complication.
 
LightningZ71
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Re: B-36 Question

Mon Jul 15, 2019 12:02 pm

Reading the other thread referenced by SSteve, I'm reminded of a story that my USAF veteran father would tell me from his time in the AF in the lead up to the Korean war and the few years after. He was a mechanic that was primarily assigned to B-47s and F-86Ds, but was piston engine qualified and would routinely be "lent out" to other units that needed extra manpower. For one of those assignments, he spent some time in the air on a KC-97 that was doing refueling duty for B-47s (I later figured out that it was an RB-47 unit that was doing recon work). The KC-97 had a very difficult time with this procedure as its maximum cruise speed and the B-47's stall speed (or, at least, lowest manageable air speed at altitude) weren't that far apart. He described the flight engineer sweating as he nervously scanned his monitoring panel while the pilot held the engines at near take off power for the duration of the operation. The oil usage was crazy. They had a pair of 55 gallon oil cans strapped in in front of the wing root with two guys basically constantly pumping oil into the belly mounted oil tank that was pumping oil out to the engines just as fast as it was pumped into the tank.

Now, it was a good fifty years from when that actually happened and when my dad told me the story, but, from everything that I've read, it matches with the documented issues the pair had when operating together. He got to watch them practice the procedure at low altitude in South Florida often. He described the B-47 struggling to stay stable in the air as the engines wailed on the tanker. I wish he was still around to ask him more about it. He also had some rather choice words for the designers of both the R-4360 and the 3350-TC. While both were amazing pieces of engineering, they were pushing the technology farther than the metallurgy was ready for. The 3350 had a nasty habit of cooking valves, though, for its weight and size, it delivered amazing power and efficiency. The 4360, especially as it was mounted on the B-36, had cooling airflow issues to the rear two rows of cylinders. They would cook at lower altitudes and lower airspeeds, though, once at cruise, they seemed to do ok. For the 4360, it was just so many cylinders, that there was almost always something about to go wrong with one of them. While quality control was very good, it was such a high number of parts that there was always something that was on a margin.
 
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SheikhDjibouti
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Re: B-36 Question

Thu Jul 18, 2019 11:36 am

GalaxyFlyer wrote:
Then, there’s the one-off cargo version, the XC-99 which flew on for a number of years. Used to be parked at Kelly AFB looking rather sad. Carted off somewhere.
GF

This photo says it all, and anybody on the ground beneath this pair would have suffered an "aluminum overcast" (*)
This is an early model B-36B flying with the XC-99, so just the twelve engines between them (no jets on either).
The prop wash behind that pair must have been quite extreme.

Image
Thx as usual to Wikipedia.

ps If the serial is to be believed, the contract for the XC-99 dates way back to 1943!

(*) The "aluminum overcast" (sometimes "magnesium") moniker was applied to the B-36 decades before the name was applied to the currently flying/restored EAA B-17G
Nothing to see here; move along please.
 
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Phosphorus
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Re: B-36 Question

Thu Jul 18, 2019 7:06 pm

SheikhDjibouti wrote:
... If the serial is to be believed, the contract for the XC-99 dates way back to 1943!
....


I saw a reference to the order for the prototype was placed December 31, 1942

Pan Am is mentioned among civil customers, who placed an order for 15 planes, but later withdrew, when performance targets were impossible to meet, especially with the engines that were giving trouble..
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