wuzak
Captain
The Griffon sounds different because it has a different firing order.
Bell Kingcobra
- Thread starter rogerwilko
- Start date
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The Griffon sounds different because it has a different firing order.
wuzak
Captain
So, are you saying that if you block one of the exhaust holes that the exhaust from both exhaust valves will exit the remaining hole?
GregP
Major
Yes, probably not as efficiently. If that happened, I'd expect some blowback into the cylinder. The pressure might actually blow out the divider wall itself and send it out the exhaust stack. I don't know, but wouldn't be surprised.
The thing to remember is that when he overhauls an Allison for an aircraft, it comes out per factory specs.
If he does one for a tractor or a boat or a car, it can be modified in any way he wants, and he KNOWS how to make an Allison sing.
The thing to remember is that when he overhauls an Allison for an aircraft, it comes out per factory specs.
If he does one for a tractor or a boat or a car, it can be modified in any way he wants, and he KNOWS how to make an Allison sing.
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wuzak
Captain
GregP
Major
Yah, I have that one. You can put your index finger into one port and flex you fingertip and come out the second one (if it is for the same cylinder, that is). Next time I'm out at Joe's. I'll try to remember to get a pic of that. On the relative scale of importance (1 - 10), it is a zero and maybe a 1 at best, but it seems to be of interest.
The seeming "ports" are really Allison basic exhaust flanges that get the stack material welded to them. It might not be really obvious, but each one has five studs holding it on. Three across the top and two bewteen the pipes on the bottom. It's really a minor thing to cause so much excitement.
The seeming "ports" are really Allison basic exhaust flanges that get the stack material welded to them. It might not be really obvious, but each one has five studs holding it on. Three across the top and two bewteen the pipes on the bottom. It's really a minor thing to cause so much excitement.
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GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The 1710 did have dual exhaust ports per cylinder, but having a single stack for both ports wouldn't hurt anything.
As short as the stack is, there wouldn't be much different in back pressure if it was a single stack per port or a single stack for both. It would be interesting to read the technical bulletin regarding the change. Perhaps to simplify service?
Even the L-6 in my 1962 Chevy has an exhaust manifold that doubles the ports of cylinders #2 #3, #4 #5 (with #1 and #6 having their own port) and with the back pressure that exists, there's no "blow back" into the adjacent cylinder when the valve is closed.
As short as the stack is, there wouldn't be much different in back pressure if it was a single stack per port or a single stack for both. It would be interesting to read the technical bulletin regarding the change. Perhaps to simplify service?
Even the L-6 in my 1962 Chevy has an exhaust manifold that doubles the ports of cylinders #2 #3, #4 #5 (with #1 and #6 having their own port) and with the back pressure that exists, there's no "blow back" into the adjacent cylinder when the valve is closed.
GregP
Major
RIght about teh back pressure , Graugeist, but I have no idea how much back pressure could be eliminated by removing the center bridge. As I said earlier, anything that goes into an aircraft must be pretty stock.
While trying for more flow by making it one port all the way through would be fun to try, it couldn't be done for any except an experimental or experimental exhibition aircraft. Certainly not one in the limited category.
While trying for more flow by making it one port all the way through would be fun to try, it couldn't be done for any except an experimental or experimental exhibition aircraft. Certainly not one in the limited category.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Greg, there would be virtually no back pressure with or without the bridge. These aircraft engines are alot like Dragsters that run open exhaust. So as you know, those stacks are there to move the exhaust out and away from the engine/cowling. There had been attempts by various manufacturers at "shaping" the exhaust gasses in the attempt to boost air-speed, even if marginally...and I'll admit to not having much knowledge in that area, someone else can elaborate on that if they like.
You'll see more "traditional" exhaust systems on the night fighters as they used a form of a manifold to conceal the glowing exhaust gasses in order to avoid alerting their prey or becoming a target for enemy night fighters while on the prowl.
You'll see more "traditional" exhaust systems on the night fighters as they used a form of a manifold to conceal the glowing exhaust gasses in order to avoid alerting their prey or becoming a target for enemy night fighters while on the prowl.
GregP
Major
You might be right, but I have the feeling that removing the bridge would increase the area by something like 8% or so, which MIGHT improve flow and might not in a supercharged engine. I'm not sure at all and haven't even thought it all the way through. Would be fun to try, but I have no opportunity to do so.
The Allison I saw configured that way was not in any way dyno tested. It was run until the rings seated ... it wasn't tested at full power. The intent was to seat the rings and pre-oil the engine so the customer only has to install it and hook up the various lines ... not to wring out a new engine before it was even broken in.
The Allison I saw configured that way was not in any way dyno tested. It was run until the rings seated ... it wasn't tested at full power. The intent was to seat the rings and pre-oil the engine so the customer only has to install it and hook up the various lines ... not to wring out a new engine before it was even broken in.
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varsity07840
Airman 1st Class
- 176
- Jun 25, 2013
The a/c in both pics areP-39Fs, 12 stacks with a 37mm gun. Visually similar to the P-400 except for
the long muzzle 20mm gun. The Brits modified their P-400s with six stacks with wide flanges.
Duane
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swampyankee
Chief Master Sergeant
- 4,031
- Jun 25, 2013
If the Wikipedia entry on the sky claimed it was blue in colour I would go outside and look, just to check for myself
Last year, one of my eighth grade students pretty much summarized the issues with Wikipedia: she noted that one article stated that triangles have four sides.
Vandalism
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
technically, that is true...if they are talking about a pyramid
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
hmmm....double post...
Unfortunately the 12 exhaust pipes aren't main difference between the D and F variant. The main one was the Aero-Prop propeller used for the F type instead of the Curtiss Electric one of the early P-39. Also if you have a look at the tail of the damaged P-39 with the serial ( 41-7031) and compare it to the list of serials for P-39 you will find that the number belonged to the batch of 394 aircraft of P-39D ( 41-6722...41-7115 ). Also it is possible that the P-39 of the serial was later modified to the D-3 recconnaissance variant equiped with the K-24 and K-25 cameras.
As far as the second P-39 is concerned.. the serial isn't seen. but the she looks like the D variant of the fighter. So I believe in the caption.
Shortround6
Major General
technically, that is true...if they are talking about a pyramid
tetrahedron
pyramid has 5 sides
GregP
Major
A pyramid has 4 sides and 5 faces or surfaces, including the base.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
I was being a smartass
However, based on that same logic, these idiots nowdays come up with all sorts of way to challenge common sense.
And one way they"ll challenge the concept of the trinagle's three sides, is that it has three sides that create it's shape...and an "inside", which makes the fourth "side".
Correct, no...stupid, yes.
However, based on that same logic, these idiots nowdays come up with all sorts of way to challenge common sense.
And one way they"ll challenge the concept of the trinagle's three sides, is that it has three sides that create it's shape...and an "inside", which makes the fourth "side".
Correct, no...stupid, yes.
varsity07840
Airman 1st Class
- 176
- Jun 25, 2013
The P-39D had six stacks, the P-39F had twelve. The a/c in the second pic has twelve. With the absence
Of a serial number and no way to identify the prop type, why would you assume it's a "D" when it has the visual aspects of an "F"?
Just Schmidt
Senior Airman
I was being a smartass
However, based on that same logic, these idiots nowdays come up with all sorts of way to challenge common sense.
And one way they"ll challenge the concept of the trinagle's three sides, is that it has three sides that create it's shape...and an "inside", which makes the fourth "side".
Correct, no...stupid, yes.
Common sense rising to the Challenge: If the fourth side of a triangle is the inside, surely the outside must be a Fifth?
