P-40 what-if

[Elvis]

Shortround6,

That was a nice little exercise you showed, concerning how where the weight is placed, affects the CG, but you forgot that my solution to that problem was to attempt to take the extra 22" of length out of the -45 engine, by setting the stages side-by-side, instead of in-line.

...by the way, you never did state whether you were into that idea or not. So which is it? (CLAY, this means you, too).

As for the history of the -45, I believe I already touched on that, however, whatever you're using for a source is incorrect.
The -45 engine had two speeds, 8.1:1 and 6.85:1, but used the same size of impeller - 9.5".
My source lists applications for the -47 engine as: XP-39E, XP-63, XP-63A and P-76.
The description I have for that engine states that it was similar to the -45, except: "E" series engine with extension shaft, remote reduction gear and independant internal hydraulic system.
My source for the -93 engine lists its applications as: XA-42, XB-42, F-63A and F-63C.
Its differences from the -47 are that it used a different propeller shaft, some of the power ratings are a little different and it has a longer OAL.
This is all according to Official USAF Documentation.

Lastly, thanks for explaining those SCing terms. My diagrams were showing a system that was in parallel, feeing into a common manifold inlet (i.e., no prescribed banks).
FWIW, I like the "in parallel" system better than the "in series" system. Seems like it would be less hard on the equipment and if one of the stages were to fail (for whatever reason), you'd still be making some power (basically, it would become a single speed, single stage system).



Elvis

 

[Shortround6]

Most of what I am using for a source is "Vee's for Victory, The story of the Allison V-1710 Aircraft engine 1929-1948" by Danial Whitney. 1998.

You are right there were more than three -47s the chart says 3+

The -45 did use two gears. one gear was for the engine supercharger and the other gear was for the auxilary stage supercharger.

No F-63s were ever built as such. ALL P-series fighters were redesignated as F-___ after the war.
By the way, no P-76 were ever built.

I am not really in favor of the side by side setup. While it just might fit using a a pair of small superchargers I think it would introduce at least as many problems as it would solve.

A problem with your parallel system is that it won't give the high altitude performance you are after. Centrifugal superchargers are not positive displacement units. If the pressure of the area they are trying to discharge into is too high they just don't flow anymore. I have explained the compund nature of the 2 stage system. Putting two superchargers in parellel not only doesn't get the compund effect, it won't even give you an add effect in regards to pressure. It will in volume but not in pressure.

 

[vanir]

If I might jump in on parallel supercharging, one issue is diameter of the casing/impeller. Bear with me as I'm adapting auto industry application to aero.
Bigger diameter raises the altitude regime of best performance, which is great if you want to make a high altitude a/c but loses out on low alt performance (I'll assume this is related to pressure ratio and power wasteage as described by Shortround). The bonus of bigger diameter unit though is higher cfm or passage volume, which means more power output (more in=more out).
The tandem supercharger is designed for this application, where you want more power without raising the throttle heights. You raise the volume without raising the diameter(s) of the casing/impeller.

In other words to get more power you can put a bigger supercharger on, but it raises the throttle heights and reduces performance at low altitude.
Or you can put a tandem supercharger on, which raises the output and won't affect the throttle heights.
Or you can put a series supercharger on, which retains similar low altitude performance but raises the throttle heights and thus gives higher *relative* output in the second stage (if using an intercooler low altitude output will of course be increased for this reason).

Like I said, adapting auto supercharging to aero application (where rpm ranges would substitute throttle heights)

Sound about right Shortround?

 

[Elvis]

Well put Vanir.
It would be interesting to read what Shortround6 has to say about that.


Elvis

 

[Elvis]

I wanted to throw one more thing into the conversation, and this is in relation to Clay's idea about usage of the H-S prop.

What if one were to build a larger displacement Allison?

I was fooling around with that the other day and found that if the bore were taken out .25" and the stroke lengthened by .5", the resulting displacement would increase to 2025 cu.in.

Now that gets more into the DB601/605 and Griffon territory and may result in enough power increase to make working with the larger, broader propeller more feasible.
You'll loose a little engine speed, but that could be made up with less reduction at the prop (I figured out that a change from 2:1 to 1.8:1 would keep prop speed the same, with the engine operating at 300 RPM less).
That does put more stress in that transmission, though.
Can it handle it? Beats me.

What do you think, Clay?
Seems this addresses your initial question in this thread a little closer, rather than expounding on mods to the existing V-1710.

Anyway, just an idea, based on looking at the engine power situation from another angle.
Would still like to expound on the two-stage, two-speed idea (applied to the V-1710), as well.


Elvis

 

[Elvis]

Most of what I am using for a source is "Vee's for Victory, The story of the Allison V-1710 Aircraft engine 1929-1948" by Danial Whitney. 1998....The -45 did use two gears. one gear was for the engine supercharger and the other gear was for the auxilary stage supercharger.

Interesting, but doesn't that make the system two-speed, two-stage?

No F-63s were ever built as such. ALL P-series fighters were redesignated as F-___ after the war.
By the way, no P-76 were ever built.

In case you didn't notice, the link has information that dates from 1949.
As you stated, by that time, fighter designation had been changed from "P" to "F".
As it is official government documentation, the applications mentioned, that are fighter planes, would then have to be mentioned with the "F" designation, regardless if the plane was still in the inventory or not.
They're simply saying that those were the applications for that particular version of the engine, phrased in a modern format.

I am not really in favor of the side by side setup. While it just might fit using a a pair of small superchargers I think it would introduce at least as many problems as it would solve.

Thank you for answering my question, but how does it introduce new problems?
Are you concerned about the strength of the gearing, or the "fit" of the engine, or something else?

A problem with your parallel system is that it won't give the high altitude performance you are after. Centrifugal superchargers are not positive displacement units. If the pressure of the area they are trying to discharge into is too high they just don't flow anymore. I have explained the compund nature of the 2 stage system. Putting two superchargers in parellel not only doesn't get the compund effect, it won't even give you an add effect in regards to pressure. It will in volume but not in pressure.

According to this page, pressure will increase by the square of the increase in engine speed.
This is where the R&D work comes in.
You need to set the gearing so that you don't exceed that max. pressure.
If this is done correctly, the SC's will always produce more power, as engine speed increases, within the limits of the engine's operating speeds.
If you set the system up so that the engine is only initially running on the primary SC, and it is optimized to work from SL to a certain altitude, then kicks in the aux. SC, only when the initial altitude is exceeded, and optimize that aux. SC so that it helps maintain that amount of power to a much higher altitude, then I don't see how the system doesn't work.
There's also a sort of "safety" built into this type of design.
If you use the primary SC only as a feed to the aux. SC, then if that aux. SC is damaged in such a way that it no longer operates, you've pretty much lost all of your SCing effect, because the aux. SC now acts as an obstruction in the line, rather than a power augmenter.
If setup in the way I just explained, then at least you still see some amount of boost.
Although engine power at the higher altitude will be lost (because you're now basically running a single-stage, single speed SC optimized for low altitude work), it won't be as much of a power loss as running the system in series...and I get the idea you prefer the "in series" setup to the "in parallel" setup, correct?



Elvis

 

[Clay_Allison]

I wanted to throw one more thing into the conversation, and this is in relation to Clay's idea about usage of the H-S prop.

What if one were to build a larger displacement Allison?

I was fooling around with that the other day and found that if the bore were taken out .25" and the stroke lengthened by .5", the resulting displacement would increase to 2025 cu.in.

Now that gets more into the DB601/605 and Griffon territory and may result in enough power increase to make working with the larger, broader propeller more feasible.
You'll loose a little engine speed, but that could be made up with less reduction at the prop (I figured out that a change from 2:1 to 1.8:1 would keep prop speed the same, with the engine operating at 300 RPM less).
That does put more stress in that transmission, though.
Can it handle it? Beats me.

What do you think, Clay?
Seems this addresses your initial question in this thread a little closer, rather than expounding on mods to the existing V-1710.

Anyway, just an idea, based on looking at the engine power situation from another angle.
Would still like to expound on the two-stage, two-speed idea (applied to the V-1710), as well.


Elvis

I like that. You know they say there's no replacement for displacement.

 

[Elvis]

True!


Elvis

 

[Shortround6]

Interesting, but doesn't that make the system two-speed, two-stage?

No, it means the engine supercharger spun at at one fixed speed in relatio to the engine crankshaft while the auxilery supercharger spun at a different fixed speed in relation to the crankshaft. two stage yes but a single speed two stage.

In case you didn't notice, the link has information that dates from 1949.
As you stated, by that time, fighter designation had been changed from "P" to "F".
As it is official government documentation, the applications mentioned, that are fighter planes, would then have to be mentioned with the "F" designation, regardless if the plane was still in the inventory or not.
They're simply saying that those were the applications for that particular version of the engine, phrased in a modern format.

I did notice that well over a year ago when I first ran across that list.
just noting that there are a number of mistakes, typos, omissions and/or other types of errors in that list. It is very useful but shouldn't be take as the last word.

Thank you for answering my question, but how does it introduce new problems?
Are you concerned about the strength of the gearing, or the "fit" of the engine, or something else?

Yep, plus cost (difficulty of manufacture) , weight, possible vibration problems and more that I haven't thought of.

According to this page, pressure will increase by the square of the increase in engine speed.
This is where the R&D work comes in.
You need to set the gearing so that you don't exceed that max. pressure.
If this is done correctly, the SC's will always produce more power, as engine speed increases, within the limits of the engine's operating speeds.
If you set the system up so that the engine is only initially running on the primary SC, and it is optimized to work from SL to a certain altitude, then kicks in the aux. SC, only when the initial altitude is exceeded, and optimize that aux. SC so that it helps maintain that amount of power to a much higher altitude, then I don't see how the system doesn't work.
There's also a sort of "safety" built into this type of design.
If you use the primary SC only as a feed to the aux. SC, then if that aux. SC is damaged in such a way that it no longer operates, you've pretty much lost all of your SCing effect, because the aux. SC now acts as an obstruction in the line, rather than a power augmenter.
If setup in the way I just explained, then at least you still see some amount of boost.
Although engine power at the higher altitude will be lost (because you're now basically running a single-stage, single speed SC optimized for low altitude work), it won't be as much of a power loss as running the system in series...and I get the idea you prefer the "in series" setup to the "in parallel" setup, correct?

Elvis

The whole idea of running the superchargers in series is for high altitude work.
IF your engine needs, say 45in of boost to makes it rated power at sea level (30in pressure) your supercharger only needs to deliver a pressure ratio of 1.5 to 1 which is very easily done. as the plane climbs if you want to keep your manfold pressure at 45in at just under 11,000feet where the pressure is 20in your supercharger needs a pressure ratio of 2.25 to 1. At 18,000 ft the pressure is just about 15in and you need a supercharger that can deliver a pressure ratio of 3 to1.
This was the problem in the very late 30s. NOBODY's single stage supercharger could deliver a pressure ratio of 3 to 1 in a useable manner. simply gearing the supercharger to spin faster ment that the power to drive it went up with square of the speed. The air coming out of the supercharger was much hotter and much more likily to cause detonation in the cylinders.
The "series" setup was already known to need less power to reach a given pressure ratio and cause less charge heating even without an intercooler.
PLease note that if your engine required less than 45in at sea level the existing supercharges could maintain the sealevel power a little higher up while if your engine required more than 45in it's critical hight would be lower.

Agiain, please note that the centifugal supercharger is NOT a positive displacement device. There is a lot of room arouond the impellor for air flow if the impellor is stopped. I believe that one of the Navy R-2800s actually sucked through the un driven auxialry stage when operating at take-off and at low altitudes.

THe centifugal water pumps we use at work will rotate just fine with their output blocked, at least until the churning of the water raises the teperature to the boiling point.

That is the problem with your system. the aircraft system needs TWO things. it needs Pressure and volume. putting two centifugal impellors in parallel actually can solve a volume problem but it doesn't do much for the pressure problem.
We used to have old fire pumps that actually could be switched from one to the other. Two impellors and piping that would change them from series to parallel. if your situation required lots of water at low (under 150lbs) pressure you pumped in parallel (capacity) if you need higher pressure You pumped in seies (pressure). New fire pumps are driven by much larger engines and they just use one big impellor

If all you want is low altitude just stick a big enough single stage impellor on the engine and get on with it.

British created low altitude engines by turning down the impellors to smaller diameters and locking the two stage gearboxes in low gear.

 

[Clay_Allison]

what effect would intercooling a single stage supercharger have?

 

[Shortround6]

I wanted to throw one more thing into the conversation, and this is in relation to Clay's idea about usage of the H-S prop.

What if one were to build a larger displacement Allison?

I was fooling around with that the other day and found that if the bore were taken out .25" and the stroke lengthened by .5", the resulting displacement would increase to 2025 cu.in.

Elvis

basicly you are working with a whole new engine. Which equels how much development time?

Most aircraft engines were not built with anywhere near the amount of stretch in them that car engines have.

Aircraft engines are usually built to a much tighter power to weight ratio than car engines so they are not over built to any great extent. And in the 1930s a lot less was known about combustion behavior and other aspects of engine design. There were reasons why Mukulin used just about the same bore and stroke in all his engines and why the bore and stroke didn't change much from their BMW ancestors. Or some other familys of engines.

Trying to splice an extra 1 1/2 inches of bore into a V-12 engine means one of two things. Less water circulating between the cylinders or a new longer crankshaft and crankcase.
I guess you could try bigger pumps to shove the water through quicker but the faster moving water (OK ethylene-glycol) might not have the same heat transfer rate if it is moving faster. One more series of tests for R&D.

As a" for instance" when it comes to airplane engines the very late model Allisons that could run at 3200rpm used a crankshaft that weighed 27lb more than the earlier 3000rpm engines. the extra weight was actually in the counterbalances which were needed for the increased vibration at the higher rpm. Although the new crank did exhibit much lower bearing loads than the older crank did even at the higher rpm.

Remember, walking home after blowing an engine is not really an option in an airplane.

 

[Shortround6]

what effect would intercooling a single stage supercharger have?

On the size engines we are talking about here it might be worth around 100hp. At least that is around what the Germans got on some of their Jumo 211s.

But it is not going to change the critical altitude much. You are still limited by the effective pressure ratio of the supercharger. THings did improve after Hooker got involved and both the Russians and the French were working on higher efficinecy compressors in 1940-41 that used variably sized or angled inlet guides and /or extra axial stages. But compare a series 40 something Merlin (Hooker single stage supercharger) to a 60 series engine for altitude performance.

And you have to fiind space for the intercooler. ANd it has to work at altitude. It is mass air flow that does the trick. say you want a 40% efficient inter cooler (or after cooler on a single stage engine) . You need just about the same mass of cooling air going through the inter cooler as you do induction air. easy enough at sea level but at 22,000feet you need twice the cubic feet of air as you did at sea level to get the same mass. More airflow will get you even lower charge temperatures but after 40-50% it gets into diminishing returns pretty fast.

 

[Elvis]

Shortround6,

Ok, I'll concede to your penchant for running the system in series, as opposed to in parallel.
After your further explanation, that does make sense.
It may be more fragile, in war-time conditions, but nothing is perfect and it achieves the goal of more high altitude performance better than the in parallel idea I mentioned.

...in fact, I think my idea of changing the arrangement of the SC's in the -45 is not a good one to begin with.
It not only does not work as well, but changes the engine and no longer makes it a "-45" varient (duh! c'mon Elvis!)....and then there's the time factor you mentioned.

Same goes for the larger displacement engine idea. Too much R&D time needed.

However, I understand that none of the production WWII era Allisons had intercooling. It seems they were stuck on using water injection only as a way to prevent detonation and that alone, apparently, was not enough to allow the engine to put out the power numbers it needed to be more competitive with Axis aircraft (ok, the 109!).
So maybe augmenting the -45's water injection with some form of intercooling (place it in front of, or behind, the oil cooler?) is the answer to preventing detonation (or at least keeping it to a minimum).

So I guess its the -45 engine, augmented with an intercooler, using the H-S prop that makes the P-40 a high altitude "winner".

So how can we address any CG issues the engine change might incur?




Elvis
P.S. If you wanna call it "coolant", It's ok by me.

 

[Clay_Allison]

Shortround6,

Ok, I'll concede to your penchant for running the system in series, as opposed to in parallel.
After your further explanation, that does make sense.
It may be more fragile, in war-time conditions, but nothing is perfect and it achieves the goal of more high altitude performance better than the in parallel idea I mentioned.

...in fact, I think my idea of changing the arrangement of the SC's in the -45 is not a good one to begin with.
It not only does not work as well, but changes the engine and no longer makes it a "-45" varient (duh! c'mon Elvis!)....and then there's the time factor you mentioned.

Same goes for the larger displacement engine idea. Too much R&D time needed.

However, I understand that none of the production WWII era Allisons had intercooling. It seems they were stuck on using water injection only as a way to prevent detonation and that alone, apparently, was not enough to allow the engine to put out the power numbers it needed to be more competitive with Axis aircraft (ok, the 109!).
So maybe augmenting the -45's water injection with some form of intercooling (place it in front of, or behind, the oil cooler?) is the answer to preventing detonation (or at least keeping it to a minimum).

So I guess its the -45 engine, augmented with an intercooler, using the H-S prop that makes the P-40 a high altitude "winner".

So how can we address any CG issues the engine change might incur?




Elvis
P.S. If you wanna call it "coolant", It's ok by me.

Lengthen the tail with a spacer, Kurt Tank style.

 

[Shortround6]

However, I understand that none of the production WWII era Allisons had intercooling. It seems they were stuck on using water injection only as a way to prevent detonation and that alone, apparently, was not enough to allow the engine to put out the power numbers it needed to be more competitive with Axis aircraft (ok, the 109!).
So maybe augmenting the -45's water injection with some form of intercooling (place it in front of, or behind, the oil cooler?) is the answer to preventing detonation (or at least keeping it to a minimum).

So I guess its the -45 engine, augmented with an intercooler, using the H-S prop that makes the P-40 a high altitude "winner".

So how can we address any CG issues the engine change might incur?

Elvis
P.S. If you wanna call it "coolant", It's ok by me.

None of the Mechanical drive 2 stage engines used intercoolers but all of the P-38 turbocharged engines did. Allison hoped their more efficient compressor compared to the GE one wouldn't cause as much temperature rise. The other situation that Allison may have faced was that the "target" kept changing. What was the target "goal" for horsepower and manifold pressure may have changed from 1940 to 1942. THe -47 supercharger set up was better for a service aircraft in any case although I am not sure how much delay that entails. The goal of that set up being to use only just enough power to drive the auxilary stage to provide sea level pressure (or just slightly above) to the engine supercharger and thus have more power available at the lower altitudes.

A 'FUN' program to play with is here: motorgeek.com :: Turbo/Engine Flow Calculations and Maps

But please read the notes.
THe program makes no allowances for increase friction at higher rpms nor does it subtract the power needed to drive a mechanical supercharger. It tells you to try to use the SFC number to "adjust" for those effects.
Still it does give an idea of the effects of intercooling and water injection.
you have to 'add' enough manifold pressure to the

I would think you would want to give the intercooler it's own supply of air. either using already heated air or trying to feed heated air to the oil cooler doesn't sound like a good idea. besides, you might want to be able to control the cooling of each device independantly.

 

[Elvis]

So how can we address any CG issues the engine change might incur?

Lengthen the tail with a spacer, Kurt Tank style.

Quite true, but I'm wondering if there's room between the engine and the cockpit to allow (at least some of) that extra length to fit, as well?
This way, we don't rely solely on lengthing of the aft section of fueslage.

Can someone provide a sectional view of the aircraft?
I tried looking for it last night, but couldn't locate one.



Elvis

 

[Elvis]

THe -47 supercharger set up was better for a service aircraft in any case although I am not sure how much delay that entails.

I thought the only difference between the -45 and the -47/-93 engines was the extension shaft used on the latter engines for usage in the P-63?
You're saying the SC setup is different, as well?
Didn't realize that.


Elvis

 

[Shortround6]

I thought the only difference between the -45 and the -47/-93 engines was the extension shaft used on the latter engines for usage in the P-63?
You're saying the SC setup is different, as well?
Didn't realize that.


Elvis

The -45 used a single speed fixed gear for the auxilary stage. the -47 used a single speed gear with a hydraulic clutch that could be 'slipped' to vary the actual rpm of the inpellor. Much like the drive on the German DB engines.
Because of Allison 'modular' aproach to engine building the front drive, whether reduction gear or extension shaft, could be bolted to any block so using the power figures from the -47 isn't really much of a stretch. Granted the maximums aren't any different but the engine might require less attention in combat. -45 need attention to throttle settings to avoid over boosting.

As for a cutaway drawing I found this although it is not very good.

1941 | 0682 | Flight Archive

 

[renrich]

According to dean, "America's Hundred Thousand" the two stage supercharger used in the R1830 and R2800 engines had an air to air intercooler. The second stage blower was placed between an outside air intake and the intercooler. The outside air was used to cool, by close passage of outside air, the charge air compressed by the auxiliary stage blower before it entered the carburetor. In this scheme the main blower compressed a fuel air mixture whereas the auxiliary blower compressed air only. The system had three modes of operation. Neutral blower where the second stage was declutched. Low blower with a low ration clutch and high blower with a high ratio clutch.

 

[Elvis]

The -45 used a single speed fixed gear for the auxilary stage. the -47 used a single speed gear with a hydraulic clutch that could be 'slipped' to vary the actual rpm of the inpellor. Much like the drive on the German DB engines.
Granted the maximums aren't any different but the engine might require less attention in combat. -45 need attention to throttle settings to avoid over boosting.

As for a cutaway drawing I found this although it is not very good.

1941 | 0682 | Flight Archive

You know, I found something the other day that stated that the -45 engine also used a hydraulic clutch for the aux. stage.
It even stated its reference source was the same as yours - Vee's for Victory.
I can't seem to find it now, but if I ever do, I'll post the link for you.
As for the picture, thanks.
When you blow it up to like 400%, you'll see its actually fairly well detailed.
That pic, plus the one I found here (note the 3rd plane down from the top), both seem to show a little room behind the engine. I wonder if that space couldn't occupy at least some of the second stage (I'm assuming the extra length is coming from the addtional SC and its plumbing).
This would mean that the nose wouldn't stick out quite so far and adding length to the rear of the fuesalage, as Clay had mentined earlier, would be a less drastic affair.
I wonder how bad it would be to push the cockpit back, maybe 3"-4"?
Would it be that different to fly/taxi?
I'm just thinking about the combined weight of the H=S prop and the -45 engine.



Elvis