P-40 what-if

Elvis said:

Colin,
Still looking into the links you posted, but a quick check at Wiki says the Griff-powered Spit Mk. IV used a four bladed Rotol prop of 10.5 ft. diameter.
The P-40 was already using an 11' Curtiss-Electric prop, so maybe upping the blade count from 3 to 4 would be all that were needed...

Click to expand...

One of the reasons the Griffon adopted the 5-bladed screw was that the 4-bladed screw of the Merlin had already used up all of the ground clearance - there was nowhere for a bigger screw to go so they started down the path of more blades.
If the P-40 has more ground clearance to move into than the Spitfire then options for absorbing the extra power of the Griffon are a little more open for the P-40; a 4-bladed hydromatic unit probably.

INTERESTING!

I didn't know that...maybe a 5-bladed screw IS in order (and wouldn't that just be so cool!)


Elvis

Colin1 said:

One of the reasons the Griffon adopted the 5-bladed screw was that the 4-bladed screw of the Merlin had already used up all of the ground clearance - there was nowhere for a bigger screw to go so they started down the path of more blades.
If the P-40 has more ground clearance to move into than the Spitfire then options for absorbing the extra power of the Griffon are a little more open for the P-40; a 4-bladed hydromatic unit probably.

Click to expand...

IIRC, the P-40 had a good deal more ground clearance and easier ground handling than the Spitfire.

Clay,

Was that due to the landing gear arrangement?
I agree about ground clearance. The P-40 was already using an 11' prop, so it much have more ground clearance than a Spitfire.
While the idea of the 4-bladed version from the P-51D is a good one, I had the thought last night that 51D was Merlin powered and the Griff is going to generate a good deal more torque, thus it may actually requrire more prop.
Man, imagine it - a P-40 with an 11' 5-bladed prop....that'd be a sight ( ).
I would think it would climb like a freakin' monkey, compared to what was actually used during the war.



Elvis

Elvis said:

Clay,

Was that due to the landing gear arrangement?
I agree about ground clearance. The P-40 was already using an 11' prop, so it much have more ground clearance than a Spitfire.
While the idea of the 4-bladed version from the P-51D is a good one, I had the thought last night that 51D was Merlin powered and the Griff is going to generate a good deal more torque, thus it may actually requrire more prop.
Man, imagine it - a P-40 with an 11' 5-bladed prop....that'd be a sight ( ).
I would think it would climb like a freakin' monkey, compared to what was actually used during the war.



Elvis

Click to expand...

In answer to your question, yes. The P-40 had wide, inward-folding landing gear, the Spit had almost as narrow a landing gear arrangement as the 190.

The P-40 was a bigger plane than the Spitfire overall, a bit more of an armored warhorse than a racehorse. An 11' five blade would be my guess as to the best prop arrangement. I think it would climb like crazy and could have been a good second-choice plane until the end of the war, particularly for the Brits where it could have completely replaced the Hurricane in the Pacific theatre.

Clay_Allison said:

In answer to your question, yes. The P-40 had wide, inward-folding landing gear, the Spit had almost as narrow a landing gear arrangement as the 190.

The P-40 was a bigger plane than the Spitfire overall, a bit more of an armored warhorse than a racehorse. An 11' five blade would be my guess as to the best prop arrangement. I think it would climb like crazy and could have been a good second-choice plane until the end of the war, particularly for the Brits where it could have completely replaced the Hurricane in the Pacific theatre.

Click to expand...

I actually like the thought that we had indeed given the Brits the P-40, instead of the designing the P-51, and it was during the time that they had the planes, that the idea for the Griffon powered P-40 came into being.
...pretty cool thought.
BTW, the P-40's landing gear did not retract inward, but rather, rearward. The whole assembly also rotated 90 degrees so that the wheels would sit flat with the wing, when retracted.
I'd post a pic, but this computer is super slow.
Just google "P-40" and click "image". You'll see what I mean.
Also, the 190 actually had a fairly wide landing gear arrangement. Now THAT one did fold inwards, from about 1/2 way out on the wing.
The Spit and the 109 both had rather narrowly tracked landing gear, due to how they extended and retracted, although I think the 109 was "tippier" than the Spit, in that regard.

I'm tellin' ya Clay, the more I think about this, the more I like the idea.
I really wish someone here could slap together some drawings, though.
I'd really like to see what one would look like, even if its just an "artists rendering".


Elvis

Elvis said:

I actually like the thought that we had indeed given the Brits the P-40, instead of the designing the P-51, and it was during the time that they had the planes, that the idea for the Griffon powered P-40 came into being.
...pretty cool thought.
BTW, the P-40's landing gear did not retract inward, but rather, rearward. The whole assembly also rotated 90 degrees so that the wheels would sit flat with the wing, when retracted.
I'd post a pic, but this computer is super slow.
Just google "P-40" and click "image". You'll see what I mean.
Also, the 190 actually had a fairly wide landing gear arrangement. Now THAT one did fold inwards, from about 1/2 way out on the wing.
The Spit and the 109 both had rather narrowly tracked landing gear, due to how they extended and retracted, although I think the 109 was "tippier" than the Spit, in that regard.

I'm tellin' ya Clay, the more I think about this, the more I like the idea.
I really wish someone here could slap together some drawings, though.
I'd really like to see what one would look like, even if its just an "artists rendering".


Elvis

Click to expand...

190 was a typo, I meant 109, both the 109 and the Spit had landing gear as narrow as landing on a bicycle.

LOL! Good thing a lot of the German pilots were trained on gliders!





Elvis

Just thought of something and thought I'd resurrect this thread to ask about it.

I was just reading about that 4-blade Hamilton standard propeller and what it did for the P-38K (but ultimately wasn't allowed to do)

What about putting the Paddle-Prop on the P-40? It seemed to just have the same "toothpick-three" that the P-38 had originally, and since its' problem was high alt performance, better props tend to improve that. Also since by that point in the war it was a defensive interceptor and fighter-bomber, it should improve climb and takeoff distance to have the bigger prop.

The guys who designed the propellors did a pretty good job. problems came up with trying to meet production quotas.
There were formulas in some fairly basic aviation books for propellor design. You need a certain amount of blade area (not the same as propellor disc area) to transmit a given amount of power. As the engine guys kept increasing the power of the engines the props need more blade area (wider blades or more of them or both). How ever just putting bigger blades on an existing engine is not magic.
Like everything else that moves through air there is drag on propellor blades. A big, high altitude, wide bladed propellor will have much more drag at low altitudes than one of those " toothpick-three" propellors and might very well hurt low altitude performance.

When comparing a P-38 to a P-40 you have to keep in mind that while they both used allison engines the actual perforamce could be rather different. Late model P-38s could get 1600hp WEP at 25,000-30,000ft and so could very well use bigger/wider prop blades to transmit the power at those altitudes.

A P-40 flying at 12,000-15,000ft in air twice as dense doesn't need quite the same prop blade area to transmit the power even if it made 1600hp at WEP. The less power it makes the less it needs the bigger propellor.

Please not on the P-47 that it's original porpellor was supposed to handle 2000hp. Maybe it was marginal for that, maybe it was OK, maybe it wasn't very good, I won't tell you I know for sure. When the paddle blades came along the engines were giving any where from 2300-2500hp with water injection and at WEP ratings. so the old prop was trying handle 15-25% more power than it was designed for.
Same with P-38 Props, they went from handling 1100hp to 1425HP even without WEP.

Shortround6 said:

The guys who designed the propellors did a pretty good job. problems came up with trying to meet production quotas.
There were formulas in some fairly basic aviation books for propellor design. You need a certain amount of blade area (not the same as propellor disc area) to transmit a given amount of power. As the engine guys kept increasing the power of the engines the props need more blade area (wider blades or more of them or both). How ever just putting bigger blades on an existing engine is not magic.
Like everything else that moves through air there is drag on propellor blades. A big, high altitude, wide bladed propellor will have much more drag at low altitudes than one of those " toothpick-three" propellors and might very well hurt low altitude performance.

When comparing a P-38 to a P-40 you have to keep in mind that while they both used allison engines the actual perforamce could be rather different. Late model P-38s could get 1600hp WEP at 25,000-30,000ft and so could very well use bigger/wider prop blades to transmit the power at those altitudes.

A P-40 flying at 12,000-15,000ft in air twice as dense doesn't need quite the same prop blade area to transmit the power even if it made 1600hp at WEP. The less power it makes the less it needs the bigger propellor.

Please not on the P-47 that it's original porpellor was supposed to handle 2000hp. Maybe it was marginal for that, maybe it was OK, maybe it wasn't very good, I won't tell you I know for sure. When the paddle blades came along the engines were giving any where from 2300-2500hp with water injection and at WEP ratings. so the old prop was trying handle 15-25% more power than it was designed for.
Same with P-38 Props, they went from handling 1100hp to 1425HP even without WEP.

Click to expand...

I know from previous arguments with you that you don't think high altitude performance is at all important (neither did the army) and that the P-40 should never have been anything but a fighter-bomber that defended itself reasonably well.

I still think that it's a bad idea to resign yourself to giving up the high ground and think that the P-40 could have been balanced toward a higher critical altitude.

The Warhawk fought best on the climb and dive and it makes it difficult when you don't have a comfortable cruising altitude that allows you to take advantage of your dive speed for long.

Click here to read the sad but amazing story of the P-38K.

Hey Clay,

I have to agree with Shortround6 on this one. You'd need more power to take advantage of the bigger prop....so lets replace the V-1710-39 engine with its two-speed, twp-stage kin, the V-1710-45 engine!
The -45 made a little more power at sea level and matched the -39's power at altitude, but the -45 made that power at a much higher altitude (over 10,000 feet higher up), so I'm thinking it was probably making more power at the -39's rated altitude.
This may be enough of a change to warrent the use of the Hamilton Standard.
Its an impressive looking propeller, to be sure...






Elvis

Clay_Allison said:

I know from previous arguments with you that you don't think high altitude performance is at all important (neither did the army) and that the P-40 should never have been anything but a fighter-bomber that defended itself reasonably well.

Click to expand...

I don't believe I have said that high altitude performance wasn't important. You are correct in that I don't believe the P-40 was the plane to try and get high altitude performance out of. they are not the same thing.

Clay_Allison said:

I still think that it's a bad idea to resign yourself to giving up the high ground and think that the P-40 could have been balanced toward a higher critical altitude.

Click to expand...

1. The army hadn't resigned itself to giving up the high ground, that is why they were paying for P-38s and P-47s
2. With out some sort of 2 stage supercharger and some sort of inter/after cooler you just aren't going to get a big increase in critical altitude. You can get a small one by totally redesigning your single stage supercharger and you can get an even smaller increase (depending on your original critical hight) by going to a 2 speed supercharger.

Clay_Allison said:

The Warhawk fought best on the climb and dive and it makes it difficult when you don't have a comfortable cruising altitude that allows you to take advantage of your dive speed for long.

Click to expand...

Quite true but designing and building a totally new engine installation, High powered, high altitude flight may require larger radiators and oil coolers among other things, may mean NO Warhawks at all in one theater or another for several months.

I'm all for increasing P-40 performance but keeping it below 18,000ft.
The USAAF tried the Merlin 20-series trimmed for aerial combat in the L variant in North Africa and it was a non-event. You could WEP +18lbs in that type for what...1650hp? But English based units were being transferred retaining their Spits and these were used to fly top cover while the P-40s did low-med altitude interception duties (mostly decimating whatever was left of the Luftwaffe transport force whilst the Spits handled their escorts).

I mean look at the ca.40mph performance improvement of the Schmood design with the same Allison as the P-40M and it's a heavier a/c.
Let's use that as a rule of thumb and put a Merlin 60/70 series with Rotol into the P-40N. Still having troubles breaking 600km/h at altitude. The second stage is a waste imho, keep it under 18,000ft and loaded with bombs.

The great engine combo would've been Merlin 50 and Rotol and something like that really should've entered production at the time of the P-40M, though really the -81 isn't far off the mark at WEP (60" rated) but I agree it's lacking a decent prop by this stage and would've liked to see the Allison of that time cleared for 66".
Then I think you'd have something about as good as an LF MkVc and after all these were still in front line service in 44. I think that would've been super handy in the South Pacific at the start of 43.

Elvis said:

Click here to read the sad but amazing story of the P-38K.

Hey Clay,

I have to agree with Shortround6 on this one. You'd need more power to take advantage of the bigger prop....so lets replace the V-1710-39 engine with its two-speed, twp-stage kin, the V-1710-45 engine!
The -45 made a little more power at sea level and matched the -39's power at altitude, but the -45 made that power at a much higher altitude (over 10,000 feet higher up), so I'm thinking it was probably making more power at the -39's rated altitude.
This may be enough of a change to warrent the use of the Hamilton Standard.
Its an impressive looking propeller, to be sure..
.Elvis

Click to expand...

Nice idea, the question is if it will give enough more performance to be worth the trouble.

Using the numbers from the V-1710-93, the first production two stage Allison and not much different than the -45 model we get 1150-1180HP at 22,400ft.

This compares to the Merlin 61 used in the MK IX Spitfire which offered 1370HP at 24,000ft.

Now the Allison engine does show a marked improvement over the single stage Allisons. The best of the later ones were rated at 1125Hp at 15,500ft or 17,300ft depending on which source you believe ( or maybe whither or not ram is taken into accout?). The Two stage Allison does keep it's 1325HP take off rating instead of falling to 1200hp like the high altitude geared single stage Allison does.

However there is a cost. The two stage Allison is about 300lbs heavier than the single stage engine and is over a foot longer. Could you get one in a P-40 airframe? Sure. but it is going to be a lot more complicated than just lengthing the engine mounts and patching some sheet metal into the gap between the cowl and the old fuselage.

And what have you got when you are done? A Bf 109G with a DB 605 engine operating at 1.3 Ata at 2600rpm was supposed to give just about 1100hp at the same altitude as the 2 stage Allison gave it's 1150-1180hp. except it is in a smaller, lighter airplane. It will improve the P-40s chances but it won't turn it into a plane that can out run or out climb the 109G.


As far as that impressive looking propeller goes, I sure would like to see a P-40 with landing gear long enough to use one

The -45 with the H-S prop looks like the solution. Kurt Tank balanced the Fw-190D by just putting a spacer into the tail. Something like that could be done. If you want to make up the 300 pounds, switch from 6x.50 MG to 2x20mm in armament. That six-gun armament package was heavy.

Overall, I've learned that there is no one magical drastic solution, but a lot of little changes that could get the P-40 to 1200 horses at 20,000 feet.

No, it couldn't outrun or outclimb the 109 but it could outdive it and it was more resistant to damage.

If you want a plane to fight down low take the P-39. It could dogfight respectably on the deck and the M4 Cannon could take out most targets of opportunity on the ground.

Re: H-S prop.

Personally, I'd like to see that prop's diameter lessened to something closer to the C-E prop's diameter.
Sticking with the WWII-era power figures we have available to us, I fugre either the prop gets longer blades, wider blades or more blades, but not a combination of those aspects. I just don't think the ponies were there, at that time.
Wider, ok, but not wider and wider (so to speak). To me, this seems a case of picking only one.
---------------------------------------------------------------------------------------------------------------

Re: Weight

What is the weight of the Merlin XX?
What is the weight of the Allison -45?
---------------------------------------------------------------------------------------------------------------

Re: CG

Quite true, the engine is 22" longer with the extra stage added, but I wonder if we couldn't re-engineer that setup (I know, firghtful words) so that it would keep the length closer to the single stage setup.
While I've never seen a pic of an Allison with the two-stage setup, from what I can tell, I suppose those stages were in-line with the engine, thus the added length.
What if we were to take the two stages and position them to each side of the crankshaft.
This way, they could both drive off a single gear.
Forgive my rather rudimentary representation, but I'm thinking along these lines...

o0o

The smaller "o's" are the stages. The larger "0" is the drive gear that is connected directly to the crankshaft.

You could even place a second gear in there that could move in and out, thus engaging and disengaging the second stage.
This would also allow one of those turbines to rotate in the opposite direction, so the piping could run straight up the vertical centerline of the engine, making the setup even more compact.
Kinda like this:

db

I think that would be a more balanced arrangement than not having that gear, which would yield the manifolding to look more like...

dd

...and you really want to keep all that piping as close to the same length for each stage, as possible.

While this would probably put the length back close to the single stage's 85", I dont' know how it would fit width-wise, especially considering that the nacelle actually narrows towards the bottom rear (remember, its sorta shaped like an upside down egg)....hmmm, maybe if we rotated those stages upwards a little, so they were more inside the wide part of the "V".

Anyway, what do you guys think about setting the stages side-by-side like that, instead of in-line?

Would that work, or am I just Nuckin' Futs?




Elvis

You are "just Nuckin' Futs?"

No, not really. you would be surprised at some of the stuff that was actually tried, sometimes more than once, that never made it into production.

For propellors. I think you are correct. Spitfire needed those 5 blades because it more than doubled the engine power. A 20% increase would only require modest increase in blade area.
However everthing is a trade off. Propellor blades are like wings. Sure, a larger wing(blade) can give you more Lift(thrust) but it also has more drag, weight and may have a twisting motion.
The extra weight may be minimal. The extra drag may be trumped by the extra thrust at full throotle but it may shift the other way at cruising speeds.

Weights, The Merlin XX weighed 1450lbs or so depending on source. The -45 (one made) weighed 1515lbs but the first production engine By Allison went 1620lbs. THis is for the P-63 and may include the drive shaft?

Another table gives 175lbs as the weight of the auxilary stage of the -93 model used in the P-63.

Allison changed the drive set up from the -45 to the later models. THe -45 used a single speed drive while all the later models uses a hydraulic clutch like the German DB series of engines which gave a variable speed drive so the engine only used just enough power to drive the aux stage at low levels and didn't waste power like ALL gear drive superchargers did at low level. Yes there was a shaft that spaced out the second compressor.
In a test an Allison was fitted with the 2 stage supercharger from a Merlin. THere were bearing problems and it took 3 supercharger assembies to complete the test as each supercharger was appearently destroyed in succession.
You do need to route the output of one compressor from the outside or periphery of the compressor casing to the inlet or hub of the second compressor with a minimum of sharp bends.

Am I confused or are your diagrams trying to show two superchargers working in parallel rather than series?

Don't be confused by the diamiater of the compressor impellor given in many data sources. The diameter of the casing (diffuser) was much larger than the impellor.

There was a late model Corsair engine that used TWO impellors turned 90 degrees to the crankshaft running in parallel to feed a third impellor running in line with the crankshaft. Please note that this was still a TWO stage system

Shortround6,

My diagrams were attempting to show each turbine, with the initial outlet piping that would lead up to the intake manifold.
Maybe I should've "drawn" them as such, instead...
d0b
d0d
Is that a clearer picture?
Without the extra gear, both impellers would rotate in the same direction, thus the piping would come off of the same side of their respective housings.
That is what the second diagram was attempting to show.
Setting up the stages that way would've led to unequal length piping, which (apparently) is a big "no-no" when setting up any kind of forced air induction system (I'd have to consult my book as to why, as I cannot recall, off-hand).

What bearing were destroyed in the test you referred to? Engine bearings or turbine bearings?

AFAIK, the "-45" engine was never used in any plane (my reference shows no application for that particular engine), but the "-47" is only slightly heavier, and that version does show application for the P-63 (or "F-63", as its notated in my resource), so I don't think the extension shaft is included in the listed engine weight.
However, both the "-47" and the later "-93" show a much longer length (217+", IIRC).
Since both of those engines were applied to the P-63, maybe the shaft is included in the dimensions, but not the listed weight?
Seems odd, but we are talking about a division of the United States Government and who knows what those boys are up to, half the time!
I think, though, you see my point about the weight of those two engines, right?
Only about 65 lbs. and it didn't require any modification to the fuselage when the Merlin was installed in the P-40 (and actually, the weight difference there is more. About 135 lbs., comapred to the "-39" engine that the Merlin replaced).
I'm thinking, though, that setting that additional weight 2' farther out from the center would create a noticiable difference in the CG point, but Curtiss could've simply gotten around that by extending the aft section of the fuselage (I believe F-W did the same thing during the lifespan of the 190).

I believe the "twisting motion" aspect of changing the prop could be countered (at least somewhat) by shortening the diameter back down to 11' (as the pic I posted earlier shows the H-S prop to have a larger diameter, although I don't know by how much).
I would really hate to have to increase wingspan, in order to counter any additional "twist". That plane had a really great roll rate and I'd hate to mess with that aspect.

In your post, you seemed to alude to the fact that both stages are working at all altitudes.
Is that a correct assumption?
My comment concerning the additional gear was so that one stage would be enacted at lower altitudes, then, as altitude continued to increase, the gear would move in and enact the second stage, and only then would both stages work in unison.
This way, one could better tailor each stage to work at the presecribed altitude ranges, more accurately.

Lastly, could you please explain "in series" and "in parallel", please?
I think I know what you're getting at, but those terms, in relation to supercharging, are foreign to me.
I just want to make sure we're both on the same page.

Thanks.



Elvis

Going in reverse order.

2 impellors/superchargers each with it's own intake and each one feeding one bank of a V-12 engine would be operating in parallel. Or two impellors/superchargers feeding into a common intake manifold. If your compressor's could only achieve a pressure ratio of 2.8 to one then that is your maximum pressure in your manifold. 2.8 times the the airpressure at what ever altitude you are at.

Having 1 impellor/supercharger's output feed into a second superchargers inlet would be operating in series. Now the first supercharger could raise the pressure by 2.8 times the ambiant pressure and then the second super charger could raise it by 2.8 again giving you an overall pressure rise of 7.84.

This is in theory, in practice the overall pressure ratio was closer to 5-6 to 1 for a variaty of reasons

On the -45 engine both stages would be turning at all times and both stages would be turning in direct proportion to the engine speed/rpm. The -45 engine also only had a single gear ratio so at low altitude in thick air the supercharger/s would be turning much faster than was needed, wasting power. The later units with the hydraulic drive could "slip" and reduce the speed of the auxliary unit. Since centrifugal superchargers output goes up with the square of impellor speed ( as does their power consumption) large changes in impellor rpm are not needed to make large changes in power consumption or in output.

The Merlin was set up so that both impellors turned at the same speed and both impellors turned all the time. the Merin did have a two speed gearbox so it could use a slower speed at low altitudes.

R-2800s used by the Navy had a single speed supercharger on the engine, it rotated at a fixed ratio to the crankshaft. The other impellor,which was hidden inside the same large housing on the back of the engine had two speeds plus a neutral. At take off and low altitudes the auxialry stage was in neutral and provided no boost, it also didn't require any power to drive. As the plane climbed the low gear was engaged to provide pressureize air to the engines supercharger. as the plane climbed higher into thinner air the higher gear was selected to again provide sealevel (or slightly higher ) pressure to the inlet of the engine supercharger. SEE: http://www.zenoswarbirdvideos.com/Images/F4U/F4USEC.GIF
for an idea of how this works.

AS for the propellors I am sorry for any confusion. a larger propellor blade will have a larger twisting motion in relation to itelf. The outer part of the blade will try to twist in relation to the shank or part that goes into the hub. Depending on how much strength is already there it might require heavier construction, it might not.

AS to what the -45 was used in? as far as I know, nothing. it was developement engine. Only ONE was listed as being built. the -47 was listed as THREE built. used in XP-39Es which was the sort of prototype for the P-63. THe production version was the -93.

You might be able to work out or visualize the weight problem. how far from the center of gravity of plane was the center of gravity of the existing engine? weight X distance.
using a heavier engine of nearly the same size means the weigh goes but the distance stays the same.
A lighter engine further forward might balance out the same.
A heavier engine another 1 1/2 feet further out ?

see:More P-40 Stuff from a real Curtiss P-40 Warhhawk pilot's manual

Let us assume the center of the P-40s 1310lb engine is 80 in front of the desired center of gravity.

This gives us 104,800 in lbs of torque try to pull the nose down.
Using a 1500lb engine 100in from the CG gives us 150,000 in lbs of torque.
Now add the weight of the propellor and cowling to the weight moved foward.
Of course you can move the oil tank and some of the other stuff and move the new engine back a bit. you can also move the radiators and oil coolers back ( which was done on the P-40 Q)
And you can extend the tail for balance but that can bring in a few problems of it's own. Moving the control surfaces futher from the CG changes their effectivness which might be a good thing or it might be a bad thing.

More later.

Edit>

THE Bearings that were destroyed were in the supecharger, the Merlin had no turbine. Something to do with the supercharger being remote form the engine ( it was a test lash up) and the temperatures not being the same as when the supercharger was attached to the engine fouled up the tolerances.

Some cars have used two superchargers in parallel but the problem they were trying to solve was a bit different. Car engines operate over a much wider rpm range than aircraft engines and need better throttle response over this wide rpm range. THey were trying to match the volume of flow required at different rpm ranges which is not the same as the pressure variations that aircraft engines have to deal with. Unless you are racing up Pike's peak