Spitfire MK.XIV and La-7

[Anonymous]

What are you babbling about "used" and "available" torque? Do you really understand what you write? Face this: if an engine is running at x rpm at full throttle, there is no "available" torque to accelerate anything unless the load is reduced!!! You are completely mixing part throttle and full throttle operation and inventing garbage like "available" torque.

Now, in ordinary car engines the power decreases relatively steadily as the rpm is decreased from the full power rpm down. On the other hand, torque curve starts rising with decreasing rpm (from that full power rpm) until it reaches the peak at a certain point that is highly variable with each engine. All this at FULL THROTTLE, i.e. CONSTANT MANIFOLD PRESSURE.
In supercharged aero engines the curve is of different shape as it CANNOT BE OPERATED AT CONSTANT FULL POWER MAP EXCEPT AT HIGH RPM. Get it???

Available torque is a measurment taken at less than FULL THROTTLE. Go back through this debate and you will see that the issue is available power at less than FULL THROTTLE.

So why are you babbling about FULL POWER MAP? That was not the issue we were discussing. We were discussing the ability of the engine to power up to FULL THROTTLE AND MAP when running at a lower rpm/power level, or to sustain good power levels at lower than peak rpm. And for this, AVAILABLE TORQUE is the relevant measure of that ability.

Don't you remember the point behind all this? It was that the Spitfire XIV had a higher need to maintain full RPM to sutain good power output because at less than full RPM its available torque curve drops off more sharply than that of a larger displacement engine (i.e. R-2800). Simply put, the cost in actual available power of droping RPM on the Griffon is more severe than the same % drop in RPM on the R-2800. Therefore, a smaller diameter 5 bladed prop was more beneficial to the Spitfire than it would have been to a P-47.

Get it?

=S=

Lunatic

 

[Iskandar Taib]

First off, the Spitfire did not use any significant "Meredith Effect". Just because it's a liquid cooled engine radiator does not mean it exploits the effect. To achieve any significant Meredith effect, the system must include an expansion chamber prior to the radiator, a compression chamber after the radiator, and a thrust regulating exhaust nozzel. And finally, the exhaust flow must be directed into the vacuum wake of the fuselage to cancel out some or all of the parasitic drag. The Spitfire (and 109) lacked any of these features. Look in detail at the cooling system of the P-51 (as outlined in other threads on this forum) or the Mosquito to see examples of cooling systems which do significantly exploit this effect.

The Spitfire radiator was indeed designed to take advantage of the Meredith effect. See Quill's book. The Meredith effect was discovered in 1935, at the RAE, and Supermarine must have known about it. Just because the Mustang did it better does not mean others didn't use it.

Secondly, radial engines can exploit the effect, though I'm not sure exactly what the mechanism is. I know the Zero gained about 5-10 mph from the effect, and this part of the desing was stolen and transfered to the F4U Corsair for a gain of 10-15 mph. It may also have been exploited by the Soviets on the LA7 design. Also, the oil cooler looks like a very small P-51 radiator, some meredith effect may have been generated there (note this is a significant difference between the La5 and the La7).

Yes, they can definitely use it. Same principle. Heat from the engine is used to expand air and produce thrust. I'd be very surprised if everyone wasn't using it to some degree or another by 1944. If you didn't, and the effect is as large as people say it is, then your fighters are going to be pretty slow compared to everyone else's.

Thirdly, the La7 cowl cooling inlet is in fact very narrow just like that of the Tempest II and P-47J. It is exactly what you are describing when you say "cut down on the cooling inlet". The combination of a large bullet spinner feeding into a small cowl inlet was definitely a part of the La7 cooling system design. Take a look at the attached image - just how much more do you think the cooling inlet can be cut down?

Who knows.. It certainly isn't two inches like it is on the Reno heavy metal, though indeed it might be optimal and can't be reduced any further. The point is that it exists and is non-zero, and MUST be causing some drag. Probably a HUGE amount of drag.

We don't know how much drag the cooling inlets caused on either airplane, and we don't know how much of this was offset by thrust recovered from the engine heat on either airplane. So why do people fault the Spitfire for the radiators and ignore the cooling inlet for the Lavochkin? Silly, isn't it?

 

[Anonymous]

Who's ignoring the cooling inlet of the La7? The point is that it was very streamline. You cannot really argue the Spitfire was more streamlined because it didn't have a radial engine - by this point advanced cowl designs were very aerodynamic and did not cause much if any more drag than wing scoops.

If you actually investigate the F. H. Meridith document, you will see that it does not really describe a usable system. It is a series of equations showing that the effect should be possible, that's about it. The whole Lee Atwood argument that he brought this info over from England and it was used to create the P-51 radiator thrust system is highly dubious - it appears to be one of several attempts by Atwood to claim credit for the P-51 design that he doesn't really deserve. If his claims were legitimate he would not have waited until after Edgar Schmued died more than 40 years after the end of WWII to make them. Atwood was always jelous of Schmued's acclaim and also probably upset that "Dutch" Kindleberg gave Schmued the P-51 project instead of giving it to him. Clearly Kindleburg knew who had the right stuff. Lee Atwood's project - the B-25, showed nothing but conservativism of design - practically no innovation. The P-51 on the otherhand...

Here, read part of Ed Horkey's rebuttal to Lee Atwood's claim to have imported the "meridith effect" technology from Britian, a few years after Edgar Schmued passed away:

Atwood's article brought a rebuttal from aerodynamicist Ed Horkey, who had come to North American from the California Institute of Technology in 1938 to work under Schmued. The aft location, he said, was an obvious choice; there was no room for a suitable radiator anywhere else. Neither he nor Irv Ashkenas, another Caltech-trained aerodynamicist who worked on the Mustang, remembers Lee Atwood having had a role in that decision. Horkey dismisses the algebra that Atwood used to explain the Meredith Effect to the lay reader with the words, "We used calculus." The British Purchasing Commission, Horkey thinks, was impressed less by the Meredith effect than by Dutch Kindelberger's magnetic personality and Ed Schmued's German accent.
http://www.airspacemag.com/ASM/Mag/Index/1996/AS/wmtm.html

Again, w.r.t. the meridith effect, without the compression and expansion chamber and a pressure regulated exhaust nozzel, there simply cannot be much if any effect. The system is a heat pump in reverse, and lacking the above features, it is not going to produce much thrust. It's like comparing a pressure cooker to a open pot. And also, it does not vent the expanding air into the parasitic drag wake of the Spitfire, again minimizing the overall effect.

Just because a plane has radiators does not mean it had any meaningful thrust from the system. The fact is the Spitfire was not considered to produce hardly any Meridith effect. This can be seen by the fact the Spit IX is compared to the P-51 to estimate the effect, which is attributed about 350 HP equivalent for the P-51 over the Spit at full level speed (not accounting anything to the Spit for its lighter weight, lower Coef of Drag, and lower Mach number).

=S=

Lunatic

 

[pasoleati]

Lunatic, you don´t have a single piece of evidence to support your theory that Griffon´s torque would drop faster that that of the R-2800. It was you who started babbling about car engines and their torque. In short, please provide PROOF (e.g. maker´s torque curves) on the R-2800 vs. Griffon affair.

And anyway, what does this have to do with propeller blade count. If you want greater diameter without increasing tip speeds, just change the reduction gear ratio. It would be insane to permanently reduce engine max rpm just to keep tip speed down. It would just indicate a bad design error.

 

[Soren]

As for manuver, the La7 was a very manuverable plane. It was considered much more manuverable than both the 190 and the 109. Roll rate was very good at all speeds up to about 400 mph. Turn rates were also excellent and energy retention in a turn was quite good. The La7 could exceute a 225 mph 360 degree turn at 1000 meters in under 20 seconds in either direction with no loss of speed.

See now your relying on fairytales again ! The La-7 Wasnt noticable more maneuverable than either the 190 or 109, and the Germans had 'no' problem shooting them down, and they did it in masses.

The La-7 had one of the most streamline cowls of any radial engined fighter of WWII. It was more streamlined than any of the FW/TA designs, and comperable to the P-47J and Tempest II. It certainly had a little more nose drag than the Spitfire, but it had no wingscoop drag.

OMG are you trying to tell me that the Spitfires intakes induce more drag than the La-7's front nose section ?! The Air that hits the Spitfire's intakes will run almost straight through, while the air that hits the La-7's front nose section just smashes straight into it going virtually nowhere=Alot of drag !

The La-7's front nose section has bigger surface area than the two intakes under Spit's wings combined !

The La-7 also had leading edge slats, I'd think you'd be in love with it Soren!

Sure, but the Spit XIV had a new and larger wing. As for the leading-edge-slats well, first of they were VERY small on the La-7, and the La-7 had alot of weight to carry around with those small wings. Its wing span was only 9,8m.

Lastly where did you get those wild Climb rate numbers from ?? The Russians never gave it such wild climb rate stats !

 

[KraziKanuK]

Sure, but the Spit XIV had a new and larger wing.

I did not know the Spit IX at 242sqft was smaller than the 242sqft of the Spit XIV.

 

[Soren]

Sure, but the Spit XIV had a new and larger wing.

I did not know the Spit IX at 242sqft was smaller than the 242sqft of the Spit XIV.

Oh wasnt the Spit's wing larger than the La-7's maby ??

Spit= 22.48 m2 vs La-7=17.5 m2.

I dont have the Root profile for the La-7's wing, but it wasnt thick thats for sure.

 

[Iskandar Taib]

The Spit XIV started out as a Spit VIII. The Spit VIII was a Spit V with a two stage Merlin, some added tankage, tropicalized, a retractable tail wheel, and couple other refinements. The IX was basically a Mark V with a two stage Merlin in the nose, and was supposed to be a stop-gap measure. It ended up equipping most of Fighter Command's Spitfire squadrons while the more advanced Mark VIII was sent overseas (you hear about them in India and Burma, mostly). As far as I know, the wing was unchanged in all of these versions.

The new wing came with the Mark XX.

 

[Soren]

The new wing came with the Mark XX.

Don't you mean the XXI ?

 

[Anonymous]

Lunatic, you don´t have a single piece of evidence to support your theory that Griffon´s torque would drop faster that that of the R-2800. It was you who started babbling about car engines and their torque. In short, please provide PROOF (e.g. maker´s torque curves) on the R-2800 vs. Griffon affair.

If only I could. This info is not available.

Look, it's always true that, unless the larger engine is very poorly designed by comparision with he smaller one, that if they have equal peak HP that the larger engine will have a more favorable torque curve below peak power. That is a truism of engines within the size we are talking about (much bigger than about 5.5" diameter pistons starts becomming inefficient).

And anyway, what does this have to do with propeller blade count. If you want greater diameter without increasing tip speeds, just change the reduction gear ratio. It would be insane to permanently reduce engine max rpm just to keep tip speed down. It would just indicate a bad design error.

Grrr....

Reducing prop RPM makes the thrust output less efficient. Even thicker blades are needed, which makes torque roll even more of a problem.

They don't "perminently reduce engine max. rpm", they reduce rpm at very high altitudes. This reduces the prop-tip speed at very high altitudes where that speed is approaching mach. It's a trade-off between more optimal performance in the expected combat altitude range vs. peak performance at very high altitude - where little actual combat occures. With the R2800, a reduction in RPM at high altitude means much less of a drop off in available torque, so if the plane tips its nose up it will not bog the engine so easily as it would a smaller engined plane running at similar reduced rpm.

=S=

Lunatic

 

[Iskandar Taib]

Hmm.. You might be right. I could've sworn there was a Mark XX pictured in Quill's book, but I'll have to go get it out of storage. The Spitfire Society's web page shows no such Mark.

 

[pasoleati]

So where is the source for this "truism"? It is interesting that of the numerous engine related books none has ever mentioned this "truism". Honestly speaking, your truism is simply illogical!

As for "reducing prop RPM makes the thrust output less efficient". Please prove this with primary sources. Again a purely illogical claim on your behalf.

Perhaps we should ask Graham White, the leading authority on the R-2800, what he thinks about it. Be warned, he don´t suffer fools gladly.

 

[Soren]

Hmm.. You might be right. I could've sworn there was a Mark XX pictured in Quill's book, but I'll have to go get it out of storage. The Spitfire Society's web page shows no such Mark.

Im sure it was the XXI, never heard the XX having it thats for sure.

 

[Anonymous]

As for manuver, the La7 was a very manuverable plane. It was considered much more manuverable than both the 190 and the 109. Roll rate was very good at all speeds up to about 400 mph. Turn rates were also excellent and energy retention in a turn was quite good. The La7 could exceute a 225 mph 360 degree turn at 1000 meters in under 20 seconds in either direction with no loss of speed.

See now your relying on fairytales again ! The La-7 Wasnt noticable more maneuverable than either the 190 or 109, and the Germans had 'no' problem shooting them down, and they did it in masses.

Well, this is not what either the Russians or the Germans report.

The La-7 had one of the most streamline cowls of any radial engined fighter of WWII. It was more streamlined than any of the FW/TA designs, and comperable to the P-47J and Tempest II. It certainly had a little more nose drag than the Spitfire, but it had no wingscoop drag.

OMG are you trying to tell me that the Spitfires intakes induce more drag than the La-7's front nose section ?! The Air that hits the Spitfire's intakes will run almost straight through, while the air that hits the La-7's front nose section just smashes straight into it going virtually nowhere=Alot of drag !

The La-7's front nose section has bigger surface area than the two intakes under Spit's wings combined !

Ahh but you are forgetting that the nose of the Spitfire is not drag free either. For the Spitfire, you have to add the nose drag plus the scoop drag to come up with a comparable figure for the La7's nose/cooling drag. And, I would bet that the inlet area on the La7 is significantly smaller than the scoop inlet area on the Spit XIV (remember, it's scoops were over-large to compensate for boundary layer injestion). Look for yourself - those Spit XIV scoops are HUGE!:

www.warbirdphotos.net

www.btinternet.com

The La-7 also had leading edge slats, I'd think you'd be in love with it Soren!

Sure, but the Spit XIV had a new and larger wing. As for the leading-edge-slats well, first of they were VERY small on the La-7, and the La-7 had alot of weight to carry around with those small wings. Its wing span was only 9,8m.

The wingslats on the La7 were a 35% of the length of the leading edge of the wing, as compared to about 45% for the Bf109 (with squared off wingtips, it'd probably be closer to equal for the round tiped 109 wings).

The La7-FN(V) had a wingloading of 37.7 lbs/sq-foot, as compared to the Spitfire XIV's wingloading of 35.7 lbs/sq-foot. Yes the Spit has a little advantage here, but it's not huge., a difference of only 5.6%. On the other hand, the Spitfire's 11.23 meter wingspan is 14.6% wider than that of the La7, a disadvantage for high speed manuver and for rolling.

Lastly where did you get those wild Climb rate numbers from ?? The Russians never gave it such wild climb rate stats !

http://www.btinternet.com/~fulltilt/Perform.html

These are Russian test results, specifying the serial number of the actual planes tested.

=S=

Lunatic

 

[Anonymous]

So where is the source for this "truism"? It is interesting that of the numerous engine related books none has ever mentioned this "truism". Honestly speaking, your truism is simply illogical!

You must not have much engine experiance. I worked for a major engine analyser company for a year. More cubes = more avialable torque.

As for "reducing prop RPM makes the thrust output less efficient". Please prove this with primary sources. Again a purely illogical claim on your behalf.

To give the same thrust at a lower rpm the blades have to be wider. Isn't that obvious?

Perhaps we should ask Graham White, the leading authority on the R-2800, what he thinks about it. Be warned, he don´t suffer fools gladly.

Go right ahead. Ask him the question: "Why didn't the P-47 or F4U-4 use a 5 bladed prop like the Spit XIV?"

=S=

Lunatic

 

[Soren]

Well, this is not what either the Russians or the Germans report.

Your kidding me right ?! The La-5's and La-7's were shot down in masses, the 109 had a really good kill ratio against these two aircraft !

Leykauf said he never had problems with the Yak's or Lagg's, and found the Spitfire to be a MUCH tougher opponent ! (And that is what you'll hear from about every other 109 pilot)

Also you will find that the Germans saw their 109 as a better T&B fighter !(Yeah thats right, and even some Russian La pilots claim the same)

Ahh but you are forgetting that the nose of the Spitfire is not drag free either. For the Spitfire, you have to add the nose drag plus the scoop drag to come up with a comparable figure for the La7's nose/cooling drag. And, I would bet that the inlet area on the La7 is significantly smaller than the scoop inlet area on the Spit XIV (remember, it's scoops were over-large to compensate for boundary layer injestion). Look for yourself - those Spit XIV scoops are HUGE!:

www.warbirdphotos.net

You couldnt find a more illustrative picture of the scoops, maby one where they not at thier largest !

You see here's a better picture, and they are not HUGE:

Now thats is a HUGE nose:

The wingslats on the La7 were a 35% of the length of the leading edge of the wing, as compared to about 45% for the Bf109 (with squared off wingtips, it'd probably be closer to equal for the round tiped 109 wings).

I'd say its more like 32-33%, but could be 35%. Still this is very small, and WW2 Russian fighters aint known for their mechanical reliability, so those slats would most most likely Jam alot !

The La7-FN(V) had a wingloading of 37.7 lbs/sq-foot, as compared to the Spitfire XIV's wingloading of 35.7 lbs/sq-foot. Yes the Spit has a little advantage here, but it's not huge., a difference of only 5.6%. On the other hand, the Spitfire's 11.23 meter wingspan is 14.6% wider than that of the La7, a disadvantage for high speed manuver and for rolling.

Well its more a matter of lift-loading, and here IIRC the Spitfire is for once superior. The La-7's wings were thin !

http://www.btinternet.com/~fulltilt/Perform.html

These are Russian test results, specifying the serial number of the actual planes tested.

These are Official 'Russian' specifications for the La-5FN and La-7:

La-5FN:
Maximum speed: 648 km/h (405 mph)
Range: 765 km (478 miles)
Service ceiling: 11,000 m (36,080 ft)
Rate of climb: 1,000 m/min (3,280 ft/min)


La-7
Maximum speed: 680 km/h (425 mph)
Range: 990 km (618 miles)
Service ceiling: 9,500 m (31,160 ft)
Rate of climb: 1,100 m/min (3,608 ft/min)

Source: "Lavochkin's Piston-Engined Fighters"

 

[Anonymous]

Well, this is not what either the Russians or the Germans report.

Your kidding me right ?! The La-5's and La-7's were shot down in masses, the 109 had a really good kill ratio against these two aircraft !

Leykauf said he never had problems with the Yak's or Lagg's, and found the Spitfire to be a MUCH tougher opponent ! (And that is what you'll hear from about every other 109 pilot)

LOL - Lagg's.. he probably faced Lagg-3's, they were known as "wooden coffins".

Also you will find that the Germans saw their 109 as a better T&B fighter !(Yeah thats right, and even some Russian La pilots claim the same)

Not that I've seen. I've watched lots of interviews and none say what you're saying. Lets see some of these claimed comments.

Ahh but you are forgetting that the nose of the Spitfire is not drag free either. For the Spitfire, you have to add the nose drag plus the scoop drag to come up with a comparable figure for the La7's nose/cooling drag. And, I would bet that the inlet area on the La7 is significantly smaller than the scoop inlet area on the Spit XIV (remember, it's scoops were over-large to compensate for boundary layer injestion). Look for yourself - those Spit XIV scoops are HUGE!:

www.warbirdphotos.net

You couldnt find a more illustrative picture of the scoops, maby one where they not at thier largest !

"at their largest" - ummm, they came in one size for the great majority of production.

You see here's a better picture, and they are not HUGE:

Look huge to me!

Now thats is a HUGE nose:

Your not being serious here. The inlet size is tiny by comparison. The nose appears huge only because the taper toward the rear is not visible, it's about the same as the Spitfire nose from a similar view. And this photo also obviously is distorted to make the nose look "fatter" than it really is because the camera is too close to the plane. The photo's I provided were of the two planes from very similar angles and distances. Be fair about your choice of images please.

The wingslats on the La7 were a 35% of the length of the leading edge of the wing, as compared to about 45% for the Bf109 (with squared off wingtips, it'd probably be closer to equal for the round tiped 109 wings).

I'd say its more like 32-33%, but could be 35%. Still this is very small, and WW2 Russian fighters aint known for their mechanical reliability, so those slats would most most likely Jam alot !

By the La7 they'd had pleanty of experiance with them and they probably didn't jam much more than the German slats.

The La7-FN(V) had a wingloading of 37.7 lbs/sq-foot, as compared to the Spitfire XIV's wingloading of 35.7 lbs/sq-foot. Yes the Spit has a little advantage here, but it's not huge., a difference of only 5.6%. On the other hand, the Spitfire's 11.23 meter wingspan is 14.6% wider than that of the La7, a disadvantage for high speed manuver and for rolling.

Well its more a matter of lift-loading, and here IIRC the Spitfire is for once superior. The La-7's wings were thin !

I don't think so, but I'd have to look up the NACA profiles to be sure.

http://www.btinternet.com/~fulltilt/Perform.html

These are Russian test results, specifying the serial number of the actual planes tested.

These are Official 'Russian' specifications for the La-5FN and La-7:

La-5FN:
Maximum speed: 648 km/h (405 mph)
Range: 765 km (478 miles)
Service ceiling: 11,000 m (36,080 ft)
Rate of climb: 1,000 m/min (3,280 ft/min)


La-7
Maximum speed: 680 km/h (425 mph)
Range: 990 km (618 miles)
Service ceiling: 9,500 m (31,160 ft)
Rate of climb: 1,100 m/min (3,608 ft/min)

Source: "Lavochkin's Piston-Engined Fighters"

Well jeeze, so the Soviets use a more realistic method of specifying rate of climb than the most nations, which use initial rate of climb as the climb figure, which is totally misleading. The La7-FN(V) climbed to 6000 meters in 5.45 minutes, which is a climb rate of 3612 ft/min. The figure you've given is probably the 20,000 foot climb figure.

The P-51D had an initial rate of climb of 3,475 fpm, which would mean a 5.75 minute climb to 20,000 feet. Surely you are not suggesting this is a realistic assesment of the P-51D climb?

=S=

Lunatic

 

[Soren]

LOL - Lagg's.. he probably faced Lagg-3's,

Lagg's a La's look similar, also the Germans always refered to them as Lagg's.

they were known as "wooden coffins".

By the Russians, yes.

Not that I've seen. I've watched lots of interviews and none say what you're saying. Lets see some of these claimed comments.

Certainly !:

Interview with Major Kozhemyako, who mostly flew the La-5:

"The Me109 was exceptional in turning combat. If there is a fighter plane built for turning combat , it has to be Messer! Speedy, maneuverable,(especially in vertical) and extremely dynamic."

And there's more where that came from.

"at their largest" - ummm, they came in one size for the great majority of production.

Look at the picture at the bottom of the page.

Look huge to me!

Well it doesnt look HUGE to me.

Your not being serious here. The inlet size is tiny by comparison.

The nose-inlet on the La-7 is 360* remember.

The nose appears huge only because the taper toward the rear is not visible, it's about the same as the Spitfire nose from a similar view. And this photo also obviously is distorted to make the nose look "fatter" than it really is because the camera is too close to the plane. The photo's I provided were of the two planes from very similar angles and distances.

The picture of the Spitfire I presented is WAY closer than the picture I presented of the La-7 !

Be fair about your choice of images please.

And thats comming from you !!! Im not the one who presents a picture of a Spitfire with white painted fully open Radiator's ! ( Yes that does make'em look bigger ! )

By the La7 they'd had pleanty of experiance with them and they probably didn't jam much more than the German slats.

Russian aircraft were very unreliable, also late war La's ! Mostly because of the Russian industry's culture of production was much inferior to that of
the Germans. Btw, the La-7 used alot of Wooden parts !

Well jeeze, so the Soviets use a more realistic method of specifying rate of climb than the most nations, which use initial rate of climb as the climb figure, which is totally misleading. The La7-FN(V) climbed to 6000 meters in 5.45 minutes, which is a climb rate of 3612 ft/min. The figure you've given is probably the 20,000 foot climb figure.

The P-51D had an initial rate of climb of 3,475 fpm, which would mean a 5.75 minute climb to 20,000 feet. Surely you are not suggesting this is a realistic assesment of the P-51D climb?

Were talking Max. Climb rate here RG !

 

[Soren]

The Radiators aint at all HUGE:

 

[the lancaster kicks ass]

great pics though.........