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sea-level engine vs. altitude engine


ACEOFACES
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INTRODUCTION

Based on what was said in another thread in this forum, i.e.

 

Aircraft Performance thread

 

The question came up as to weather the P39/P400 power plants can be qualified as 'sea-level' engines or 'altitude engines'.

 

Initially some were saying the P39/P400s had no superchargers at all, that the P39/P400 Powerplant was nothing more than a normally aspirated engine. That statement was quickly proven to be in error. After that some were than saying the P39/P400 Powerplant, even though it has a supercharger, only qualifies as a 'sea-level' engine as opposed to a Fw190 that has an 'altitude engine'.

 

PURPOSE

First I will show that calling the P39/P400 powerplant a 'sea-level' engines is wrong!

 

Second I will show that what qualifies a 'sea-level' or 'altitude' engine has nothing to do with it having a supercharger or not, and everything to do with the power output above sea level!

 

PROOF

As in any situation where there is confusion, the best thing to do is to start with the definitions.

 

From the Aviation Glossary Defining the Language of Aviation website we can find the following definitions of a 'sea level engine' and an 'altitude engine'

.

14 CFR 1.1, FAA, Regulatory on SEA-LEVEL Engine

Sea level engine means a reciprocating aircraft engine having a rated takeoff power that is producible only at sea level.

.

14 CFR 1.1, FAA, Regulatory on ALTITUDE Engine

Altitude engine means a reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.

These 'exact' definitions can also be found in the FAA-H-8083-25 Pilot's Handbook of Aeronautical Knowledge in the section titled SUPERCHARGERS AND TURBO SUPERCHARGERS.

 

The Pilot's Handbook of Aeronautical Knowledge also provides an example of an early single-stage, single-speed supercharger and a two-speed supercharger. Following is the full quote from the Pilot's Handbook of Aeronautical Knowledge.

 

.

SUPERCHARGERS AND TURBO SUPERCHARGERS

An early version of a single-stage, single-speed supercharger may be referred to as a sea-level supercharger. An engine equipped with this type of supercharger is called a sea-level engine. With this type of supercharger, a single gear-driven impeller is used to increase the power produced by an engine at all altitudes. The drawback, however, is that with this type of supercharger, engine power output still decreases with an increase in altitude, in the same way that it does with a normally aspirated engine. Single-stage, single-speed superchargers are found on many high-powered radial engines, and use an air intake that faces forward so the induction system can take full advantage of the ram air. Intake air passes through ducts to a carburetor, where fuel is metered in proportion to the airflow. The fuel/air charge is then ducted to the supercharger, or blower impeller, which accelerates the fuel/air mixture outward. Once accelerated, the fuel/air mixture passes through a diffuser, where air velocity is traded for pressure energy. After compression, the resulting high pressure fuel/air mixture is directed to the cylinders. Some of the large radial engines developed during World War II have a single-stage, two-speed supercharger. With this type of supercharger, a single impeller may be operated at two speeds. The low impeller speed is often referred to as the low blower setting, while the high impeller speed is called the high blower setting. On engines equipped with a two-speed supercharger, a lever or switch in the cockpit activates an oil-operated clutch that switches from one speed to the other. Under normal operations, takeoff is made with the supercharger in the low blower position. In this mode, the engine performs as a ground-boosted engine, and the power output decreases as the aircraft gains altitude. However, once the aircraft reaches a specified altitude, a power reduction is made, and the supercharger control is switched to the high blower position. The throttle is then reset to the desired manifold pressure. An engine equipped with this type of supercharger is called an altitude engine. Figure 5-11

Now depending on your background and experience this example can be confusing.

 

So lets take a look at this FAA example in more detail..

 

But before we do, allow me to post a few figures that I will be referring to in the following discussion.

 

FAA_FIG5_11.jpg

FAA Figure 5-11

 

 

FAA_EXAMPLE.jpg

My example that includes Figure 5-11

With that, let's begin..

 

.

 

An early version of a single-stage, single-speed supercharger may be referred to as a sea-level supercharger. An engine equipped with this type of supercharger is called a sea-level engine.

First thing to note here is the FAA points out this example is relative to an early type of supercharger.

 

Also note the conditional qualifier 'may be referred to as', which should not be confused with the absolute qualifier 'is always referred to as'!

 

Therefore an engine 'can only be referred to as' a sea-level engine if the engine performs as the FFA goes on to describe later in their example.

 

.

With this type of supercharger, a single gear-driven impeller is used to increase the power produced by an engine at all altitudes.

In this statement the FAA is saying an engine equipped with this type of supercharger will produce more power than a equivalent engine that is not supercharged, i.e. a normally aspirated engine.

 

Granted, this may seem like a DUH for some!

 

But worth pointing out, in that it seems to be 'the' point of confusion for some members of this forum.

 

.

The drawback, however, is that with this type of supercharger, engine power output still decreases with an increase in altitude, in the same way that it does with a normally aspirated engine.

Note the FAA points out that, even though an engine with this type of supercharger will have more power than an equivalent normally aspirated engine, this type of supercharger still decreases in power with an increase in altitude.

 

At this point refer to the figured titled FAA EXAMPLE and ALLISON V-1710-33

 

Note I assigned some simulated values to the the FAA examples of a 'two speed supercharged engine' and 'normally aspirated engine' from their figure 5-11 an included the ALLISON V-1710-33 data from 1939 that Crump provided. I set the power of the two speed supercharged engine at sea level equal to that of the ALLISON V-1710-33 at sea level and set the power of the normally aspirated engine at sea level to value of 500bhp less than the ALLISON V-1710-33 to simulate an equivalent engine without supercharging, aka a normally aspirated engine.

 

Note the ALLISON V-1710-33 data (RED) shows the engine power output decreases with an increase in altitude, just like the normally aspirated engine (GREEN) power output decreases with an increase in altitude.

 

Therefore, by definition, the ALLISON V-1710-33 is a sea-level engine, even though it has a supercharger! Based on this, it is clear the ALLISON V-1710-33 used in this test must have one of the early type of superchargers that the FAA was referring to. Looking at the test date of 1939, I think that may be a safe assumption to make.

 

At this point I should point out the ALLISON V-1710-33 engine was not used in the YP-39 or later P39s. The ALLISON V-1710-33 engine is known as a 'C' version of the ALLISON V-1710s. The prototype YP-39 used an 'E' version of the ALLISON V-1710s, skipping the 'D' version of the ALLISON V-1710s.

 

.

V-1710C

"C" series engines, military model -33, producing between 750 and 1050 hp at 2600 rpm. These engines came in two groups, one group rated at full power at sea level, the other rated at full power at high altitude.

.

V-1710E

"E" series engines, 35, -37, -83, -85 producing 1100 to 2830 hp at 3000 rpm. These engines were a complete redesign, and did not share many components with the earlier engine series. Almost all components were interchangeable with later series engines and the V-3420, and could be assembled as right hand or left hand turning engines in either pusher or tractor applications.

Note the 'E' version states These engines were a complete redesign, and did not share many components with the earlier engine series. Therefore the 'E' version used by the YP-39 prototype and later P-39s and P-400s was very different from the early ALLISON V-1710-33 'C' version data that Crump provided as proof of the P39/P400s having 'sea-level' power plants. Knowing this, one has to wonder why Crump even provided the ALLISON V-1710-33 as proof of the P39/P400s being sea-level engines. Only Crump can answer that question.

 

Now lets continue

 

.

In this mode, the engine performs as a ground-boosted engine, and the power output decreases as the aircraft gains altitude

Note the FAA points out that, even though an engine with this type of supercharger will have more power than an equivalent normally aspirated engine, this type of supercharger still decreases in power with an increase in altitude. The difference here is this description is that of a two stage supercharger! As is noted when you read on, i.e.

 

.

However, once the aircraft reaches a specified altitude, a power reduction is made, and the supercharger control is switched to the high blower position.

Note in Figure 5-11 of the Pilot's Handbook of Aeronautical Knowledge it shows the power is equal to the rated power at sea level

 

Note here the FAA example is no longer referring to the early version of a single-stage, single-speed supercharger that decreases in power with altitude. Here the FAA example is talking about a two-speed supercharger that decreases in power as the altitude increases, However, once the aircraft reaches a specified altitude the supercharger control is switched to the high blower position and based on Figure 5-11 (and my FAA EXAMPLE and ALLISON V-1710-33 Figure) the power plant is capable of generate power equal to that of the rated takeoff power at sea level, and therefore qualifies as an 'altitude engine' which the FAA example states in the following, i.e.

 

.

An engine equipped with this type of supercharger is called an altitude engine. Figure 5-11

At this point it should be clear that what constitutes a 'sea-level' or 'altitude' engine has nothing to do with the Powerplant having a supercharger or not! In that there are other methods of obtaining rated takeoff power above sea level! For example there are turbochargers and turbo-superchargers just to name a few. So it makes since that the definition would not contain the method of doing it, only the criteria of doing it.

 

The only thing that sets the two apart is weather or not the power plant can obtain, or even exceed, the rated takeoff power at an altitude above sea level. If it can, it qualifies as an 'altitude engine' if it cant, it qualifies as a 'sea-level' engine.

.

IT IS THAT SIMPLE!

Now with that in mind lets take a look at some actual/real P39 power plant data, where I picked two of the eight tests that I provided in the previous thread, i.e.

 

.

February 5, 1941
Pursuit		One-Engine YP-39, A.C. No. 40-30
Subject:	Acceptance Performance Test
Section:	Flying Branch5.Serial No: PHQ-M-19-1185-A
Engine:		Allison V-1710-37

.

October 9, 1943
Pursuit Single Engine P-39Q-5, AAF No. 42-19615
Subject:        Flight Tests
Section:        Flight
Serial No:      ENG-47-1651-A
Engine:         Allison V-1710-85

Note I picked the YP39 prototype with a -37 'E' version of the ALLISON V-1710, and the P-39Q-5 with a -85 'E' version of the ALLISON V-1710.

 

P39_TESTS.jpg

 

As you can see in both cases, the rated takeoff power at sea level is obtainable at altitudes above sea level!

 

Therefore, BY DEFINITION, these P-39 powerplants qualify as 'altitude engines'

 

I hope this helps clear up some of the confusion out there, if not please feel free to PM me if you have any questions

 

S!

Edited by ACEOFACES
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Hey Ace! I have that book. It's got some good descriptions of aircraft systems and structure for period aircaft. Found the bits about the Merlin very interesting! 

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Let's see how engines were rated during WW2:

 

1-Boost-defiinitions-page-001_zps2f93aa0

 

 

From which I quoted the following

 

At normal R.P.M. this altitude is termed the rated altitude, and if the engine is made to climb still higher, the boost pressure will progressively fall, resulting in a decreasing engine power. From the rated altitude the engine power falls off in a similar manner to that of the un supercharged engine from ground level to altitude.

 

Nice to see the 'old' UK description of a supercharged engine capable of sea level rated power above sea level complies with the 'modern' FAA definitions of altitude engine! ;)

 

Hey Ace! I have that book. It's got some good descriptions of aircraft systems and structure for period aircaft. Found the bits about the Merlin very interesting! 

Actully that is NZTyphoon book.. I need to get a copy of this book someday, looks like alot of good info in there. Edited by ACEOFACES
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I see one simple problem there. Maybe I missed something, but no definition whether the engine is sea-level or high altitude states if the rated power is counted with or without the ram effect. Crumps chart of V 1710-33 is the only one I've seen so far which used the engine characteristics without ram effect.

 

Btw performance chart of specific airplanes has nothing to do with the fact whether the engine is or isn't altitude/sea level. As well as the fact that if there is constant manifold pressure. The only applicable chart here is the one shows output performance of specific engine. 

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 see one simple problem there. Maybe I missed something, but no definition whether the engine is sea-level or high altitude states if the rated power is counted with or without the ram effect.

 

 

 

RAM effect does not change the shape of the curve.  You can see on this BMW801 chart the effect of RAM at various airspeeds.

 

This one of the question's the FDSO asked me when I got my 8610-2.  "If you open the cowling on a turbocharged Mooney, how do you tell if it is an altitude engine or a sea level engine?"

 

Answer:  The altitude engine has a density controller and the sea level engine does not.

 

That means the Mooney with the sea level engine, the pilot has to keep a watch on his manifold pressure and advance the throttle as he climbs because it will decrease with altitude.  He shoves the throttle forward to the take off rating, clears his obstacles, and retards it to climb rating.

 

He then advances the throttle as he climbs to maintain the manifold pressure.

 

A pilot with an altitude engine does not have to touch his throttle because the density controller or pressure relief valve will maintain the set manifold pressure.

 

Allison built both sea level engines and altitude engines during the war.

 

The RAF got sea level engines in their P-400 export variants of the P-39.

post-1354-0-58779700-1359376060_thumb.jpg

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An early version of a single-stage, single-speed supercharger may be referred to as a sea-level supercharger. An engine equipped with this type of supercharger is called a sea-level engine. With this type of supercharger, a single gear-driven impeller is used to increase the power produced by an engine at all altitudes. The drawback, however, is that with this type of supercharger, engine power output still decreases with an increase in altitude, in the same way that it does with a normally aspirated engine.

 

http://aviationglossary.com/sea-level-engine-14-cfr-1-1/

 

 

Sea level engine means a reciprocating aircraft engine having a rated takeoff power that is producible only at sea level.

 

 

allison1710e4ratings.jpg

 

The Take off rating on the V-1710E4 engine found in the RAF P-400 is 44.5 inHG at 3000 rpm and is the highest power setting the engine is allowed to maintain.  The take off rating is only allowed for take off and no other condition of flight.

 

Why?  The supercharger pressure production falls off at altitude and the take off rating is no longer available.  It is a sea level engine.

 

 

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Yet you previously said crump,

 

I thought you were clear on this. If the supercharger cannot maintain manifold pressure with an increase in altitude, it is a sea level engine. The pilot must manually reach up and advance the throttle.

 

That is the difference. An altitude engine maintains manifold pressure and the pilot does not have to keep advancing the throttle.

 

If he sets the throttle to max cont on sea level engine, the manifold pressure will drop with altitude unless he keeps advancing the throttle to manually compensate.

 

Understand, Milo? You see how some authors have confused a sea level engine with an unsupercharged engine in the history of the P-400?

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Crump, thank you for explanation about the ram effect influance.

 

But about the V 1710-E4 chart. The engine limitation said nothing there I fear. It's in fact not a physical limitation of engine itself, it's more about recommendations of how to operate the engine. It was based on peace time philosophy where the long lifetime of engine not the highest performance was the priority. Actually after the 1942 the V 1710-E4 was rated to WER with 56Hg (I'm not sure about the exact number, but it was higher than 45). As soon as I get home, I check it and post the exact manifold pressure. I don't say you're wrong, I just say that the E4 engine could operate at even higher man. pressure and that you're not exactly right when you say the "45/3000 was highest power setting allowed to maintain". But to be precise, the higher setting was available for lower altitude only (if I remember it right it was up to 4,300ft).

Edited by I/JG3_Pragr
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The V-1710 had an automatic manifold pressure regulator. Thus it could maintain a constant manifold pressure to its critical altitude for what ever throttle position.

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I think there is no simple solution guys. The basic problem is that there is nothing like the single V 1710 engine.

 

Quote from the Vees for Victory about improving the performance of V-1710 design from October 1939

"At the same time Allison made note of the considerable and extensive development program that was then underway. It's major features were:

 

- Durability tests of V-1710-19 at 1090bhp at 13,200ft in support of releasing the engine for production.

- Conversion of four V 1710-23 engines to sea-level V-1710-41's for the Bell YFM-1B aircraft.

...

- Company sponsored development testing in anticipation of an Air Corps experimental program involving four V-1710-F3R high horsepower at high critical altitude engines.

..."

(See page 45)

 

About the -E4 engine.

Military Power Rating: 1150 bhp, at 42/3000 (critical altitude 12,000ft)

War Emergency Rating: 1490 bhp at 56/3000 (critical altitude 4,300ft)

(See page 149)

 

As you can see there is really nothing like only one V-1710 engine and different versions could had a different characteristics.

Edited by I/JG3_Pragr
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allison1710e4ratings.jpg

 

The Take off rating on the V-1710E4 engine found in the RAF P-400 is 44.5 inHG at 3000 rpm and is the highest power setting the engine is allowed to maintain.

Depends..

 

.

The take off rating is only allowed for take off and no other condition of flight.

So let me see if I understand your logic here..

 

Your saying the take-off power can NOT be used for any other flight condition.. Right?

 

Now take a look at the time limit associated with the take off MP setting..

 

Note it say the take off power setting time limit is 5min..

 

So are you saying it takes 5 mins to take off?

 

I know that your not, that would be silly! I only point that out to make a point..

 

That being it does NOT take 5 min to take off!

 

Therefore the pilot can make use of this power setting for 5min..

 

On that note

 

Now take a look at the climb data from that same report..

 

Note it only takes 5.15 min to climb to 10,300ft at a lower MP setting!

 

It is common, especially during testing, to climb at a slightly lower power setting..

 

Which can be seen in the power setting time limits for a climb..

 

Where the time limit is set at 30min at 2600 RPM..

 

Why?

 

Because a climb test is a continuos test from sea level to, in this test, 29kft

 

Thus the lower power setting used for a climb is NOT because the engine can not produce the rated takeoff power at higher altitudes..

 

The lower power setting is for engine stress and overheat issues due to the longer nature of the continues climb test..

 

That is to say, if they only wanted to climb to say 10kft, they could have used a higher power setting..

 

Since the time limit for the take off power setting is 5min, they could have climb at that power setting for 5min..

 

In that a climb test scenario is very similar if not just like an extended take off scenario

.

Why? The supercharger pressure production falls off at altitude and the take off rating is no longer available. It is a sea level engine.

What data are you basing that statement on?

 

In that I don't see anything in the report you referenced to support that..

 

Are you just assuming the power drops off?

 

Or worse yet are you basing this on the 1939 Allison V-1710-33 test data?

 

Where the V-1710-33 is a very different engine from the 1941 V-1710-35

 

But don't take my word for it!

 

.

V-1710C

"C" series engines, military model -33, producing between 750 and 1050 hp at 2600 rpm. These engines came in two groups, one group rated at full power at sea level, the other rated at full power at high altitude.

.

V-1710E

"E" series engines, 35, -37, -83, -85 producing 1100 to 2830 hp at 3000 rpm. These engines were a complete redesign, and did not share many components with the earlier engine series. Almost all components were interchangeable with later series engines and the V-3420, and could be assembled as right hand or left hand turning engines in either pusher or tractor applications.

As you can see, the engine used in this test is TWO VERSION removed from the 1939 data you posted in another thread.

 

Also note,

 

In the early 'C' version they had TWO versions!

 

1) Full power at sea level (ring a bell?)

2) Full power at high altitude!

 

Sounds to me like one of those 'early' superchargers situations the FAA was describing

 

Which begs the question..

 

Which of the two versions is that 1939 Allison -33 data from?

 

You know, the data you keep trying to say has something to do with the later versions of V-1710 used in the P39/400s

 

Which is odd when you consider the FACT that as early as the YP39 prototype they were already using the later 'E' version

.

The RAF got sea level engines in their P-400 export variants of the P-39.

Really?

 

Crump, would you be so kind as to tell us what that statement is based on?

 

As in citation needed here!

 

Because that statement is in direct conflict with most if not all information that can be found on the subject.

 

Based on my research I found the following..

 

.

P-39/P-400 MODELS

XP-39

first flown 6 April 1938.

Powered by an Allison V-1710-17 (E2) engine (1,150 hp/858 kW)

Fitted with a B-5 two-stage turbosupercharger.

 

XP-39B

first flown 25 November 1939.

Powered by an Allison V-1710-37 (E5) engine (1,090 hp/813 kW)

Streamlined XP-39 based on NACA wind tunnel testing. Turbosupercharger replaced with single-stage geared supercharger

 

YP-39

first flown 13 September 1940.

Powered by an Allison V-1710-37 (E5) engine (1,090 hp/813 kW)

 

P-39C

first flown in January 1941

Powered by an Allison V-1710-35 (E4) engine (1,150 hp/858 kW)

Identical to YP-39 except for V-1710-35 engine

Twenty produced out of an order of 80 the remainder were redesignated P-39D

 

Airacobra I

first flown in January 1941

Powered by an Allison V-1710-35 (E4) engine (1,150 hp/858 kW)

Airacobra I Royal Air Force designation for three P-39Cs sent to United Kingdom England for testing.

 

Airacobra IA

Powered by an Allison V-1710-35 (E4) engine (1,150 hp/858 kW)

The designation IA indicates direct purchase aircraft; 675 built.

The USAAF operated 128 former RAF aircraft with the designation P-400.

As you can see

 

By the time the P-39C aka P-400 was rolling off the assembly lines they were well past the early Allison 'C' versions of engines..

 

You know the 'C' version you posted data on in another thread.

 

Also note the P-39C aka P-400 was well past the Allison 'D' version of engines..

 

Such that even at the early stages of the XP-39 prototypes they were already using the Allison 'E' version of engines..

 

Which as I pointed out earlier, were a complete redesign from the earlier 'C' version.

 

For those who are confused by the engine notation, I have provided the following.

 

"ALLISON ENGINE MODELS"
"MIL    AEC NOTE : 5 built for XFL-1 and XP-39"
-06     E1
-17     E2
-37     E5

"MIL    AEC NOTE : P-39A/C engine"
-35     E4
-63     E6

Hope this helps! S!

Edited by ACEOFACES
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Early V-1710 came without automatic boost control. ABC was added with the V-1710-81 in the P-40 (M models) and the V-1710-83 models in the P-39 (L models). But the E.4 engine did not have it.

 

The V-1710.E.4 could produce 44.5" Hg to an altitude of 10800', but throttle would have to be adjusted continuously. At this altitude, the power output would be higher than take off power at sea level.

Edited by JtD
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The V-1710.E.4 could produce 44.5" Hg to an altitude of 10800'

Thanks for the input JtD!

 

Can you tell us where this info came from?

 

Thanks in advance!

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I think there is no simple solution guys. The basic problem is that there is nothing like the single V 1710 engine.

 

Quote from the Vees for Victory about improving the performance of V-1710 design from October 1939

"At the same time Allison made note of the considerable and extensive development program that was then underway. It's major features were:

 

- Durability tests of V-1710-19 at 1090bhp at 13,200ft in support of releasing the engine for production.

- Conversion of four V 1710-23 engines to sea-level V-1710-41's for the Bell YFM-1B aircraft.

...

- Company sponsored development testing in anticipation of an Air Corps experimental program involving four V-1710-F3R high horsepower at high critical altitude engines.

..."

(See page 45)

 

About the -E4 engine.

Military Power Rating: 1150 bhp, at 42/3000 (critical altitude 12,000ft)

War Emergency Rating: 1490 bhp at 56/3000 (critical altitude 4,300ft)

(See page 149)

 

As you can see there is really nothing like only one V-1710 engine and different versions could had a different characteristics.

Yep, making blanket statements is unhelpful and another reason is why it is important to use source material from the 1940s, rather than trying to use modern, civilian practices to define the characteristics of high powered military engines. Thanks for the heads-up on Vees for Victory - now on order from Amazon.

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The V-1710.E.4 could produce 44.5" Hg to an altitude of 10800', but throttle would have to be adjusted continuously. At this altitude, the power output would be higher than take off power at sea level.

 

 

I am sure like most engines during WWII it was developed and improved.

 

Unfortunately, the RAF P-400 as tested did not seem to benefit from it as tested and it was not approved to 44.5 inHG at 3000 rpm beyond take off.

 

 

About the -E4 engine.

Military Power Rating: 1150 bhp, at 42/3000 (critical altitude 12,000ft)

War Emergency Rating: 1490 bhp at 56/3000 (critical altitude 4,300ft)

(See page 149)

 

 

The War Emergency Rating you listed does not appear on any of the RAF P-400 aircraft documentation.  Any idea on the timeframe that it was approved for operational use?

Edited by Crump
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I am sure like most engines during WWII it was developed and improved.

 

Unfortunately, the RAF P-400 as tested did not seem to benefit from it as tested and it was not approved to 44.5 inHG at 3000 rpm beyond take off.

No improvement necessary here..

 

In that the P-39C and P-400s aka Airacobra both had the same engines

 

As for why the RAF didn't obtain the same power levels, apparently the RAF didn't push the Airacobra (P-400) as hard as the US did when testing the P-39C

 

As I already pointed out the Airacobra is the same as a P-39, only with a 20mm in place of the 30mm. Which is one of the reason the US designate the Airacobra's P-400.

 

But don't take my word for it! Simply look at the RAF vs. the US report and you will see they both were done in July of 1941, and both had the -35 (E4) versions of the Allison V-1710..

"RAF"
"A.H.574"
"1941 July 29"
"Airacobra"
"V-1710-35 (E4)"

"ALT    RPM     MP"
    0   2600    37.2
 2000   2600    37.2
 4000   2600    37.2
 6000   2600    37.2
 8000   2600    37.2
10300   2600    37.2

"Wright Field"
"W-535"
"1941 July 17"
"P-39C"
"V-1710-35 (E4)"

"ALT    RPM     BHP"
0       3000    1150
5000    3000    1150
1000    3000    1150

The only notable difference in the two test is the RAF preformed the climb test at 2600 RPM and the US performed the climb test at 3000 RPM, which in turn resulted in the 1150 rated power.

 

Hope that helps!

 

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... The War Emergency Rating you listed does not appear on any of the RAF P-400 aircraft documentation.  Any idea on the timeframe that it was approved for operational use?

According to the Vees it was post 1942 limitation. But no simple easy answer is possible I fear. I haven't found any specific test of P-39 with such limitation but on the other hand it's damn hard to find such things.

 

I'll use P-40E as example. That plane use V-1710-F3R engine officially limited with 44''/3000rpm/1150bhp.

According to this:

http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/1710-39.pdf

and this:

http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/Allison%201710-39%20abuse.pdf

 

the F3R/F4R engines were operated at up to 70''/3000rpm in operational service. They were "simply" resetting the throttle stops. Anyway I can't find any hard data from test of P-40 with such high boost. By the way the same thing was done to P-38's Allisons which were rated for 1150bhp too, but sustained higher boost with higher engine output. 

I'm not sure how the throttle control worked in P-39, but according to the fact F3R and E4 engines were very similar I think (this is my opinion not proven fact) the same thing like in P-40 could be done to P-39.

 

One last thing, the Military power rating was based on test where the engine should proof to be able worked for 50 hours at least under tested settings.

 

I hope this will help a bit.

Edited by I/JG3_Pragr
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I haven't found any specific test of P-39 with such limitation but on the other hand it's damn hard to find such things.

 

 

 

It should not be very hard to find if it existed.  If it was approved, then a copy would exist in every AFM (Airplane Flight Manual) in operation along with the T.O.'s required to be in every previous copy of the AFM as well as in every AMM (Airplane Maintenance Manual).

 

Each aircraft had to have the updated technical information in its serial number specific operating instructions.

 

I don't think it would be that hard to find.  If data on such engines as the BMW801S exist's in quantity from the final days of the Luftwaffe, an allied mass production would exist in quantity.

 

 

 

They were "simply" resetting the throttle stops.

 

 

 

All sides did this kind of stuff.  We hear about the success stories but there are very good engineering why the manufacturer's have not approved the engine for such overboost conditions.   Not really on topic either....

 

According to Boscomb Down's own investigations of the aircraft's performance, the fact remains the British got sea level Allison's in their export model of the P-39. 

 

 

allison1710e4ratings.jpg

 

 

 

That was the topic of this thread.  Not the myriad of different engine variants produced by Allison under the V-1710 series, no such statement was blanket claim as too all Allison's being sea level engines was ever made.  The topic is specific to one engine type in a specific installation, the RAF P-400.  It is a fact, the P-400 recieved a sea level engine as exported to the RAF.

British P-400.pdf

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Rule 5. Do not make sarcastic little comments just to score points.

Quite right, MM. I'm sure we all agree to that, don't we?

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According to Boscomb Down's own investigations of the aircraft's performance, the fact remains the British got sea level Allison's in their export model of the P-39. 

 

 

allison1710e4ratings.jpg

 

 

 

That was the topic of this thread.  Not the myriad of different engine variants produced by Allison under the V-1710 series, no such statement was blanket claim as too all Allison's being sea level engines was ever made.  The topic is specific to one engine type in a specific installation, the RAF P-400.  It is a fact, the P-400 recieved a sea level engine as exported to the RAF.

 

 

Crump's own definition of a "sea level engine" has nothing to do with the 5 min take off rating:

 

 

Milo, it does not have anything to do with any overboosted condition.

 

An engine is classified by it's sea level performance at maximum continuous.  14 CFR Part 1 will tell you it is by Take Off rating but that is because there are only two major types of superchargers used today and you can tell by the take off rating application whether you have a sea level supercharger or altitude engine.

 

The premise is the same though today.

 

the V-1710-E4 in the two P-400s tested maintained continuous maximum power up to their critical rated altitudes http://forum.il2sturmovik.net/topic/465-sea-level-engine-vs-altitude-engine/?p=8340  The E4 export engine is identical to the V-1710-35 used in the P-39C and is not a so-called "sea level" engine.

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I would be more inclined to consider Crump's use of the word FACT..

 

If he provided anything that would support his claims prior to its use..

 

Even more incline if he didn't ignore the preponderance of evidence showing the engines used in the P-39C, Airacobra, P-400 are one in the same..

 

But until that day comes..

 

I think I will have to stick with 14 CFR 1.1, FAA, Regulatory definition over his personal definition..

 

In the mean time

 

Based on what others and I have presented thus far..

 

I think most of us can agree that it is clear that the Allison -35 engine power levels above sea-level meet the 14 CFR 1.1, FAA, Regulatory definition of an 'altitude engine'

 

For those who are still not fully convinced..

 

Consider the definition of 'critical altitude'

.

McGraw-Hill Dictionary of Scientific and Technical Terms : Critical Altitude

The maximum altitude at which a supercharger can maintain a pressure in the intake manifold of an engine equal to that existing during normal operation at rated power and speed at sea level without the supercharger.

As can be seen in all of the P-39/P400 data presented thus far, the critical altitude is well above sea-level!

 

Even the RAF reference Crump uses shows the critical altitude to be 10,300ft.

 

Now ask yourself..

 

How can a sea-level engine have a critical altitude above sea-level?"

 

Hope that helps! ;)

 

.

Edited by ACEOFACES
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How can a sea-level engine have a critical altitude above sea-level?"

 

Same as a normally aspirated engine can have one for a given rating.   You need me to film it in action for you Tagert since I know you cannot fly?  It would give you some insight into the difference between a sea level and an altitude engine.

 

 

 

 think I will have to stick with 14 CFR 1.1, FAA, Regulatory definition

 

Sure......  :salute:

 

 

14 CFR 1.1 says:

 

 

 

Sea level engine means a reciprocating aircraft engine having a rated takeoff power that is producible only at sea level.

 

http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&rgn=div8&view=text&node=14:1.0.1.1.1.0.1.1&idno=14

 

 

According to the engine limitations, the take off rating at sea level on a standard day is only producible at sea level. 

 

allison1710e4ratings.jpg

 

 

;)

Edited by Crump
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On the V-1710.E.4 the take off limit is neither only cleared for sea level, nor is it producible only at sea level nor does the take off rating produce more power at sea level than the maximum for level flight at 12000'.

 

The take off limit is cleared for any altitude, if you had to take off from an airfield at 10000' feet you were still supposed to use it.

The take off limits are obtainable to an altitude of 10800'.

The rate take off power is 1150hp. The maximum for level flight produces 1150hp at 12000'.

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The take off limit is cleared for any altitude,

 

As it is in any aircraft engine, JtD. Density altitude changes and is rarely standard.  Does not mean you can use take off rating for "any altitude".  Take off rating is for getting the airplane off the ground and clear of any immediate obstacles and nothing else. 

 

Although there are not many airports above the critical altitude for most normally aspirated engines.

 

 

The rate take off power is 1150hp. The maximum for level flight produces 1150hp at 12000'.

 

 

Sure it does.

 

BHP = PLANK/33,000

 

P = Brake Mean Effective Pressure

L = Length of the Stroke (does not change)

A = Area of the Piston Head in square inches (does not change)

N = Number of Power Strokes (RPM / 2)

K = Number of Cylinders (does not change)

 

So Explain how any power setting with a lower manifold pressure than the take off rating can produce more power?

 

It cannot unless physics as we know it is altered.

 

So the fact is, the V-1710-E4 is a sea level engine as used in the RAF P-400 series.

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Self explanatory (Aircraft power Plants, Northrop Aeronautical Institute, 1948)

 

TitlePage-001_zps8b5cf3ab.jpg

Sealeveltoaltitude_zps552593f3.jpg

Singlestagechartandgearratios_zpsc2191e5

Sealevelandsingle-stagealtitudesuperchar

Example of "overboosting"

http://www.raafwarbirds.org.au/targetvraaf/p40_archive/pdfs/Allison%201710-39%20abuse.pdf

 

Allison V-1710E4 and E.12 used different gear ratios - sea level superchargers do not have these gears to drive the blower at a higher speed.

 

1-Airacobra-page-0012_zps80755cc6.jpg

 

The take off rating using overboost has nothing to do with the engine's rating because it is a condition which can limit the life and reliability of the engine.

 

The important figures are power output up to the critical altitudes - an engine with a sea level supercharger cannot and will not provide continual or improving power figures up to the critical altitude.

Edited by NZTyphoon
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Take-off rating,

 

or the maximum horsepower which it is permissibile to use at sea level and at low altitudes.

 

 

A.P 129 defines low altitude for take off rating as 1000 feet above the ground or sea level and 3 minutes of use or when 1000 feet altitude is reached whichever is sooner.

 

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf

 

It is not a hidden WEP rating.  It is an allowable overboost and stressful period on the engine to get it safely into the air.

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Self explanatory

 

Actually it has been explained several times already, NzTyphoon.

 

Nice that you have "found it"!!

 

;)

 

 

 

 

Posted 28 January 2013 - 14:56 Crumpp says:

 

I thought you were clear on this. If the supercharger cannot maintain manifold pressure with an increase in altitude, it is a sea level engine. The pilot must manually reach up and advance the throttle.

 

That is the difference. An altitude engine maintains manifold pressure and the pilot does not have to keep advancing the throttle.

 

 

 

Posted 28 January 2013 - 12:43 Crumpp says:

 

This one of the question's the FDSO asked me when I got my 8610-2. "If you open the cowling on a turbocharged Mooney, how do you tell if it is an altitude engine or a sea level engine?"

 

Answer: The altitude engine has a density controller and the sea level engine does not.

 

That means the Mooney with the sea level engine, the pilot has to keep a watch on his manifold pressure and advance the throttle as he climbs because it will decrease with altitude. He shoves the throttle forward to the take off rating, clears his obstacles, and retards it to climb rating.

 

He then advances the throttle as he climbs to maintain the manifold pressure.

 

A pilot with an altitude engine does not have to touch his throttle because the density controller or pressure relief valve will maintain the set manifold pressure.

 

Allison built both sea level engines and altitude engines during the war.

 

The RAF got sea level engines in their P-400 export variants of the P-39.

 

 

 

You have all the right information.  You just failed to put it all together in a practical and meaningful way.

 

The sea level engine curve drops off with altitude ONLY at red line.  Anything below maximum output, a sea level engine emulates an altitude engine simply because the pilot can advance the throttle to get his boost pressure back.

 

That is why our Allison curve drops steadily at red line.

 

post-1354-0-58506600-1359551369_thumb.jpg

 

post-1354-0-92628400-1359551390_thumb.jpg

 

An altitude engine at red line increases in power with altitude or maintains sea level power:

 

post-1354-0-19904500-1359551508_thumb.jpg

 

So only at red line, can we tell the difference on a chart. 

 

In the air, the practical difference is the pilot has to constantly adjust the throttle to maintain manifold pressure in a sea level engine.

 

You can see on the engine limitations if the sea level take off rating does not match the altitude ratings.  In otherwords, the sea level power is not reproducible at altitude.

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The important figures are power output up to the critical altitudes - an engine with a sea level supercharger cannot and will not provide continual or improving power figures up to the critical altitude.

 

 

 

Anything below red line it certainly will Nztyphoon as long as the pilot advances the throttle to maintain manifold pressure.

 

That is why the FAA changed the definition and put it in terms of take off power.  For most engines, take off power is the highest overboost permitted and represents red-line.

 

For the pilot, if you have to keep advancing the throttle with an increase in altitude to maintain manifold pressure or boost, it is a sea level engine.

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On the V-1710.E.4 the take off limit is neither only cleared for sea level, nor is it producible only at sea level nor does the take off rating produce more power at sea level than the maximum for level flight at 12000'.

Exactly!

 

.

The take off limit is cleared for any altitude, if you had to take off from an airfield at 10000' feet you were still supposed to use it.

Good point!

 

.

The take off limits are obtainable to an altitude of 10800'.

The rate take off power is 1150hp. The maximum for level flight produces 1150hp at 12000'.

That agrees with all the data I have seen thus far.. Still not clear as to why the RAF decided to run the P39/P400 -35 motor at 2600RPM instead of 3000RPM as used in the US testing.. But that does shed some light on why the RAF was not able to obtain the same values the US testing was obtaining
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Self explanatory (Aircraft power Plants, Northrop Aeronautical Institute, 1948)

NICE!

 

In light of this information

 

I think we can safely say this does end the debate! ;)

 

That being, the "E" motor used in the P39/P400 is an altitude engine, by definition!

 

But.. apparently some members are still holding out or a little confused by the info..

 

Even though you put a red border around some of the more important notes!

 

So I decided to re-post some of those here in the hope it sinks in on a 2nd read..

 

Lets begin!

.

NORTHROP AIRCRAFT POWER PLANTS

The sea-level engine can be converted to an altitude engine by providing a gear ratio that will drive the blower at a higher speed and a control device to limit the degree of supercharging at lower altitudes.

That makes perfect since, and fits nicely into the definitions I already provided..

 

Where the normally aspirated engine can be converted to a sea-level engine by installing an early 1:1 gear ratio type of supercharger (SC)..

 

Where this type of SC increases the power at all altitudes..

 

But, this increase in power drops off with an increase in altitude 'starting' at sea-level just like the normally aspirated engine does..

 

Where as an altitude engine uses a larger gear ratio to spin (drive) the blower at a higher speed and thus produces more power..

 

The problem here is it can produce too much power and damage the engine!!

 

Hence the need for the pilot to monitor the boost in cases where there is no control device provided to limit the supercharging..

 

The key difference here is the power in an altitude engine does NOT drop off with an increase in altitude like the normally aspirated engine or sea level engine (aka ground boosted engine)..

 

Apparently the P39/P400 didn't have a control device (per JtD)..

 

Thus it was up to the pilot to make sure he didn't over boost the engine at low altitudes..

 

.

NORTHROP AIRCRAFT POWER PLANTS

This control device is necessary in order to avoid over boosting, which means stressing the engine beyond it approved rating.

Note they go on to point out the pilot can override the control device to over boost the engine, i.e...

 

.

NORTHROP AIRCRAFT POWER PLANTS

A slight degree of over boosting is sometimes used to obtain extra power for emergencies, but it reduces the life and dependability of the engine.

As noted above, apparently the "E" motor used in the P39/P400 didn't have a control device..

 

Therefore a savvy pilot could get a little more juice when needed.

 

.

NORTHROP AIRCRAFT POWER PLANTS

However, increasing the gear ration enough to supply the full weight of air at that altitude also makes it necessary to provide an additional 120 hp. to run the supercharger, thus reducing the net horsepower output.

That explains why a sea level engine has more power at sea level than an altitude engine! As noted in the following..

 

.

NORTHROP AIRCRAFT POWER PLANTS

The chart shows that the power output at take-off, and for the first few thousand feed of climb, is less than that provided by the sea-level engine, but this does not mean that it is impossible to obtain greater horsepower at the lower levels. If the controls were removed and the engine operate with the throttle wide open, more power would be obtained. For example, at 10,00 ft., a condition of 'over boosting' would exist and there would be 115-hp. output. Likewise, at sea level, the theoretical power output would be about 1600 hp

NICE!

"1150 hp at 10,000 ft from a 1000hp motor!"
"1600 hp at sea level from a 1000hp motor!"

 

As noted, apparently the "E" engine used in the P39/P400 didn't have this control device..

 

Thus no need to remove or disable them!

 

Thus there was nothing stopping the P39/P400 pilot from getting a little more juice out of the "E" motor in an emergency situation.

 

Where emergency situation should not be confused with the test data provided thus far.

 

No wonder the Russians loved this plane!!! ;)

 

PS I will have to PM you to get some of those originals drawings.. I would like to update my original post to include some of those drawings and text!

Edited by ACEOFACES
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The British used 2600 rpm for testing because they tested climb performance with the climb rating, 37" / 2600 rpm for the entire climb.

 

The US testing went with military rating of 42"/ 3000 rpm for the first 5 minutes, after which they reduced to climb rating, 2600 rpm.

 

This is simply a matter of different testing philosophy.

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They used the climb rating in the climb because that the maximum climb performance the engine could handle.

 

That is why the Allison engineers designated it as the climb rating. Notice that both 37" and 42" are less power than the sea level take off rating of 44.5".

 

;)

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BTW - just because a pilot had to advance the throttle on an early V-1710, it does not mean the supercharger was not fitted with boost control, nor does it mean it was a "sea level" supercharger: it simply meant the boost control was a stop on the throttle lever or that the Claudel Hobson boost control initially fitted was not fully automatic.

 

The supercharger still meets the conditions laid out in the Northrop Aeronautical Institute book - the supercharger was fitted with gears to drive the blower at high speeds and it had a form of boost control.

 

MustangIPNs1_zps2bea1183.jpg

 

MustangIPNs2_zps19665514.jpg

 

MustangIPNs3_zps7f0e5fe1.jpg

 

Automatic boost control for Allison engines came later.

Edited by NZTyphoon
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BTW - just because a pilot had to advance the throttle on an early V-1710 it does not mean the supercharger was not fitted with boost control, nor does it mean it was a "sea level" supercharger: it simply meant the boost control was a stop on the throttle lever - the Claudel Hobson boost control initially fitted was not fully automatic.

Agreed 100%

 

Granted that should go without saying, as in DUH!

 

But in light of what has been missed by some here thus far it is probably a good idea to point out the obvious!

 

The British used 2600 rpm for testing because they tested climb performance with the climb rating, 37" / 2600 rpm for the entire climb.

 

The US testing went with military rating of 42"/ 3000 rpm for the first 5 minutes, after which they reduced to climb rating, 2600 rpm.

 

This is simply a matter of different testing philosophy.

Agreed 100%

 

Sadly some read that and think you are trying to imply the RAF was too stupid..

 

That or they would have us to belive Allison made two different versions of the same V-1710E4 (aka -35) engine!

 

Both of which is just plain silly!

Edited by ACEOFACES
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Allison made two different versions of the same V-1710E4 (aka -35) engine!

 

 

Well, most countries make two different versions of military equipment when they sell it to other countries.  One is an export version and the other for domestic use.

 

Why was it called a P-400 and not a P-39?

 

 

p400.jpg

 

 

 

http://books.google.com/books?id=CDWtdzMt9AEC&pg=PA41&lpg=PA41&dq=P-400+export+version&source=bl&ots=0OXQosF7x2&sig=i63Xq8AGVQzHVvrMLOH0xFOEsKU&hl=en&sa=X&ei=WcMJUf_wNabH0QGO7YHoDA&ved=0CFsQ6AEwCDgU#v=onepage&q=P-400%20export%20version&f=false

Edited by Crump
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