Jumo 213 vs. Napier Sabre

[yulzari]

IIRC Setright never claimed it to be a sustained power reading but only a flash reading on the dynamometer held only momentarily. An indication of what it might be able to achieve as opposed to what it could sustain at that point in time.

 

[Simon Thomas]

In the table at the back, he claims it is "Based on best recorded power outputs during type or approval test..."
IIRC, the British type test was 100 hours, although only 10 hours was at full noise. I might have mixed up the civil and military. Either way it was meant to be a sustained test.

 

[Shortround6]

I have no idea of what sort of mental gymnastics are required to turn power from the turbine into bemp.

Information from an old "Aircraft engines of the World (1956)" says the Nomad NNm.8 had an after cooler and exhaust manifold reheat. It also made 4414shp plus 230lbs of thrust and weighed 3750lbs.
The NN M.7 at 3476shp and 250lbs thrust was figured at 87.2 eshp per liter and 205 BMEP.

It is a secondary source so take it as you will

 

[Deleted member 68059]

In the table at the back, he claims it is "Based on best recorded power outputs during type or approval test..."
IIRC, the British type test was 100 hours, although only 10 hours was at full noise. I might have mixed up the civil and military. Either way it was meant to be a sustained test.
View attachment 727214

Sadly the "19" on that chart is just a plain old catastrophic error.

Its actually not very good that this has been published, as he should have seen from the graph that having a single outlying point
50% better than anything else was a clear indication that some very serious error in calculation or source-facts had occurred.

Proposing that a service military engine had DOUBLE the hp/litre (during a 100 hour type test) of a Schneider Trophy engine (the "R" was given a life of 4 hours, by the way),
is obviously a sign that further interrogation of the data is urgently required.

 

[Deleted member 68059]

Another Napier internal document with a bit of a description of each variant and the power, boost and rpm achieved. This is in amongst papers all dated 1947.

 

[GregP]

Except the ferocious torque of the Griffin would have made the P-51's already 'exciting' tendency to drop a wing and roll as it unstuck even more 'exciting' - it was a borderline dangerous plane until it got moving and gained enough control authority.

Where do you GET this stuff? I know 5 or 6 people who own and fly them and they don't say anything close to what you are saying. Of course, most of them aren't flying them over 10,000 pounds. But ALL have talked with the guys who did, nd nobody ever said it was a death trap or close to one. It ea spitch-sensiotive at takeoff, but that doesn NOT equate to dangerous unless you are flying aerobatics in it and get it wrong.

 

[J.A.W.]

Did they ever actually do so really? And would a two stage supercharger be worth it aside from higher altitude performance? Sleeve valves didn't like large amounts of boost.

Actually, they didn't need such high boost pressures to make power.

Compare the boost-to-power requirements for the R/R Griffon and the Napier Sabre, both being nominally equivalent in 'swept volume'.

The higher volumetric efficiency of the sleeve valve system ensures that its fuel is converted to power (seen in higher fundamental metrics
such as BMEP/BSFC) due to less compressing of the fuel/air being necessary (& it also does not need 150 grade plus ADI for +20lb).

The strength of the Sabre can be seen in its ability to produce 'normal/climb' power for a period which lasts as long as the internal fuel,
which is also at higher power output than the Griffon (or R-2800) can manage - with all in their final production forms.

 

[wuzak]

Actually, they didn't need such high boost pressures to make power.

Instead the Sabre used rpm.

Compare the boost-to-power requirements for the R/R Griffon and the Napier Sabre, both being nominally equivalent in 'swept volume'.

The Sabre used higher compression and rpm to generate power.

The higher volumetric efficiency of the sleeve valve system ensures that its fuel is converted to power (seen in higher fundamental metrics
such as BMEP/BSFC) due to less compressing of the fuel/air being necessary (& it also does not need 150 grade plus ADI for +20lb).

Care to produce numbers for that claim?

The higher rpm will help bring more air through the engine, thus more fuel and more power.
It doesn't necessarily mean it was more efficient.

What version of the Sabre had +20psi boost without ADI?

The Sabre VII used +17.25psi boost and required ADI, and then +20psi boost still with ADI.

What fuel was it using? PN 145 vs PN150?

What version of the Griffon used ADI during WW2?

The post war Mk.57 for the Shackleton used ADI at take-off, but the 2 stage engines used +25psi boost without ADI.

The strength of the Sabre can be seen in its ability to produce 'normal/climb' power for a period which lasts as long as the internal fuel,
which is also at higher power output than the Griffon (or R-2800) can manage - with all in their final production forms.

Fair to say that Rolls-Royce didn't spend so much time developing the Griffon post war.

 

[J.A.W.]

ADI? No, I meant 100/130 with ADI, didn't need 150 grade for +20lb.
ADI was developed postwar for the Griffon in maritime patrol use.

Sabre piston speed was not excessive at higher rpm (unlike the Jumo 213 - Fedden was incredulous - at 3,700rpm for it).

(The BMEP/BSFC/ fuel grade figures are in the Wilkinson tome, & available at wwiiaircraftperformance.org).

 

[z42]

Sabre piston speed was not excessive at higher rpm (unlike the Jumo 213 - Fedden was incredulous - at 3,700rpm for it).

Sabre was oversquare, and had twice the number of pistons at roughly equal swept volume as the Griffon. Precisely to be able to reach high rpm without excessive piston speed. Not saying those aspects of the Sabre were a bad idea, but a very different design philosophy compared to the Griffon. It was also a couple hundred kg's heavier than the Griffon, so in effect in a different size class.

 

[J.A.W.]

Sabre was oversquare, and had twice the number of pistons at roughly equal swept volume as the Griffon. Precisely to be able to reach high rpm without excessive piston speed. Not saying those aspects of the Sabre were a bad idea, but a very different design philosophy compared to the Griffon. It was also a couple hundred kg's heavier than the Griffon, so in effect in a different size class.

No, it was in the same general size class for engines, with almost equal swept volume ~36 litres, but capable of doing more with it.
On a power to weight basis, or fuel consumption for output basis, & for sustained power setting levels.

Yes ok, props tend to become an issue at well over 2,000hp - during this period,
and the 14ft unit rotated by the Sabre was big for a fighter.

Can you present a single piston engine powered - WWII fighter aircraft - with a bigger prop?

 

[z42]

No, it was in the same general size class for engines, with almost equal swept volume ~36 litres, but capable of doing more with it.
On a power to weight basis, or fuel consumption for output basis, & for sustained power setting levels.

Swept volume ultimately isn't what aircraft designers are interested in. They're looking at power, weight, and dimensions (in particular frontal area). If swept volume would be the criteria for how we define 'size classes', we'd have the Liberty L-12 (27L, 400 hp, 380 kg) in the same class as the Merlin 61 (27L, 1600 hp, 750 kg), which I'm sure you'll agree is clearly nonsensical.

Sabre is about 200kg heavier than the Griffon (almost as much as the difference in weight between the Merlin and the Griffon!), but produces more power. A plane designed around the Griffon will likely be overweight with a Sabre, and conversely a plane designed for the Sabre will likely be underpowered with a Griffon.

Yes ok, props tend to become an issue at well over 2,000hp - during this period,
and the 14ft unit rotated by the Sabre was big for a fighter.

Can you present a single piston engine powered - WWII fighter aircraft - with a bigger prop?

Not sure what the relevance of this is to the rest of the thread, but yes, probably at 2000+hp we're getting close to the point where countra-rotating props start to become a pretty good idea.

 

[tomo pauk]

ADI? No, I meant 100/130 with ADI, didn't need 150 grade for +20lb.

Care to post some docs that show Sabre's boost with 100/130 + ADI?

Sabre piston speed was not excessive at higher rpm (unlike the Jumo 213 - Fedden was incredulous - at 3,700rpm for it).

IIRC Fedden didn't design neither Sabre nor Jumo 213.

No, it was in the same general size class for engines, with almost equal swept volume ~36 litres, but capable of doing more with it.
On a power to weight basis, or fuel consumption for output basis, & for sustained power setting levels.

As noted by the above member, swept volume was not what was propelling the aircraft.
On the p/w basis, a host of other engines were doing at least as good. What Sabre was not good was power at higher altitudes, but that somehow ends swept under the rug when people talk about the Sabre as it was the next best thing after the sliced bread.

 

[Metrallaroja]

ADI? No, I meant 100/130 with ADI, didn't need 150 grade for +20lb.

Just like many engines.
Every R-2800C with just 100/130 can use 70'' with water injection.

 

[z42]

IIRC Fedden didn't design neither Sabre nor Jumo 213.

Nope, but he was sent to Germany after the war to get a better picture of what the Germans had been up to. Don't know details, but presumably Fedden's comments mentioned are from that mission.

Fedden Mission - Wikipedia

en.wikipedia.org

What Sabre was not good was power at higher altitudes, but that somehow ends swept under the rug when people talk about the Sabre as it was the next best thing after the sliced bread.

They probably spent so much elbow grease trying to get the sleeves working and the engine working even remotely reliable, that they just ran out of time and manpower to make a good two-stage supercharger.

 

[tomo pauk]

Nope, but he was sent to Germany after the war to get a better picture of what the Germans had been up to. Don't know details, but presumably Fedden's comments mentioned are from that mission.

Thank you.
I was trying to point out that Jumo 213 was doing it's job, Fedden approving or not.

 

[Metrallaroja]

Care to post some docs that show Sabre's boost with 100/130 + ADI?

Posted it here before:

Spoiler: 100/130 + ADI

Just like many engines.
Every R-2800C with just 100/130 can use 70'' with water injection.

Spoiler: 28R

 

[z42]

Thank you.
I was trying to point out that Jumo 213 was doing it's job, Fedden approving or not.

To be fair, I'm not sure anything is known about the reliability of the 213J (the prototype version running at up to 3700 rpm) in service use. The MPS is beyond anything else in use during WWII, so I guess some scepticity is warranted.

 

[tomo pauk]

To be fair, I'm not sure anything is known about the reliability of the 213J (the prototype version running at up to 3700 rpm) in service use. The MPS is beyond anything else in use during WWII, so I guess some scepticity is warranted.

Funnily enough, I don't think that Jumo 213 have had any advantages over the Sabre, power-wise.

 

[Deleted member 68059]

Funnily enough, I don't think that Jumo 213 have had any advantages over the Sabre, power-wise.

A pretty decent achievement on 87 octane fuel.