MOST UNDERRATED AIRCRAFT OF WWII?

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James W. said:
You have Wilkinson? He lists the factory data sets for fuel/oil consumption, power-density such as here:

Sabre VII cruise fuel consumption 205 g/hp/hr, & oil 6 g /hp/ hr, weight to hp 0.33 kg/hp, all rather better than a Griffon, or R-2800..
Click to expand...

A little more pick and choose on the figures and lets throw in a typo too?
How many Sabre VIIs were built? How many flew?
1947 Wilkinson says fuel consumption 205 g/hp/hr, & oil 6 g /hp/ hr, weight to hp 0.37 kg/hp. the page is revised from the 1946 edition.

Now if I pick and choose which entry for the Griffon I quote from I can find fuel consumption 210 g/hp/hr, & oil 3 g /hp/ hr, weight to hp 0.41 kg/hp for a Griffon 130. For a Griffon 88 I get fuel consumption 225 g/hp/hr, & oil 4 g /hp/ hr, weight to hp 0.43 kg/hp.
Since the Griffon 88 is using a two stage supercharger it keeps some of it's performance better at high altitudes but it pays for it in the weight of the supercharger.

Figures for a P & W R-2800 CA 19 which is a commercial engine are 190 g/hp/hr, & oil 7 g /hp/ hr, weight to hp 0.45 kg/hp.
Of course the power to weight ratios are for the "dry" weight of the engine and the two liquid cooled engines don't count the weight of the coolant and radiator/s so the air-cooled engines always look worse in this type comparison.

In the 1946 edition the Sabre VII is rated at 230 g/hp/hr, & oil 15 g /hp/ hr, weight to hp 0.37 kg/hp.
and the more common Sabre VA is rated at 225 g/hp/hr, & oil 15 g /hp/ hr, weight to hp 0.44 kg/hp.
The power to weight figure for the Sabre VA is for 2600hp.

The Sabre VII was a remarkable engineering achievement but since it was pretty much post war it means very little to what should or should not have been produced during the war.

I would note that during testing a P & W engineer pushed a "B" series R-2800 engine to 3800hp on a test stand using 150in of map (or about 60lb boost) and lots of ADI and the engine survived. I am sure the power was of very short duration and a lot of the air-supply may have been coming from an outside source (?) but it shows that many of these engines were capable of making much more power than they were rated at (although at a cost in durability and reliability) and that test stand figures are sometimes in no way connected to service capabilities. Service "B" series engines were never rated more than a bit over 2500hp using ADI in Thunderbolts using turbos.
 
There are occasional accidents in Yorkshire with Dutch/German motorists off the Hull ferry. It isnt a question of difficulty it is concentration. I have set off on the wrong side of the road 3 times, every time was on a weekend at home, Sunday morning when there was no traffic, I only know one guy who had a crash but I dont know anyone who has driven a left hand drive car who hasnt grabbed the window winder instead of the gear leaver at some time.
 
Whatever the short comings of the Hurricane were, it was easy to build. In 1940 the RAF were running short on pilots only the LW were running short of pilots and planes.
 
pbehn said:
Whatever the short comings of the Hurricane were, it was easy to build. In 1940 the RAF were running short on pilots only the LW were running short of pilots and planes.
Click to expand...

An important point you have raised, quite right too. In late 1939, early 1940, they were producing about five a day (two Hawker, three Gloster). By the BoB this was up to around seven a day, mainly down to Gloster's increased rate.
There were only three weeks between July 1940 and the beginning of November 1940 in which Hurricane losses exceeded production.

I would note that the British were never short of pilots, as Douglas and the men at the Ministry were keen to point out (and did in the thoroughly misleading BoB pamphlet), they were short of operational pilots, as Dowding, Park et alter were equally keen to point out.
This is what led to the much disliked system whereby rather than entire squadrons being rotated in and out of 11 Group and to a lesser extent 12 Group, squadrons in other Groups were stripped of their experienced hands and reduced to B or C Class status. A C class squadron was not in any sense operational, typically including only three operational pilots. Even a B Class squadron might include up to six non operational pilots. Only A Class squadrons were required to maintain a minimum strength of sixteen operational pilots. Most of these were in 11 Group, there were a few in 10 and 12 Groups, none in the others.

Cheers

Steve
 
James W. said:
No typo, 0.73 lb/hp 0.33 kg/hp, obviously for the most highly rated example, & the issue was sleeve valves not date of test.
Installed weight is a separate issue, so the thirsty R-2800 hauling the draggy P-47N made for a virtual flying gas-tank.
Click to expand...

Gee, my copy of the 1947 Wilkinsons says 0.83 lb/hp 0.37kg/hp on page 171 for the Sabre VII.
We can double check the math???? 2540lbs divided by 3055hp (Miltary power at 2,250ft) in low gear = 0.8314
to get to 0.73 lb/hp the 2540lb Sabre VII would need to make 3480hp.
Forget test stand, what was it rated at for flying?

Not sure why you are complaining about the R-2800 and installed weight. The air-cooled vs Liquid cooled DRY weight comparison affects all engines of both types. And apparently the R-2800 isn't any thirstier than many other engines. Fuel consumption being between 190 g hp/hr and 215 g hp/hr depending on model and conditions according to other editions of Wilkinsons's.
Chart for the engine in an F4U Corsair shows 1070hp for 83 gallons an hour at low altitude. If you are going to cruise using 1000hp you are going to use a lot of fuel per hour, doesn't matter what engine.
Check out P-47 chart here: http://www.zenoswarbirdvideos.com/Images/P-47/47SEFC.gif
1200hp for 105 gallons (630lbs) an hour cruise at 25,000ft. (.525lb hp/hr. 238 g an hour)
 

Not as fighter squadrons. 1950 was when the Tempest VI were retired from squadron service.
 
James W. said:
Of course, the RAF wanted an all-jet front line, & when the Vampire FB 5 was available, it took over, as intended.
The Sabre Tempests were still in "service", however.
Click to expand...

As target tugs. The last user, No. 233, was using the Tempest until July 1955.
 
This thing with the sleeve valves started back around post #158 with this statement

"SR6, one of the justified claims of the sleeve valve mill was the ability to make more power on lesser octane fuel.
R-R lobbied hard to have the Sabre abandoned as a quid pro quo with the Vulture, until Camm did his block''.

In the 1920s this was proven to be true on test stands and with one and two cylinder test rigs. One full point more of compression could be used in the sleeve valve cylinders. 6.0 to 1 instead of 5.0 to 1 for example.
However this was for normally aspirated engines (no superchargers) using gasoline that was lucky to be 70 octane. If the tests were even being run after the invention of the octane scale. The poppet valve engines had plain steel (or alloy steel) exhaust valves with severe cooling problems which did cause major hot spots in the cylinder head (along with inadequate fining in some areas due to ports and valve gear space requirements.)
The Sleeve valve boys were aiming at a moving target as the poppet valve boys introduced the sodium cooled exhaust valve , more fin area and longer valve guide area to soak up the heat from the exhaust valve.
Valve springs in the 20s were also a major source of trouble and spring failure or breakage was common. A reason why many designers did let the valve gear flop around in the airstream. Better cooling for the springs and valve gear (and if you are using grease from grease guns for lubrication it is stuck there for the duration of the flight, not cycled through the oil cooler and replenished by somewhat cooler oil on a continuing basis). But better metallurgy provided better valve springs, differnt alloys, different and better wire drawing had fewer imperfections, shot peening the springs increased fatigue life and better/different finishes fought corrosion better. Valve spring life got much, much better around 1930 and the early 30s to the point were valve spring failure was pretty uncommon before the engine reached normal overhaul life.
As foundry techniques improved fins could be made longer and closer spaced (without ruinous scrap rates) which aided cooling and allowed more power from each air cooled cylinder before oil film failure or detonation set in. This also helped the Sleeve valve boys (the first Perseus cylinders look like WW I relics) as the Perseus I started at 515hp.

A lot of what was claimed for advantages for the sleeve valve were true, if the comparison was against 1920s engines. Unfortunately for the sleeve valve boys, the Poppet valve boys had not stood around with their thumbs up their bums and and found solutions for most of the problems. If not quite the ideal they were certainly workable solutions and showed major improvements over the 1920s engines.
Bristol didn't have the resources to develop both types and bet on the sleeve valve, doing only the most minor improvements to the poppet valve series of engines during the 30s (the sales of which was financing the Sleeve valve project).

Practical difference between the types of engine were so small during WW II as to be ignored.
Sabre gets most of it's power from using 24 small cylinders and running at high rpm for a higher airflow than similar sized but slower running engines. I mean come on, what is the great surprise about a 36.7 liter engine running at 3850 rpm making a lot more power than a 36.7 liter engine running at 2750rpm? 40% more RPM means 40% more power if everything else is equal (which it never is).
A Sabre should have been able to make 2800hp running the same boost and compression as a 2000hp Griffon using this admittedly simplistic scenario. But the Sabre (V) used higher compression and lower boost. 7.0 to 1 compression instead of 6.0 to 1 and 15lbs boost instead of the 18lbs of the Griffon (37) so the Sabre was actually burning less fuel/air per revolution.

Of course the strength of the engines also have to be taken into account
 
James W. said:
No, scroll down further, its there, 3,500 hp take-off rating at + 20 lbs boost on ADI.
Click to expand...
a bit more pick and choose the best numbers?
The Page showing the 3500hp take-off number is from a 1949 or later edition.
I have next to my desk the 1946, 1947, 1948 and 1949 editions. First one that shows 3500hp is the 1949 edition and it has a different page number than the one in the link.
want to start comparing the Sabre VII to 1948/49 engines like the P & W R-2800 "E" series or 1949 Griffons or experimental R-4360s?
 
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