Japanese engines

[tomo pauk]

Folks, there is issue about jap's aircraft engines that I found interesting.
Eg. Hayate was capable of some 630 kn/h, but the engine is said to have 1900 HP. Ki-100 had engine of 1500 HP, but it was capable of 590km/h only. Both planes seem to be aerodynamically clean, with moderate dimensions.

When I've asked this on another forum, people told me that engine makers, to put it simple, lied about power of their products. Is that true?

[FLYBOYJ]

No.

Sometimes engines are de-rated to support airframe structural limitations. Additional HP doesn't always mean more speed.

[tomo pauk]

Originally Posted by FLYBOYJ

No.

Sometimes engines are de-rated to support airframe structural limitations.


The 'dicrepancies' I found are allways connectet to Jap's planes; Raiden has 1850HP onboard for 615km/h etc.


Additional HP doesn't always mean more speed.

But it helps, never the less...

I've also heard that Italian licence-built DB-605s could muster 100 HP less than ones produced in Germany. Any creditable info about this?

[mad_max]

Engines are also derated when there are sparkplug problems, design problems, and also for quality of fuel problems.

Merlins in their infancy had a few design problems as did the DB series did. The DB and BMW had spark problems as did the USA with the Packard Merlin. British plugs were used until the USA figured out how to design a plug for the Merlin.

Esp. the German and Japanese fuel had quality problems at different times throughout the war.
The British had problems blending the 100/130 fuel at first. The additives would come out of suspension.

[FLYBOYJ]

Originally Posted by tomo pauk

I've also heard that Italian licence-built DB-605s could muster 100 HP less than ones produced in Germany. Any creditable info about this?

Possible.

That might be due to assembly tolerances and again fuel.

[kool kitty89]

Or they were just copies of older variants of the 605 compared to those being built in Germany at the same time.

[net_sailor]

The 100PS less power on Italian R.A 1050 "Tifone" was discovered during famous Guidonia test on February 1943'. Among other planes the regular Bf 109G-4 (with original DB 605A-1 engine) and Fiat G.55 prototype (powered by licence build A-1 engine) were compared. Unforturnatly no reason about this loss were stated in report. It's just single-sentence note that Fiat is about 25 km/h slower cause the poor engine power.

[red admiral]

The Italian built engines were limited to 1350hp because rpm was limited to 2650rpm instead of the 2800rpm overboost. Also, they were not equipped with MW or GM kits which limited their abilities at altitude.

[kool kitty89]

MW would be used at low altitudes as well.

[Ivan1GFP]

Sometimes the issue isn't whether the engine has been derated. It could also be because of supercharger ratios. Some engines have multi stage and / or multi speed superchargers. Others may not.

A classic example of this is the P-51 Mustang. The early P-51A models with the Allison engine were actually quite fast down low and faster than the later Merlin Mustangs. Both were capable of around 360-370 mph at sea level.

The P-51A hit its maximum speed at around 12,000 feet at 410 mph and could only make about 390 or so past 20,000 feet. The P-51B/C could hit about 440-450 out at 27,000 feet because its supercharger maintained rated power to a higher altitude.

This is quoting from memory, so please allow some room.

The point is that maximum speed has a great dependency on the altitude to which the engine can maintain power because it is at altitude that the plane will achieve its maximum speed.

BTW, on the subject of Japanese aircraft, I am pretty convinced that the quoted maximum speeds for most are not accurate and well below the actual value.

- Ivan.

[kool kitty89]

I beleive the P-51 did 415 mph at 10,400 ft. The A model's V-1710 had a higher supercharger gear ratio (9.6:1) than the earlier P-51/Mustang Mk.I (8.8:1) (and much more than the A-36's very low altitude engine, which was rather unnecessary IMO) the P-51A's V-1710-81 produced 1480 hp WEP at 57" Hg at 10,400 ft (at high speed; for climb this was ~2,000 ft lower) and 1,125 hp at 17,500 ft.

However it porbably would have done a bit better still with the 2-speed Merlin 20 (V-1650-1) or single speed Merlin 45 (same as 20 series minus the low speed gear). The exception would be that (at least early on) the WEP boost limits on the V-1650-1 were far lower than thier British counterparts for reasons I don't know. (max power 1,300 hp at 51.1" Hg/+10.3 psi rather than the +12 psi -1390 hp- increased to +14 psi -1480 hp- and to +16 psi with ~1530 hp with more at low alt in low blower)