Manifold and RPM inconsistency

**Tibsun** · Sep-23-2017, 11:41

Hey TF, originally I was thinking to wait for this report... but recently I changed my mind because you were going through engine powers anyway.

So heres the issue.
This issue applies to all planes (also Blenheim and other 2-pitch planes) except for the Spitfire and Hurricane with the csp.
First, you made it available to get manifold pressure back in higher altitude.
As you raise rpm from 2400 to 2700 you only gain the manifold back, but you don't gain power from the higher rpm.
A made a showcase video so you can see what's happening, watch the speed, rpm and ata.
I made a comparison with the same ata, but different rpm, to showcase the max rpm power is fixed at 2400

To showcase that the power of 2400 rpm is fixed I made an emergency boost test with 2500 rpm.

I didn't make any research if the E-1 was capable of 1.40 ata 2500rpm but the shown manifold drop of 0.2 ata at 2500 applies to the DB601Aa too. Here again you also lose power when you run at 2500 while you should be able to reach also full 1.40 ata (despite the manifold historical varaition of +/- 0.2 ata - we only lose but never gain more ata.)

https://www.youtube.com/watch?v=59RxUuRLboI

Here is the test result taken from the video:

TF 4.312

Power test with equal manifold pressure.

1.0 ata 2000 rpm ~370 km/h
1.0 ata 2400 rpm ~390 km/h -- power gain
1.0 ata 2900 rpm ~390 km/h -- no power gain / rpm power same as 2400 rpm

Manifold drop test with emergency boost/full throttle

2400 rpm = 1.4 ata
2500 rpm = 1.38 ata powerloss because of 0.2 ata manifold drop

All tests made with BF 109 E-1 full rads to make it easy to reproduce.

TF Bug Tracker: https://tfbt.nuvturais.de/issues/917

Tibsun

**RAF74_Buzzsaw** · Sep-23-2017, 15:45

Has all been changed for TF 4.5.

Although you need to understand... Superchargers only will turn at a certain maximum rpm, no matter how fast the engine's rpm is. So they will not increase increasing pumping and power past the supercharger max rpm.

And the reciprocating piston engines will also not produce more power past a certain rpm... because of inefficiencies in valves opening and closing (spring bounce and rhythms set up in the spring metallurgy.... the reason why F1 cars use compressed air to open and close valves) and the inability of the engine to properly flow enough air/fuel mixture given the limited size of the venturis.

**Tibsun** · Sep-23-2017, 16:51

Great to hear Buzzsaw

I do understand your points and of it getting inefficient the higher it goes, though increasing inefficiency should'nt mean a hard border next to the rated rpm/boost.
And 2500/2600 was rated for the 109 engines and 2520 for the G.50.
Test is also done with same manifold pressure of 1.0 ata, no supercharger problem seen here and would be anyway supported by the increased rpm.
At the Manual of F-1/F-2 with db601/N engine it was noted that at fullthrottle height - level flight, the F-1/F-2 was able to use 2800 rpm to gain 10km/h you probably know that already. I know it's for the 109 F but still reasonable.

Spitfire and Hurricane without csp got also manifold drop behavier when running higher than 3000 and into the rpm limiter. Beside that the gauge isn't quite able to show higher rpm.. but is doing less power and drag.
Would be interesting if the manifold will drop when climbing at 4200m with 280km/h IAS for the 109 E-4/N and similar for the other planes anytime.

Thanks for your great work