Throwing some light on rates of turn

[Ernst]

I just remembered this:

http://www.youtube.com/watch?v=TFl8X4y9-94

[IvanK]

I think this "G" is in fact a Buchon.

[MiG-3U]

Originally Posted by Crumpp

The RAE's use of a single chart given the absence of any differientiation between power levels makes perfect sense with the Merlin XX predictions.

The Merlin XX was predicted to maintain similar power from sea level to 20,000 feet.

1020 Hp at Sea Level and 1075HP at 20000 feet:

http://www.enginehistory.org/members...a/Table-04.jpg

http://www.enginehistory.org/members...lysisR-R.shtml

1. The Merlin XX had a two speed supercharger. The first page you refer gives power at high altitude gear at sealevel due to analysis. See the appendix A at bottom of the second page for power at low altitude gear at sealevel.

2. Even at constant KEAS speed and constant power, the resulting force, thrust, decreases when the altitude increases because force is power divided with true speed. To maintain given angle of bank at given KEAS, power must increase with altitude.

[MiG-3U]

IvanK,
Could you please post parts of the report on turning performance at 20k?

TIA

[IvanK]

This is I think the only relevant bit that includes Sustained turn boundaries for 20,000',25,000',30,000', and 35,000'. "Angle of straight Climb" is Ps=0

[MiG-3U]

Thanks IvanK,

So power is higher, 1100hp at 20k, than 1050hp at 12k. Time to turn 360deg is about 30s at 20k, while it was 18.6s at 12k.

Originally Posted by Ernst

I just remembered this:

This video which claims to "proof" that the 109 was equivalent in turn to the spit is pretty much useless. The first interviewed guy never flew a spit as he admitted himself. The second guy we don't learn about his flight experiences. We therefore just learn that the 109 was a good turner (perhaps better than ingame but that's another discussion) and better turner than the P51. Now that is nothing new at all.

Fun to watch but not even anecdotical evidence on how close the Spit and the 109 were.

[Kurfürst]

Originally Posted by IvanK

I think this "G" is in fact a Buchon.

It's a bit offtopic, but I never quite understood this 'Buchon' thing. Sure the Buchon handles slightly differently (from what I gather, directional stability was worse than on the 109, which already exhibited low directional stability characteristics), but in essence it was just a German built G-series airframe, with a very similar Merlin/HS engine wrapped onto it.

[IvanK]

A Merlin installation v a DB605 installation is significantly different though.

Though I havent seen any Specfic excess power differences between the two I am sure they would be significant thus affecting sustained turn and climb performance. My Gut feeling is the DB605 variant would be the lesser performing aeroplane.

[Holtzauge]

The additional data posted by IvanK now gives the engine power as well and the turn time at 20,000 ft can as MIG-3U points out be read out of that figure to be in then order of 30 s. In fact the same report contains an even more precise figure of radius 1045 ft, bank angle 51 degrees and turn time 31.5 s in table 4 on page 4.

While we are waiting for Crummps 21 s 68 degree bank proof here are some C++ simulation results showing the relative performance between the 1.3 ata Me109E and Spitfire Mk1 at +6.25 boost:

As expected the Spitfire is somewhat better at 20,000 ft due to the lower wing loading. However, the interesting thing is however that at low level (1 km) my simulations show that while the Spitfire turn better at low speeds, the Me109E turns better than the +6.25 boost Spitfire Mk1 at TAS speeds over 290 Km/h. However, if one assumes the +12 boost then it is of course no contest, either at low or higher speeds.