Lift to Drag Ratios Compared

[JtD]

Nice testing, interesting results.

With the exception of the 250/300 km/h points on the 109, the light planes are the worse gliders.

[Letum]

The fact that these things can be sensibly tested, measured and compared at all is a great testament to IL2's flight model.

[B25Mitch]

In one of the hyperlobby servers I once glided some 25 km in an FW-190 after losing my engine over the enemy airfield. I wouldn't have made it home in many other planes!

It would be interesting to see where the Go-229 sits on some of these graphs. It seems to be able to glide twice as far as anything else.

[AndyJWest]

A nice set of tests, which seem to confirm that the IL-2 flight model is fairly accurate in general principles, if not necessarily in particular cases. One word of caution though - there seem to be some 'ground effect' factors that can kick in, which could possibly be distorting the results slightly - you might de better to test from say 1000m to 500m, rather than from 500m to sea level.

[JG27_PapaFly]

Originally Posted by AndyJWest

here seem to be some 'ground effect' factors that can kick in, which could possibly be distorting the results slightly - you might de better to test from say 1000m to 500m, rather than from 500m to sea level.

Ground effect is a decrease in induced drag and only relevant in very low-level flight up to an altitude equaling about the plane's wingspan. BTW i've specifically tested whether ground effect is present in IL2FB some time ago, the results were a clear no. Which is OK, the effect is not THAT big or relevant in RL except during flareout. No, i stand by my experimental setup, it's clean.

[AndyJWest]

Originally Posted by JG27_PapaFly

Ground effect is a decrease in induced drag and only relevant in very low-level flight up to an altitude equaling about the plane's wingspan. BTW i've specifically tested whether ground effect is present in IL2FB some time ago, the results were a clear no. Which is OK, the effect is not THAT big or relevant in RL except during flareout. No, i stand by my experimental setup, it's clean.

Ground effect is modelled, in IL-2 '46, and can be measured. One of the TD team confirmed it was in the 4.09 code, and I did extensive testing using my prototype autopilot setup (though you can demonstrate it without): There is a long thread on the subject over at the Ubi forum: http://forums.ubi.com/eve/forums/a/t...458#3121062458. Note that there seem to be two different 'ground effects' modelled - a 'true' effect that only kicks in at about half-wingspan and below, and a rather curious terrain and time related effect that seems to only occur with the 'wind and turbulence' on (even in calm weather). I think the conclusion we reached about the 'true' effect was that it didn't work in quite the way it should, but was definitely there. Whether 4.10 has been altered in this regard, I don't know, though I believe it was discussed.

[JG27_PapaFly]

Cool Andy, good to hear they've implemented ground effect. I did my ground effect tests in a way very similar to yours, but before 4.08.
Taking into account that real ground effect is only there between 0-10m, it has no significant effect on the average sink rate measured over 500 m of altitude.
I've also experienced "the other" ground effect. I reproducibly experience it as a sudden turbulence when i pass above a coastline ingame. However, it had no effect on this test, as i flew above water at all times. I even have all tracks, really boring stuff though

[JG27_PapaFly]

Originally Posted by JtD

Nice testing, interesting results.

With the exception of the 250/300 km/h points on the 109, the light planes are the worse gliders.

Very good observation there JtD. Indeed gliders load water ballast into their wings when going out on days with good conditions. The increased wingload will shift the polar curve to the right, allowing them to fly at higher speeds with less sink. Without water ballast a Discus 2b will sink 2.2m/s at 170kph. Loaded with 200 litres it'll sink only 1.4m/s at the same speed

[Letum]

Anyone got a graph that compares wing area and weight to vertical speed and TAS for a theoretical plane?

That would be nice to see.

For example, it would show the extent to which ww2 planes would have better energy retention if they had more weight.
i.e. what's the optimum fuel loadout in a P51 for the best energy retention or the highest wingload to v-speed ratio.

[JG27_PapaFly]

Originally Posted by Letum

Anyone got a graph that compares wing area and weight to vertical speed and TAS for a theoretical plane?

That would be nice to see.

For example, it would show the extent to which ww2 planes would have better energy retention if they had more weight.
i.e. what's the optimum fuel loadout in a P51 for the best energy retention or the highest wingload to v-speed ratio.

That would be nifty.
This NASA document states a L/D ratio of 14.6 for the P-51. No idea whether that was a regular pony or the one they tested as a glider without propeller (see this NACA document).

In my tests, the P51 tops at an L/D of 11, which is quite plausible.

Energy retention depends on many factors, and is itself just one aspect of plane design. Compromises have to be made. In gliding, 2 design aspects are in conflict: one is energy retention, meaning the ability to cruise at high speed and loose as less altitude in the process as possible. The standard recipe to increase that energy retention at high speed is to load water ballast. One of the most advanced gliders, the polish Diana 2, can load more than double its weight with water.
However, just as important for gliders is a second aspect:the ability to turn very tight at slow speed. Thermal winds are very narrow, and the zone of the optimal lift is quite close to the core. The slower a glider can fly in a steep turn (45-60 deg bank), the closer to the core it'll be, and the better it will climb. While an empty glider will happily climbt into thermals at 80-90kph, a fully loaded one will do 110-120 kph, thus climbing less efficiently.
One way to bring both design requirements together is the use of flaperons. Modern gliders and jets make extensive use of these flaps that can go both ways: down to increase lift, and up to decrease lift + reduce drag. The F16 is a good expamle. Imagine a D9 or P51 using flaperons...they could prolly accelerate in level flight up to speeds where prop efficiency and compressibility would be limiting.