posted 01-25- 05:50 PM               

Engine - 1850hp@2400rpm
Prop Radius - 1750
Prop Blades - 3
aircraft weight (empty) 6334Lbs

Tests:
speeds/time.. Given - Tested - Prop Pitch
1,000ft 362 367 42
20,000ft 403 404
climb to 15,000 5.2min 3.1min

1,000ft 362 378 45
20,000ft 403 426
climb to 15,000 5.2min 3min

1,000ft 362 356 40
20,000ft 403 426
climb to 15,000 5.2min 3.2min

As you can see, I can get the speeds right, but then the climb rate wont come into line, currently it climbs at around 280mph @ +18º which is obviously to high. How can I get the climb rate in there without totaly screwing the speeds up? Or, what tradeoff is preferred here?

Thanks for any help guys, it's kinda buggin me getting this right (don't we just love FM's lol)

~Nat~

posted 01-25- 07:26 PM               

Open the model in OPS. Click on the propeller, and open the properties tab. You'll see a line marked "propElements." This is a set of "coordinates" representing "prop station," i.e. distances out from the hub to the blade tip, and the "chord length" of the prop at each point moving outwards. For an experiment, cut the second number of each pair in half, and see what happens. It will cut your climb rate quite a bit, but won't have too much of an effect on speed. Basically, you're "shaping the prop blades."

Use trial and error to tweak the climb rate. Tailslide probably has a pretty good understanding of which of the propElements have the most effect on speed, and which on climb, which parts affect high alt performance, and which affect low alt. I don't understand the props all that well, so I basically just increase and decrease all the elements together by about the same percentage until I "zero in" on the right climb rate.

From what I've seen, you will probably be able to get the time to climb to 20K down pretty well, and the time to climb to 10K will end up being a little bit fast, but the "optimum" climb speed will be in the ballpark (180-200 mph).

Also, if you look at the FW-190A4 in PP6, it uses an airfoil called "drag" for the wheels. You can substitute this airfoil for the "CYL" airfoil on the fuselage and see what that does. It has a HUGE drag component, with little or no lift component. You will probably need to (greatly) decrease the airChord and airArea of the existing drag airfoil the plane is using or it will really bog it down, but this is another way to cut the climb capability. However, this one will also cut the speed a lot, so you'll have to recalibrate the speeds again

posted 01-25- 07:50 PM               

Thanks alot for this Jedi, I'll post here how I get on

posted 01-25- 10:39 PM               

I ended up having to make the prop almost completely flat before I got a marked difference, at best I gott he climb speed down to about 221mph, taking 4mins to climb to 15,000ft as in the tests above, what this has done though is to take the low alt top speed down to about 300mph instead of 361, and the high alt down to about 350 instead of 403. I'm still tweaking editing and testing in the hope of what will now be a fluke to get things within acceptable +/- ranges.

I don't consider this a loss though, damn annoying yes, but still, I'm learning more about this crap cause of doing it so much, and what Jedi has told me above is still interesting to know.

If anyone feels they might have a better shot at getting the La5 to within +/- 5mph on speeds, and +/- 20 seconds on climb then feel free to give me a shout, learning is one thing, but I gotta accept that I just don't have the ability yet to sort out some things.

If in the end I just can't get it close enough, then I'll settle for a rate of climb thats to high and keep the speeds correct and leave it at that till she's all finished up, then maybe take another look.

~Nat~

posted 01-26- 12:04 PM               

Try reducing the airK value.

This should significantly increase the drag when lift coefficient is high (ie while climbing). The formula for induced drag is something like:

CDi = CL^2/(pi*wingAR*airK)

Which means that the induced drag will go up exponentially as the lift increases (ie at higher angles of atttack). By decreasing airK you increase the effect of induced drag.

Not too sure how this will effect other aspects of the plane's performance.. ie it will make it bleed more energy in tight turns..

posted 01-26- 12:43 PM               

Here are a few:

LA-7 : 0.7373
LaGG-3: 0.7607
Mig-1 : 0.8486
Mig-3 : 0.8406
IL-2 : 0.5527

posted 01-26- 12:48 PM               

I used some common sense to set the aspect ratio, area, chord, etc to match the planes fuselage but unfortunately I forgot to add instructions for this to the FAQ.

TS

posted 01-26- 02:33 PM               

LOL... proved me wrong

I was also assuming that the CYL airK would be set the same as the wing airK.

Those real values make a pretty interesting point though, I have a book with a chart that shows the "theoretical" airK for a rectangular (non-tapered) wing of AR=10 is about 0.9. Also I think the open plane documentation says most tapered wing planes are 0.85.... IL-2 : 0.55.

posted 01-26- 06:10 PM               

After much more testing and tweaking I've got the climb to 15,000ft to 5 mins, 20 seconds to fast, I can live with that (it climbs steady at about 225mph, but since it's taking almost the right amount of time then this must be acceptable), speed at 20,000ft is 398mph (within 5mph of actual) but the low level speed is to 50mph to low, but this changes quickly with even slightly higher alt. at 5,000ft it's already upto a top speed of aboug 335mph, so right now it's looking acceptable, I'll still be trying to get it closer though and maybe using the right airK will help, cheers Tail

Other problems I'm having are ofcourse ground handling, but I'm working on this one and have a couple of ideas, one thing that was a major problem was the torque roll, the engine generates so much it would flip the aircraft over as the wheels lift off, this I've counteracted quiet easily.. since I use the advanced engine (this 14cylinder radial is built up of 7 engines) I just run 3 of the engines backwards on a hidden prop running backwards, thereby generating negative torque to balance the aircraft, there was simply no way it would stop rolling over, and also even in taxying it would pull round, so this was a good solution.

What I shall do once a few small bugs are worked out is to ask for test volunteers to see what they think of it. I've been testing AI missions against 109e4's and Spit IX's with good results (AI only), the La5 doesn't seem overpowered in anyway, infact, it has less power in steep climbs, but has a good sustained climb. What I have really liked i the way the advanced wing DM affects the overal FM, in that the high speed departures and stalls seem very realistic to me, you through La5 around and it will snap roll, stall or a few other nasty things, some are very hard to recover from, others can be recovered fairly easily, but it makes it fun to fly and in no way a "yank and bank" aircraft, the bonus here has been the IL2, what I've learnt from that has made the La5 alot easier to work on.

Current status:
IL2, needs damage models and cockpit panel then is essentialy finished bar the tweaking and beta testing
La5 - cockpit needs reshaping, damage models built ready for adding, FM needs touching up a little more.

I'm trying to get as much done as quickly as I can since I'll be busy with something else for a while in the very near future