Why still no dive acceleration difference?

[BlackBerry]

Originally Posted by MadBlaster

about this part of the equation, Propellerthrust/weight ->

Simply lower the rpms to bring the p47 tips speeds down to optimal range .7-.9? Won't that give you better acceleration? It seems to work that way in game. Starting at 250 mph, full throttle, and 100% pp, nose trim 2 notches down, rads closed. if I nose it down into dive and crank down the prop pitch to 0% quickly and then bring it back up to ~77% and gradually lower throttle to about 77% in a dive from 250 mph, the planes gets to ~ 400 mph ias very quickly.

Yes, that works. But even you can get same propeller efficiency as 190, your weight is too great to overcome, Propellerthrust/weight is still inferior to 190's.

We need to know if 190's airscrew tip compressibility loss is modelled or not at high mach number where 190's huge "advance ratio" making efficiency even worse than P47's.

[MadBlaster]

agree, but better to do it than not if your p47 guy. for 190 guy, you have revealed something that I think goes ignored. sometimes it is good to over ride the vdm auto prop pitch control and go to manual mode for same reason, to keep tip speeds at optimal ranges.

[mayshine]

Thanks to BlackBerry and everyone,

all your threads have done greatly to help me to understand more.

and may be there is a chance to involve the Prop calculation in IL2

to knock down Cliff of Dover and be the most perfect all the way?

Sorry for offensive language to someone l

I am tricky and want this topic to enjoy a long life and drag more men
to research in their full strenth,

So that I deliberately use somewhat offensive language.

sorry again JTD or so

[BlackBerry]

Originally Posted by MadBlaster

agree, but better to do it than not if your p47 guy. for 190 guy, you have revealed something that I think goes ignored. sometimes it is good to over ride the vdm auto prop pitch control and go to manual mode for same reason, to keep tip speeds at optimal ranges.

That dosn't help much, I'll show you how terribly drop of propeller efficiency for SMALLER propeller.

Again, NACA Figure24, Both fw190's 3 meter prop. and p47's 4-meter prop @19500ft , 1350rpm for propeller CSP,

1)A point=126m/s TAS=453km/h TAS=323km/h IAS

P47's advance ratio=126/(4*22.5)=1.4

fw190's advance ratio=126/(3*22.5)=1.86

2)B point=180m/s TAS=648km/h TAS=462km/h IAS

P47's advance ratio=2.0
fw190's advance ratio=2.66

3)C point=216m/s TAS=777km/h TAS=555km/h IAS=345m.p.h. IAS

P47's advance ratio=2.4

fw190's advance ratio=3.2

dive.JPG

B piont--->When both p47 and fw190 dive to 20000ft/462km/h IAS=287m.p.h. IAS, p47's efficiency is 70%, almost twice of fw190's 38%!

C point---->When dive to 20000ft/555km/h IAS=345 mph IAS, fw190 almost lost its propellerthrust while p47's remaining 55%.

So when speed building up @high altitude, the third part of acceleration formular will also be p47's advantage. Thus we could image how "Thunderbolt" really is!

P47's exhaust turbine boost leads to the lost of exhaust boost for propeller, but that can't help fw190 much.

Finally, we can completely understand why Republic's engineers want the biggest propeller as possible.

[MadBlaster]

interesting. I'm suggesting that at point A with a canister of mw50 on board that the 190 guy trade high rpms and prop efficiency while TAS is low, for thrust 'instantaneously' (limited by rate of change of the blade angle) by over-riding auto prop pitch (slower response). The prop would not be spinning at 1350 rpm. It has a load on now, so is spinning at say the lower end of the power curve for the bmw engine, guesstimate, 1050 rpm. Point C for 190 is irrelevant because dive speed limitations are upon him. The race is for point B. How long does it take for p47 turbo to spool up??? How long does it take to get power from mw50???

[BlackBerry]

Originally Posted by MadBlaster

interesting. I'm suggesting that at point A with a canister of mw50 on board that the 190 guy trade high rpms and prop efficiency while TAS is low, for thrust 'instantaneously' (limited by rate of change of the blade angle) by over-riding auto prop pitch (slower response). The prop would not be spinning at 1350 rpm. It has a load on now, so is spinning at say the lower end of the power curve for the bmw engine, guesstimate, 1050 rpm. Point C for 190 is irrelevant because dive speed limitations are upon him. The race is for point B. How long does it take for p47 turbo to spool up??? How long does it take to get power from mw50???

1) German tried MW50 on BMW801 but finally gave up. It's said that MW50 is harmful to BMW801's piston. 1945 version Dora's Jumo213A(liquid cooled) was equipped with MW50. However, 20000ft(6000m) is probably above 190's FTH, so there is little benifit from WEP.

At "A" point, if fw190 uses 1050rpm propeller, tip rotating speed is 165m/s, TAS is 126m/s, Mach number=207/310=0.67. Quite below 0.9mach. But I'd to say the propeller's has a certain optimised rpm, if you use full 100% throttle while reducing propeller's rpm incorrectly, you will lose efficiency. Your propeller probably couldn't absorb engine's output.

2) C point is above fw190's max allowable diving limit?

3)I don't know how long does it take for p47 turbo to spool up. I guess it's several seconds?

4)Last but not least, Do you have the information of Dora's 41276.16 V propeller? The size of it, the reduction ratio etc. As we all known before 4.11m, Dora flys so fast.

[MadBlaster]

Originally Posted by BlackBerry

1) German tried MW50 on BMW801 but finally gave up. It's said that MW50 is harmful to BMW801's piston. 1945 version Dora's Jumo213A(liquid cooled) was equipped with MW50. However, 20000ft(6000m) is probably above 190's FTH, so there is little benifit from WEP.

ah, okay. I read wiki they had used a version of a-4. But if it didn't work, it's not relevant. Lets leave out the dora/jumo too. Actually, iirc, dora was modified to handle mw50 at higher alts than 109 @ 6000 meters. Definitely the Ta 152 was. And then there was the gm1 (forgot the name). Actually, I fly UP 3.0 RC4 which uses 4.10 as base. Haven't tried 4.11 yet. But I checked all the fw190As in ultrapack, and none have mw50. some have the added fuel injection. so there you go.


At "A" point, if fw190 uses 1050rpm propeller, tip rotating speed is 165m/s, TAS is 126m/s, Mach number=207/310=0.67. Quite below 0.9mach. But I'd to say the propeller's has a certain optimised rpm, if you use full 100% throttle while reducing propeller's rpm incorrectly, you will lose efficiency. Your propeller probably couldn't absorb engine's output.

yea, I was thinking like a range of acceptable efficiency (going back to the .7-.9 range for the p47 prop). so your running auto pitch at about 400 kph about to start your dive. then you go manual mode using the vdm 3 way switch. So you quickly run up the rpms (toggle the switch) and atas ~1.4 to get the tip speed at the high end of the mach range. then put the load on by toggling the three way switch to the other position and slowly back off the atas as your in your dive. your accelerating, tas is going up and prop efficiency is going down. When your rpms are at 2100 on the indicator and your at the low end of the mach range for the prop, you go to auto prop pitch and your atas are running ~1.0 or so and your prop self adjusts to the TAS at that moment . Assuming they engineered out the rate of change on the blade angle so that you do not lose power in the transition. I think its like 3 degrees every one second or something like that. I forgot. All this happens very fast. like in a few seconds. I coded a 3 way switch in glovepie to do this, btw.

2) C point is above fw190's max allowable diving limit?

yes, but getting close. your tas is still increasing. its time to make a decision
and there is only one thing to do. p47 has a lot more headroom @ 1000 kph.

3)I don't know how long does it take for p47 turbo to spool up. I guess it's several seconds?

yes. i think so. I was thinking mw50 is instant satisfaction verses turbo lag. but since mw50 not on a4. but dora, yes. So we can ask DT if turbo lag is modeled correctly.

4)Last but not least, Do you have the information of Dora's 41276.16 V propeller? The size of it, the reduction ratio etc. As we all known before 4.11m, Dora flys so fast.

sorry,I'd have to google. I wasn't really intending to change discussion to dora. It's a different plane. jumo was way better engine. much higher rpms capability. I guess that is germans partial answer to opponent with bigger prop size. in ultrapack doras, there is a torque limiter. So you can crank a load from say 3700 rpm to 3000 rpm with mw50 on max ata. then you have to switch it off/cut ata and you can crank the load from 3000rpm to say 2700 rpm.

.

[BlackBerry]

I know you are trying to get best propeller efficiency by adjusting rpm manually, thinking that fw190 is quite an automatic plane but the pilot is oblidged to be so busy....

I'll carefully calculate Fw190 A8's prop. efficiency.

BMW-801D 2700rpm VDM 3m diametre has a 0.54 prop reduction gearing. Fw190A8 :VDM 9-12176A, 10 ft, 11 ¾ in. diameter 390 lbs

FockeWulf190 BMW 801D radial VDM prop mechanism was built into the nose case of the engine itself, along with 1.72 to 1 cooling fan drive, 0.54 prop reduction gearing, magneto, oil pump, and front camshaft drive.

http://www.enginehistory.org/Convent...20Electric.pdf

Prop diameter: 11.98feet=3.33 metre

Prop rpm: 2700*0.54=1458rpm =24.2 rps(100% pitch)

Notice that "B" point is just Fw190A8 max. level speed @19500 ft, that is 648km/h=180m/s

advance ratio=180/(3.33*24.2)=2.23

P47's advance ratio=2.0

So fw190's ratio is NOT so bad as 2.66, just 2.23. My 3-meter vs 4-meter comparation is just a demonstration of how important the diameter of prop. is.



You can see Fw190A8 gets its max. level by using 2700rpm-engine, this is the best rpm for A8, if you fly A8 at "B" point, don't decrease rpm because this will increase your advance ratio, which leads to the moving to rightside on the curve.



At "B" point, A8's tip speed=(180^2+253^2)^0.5=310m/s.

Mach number is 310/316=0.981 Mach, almost 1 Mach.

That means @19500ft, fw190A8 have to make it's propeller's tip speed just equal to 1 Mach, this is the best result, if you decrease rpm, you lose efficiency because "advance ratio" will be greater.

Actually, fw190A8's prop. working piont is "D" with efficiency 0f 60%+, less than P47's 70%, if P47 using 16:9 reduction, thundebolt's working point is "E", 75% efficiency.
dive.JPG
I am not saying that manual operating rpm is useless, it may help you a bit, but not much.

P47's efficiency advantage may or may NOT overcome its huge weight at high speed, but at least P47 could shrink the third part of the formular which is propitious to fw190. Even fw190 could maintain 100% efficiency all along diving, the importance of 3rd part of firmualar will also be less and less. Don't forget another foumular:

output(HP)=speed(m/s)*thrust(KN)

When you double your speed, the 3rd part of formular will become 50% (and even smaller due to efficiency lose) important as before, the 2nd part will become 400% important as before.
When P47 building up speed quickly, fw190A is doomed to be outdived.