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Old 06-10-2014, 08:12 AM   #41
Pman
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Hi tempestglen

Give me an easy one why dont you.

Yes DCS is capable of simulating those effects. There Spitfire was a spitfire specifically rigged for speed tests, it was a MkXI with a special prop and basically everything that could be removed was removed, Diving at 45 degrees from 45'000 feet.

You will not be able to do that in our spitfire, for one thing the MkXIV does not have a pressurised cockpit so you really wont want to be climbing that high. Plus the aircraft will start tearing itself apart at those speeds. The Spitfire in question suffered severe damage as a result of that dive.

Only picture that I know of for this is here



As you can see, if this happened at Mach 0.92 as was recorded by specifically designed instruments with all the modifications then I agree with your quote that I dont think its possible for a Spitfire to achieve 0.96 without catastrophic damage. As such I agree that its instruments were probably faulty.

Some of the mathmatical equations I have seen (I am not going to pretend that I understand them in their entirety but I know enough) indicate that at its peak the prop may fall as low as 44% eff.

Obviously this is at the extreme end of the spectrum and I would expect more like 60% in most situations.

Hope that helps answer your question

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Old 06-10-2014, 08:57 AM   #42
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Hi tempestglen

Give me an easy one why dont you.

Yes DCS is capable of simulating those effects. There Spitfire was a spitfire specifically rigged for speed tests, it was a MkXI with a special prop and basically everything that could be removed was removed, Diving at 45 degrees from 45'000 feet.


Pman
Great stuff, Pman. Happy to hear DCS can handle transonic aerodynamics, after all, it's medern airacraft simulation!

Let's forget about 0.96 mach. In late piston aircraft manual(P51, spit XIV?), 500MPH( 800km/h) is the limit of low altitude dive. I am interested in 680-850km/h speed range where the propeller efficiency is a mystery for me. 3-blade vs 4-blade, conventional airfoil vs laminar......That puzzles me.

For instance, if my propeller efficiency 10% higher than yours in a contineuous shallow dive, I steal 10% engine output from you, it's quite a tactic advantage.
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Old 06-10-2014, 09:27 AM   #43
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Great stuff, Pman. Happy to hear DCS can handle transonic aerodynamics, after all, it's medern airacraft simulation!

Let's forget about 0.96 mach. In late piston aircraft manual(P51, spit XIV?), 500MPH( 800km/h) is the limit of low altitude dive. I am interested in 680-850km/h speed range where the propeller efficiency is a mystery for me. 3-blade vs 4-blade, conventional airfoil vs laminar......That puzzles me.

For instance, if my propeller efficiency 10% higher than yours in a contineuous shallow dive, I steal 10% engine output from you, it's quite a tactic advantage.
Yes in theory you would have an advantage. How much that advantage is really depends on the efficiency of the propeller vs airspeed.

For example, if you had 5% advantage but that 5% actually translated to 7 mph at the top end of the spectrum then the advantage is almost negligible.

Reverse that at say in envelope speed and the speed difference could be substantial.

Hope that makes sense

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Old 06-10-2014, 03:05 PM   #44
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Yes in theory you would have an advantage. How much that advantage is really depends on the efficiency of the propeller vs airspeed.

For example, if you had 5% advantage but that 5% actually translated to 7 mph at the top end of the spectrum then the advantage is almost negligible.

Reverse that at say in envelope speed and the speed difference could be substantial.

Hope that makes sense

Pman
Assume that everything else being equal but my Spitfire XIV propeller efficiency is 10% more than your Spitfire's at 750km/h IAS when diving to low altitude. That's 200HP difference, this means my spitfire is 21lbs boost(2200HP) but yours degraded to 18 lbs (2000HP), your 145/110 fuel and engine mechanical modification for higher boost are meaningless in this scenario. I can imagine how angry those royce-rolls engineers are. High speed diving is a frequently used evade maneuvor in WWII, even ordinary pilots can easily get themselves out of trouble by out-diving ACE enemy.

The question is whether the efficiency difference is as big as 10% when compared various aircrafts at high speed diving. If so, it's worthy to research it.

There are several funny stories in WWII. One of them is German 3-blade wide chord wood propeller.

German always kept 3-blade configuration in WWII, perhaps for the cannon fire rate reason(gun synchronizer). In order to absorb ever increasing engine power, they developed wood(better energy absorption)wide chord propeller while allied did the same thing but preferred to 4-blade metal configuration. (RAF developed 5-blade wood propellers.)

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Once more, just as the NACA was aware and used Gottingen airfoils, so did the German designers use NACA airfoils. The Focke Wulf FW-190A uses the NACA 23015.3 at the root and NACA 23009 at the tip.
http://digital.library.unt.edu/ark:/...dc62616/m1/19/

Three-blade Hamilton standard no. 6507A-2 propeller on a Republic P-47D airplane, drops its efficiency to 75-70% at 0.65Mach=800km/h-500MPH TAS, that’s 450MPH? IAS, below 500MPH IAS limit. Fw190 dive limit is 466 MPH (750km/h)IAS.

But I can say the 3.3-meter diameter propeller in fockwulf suffers much more efficiency drop than 4-meter propeller on p47. advance ratio=J=V/(d*n). d=diameter. When dive to same V=450MPH IAS, Fw190’s advance ratio is quite higher than p47’s, so worse efficiency.

1944 early, both German and allied began to use wide chord airfoil in fighters: fw190a8 and p47d-25 with wide chord design, German get better climb and turn performance, so was allied.

http://www.368thfightergroup.com/P-47-R2800.html

p47 got more than 10% climb rate due to wide chord paddle propeller.

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I have all the data on VDM propeller series. The wide chord wooden props for the Luftwaffe dropped top level speed by about 4 percent but increased turn and climb rate by about 15 percent. The Luftwaffe conducted several indepth studies. I am sure the USAAF did the same. Blade width does help efficiency to a point.
Another forum, a guy named crumpp said so. You see, even at not-so-high max level speed (680km/h TAS or so), the wide chord propeller loses 8% efficiency compared old narrow type (4% speed lose means 8% output lose). Obviously, 3-blade wide chord increase efficiency at low-medium speed(clime rate/turning) at the expense of 680km/h's efficiency. Can I say there is more sacrifice at 750-800km/h TAS(<466MPH IAS fw190 dive limit)?

To sum up, it's probably that allied 4/5 blade+greater diameter propellers get 10% more efficiency at 750-800TAS diving than german 3-blade+smaller diameter ones.
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Old 06-10-2014, 03:14 PM   #45
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if crump said it it's not true.
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Old 06-10-2014, 03:15 PM   #46
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The question is whether the efficiency difference is as big as 10% when compared various aircrafts at high speed diving. If so, it's worthy to research it.
Alot of what you state is very true (not all of it, but a fair bit), however I think this sums it up. For informational use this may be quite interesting but when it comes to programming aircraft for a simulator you cant do it this way. Ours is not an art of balance but more of precision.

Our job is to simulate the aircraft as close to its real counterpart as possible.

We will simulate everything we can regarding air cushioning effect and other aerodynamic influences, how they compare to other aircraft or how other 3rd parties do them isnt something we can control

What I can tell you is that I have 5 real world Spitfire pilots who have agreed to fly our simulator to ensure that we have the highest level of precision in any Spitfire Mk XIV simulator anywhere

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Old 06-10-2014, 03:24 PM   #47
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What I can tell you is that I have 5 real world Spitfire pilots who have agreed to fly our simulator to ensure that we have the highest level of precision in any Spitfire Mk XIV simulator anywhere

Pman
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Old 06-10-2014, 03:25 PM   #48
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Originally Posted by Pman View Post
Alot of what you state is very true (not all of it, but a fair bit), however I think this sums it up. For informational use this may be quite interesting but when it comes to programming aircraft for a simulator you cant do it this way. Ours is not an art of balance but more of precision.

Our job is to simulate the aircraft as close to its real counterpart as possible.

We will simulate everything we can regarding air cushioning effect and other aerodynamic influences, how they compare to other aircraft or how other 3rd parties do them isnt something we can control

What I can tell you is that I have 5 real world Spitfire pilots who have agreed to fly our simulator to ensure that we have the highest level of precision in any Spitfire Mk XIV simulator anywhere

Pman
5 real world Spitfire pilots, that's very good. If you simulate efficiency drop at high speed diving, that's fantastic.
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Old 06-10-2014, 03:29 PM   #49
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if crump said it it's not true.
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Old 06-10-2014, 03:30 PM   #50
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5 real world Spitfire pilots, that's very good. If you simulate efficiency drop at high speed diving, that's fantastic.
We will don't worry, we just can't make statements how our aircraft will compare to another aircraft we haven't made

We have very good access to both personell and 2 aircraft that will enable us to make an amazing SIM for everyone

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