PDA

View Full Version : prop pitch on american planes



GoodKn1ght
01-26-2004, 02:38 PM
why do american planes have prop pitch if there seems to be no advantage in using it?

"Friends don't let friends fly arcade"

GoodKn1ght
01-26-2004, 02:38 PM
why do american planes have prop pitch if there seems to be no advantage in using it?

"Friends don't let friends fly arcade"

TheGozr
01-26-2004, 02:40 PM
to slow down etc..

-GOZR
"TheMotorheads" All for One and One for All (http://www.french.themotorhead.com/themotorhead_fighters/)

Raider_356th
01-26-2004, 02:44 PM
S!
There is an advantage in the P51. I fly with radiator closed, and drop pp to 90%, to decreased the heating speed and it also increases top speed, so i can fly around of the real speed. Closing of the radiator decreases drag and increases top speed and climb rate.

Wildman
5E_B
364thFG Commanding Officer
"Too Tough To Tame"
"Fighter Aircraft Are Designed-And Fighter Pilots Are Trained-To Fight. If There Are Enemy Aircraft In The Air, And Contact Is Not Made, Somthing Is Wrong"
-From VMF-214 ("BlackSheep") Offical History, Appendix E: Major Boyington's Combat Tactics
www.freewebs.com/wildmanshanger/wildmansig.jpg

michapma
01-27-2004, 04:38 AM
Let's see... why would you ever want to control rpm:

1) fuel economy
2) keep the engine running cooler

Need more reasons? I admit it doesn't seem all that attractive in a 10-minute dogfight server.

I'd like to see a track that demonstrates that reducing rpm increases speed. There's no theoretical reason for it to be so, and I've never been able to reproduce these claims. I don't see any reason to believe it.

http://www.baseclass.modulweb.dk/69giap/fileadmin/Image_Archive/badges/69giap_badge_chap.jpg (http://giap.webhop.info)

The ongoing IL-2 User's Guide (http://people.ee.ethz.ch/~chapman/il2guide/) | Forgotten Skies (http://www.forgottenskies.com/)

BaldieJr
01-27-2004, 07:26 AM
Umm...

In the P51, I have to choke down the prop rpm pretty tight. Otherwise, the engine is way over-reved. 90% isn't enough, unless you run at 20% throttle all the time.

Maybe something changed since the last patch?

Also: in real life the mustangs radiator stayed open, if you wanted to go fast. If you close it, aerodynamic loses drop your speed. When open, you gain thrust from the heated output.

<pre class="ip-ubbcode-code-pre">
______ _____
(, / ) /) /) , (, /
/---( _ // _(/ _ / __ ,""""]
+----/ ____)(_(_(/_(_(__(__(/____/__/ (__--------,' /---+
| / ( / ,' NR / |
|(_/ ..-""``"'-._ (_/ __,' 42 _/ |
+-.-"" "-..,____________/7,.--"" __]-----+

</pre>

Maple_Tiger
01-27-2004, 08:18 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by GoodKn1ght:
why do american planes have prop pitch if there seems to be no advantage in using it?

"Friends don't let friends fly arcade"<HR></BLOCKQUOTE>


It's not a BF109, it dosent have Manual prop pitch. in Fb 100% prop pitch setting will set your RPM at 3200. 3200 is combat RPM for the P-51.

In real live the pilot did not run at combat RPM all the time lol. You can set the RPM at cruze, i think its like 2700RPM = 75% prop pitch. Whats nice about CPS is that the RPM will stay at 2700 or close to it.

I beleave in real live the P-51 pilot would not just move throttle but prop pitch setting at the same time.

ZG77_Lignite
01-27-2004, 09:36 AM
Are you sure on that 3200 RPM for combat (maximum) power Maple-Tiger? I was under the impression it was 3000RPM, though I could be wrong. Do you have a source for the 3200rpm? Thanks in advance.

michapma
01-27-2004, 10:24 AM
This raises an interest point. I will have to re-think my advice about having the radiator closed during combat. I honestly don't know in which planes you can go faster for extended periods using full or partial WEP with the radiator partially or fully open. I try to keep my radiator closed during combat, only opening it for a short time when I have a chance. I don't like the idea of exposing my radiator to flying chunks-a-metal.

Can you tell me more about the Mustang and other planes flying with the radiator open in combat?

http://www.baseclass.modulweb.dk/69giap/fileadmin/Image_Archive/badges/69giap_badge_chap.jpg (http://giap.webhop.info)

The ongoing IL-2 User's Guide (http://people.ee.ethz.ch/~chapman/il2guide/) | Forgotten Skies (http://www.forgottenskies.com/)

BaldieJr
01-27-2004, 10:30 AM
michapma,

Search for 'meredith effect' (i may have mispelled it). It only effect the P51, and I can't say with any certainty that it is modeled in the game.

The meat of the issue: you gain forward thrust when opening the mustangs radiator due to the expansion of the hot air at the exhuast outlet of the radiator.

<pre class="ip-ubbcode-code-pre">
______ _____
(, / ) /) /) , (, /
/---( _ // _(/ _ / __ ,""""]
+----/ ____)(_(_(/_(_(__(__(/____/__/ (__--------,' /---+
| / ( / ,' NR / |
|(_/ ..-""``"'-._ (_/ __,' 42 _/ |
+-.-"" "-..,____________/7,.--"" __]-----+

</pre>

WhiskeyRiver
01-27-2004, 10:44 AM
Baldie, I think the spitfire radiators also took advantage of the meredith effect to some extent. I remember reading that the Spit designers were able to gain some thrust from the radiators.

To kill me you've got to hit the heart Ramon--Clint F*cking Eastwood

michapma
01-27-2004, 10:53 AM
Cool, thanks. It would be pretty easy to test in FB, eh? http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

http://www.baseclass.modulweb.dk/69giap/fileadmin/Image_Archive/badges/69giap_badge_chap.jpg (http://giap.webhop.info)

The ongoing IL-2 User's Guide (http://people.ee.ethz.ch/~chapman/il2guide/) | Forgotten Skies (http://www.forgottenskies.com/)

BaldieJr
01-27-2004, 10:58 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by WhiskeyRiver:
Baldie, I think the spitfire radiators also took advantage of the meredith effect to some extent. I remember reading that the Spit designers were able to gain some thrust from the radiators.

To kill me you've got to hit the heart Ramon--Clint F*cking Eastwood<HR></BLOCKQUOTE>

Right. The cooling system design of the spitfire was intended to take advantage of Meredith Effect, however, it was not nearly as successfull as the efforts of North American when designing the P51's cooling system.

Estimates showed that 200 hp of the spitfires engine was used up in cooling losses, while the mustang required only 40 hp to keep cool.

My own opinion: North American just got lucky. Althought engineers had some idea of what meredith effect was, it appears that no concrete math on the subject existed at the time.

<pre class="ip-ubbcode-code-pre">
______ _____
(, / ) /) /) , (, /
/---( _ // _(/ _ / __ ,""""]
+----/ ____)(_(_(/_(_(__(__(/____/__/ (__--------,' /---+
| / ( / ,' NR / |
|(_/ ..-""``"'-._ (_/ __,' 42 _/ |
+-.-"" "-..,____________/7,.--"" __]-----+

</pre>

GoodKn1ght
01-27-2004, 11:04 AM
i dont think the radiator speed increase is modeled in fb.

"Friends don't let friends fly arcade"

TgD Thunderbolt56
01-27-2004, 11:10 AM
I've tested the modeling of the "Meredith effect" (albeit not in great detail) and have found no applicable speed advantages by running the P-51 with the radiator open. Not even short term.

If indeed it was a proven attribute, it should be modeled. If it was just a "claim" then leave it alone...easy enough, right?



http://home.earthlink.net/~aclzkim1/sitebuildercontent/sitebuilderpictures/il2sig2.jpg

GoodKn1ght
01-27-2004, 11:16 AM
easier said than done http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

"Friends don't let friends fly arcade"

Chadburn
01-27-2004, 11:38 AM
IIRC, Oleg discussed the merridith effect and dismissed it. Essentially, the drag created by air ramming into an open rad cannot be compensated for by the heated exhaust procuced

[This message was edited by Chadburn on Tue January 27 2004 at 10:59 AM.]

arjisme
01-27-2004, 12:06 PM
But when the P-51 radiator is open, it is open toward the rear. Are you saying when it is closed, air is not ramming into the radiator (on the P-51)? I thought by opening the radiator, you were increasing the volume of air that could flow through it, thus generating greater cooling.

Chadburn
01-27-2004, 12:28 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by ar****e:
But when the P-51 radiator is open, it is open toward the rear. Are you saying when it is closed, air is not ramming into the radiator (on the P-51)? I thought by opening the radiator, you were increasing the volume of air that could flow through it, thus generating greater cooling.<HR></BLOCKQUOTE>

I have no opinion on it. I'm just reporting what I recall Oleg stating in reply to a question about the meridith effect from SkyChimp.

EDIT: Found the thread so here it is:

"posted 04-11-03 09:54
RE: The Mustang, its radiator and speed.

1. Finally we plan to have it Auto. In real life the temperature of the coolant determided by thermostat, Like on many other aircraft (Bf109F-G-K, Yak-3, Yak-9 late, etc).

2. The drag is present anyway for the closed radiator in P-51D. But in this position the construction of radiator cowling with laminar flow around it really has small drag that allow to get greater speed of the plane itself in comparison with usual radiator cowl placed in that aerodynamically 100% _optimal_ area (like say on Yak-3 or on Yak-9U, that has it in the same place, but hasn't laminar airflow in the place beween radiator airintake and fuselage. Germans also tried to place there after great experimantal works, but it was too late...You may see it on experimental FWs and Bfs). But when it begins to open - drag will increases anyway. So you are worng in your opinion. I know where you took that info But this isn't professional aerodynamical magazine, be sure. There was just private opinion. The only thing there is correct that the design of radiator cowling was really best comapring to other planes.


SkyChimp wrote:
- Just in case its modelled this way, the P-51's
- radiator air outlet shutter should be automatic. In
- real life, the temperature of the coolant determined
- how much the flap opened. Otherwise, there was a
- switch in the cockpit with "auto", "open", "closed"
- and "off." "Auto" was the usual setting.
-
- And when the P-51's radiator opens (the flap opens
- up), the Mustang should not loose speed. In fact,
- the Mustang's radiator design created thrust.
-
- If the Mustang is loosing speed with an open
- radiator, it should not.
-
- Regards,
-
- SkyChimp"


http://home.cogeco.ca/~jkinley/FB_JG27.jpg

[This message was edited by Chadburn on Tue January 27 2004 at 11:39 AM.]

[This message was edited by Chadburn on Tue January 27 2004 at 11:40 AM.]

SpremeCommander
01-27-2004, 02:24 PM
"there seems to be no advantage in using (prop pitch)".

Another great Goodknight quote.

DaBallz
01-27-2004, 03:43 PM
I have found little or no difference between
closed and open except at high altitudes. Auto
seems to provide the fastest speeds all around.

In a real life situation the radiator door open and coolant hot
should provide enough thrust to cancel radiator drag.

So the modeling is very close to real life.
With an over heated engine you might be faster
with it open.

In IL2 use auto, or open it turn fighting.
Also use 85% prop for most situations.
I like to play with the pitch climbing.
The prop seems to cavitate in low speed high
angle of attack situations, feeding
it more pitch seems to help. After the RPM
stabilizes, go back to 100%

Da

michapma
01-28-2004, 04:32 AM
Have any of you done testing with the "normal" radiators? Let's take it for granted that in all piston-engined aircraft, opening the radiator is associated with a drag penalty. (If this is not so, then I only want to discuss those for which it is so.) In this case, I want to explore the middle- to long-term top-speed performance.

Approach 1: Close radiator and run the engine at the highest power setting that will prevent overheating during continual operation in level flight for 3 or more minutes, for example redline rpm and 100% throttle, or less if that won't prevent overheating.

Approach 2: Partially or fully open the radiator and push the engine into a partal or full WEP status that will prevent the engine from overheating during operation in level flight for 3 or more minutes.

Which approach will produce a higher top speed for the described period of operation? Obviously absolute top speed for level flight is achieved over a limited time with WEP on and radiator closed.

http://www.baseclass.modulweb.dk/69giap/fileadmin/Image_Archive/badges/69giap_badge_chap.jpg (http://giap.webhop.info)

The ongoing IL-2 User's Guide (http://people.ee.ethz.ch/~chapman/il2guide/) | Forgotten Skies (http://www.forgottenskies.com/)