Aces High Bulletin Board

General Forums => Aircraft and Vehicles => Topic started by: funkedup on December 08, 2001, 07:51:00 PM

Title: Ram Effect
Post by: funkedup on December 08, 2001, 07:51:00 PM

I just realized that if you take an AH plane above rated altitude, manifold pressure will increase with airspeed.  Neato.   :)

Title: Ram Effect
Post by: R4M on December 08, 2001, 08:26:00 PM

oh.....  :(

I was thinking you were about to talk about me and my wonderful effect in this game  :D

BTW, Manifold gauges in LW planes still don't change with altitude. -----------> Had to hijack yet another thread! MUHAHAHAHAHAHAHAH  :D

Title: Ram Effect
Post by: Tac on December 08, 2001, 08:29:00 PM

I thought the alt monkey allied pimps shot them down before they got to altitude  :)

Title: Ram Effect
Post by: funkedup on December 08, 2001, 08:40:00 PM

Yeah I only tested this on the P-51B.  I'll check some others.

I'm also doing some testing vs. real world fuel consumption charts.  So far HTC engine model is looking pretty impressive.   :)

Title: Ram Effect
Post by: Glasses on December 12, 2001, 06:42:00 AM

Funked when you get the results could you post some Manifold /RPM settings for Endurance in the tested aircraft?

Since I asked even Pyro last time and he was "too drunk" to say anything about Vy ,Vx or fuel endurance.  :p

Title: Ram Effect
Post by: funkedup on December 12, 2001, 02:32:00 PM

P51-D, Sea Level Aces High (10x Fuel Multiplier) Manual
RPM MP Gallons Time Speed GPH MPG Speed GPH MPG
3000 61" 85 205 355 149 2.4 N/A 182 N/A
2700 46" 85 317 325 97 3.4 315 86 3.7
2500 43" 85 390 305 78 3.9 300 74 4.1
2150 40" 85 499 285 61 4.6 280 61 4.6
1800 36" 85 605 255 51 5.0 255 51 5.1
1600 30" 85 783 200 39 5.1 220 39 5.6

[ 12-12-2001: Message edited by: funkedup ]

Title: Ram Effect
Post by: Seeker on December 12, 2001, 03:10:00 PM

What does this mean and why is it interesting?

<areoengineeringly challenged.....>

Title: Ram Effect
Post by: funkedup on December 12, 2001, 06:14:00 PM

It's interesting because it shows you which engine settings to use for maximum range, and it shows that at least on the P-51D, HTC have a quite accurate model of power and fuel consumption with respect to manifold pressure (throttle) and RPM.

The chart is a comparison of real life P-51D fuel consumption and AH P-51D fuel consumption, at sea level, full internal fuel load.

1st column is RPM, 2nd column is Manifold Pressure in inches Hg.  These settings are right out of the manual for the airplane.

3rd column is how much fuel I burned in my test (I burned off the fuselage tank), 4th column is the time to burn off the fuel (in seconds), 5th column is my TAS in mph, 6th column isis gallons per hour, adjusted for the 10x fuel multiplier, 7th column is miles per gallon, also adjusted.

8th, 9th, 10th columns are TAS, gallons per hour, and miles per gallon from the manual for the airplane.  

As you can see there is some variation between AH and the manual, but not a heck of a lot.  Looks like a very nice job by HTC of matching historical performance in this area.

[ 12-12-2001: Message edited by: funkedup ]

Title: Ram Effect
Post by: funkedup on December 12, 2001, 06:28:00 PM

It just occured to me that Seeker might have been asking about the ram comment.

The air intake on the Mustang (under the prop spinner) was designed (like a lot of other WWII planes) to use the speed of the plane to "ram" air into the engine.  This increases manifold pressure and gives more power.

Above rated altitude, the supercharger can no longer provide the maximum allowable manifold pressure (61").  So the ram effect really comes in handy to increase power.  And in AH you can see the manifold pressure increasing as you speed up above rated altitude, which indicates that AH is calculating the manifold pressure increase due to ram effect, which says something for the engine model.

Title: Ram Effect
Post by: Seeker on December 12, 2001, 07:07:00 PM

Thanks Funked.

One more thing though, do super chargers have waste gates, or blow off valves? How do you avoid over pressurizing the system in a high speed dive?

Title: Ram Effect
Post by: funkedup on December 12, 2001, 08:05:00 PM

Merlins in the Mustangs in AH (V-1650-3 and V-1650-7) had an automatic manifold pressure regulator on the carburetor which automatically varied (opened and closed) the throttle butterfly to maintain constant manifold pressure as set by the pilot's "throttle" lever.  So if too much air was being rammed in a dive the regulator would gradually close the butterfly until the manifold pressure was at the desired level.

I think some of the turbosupercharged planes might have had a wastegate.  I'll look into it.

Title: Ram Effect
Post by: Seeker on December 12, 2001, 08:21:00 PM

That's exactly what I meant, Funked. All the turbo engines I've ever seen have some kind of waste gate to avoid over boost, and it suddenly struck me that I can't remember a reference to a similar facility in a super charged engine, which begs the question: why not?

Title: Ram Effect
Post by: funkedup on December 12, 2001, 10:16:00 PM

In airplanes it's a really bad thing for range and endurance to dump unburned fuel.  And except for injected engines like BMW 801 or DB or Ash-82FN I think they generally added fuel upstream from the supercharger(s).

[ 12-12-2001: Message edited by: funkedup ]

Title: Ram Effect
Post by: Seeker on December 12, 2001, 10:42:00 PM

You're obviously right with regard to the importance of economy on those engines, but even F1 turbo cars have waste gates, and their fuel is measuerd pretty much to the metre.

Odd, isn't it?

Title: Ram Effect
Post by: Staga on December 12, 2001, 11:38:00 PM

One quite big difference between turbo-chargers and mechanical driven blowers is superchargers' rpm (and thus airflow thru charger) is dependable about engines rpm (well there's two-stage/two-speed and variable speed like in Daimler-Benz's engines 'cause engines need to adjust to different heights/air pressures) when pressure turbo-charger gaves depends how much exhaust gas engine produces.
"Pop-Off valves" and WasteGates usually works when you cut the throttle in turbo-charged engines when turbo-charger is stil giving full pressure thus dramatically increasing pressure in inlet manifold.

btw co-worker use to drive a Volvo 142 which was faster in 1/4 mile than Porsche 911... That car was a real "sleeper" with Garrett turbo and water-injection   :D

Title: Ram Effect
Post by: fdiron on December 13, 2001, 03:39:00 AM

What does 'rated altitude' mean?

Title: Ram Effect
Post by: Sundog on December 13, 2001, 01:47:00 PM

What I think is really interesting about everything Funked is posting is that it demonstrates why it takes HTC time to get new planes in game.

Title: Ram Effect
Post by: gripen on December 14, 2001, 05:04:00 AM

AFAIK the waste gate is used to adjust how much exhaust gases are directed to the turbo. At low altitude waste gate is more open than at high altitude because less exhaust gases (lower turbo rpm) is needed to keep wanted MAP. At high altitude the waste gate is nearly or fully shut because more exhaust gases (higher turbo RPM) is needed to keep wanted MAP.

gripen

Title: Ram Effect
Post by: Glasses on December 14, 2001, 07:22:00 AM

Now if you could test some of the LW Iron...  :D

Title: Ram Effect
Post by: bolillo_loco on December 14, 2001, 12:16:00 PM

fuel is added well after the turbo charger is done figuring out what MAP to maintain. waste gate does not dump air/fuel mixture over board. it does not affect fuel economy.

Title: Ram Effect
Post by: Captain Virgil Hilts on December 14, 2001, 01:06:00 PM

A waste gate simply dumps exhaust gas pressure directly to the exhaust outlet or the atmosphere, rather than routing it through the turbine housing of the turbocharger to drive the turbine.

 On modern engines, it is sometimes controlled by a solenoid, and is often operated by intake manifold pressure. It may be adjusted manually, or controlled by a computer.

On planes like the P-38, the P-47, the B-17, and the B-24, it was controlled by an oil pressure regulated system.

It was common to have problems with the P-38 and the P-47 especially at high altitudes, because pilots were bad about not controlling oil temperature. The oil would actaully congeal in the regulator, and the regulator would no longer function. the turbo would either build only about 5 psi with the wast gate stuck open, and provide no power, or it would build in excess of 80 psi, blowing the engine, the intercooler hoses, rupturing the intercoolers themselves, or overspeeding the turbo to destruction. The P-38 actually had an armor ring around the turbo to protect the pilot and plane from fragments.

All of those planes above shared the General Electric B-2, B-33, and B-34 turbochargers. The U.S. did not allow these systems to be installed on aircraft sold to toher countries.

Title: Ram Effect
Post by: funkedup on December 14, 2001, 01:21:00 PM

LOL I forgot where the wastegate was.  Me tard.    :)
Just explained to some guys how it worked at the USAF museum in October too.  Must be Nutrasweet brain damage affecting memory.   :)

[ 12-14-2001: Message edited by: funkedup ]