Escorts could only stay with bombers for 20-40 minutes?

[DaveBB]

"By Joe Supercool" 

109 of course could only run at WEP as long as it had a supply of MW50 for anti-detonation and cooling.  Mustang had no such limitations and even went to 80" of manifold pressure for extreme situations.

https://en.wikipedia.org/wiki/MW_50

[GScholz]

109G-14, G-10 and K-4 had enough MW50 for more than 30 minutes of use. 109 pilots were instructed to limit WEP use to 10 minute intervals with 5 minute cool down. P-51 pilots were instructed to not use WEP for more than 5 minutes. However, these limitations were often exceeded in emergencies.

Do you concede any of the arguments in this thread, or will you just keep on trolling?

[Vraciu]

Not really. Not a lot. It's a difference of about 10%.

P-51D
Length: 32 ft 3 in
Wingspan: 37 ft 0 in

Bf 109G-K
Length: 29 ft 7 in- 91% of P-51D
Wingspan: 32 ft 6 in - 88% of P-51D

(Image removed from quote.)

(Image removed from quote.)

(Image removed from quote.)

The first two are a tad misleading being Buchons.   

But even ten percent is significant I would argue.

[DaveBB]

109G-14, G-10 and K-4 had enough MW50 for more than 30 minutes of use. 109 pilots were instructed to limit WEP use to 10 minute intervals with 5 minute cool down. P-51 pilots were instructed to not use WEP for more than 5 minutes. However, these limitations were often exceeded in emergencies.

Do you concede any of the arguments in this thread, or will you just keep on trolling?

What data have you provided? Also what arguments are you speaking of?  At the very least, provide some data to show the thrust that the 109 produces with its radiators.  You suddenly jumped the conversation to "Evaporative cooling racing Mustangs" when I asked about that. 

Dumping water and alcohol into the engine for 30 minutes? That must be a big reservoir tank.  Please provide data on that too.

[FLOOB]

Can't you two see that you love each other?

[drgondog]

The 109 was a.) a lot smaller in wetted area, b.) much draggier but total D in pounds was compensated for by the smaller wetted area to offset the 50+% greater CDparasite.

The last round of 109G-10 and K series were about as fast as the P-51D, even with 72" MP and accelerated slightly better intitially from medium speed envelope.

As near as I have been able to find, there is zero NAA 'official' thrust number for the Meridith effect. I spent some energy trying to calculate pressure drag of the radiator, exit velocity of the pass through air through the radiator with coils at 200 degrees F, estimating the mass flow rate of ambient air (at both SL, STP and 25000 feet), and exit velocity out the butt (closed) - assuming no mass flow rate loss and some other factors to 'assume' heat transfer rate into the 'system'.

I could never get more than ~30-40 pounds of net thrust. BTW, that is about 30% of Max Exhaust Thrust (axis component) at 67" EDIT about 3% of Max Exhaust Thrust. Then the other side of the equation is to apply the Drag of the Radiator duct, the stagnation Pressure against the radiator to figure out the Net. At 2x10^^ the Cdp for the radiator duct is .0019 (below 100mph). You have to go the CD vs RN to pick the correct CD (reduced) for RN for the velocity you are basing your calcs on.

Lee Atwood's claims of '300' or whatever else he stated was way overstated. You will note that Ed Horkey and Edgar Schmued never backed up Atwood's claims.

[save]

"The amount of MW booster fuel being carried (75 liters) is sufficient for 26 minutes of flight while using the Sondernotleistung. Therefore  Sondernotleistung can be used for two 10 minute periods, or in any other subdivision; in no case should one fly with Sondernotleistung for over 10 minutes. For further servicing instructions, see  L. Dv. T. 2109 K-4/Fl.

    Between two uses of the Sondernotleistung the engine must be run at a lower power output for ca. 5 minutes."

[drgondog]

Here's a good article, maybe help get your math straightened out:

http://www.supercoolprops.com/articles/meredith_effect.php

It is an interesting article and parallels the model I used to get my 30-40 pounds of Net Thrust.

What the article leaves conveniently untouched are the Major assumptions and calculations of the pressure drag of the impinging airflow on the radiator as well as the drag of internal flow losses.

The Model must have a.) Mass flow - Inlet, b.) Physical dimensions of inlet, c.) Drag due to internal flow between inlet and radiator, d.) Radiator (both heat transfer to the passing fluid and pressure drag of flow impinging on coils), e.) Drag due to higher energy flow in Plenum, f.) physical dimensions of exit shutter for the flight conditions modeled.

He treats the model as a venturi tube model - and then calculates the Net thrust based on the delta between input flow properties versus exit velocity.  This is a.) a Thermodynamic System, and b.) it is 'attached' to the airframe and, as such, a major component of drag in low to medium speeds.

Another observation that should be noted is that he is basing all of his mass flow calcs on 430 mph at Sea Level.. good for Reno, but about 60mph above top speed at 72" MP for a P-51B/D.

This is why NAA engineers separates the Cooling Drag discussions between High Speed and Climb and why they state in the Performance Calculations Report NA-8449. pg 21 of 62.

Cooling Drag
"The basic drag includes the external drag of the radiator dust for the flush exit flap position, but does not include the internal losses or drag due to change in scoop exit flap position. These added drags are given as follows:

Calculations show that for most cases a small amount of thrust is derived, however, for this work any thrust from the cooling air is neglected. High speed Cooling Drag is then considered equal to zero".

[/NOTE: I commented that the best I could extract from My assumptions was 30-40 pounds of Net Thrust. Joesupercool derives 270 pounds.  Ya think NAA engineers would ignore 270 pounds of 'found' thrust in a Performance Estimate, an amount far in excess of  exhaust thrust?

BTW - to get 430mph at SL in a P-51D would take more than 2400 Hp ~ 1775 pounds of Thrust plus another ~ 200 pounds of exhaust thrust.

[drgondog]

109 of course could only run at WEP as long as it had a supply of MW50 for anti-detonation and cooling.  Mustang had no such limitations and even went to 80" of manifold pressure for extreme situations.

https://en.wikipedia.org/wiki/MW_50

The P-51H with 50 gallons of coolant could run 80" at WEP with 150 octane and 90" with WI with the new 1650-9. Impossible with 1650-7 or -3 in combat conditions.

That said, when the CC notices the wire 'gate' is broken at 61", there is a discussion. The specs state 5 minutes at WEP.  Not 5 minutes, 'rest', 5 minutes more...

5 minutes at WEP. Period.  Some P-51s came home, some P-51s landed in Germany well short of home after running at WEP too long - the 'book' sez 5 minutes.

[GScholz]

The first two are a tad misleading being Buchons.   

But even ten percent is significant I would argue.

Nah, the Buchon is just a license produced 109G with a Merlin engine. 109G fuselage. 109G wings. I'll bet that last 109G-6 started life as a Buchon too, as with most rebuilt 109Gs.

I agree that 10% isn't insignificant, but I wouldn't call it "a lot". If we were to compare with Jugs or Lightnings however... It seems to me that people tend to overestimate the size of the P-51 and underestimate the size of the 109. People also typically overestimate the size of the Fw 190A, often comparing it to the Jug. In reality the early 190As were shorter than the 109G, albeit with a slightly wider wingspan (each wing less than a foot longer).

[GScholz]

5 minutes at WEP. Period.  Some P-51s came home, some P-51s landed in Germany well short of home after running at WEP too long - the 'book' sez 5 minutes.

Well, you know what they say about limits on combat aircraft. The aircraft limits are only there in case there is another flight planned for that particular airplane. If subsequent flights do not appear likely, there are no limits.

[Vraciu]

Nah, the Buchon is just a license produced 109G with a Merlin engine. 109G fuselage. 109G wings. I'll bet that last 109G-6 started life as a Buchon too, as with most rebuilt 109Gs.

I agree that 10% isn't insignificant, but I wouldn't call it "a lot". If we were to compare with Jugs or Lightnings however... It seems to me that people tend to overestimate the size of the P-51 and underestimate the size of the 109. People also typically overestimate the size of the Fw 190A, often comparing it to the Jug. In reality the early 190As were shorter than the 109G, albeit with a slightly wider wingspan (each wing less than a foot longer).

The Buchon with the Merlin has a way bigger nose not to mention protrusions for the valve covers. 

All else I agree is the same. 

[GScholz]

I can't say I agree that it's got a "way bigger nose". The different engine and propeller makes the nose look different. With the long chin scoop and upright V-12 the Buchon nose is taller, but I think the DB engine 109G is actually slightly longer. Difficult to say.

[Vraciu]

I spent a lot of time around Buchons.  They're definitely fatter-nosed.   The DB engine is a lot smaller. 

Also the Buchon's Merlin protrudes in odd places.  When you see them in the flesh the difference is stark.

[Devil 505]

You don't even need to see one in person to tell that the difference is huge. Hell, when I was a kid watching HBO's "Tuskegee Airmen" I thought the Buchon was a P-40 painted like a 109.