Upengined Ta 152H-1

[wuzak]

How does the increase in number of valves increase the PS?

Reduces pumping losses.

 

[silence]

Reduces pumping losses.

From backflow/backpressure?

 

[wuzak]

From backflow/backpressure?

Should be little or no back pressure, as it would be fitted with ejector exhausts.

Baiscally the Jumo 213 already had 2 inlet valves, so I would guess the gain is from scavenging the exhaust.

Note that the chart Tomo showed earlier says either 500lb or 600lb (can't quite read it) of exhaust thrust at 35,000ft. That may also be helped by the extra exhaust valve.

 

[GregP]

I've never seen an engine get a 46% increase in power by changing only the valves. Usually it is in single or low 2-digit percents.

My calculation with 1300 versus 1900 PS with a 5% increase in drag is 524 mph, but I seriously doubt the reality of it. But if the 1900 PS was there, and if the prop could handle the difference (most props can't handle a 46% increase in power and stay near the same efficiency due to pitch constraints) in power, then maybe so. I don't think so, but it could have been.

 

[tomo pauk]

The increase in RPM was possible via change from 3 to 4 valve head, but I'm sure engine endured other modifications too. We don't know how much weight engine gained, whether the crankshaft was substantially modified, were the counterweights incorporated etc. It goes without saying that I'd really love to see original test documentation for the 213J
The max RPMs were increased from 3250 (Jumo-213A/C/E/F) to 3700 (213J), that is from where much of extra power was gained. The benefits of the extra RPM were obvious in the evolution of DB-601, R-2600/2800, V-1710, M-105, just to name a few

But if the 1900 PS was there, and if the prop could handle the difference (most props can't handle a 46% increase in power and stay near the same efficiency due to pitch constraints) in power, then maybe so. I don't think so, but it could have been.

The table lists that prop was to be counter-rotating, ie. 'old' prop will be discarded.

 

[wuzak]

At 3250rpm the Jumo has an average piston speed of 17.88m/s. For comparison, the Merlin @ 3000rpm = 15.24m/s and the Griffon @ 2750rpm was 15.37m/s. The DB605 was at 14.93m/s.

At 3700rpm the Jumo 213J is at 20.35m/s.

At the same piston speed the Merlin would be spinning at just over 4000rpm, the Griffon at 3640rpm, the Sabre at 4800rpm and the DB605 at 3815rpm.

A lot more needed improving than just the breathing.

 

[Denniss]

Going from 211 to 213 already raised the rpm by 650 (550 if you count-in the very last generation 211 with 2700 rpm) so they must have seen it as the way to go vs larger internal volume. 3700rpm sound really high though, i doubt they would have easily achieved this in practical use.

 

[Shortround6]

Going from 3 valves to four changes the ability of air/gas to get in or out of the cylinder. This may be referred to as pumping loss?
The other thing it does is make the valve/s smaller and lighter which increases the ability of the engine (the valve train anyway) to tolerate higher RPM.

There are three things that limit an engines ability to operate at high rpm (high being relative).

1. is the ability of the valve train (top end) to operate at the desired rpm. This is dependent on the size/weight of the valves and valve train component, valve drive system (push rods/overhead cams) and the valve springs.
2. is the ability of the bottom end to turn the desired rpm without failing.
3. is the ability of the rest of the engine to supply the needed air for the power desired. it does no (or little) good to fit a car engine with a new cam or cylinder head and keep original small carburetor.

Changing one thing seldom results in a BIG power increase unless that one thing was acting like a choke on the whole system.

TO go from 3200rpm to 3700 rpm you need a supercharger that flow at least 15% more air even at teh same level of cylinder filling as the original engine to get the desired power increase ( which will bie in proportion to the rpm increase). Going to 2 exhaust valves instead of one will allow more exhaust gas to exit the cylinder allowing for more fresh air/intake charge to fill the cylinder but requires an even bigger supercharger.

Back pressure is the restriction to the exhaust once it leaves the exhaust valve. Exhaust ports, size/shape of exhaust pipes/stacks, atmospheric pressure. These affect the pressure at the exhaust valve opening and the size of the opening, the pressure on one side of the opening and the pressure on the other side govern the rate at which the exhaust gases flow out.

The problem with greatly increasing the rpm of an aircraft engine is that airplane engines are rarely designed with any great reserve of strength. That 13.8% increase in rpm from 3250 to 3700 puts a 29.6% increase in stress on all the reciprocating and rotating parts and on the parts (crankcase) that hold them. Increasing the cylinder pressure 13.8% at the same rpm puts a 13.8% increase in stress on the parts.

I am not saying the Junkers couldn't run at that RPM ( many post war racing machines (mostly ground/water) using Allisons or Merlins run at wll over 3000rpm if not 4000rpm at times) but getting it to do so reliably and for a long enough service life may be a big question. They were also trying to develop it when Germany was facing increasing shortages in elements needed for high grade steel alloys. What the Allies had available for steel alloys in production quantities in 1944/45 was not what the Germans had available for steel alloys in production quantities.

 

[silence]

I've never seen an engine get a 46% increase in power by changing only the valves. Usually it is in single or low 2-digit percents.

My calculation with 1300 versus 1900 PS with a 5% increase in drag is 524 mph, but I seriously doubt the reality of it. But if the 1900 PS was there, and if the prop could handle the difference (most props can't handle a 46% increase in power and stay near the same efficiency due to pitch constraints) in power, then maybe so. I don't think so, but it could have been.

5% drag increase? May I ask where this comes from?

Also, what kind of CR boost are we talking here?

 

[silence]

Going from 3 valves to four changes the ability of air/gas to get in or out of the cylinder. This may be referred to as pumping loss?
The other thing it does is make the valve/s smaller and lighter which increases the ability of the engine (the valve train anyway) to tolerate higher RPM.

There are three things that limit an engines ability to operate at high rpm (high being relative).

1. is the ability of the valve train (top end) to operate at the desired rpm. This is dependent on the size/weight of the valves and valve train component, valve drive system (push rods/overhead cams) and the valve springs.
2. is the ability of the bottom end to turn the desired rpm without failing.
3. is the ability of the rest of the engine to supply the needed air for the power desired. it does no (or little) good to fit a car engine with a new cam or cylinder head and keep original small carburetor.

Changing one thing seldom results in a BIG power increase unless that one thing was acting like a choke on the whole system.

TO go from 3200rpm to 3700 rpm you need a supercharger that flow at least 15% more air even at teh same level of cylinder filling as the original engine to get the desired power increase ( which will bie in proportion to the rpm increase). Going to 2 exhaust valves instead of one will allow more exhaust gas to exit the cylinder allowing for more fresh air/intake charge to fill the cylinder but requires an even bigger supercharger.

Back pressure is the restriction to the exhaust once it leaves the exhaust valve. Exhaust ports, size/shape of exhaust pipes/stacks, atmospheric pressure. These affect the pressure at the exhaust valve opening and the size of the opening, the pressure on one side of the opening and the pressure on the other side govern the rate at which the exhaust gases flow out.

The problem with greatly increasing the rpm of an aircraft engine is that airplane engines are rarely designed with any great reserve of strength. That 13.8% increase in rpm from 3250 to 3700 puts a 29.6% increase in stress on all the reciprocating and rotating parts and on the parts (crankcase) that hold them. Increasing the cylinder pressure 13.8% at the same rpm puts a 13.8% increase in stress on the parts.

I am not saying the Junkers couldn't run at that RPM ( many post war racing machines (mostly ground/water) using Allisons or Merlins run at wll over 3000rpm if not 4000rpm at times) but getting it to do so reliably and for a long enough service life may be a big question. They were also trying to develop it when Germany was facing increasing shortages in elements needed for high grade steel alloys. What the Allies had available for steel alloys in production quantities in 1944/45 was not what the Germans had available for steel alloys in production quantities.

Thanks, Shortround6.

 

[davparlr]

Let's see how I'm good at cube root law The cube root of 1900 (PS at 33000 ft) is 12.3856. Cube root from 1300 (PS at 33000 ft, Jumo 213E) is 10.91392883. Ratio between those two is 1,13483599. Multiplying the speed of the Ta-152H (~470 mph) with that number makes ~533 mph.
Corrections welcomed

My feelings has always been that around 500 mph would have been the limit of WWII aircraft due to propeller inefficiencies as propeller speed approaches Mach. Rare Bear did 528 mph with probably 4-5000 hp at 5000 ft (?).

 

[Shortround6]

You also have air-frame drag which did not stay constant. as you get closer to the aircraft going 500mph you can get local air flows separating from the air frame more than at lower speeds and causing high drag burbles and it is even possible for local air flows to go supersonic which can cause some real problems (think compress-ability in level flight).

By constant I mean we use formulas that estimate performance based on the drag going up with the square of the speed, (and power required goes up with the cube) but in real life each airframe/airfoil is a bit different and at some point begins a very dramatic rise in drag well above the "square" formula.

 

[silence]

No one has an improved CR estimate? I have no idea how to go about making one.