P-47 "quiet" engine

[Peq]

I have a question about the P-47. I'm not an expert so maybe everything's fine as it is.

 

 

As you know, when you start the Pony you can feel the bird is "alive": instrument panels are vibrating and you can even notice a subtle trembling in the wingtips from external camera. In the other hand, everything is strangely quiet in the Thunderbolt cockpit when the engine is running. Very little or no noticeable vibration at all.

 

 

I've never been in a Jug cockpit, so I'm asking from my ignorance of the subject, but is this normal? Is the P-47 that quiet when the Pratt & Whitney R-2800 is running on the ground? Maybe work in progress? Can you shed some light into this?

 

 

Thanks in advance.

[grafspee]

In p-47 exhaust are not short straight pipes, in p-47 r-2800 is equipped with exhaust manifold, this will make P-47 much quieter then any other plane using r-2800.

Exhaust is discharged below wings level at both sides of the plane. So any shock wave from exhaust is directed under the wings, so cockpit should significant quite then in for example in p-51 where exhaust pipes blow almost directly in to cockpit area.

Edited September 9, 2020 by grafspee

[BIGNEWY]

It has been mentioned before, but it is correct, the in cockpit sound is quieter thank other aircraft.

 

thanks

[Diesel_Thunder]

Ducting the exhaust the way Republic did on the Jug helped reduce the noise. Most of the radials on aircraft in that era were equipped with an engine driven supercharger, with the the exhaust from each cylinder going into a collector, and then directly overboard out the exhaust stack. The stack was usually kept as short as possible. These make a fair amount of noise.

 

V engines, such as the Merlin used on the Mustang, used a simple exhaust manifold with a very short path out of the engine. This style of exhaust makes a lot of noise. Neat factoid on the Mustang, it was found that by angling the exhaust duct rearward, they gained some thrust from the velocity of the exhaust gas (early models vented straight out).

 

The Jug on the other hand, used an exhaust gas driven turbocharger which fed more compressed air into the supercharger (turbo-compounding). The turbo was situated in the fuselage behind the pilot, and required more exhaust piping to get there. This cut down on a lot of the exhaust noise. The only exception is if the wastegate is wide open, then all the exhaust will then go directly overboard. This would make more noise similar to a typical supercharged installation on other aircraft.

 

Here's a couple of pictures to illustrate this. The first picture shows the short exhaust stacks of the Mustang.

 

The second picture shows the exhaust stack of a DC-3/C-47, note that the stack outlet is aft of the cowl flaps. The stack is also located on the outboard side of the cowlings directing the exhaust (and noise) away from the fuselage and crew.

 

The third picture is a diagram of the exhaust system of the Jug. Note the location of the wastegate outlet and where the turbo is. Given how far the exhaust gas has to go and the plumbing involved to get to the turbo, this helped attenuate the noise from the engine.

Edited September 12, 2020 by Diesel_Thunder

[grafspee]

I will add that P-47's engine has gear driven supercharger as well :)

[Diesel_Thunder]

I will add that P-47's engine has gear driven supercharger as well :)

 

Turbo compounding, I like it. :)

 

Seems a lot of material on the subject glosses over that it did have a mechanical supercharger. More emphasis is placed on that it was one of the few that had a turbo. B-17 is another one.

 

 

Here's a better picture of the exhaust manifold and stack on a decowled DC-3 that I took when I was at the Lone Star Flight Museum in Texas. Helps illustrate the point of how noisy they were, because they were essentially straight piped.

Edited September 12, 2020 by Diesel_Thunder

[grafspee]

Turbo compounding, I like it. :)

 

Seems a lot of material on the subject glosses over that it did have a mechanical supercharger. More emphasis is placed on that it was one of the few that had a turbo. B-17 is another one.

I will add that p-38 is another another one :) which was quite hard task to attach turbocharger in to supercharged V12:)

[Diesel_Thunder]

I will add that p-38 is another another one :) which was quite hard task to attach turbocharger in to supercharged V12:)

 

Forgot about that one too :doh:

 

If I recall, they had to remote mount the turbo kinda like the Jug. Except they they were on the top of the tail booms for each engine, about halfway back.

[Art-J]

Seems a lot of material on the subject glosses over that it did have a mechanical supercharger. More emphasis is placed on that it was one of the few that had a turbo. B-17 is another one.

 

I think glossing over supercharging is not an omission, but result of the fact that by the late 1930's pretty much all aero engines in the world, at least the big ones intended for anything bigger than the likes of Piper Cub or Tiger Moth, were supercharged.

 

So it's not worth extra mentioning, because it just was a common thing.

 

Turbos, however, were indeed a relatively new technology.

[grafspee]

I think glossing over supercharging is not an omission, but result of the fact that by the late 1930's pretty much all aero engines in the world, at least the big ones intended for anything bigger than the likes of Piper Cub or Tiger Moth, were supercharged.

 

So it's not worth extra mentioning, because it just was a common thing.

 

Turbos, however, were indeed a relatively new technology.

 

Turbo charging appeared in B-17 at first, making it faster then any US fighter at high alt.

Main challenge was to adapt turbo in to single engine fighter, In big bomber there was plenty space for this device.

Attempts to equipped turbocharging in to fighter appeared way before WW2 but with no success.

In case of Radial engine you can hide exhaust behind engine so you don't suffer increased frontal area, in case of V12 this is impossible.

I think it is worth mentioning just because lots of ppl miss this fact, that most of aviation engines were designed with single stage single speed supercharger by standard prior ww2 and during ww2.

[Swagger897]

Since we're on about DC-3's and their exhausts, here's one that we steam cleaned and performed engine run-up's on earlier this year. The stuttering is from performing a mag-check where one of the magnetos were a little wet causing little to no spark.

 

A good set of speakers with good bass is needed:

[Peq]

Thanks for the replies. Now I understand a bit better.

Actually I wasn't referring to the noise, but the "vibration".

 

As grafspee pointed out "any shock wave from exhaust is directed under the wings" but is it that smooth in a real P-47 cockpit? Is that subtle you can't barely notice the "trembling"?

 

Don't get me wrong. I really love DCS P-47. Probably my favourite module along the Tomcat (and Hornet, and Warthog, and... actually I love 'em all)

[Thunderchief2000]

The new beta seems to have brought a louder engine noise. Sounds much better from my POV anyway. Also the starter is much louder if not a new sound as well.

[javelina1]

The new beta seems to have brought a louder engine noise. Sounds much better from my POV anyway. Also the starter is much louder if not a new sound as well.

interesting. I'll check it out later today...

[Art-J]

The new beta seems to have brought a louder engine noise. Sounds much better from my POV anyway. Also the starter is much louder if not a new sound as well.

 

They're louder because both new -47s got Rolls Royce Merlin sounds for some reason, as noted in other threads. Not the kind of improvement some have been looking for I'd say ;).

[Thunderchief2000]

They're louder because both new -47s got Rolls Royce Merlin sounds for some reason, as noted in other threads. Not the kind of improvement some have been looking for I'd say ;).

 

Really? I'll have to compare tonight. I noticed that the turbine whistle had gone. At least the starter is better.

 

do all three versions have the same sounds? I only tried the -40.

[Art-J]

Previous -30 retained original sounds, although I haven't flown it enough to tell if they were tweaked. Both "new" variants, however, feature a mess of placeholder sounds, not only for engines, but for armament and other systemem as well.

[DHR]

If I may add to this thread. I agree the engine is too quiet. For example, sitting on the taxiway, engine running and the canopy open I can hear birds chirping in the trees about 30m away. Not very realistic either way

[BuzzU]

If I may add to this thread. I agree the engine is too quiet. For example, sitting on the taxiway, engine running and the canopy open I can hear birds chirping in the trees about 30m away. Not very realistic either way

 

That's a mouse in your baseboard.

[DHR]

That's a mouse in your baseboard.

 

Thanks for the inciteful input.

[BuzzU]

I see you object to a little humor.

[SMH]

Ducting the exhaust the way Republic did on the Jug helped reduce the noise. Most of the radials on aircraft in that era were equipped with an engine driven supercharger, with the the exhaust from each cylinder going into a collector, and then directly overboard out the exhaust stack. The stack was usually kept as short as possible. These make a fair amount of noise.

 

V engines, such as the Merlin used on the Mustang, used a simple exhaust manifold with a very short path out of the engine. This style of exhaust makes a lot of noise. Neat factoid on the Mustang, it was found that by angling the exhaust duct rearward, they gained some thrust from the velocity of the exhaust gas (early models vented straight out).

 

The Jug on the other hand, used an exhaust gas driven turbocharger which fed more compressed air into the supercharger (turbo-compounding). The turbo was situated in the fuselage behind the pilot, and required more exhaust piping to get there. This cut down on a lot of the exhaust noise. The only exception is if the wastegate is wide open, then all the exhaust will then go directly overboard. This would make more noise similar to a typical supercharged installation on other aircraft.

 

Here's a couple of pictures to illustrate this. The first picture shows the short exhaust stacks of the Mustang.

 

The second picture shows the exhaust stack of a DC-3/C-47, note that the stack outlet is aft of the cowl flaps. The stack is also located on the outboard side of the cowlings directing the exhaust (and noise) away from the fuselage and crew.

 

The third picture is a diagram of the exhaust system of the Jug. Note the location of the wastegate outlet and where the turbo is. Given how far the exhaust gas has to go and the plumbing involved to get to the turbo, this helped attenuate the noise from the engine.

 

What about when the turbo is off? How is turbo power controlled? (Waste gates. Which dump exhaust straight out of the engine, in front of the pilot.)

[Diesel_Thunder]

 

What about when the turbo is off? How is turbo power controlled? (Waste gates. Which dump exhaust straight out of the engine, in front of the pilot.)

 

If the turbo is bypassed (full open waste gate), then the engine will operate as any other supercharged radial with power output determined by RPM and throttle setting. Darn near every piston engines power output is determined by RPM and fuel rate. All the turbo did was to help put more air into the cylinders to allow more fuel to be burned and make more power.

 

The waste gate itself doesn't control power, not directly anyway. Mostly meant to keep the turbo from an overspeed condition (bad for the turbo), or overboosting the engine (bad for the engine).

[SMH]

 

If the turbo is bypassed (full open waste gate), then the engine will operate as any other supercharged radial with power output determined by RPM and throttle setting. Darn near every piston engines power output is determined by RPM and fuel rate. All the turbo did was to help put more air into the cylinders to allow more fuel to be burned and make more power.

 

The waste gate itself doesn't control power, not directly anyway. Mostly meant to keep the turbo from an overspeed condition (bad for the turbo), or overboosting the engine (bad for the engine).

 

Power to the turbo.

 

And the topic is sound. Wouldn't you hear the exhaust through the waste gates?

[Diesel_Thunder]

Ah, I see where you were going with that now. Sorry for misunderstanding that.

 

And yes, with the wastegate open, you would hear a lot more noise from the wastegate stack pipe than you would if it were closed.