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Rocket Turbo Questions


Cody Stallings

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The Garrett TH08 Turbo was in use on the C340/C414 engines.

That being said, this particular model has a larger compressor section to aid in the pressurization of said aircraft.

My question: Was the TH08 part of the Conversions? Or was a Turbo with less compressor installed.

If the TH08 did make the hopp to the Mooney, would it be considered overkill for the task considering there is no pressurized cabin?

I have no issues with it’s performance at all, just wondering if it is just loafing in cruise configuration, when others of less size would be glowing Red an Screaming.

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Blower match is a big deal.  A turbo used in an unpressurized should not have the capacity of a blower designed for a pressurized one.  Turbos run efficiently in a narrow rpm range usually above 90% rpm.  A big blower would be running at low rpm and cause lots of back pressure.  I have no idea what was used on a Rocket but that TSIO 520 was used on lots of aircraft so different blowers are probably available.

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Sounds like matching the blower size is pretty important...

1) If the Rocket uses the same set-up as the pressurized twins... the blower is now sending all the air to the Rocket’s engine... with proper fuel management that would provide for a few more HPs... :) (my Audi friends call them Uber turbos, 600hp In street form)

2) If the Rocket was to dump the excess air to not overpower the Rocket’s engine, the turbo’s pop-off valve would be belching some air continuously...

Mooney turbos have a control valve, but the name doesn’t always come to mind... Merlyn pressure controller?

3) Or... you could be one step closer to having a pressurized Mooney! :)

4) Fuel set-up procedures are pretty challenging, matching the engine and turbo... There isn’t much room for a large mis-match in equipment sizes...

How would you ask that question to Rocket Engineering?   What made the transition from the twin, and what had to be Modified to work for the Rocket?

PP thoughts only, not a mechanic...

Best regards,

-a-

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16 hours ago, carusoam said:

Sounds like matching the blower size is pretty important...

1) If the Rocket uses the same set-up as the pressurized twins... the blower is now sending all the air to the Rocket’s engine... with proper fuel management that would provide for a few more HPs... :) (my Audi friends call them Uber turbos, 600hp In street form)

2) If the Rocket was to dump the excess air to not overpower the Rocket’s engine, the turbo’s pop-off valve would be belching some air continuously...

Mooney turbos have a control valve, but the name doesn’t always come to mind... Merlyn pressure controller?

3) Or... you could be one step closer to having a pressurized Mooney! :)

4) Fuel set-up procedures are pretty challenging, matching the engine and turbo... There isn’t much room for a large mid-match in equipment sizes...

How would you ask that question to Rocket Engineering?   What made the transition from the twin, and what had to be Modified to work for the Rocket?

PP thoughts only, not a mechanic...

Best regards,

-a-

That’s a good Question Anthony, Sometimes Rocket is rather hard to get ahold of.

Think I will make that call or send that email.

The mechanical side of my brain is itching for an answer.

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18 hours ago, carusoam said:

 

1 hour ago, Cody Stallings said:

That’s a good Question Anthony, Sometimes Rocket is rather hard to get ahold of.

Think I will make that call or send that email.

The mechanical side of my brain is itching for an answer.

Let us know if you learn anything - I am always interested in learning such things even if I am not needing to change anything right now,.

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As a general rule, a centrifugal compressor has a fairly wide operational range outside of the surge margin. There are certainly times the compressor may not be at peak efficiency, never the less, it will be quite effective. It's good to note the compressor's efficiency is generally between 65% and 75% and unless it's a very modern turbocharger, will never exceed (around) 78% efficiency. Typically the surge margin is located near the 60% efficiency line. 

Think about what happens making 300HP:

At sea level, the turbine/compressor spins at a specific speed to compress 30 in/hg to 42in MP. Let's call it 44,000 RPM in our theoretical model. 

As you start the climb, HP remains at 300, and manifold pressure remains at 42, yet the turbocharger's RPM increases markedly, compensating for air density. 50,000+ RPM. 

At 28,000 feet, the turbocharger is now working amazingly hard, spinning nearer to it's 77,000 RPM operational maximum, compressing 13 in/HG to 30 in. 

 

The one on your 305 Rocket must perform outside the surge margin at any load and at any reasonable altitude. Fortunately, centrifugal compressors have wide operational ranges. Going up or down a size or two is often quite possible to achieve tuning goals. 

 

It's also good to note that compressor efficiency is not a major factor in overall system performance. It's just a measure of the efficiency of a single component. There is not much power to be gained by switching from a compressor operating in the 65% efficiency island and sizing one to be operational narrowly centered on the the very best 80% island. 

 

The pic below is not an aircraft part, but it illustrates the operational range well between 60,000 to 140,000 RPM and pressure rises as high as 3.5X

 

 

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