Climbing CHT’s and settings for M20K 305

[aviatoreb]

  On 5/21/2020 at 12:05 AM, Yooper Rocketman said:

When I had my Rocket Engine OH'd they had trouble getting the max RPM set for a bit.  I had 2700 RPM for a while (would have been really tempted to leave it there had I not been selling it).  That IS why the H.P. was dropped to 305.  I will tell you, that extra 50 RPM felt like a lot more than 5 more HP !!!!!!  I was blown away how much more power it had.  Could have been a new engine vs. a 500 over TBO old one too.  Almost as impressive as 724 HP on my 2500 pound (empty weight) Carbon Fiber garage built experimental. 

Tom

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Interesting.  But that is how - not why / the hp was dropped by 5hp.  I wonder why the wanted to knock off the 5 hp?

[N231BN]

  On 5/21/2020 at 2:10 AM, aviatoreb said:

Interesting.  But that is how - not why / the hp was dropped by 5hp.  I wonder why the wanted to knock off the 5 hp?

Most likely either cooling or fuel flow requirements.

[aviatoreb]

  On 5/21/2020 at 2:13 AM, N231BN said:

  On 5/21/2020 at 2:10 AM, aviatoreb said:

Interesting.  But that is how - not why / the hp was dropped by 5hp.  I wonder why the wanted to knock off the 5 hp?

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Most likely either cooling or fuel flow requirements.

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I was guessing it’s some kind of stc negotiation compromise with the Faa.  My experience is cooling is fantastic and I find it hard to believe that 5hp more would hurt it.  Fuel flow?  I don’t know but isn’t it using the fuel pump of a Cessna 340/tsio520nb?

[N231BN]

  On 5/21/2020 at 2:34 AM, aviatoreb said:

I was guessing it’s some kind of stc negotiation compromise with the Faa.  My experience is cooling is fantastic and I find it hard to believe that 5hp more would hurt it.  Fuel flow?  I don’t know but isn’t it using the fuel pump of a Cessna 340/tsio520nb?

There may be some other reason but you need to consider the test conditions...max-power climb at Vx on a hot day at full-gross. As far as fuel flow, the aircraft plumbing could be the limiting factor.

Most power ratings for powerplants are limited by heat rejection. As manufacturing technology improved, the ability to have more surface area for cooling allowed the engine manufacturers to increase the power ratings.

[Yooper Rocketman]

I was told it was dropped to satisfy the FAA on total HP for the airframe.  As Erik said, a negotiation to get the STC approved.  
 

Tom

[carusoam]

I like how Rocket Engineering operates....

Lots of under promise.... followed by Over Deliver...
 

Is that 310hp? It feels like 350!   

Best regards,

-a-

[N231BN]

  On 5/21/2020 at 3:05 AM, Yooper Rocketman said:

I was told it was dropped to satisfy the FAA on total HP for the airframe.  As Erik said, a negotiation to get the STC approved.  
 
Tom

That may be true, it's quite comical. Kind of like the Colemill Barons where they put IO-550s on a B55 and "limited" them to the original 260hp with a maximum manifold pressure chart.

[aviatoreb]

  On 5/21/2020 at 2:56 AM, N231BN said:

There may be some other reason but you need to consider the test conditions...max-power climb at Vx on a hot day at full-gross. As far as fuel flow, the aircraft plumbing could be the limiting factor.

Most power ratings for powerplants are limited by heat rejection. As manufacturing technology improved, the ability to have more surface area for cooling allowed the engine manufacturers to increase the power ratings.

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True - good points!

[FloridaMan]

I figured it might’ve had something to do with stall certification, such as whether the plane runs out of rudder at full power in a stall.