TLS/Bravo Power Chart

[kgbpost]

I know this has been touched on earlier but what is 75% power on this engine? I am in the process of fine tuning my new EDM-830 and there is a process in the manual where I have to tell it when the engine is at 75% so it indicates properly on the EDM-830 (neat feature). I have the K factor for the fuel flow dialed in so %hp is all I have left to set up.

The only factors are MP & RPM, right? Sooo...if 100% is 38"/2575, what MP equates to 75% at 2400?

On another note, the rpm drop and egt rise when doing mag checks are very consistent, but...my #5 cylinder CHT runs 60-80 degrees cooler than the other 5 cylinders which are all within 10 degrees of each other. The EGT of #5 is right in the middle of the spread which is 30 degress max across all six (usually more like 20 degrees). Could the #5 CHT really be that much cooler? I'm assuming the avionics shop has the correct probes on the correct cylinders. I'm thinking probe?

Thanks in advance for the help. Brian

[TLSDriver]

Brian,

You are not alone.  The TLS\Bravo POH stinks in showing power settings.  I have not had any luck finding these.  A few of the guys that have Bravo's have told me where they run theirs but seemed like they did it by feel more than spec.

If you come across anything helpful kindly foward it.

Thanks

David

[thinwing]

the #5 cylinder temp probe is doubled...one to the guage that came standard (a moritz guage in my case)and a second washer style held in by the bayonet alcor style.This results in one of the probes reading about 40 /50 degrees colder as far as performance #s...i just use 32/2400 in cruise....kpc

[drstephensugiono]

My #5 cyl is colder too, its because they tied it to the original factory probe! I have had my plane since 1994 and always used 32/2400 and fuel flow of 19.7 gal/hr.

[kgbpost]

Thanks for the info guys. I think I'm gonna call JPI on monday and ask them how they arrived at the setting my EDM-830 shipped at for %HP. I'll share my findings.

On the CHT thing that makes sense...that eases my mind a bit. Brian.

[Awful_Charlie]

Sorry, a bit late into this - but you're not going to like the answer much I'm afraid!

Get the Lycoming Operators Manual p/n 60297-23.  In there you'll find the all the graphs for the various power settings, but to get 75% will depend on your pressure altitude and the difference from ISA as well as FF/MP and RPM.  When you've worked through a few graphs, you will find that even Lycoming don't give you a straight answer!

For instance, on page 3-9 it gives 'Performance Cruise (75%)' 2400RPM and 17.1GPH and 'Economy Cruise (60%)' 2200RPM and 12.5GPH'  Now look up Figure 3-30 'Fuel Flow vs BHP' and read off 200BHP (75%) and you get about 89lbs/hour!  Now maybe they did some testing with some odd density fuel, but where can I get the POH weight and balance amendment so full fuel is only 450lbs?  To put the icing on the cake, get Figure 3-32 (Zero Ram altitude performance at 2400 RPM) and see that for 200BHP you need a touch under 28" of MP and a fuel mixture setting of 0.6Lbs/HP/HP, which comes out at 120Lbs!!  For me I can't pull 17GPH at that MP without being WAAAY ROP and well under best power, to say nothing of 20GPH (if you take 6lbs/gallon) or 21GPH (if you use 5.7)

I set the Engine constant in between the two values in the EDM manual, as the AF1B has an 8.0:1 compression, which is a bit higher than the 'standard' turbo or 7.5:1 and messed about with the EDM800 until I got the figure to go to 100 or 101% on take off, and worked with that.

Be interested to head what JPI say if you get an answer from them!

Ben

[TLSDriver]

Quote: Awful_Charlie

Sorry, a bit late into this - but you're not going to like the answer much I'm afraid!

Get the Lycoming Operators Manual p/n 60297-23.  In there you'll find the all the graphs for the various power settings, but to get 75% will depend on your pressure altitude and the difference from ISA as well as FF/MP and RPM.  When you've worked through a few graphs, you will find that even Lycoming don't give you a straight answer!

For instance, on page 3-9 it gives 'Performance Cruise (75%)' 2400RPM and 17.1GPH and 'Economy Cruise (60%)' 2200RPM and 12.5GPH'  Now look up Figure 3-30 'Fuel Flow vs BHP' and read off 200BHP (75%) and you get about 89lbs/hour!  Now maybe they did some testing with some odd density fuel, but where can I get the POH weight and balance amendment so full fuel is only 450lbs?  To put the icing on the cake, get Figure 3-32 (Zero Ram altitude performance at 2400 RPM) and see that for 200BHP you need a touch under 28" of MP and a fuel mixture setting of 0.6Lbs/HP/HP, which comes out at 120Lbs!!  For me I can't pull 17GPH at that MP without being WAAAY ROP and well under best power, to say nothing of 20GPH (if you take 6lbs/gallon) or 21GPH (if you use 5.7)

I set the Engine constant in between the two values in the EDM manual, as the AF1B has an 8.0:1 compression, which is a bit higher than the 'standard' turbo or 7.5:1 and messed about with the EDM800 until I got the figure to go to 100 or 101% on take off, and worked with that.

Be interested to head what JPI say if you get an answer from them!

Ben

[jlunseth]

Determining %HP from engine settings and air temps. is complicated in an intercooled turbocharged engine, at least on the ROP side it is complicated.  On the ROP side HP is primarily determined by air flow rather than fuel flow, because being ROP means that more fuel is being put into the engine than it can burn. 

MP and RPM's work ok for a normally aspirated engine, but in the intercooled turbo (the Bravo is such a thing), there are a number of variables.  Density altitude is a determiner in the normally aspirated engine, but the turbo intercooled engine makes its own density altitude as far as the engine induction/combustion processes are concerned.

In the turbo, air is compressed so you can fly, say 30" at 20,000 feet if you want to.  However, the price is that even though OAT may be -25 C up there, the air coming out of the turbo is in the range of 260 dF (126 C).  The cure for that is to run the induction air through the Bravo's intercooler.  The intercooler cools the induction air quite a bit, so the Inducation Air Temp. may actually be in the 50' or 60's C.  In my intercooler, it is not uncommon to see a temperature difference of 100 dF (55 C) or more.  This makes the air denser going into the cylinders (it also makes it cooler, which helps keep the CHT's in order).

The JPI %HP is, as you know, an algorithm, not a measurement.  Trying to derive %HP in an intercooled turbo would not be an exact science, there are quite a few variables.  For example, if you knew that the intercooler would cool the air temp. by "x" percent at an outside air temp. of "y", you would think you could plug y into a formula and get a result.  However, you also need to know the altitude, because at higher altitudes the air becomes thin enough that its ability to cool is not great even though the absolute temp. may be very low.  35 dF below at 20,000 is not 35 below at the surface.  So you would need a function to allow for the impaired cooling at altitude.  Further, there are variables in these systems of the engine.  An intercooler that is new, clean and well baffled will cool well, one that is old, dirty, and the baffle is worn or gone will not cool so well.  

JPI does not publish its algorithm.  Having flown with a 930 for a couple of hundred hours (M20K 231), I think the algorithm is pretty good, better than I expected.  It is still just an approximation, and seems to me less accurate at higher altitudes (results in a high calculated %HP at too low an MP).

I would call JPI.  I hear their customer support is improving.  Maybe they will help.    

[trey2398]

I was looking at a listing for a Bravo and one of the photos was of the visor with power settings and fuel flow printed on it.  I have attached that pic.  Hope this helps...

[carqwik]

Forget the visor power chart.  Bob Kromer told me that the optimum speed/fuel flow/engine longevity setting for cruise is 30"/2400rpm on the Bravo.  (Bob Kromer was a former Mooney factory guy...I forget his position there but it was important with regard to aircraft design/engineering/etc.)  I lean to about 100 ROP based on TIT.

That's the setting I use...fwiw.

[TLSDriver]

Quote: carqwik

Forget the visor power chart.  Bob Kromer told me that the optimum speed/fuel flow/engine longevity setting for cruise is 30"/2400rpm on the Bravo.  (Bob Kromer was a former Mooney factory guy...I forget his position there but it was important with regard to aircraft design/engineering/etc.)  I lean to about 100 ROP based on TIT.

That's the setting I use...fwiw.

[carqwik]

Fuel flows are approx 18.5 gph, speed at 10k is approx 180, at 15k, it goes up to 190 kts.  No TKS.  Best altitude from the TLS is high teens.

[bbillb]

I'll try this again with maybe something you can read.

Bob

 

 

 

 

 

 

 

 

 

 

[bbillb]

Well it looks like my first post went into cyberspace, so I'll try again.

Here are the Lycoming Power charts for the Bravo at 2200 and 2400rpm(revised as of 2002)

According to these charts at Standard Air Inlet temp, 28"hg and 2400rpm; Power=200Hp     202.5/270=75% Power

As others have noted Bob Kromer recommends 30"hg at 2400rpm, here is his article http://www.mooneypilots.com/mapalog/cruisepower.html    According to the charts though if you are flying at 18-19k at 30"hg and 2400rpm you will be at 225Hp which is  225/270 = 83% Power !!!!  (assuming standard air inlet temp)

I was also suprised to learn that three out of five Bravo POH recommended power settings were greater than 75%!!   I guess Mooney was not too worried about the durability of their engine.

Lycoming also recommends correcting power 1% for every 10degF variation in air inlet temp vs standard altitude temp.  My Bravo did not come with a JPI so I don't know what my IAT runs.  Any thoughts on what typical IAT variations run??  If they are upwards of 100deg hotter than standard then that would bring power down 10%;   which would bring Bob Kromer's recommendation down to about 75%...

Hopefully this sheds some more light on the subject

Regards,

Bob