cruise setting found

The world's most famous high performance general aviation aircraft
new reply
awash2002
A2A ACE
Posts: 2995
Joined: 01 Aug 2013, 06:13
Location: KCZL

cruise setting found

Post by awash2002 »

I have found my cruise power setting 2400 prop using the 75% cruise power fuel flows and 65% power fuel flows and I'm getting 167TAS at 8000 IOAT 12°C
Image
Image
Image
Image

User avatar
Scott - A2A
A2A General
Posts: 16839
Joined: 11 Feb 2004, 12:55
Location: USA
Contact:

Re: cruise setting found

Post by Scott - A2A »

I like to fly at lower RPMs if not for anything else, for just cabin noise levels. If this was my Comanche, I'd be at 1900RPM and full throttle. But I understand some like to fly at higher RPM.

Scott.
A2A Simulations Inc.

awash2002
A2A ACE
Posts: 2995
Joined: 01 Aug 2013, 06:13
Location: KCZL

Re: cruise setting found

Post by awash2002 »

I'll take any rpm setting that you give me Scott and I also fly my Comanche at 1900 and full throttle
Image
Image
Image
Image

User avatar
Scott - A2A
A2A General
Posts: 16839
Joined: 11 Feb 2004, 12:55
Location: USA
Contact:

Re: cruise setting found

Post by Scott - A2A »

The challenge with a naturally aspirated combustion engine (no turbo) is, the higher you go the less power you get so going to a lower RPM at altitudes above 10k can be tough, as the airplane / wing gets on the slow side of what it was designed for and you get that higher angle of attack. The higher angle of attack starts to work against the quest towards efficiency. So the only time I fly at 2400RPM is when I'm flying above 10k. It's sort of a compromise in terms of noise, as the engine combustion is lower yet the RPM is higher. And the only time I fly above 10k is when there is a tailwind, otherwise IMO it's always better to fly mid range altitudes (4.5-7.5k).

Since we can easily fly 1900 RPM at 25" without any risk to hurting the engine (it's actually good for it IMO), these mid range altitudes allow the airplane to get 25" as that develops the fastest speed / efficiency and lowest cabin noise.

Also, thanks to Accu-Sim's advanced sound engine (still easily superior to anything out there), beautifully replicates all of the above.

BTW speaking of turbos, this is just personal preference but I'll never own a turbocharged combustion airplane. My Aerostar 600 was faster than a turbo at all except high altitudes by a long shot, no comparison. And I have zero desire to be flying at 20k feet with all of the higher risks of fire and failure that comes with a turbo. Piper had it right with the Comanche 400, when they chose cubic inches over turbocharging. If you want to fly high, aside from cubic inches IMO a turboprop or turbojet is the only way.

Scott
A2A Simulations Inc.

awash2002
A2A ACE
Posts: 2995
Joined: 01 Aug 2013, 06:13
Location: KCZL

Re: cruise setting found

Post by awash2002 »

I won't go above 12,000 feet in the Bonanza With just me in it and 24 pounds of bags with the IO-520 I get 175kts TAS at 8,000 feet
Image
Image
Image
Image

User avatar
AKar
A2A Master Mechanic
Posts: 5208
Joined: 26 May 2013, 05:03

Re: cruise setting found

Post by AKar »

One interesting aspect of rpm optimization is that of taking also the propeller into account. Propellers, like windmills, tend to operate best at around some specific advance ratio, usually very close to one in case of general aviation constant speed props. As a rule, higher the true airspeed, the higher the optimal rpm tends to be, which is also intuitively appealing. Thus, at high altitudes where true airspeeds at given power output are higher, the optimal way to achieve that power setting tends somewhat towards higher rpm.

-Esa

awash2002
A2A ACE
Posts: 2995
Joined: 01 Aug 2013, 06:13
Location: KCZL

Re: cruise setting found

Post by awash2002 »

So true Esa I'm currently at 7000 going from Lakeland FL to Hilton Head HXD from LAL 7000 feet 2400rpm 15.0gph 167TAS
Image
Image
Image
Image

User avatar
Scott - A2A
A2A General
Posts: 16839
Joined: 11 Feb 2004, 12:55
Location: USA
Contact:

Re: cruise setting found

Post by Scott - A2A »

Great point Esa and it makes physical sense when you think of it being both the blade pitch and the speed of the blade that determines the speed of the flow. These physics are present in our core Accu-Sim prop / engine physics.

Scott
A2A Simulations Inc.

User avatar
ClipperLuna
Technical Sergeant
Posts: 753
Joined: 23 May 2014, 12:50
Location: KPUW

Re: cruise setting found

Post by ClipperLuna »

AKar wrote: 11 Oct 2021, 03:41 One interesting aspect of rpm optimization is that of taking also the propeller into account. Propellers, like windmills, tend to operate best at around some specific advance ratio, usually very close to one in case of general aviation constant speed props. As a rule, higher the true airspeed, the higher the optimal rpm tends to be, which is also intuitively appealing. Thus, at high altitudes where true airspeeds at given power output are higher, the optimal way to achieve that power setting tends somewhat towards higher rpm.

-Esa
So, if we imagine an aircraft that is at a relatively high true airspeed, you would want the prop turning fast to get the higher advance ratio, right?. However, since engines tend to run more efficiently at lower RPMs, is it fair to say that getting the best overall efficiency for the whole aircraft means finding a kind of compromise prop setting, where the prop can still be as fast as we can get it, but the engine as slow as we can get it?

User avatar
Paughco
Senior Master Sergeant
Posts: 2095
Joined: 30 Nov 2014, 12:27

Re: cruise setting found

Post by Paughco »

Check this: http://www.tcmlink.com/pdf2/CSB09-11A.pdf

Continental Motors, Inc.(CMI) examined occurrences of crankshaft counterweight release and
subsequent engine stoppage in two, high time IO-520 and two, high time TSIO-520 engine
models. Investigation and reported service history led us to believe that these occurrences are
associated with engine operation at a sustained cruise engine RPM of less than 2300 RPM.
Engine model specifications, for many of the affected engines indicate power settings of less than
2300 RPM, are within the recommended cruise operating range. The reported population of
aircraft (equipped with the affected engine models that operate using an RPM less than 2300 RPM
for extended cruise operation) is limited. CMI will continue to evaluate any counterweight
releases reported to CMI in an attempt to establish a root cause, including any possible connection
with power settings.
II. Action Required
Effectively immediately, Continental Motors strongly
recommends the following action be observed for all affected
engine models:

Engine cruise RPM settings should be no lower than 2300 RPM
NOTE: This service document applies only to cruise operation and does
not supersede the aircraft manufacturer’s recommendations for other
operational modes such as emergency or holding procedures.
Engine models identified in the “Models Affected” section of this service bulletin with a history
of consistent cruise operation below 2300 RPM should contact CMI Customer Service at 1-888-
826-5465 or 1-251-436-8299 for further information and instructions

Seeya
ATB
Image

User avatar
AKar
A2A Master Mechanic
Posts: 5208
Joined: 26 May 2013, 05:03

Re: cruise setting found

Post by AKar »

ClipperLuna wrote: 11 Oct 2021, 18:48
AKar wrote: 11 Oct 2021, 03:41 One interesting aspect of rpm optimization is that of taking also the propeller into account. Propellers, like windmills, tend to operate best at around some specific advance ratio, usually very close to one in case of general aviation constant speed props. As a rule, higher the true airspeed, the higher the optimal rpm tends to be, which is also intuitively appealing. Thus, at high altitudes where true airspeeds at given power output are higher, the optimal way to achieve that power setting tends somewhat towards higher rpm.

-Esa
So, if we imagine an aircraft that is at a relatively high true airspeed, you would want the prop turning fast to get the higher advance ratio, right?. However, since engines tend to run more efficiently at lower RPMs, is it fair to say that getting the best overall efficiency for the whole aircraft means finding a kind of compromise prop setting, where the prop can still be as fast as we can get it, but the engine as slow as we can get it?
Yes, should the optimal propeller rpm be higher than the optimal engine rpm, the best combination would be somewhere in between. And of course, it is somewhat more complicated, as the prop's efficiency also depends on the blade angle at certain advance ratio (again, which makes sense). Even if we did have full charts for the propeller that we are using (usually we don't), we still would not have a direct indication of the blade angle at a given moment. The range of typical propeller efficiencies for advance ratios and blade angles 'achievable' by manipulating the engine and prop controls, I'd estimate against the graphs, range from around 75 % to 90 %, with little to be gained from fine tuning around the peak efficiency, but lots to be lost with grossly inappropriate settings.
Paughco wrote: 11 Oct 2021, 19:57 Check this: http://www.tcmlink.com/pdf2/CSB09-11A.pdf
Indeed, this SB has apparently created some controversy around the decade it has been pending followup. This is, again, something that intuitively makes sense, as the dynamic counterweights that are rocking around are tuned for certain rpm and torsional vibration combinations. Lycoming, the other manufacturer, also warns against, basically, exactly the opposite (high engine speed, low manifold pressure) in their standard print in probably every operator's manual. I have no doubts that some less-than-optimal dynamic forces can be caused by grossly misapplying engine and propeller controls, however, what exactly is the tuning point of the engine, and how far off can one safely remain for extended periods of time, I don't know nor have I seen any credible material of.

-Esa

awash2002
A2A ACE
Posts: 2995
Joined: 01 Aug 2013, 06:13
Location: KCZL

Re: cruise setting found

Post by awash2002 »

That's what I'm using is 65% power 2300rpm
Image
Image
Image
Image

new reply

Return to “Bonanza "V-Tail"”

Who is online

Users browsing this forum: No registered users and 4 guests