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  #21  
Old 10-29-2017, 09:37 AM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by David Paule View Post
I use a very simple equation for any normally-aspirated engine:

% Power = (MP / 29.92) * (RPM / Max RPM).

It seems to get close enough, for me anyway, and is independent of compression ratio and leanness. This puts your final point at 64% power instead of the 71% power mentioned.

Dave
AFR, exhaust back pressure (related to altitude), ignition timing and IAT also affect hp to a significant degree.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW- 416.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #22  
Old 10-29-2017, 09:45 AM
David Paule David Paule is offline
 
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Originally Posted by rv6ejguy View Post
AFR, exhaust back pressure (related to altitude), ignition timing and IAT also affect hp to a significant degree.
Wouldn't anything that affects horsepower also affect manifold pressure and rpm on a normally-aspirated engine? That suggests that the overall power will be affected, but not the percent power.

Example - leaning: as I lean the mixture, the power goes up, and then it drops. Fuel flow changes and so does airspeed. Since the engine can only make a certain amount of maximum horsepower, the percent power is changing along with the fuel consumption and airspeed.

Dave
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  #23  
Old 10-29-2017, 01:04 PM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by David Paule View Post
Wouldn't anything that affects horsepower also affect manifold pressure and rpm on a normally-aspirated engine? That suggests that the overall power will be affected, but not the percent power.

Example - leaning: as I lean the mixture, the power goes up, and then it drops. Fuel flow changes and so does airspeed. Since the engine can only make a certain amount of maximum horsepower, the percent power is changing along with the fuel consumption and airspeed.

Dave
If we say X engine puts out 180hp at 29.92 inches and 15C IAT at SL, with all other significant factors (many more than MAP and RPM) taken into account, we may call that 100% power. Actual hp varies with these multiple parameters and can also be expressed as a percentage. Overall (actual) power and % of our nominal maximum are therefore really the same thing. 90hp and 50% power for example in this case.

On leaning, it depends where you start from- richer than about 12.5 AFR and yes, you'd will gain power as you approach 12.5 and then start losing power leaner than that.

With a C/S prop, rpm changes are masked since the governor tries to maintain the set rpm by changing blade pitch. AT WOT assuming minimal restriction across the throttle plate and throat, there would be little resultant change in MAP since MAP should be close to the same whether the engine is running or not.

MAP does not change significantly with IAT, nor exhaust back pressure either.

I agree, fuel flow, hp and TAS are affected by leaning.

There are so many factors that influence HP and therefore % of power, that's it's virtually impossible to calculate % of power at altitude accurately without significant testing of that particular engine in an altitude dyno cell. Some of the factors are quite interrelated, such as ignition timing and AFR.

I wouldn't attempt to split hairs by 1-2% based on a simple formula which doesn't account for all influences. Your formula would get you in the ballpark however.

I would do all flight testing at WOT to minimize pumping loss effects in the data. The same goes for rpm and AFR.

In the end, the aircraft does what it does for TAS vs. FF at a given altitude and power level. That's really what matters and really your "dyno".

I'm a big fan of the F-4 Raider concept BTW but you really need a turbo on there to get back the knots lost with 2 less cylinders. No reason why a good 360 turbo can't exceed atmo 540 numbers above 10,000 feet or a little lower running a bit of boost. The price delta is significant these days and the lighter weight is also a big plus to get back some of the climb performance. If you're going to have a Rocket of sorts, make it one in performance too which is the main reason people want Rockets rather than RV8s IMO.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW- 416.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm



Last edited by rv6ejguy : 10-29-2017 at 01:13 PM.
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  #24  
Old 10-29-2017, 01:13 PM
David Paule David Paule is offline
 
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Ross, nice discussion, thanks.

Dave
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  #25  
Old 10-29-2017, 02:52 PM
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Toobuilder Toobuilder is offline
 
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The performance of a 540 Rocket has significant appeal no doubt, but the ergonomics of the Rocket are also compelling when compared to the RV-8. I'd bet this fact alone will drag some potential RV-8 people over to the dark side.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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RV-8 - Flying
1940 Taylorcraft BL-65 -flying
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  #26  
Old 10-29-2017, 05:20 PM
Robertcropdust Robertcropdust is offline
 
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Default Rocket

Hey guys can someone tell me if I can list a rocket airframe in the main classified page? I donít want to upset anyone but didnít know who to ask.
Iím currently flying a 200hp fast back rv8 that is a blast to fly. I had a hr2 290hp before the 8 and put close to 500hrs on it. I was figuring out my fuel exspenses for 2016 a few months back and they are very close within 2%. The insurance was 600.00 more on the rocket for the year. I think the F4 will be a very popular option and will have many advantages over the rv8.
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  #27  
Old 10-29-2017, 09:10 PM
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Mike S Mike S is offline
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Quote:
Originally Posted by Robertcropdust View Post
Hey guys can someone tell me if I can list a rocket airframe in the main classified page? I donít want to upset anyone but didnít know who to ask.
Far as I am concerned it is fine-----been done before without any issues.
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  #28  
Old 10-30-2017, 12:17 AM
Gt-401 Gt-401 is online now
 
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Default Turbo rocket!

"I'm a big fan of the F-4 Raider concept BTW but you really need a turbo on there to get back the knots lost with 2 less cylinders. No reason why a good 360 turbo can't exceed atmo 540 numbers above 10,000 feet or a little lower running a bit of boost. The price delta is significant these days and the lighter weight is also a big plus to get back some of the climb performance. If you're going to have a Rocket of sorts, make it one in performance too which is the main reason people want Rockets rather than RV8s IMO."


That sounds very interesting, but I'm afraid I know just enough about turbo installations to know that I don't know nearly enough to do it right. It sounds like maybe you, RV6ejguy, have done a couple, and might know what it would take to do it right, how would you setup A turbo 360 in a rocket? Would you use twin turbos? Would you use intercoolers? Automatic wastegates? Or would the simple approach be the right one, one turbo, no waste gate, no intercooler.
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  #29  
Old 10-30-2017, 07:44 AM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by Gt-401 View Post
"I'm a big fan of the F-4 Raider concept BTW but you really need a turbo on there to get back the knots lost with 2 less cylinders. No reason why a good 360 turbo can't exceed atmo 540 numbers above 10,000 feet or a little lower running a bit of boost. The price delta is significant these days and the lighter weight is also a big plus to get back some of the climb performance. If you're going to have a Rocket of sorts, make it one in performance too which is the main reason people want Rockets rather than RV8s IMO."


That sounds very interesting, but I'm afraid I know just enough about turbo installations to know that I don't know nearly enough to do it right. It sounds like maybe you, RV6ejguy, have done a couple, and might know what it would take to do it right, how would you setup A turbo 360 in a rocket? Would you use twin turbos? Would you use intercoolers? Automatic wastegates? Or would the simple approach be the right one, one turbo, no waste gate, no intercooler.
You have lots of space behind the engine so I'd be tempted to use one turbo mounted up high to avoid an oil scavenge pump. Would certainly use an intercooler and automatic wastegate- all automotive type stuff, not archaic, clunky aviation hardware.

You could do a nice installation with all that cowling space.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW- 416.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #30  
Old 10-30-2017, 09:38 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by David Paule View Post
Wouldn't anything that affects horsepower also affect manifold pressure and rpm on a normally-aspirated engine? That suggests that the overall power will be affected, but not the percent power.

Example - leaning: as I lean the mixture, the power goes up, and then it drops. Fuel flow changes and so does airspeed. Since the engine can only make a certain amount of maximum horsepower, the percent power is changing along with the fuel consumption and airspeed.

Dave

Consider the real world example of ignition influence I found when testing CPI - I get to my cruise altitude, power (WOT) and RPM setting. I'll go LOP and the airspeed sags (as expected). This would normally be your "calculated" % power setting (MP, RPM, FF) on the EFIS. However, when I flip the LOP switch for another few degrees of advance, the TAS creeps back up a few knots, yet there is no change in any of the aforementioned parameters.

Eking out a few more knots after you hit the drag wall is a noteworthy change in power - yet it wont show up in a EFIS algorithm. As Ross indicates, the best dyno is the one you fly.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
PA-20-inspired "family truckster" -in work
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