J

jayres

Member
Can anyone out there tell me what the % power vs. rpm is for an O360-180hp, fixed pitch (72x85) for an RV7A? I would like to check my speeds against Van's spec's but I don't know where 75% & 55% power settings are. I have no MAP indication.
 
jayres said:
Can anyone out there tell me what the % power vs. rpm is for an O360-180hp, fixed pitch (72x85) for an RV7A? I would like to check my speeds against Van's spec's but I don't know where 75% & 55% power settings are. I have no MAP indication.
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It is tough to do using all the inputs of RPM, MAP, temperature and altitude. With all that stuff you still need a computer or very complicated chart. I think all you will be able to do is make a very rough guess or maybe get in a situation where you are full throttle and derive a likely manifold pressure by calculation and comparison to other similar airplanes.
 
jayres said:
Can anyone out there tell me what the % power vs. rpm is for an O360-180hp, fixed pitch (72x85) for an RV7A? I would like to check my speeds against Van's spec's but I don't know where 75% & 55% power settings are. I have no MAP indication.
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75% is easy. Climb to 8500' and let it roll at wide open throttle. It is close enough for the comparison and government work.

55% @ WOT is about 15,500'.

The only other practical way I know to get these performance numbers is to use fuel flow. It takes fuel to make horse power.
 
jayres said:
Can anyone out there tell me what the % power vs. rpm is for an O360-180hp, fixed pitch (72x85) for an RV7A? I would like to check my speeds against Van's spec's but I don't know where 75% & 55% power settings are. I have no MAP indication.
Click to expand...

I've been told that straight & level full power RPM - 10% = 75% power setting.

Also, here is a fairly accurate formula for calculating speed.
RPM X Pitch X .000947 = MPH
 
David-aviator said:
75% is easy. Climb to 8500' and let it roll at wide open throttle. It is close enough for the comparison and government work.
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I tried this tonight and it works pretty well! The ride down was fun too! It's always fun to play with VNE. :eek:
 
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Geico266 said:
I've been told that straight & level full power RPM - 10% = 75% power setting.

Also, here is a fairly accurate formula for calculating speed.
RPM X Pitch X .000947 = MPH
Click to expand...

...a Grumman Tiger (O-360, FP prop) chart someone sent me.

If your RV-7 is pitched so that 2700 rpm at 8000 ft DA is full throttle - which is the recommended "standard", and Lycomings 75% power point - then these numbers should be pretty close.

As mentioned above - use DA for Alt.

Alt -------- 65% ------- 75%

2000 ------ 2425 ------ 2550
4000 ------ 2450 ------ 2600
6000 ------ 2510 ------ 2645
8000 ------ 2565 ------ 2710
10000 ----- 2610
12000 ----- 2700

The numbers were extracted by Excel, so I rounded to the nearest 5 rpm... still should be to the level of accuracy you need...:)

Sorry, the table did not have the 55% curve in it...:(
 
Thank you guys for the wealth of information you have provided. Please forgive my rustiness but if my field elevation is 500' and the DA is 1500', does that mean that I need to climb to 9000' agl to reach 8000' DA?
 
Rough calculation...

jayres said:
Thank you guys for the wealth of information you have provided. Please forgive my rustiness but if my field elevation is 500' and the DA is 1500', does that mean that I need to climb to 9000' agl to reach 8000' DA?
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...says climb to 7000 ft. for the case you mention.

Think of the DA difference as a constant offset as a very rough calulation....

Using the calculator is best though....:)
 
Found a good chart

This thread got me thinking about configuring the Horsepower Calculation page on my engine monitor (MVP-50). The Lycoming power chart that I have is a real eye test and tough to use, so I googled Lycoming Power Chart. Right at the top was a link to a chart that Larry Pardue put together for an O-360. Here's the link to it: http://n5lp.net/Power.htm

The only problem with this chart is that it only goes up to 80% power.
 
Rick_A said:
...The only problem with this chart is that it only goes up to 80% power.
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My chart was developed for my use with a fixed pitch climb prop used at high altitudes but it was developed with the use of one of Kevin Horton's power spreadsheets. I think many people should find these very useful as it is much easier to just punch the numbers in your computer than to deal with Lycoming's charts. You could also use his spreadsheet to develop your own chart.

Kevin's page is at http://go.phpwebhosting.com/~khorton/rv8/

Look down the left hand side for "Top Links."
 
Van's numbers

Based on the excellent info from you guys, I think I know how to figure my 75% pwr speed. Now I have another question: Van's performance spec's for the RV7-180hp-c/s are; 210 mph top speed, and 200mph 75% @ 8000'. So if full throttle at 8000' yields 75% power, what is Van's top speed based on?
 
jayres said:
... So if full throttle at 8000' yields 75% power, what is Van's top speed based on?
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Top speed in a normally aspirated airplane would normally be found at sea level at full power.
 
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Based on the excellent information given, I have another question:
Van's performance specs for RV7-180hp says: 200 mph @ 75% @ 8000' c/s. If 75% pwr is full throttle at 8000', what is Van's top speed of 210 mph based on?
 
jayres said:
Based on the excellent information given, I have another question:
Van's performance specs for RV7-180hp says: 200 mph @ 75% @ 8000' c/s. If 75% pwr is full throttle at 8000', what is Van's top speed of 210 mph based on?
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Full throttle at sea level at standard temperature. I.E 100% power.
 
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