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  #1  
Unread 09-04-2007, 12:53 PM
jtreed jtreed is offline
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Default What kind of performance #'s are YOU seeing?

You know what Power Flow's performance numbers are, so now that you have our system, what benefits have YOU noticed?
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  #2  
Unread 10-22-2007, 03:09 PM
Morten Morten is offline
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Exclamation M20F Performance Data Coming Soon

I am currently installing a PowerFlow exhaust system in my 1970 M20F; stay tuned for a before/after performance report by this time next month. Captured data will include climb performance as well as cruise at 8,500, 11,500 and 14,500 feet. M
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  #3  
Unread 11-22-2007, 07:17 PM
Morten Morten is offline
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Smile M20F Performance Data

Okay folks, here are the results of my before/after tests.

CAVEAT: Test run with PowerFlow installed had some minor advantages which may have influenced the test results: Air temperatures were lower (about 5 degrees C at altitude), gross weight slightly less (2220 vs. 2300 lbs) and airplane had been recently washed (it was somewhat dirty when I did the pre-PowerFlow test run).

1. TIME TO CLIMB: Climb from 1,000 to 14,000 MSL took 25:40 before and 21:15 after, an improvement of 4 minutes 25 seconds or 17%.

2. RATE OF CLIMB: Average rate-of-climb from 1,000 to 14,000 MSL improved from 506 fpm to 611 fpm, an improvement of 105 fpm. ROC at 1,000 MSL improved from 750 to 1090 fpm while ROC at 14,000 improved from 340 to 390 fpm.

3. CRUISE:
  • Cruise speed at 8,500 MSL increased from 146 KTAS to 151 KTAS, an increase of 5 knots.
  • Cruise speed at 11,500 MSL increased from 142 KTAS to 148 KTAS, an increase of 6 knots.
  • Cruise speed at 14,500 MSL increased from 138 KTAS to 142 KTAS, an increase of 4 knots.
EDIT 2008-2-1: My findings as originally posted here indicated lower fuel burns. I have since figured out that some recalibration of my fuel flow instrument was necessary after the PowerFlow installation. It now appears the fuel burn after the PowerFlow installation is similar to before. I will post additional information if and when I am able to accumulate meaningful fuel data.

4. RANGE: The improved climb and cruise results in a range increase; I calculated that my VFR zero-wind range at 11,500 MSL increased from 900 NM to 940 NM.

5. CONCLUSION: The PowerFlow system works as advertised! I won't be sending mine back.

Fine Print: 1970 M20F. Climbs performed at full throttle, 2560 rpm, Ram Air above 4,500 MSL. Prop governor was adjusted to give full rated 2700 rpm at time of PF system installation, but test run with PF was done at 2560 for consistency. All cruise numbers at 2500 rpm leaned for best power. Post-PF test-run benefitted from K&N Challenger air filter under 4,500 MSL. Shop charged 7.3 hours for installation but advised they used significantly more time to troubleshoot problem; turned out one of the pipes was the wrong size and had to be cut. Mechanic advises PF adds about $300 to cost of each annual as it must be removed and inspected, which eats up bulk of any fuel savings.

Last edited by Morten; 02-01-2008 at 04:52 PM.
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  #4  
Unread 01-08-2008, 12:15 PM
wsinsel wsinsel is offline
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Default Speed

I own a powerflow and would not choose to be without it but I cannot see how it would possibly increase speed. The prop moves the same amount of air at the same RPM as it did before the system was installed, propelling the aircraft a specific distance for each revolution of the prop. Unless the pitch or the RPM is increased the speed could not possibly be changed. Any change in speed would have to be a result of less drag, more RPM, or an increase in pitch. Please explain this phenomenon for me. Rate of climb is better. The fuel usage is different as is takeoff roll. Time spent in a climb is less, shortening the overall time by a few minutes but I cannot see how it is possible to increase the speed.
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  #5  
Unread 01-08-2008, 03:07 PM
dtilman dtilman is offline
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Default How can I go faster at the same RPM?

In response to wsinsel's post:

On aircraft with a constant speed propeller (such as a Mooney) the engine generates a certain amount of torque. The constant speed mechanism tries to keep the engine/propeller at the same RPM, and it does this by changing the blade pitch. If more power and therefore torque is being developed (like when you open the throttle/increase manifold pressure) the governor drives the propeller to a higher pitch to keep the RPM the same. If you had a fixed pitch propeller, the engine would respond by simply making higher or more RPM.

So you are correct, that a pitch change has to be occuring on a constant speed aircraft. We don't have a way to measure blade pitch in flight, but when the airspeed is higher for the same given manifold pressure, RPM and fuel flow as with the standard exhaust, physics tells us that must be because of the blade pitch changing.

It is for this same reason that your rate of climb is higher, assuming that you are climbing with the same power settings and airspeeds as before the PFS was installed. The blades are going to a higher pitch/taking a bigger bite out of the air.

It is normal to see a slightly higher fuel flow than before on takeoff, climb and lower altitude max cruise in a constant speed aircraft. This is because the engine is developing more power than before and it may need a small amount of additional fuel to do this.

I hope this answers your question - but if not, lets talk about it some more.
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  #6  
Unread 01-11-2008, 03:43 PM
wsinsel wsinsel is offline
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Default Fixed pitch

I understand the physics involved in constant speed propellers. I have been a mechanic for many years. Thanks anyway. I still contend that the claims of more speed from fixed pitch users are unsubstantiated, unless they change the prop or simply overspeed the engine. I see these claims all the time with no mention of changing the prop. I like the system you sell but I'd rather see truthful accounts than "wish accounts".
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  #7  
Unread 01-11-2008, 05:15 PM
dtilman dtilman is offline
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Default Speed improvements for fixed pitch props

wsinsel wrote:
I still contend that the claims of more speed from fixed pitch users are unsubstantiated, unless they change the prop or simply overspeed the engine. I see these claims all the time with no mention of changing the prop. I like the system you sell but I'd rather see truthful accounts than "wish accounts".
Fixed pitch propeller aircraft will have the ability to generate more RPM at full throttle with a Power Flow Exhaust than they did with the standard stock exhaust. The average C172 sees about 75 more RPM, but the range we state is 30-130.

You are correct, the only way you can go at a faster airspeed, without changing the physical pitch of the propeller is to turn higher RPM. In general, every 100 RPM gain in RPM is worth 5 knots additional airspeed.

If someone tells me they are going 7 knots faster at the same RPM and they have a fixed pitch propeller, they have done something wrong or more things have changed than was stated. It isn't possible.

What it turns out a lot of people are referring to is the fact that when they push the throttle to wide open, they wind up going faster with the PFS installed than they used to at that altitude with the old stock exhaust... This would be correct.

Keep in mind that many models of fixed pitch aircraft don't "overspeed" in level flight above 3000 feet. Some aircraft can only develop 2600 RPM with their stock exhaust and a mid-range pitch propeller. They have until 2700 RPM before they are overspeeding.

I try to make sure that people with fixed pitch propellers understand that they can get a speed improvement, but only if they open the throttle up and go faster.

Thanks for your feedback.
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  #8  
Unread 01-11-2008, 05:35 PM
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tstrohmayer tstrohmayer is offline
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Default

I think Darren may have been confused about your post since it is in the Mooney subforum and he might have assumed you were talking about constant speed props.

You're original post stated that a speed increase with a fixed pitch prop is impossible without an RPM increase or a pitch change. We agree with this statement. But there are many substantiated claims of speed increases with fixed pitch props.

Many aircraft cannot maintain redline RPM all the way to higher cruise altitudes. For example: Our Cessna 172N would go 100KIAS at 8500' turning 2560RPM with the stock exhaust system. This was the maximum RPM the engine would turn at that altitude. With the PFS exhaust, the engine was able to turn 2640RPM and the aircraft would go 107KIAS.

That is a truthful account and a perfect example on how a fixed pitch airplane can fly faster with a Power Flow Exhaust. But don't believe me, here are links to customer comments:

http://powerflowsystems.com/forum/showthread.php?t=7

http://powerflowsystems.com/forum/showthread.php?t=38

http://powerflowsystems.com/forum/showthread.php?t=34

I'm sure each of these individuals would be happy to share their experiences if you would like to hear it directly from them.

Best Regards,
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Last edited by tstrohmayer; 01-11-2008 at 05:42 PM.
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  #9  
Unread 01-11-2008, 09:30 PM
wsinsel wsinsel is offline
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Default Fixed pitch

I agree totally that a fixed pitch with Powerflow might MAINTAIN a higher RPM than with a stock exhaust. This was certainly the case with the ac we installed your system on. It not only oversped the engine and required us to change to a 60 pitch from a 58 pitch, it also would maintain rated RPM for most of the climb to near it's service ceiling. It DID cruise faster in level flight because it had a change in pitch. (new prop) It also had 4 new Lycoming nitride factory cylinders so it truly did have more torque as well.
I agree that you have a truly superior system and the best part of it all is that we did not ever have to deal with the broken baffles, cracked pipes and leaky welds that the old factory system presented to us at every annual. The Powerflow was trouble free for us and was far, far superior to the old troublesome factory system. My point here is most of the customers report faster speeds and I think they tend to mislead, even if unintentionally, folks who are shopping for your system. Or perhaps they just do not understand the physics involved. I wish you would help to clarify this on your website. I am considering putting the system on the Mooney and I am glad to see you are working to overcome the problem with the cabin heater. I worry constantly about the factory system poisoning us in flight and I really keep an eye on it. I think this would be far less likely with the Powerflow system.

I appreciate your time spent here with me.

Willie Sinsel
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  #10  
Unread 01-14-2008, 10:38 AM
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tstrohmayer tstrohmayer is offline
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Default

We definitely understand your concerns. Our sales staff does its best to make it clear to customers with fixed pitch aircraft that there are no free rides when it comes to cruise speed. Our main website does contain some information regarding this:
http://www.powerflowsystems.com/faqs.php#q7

General Aviation is full of myths and old wives tales, we certainly do not want to have a hand in propagating any additional ones. We'll see what we can do about adding some threads to this forum to directly address this.

It sounds like you had great success in your application and we hope that you do consider the system for your Mooney, you won't be disappointed.
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