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  #21  
Old 11-11-2011, 02:27 PM
steve91t steve91t is offline
 
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I'll definitely force my dad to run out to the airport on a calm afternoon and go fly to try out the box pattern idea at 8000 ft

I still don't think that's it. The ETA would always be way off if he had bad readings. Either that, or the GPS would show a tail wind all the time.

The builder of the plane thinks it's probably the prop. He said when he would take off in formation, he would leave them in the dust in the take off and climb, but then once in cruise, they would walk away from him.

Does MT sound right? Composite 3 bladed prop out of Florida?

Maybe the design of the prop is designed for climb performance. But at the same time, RPM is RPM, and I can't imagine there's "that" much of a difference.
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  #22  
Old 11-11-2011, 02:34 PM
gereed75 gereed75 is offline
 
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Default Don't have my charts or numbers in front of me

But my gut is saying that 8.5 indicates your running either LOP or less than WOT at that Alt. In my 180 hp 6, WOT at 8000' at 2450 I would be seeing more like 10.5 gph and 165 KTAS+.

He is running either less than WOT or LOP.

Finley, don't you have that opposite - Best power (150 ROP) at 112 hp and 62% with Economy (LOP) 90 hp and 50%????

At anyrate, 8000' and 8.5 gph at 150 KTAS or so looks about right. Does'nt much matter how you are burning it (ROP or LOP). Horsepower and thus speed will be relative to fuel burn. Firewall it ROP and you will see that 165 KTAS at least, but at 10 - 10.5 gph.
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Last edited by gereed75 : 11-11-2011 at 02:41 PM.
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  #23  
Old 11-11-2011, 02:39 PM
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DanH DanH is online now
 
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Quote:
Originally Posted by steve91t View Post
I'll definitely force my dad to run out to the airport on a calm afternoon and go fly to try out the box pattern idea at 8000 ft
It's a bit more than an idea. Go here for the tools:

http://www.kilohotel.com/rv8/phplink...e093cf6eedfb88

I suspect a whole lot of folks will not take your issue seriously until you calibrate.

BTW, the winds need not be calm. You do need to hold an accurate altitude and heading, so best to do it before the thermals crank up.
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Last edited by DanH : 11-11-2011 at 02:42 PM.
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  #24  
Old 11-11-2011, 02:46 PM
Finley Atherton Finley Atherton is offline
 
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Quote:
Originally Posted by gereed75 View Post
Finley, don't you have that opposite - Best power (150 ROP) at 112 hp and 62% with Economy (LOP) 90 hp and 50%????
Remember my figures are for the SAME rpm and FF. At Best Economy settings you are getting better fuel efficiency so the same amount of fuel produces more power. Have a look at Lycoming's Part Throttle Fuel Consumption graph.

Fin
9A
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  #25  
Old 11-11-2011, 02:56 PM
Finley Atherton Finley Atherton is offline
 
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Quote:
Originally Posted by gereed75 View Post
Does'nt much matter how you are burning it (ROP or LOP). Horsepower and thus speed will be relative to fuel burn.
I think it does matter. Horsepower will be relative to fuel burn (FF) and how efficiently that burn is happening. The fuel will burn more efficiently and produce more power at Peak or LOP than at richer mixture settings.

Fin
9A
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  #26  
Old 11-11-2011, 02:57 PM
gereed75 gereed75 is offline
 
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Default Thanks Fin

thats interesting, and confirms the definitive answer to a question I've always had - Will you get better range burning the same gph at best power and less throttle or best efficiency (LOP) and WOT??

Sounds like LOP/WOT by far. 22 More horsepower on same fuel according to the chart! Suspected it was true (Best efficiency at close to ideal A/F ratio - duh) but did'nt think it would be that much.

Thanks again Fin.
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Last edited by gereed75 : 11-11-2011 at 03:06 PM.
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  #27  
Old 11-11-2011, 03:22 PM
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Mike S Mike S is offline
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If my poor old brain is firing on all cylinders, I seem to remember that in WW2, Lindbergh proved that the best range was obtained by running the engine slowly, with WOT, and leaned out as far as possible.
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  #28  
Old 11-11-2011, 03:23 PM
Finley Atherton Finley Atherton is offline
 
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Quote:
Originally Posted by steve91t View Post
I was incorrect in my first post. He actually runs it at 2450 revs. I know he runs it just rich of peak. Not sure exactly how much, but I know he said it's why Lycoming recommends.
So to be clear he is running at 2,450 rpm and 8.5 g/h? If so this would be about 118 hp at Best Economy or about 92 hp at Best power (150 ROP).
Any setting richer than peak will reduce the hp for the same FF (assumes constant rpm). Lets say he was running 50 degrees ROP. I am not sure if the relationship is linear but if we interpolate the above figures then 50 degrees ROP would give about 109 hp which is 9 hp less that that possible at Peak or LOP and could explain some of the slower speed.

Fin
9A

Last edited by Finley Atherton : 11-11-2011 at 03:27 PM.
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  #29  
Old 11-11-2011, 03:35 PM
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RV10inOz RV10inOz is offline
 
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That is true! Just for the record, best economy is usually Round 20-40lop and for a combination of economy and a bit more speed from 10-20lop. Best power is more like 75ROP, and at 8000 feet that is ok, but do not do WOT/2700/75ROP at 1500 feet for very long. It will clean out your heads nicely but if you do it all the time .

Kevin Hortons GPS box is critical. Static Port errors are amazing

I have been test flying Jamie Lee's RV7 lately and it generally does 155 with its cruise Catto 3 blade. I doubt that you will get near the fastest of the 2 bladers but that is the trade off.

Mt opinion for what it is worth, 3 blade props are a waste of money unless you have 310 HP or more to play with. You can argue all you like about this and that, but at the end of the day, facts are what they are. They are slower, and a fixed three blader that is pitched for cruise is not that lively off the deck as you only generate 150 HP out of your 180 HP engine.

I know an RV6 down here with a 160hp & fixed 2 blade, it runs rings around the 3 blade, well almost, but it is quicker and no slower off the deck on a smaller engine

PS: for csu planes, unless you are really needing to pull the throttle, it stays WOT all the time. You would not fly around with a filter full of dirt would you? Think about hat for a bit!

Last edited by RV10inOz : 11-11-2011 at 03:38 PM.
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  #30  
Old 11-11-2011, 03:42 PM
gereed75 gereed75 is offline
 
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Default Yep

Yep yep yep, agree Fin and Dave.

The OP's numbers and comments would still indicate he is at something less than max power (either via less than WOT or less FF than Best Power or some combo of both) and the TAS is in line with some less than max power condition.

You want 165+ KTAS?? - make more power!!

Mike, My work with trying to determine a best practical range showed that lower RPM helped. What exact RPM is optimal will have much to do with other factors (altitudes, props, chosen airspeed etc). I ran lots of runs and found down as low as 1800 RPM, WOT, LOP generated some incredible range numbers if you could stand the slow speeds (and had favorable winds). I like the 1.3 Vy speed at low RPM, WOT, LOP if I was in extremis - lost over open ocean or trying to get out past zero/zero weather to a far away alternate (with an adjustment for wind).

Fin, What do the charts say relative to RPM and efficiency??
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Last edited by gereed75 : 11-11-2011 at 03:50 PM.
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