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  #11  
Old 08-26-2017, 11:08 AM
TXFlyGuy TXFlyGuy is offline
 
Join Date: May 2012
Location: Jazz Town, USA, TX
Posts: 270
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Quote:
Originally Posted by Dreamin9 View Post
Hi, OP here, I don't mind the hijack.

From what little I know, those issues listed become more a concern as the tip approaches the speed of sound.
Please accept my apology. Thank you for your reply to my question.

Last edited by TXFlyGuy : 08-26-2017 at 12:13 PM.
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  #12  
Old 08-26-2017, 01:06 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 2,139
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Carl,

Just a heads-up: As Sam and others said, you're limited to 2600 rpm with that prop, so you'll never see 75% at altitude. If your %'s are from your EFIS, it's lying to you (or more likely, computing based on being lied to). You can't make 75% power at the 8k' altitude ranges without turning *the full rated rpm of the engine* (2700rpm). Because the prop is *restricted by the mfgr* to 2600 rpm, you can't make 75% at that cruise altitude.

I'd suggest calling Van's & try to get them to tell you expected cruise performance *with your prop*, *at [x] altitude*, full throttle, leaned, at the rpm you're seeing. Include your MAP at that altitude; if you have any kind of intake restriction they'll be able to see the discrepancy from expected pressure at that altitude.

Charlie
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  #13  
Old 09-05-2017, 03:52 PM
lr172 lr172 is online now
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by TXFlyGuy View Post
Here is my question on props, and rpm...according to the Warp Drive calculator, the most efficient rpm for the prop in cruise is 475 mph tip speed. Above that, the prop loses aerodynamic efficiency, makes lots of noise, and you lose IAS.

True? False? Old wives tale?
I am not aware of a prop that will not deliver increasingly higher airspeed with an increasingly higher RPM, up to it's design limit. True, it may become less efficient beyond a certain RPM, but will not lose airspeed with increasing RPM, up to it's design speed.

Larry
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RV-6A / IO-320, Flying as of 8/2015
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  #14  
Old 09-11-2017, 06:23 PM
TXFlyGuy TXFlyGuy is offline
 
Join Date: May 2012
Location: Jazz Town, USA, TX
Posts: 270
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Quote:
Originally Posted by lr172 View Post
I am not aware of a prop that will not deliver increasingly higher airspeed with an increasingly higher RPM, up to it's design limit. True, it may become less efficient beyond a certain RPM, but will not lose airspeed with increasing RPM, up to it's design speed.

Larry
That certainly makes sense.
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  #15  
Old 09-13-2017, 02:27 PM
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smokyray smokyray is offline
 
Join Date: Jan 2005
Location: TX32
Posts: 1,613
Default Prop me up!

Quote:
Originally Posted by Dreamin9 View Post
Here's some numbers from a recent test flight, I'd like to find more speed in the 6.5 to 12.5 altitude range. Considerations are re-pitch or new prop or burn gas.

RV-9A, O-320 160hp, 405hrs
Prop Sensenich metal 70/79 (actually 69.5 after repair from nose collapse/flip at 13 hrs)
Power set to 75% after initial climb for CHT cooling, leaned to peak, AS in knots, static +/- 2200
This engine runs smoothly LOP; FF/RPM/speed/CHT's drop off quickly LOP.

ALT DALT RPM MAP %pwr FF TAS

Rotation 750 2140 2275 29.4 93 12.5 72

Level@ 1800 3100 2380 25.1 78 12 138

Level@ 6500 7800 2470 23.4 76 8.4 144

Level@ 8500 9815 2510 22.5 70 7.5 147

Level@ 10500 11840 2480 20.9 67 7.1 148

Thanks,



Carl
Carl,
I've never been a fan of the Sensy FP metal props for the 0-320. Why? Having tested nine different props on my RV4 over a 10 year period it was the worst of the lot. I kept the results in a log I shared with the prop makers afterward.
As Sam pointed out, it's heavy metal, 2600 RPM restriction and not revving up enough to give you rated HP(0-320 is rated 150HP@2700) poor takeoff performance and aerobatics not recommended by MFR. Three major strikes for me, I'm out. Van's used to post a MP/RPM formula that roughly translates %power. Take the 1st 2 numbers of RPM and MP and add them. 48 is roughly 75%. That said, a prop turning 2700 with 20"MP (WOT) at 11,500 is around 65% power. You're not hurting the engine running higher RPM at higher altitudes.

Test Results: My 0-320 RV4 with single Electroair EIGN/1Mag and a Carb: WOT at 11,500' leaned out.

1. Ed Sterba Wood 69X69 2850 at 168 KTAS and 8GPH.
2. Catto props 69/69 2900 165KTAS 8GPH
3. Gary Hertzler Silver Bullet. 170KTAS 2600 7GPH
4. Sensy Metal 70CM/77 160KTAS 2500 8GPH
5. Bernie Warnke 69/70 167KTAS 2550 7GPH
6. Margie Warnke 70/69 169KTAS
7. Catto 3 blade 165KTAS at 3000 RPM 8.6GPH (great takeoff and climb)
8. MT Fixed Pitch 69/69 167KTAS at 2650 8GPH
9. Catto Gen-3 2 Blade 70/72 (RVX 180HP) 170KTAS at 2600 8.8GPH

My favorites were (in order) the Silver Bullet, Catto Gen 3 and the Sterba. The Sterba wins the economy award for best bang for buck. Great value.
If it were me I would sell the Sensy metal online and install a woodie or composite or get it re-pitched so it will turn 2600 at 11K.

My Dos Centavos...
V/R
Smokey

PS: Last year I delivered a 0-320 9A with a Catto 2 blade from OR to TX at 11,500'. 2800 WOT at 7.5 GPH 165KTAS.
Performed very well at lower altitudes, good STOL.

Last edited by smokyray : 09-13-2017 at 02:34 PM.
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