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  #1  
Old 11-12-2020, 06:07 AM
n700jl n700jl is offline
 
Join Date: Jan 2005
Location: McCordsville IN
Posts: 286
Cool Join the Fastest TAS Club

Hello RV Friends! Many years ago i brought you the Join the 200kt Club. Many of our fellow RV pilots joined the club and showed us just how incredible these airplanes are. They also show us some fantastic airmanship by selecting the perfect altitude for getting the 200kts GS. Now lets up the game. I want to see and I know that you do to, those TAS numbers straight and level! Bring those power levels all the way forward(just keep it under VNE)! Have fun be safe and show us what you have. This should be fun, plus this is very informative.
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RV-6 Flying IO-320X tip up 500+hrs G3X 2004 Oshkosh Outstanding workmanship award, 2004 Sun N Fun Best Workmanship 2006 Sun N Fun Outstanding Aircraft
RV-10 Flying IO-540-C4B5X 500+hrs G3X 2011 Bronze Lindy Award Winner
"Negative Ghostrider the pattern is full"
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  #2  
Old 11-12-2020, 09:03 AM
Dugaru's Avatar
Dugaru Dugaru is offline
 
Join Date: Jan 2016
Location: Richmond VA, USA
Posts: 494
Default Calcluating TAS

Should be fun.

I think I'll need to use the GPS method for calculating this, rather than just reading it off the EFIS. My builder put temperature probes in the NACA vents, and they appear to read much higher than real OAT, which (if I remember correctly) goes into the EFIS's TAS calculation.
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2021 Dues Paid
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  #3  
Old 11-12-2020, 09:35 AM
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rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
Posts: 3,544
Default difference is small, I think

Quote:
Originally Posted by Dugaru View Post
Should be fun.

I think I'll need to use the GPS method for calculating this, rather than just reading it off the EFIS. My builder put temperature probes in the NACA vents, and they appear to read much higher than real OAT, which (if I remember correctly) goes into the EFIS's TAS calculation.
if the online calculators are to be believed, it seems like 5c of temperature difference shows a couple of knots higher/lower. Do you feel OAT at the wingtip and OAT in the NACA will be more than 5c of difference?
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  #4  
Old 11-12-2020, 10:04 AM
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MacCool MacCool is offline
 
Join Date: Aug 2020
Location: central Minnesota
Posts: 340
Default

I would think that the venturi effect of a NACA duct would make temperature readings there unreliable, although I'd expect them to be lower than OAT.
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  #5  
Old 11-12-2020, 10:22 AM
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Tandem46 Tandem46 is offline
 
Join Date: Jan 2005
Location: CO
Posts: 651
Default

183KTAS straight and level.
2003 RV-7
IO-360 w/ one mag, one LSE
WW 200RV CS prop
Can’t seem to get a single knot more out of her.
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  #6  
Old 11-12-2020, 10:39 AM
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rv8ch rv8ch is offline
 
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Location: LSGY
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Default

Quote:
Originally Posted by MacCool View Post
I would think that the venturi effect of a NACA duct would make temperature readings there unreliable, although I'd expect them to be lower than OAT.
I think the assumption is that engine heat might affect the OAT measurement. I have not done any comparison so I not sure if this is correct or not, but I'm sure someone here has done this. I can't imagine it being more than 5-10c, which seems to translate into a few kts of TAS difference.
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  #7  
Old 11-12-2020, 10:50 AM
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airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,312
Default

It's not hard - down low I can hit Vne with my airplane, of course I'm running the 360 and a constant speed. I've only done that twice, once during testing and once afterward, I generally don't fly low.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2021 dues paid
N16GN flying 750 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, IFD440
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #8  
Old 11-12-2020, 11:06 AM
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Dugaru Dugaru is offline
 
Join Date: Jan 2016
Location: Richmond VA, USA
Posts: 494
Default temp probes in the wrong spot

The other day my EFIS said the OAT was 64F, and it couldn't have been over 35F out there. Probably lower. That's the biggest difference I've seen, but it's not atypical.

I think the effect is due to warmth from the engine. And there's probably not a huge countervailing venturi cooling effect, especially in the winter, because I plug the leaky plastic vent up on the cabin side.

This whole thing likely didn't worry the builder any because he was in Texas, and presumably spent a lot of time flying when the OAT was hotter than the engine....

I'd agree it likely doesn't make a HUGE difference. My GPS groundspeed seems to match up pretty well with my TAS minus the EFIS-calculated headwind component, but again that entire calculation is presumably a bit suspect.

Obviously I still think I have the fastest -9A on Earth and will attempt to verify this with GPS and mathematics only, assuming somebody else handles the math.

Quote:
Originally Posted by rv8ch View Post
I think the assumption is that engine heat might affect the OAT measurement. I have not done any comparison so I not sure if this is correct or not, but I'm sure someone here has done this. I can't imagine it being more than 5-10c, which seems to translate into a few kts of TAS difference.
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  #9  
Old 11-12-2020, 12:14 PM
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DeeCee 57 DeeCee 57 is offline
 
Join Date: Sep 2018
Location: LSZF
Posts: 542
Default

Hi Jon

This as stupid as the "200kt Club" which you brought to us

There is only one way to compare speed between RVs (ok, maybe with other contenders as well), and this is head to head, shoulder to shoulder, side by side, WOT, on the same day/altitude/humidity/time/etc.

Anything else is just conspicuous myth
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RV-6.9 #25685, slider, O-360-A3A (carb/dual Lightspeed II), MTV-12-B, HB-YLL owner & lover
RV-4 #2062 HB-YVZ airframe builder
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  #10  
Old 11-12-2020, 12:31 PM
romaja romaja is offline
 
Join Date: Jan 2016
Location: Portland Oregon Area
Posts: 96
Default

Quote:
Originally Posted by MacCool View Post
I would think that the venturi effect of a NACA duct would make temperature readings there unreliable, although I'd expect them to be lower than OAT.
It is a possibility that the temp is slightly higher in the Naca vents due to Ram Rise. Although I am not sure it would be significant enough at these speeds. Not sure how much the airflow is accelerated through the vents.

Someone on the forum will surely know.

Ram Rise:

https://www.pittspecials.com/article...irTempRise.htm
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