Join the Fastest TAS Club

[n700jl]

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.

[Dugaru]

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.

[rv8ch]

Originally Posted by Dugaru

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?

[MacCool]

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.

[Tandem46]

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.

[rv8ch]

Originally Posted by MacCool

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.

[airguy]

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.

[Dugaru]

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.

Originally Posted by rv8ch

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.

[DeeCee 57]

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

[romaja]

Originally Posted by MacCool

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