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-   -   Mods and new cruise speed (https://vansairforce.net/community/showthread.php?t=132749)

RONSIM 12-25-2015 12:37 PM

True Air Speed (TAS) is the performance measure
 
Indicated air speed, and ground speed should not be used when comparing aircraft performance. True air speed, calculated by your EFIS or (better) using a calculator, and based on Calibrated air speed (indicated good enough for government work), pressure altitude, and outside temperature is the best way to compare airplane speeds. (IMHO)

R.

judoka5051 12-27-2015 06:10 AM

Hey Bernard,
 
Check this post. The picture in post 21 shows what I did (the center example).

http://www.vansairforce.com/communit...ng+ramp&page=3

hlangebro 12-27-2015 03:12 PM

Answers...
 
So, just back from vacation. As someone said here on the thread, NEVER use indicated airspeed to compare performance. It is utterly useless, unless you have enough data to compute the true airspeed. As you can see in my pics, the true airspeed is in ktas. I use knots as that is the standard since the mid 70's. Anyone who wants to use mph, feel free to do so, but that is not the standard unit of measure for aircraft. Enough about that.

Someone asked about the aileron fences. Since both the flaps and ailerons are slightly reflexed, the current spanloading now has a slight peak at the wingtip, as it is operating at a slightly higher aoa. In order to avoid vortices and extra drag, I am "blocking" the flow from the lower surface flowing to the upper surface, and thus minimizing drag. Ideally, I would at some point modify the wingtip with reflex as well.
As far as an exhaust fairing, I have one as well, not used for this test though. I will do some modifications to it, and then I will try it again. I have already a nice ramp on the inside of the cowling -exit, so it might not do that much for performance. I also have an adjustable cowl flap, which make more of a difference.
Next goal is to get to 173-175ktas, which will be very tough...

For all of you with 180-200hp in your RV-7A's, what is you true cruise speed at 8000-8500ft density altitude, at 65 and 75% power?
A buddy of mine has a clean 6, and a souped up engine. His cruise speed is 185ktas, but of course, he burns a bit more fuel and he has around 210hp I would guess...

hydroguy2 12-27-2015 05:40 PM

mines a 7 not a 7A, but I cruise 178KTAS at 8.5gph 2440rpm around 8500'. normally though I cruise above 9500 to 12500 most trips. I see 178-180ktas burning 8.2gph 2380-2420rpm. If I want to burn more, I'll pushing the mixture to the ROP, where 9.5gph is about 182ktas.<---Not positive on these numbers since i don't spend much time there.

hlangebro 12-28-2015 04:24 PM

performance
 
What was your density altitude for those numbers? What engine do you have (hp)? I assume that these numbers are LOP?

AX-O 12-28-2015 06:08 PM

Quote:

Originally Posted by hlangebro (Post 1040441)
Someone asked about the aileron fences. Since both the flaps and ailerons are slightly reflexed, the current spanloading now has a slight peak at the wingtip, as it is operating at a slightly higher aoa. In order to avoid vortices and extra drag, I am "blocking" the flow from the lower surface flowing to the upper surface, and thus minimizing drag. Ideally, I would at some point modify the wingtip with reflex as well.

Thanks. Were you able to isolate the effects of the aileron fence by themselves?

hydroguy2 12-28-2015 08:12 PM

Quote:

Originally Posted by hlangebro (Post 1040688)
What was your density altitude for those numbers? What engine do you have (hp)? I assume that these numbers are LOP?

I went back and found couple pics of my panel with the numbers. DA varies. also note the MP gage reads high by 0.4 or something like that. and I have a airspeed error of ~2kts at this speed. I run a Lyco IO-360 parallel valve engine, 9:1 pistons, superior forward sump, AFP injection w/RamAir and Pmags, Vetterman 4pipe. swinging a WW200RV prop, Sam James long cowl w/plenum.

The cruise fuel burn in this pic is higher than i am used to seeing, can't recall why.





hlangebro 12-28-2015 10:42 PM

Fences
 
No I wasn't able to isolate the effect of the fences. I added up a lot of things for this test (which I shouldn't have) so it is difficult to say. It should help, if nothing else, with better aileron effectiveness and lower induced drag. Induced drag is low at high speed, so the effect would be slightly higher climb, which I can not confirm yet.

hlangebro 12-30-2015 05:09 PM

Fairings
 
I tested (again...), my exhaust fairing. I spent some time cleaning and painting it and applied a heat shield, as last time there was burn marks from the exhaust. It didn't do anything for the speed at normal altitudes, however it will work better at 10,000 and up as it closes the exit more. This, on the other hand showed up by over pressurizing the cowl at 12,000 and the oil door popped open!!!! I need to fix that somehow. It was kinda funny how adjusting the cowl flap acted as a throttle for the door!
Otherwise, the speeds were the same as last time; 8500ft DA, 65, 70 and 75%, 160, 165 and 170ktas.
At 10,500ft/11265ft DA, at 65%, the speed was 164ktas, which is a good cruising altitude and speed for cross country!

Exhaust fairing and cowl flap



Oil door popped open....scary when it happened...








164ktas at 11245ft DA at 65%



Here is the 2 piece fairing for the trim actuator rod


DanH 12-30-2015 07:37 PM

Quote:

Originally Posted by hlangebro (Post 1041245)
This, on the other hand showed up by over pressurizing the cowl at 12,000 and the oil door popped open!!!! I need to fix that somehow. It was kinda funny how adjusting the cowl flap acted as a throttle for the door!

Increasing cowl pressure increases exit velocity, decreasing cooling drag. Pressure is good.


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