How to test a prop? At which altitude? At which pressure?

[swisseagle]

Hello

I'm helping a buddy whith his RV-7A, he bought a new prop, what a beauty! Now to compare apple to apple, how should we test a propeller thoroughly?

- At which Altitude? 5000 and 8000ft?
- At which pressure? Density altitude or pressure altitude?
- Other values to record? OAT, % power, FF?

We got the Catto description as follow:
2-Bladed Glass/Carbon Composite Propeller for RV-7A
72" Diameter x 74" Pitch
TMX-IO-360 Red Gold 180+HP@2700RPM
Top Speed at Target RPM- 200-204MPH@2750RM
The static rpm on this propeller is just at 2300rpm
At 110kts climb speed the rpm is 2450
For cruise 2450rpm is about 155kts.

We are a bit off these values now:
- Static we could only got 2080rpm (field elevation 1300ft)
- Climb at 110kt (at 10'000ft) 2310rpm
- Full power 161kt (171TAS), 2670rpm, at about 5000ft



For sure we will contact Craig, but we want to do this with clean data.

Thanks for any input.

[humptybump]

I adopted a test procedure from the late Bob Axom. Here it is ...


click for larger version

This method will allow comparing tests from different days, times of day, etc. Here is a blog write up on the subject and another with my personal data.

[1001001]

Originally Posted by swisseagle

Hello

Zurich, eh? I have friends who live in Zurich and attended their wedding in 2013 in Sarnen. What beautiful scenery you have in that part of the world! During our trip I kept watching the helicopters and planes running up and down the valley wishing for a chance to fly there.

Sorry for the off topic comment, but just wanted to say hi.

[swisseagle]

What beautiful scenery you have in that part of the world!

https://picasaweb.google.com/1100901...6AFliegenBerge

[Andy Hill]

Hi swisseagle

I suspect there are 2 differences between your readings and Catto's spec:

field elevation 1300ft

The Catto spec is presumably at ISA?

TMX-IO-360 Red Gold 180+HP@2700RPM

v

TMX-IO-320

although that might refer to your RV-7A and not your friend? But the Catto figures seem to be based on a beefed up 180HP engine of undefined HP.

With a FP prop you get the iteration that more HP = more RPM = more speed = better prop efficiency = more HP and round again i.e. only a small difference in one factor helps everything. An example is the wheel spats (pants) where speed increases on 10K+ are quoted. With a VP prop I do not find that since the above rule does not apply - but with a FP prop it does.

Given Catto states:

Top Speed at Target RPM- 200-204MPH@2750RM

and you are getting

Full power 161kt (171TAS) [197mph], 2670rpm, at about 5000ft

it seems fairly close?

[brad walton]

8000 ft. density altitude is the altitude at which you will get about 75% power at the design rpm. So Craig has probably designed your friends prop to reach 200 to 204 mph at 2750 rpm. I specified to Craig I wanted Vans numbers at 2700 rpm and 8000 density altitude and I get 204 mph (178 knots) true air speed at 2700 rpm at 8000 da. But I am not at wide open throttle at that da and rpm. So if I want to run at a higher rpm, I can get considerably more true air speed. Or I can run 2700 rpm at a much higher density altitude

[swisseagle]

Thanks for all your reply's, now we can start testing. But at the moment, bad wether keep us on ground.

We made a groundrun ... somhow I have the fheeling that the engine does not make full power, at least on ground. My buddy removed the airfilter, and he got another 30 RPM!?

I understand that a airfilter acts as a restrictor, but I was surprised to see 30RPM.

The engine is a TMX-IO-360, horizontal induction, red-gold package (all rotating parts are dynamicaly balanced, cylinder matched, ports made). At the dyno after a hour run in, it was showing 189HP.

We will see.