RPM with wheel fairings

[Daver]

I've finished up my Ph 1 testing officially but I have not installed the wheel fairings.

Gear leg fairings installed.

So far, my max RPM is about 2450 which has yielded about 150 kts at 8500'

I get about 2200 static.

I'm getting ready to install the wheel fairings and was just wondering if anybody knows how much RPM increase I might see.

I know I might be overpitched alittle but I've been getting very good economy (~5 gph or so for the first 46 hrs).

Dave
-9A flying

 

[rv9av8tr]

I suspect adding the wheel pants alone will add 10-15 mph... so perhaps RPM will go up 50-100ish?? It's not clear to me why you'd fly nearly all your Phase 1 without fairings. All the performance data you've collected to this point (if any) doesn't mean much unless you plan to fly most of the time w/o fairings.

2450 WOT at 8500 ft. Yes, you are over pitched It's a good thing the RV's get off short by design. Just the same, I hope short field / high density alt operations at gross weight doesn't cause you grief.

For fixed pitch prop, I'd be shooting for 2650 WOT at 8500 ft, which would bring your static up to around 2400. Then you'd really enjoy the performance of your RV. Still want 5 gph... just throttle back a little. However, with a carb, throttling back requires close watch of EGT's on all 4 cylinders, because it will cause the EGT's to spread.

 

[AK4x4]

RPM low

Your rpms seem low to me. Not knowing your specific engine/prop combination, on a lycoming, with a prop without rpm restrictions, you should be able to hit 2700 rpm WOT @ 8500' density altitude. This is 75% power output. In your case it appears that either the engine is not making proper power, or an incorrect propeller is installed. Your propeller manufacture should provide static rpm numbers for your engine/prop combination. If the ground static numbers are good then the engine is making proper power and the prop just isnt letting you have all the performance your RV is capable of producing. Good Luck, Russ

 

[db1yg]

Hi Dave,

A fully faired RV with a healthy engine and a well matched prop should see from 500 to 550 rpm increase from static to wot at 8k density. Therefore, if you see 2200 static you should see 2700-2750 at 8k density.

The above is based on running a fixed pitch prop. I have a 9a with a 3 blade Catto and an 0360/180 hp Eci engine. My speed went up by 18 kts after install of leg/wheel fairings. With the fp prop you get a double benefit to the fairing install--the reduced drag allows the airplane to go faster but also allows the engine to spin up more which creates more hp and still more speed. The gear leg vs the wheel fairings account for most of the increase.

Don't be too quick to assume you are overpitched--the fairings will give you more rpm and speed and as the engine breaks in you will also see improved performance.

Cheers,

db

 

[Daver]

prop pitch

Thanks guys!

I've held off re-pitching the prop until I get the wheel fairings on.

I've tested take off performance at over 8000 DA at near gross weight and its fine with me.

I REALLY like the economy of the setup as it is and I'm not sure I want to "fix it" given the high cost of fuel. If it were pitched for 2700 RPM, it would go faster and use more fuel. Of course I could throttle back more than I have to now but I think I'd still suffer a loss of economy.

My best economy run so far has been 11,500 ft, 2100 RPM, 157 MPH TAS and 4.4 gph. I was throttled back some and leaned alittle.

I was light and the plane is perfectly trim.

Its like I'm in "overdrive" I think.

I left the wheel fairings off during testing so I could keep an eye on the wheels/brakes, etc easier.

I'll be installing them soon.

Dave