Performance questions

Hi all-
I am currently in Phase I testing ( 7 hrs so far) with my 9A and have some serious concerns about some of the engine performance data.
I do not have fairings or wheel pants installed.
O-320 D1A new engine
Sensenich FP 70/79 prop as recommended by Vans.

Static RPM = 2150 with MAP 28"
At WOT on takeoff only getting around 2300 RPM
At 9500' leaned, I get 21" MP 2330 RPM WOT 7.3 GPH KIAS only 115 KTS
AT 8500' leaned, I get 22" MP 2390 RPM WOT 8.4 GPH KIAS only 115 KTS
At 7500' leaned, I get 22.5" MP 2340 RPM WOT 8.0 GPH KIAS only 118 KTS

I have NEVER been able to get close to redline (2600 RPM for my FP) unless I am in a descent. It appears to me that my engine is not developing full power. I have had my pitot/static checked by an A&P and there are no leaks and the IAS calibrates well with his test instrument. I have a DYNON EFIS and a UMA mechanical tach as well and the two correlate.

I have checked the mixture and throttle cables and they function appropriately to the respective stops.

I would appreciate some thoughts as to where to go next.

2 thoughts right off the bat...

Check your IAS in flight with a portable GPS and a three-heading triangle to reference to groundspeed and TAS, just to make sure your ASI is indicating correctly in flight.

If that checks out, you could try borrowing a little less aggressive prop from someone else to get your RPM's up, and see where that goes. Pants and fairing are generally good for about 15 knots according to common wisdom, but getting your RPM up is key.

With a fixed pitch prop on an RV every knot faster you go gives you more RPM which gives you more power, which gives you more speed, which...you get the idea.
Adding all the fairings will change your speed and RPM quite a bit (more so than a constant speed prop RV) but with that said,,,115 Kts??? Something is very wrong. Either with your ASI has a problem or I am misinterpreting the info you are providing.

performance

HI,
I had the same thoughts on my -9a...with all fairings in place! ( 150 hp)
I have the 77 pitch prop, but can only turn up 2100 static, maybe 2200 on t/off roll. Couldn't redline with JATO.
everything else seems kosher as you've stated.
I haven't done any GPS speed checks, but on a cross-country, I got there about when I figured I should, indicating about 125 kts. at 6500'. Don't recall the MP, never learned how to use it yet!
wouldn't hurt to check the timing I guess, and the carb could be jetted wrong, but I'm not keen to mess with that kind of science.
somehow I don't think I'm going to see the 198 mph in the brochure...but I'm still feeling things out at 20 hours, so top speed is not my main interest right now.

Forget all the 3 heading gps confirmation etc. This early in the testing process you should be concentrating on
engine temps and handling. Have another RV er fly some side by side to confirm airspeeds, doesn't need to be another 9 or whatever. KISS, you don't want to be fixating on one thing.
ymmv
Tom

I agree with Greg and Scott on this---check that your airspeed indications are accurate first--I assume after 7 hrs you know the engine operates within temp parameters. My fp Catto was cut for cruise and as such required a fully faired airframe to reach redline rpms. If memory serves, my airspeed increased a tick over 20 kts after the plane was fully faired--just like Craig Catto said it would---less drag/more speed/more rpm/more power/more speed etc. If you pick up 20 kts, your indicated will be around 135 and, depending on temp/altitude, you may not be too far off the book values in TAS at altitude.

BTW, I understand from Craig that fp prop manufacturers strive for around 500-550 rpm spread between static and top rpm when designing their props. This suggests that with a 2150 static you should see 2650 to 2700 rpm with a fully faired airframe. If you can't achieve this after the fairings are on and the airframe is correctly rigged, then you need to be looking at some reason engine power may be down.

Hope this helps,

Cheers,

db

One other question; where those altitudes MSL or density? You want to do those test runs at density altitude, which could be lower than MSL depending on the OAT's.

Another suggestion

You have a number of excellent suggestions above and the fairings will make a big difference.

First, I suggest you determine your aircraft's drag independently of the engine. You can do that by applying what you can learn from my article:
http://www.vansairforce.com/community/showthread.php?t=42703
If you have fuel flow readout, start with Method 2, version 1, then version 2. If not, go directly to version 2.

There is a CAFE report on the -9A and you can compare their findings to yours for drag and various other performance numbers. The link to CAFE is in my article.

Your static and initial climb look OK for a FP prop set up for best cruise, as explained by others above. You will have a clearer route to the results you want if you can look at drag independent of power.

takeoff altitude and MAP and FP props

Takeoff DA with 28" MAP? What's the MAP with the engine off? Difference?

Also, in one of the RVAtors, perhaps the thick compendium, can't remember, there is a lenghty discussion of how the FAB and cowling designs were arrived upon, factors that affect MAP drop fm intake to sensor, etc...

At 2150 RPM, you are more than 50% down from rated HP in a typical Lyc engine. My experience in an RV6, when it was FP prop, 160HP also, was that 2250 RPM static at SL would not quite yield 2600 RPM straight and level/1k' on a hot summer day here in FL. RV9 airframe could produce different prop RPM range I suppose, guessing it's larger?