Is my RV-8 slow ?

[flyenforfun]

I know there is a ton of threads on performance, but everyone is posting numbers at WOT at 8k ft, etc. I wanted to see if what I am seeing in my plane is normal or below average because I am wondering if I am having a drag issue somewhere that is also a possible cause for my heavy wing. Also the only numbers I have right now are IAS, wasn't thinking of TAS, but I will update everything after I fly next. I also wasn't planning on getting this thread going so I haven't done any official testing, just something I was thinking about this morning.

Also, I need to go around to all the fiber glassing on my plane and make it better, all stuff I planned on doing before I get it painted. Toward the end of the build I was in just get it done mode. I know I can probably gain a few kts from cleaning up the fiberglass

Anyway, here is what I am seeing. I have an O-360, 180 hp, FP sensenich prop, the one that Vans recommends for this setup. I have trouble getting WOT numbers because if I go WOT in level flight my RPM will creep above redline.

So far what I've been seeing with all fairings on is at about 4000 feet, I am indicating 170 mph ( ~150 kts) at 65% power. 75% can yield up to 180 mph (~156 kts). Now I know this is IAS and there are errors, next flight I plan on climbing to 8k ft and getting TAS numbers to compare with the specs on Van's website. But what is everyone else with a similar setup indicating at these power settings? Is it normal that WOT level flight puts me over red line, and yes I know buying a CS prop will solve that problem

Thanks for the input everyone

[Ron Lee]

Get TAS numbers then you can make a valid assessment.

[flyenforfun]

Originally Posted by Ron Lee

Get TAS numbers then you can make a valid assessment.

I figured. Will do.

[humptybump]

A climb prop could exceed max rpm at wot. A properly matched cruise prop is typically designed to achieve max rpm at wot (or some other chosen rpm). With a fixed prop, wot rpm will varry with altitude.

[flyenforfun]

Originally Posted by humptybump

A climb prop could exceed max rpm at wot. A properly matched cruise prop is typically designed to achieve max rpm at wot (or some other chosen rpm). With a fixed prop, wot rpm will varry with altitude.

Thats what I've learned when asking around the airport, just wanted to see other peoples opinions and what they are seeing. I am ok with the prop as is because I figure I would suffer in climb with more of a cruise prop. This one seems like a decent compromise for a FP. Someday, I'll go CS

[humptybump]

Matt,

My experience is that if you either fly off of a nice, moderate length, runway or fly solo most of the time, even an extreme cruise props will be fine. I've got a 150hp RV-8 with an extreme cruise prop and fly 1600lbs off of 1900' grass in warm humid conditions with no problem. At gross I am still off in time but I like a big margin so I don't do that without other favorable conditions.

[rv7charlie]

How are you determining %power numbers? (If that's off, any comparisons will also be off.)

Charlie

[rvbuilder2002]

Originally Posted by humptybump

A climb prop could exceed max rpm at wot. A properly matched cruise prop is typically designed to achieve max rpm at wot (or some other chosen rpm). With a fixed prop, wot rpm will varry with altitude.

Altitude will effect RPM. For that reason it is actually possible that a prop is both a climb, and a cruise prop., depending on what altitude you are wanting to cruise at.

I suggest the original poster should obtain some TAS speed data, and check out THIS old thread.

[RV10inOz]

History has shown, if you build it 99% right it will perform as advertised.

Biggest performance errors are perceived ones from an inaccurate static source in flight. Closely followed by power setting mis beliefs.

Accurate TAS calcs are the beginning, and do a gps box test at the same time to compare your measured TAS to yor ACTUAL TAS.

[RVZoomie]

I'll probably catch some criticism on this one, but I see similiar numbers with an -8, 180 hp 0-360 and same sensenich prop. I was told by an A&P and read that this prop doesn't have an rpm limit and when I come up initial ~ 3500 ft MSL (towered airfield). My goal is 200 mph (feels slow) so at WOT I will exceed 2700 rpm (told not a problem, literature seems to verify this) and speeds as measured by GPS ground speed and verified with IAS don't quite reach my goal during calm winds. I have no way to measure percent throttle, only MAP. I've always thought I was on the slower end of the factory specs but am waiting on my panel upgrade to verify with TAS to tell.