flyenforfun

flyenforfun

Well Known Member
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 :D

Thanks for the input everyone
 
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.
 
humptybump said:
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.
Click to expand...

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
 
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.
 
humptybump said:
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.
Click to expand...

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.
 
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.
 
similiar setup, was wondering same thing

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.
 
fwiw

I see the same IAS on my lightweight (1050lbempty) 160hp fixed pitch RV-6. How heavy is your plane?
 
Some things just happen.
Half of the planes preform below the average :rolleyes:
You can't reasonably expect your aircraft to perform perfectly on the initial flights. Some do, I doubt I could ever be so lucky.
Now that you have successfully constructed your plane, move to the next step: Aircraft developement.
I recently bought a 28 year old Thorp T-18. The logs & notes are full of compliments on construction and flight quality. Our standards are higher today.
I spent the initial flight hours working on heavy wing and stall issues so my wife could transition to it. A few well placed changes make the difference between a marginal plane and an excellent one.
Have a go at it, and enjoy the experience.
 
rvbuilder2002 said:
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.
Click to expand...

I'll be doing some testing hopefully this weekend to get good TAS numbers to post on here.
 
SHIPCHIEF said:
Some things just happen.
Half of the planes preform below the average :rolleyes:
You can't reasonably expect your aircraft to perform perfectly on the initial flights. Some do, I doubt I could ever be so lucky.
Now that you have successfully constructed your plane, move to the next step: Aircraft developement.
I recently bought a 28 year old Thorp T-18. The logs & notes are full of compliments on construction and flight quality. Our standards are higher today.
I spent the initial flight hours working on heavy wing and stall issues so my wife could transition to it. A few well placed changes make the difference between a marginal plane and an excellent one.
Have a go at it, and enjoy the experience.
Click to expand...

I'm thinking once I get some TAS numbers I'll be able to make a more accurate determination. If after that I find out that I am a bit below average, I think improving alot of my fiberglassing will reduce drag a bit.
 
Just reading the info from the Dynon, haven't considered that it could be inaccurate actually.
Click to expand...

If it is setup right you will have good data.

Simple mental maths will work too to check.

If ROP, take the % of MP and % of rated RPM, multiply and bingo.

So 26" and say 2430RPM would be 0.9 x 0.9 which is 81%

On the LOP side, Fuel flow in GPH x 14.9 for a standard compression N/A engine.
 
I have some numbers for you guys.

8k feet:

55% - 163 kts TAS
65% - 170 kts TAS
2700 rpm (WOT puts me over red line rpm) - 175 kts TAS

Thoughts?
 
I don't believe that you are slow with those numbers Matt. 170 kts TAS at 65% is about normal.


If you want to find the absolutely top speed, get down low (seal level - along the beach is good) on a hot day at WOT - you'll burn huge gobs of fuel, but you'll see top speed. Watch out for birds...heck, watch out for big BUGS!!
 
I know an RV owner who came within 1 second of a mid air ..... with a Whale :eek::eek::eek:

True story

Imagine the ATSB/NTSB and insurance report:eek:
 
Mat I have the same problem with mine. See previous posts. My engine was not new IO-360 AIB6 with a blended Hartzell prop. I get 160 knots indicated at 8000. I am putting it down to tired engine (worn Cam,Cylinders). I have a new IO-390 going in this week so will advise figures once Ihave them. The Rod Bower Intake gave me another 7 Knots
Ben
 
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