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RV-7 max cruise speed

Sylvainsting

Active Member
Hello,

On the Van's Aircraft performances table, RV7 with 200 hp fly 180 kt (207 mph) at 8500 ft 75% power, solo weight and 2 blade C/S prop.

I have a brand new RV7 with IO375 (195 HP) from Aerosport Power and WW 200RV prop ( 2 blade C/S).

At 8500 ft, 75% means full Throttle, but I cannot reach those performances, only a little 170 kt (195 mph). I precise I fly LOP ( FF 31l/h)

Is the Van's Aircraft performances table wrong or is it me ?

Is anybody with a similar configuration who reach better results ?

Take a look on the pic, screen shot test at 7500 ft.

In advance thank you
Sylvain



http://img4.hostingpics.net/pics/327906screenshotFPSEDSN221681410367420160804101703841enUS.jpg
 
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Look at your own gauges. They show 66% power, not 75%. Issue is the density altitude (over 9000') along with the LOP mixture (as opposed to best power mixture). IF you could up your power 13% to 75%, speed should increase about 4% getting you close to 180.
 
Not flying yet but a question, if we bring the prop RPM up closer to 2700 will we be making more HP, or will the increase prop drag cancel this?
 
Adjust your knobs

mixture (richer), rpm (2600-2700), lower density altitude(7500-8000) and see what that yields. Report back.

Bret, it probably depends on the prop. Hydroguy reports best with 2600 on his 180 hp WW200 prop. I plan to explore this and document.
 
Costs money to go fast.

Like others have said, push everything up and your speed as well as your costs will go up proportionally. You'll get a little speed for a lot of money.

In my 8 I can cruise along at 176 KTAS at a realistic weight burning just under 10 gph or 165 KTAS on slightly nder 8 gph. That about 6 % slower on 20% less fuel. Depends on airframe straightness, weight, DA, CG, etc.

I guess it's fun to say you can cruise at 180KTAS, but it's expensive..
 
I have an RV7A with same IO-375 engine from Aerosport, mine has normal or low compression, nice new paint, clean looking airplane.

I also do not achieve Van's performance numbers and have been planning a project to find out why. At altitude, say 8,000', I routinely see 160 knots in cruise at ROP mixture settings and 2400 RPMs. If I go LOP, depending on how far lean I go, I will lose between 5 and 10 knots.

I can count on 150 knots @ 7.5 GPH running LOP at 8,000' and above. This gives me about 4 hrs endurance with decent reserves.

When I see reports of people getting up around 180 knots I can't help but think I must have something rigged improperly. This winter I hope to dig in and learn more about what is going on. At 195HP with a Whirlwind RV200 prop I think I should at least achieve Van's numbers for 180HP.

I look forward to any other reports and what others have found.

My airplane looks very clean as in there is nothing obvious as far as what would cause some lack of speed. I have heard that improper rigging of the wheel pants can cause considerable speed degradation so that is where I will start looking, but it would be great to learn from what others have found.

Randall from Sedona
 
Not sure if mine is typical. I have IO360 with two Bendix mags, CS prop, 1123 empty weight. At 8,000' I can just reach 200 statute mph (TAS) with WOT/2670 RPM/best power fuel mixture, fairly cool air, no passengers. Cant remember what the fuel burn was but guessing between 9 and 10 gph. Basically, everything maxed out......I typically cruise 180 mph (157 kts)TAS at 2400 rpm, 30-50 deg LOP, burning about 8.2 GPH.
 
As others said, full performance requires more power. Van's uses 75% at 8000' density altitude. That will take 2700 rpm and ROP mixture. Anything less gets less speed. You will also want to verify your actual speed. My Dynon calculated true airspeed is 3 knots slower than actual.
 
Unless we are all talking apples to apples, it is difficult and misleading to compare performance. True air speed and density altitude are the only relevant numbers in my opinion.
 
As others have pointed out, many issues at play and your single data point is not sufficient to answer your root question.

Here is a short list of things to consider:
- The WW prop is not, in my opinion, a top cruise performer. This prop offers other features so you balance what you want.
- Weight. You don't mention aircraft weight. Van's data is for a light airplane.
- Rigging. Of all the issues I've seen on flying RVs rigging is at the top. Rigging includes flaps, ailerons, wing tips, wheel pants, gear fairings and HS angle of attack. Flap alignment and aileron rigging is the first area to inspect.

While top speed is nice to know, most strive for efficient cruise speed. I note that your engine has very well balanced injectors, nice job. The engine setting in the screen shot are for fast LOP cruise. Without knowing anything else I'd expect 171-173 kts TAS.

CHTs are a touch high - perhaps the screen shot was taken right after the climb.

Carl
 
Not 75%

Look at your own gauges. They show 66% power, not 75%. Issue is the density altitude (over 9000') along with the LOP mixture (as opposed to best power mixture). IF you could up your power 13% to 75%, speed should increase about 4% getting you close to 180.

This comment should get more attention.
 
I get very similar numbers to you when LOP and 7.5 gph. It really is surprising how much more speed you get when you crank up the rpm to 2700. There's a reason the racers turn 3000 rpm and above. I think the formula is something like 14.7*gallons per hour = horse power when lean of peak. I was under the impression that I was running at higher horse power/% power until I ran this formula. On a 195 hp engine, 146 hp is about 75% power which would equal a fuel flow, lean of peak, of very close to 10 gallons per hour.
It would be great if someone who is not a music major could check the formula and my numbers:D
 
At 195HP with a Whirlwind RV200 prop I think I should at least achieve Van's numbers for 180HP.

at 7.5 Gal/hr, you are producing nowhere in the vicinity of 195 HP. HP is a function of Fuel, air and volumetric efficiency all related to RPM. You should spend a bit of time reviewing the performance charts in your Lycoming handbook. Very generally speaking, you can equate your fuel flow to speed at any given altitude, when using typical RPM/MAP combinations.

Larry
 
Not flying yet but a question, if we bring the prop RPM up closer to 2700 will we be making more HP, or will the increase prop drag cancel this?

I explored this quite a bit in my phase one testing and for my 74" Hartzell BA, I repeatedly got highest IAS at 2640 RPM. 2700RPM dropped it by at least one knot every time.
 
I have very similar numbers with same engine, same prop.
I can just reach 170-172 KTAS at around 7000ft, full throttle and 2500 RPM. FF almost 10GPH. I usually cruise 9500 ft, 60% LOP, 160 KTAS, FF 7.9 GPH.
 
I have an RV7A with same IO-375 engine from Aerosport, mine has normal or low compression, nice new paint, clean looking airplane.

I also do not achieve Van's performance numbers and have been planning a project to find out why. At altitude, say 8,000', I routinely see 160 knots in cruise at ROP mixture settings and 2400 RPMs. If I go LOP, depending on how far lean I go, I will lose between 5 and 10 knots.

I can count on 150 knots @ 7.5 GPH running LOP at 8,000' and above. This gives me about 4 hrs endurance with decent reserves.

When I see reports of people getting up around 180 knots I can't help but think I must have something rigged improperly. This winter I hope to dig in and learn more about what is going on. At 195HP with a Whirlwind RV200 prop I think I should at least achieve Van's numbers for 180HP.

I look forward to any other reports and what others have found.

My airplane looks very clean as in there is nothing obvious as far as what would cause some lack of speed. I have heard that improper rigging of the wheel pants can cause considerable speed degradation so that is where I will start looking, but it would be great to learn from what others have found.

Randall from Sedona

Just for comparison, I have the box stock 180 IO-360-M1B and Hartzell 74" BA on my 7A. I get EXACTLY what Vans advertised for 75% cruise (172Kt). To the penny, and a lot of them ROP of course :rolleyes:. 15 more HP would not get my bird to 180Kt. Using the cube rule of thumb, it would be more like 176Kt. And like others have said, I normally cruise 162kt plus or minus a couple depending on the power settings LOP.

Thread creep alert.....Yeah...so this is where I really like the CS prop. I can go downhill cheap (LOP) and FAST. Watching TAS of course.
 
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I explored this quite a bit in my phase one testing and for my 74" Hartzell BA, I repeatedly got highest IAS at 2640 RPM. 2700RPM dropped it by at least one knot every time.

I was thinking something was wrong with my numbers, because I saw the same thing with my 9A, IO360, and WWRV200 prop. I broke it down into 25-rpm increments and saw my peak at 2650.
 
I see 165 Knots TAS at LOP 7.2 GPH at 9500 ft in my 7.I am running 195 HP with CS prop, Sam James cowling and E mag P Mag
 
DA Alert

Sylvain,

Please note that the density altitude in your snapshot is 9380. So, your numbers are at 66% power and 9380 DA, not 7500 feet.

Cheers, David
RV6-A KBTF
 
Speed Trial Data - I'm grinning

Deviated from the flight plan and ran a speed trial yesterday: 8000 ft baro altitude (~7600 density alt.).

Screenshot is from the full power southbound leg of a N/E/S/W square pattern. The leg was 1 minute 35 seconds stable autopilot flight, and had an average TAS of 180.2 kts. 207.2 mph - I'm happy. The average TAS for all four legs was 207.4 mph. It must be the new paint.:p

206mphScreenshot.JPG


Catto three blade 66 dia./74 "pitch prop on a standard IO-360-M1B Lycoming.

Also ran trials at 75% (203.3 mph and close to Van's number), and at 65% (189.8 mph).

The RVs have an amazing speed range. I don't claim any records, but it's fun.
 
Wow... that?s pretty amazing! I?ll be running that same basic engine/prop setup on my -7 when it?s finished, so those numbers excite me.
 
Here's another data point:
RV-7A, O-360 carbureted, Sensenich fixed pitch prop
Typical cruising power
8500 ft., 2650 rpm,155-160 kts., 8.5 gph as close to LOP as you can get using a carbureted engine.
 
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Throttle position?

75% at altitude (~8000-8500 feet) requires wide open throttle & 2700 rpm, properly leaned. Fixed pitch props often make it difficult to do this, because they're too under pitched to allow full throttle without overspeeding the engine. All the boxes must be checked to make the measurement real.


The claims of C172 and Cherokee pilots of '75%@6.5 gph' probably outnumber the number of pilots in the country, but it doesn't make them able to violate the laws of physics.

;-)

If a 180hp engine isn't burning 10gph, or at least very close to it (using ignition advance), it ain't making 75%.
 
I enjoy reading what other Vans drivers are achieving wth various combinations, it's all variable.
I drive an RV8 slightly faster than a stock 7 (so Vans say) and although it will do 180 ktas (180hp) it drinks the gas 36lph. I never run LOP, old school I guess, I like best power. I normally drive around at 22/2300/28lph, I get 155 ktas, gotta luv that! Oh and I keep the love of my life highly polished, that's good for a few more kts -:)
We all still enjoy spirited perf thanks to a great design/s����
 
Here's my -7A at nearly full throttle but not at cruise ALT.

At 10.5k, I cruise at 2550 RPM, 160 KTAS and 8 GPH. Lower at 8.5k same RPM but only 155 KTAS and 8 GPH.

m9ItG5kl.png
 
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