AndyRV7

AndyRV7

Well Known Member
Hi,

I am scratching my head a bit these days trying to figure out the real speed of an RV7. I was hoping someone could help.

I flew my transition time with Jan Bussell recently. It was my first flight in a 6/7 (Can't recommend him enough!). His plane cruised at 185mph and I was surprised because I thought it would be closer to 200 with 180HP engine. It turns out that every plane I have inquired about or flown in since Jan's has been slower. On the order of 170-178 mph versus his 185.

I realize there are a lot of variables like weather, prop type power setting, altitude, and weight, but for the sake of argument, these numbers seem to be the true or real-world cruise speed of these particular planes. I didn't get the impression that these slower speeds were at an economy power setting, yet the planes are a full 19-21 knots slower than Van's numbers say they should be.

So I am trying to get a better handle on what kind of speed I could expect from an RV-7. Maybe my expectations are too high??

Thanks. Andy
 
Last time I checked I was at or higher than the Vans official spec number. I do not cruise at that setting (fixed pitch prop) but can match his numbers.
 
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I am real close to Van's numbers and I do not have my fairings slicked up yet and do not have lower intersection fairings on yet. I get ~ 170KTAS @ 8000ft wide open throttle now with rough glass and no lower intersection fairings solo. I have a carbed O-360 with a FP Sensenich prop.

You have to compare apples to apples to get a good comparison.

Was it IAS or TAS, 75% power or ??, solo vs gross weight, what prop, what eng., etc, etc...
 
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Andy,

Van's published performance numbers are accurate, and have been verified time and time again by professional testing, not to mention almost 7,000 completed aircraft. Even allowing for slight differences due to props, constructions quality, etc. the published numbers are right on the money.

The industry standard for measuring cruise performance is 75% power at 8,000 feet, leaned for best power. In a normally aspirated engine this is wide open throttle, and probably at or near redline. If your testing conditions were not these, then your numbers are not valid for and apples to apples comparison. If you have the opportunity, fly again in that same airplane and fly it in the above conditions and see what you get.

For example, my airplane will consistently true out at 173 kts (+/- 1) at those conditions. However, I flight plan for a more fuel efficient 160 kts. So, what would you say is the cruise speed of my airplane?
 
Thanks for the insight. I hesitated to even post this because there ARE so many variables. I was figuring cruise to be 75% power like Van's publishes, but I guess that didn't have to be the power setting that was used by the people quoting me the performance of their plane. I just figured if someone was trying to sell a plane and told someone how fast it was, they wouldn't be telling that person what the economy speed was. Incidentally, one plane was a Catto 2 blade fixed. The other was a 3 blade constant speed. Jan has a fixed 2 blade Sens on his.

I have figured that 190mph was a safely conservative performance margin from the 200mph Van's quotes. That works out to about 165 knots. So if I could find a plane that "cruises" at 165kts, I would be happy. When I started to see these planes coming in 10-15 knots slower I was confused and figured I ask some other opinions.

I do agree that a good test would be to take another ride in a plane and see what the actual power setting and speed was. I am still learning!!

Thanks for the responses.

Andy
 
I had not been pushing my plane at higher power setting since the breaking period and really didn't know my top speed, but consistently cruised at 187 mph or 163-164 knots.
A couple of nights ago, I was calibrating my TAS and decided to go to WOP at 25 square and at 5000 feet, my TAS was 177 knots or roughly 204 mph. I thought it would be faster but I am happy with that. I am going to try it at 8000' tomorrow.
 
159 kts last night 8500 ft 2500/22"

Last night in my -8, 8500 ft, hot, hot day (I don't have an OAT probe) 2500/22" (WOT) leaned to best power I got 159 kts or 183 mph. This was determined using the 4-leg GPS ground speed method.

I've thought I had a slow -8 but maybe mine is in line with some of the other numbers. I will fly this weekend and go to 2700 rpm and see what speed I get.

I found an easy way to get the average of the 4 legs easily. Pick what you think the average will be. Last night I guessed 150 kts. As you do the 4 legs just keep track of a running total of how much above or below the guess is. After the 4th leg divide the + or - by 4 then add or subtrack it from the 150.

I've found you can do the calculation in your head.

Example:

DATUM 150
N 165 +15
E 160 +10 (subtotal = +25)
S 150 0 (subtotal = +25)
W 161 11 (subtotal = +36)
+36/4 = 9
ave 159 159 (150 + 9)

Looks like Brantel and Ron Lee are kicking a** with their planes.
 
I'm getting smarter by the minute.

Just to be a little clearer too, I do not fly a CSP plane, so when people speak to me about pressure and RPM, I have no idea what they are talking about. I usually just try to remember the numbers and go home and ask someone else what that meant!!:eek:
 
AndyRV7 said:
Thanks for the insight. I hesitated to even post this because there ARE so many variables. I was figuring cruise to be 75% power like Van's publishes, but I guess that didn't have to be the power setting that was used by the people quoting me the performance of their plane. I just figured if someone was trying to sell a plane and told someone how fast it was, they wouldn't be telling that person what the economy speed was. Incidentally, one plane was a Catto 2 blade fixed. The other was a 3 blade constant speed. Jan has a fixed 2 blade Sens on his.
Click to expand...

The majority of the problem is because of two things...

#1
A large protion of the pilot community does not know what power conditions (MP, RPM, and Mixture) actualy produce 75% power.

#2
A large portion of the RV fleet with fixed pitch propellers are running with a pitch that will only produce 75% power at low altitudes. It is the higher altitudes (8000 ft +) and 75% power that produce the True airspeeds quoted by Vans.
 
rvbuilder2002 said:
#2
A large portion of the RV fleet with fixed pitch propellers are running with a pitch that will only produce 75% power at low altitudes. It is the higher altitudes (8000 ft +) and 75% power that produce the True airspeeds quoted by Vans.
Click to expand...

Now THIS is exactly what I was afraid of. If so, then you could truly be in a plane that tops out at substantially less than the capability of the plane.
 
AndyRV7 said:
Now THIS is exactly what I was afraid of. If so, then you could truly be in a plane that tops out at substantially less than the capability of the plane.
Click to expand...


Which is a good reason to put a C/S prop on the plane.
 
My plane is about the same speed as other RVs at the airport. I often have to have the CS prop guys pull power back a bit because I don't like running the RPM around 2700. Full power...side by side....very close in speed.
 
They often compromise, Andy....

...when the prop is ordered. Some guys want more vertical pulling power for aerobatics, so their pitch is a little flatter and give up some speed willingly, for the better uphill performance.

I personally, wanted max speed and I told Catto that. He asked if I would be willing to run the engine at 2700-2800 and I said .."Gladly". He then said that he would build the prop accordingly and that I should at least equal Van's numbers and I did...better than 2 MPH faster after it was all said and done, with a 4 way GPS run at 2760 RPM at 8000' WOT and leaned.

Some of these airplanes are bought already built, possibly Jan did too, so they don't really know what the pitch of the prop is and don't really care, because even 190 MPH ain't too shabby.

Best,
 
Pierre, Is that setting pretty close to 75% power at 8000'? I don't get up that high in my rental, but it sounds like you are approximately WOT anyway once you get to 8000' or so, and that is just to make 75% power.

I am speaking for Jan without his knowing, but if I remember correctly, he built the 6 and bought the 6a??? And I think he told me he was probably slightly underpitched because he was able to spin the motor at about 2750 with his prop.

For what it's worth, I have been looking for a cruise prop since day 1, not a climb prop!:)
 
Andy,

Another thing to consider with Jan's airplane is that it has no wheel fairings (at least it didn't when I flew with him a few years ago). His plane is a workin' machine, set up for the slings and arrows of training, not for speed.

As far as the other airplanes you've flown in goes, as the others have said, ya gotta compare apples to apples. As Bob Axsom and others will tell you, getting a good comparison takes pretty consistent procedures.

But in most posts here that I've read, it seems folks are pretty happy with speeds, and it seems common to get "book" numbers (very unscientific, memory-driven interpretation, FWIW).

Cheers,
Bob
 
How important is hitting a number?

I understand you have said you are trying to compare information so that you could possibly make a buying decision but I think you really have to ask yourself a simple question.

The question is this: How fast is FAST ENOUGH?

At some point in your desire for speed the idea of FAST will become a relative term.

This is what I mean: When you compare how fast you are now flying in your rental C-172 or Cherokee 140 or whatever it is, to how fast you are going to fly in any given one of these RV's how important is it that one is 165 kts vs another that is 164 kts vs another that is 168 kts? Any one of them is going to be SCREAMING FAST compared to your rental aircraft you are currently flying.

The difference in speed between all of the fast planes you have to choose from will be so nominal that compared to what you are experiencing now, with the rental planes, that difference between the fast RV's will not be relevant. ALL of them will only have relevancy in relation to how much faster they ALL will be in comparison to the rental planes.

I am describing here something akin to Einstein's Theory of Relativity!

The idea of the differences in speed of these RV's IS ALL ABOUT RELATIVITY!

The speed is relative to your current experiences now and, later on if you buy or build an RV, relative to those other RV's or any other make of airplane around you. So, given this notion of relativity, you have to ask yourself how crucial is it for you that one airplane you are looking at is 1 or 2 or 3 or even 10 knots faster or slower than another? If it is faster than most all other airplanes you will be flying around except for some of those other RV's that you will, once you join the fraternity, be bonding with.

How important are those differences to you?
 
RVbySDI said:
I understand you have said you are trying to compare information so that you could possibly make a buying decision but I think you really have to ask yourself a simple question.

The question is this: How fast is FAST ENOUGH?

At some point in your desire for speed the idea of FAST will become a relative term.

This is what I mean: When you compare how fast you are now flying in your rental C-172 or Cherokee 140 or whatever it is, to how fast you are going to fly in any given one of these RV's how important is it that one is 165 kts vs another that is 164 kts vs another that is 168 kts? Any one of them is going to be SCREAMING FAST compared to your rental aircraft you are currently flying.

The difference in speed between all of the fast planes you have to choose from will be so nominal that compared to what you are experiencing now, with the rental planes, that difference between the fast RV's will not be relevant. ALL of them will only have relevancy in relation to how much faster they ALL will be in comparison to the rental planes.

I am describing here something akin to Einstein's Theory of Relativity!

The idea of the differences in speed of these RV's IS ALL ABOUT RELATIVITY!

The speed is relative to your current experiences now and, later on if you buy or build an RV, relative to those other RV's or any other make of airplane around you. So, given this notion of relativity, you have to ask yourself how crucial is it for you that one airplane you are looking at is 1 or 2 or 3 or even 10 knots faster or slower than another? If it is faster than most all other airplanes you will be flying around except for some of those other RV's that you will, once you join the fraternity, be bonding with.

How important are those differences to you?
Click to expand...

If he's gonna get all philosophical like that, I'm gonna need a drink first....
 
My rv9 has a climb pitched prop. It will climb better than ay airplane I have flown. I see climb rates of 1800- 2000fpm solo. Yeah my 158ktas @8kDA and 2800 rpm is not quite the Vans number, but there's just something sweet about flying a brand new airplane that has a $35/hr operating cost.
Sure it cost me $65k to build it, but I don't know anywhere you can get my performance for a 2010 model and at that price.
 
RVbySDI said:
How important are those differences to you?
Click to expand...

Very important!!

If in fact they are all within 2-3 knots of eachother, then they are the same to me. If they are within 25 knots of eachother, then they are different. I am simply trying to learn why they are different (if in fact they are).

Also, even if they were 10 knots different, I would want to know why. Is my slower plane gaining some other benefit like climb performance, or have I just gotten the equation wrong?

I've already gotten some good insight here so thanks for all the responses!

Incidentally, I assumed all guys were addicted to speed. I may get used to whatever speed I can build or buy, but there is no sense leaving some on the table on day 1. The plane is going to cost way too much for that.
 
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RVbySDI said:
The question is this: How fast is FAST ENOUGH?
Click to expand...

I don't think that Andy is saying 165 +/- kts is not fast enough, but rather he's asking "is a particular plane flying as fast as it should based on Van's numbers?" This would certainly be a issue for me. If a plane is not achieving the performance numbers that its designed for (based on a proper and valid evaluation) then there's something slowing it down, right? As a buyer I would certainly want to know that to determine a fair purchase price. A slower airplane is worth less than a faster one (again, all things being equal) so how do you know the right price to pay unless you can judge the plane's performance "relative" to its contemporaries... ;)

Andy, I see that you just posted a similar response before this one, so I'm sorry for any redundancy. And I agree with you about not leaving any performance on the table!
 
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One other thing that hasn't been mentioned is weight - the heavier the airplane, the more lift it requires for level flight, and hence, the more drag. Louise and I routinely fly our airplanes on long cross-countries, loaded to full gross, and they lose about 6-7 knots off the cruise speed for the same power. That's just one more variable for you. But when I do an all-out speed run or 75% power cruise at Van's altitudes, I get his numbers for the RV-8, and Louise's -6 is within 2 knots of what I get with the -8!

As has been mentioned above, you have to compare apples and apples if you want meaningful numbers, and there are so many different ways that people prop, engine, and fair their airplanes (not to mention the accuracy of instrumentation, both for speed and engine power) , comparisons at the top end are almost meaningless. Flight testing is about precision, and many for many, it isn't important enough to go after that precision.

My experience, however, is that if you equip your airplane the way Van's prototypes are equipped, and fly then under the same conditions, you are probably going to get book values. He simply doesn't exaggerate. Many planes measure more slowly because folks equip them differently.

And don't forget to fly with half tanks, wearing skivvies if you are going to go head to head in a race...:)

Paul
 
Andy, are you buying or building an RV7? Regardless, get one that is light, avoid auto engine conversions, must have a minimum 180 HP engine and the best prop is constant speed. While some may say this is just my opinion, true...but I am also right.

If the plane is built well you will be fine.
 
WM, I think you got it right! At the end of the day, I had some performance number in mind that I considered conservative. When I saw a couple planes that didn't even get very close to that number, I was puzzled. I certainly didn't do any kind of scientific tests, but I just get the sense that there is more going on in my case than power setting or weight or anything like that.

Ironflight, I presume you are correct as well. But if I remember correctly from Van's site, the difference on performance between solo and gross was about 1mph. So I never gave weight much thought. Intuitively, it should be a little bigger difference, but I'm not an engineer.

Ron, I set out to build a 7 about 4 years ago but I finally realized I was never going to be able to make it happen. So I warmed up to the idea of buying and have been looking for a 7 for about a year now. I may have to buy a plane to go look at all the planes I want to look at ...

If I remember correctly, Jan and I were at gross and I did most of my X-C with him at 2350rpm and 1500 feet. From my C172 experience, I get the impression that we were not operating at 75% power?? So his plane is probably quicker than I mentioned. And given the stories he told me, AND my own ham-fisted landings, I'm sure the poor plane has a little more drag than some others might.

Off to bed. I have a nice flight planned into KJFK tomorrow morning in my buddy's Bonanza (and a nice BBQ afterward!!).:)

Thanks again for all the feedback.
 
Ironflight said:
And don't forget to fly with half tanks, wearing skivvies if you are going to go head to head in a race...:)

Paul
Click to expand...

Man, I hadn't thought of that one Paul! :p

Half tanks won't work for AVC, but I can see it now, Tom, Wayne, Mark and I... all battling it out in Sport FX in our :eek:...nah, never mind...I really don't want to see that...now or ever! (nor would anyone else, ahem!) :D

Andy, back to your question, as Paul and others have mentioned, so much is dependent on not only test conditions, but probably even more-so on build, as has been mentioned. You can build for speed in different ways...stay light, do speed "mods" as part of the build, etc. I must caveat, I didn't build mine, but am tweaking it, and learning from those that did build for speed, like the racers mentioned above. Tom (Race 109) told me once (when I asked if his EVO Rocket inlets were stock), that "nothing on this airplane is stock". At 220 knots plus, I believe it! A gent named Gary built a very fast 7 under Tom's tuteledge, and he has shown his stuff in races, as have others, so 7s (and all models) can be very fast...and without radical mods. I can't wait to see Dan H's 8 fly after watching his build! :)

Even if racing is not the goal, the efforts they put into the build provide speed, performance and economy. Hook up with those guys as you build (or perhaps as you modify a bought-flying plane) and you will learn much and be very happy with your speed...IMHO.

You won't be dissapointed in these planes, as SDI said!

Cheers,
Bob
 
Van's numbers are accurate

He is extremely dedicated to reporting accurate performance numbers and is well aware of inflated speed numbers in the industry. I do not test for anything but maximum speed myself and I always test with the same methods and procedures. When I first built the plane I had a 1.5 ft longer wingspan than the RV-6A design to accommodate tip tanks carrying 17 gallons of extra fuel and the empty weight was 1201 lbs. The speed, WOT, leaned for max speed, RPM 2720-2730, trimmed for hands off level flight, 6000 ft density altitude, in three directions (360, 129, and 240 per the old U.S. Air Race Handicap procedure) and results processed by the NTSP spread sheet to mathematically eliminate the wind effect, was 170.67 KTAS.

I have made a lot of speed mods in the past six years (many did not work out as expected) and my speeds are in the low 180 KTAS range with the best being 184.4 KTAS. In my testing I use an autopilot (Pictorial Pilot) and altitude hold (Altrak) to minimize deviations from straight and level flight.

When I fly cross country with my wife, the steps are on, the tip tanks are on, the stock tips with lights are on and I run the engine at 2450 RPM, burn ~10 GPH and cruise between 165 and 170 KTAS depending on conditions. I always flight plan for 150 KTS and I almost always beat that number for the entire flight regardless of altitude, winds aloft, temperature, humidity, etc.

If you are interested in performance numbers by RVs you can review the race results of all of the Sport Air Racing League races since 2007 at www.sportairrace.org. The RV Blue class is powered by 360 cu in engines and the RV Red class by 320s. Typically, these races are flown in many directions so real world wind effects are included in the numbers. My race speeds are usually running around 205 mph these days.

Bob Axsom
 
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TAS

At altitutude for travel (my bird likes it best above 10 thousand), I get 169-170 knots TAS. That is when I get it tweaked just right. LOP gets me 158 knots.

Thottle wide open, 2,400rpm, CS MT prop, IO360 180hp. If I drop the rpm to 2,200, it's 163 knots.

For flight planning, I use 160 knots.
 
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The following is a posting I made yesterday to a fellow's inquiry about wooden props.
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You might also consider an Ellipse design made by Catto. Present performance of an Elippse three-blade on an RV-6 with 150 HP on auto gas is 187 mph TAS at 75% power at 8400' dalt, 1440 lb, with exceptional ROC, averaging 916 fpm from 2000' to 10,000' This average is based on several GPS runs. This would translate to 191.1 mph with 160 HP, 198.7 mph with 180 HP, and 205.8 mph with 200 HP.

His other averages were: 193 mph, 2740 rpm, 4440' dalt; 192.3 mph, 2738 rpm, 6440' dalt; 184.4 mph, 2655 rpm, 10,400'dalt.
 
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