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130 IAS at 5000' and 8gph fuel flow

iaw4

Well Known Member
I am thinking of buying someone's RV-9A. I am concerned that there seem to be wide variations in performance. ideally, the builder would quote me performance numbers at 8,000'--for comparison to the Vans demonstrator and other postings--but he does not have them and I think he has stopped flying, so he cannot easily get them.

he does say that he used to cruise at 130 IAS at 5000-6000' with 8gph fuel flow. for those of you who are flying one and know performance both at 5000' and at 8000', is this great, good, average, bad, or terrible? (ideally, can you please post some IAS's at 5000' and 8000', with rpm setting and fuel flow, so that I know how to scale the numbers?)

help appreciated.

regards,

/iaw
 
There really isn't enough data here to properly assess it. First off, are we talking MPH or knots? IAS doesn't mean much and can vary depending on installation. A quick estimate at 5000' standard pressure and 68* OAT converts 130 knots indicated to 144 true, but again, that doesn't account for installation differences. 8GPH would be a pretty high cruise power fuel flow for me.

Again, it may be easier for you to specify the engine and prop on the airplane, and people with similar combos can give you a good idea of expected performance. Searching for 9A performance will also bring up a bunch of threads with that info. I have an O-320 150HP and sensenich fixed pitch metal prop. I flight plan at 140 knots and 7GPH. I am usually a bit faster than that, and usually fly above 8-10k', where the plane is most efficient. 14,500', wide open throttle, I am around 142 knots true at 6-6.5GPH. That's rich of peak - I am still playing with getting it to run well LOP.

Chris
 
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In addition to what Chris said, the builder's performance measurements may be accurate, or they may not be.

Is his fuel flow calibrated? How about his tachometer and ASI? I'd say the performance figures the builder quoted are slightly below normal for an RV-9 <assuming the builder was using Knots as a reference), but who knows what prop the airplane has, what engine (a low compression engine will burn more fuel for the same power), etc.

There are lots of builders and pilots out there who don't have good data on their aircraft's performance.

By the way, here's a TAS calculator if you'd like to calculate the impact pressure and temperature have on TAS:

https://www.dauntless-soft.com/products/Freebies/TrueAirspeedCalculator/
 
I rarely see IAS in knots above the 130?s in cruise. Typical KTAS in cruise at 8 gph is around 150 +/-. In the cold air now I can easily get in the yellow arc at low altitudes. Top end is 160 KTAS plus, but nobody really flies around at low altitudes, fire walled and/or max rpm do they? Would be helpful to know what engine / prop combination it is and from that we can tell you what to expect performance wise.
 
My Typical Numbers!

... Here is a shot of the numbers that I typically see in economy cruise.
This fight was at 8500ft. but can still provide you with a lot of information.
The typical fuel burn is 6.8 GPH at this altitude and speed. If I climb to
say 1,4000K I can go about 8 KTS faster (all speeds are in KTS) with no
fuel penalty, or, push in a little more power to increase the speed with
about a 7.8 GPH fuel burn. I really love my RV-9A, and I feel this is the
best model for my purposes. Thanks, Allan..:D

Add on info; My RV-9A has a 0-320, stock 8.5 to 1 CR, Carbureted, one
mag & one Light speed ign,160 HP, Whirlwind C/S 986LB.

https://photos.google.com/photo/AF1QipPJ0I3du2iMM-g__UPXLu5ElIMJLd7QuT_EjoQ_
 
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Ok, I am not sure I can give an educated opinion on the plane you are looking into buying. However, I can give you some info concerning what I see with my 9A. Here are a couple of pics of past flights. Both flights are running LOP so, as a side note to anyone wondering about what these engines are like running LOP, well, you might want to look at the CHT temps on both flights. Just sayin'! :D

24774906170_6eab82f9e4_z.jpg


To familiarize you with the readout: True airspeed (TAS) - top left corner (171 mph); Indicated airspeed (IAS)- left tape (152 mph); Altitude - right tape (8500 ft); Density altitude - bottom left with label D Alt (7916 ft); fuel flow - just above the MAP dial bottom right (7.4 gph). One item of interest to note. Notice the GPS ground speed? Yep, 100 mph. Had a heck of a headwind that day! Yikes!! ;)

Now that you are familiar with where to see the data on my displays, here is another flight.

28715811870_62e0b787ca_c.jpg

A couple of differences to note on this flight. Notice this one I am cruising 2K higher, but look at the D Alt. The speed is showing IAS as 6 mph SLOWER than the above flight but notice my TAS. It is actually 6 mph FASTER than the above flight. Pretty interesting! But not as interesting as the fuel flow. Notice that difference? I consider anything 10,500 or higher to be settling into the wheelhouse for the 9(A). Because of that, I would say that the plane you are looking at may not be performing its best at 5,000 ft. However, as others have said, we need more data to really say much about it.

As for what is in my 9A: ECI IO-340 9.1:1 pistons (180 hp), forward facing cold air induction, Plasma II Lightspeed Electronic Ignition + Slick Mag, 4-straight pipe, Catto 72 X 74 3-blade prop.

Oh, and lastly, what it says on the link in my signature below.
 
I consider anything 10,500 or higher to be settling into the wheelhouse for the 9(A).

Agreed. Van's plans for the 9's ought to include built-in O2, as up high is really where it is meant to be. I try to get over 10k for all but the shortest trips.

Chris
 
I'm starting to explore higher altitudes in my (relatively) new (to me) RV-9A. I've got O2. Over what distances do you think it makes sense to climb to 10K or more?

Agreed. Van's plans for the 9's ought to include built-in O2, as up high is really where it is meant to be. I try to get over 10k for all but the shortest trips.

Chris
 
I'm starting to explore higher altitudes in my (relatively) new (to me) RV-9A. I've got O2. Over what distances do you think it makes sense to climb to 10K or more?

I do it on just about anything over about 75 miles, just because it's so easy to do. For 150 miles or better I just stick it up there to 16,500 or 17,500 and turn on the oxygen. There's virtually no traffic up there, it's cool and smooth, the radio reaches out to forever, visibility is great, and you can glide for a long time on an engine-out scenario which enhances safety.

I don't try to rationalize climbing up there by virtue of fuel economy or time spent in the air or anything like that. I rationalize it exactly the same way I rationalize ownership of an airplane - I do it because I can.
 
This is extremely useful info. I'm going to start heading for the teens on my standard mission between Richmond VA and Allentown PA (about 215 nm). Perhaps the harried controllers in that area will be happy to have me above the fray!

I do it on just about anything over about 75 miles, just because it's so easy to do. For 150 miles or better I just stick it up there to 16,500 or 17,500 and turn on the oxygen. There's virtually no traffic up there, it's cool and smooth, the radio reaches out to forever, visibility is great, and you can glide for a long time on an engine-out scenario which enhances safety.

I don't try to rationalize climbing up there by virtue of fuel economy or time spent in the air or anything like that. I rationalize it exactly the same way I rationalize ownership of an airplane - I do it because I can.
 
I'm starting to explore higher altitudes in my (relatively) new (to me) RV-9A. I've got O2. Over what distances do you think it makes sense to climb to 10K or more?

I haven't done the math to find exactly when it makes sense in terms of fuel burn / speed, but anything an hour or longer I am usually up high. Winds aloft could change my decision some though. I have found foreflight's flight planner and altitude advisor to be remarkably accurate once I set it up with my plane's performance numbers.

Chris
 
Altitude Factors

Couple additional things to consider:
1. Outside air temp. My -8A was designed for 100+ degree summer days in the desert. Heating - even with second heat muff - is marginal at best. I start to get cold soaked with prolonged exposure to below freezing outside temps.
2. The view outside. I just find it more enjoyable to be relatively low.
3. Fuel burn searching for best wind altitude. Sometimes completely negates wind/altitude fuel savings.

But do what you want - because you can!
 
Just to add some more data for a typical -9A. Mine's got a 160-hp IO-320 with a Catto 70x70 FP 2-blade prop. Box-stock engine with two magnetos.

At around 11,000 feet DA (where I simply lean the mixture to hit a target fuel flow):

145 KTAS at 7.2 gph
155 KTAS at 8.0 gph
 
Couple additional things to consider:
1. Outside air temp. My -8A was designed for 100+ degree summer days in the desert. Heating - even with second heat muff - is marginal at best. I start to get cold soaked with prolonged exposure to below freezing outside temps.
2. The view outside. I just find it more enjoyable to be relatively low.
3. Fuel burn searching for best wind altitude. Sometimes completely negates wind/altitude fuel savings.

But do what you want - because you can!

#3 is why I find the altitude advisor on foreflight so useful, and it is generally pretty accurate. If you tell FF your climb airspeeds, vertical speeds, and fuel burns, as well as cruise and descent settings, it takes into account your route and winds aloft and can give you time en route and fuel burn for all different altitudes. Obviously this is based on the data you give it and forecasted winds aloft so it isn't perfect, however I have found it to be fairly reliable. My most recent trips from FL to VA and back it predicted my time en route within 10 minutes each way, and fuel burn within a gallon or so. Of course, sometimes I fly higher even if it takes a bit longer, due to weather, turbulence, clouds, etc.

Chris
 
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Don't even need to use Foreflight... Can get forecasted winds from aviation weather sources.

You certainly can, and that's where FF gets the data from. It's easy to look up the winds at altitude, however FF does the math and can give you an idea quickly if it will be worth the climb, and also your projected ETA's. You can do this all on your own of course, but if you already use FF, it makes it easier.

Chris
 
Understand and use Foreflight, myself. Saying you don't need anything more than your PPL training to outsmart the "hunting for best wind altitude" gripe.

You certainly can, and that's where FF gets the data from. It's easy to look up the winds at altitude, however FF does the math and can give you an idea quickly if it will be worth the climb, and also your projected ETA's. You can do this all on your own of course, but if you already use FF, it makes it easier.

Chris
 
In an effort to reduce thread drift that I helped cause....

I've got a slider -9A with an O-320, carbureted, Hartzell CS prop. I pretty consistently see 150KTAS at 5-6000ft and 23/23. Less sure of fuel burn at that setting, it seems to vary, but I'm guessing no more than 7.5 gph. I can usually get 160KTAS at 24/24 and maybe 8.5 gph, at the same altitude.
 
Some amazing fuel burns & speed you guys are getting out of a 9, best bang for buck:) Good to know your TAS too with today's modern glass panels as VNE can be reached (& beyond) very quickly at high Alt's
 
Why does anyone use MPH for speed?

I still can't understand any reason why someone would fly using MPH instead of Knots? It would be great to hear the reasoning.

ATC is using Knots, the charts are divided into nautical miles, etc.
Aren't most POH listing speeds in Knots?

I am disturbed that Van's lists the airplane speed in MPH, it should be in Knots.
MPH should be used when you are on the ground in a car or motorcycle IMO.

Random Rants.
 
It looks good for marketing, that's about the only reason any of the manufacturers do it.
 
...

Random Rants.

Drifting
..........Drifting
.....................Drifting

Because many of us owned and flew airplanes that were documented in MPH. Heck some of them didn't have electrical systems, radios, or noseeheels. Oh the horror of it. Can you imagine having to navigate with a paper chart, bouncing whiskey compass, and wristwatch?

Heck, some of those planes didn't even have a starter and I heard they may have had cloth over their wood wings.
 
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Drifting
..........Drifting
.....................Drifting

Because many of us owned and flew airplanes that were documented in MPH. Heck some of them didn't have electrical systems, radios, or noseeheels. Oh the horror of it. Can you imagine having to navigate with a paper chart, bouncing whiskey compass, and wristwatch?

Heck, some of those planes didn't even have a starter and I heard they may have had cloth over their wood wings.

That was then, new aircraft and associated marketing should be knots. It's got to start at Van's though. If they decide their target audience can't understand knots, I'm not sure what to think.

Bevan
 
Heck, some of those planes didn't even have a starter and I heard they may have had cloth over their wood wings.

Nahhh, that's just a dirty rumor. Things like that can't really fly, we all know that. :rolleyes:
 
I still can't understand any reason why someone would fly using MPH instead of Knots? It would be great to hear the reasoning.

ATC is using Knots, the charts are divided into nautical miles, etc.
Aren't most POH listing speeds in Knots?

I am disturbed that Van's lists the airplane speed in MPH, it should be in Knots.
MPH should be used when you are on the ground in a car or motorcycle IMO.

Random Rants.

That was then, new aircraft and associated marketing should be knots. It's got to start at Van's though. If they decide their target audience can't understand knots, I'm not sure what to think.

Bevan
I cannot answer for anyone else but me. As for me, every other speed measurement in all other aspects of my life are measured in MPH. Every non-aviator who I talk with about flying asks me how fast my plane flies. I tell them I cruise around 150 knots. They answer with: "How fast is that?" Telling them in MPH bypasses that drawn out conversation.

Besides, knots are for boats and boy scouts!
 
OK, but when you report your distance from an airport on the radio, it should be in nautical miles!

Because the difference of 3/4 sm between 5 nm and 5 sm is significant and could be the difference between life and death.

Should I make my call before or after the GPS tells me I'm 5 out. What if I'm not using a GPS and I'm guestimatting my distance? Should I include my confidence level in my estimate?

Heck, if the pilot gets his/her direction from the airport and gives the aircraft type and intentions rather than, "N123 over the firestation, inbound", I'm happy.
 
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The wind is also reported in Knots.
Knots, or nautical miles per hour have long been the standard units of velocity for both nautical and aeronautical navigation.
Knots are used almost universally for marine and aviation navigation because a nautical mile relates directly to mapping of the earth. A nautical mile is equal to 1 minute of latitude making it very easy to use Knots for speed and nautical miles for distance when already the earth's mapping uses degrees and minutes of latitude. Each degree of latitude is equal to 60 minutes of latitude.
To each his own, even if its ...
 
I cannot answer for anyone else but me. As for me, every other speed measurement in all other aspects of my life are measured in MPH. Every non-aviator who I talk with about flying asks me how fast my plane flies. I tell them I cruise around 150 knots. They answer with: "How fast is that?" Telling them in MPH bypasses that drawn out conversation.

Besides, knots are for boats and boy scouts!



Not true. It's all about standards. If it wasn't for standards when you fly into Canada, you would have to think and have your instrumentation converted to metric. Fortunately Canada uses the international standard for aviation units (as should the US).

Beside's there's only 15% difference between knots and MPH so your friend will only be 15% less impressed with knots. In Canada ground based vehicle speed is measured in Km/h (kilometers per hour). If a Canadian friend wants to know how fast 150 kts is, you first have to determine who your audience is. If they're younger than mid 40's , they will likely only understand Km/h (but will be VERY impressed), the older ones will likely know both. This is because we changed from Imperial to metric in the mid 70's (except not in aviation where the international standard prevails). I find it better to teach someone what knots are, and then carry on. It's called education.

1kt = 1.15mile (or 15% more, easy math)
1kt = 1.85Km (or almost double, easy math)

Bevan
 
I like to have both....indicated and true airspeed in knots on the EFIS, and ground speed in mph on the backup GPS.

It's fun to tell passengers how fast we're going over the ground in units they're used to, without having to do the math.
 
Once you fly the big stuff Knots is everything. If you want to impress a non aviation person about speed KPH is the way to go, sounds more dramatic:):) As has been mentioned KTS is mostly universal world wide for the measurement of speed & has it's origins dating back to the sailing days where most of early aviation was taken from with ref to maps. Remember when flying machines where invented it was a new form of transport the early pioneers didn't know what to do other than adopt some rules of the sea.
 
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Once you fly the big stuff Knots is everything. If you want to impress a non aviation person about speed KPH is the way to go, sounds more dramatic:):) As has been mentioned KTS is mostly universal world wide for the measurement of speed & has it's origins dating back to the sailing days where most of early aviation was taken from with ref to maps. Remember when flying machines where invented it was a new form of transport the early pioneers didn't know what to do other than adopt some rules of the sea.

Exactly so how did it go from knots to MPH?

Bevan
 
Exactly so how did it go from knots to MPH?

Bevan
Actually it didn't. In fact it was the reverse. Early aviation speed measurements were in MPH. That is why the old planes had air speed in MPH. It wasn't until much later on the switch was made to nautical measurements as a standard.
 
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