Airframe and engine efficiency

Guest Discussion
1

The data below indicates that the Lancair Columbia 300 airframe produces a lot less drag than the SR22. Both at 8000 feet, ISA:

Cirrus SR22 (from Paul Traina’s web site)

RPM MP %HP GPH TAS

2500 20.7 69% 17.2 171

2500 19.7 65% 16.5 167

Lancair Columbia 300 (from Lancair documentation)

RPM MP %HP GPH TAS

2500 21 67% 14.4 174

2500 20 63% 11.9 169
The power settings and airspeeds are similar, but the surprising difference is in fuel flow. In the first comparison, the SR22 uses 19% more fuel (17.2 vs. 14.4 GPH), to get 3 fewer knots. The Columbia’s engine is operated at 50 degrees rich of peak.

In the second example, the SR22 uses 39% more fuel to get 2 fewer knots. In this case, and any case below 65% power, the Lancair manual calls for 50 degrees lean of peak operation.

If the manuals are accurate there must be big drag or propeller differences at play here.

Since both planes use the same engine, does anyone know if Cirrus specifies lean of peak operation below 65% power? Does the engine run smoothly in that mode?

I wonder if comparing planes gives the same results as comparing manuals? Any experience?

2

The data below indicates that the Lancair Columbia 300 airframe produces a lot less drag than the SR22. Both at 8000 feet, ISA:

Cirrus SR22 (from Paul Traina’s web site)

RPM MP %HP GPH TAS

2500 20.7 69% 17.2 171

2500 19.7 65% 16.5 167

Lancair Columbia 300 (from Lancair documentation)

RPM MP %HP GPH TAS

2500 21 67% 14.4 174

2500 20 63% 11.9 169 >

The power settings and airspeeds are similar, but the surprising difference is in fuel flow. In the first comparison, the SR22 uses 19% more fuel (17.2 vs. 14.4 GPH), to get 3 fewer knots. The Columbia’s engine is operated at 50 degrees rich of peak.

In the second example, the SR22 uses 39% more fuel to get 2 fewer knots. In this case, and any case below 65% power, the Lancair manual calls for 50 degrees lean of peak operation.

If the manuals are accurate there must be big drag or propeller differences at play here.

Since both planes use the same engine, does anyone know if Cirrus specifies lean of peak operation below 65% power? Does the engine run smoothly in that mode?

I wonder if comparing planes gives the same results as comparing manuals? Any experience?

At what altitude. Was this for the same altitude for both or at different altitudes.

M.Myers

3

There has to be something wrong here. The fuel flow is a RESULT of the power settings, ie RPM, MP, at a certian altitude. The same engine producing the same percent of horsepower should be burning the same amount of fuel.

So once you get the same % of horsepower at a given altitude, the simple measurement of efficiency in producing thrust from the propeller (which is equal to the total drag on the airframe), is the KTAS. And these look pretty darn close, which is what you would expect from very similarily engineered machines.

That’s my analysis anyway, I could be wrong.

David T.

4

The TAS numbers are statistically insignificant. The flow of the wing, cockpit width, etc make up for most of this. (btw, I’ve flown the Columbia 300 and the SR20 and put my money on the SR20 which I have since upgraded to an SR22).

Lancair’s numbers MUST be lean of peak or at peak. Running LOP is a complicated game that can only be safely accomplished with tightly balanced injectors and EGT/CHT from EACH cylinder. Note that Lancair and Cirrus do not offer this out of the factory though we are hoping that Arnav will be doing some of this for us. I’m guessing that the Cirrus numbers are 50-100 degrees rich of peak.

Again, with an apples-to-apples comparison, you would come up with very close numbers with fuel flow between the airplanes. Different cowlings can make a difference because of cooling issues. It will be interesting to note that, because every engine is a bit different, comparing an SR22 to an SR22 will not be exact.

Gami (the folks that make Gami injectors) have lots of articles on their web site discussing LOP operation. Read these before trying this in your airplane - especially with the 550. Unless you enjoy top overhauls!

The data below indicates that the Lancair Columbia 300 airframe produces a lot less drag than the SR22. Both at 8000 feet,

ISA:

Cirrus SR22 (from Paul Traina’s web site)

RPM MP %HP GPH TAS

2500 20.7 69% 17.2 171

2500 19.7 65% 16.5 167

Lancair Columbia 300 (from Lancair documentation)

RPM MP %HP GPH TAS

2500 21 67% 14.4 174

2500 20 63% 11.9 169 >

The power settings and airspeeds are similar, but the surprising difference is in fuel flow. In the first comparison, the SR22 uses 19% more fuel (17.2 vs. 14.4 GPH), to get 3 fewer knots. The Columbia’s engine is operated at 50 degrees rich of peak.

In the second example, the SR22 uses 39% more fuel to get 2 fewer knots. In this case, and any case below 65% power, the Lancair manual calls for 50 degrees lean of peak operation.

If the manuals are accurate there must be big drag or propeller differences at play here.

Since both planes use the same engine, does anyone know if Cirrus specifies lean of peak operation below 65% power? Does the engine run smoothly in that mode?

I wonder if comparing planes gives the same results as comparing manuals? Any experience?

5

At what altitude. Was this for the same altitude for both or at different altitudes.

M.Myers

The numbers compare performance at 8000 feet, standard atmosphere for both planes. Steve

6

The -22 and -22’s have a slight twist built into the fuselage.That can slow it down at cruise.The airfoils are a bit different between the two models lancair/cirrus.The lancair is a bit cleaner design.Smaller frontal area.Cirrus has a bigger cabin for your comfort.also Angle of incidence on the wing and horizontal make a big difference.jeff

7

Actually, the tail of the tape here would be to look at the % power put out by the engine, and then look at the resulting ktas. Not too complicated really.

We would need to compare the POH’s side by side, (assuming the numbers in the POH are honest, which they always are, unless you’re a kit builder, which means you might inflate the numbers a little bit), and just see who has the higher ktas for the same % power.

Remember, drag equals thrust. I’m assuming the thrust put out by these engines has to be very similar. Thrust is a function of the %
horsepower and prop efficiency.

I think the drag efficiencies of the two airframes is pretty darn close. The numbers that we have so far indicate this.

David T.

8

Cirrus has a bigger cabin for your comfort.

A couple of postings have made this point, but it appears incorrect. Columbia 300 cabin dimensions:

Max width 50" (vs. 49.25)

Length 139.6" (vs. 130)

Max height 51" (vs. 50)

No significant difference.

Steve

9

Paul’s PIREP and photos (10.5 and 190KTAS) suggest that the SR22’s POH may be a little conservative. Imagine that?

10

Paul’s PIREP and photos (10.5 and 190KTAS) suggest that the SR22’s POH may be a little conservative. Imagine that?

I spent quite alot of time sitting in both the Columbia and SR20 (flew both as well). It is not only in cross section and width that the SR20 is larger, also in headroom through both front AND BACK seats. There is less sloping of the fuselage roofline in the rear seats of the SR20 (thus passengers won’t be banging their heads when it gets bumpy). Thus, the shape of the fuselage of the SR20 in the “passenger cabim” is significantly larger and would be expected to reduce efficiently ever so slighty. BACK SEATERS VOTE SR20!

Alex

11

You guys are all focusing on the interior cabin dimensions, which is kind of missing the point.

Many, many things contribute to drag efficiency, and the point is that the Cirrus and the Lancair are basically equivalent. (And the Cirrus is lots cheaper, and Cirrus is actually producing aircraft verses spewing hype.) The cabin interiors are pretty close dimensions anyway. The thing we should care about is the speed with which we are shooting the cabin through the air at a given fuel gph. And the Cirrus is right at the top of the list of production aircraft in this regard. A remarkable achievement really.

12

Has anyone compared the Katana 4 seater, the DA40, to an SR20?

Try calculating the fuel cost and maximum leagal payload with reserves, and the time required, for 500 and 600 mile trips.

Well, the SR20 has leather available!

13

I have some time in a grossly underpowered DA20 (never again) and sat in the demo cockpit of the DA40. There is no way that my butt and back would last through a 500 mile trip in the thing. That leather in the Cirrus is covering a real seat!!

Has anyone compared the Katana 4 seater, the DA40, to an SR20?

Try calculating the fuel cost and maximum leagal payload with reserves, and the time required, for 500 and 600 mile trips.

Well, the SR20 has leather available!

14

Had an occasion to sit in the Katana at the Long Beach AOPA convention. It was on the ramp. Mind you I am 6’4" and when seated in the pilot’s seats I had an excellent view OVER THE TOP of the WINDSHIELD. I couldn’t even think about closing the front door. I looked at the back seat and figured there was no way!

They have a nice plane, but not for taller folks.

BTW, I first got interested in the Cirrus because of cabin size … I could fit!

15

The original question was fuel and payload.

Never mind short take off, short landing and quick climb!

16

Not to mention the control sticks right between your legs. Instant birth control if you have an emergency landing…

And from what I saw, even if you have luggage payload left over after filling the seats, you’ll have to put most of it in the passengers’ laps.

Thanks but I’ll stick with Cirrus or my 260SE.

17

So buy one.

The original question was fuel and payload.

Never mind short take off, short landing and quick climb!

18

Max width 50" (vs. 49.25)

Length 139.6" (vs. 130)

Max height 51" (vs. 50)

No significant difference.

Steve

Don’t know if you’ve sat in both planes. Everyone I’ve spoken with who has experienced both interiors had the same reaction I did: the Cirrus’s cabin is roomier. (It is also more draggy.) On these figures:

  • Must be some difference in how the width is measured, because there’s clearly more space in the Cirrus’s front seat. Here’s the simplest way to illustrate it: the bolster between the pilot and co-pilot’s seat in the Lancair is like that in a movie theater or airliner, basically with room for one person’s arm. THe one in the Cirrus is about twice as wide. The windshield is also less raked-back, so there’s more of a bulbous sense in the front. You can get an idea of the difference from web site photos.

www.lancair.com/files/wa800.zip

www.cirrusdesign.com/images/gal_interior_instruments_hirez.jpg

  • The ten-inch reported difference in cabin length shows up largely as back-seat legroom. And there it makes a big difference.

These are two sides of the same coin. The Cirrus cabin is deliberately larger and less raked-back, which makes it bigger-feeling inside; while Lancair’s is deliberately more streamlined, for less drag and faster speed at given power settings. Each has its pluses and minuses. My point is, if you’ve seen them both you realize that they represent two different approaches.

19

180+ kts fixed gear.

Not too shabby, lest we all forget!

Nor is 160kts on 10gph.

And if indeed the Lancair is a hair faster, then it’s going to need more real estate to land and take-off.

And more $$$

20

180+ kts fixed gear.

Not too shabby, lest we all forget!

Nor is 160kts on 10gph.

And if indeed the Lancair is a hair faster, then it’s going to need more real estate to land and take-off.

And more $$$

Plus, it’s ugly as sin.

mdz