Baron 58P vs King Air C90GT vs Cessna Mustang

[Tom Goodrick]

I started out looking for an interesting route on which to evaluate various turboprops. I ended up comparing a piston twin to a turboprop twin and a jet twin. The route is from Huntsville, AL, (KHSV) to Green Bay, WI, (KGRB) which is 593 nm direct. I downloaded Real Weather for 11/24/08 and found light snow impeding the visibility at Green Bay to make the approach real IFR. I decided to have a professional pilot fly four passengers with luggage, making a payload of 200+4x180+150 lbs in each aircraft. The 150 can be split with the nose baggage area for better balance.

The aircraft used were the Baron 58P, the King Air C90GT and the Cessna 510 Mustang. Each has two seats up front and four seats in back. The King Air has a bathroom on board so it does not need to make a rest stop. The Baron needs a stop and one was made at KHUF about at the halfway point. The Mustang has no bathroom but moves fast enough so it does not need one. The Baron 58P was the top end of a long proud line of Baron piston twins. It ended up in competition with the King Air C90 so in Beech's eyes, the King Air won. The Mustang is one of the new Very Light Jets or minimal jets. Move up to the CitationJet and you get a toilet (not a bathroom) but no additional seats.

Here are the results:
The Baron 58P took 3:25 and used 102 gallons of 100 Octane avgas.
The KingAir C90GT took 2:30 and used 182 gallons of JetA.
The Cessna Mustang took 1:49 and used 250 gallons of JetA.

All took off from KHSV at 10:25 am. The Baron landed at KHUF in good weather at 11:55 and left at 12:25. The Baron cruised at 20,000 ft where the air was reasonably smooth. The King Air cruised at 26,000 ft and was almost knocked out of the sky just north of Chicago when the wind shifted back and forth 180 degrees. It finished the trip at 20,000 ft. The Mustang cruised at 30,000 ft where it did not encounter the big wind shift. It stayed high until about 65 nm from Green Bay and then came down steeply using spoilers. All landed with adequate reserve fuel. I am pretty sure the elapsed time from takeoff to landing even of the Baron would beat the airline time because you'd have to fly at least 3 and probably 4 different aircraft to get there on on airliners.

[hanspetter]

An obvious concern these days is economy. To compare the costs we need to know the price of gas versus jet fuel. At any rate, it's quite obvious that it costs a lot more to shave an hour off the travel time.

However, in very general terms it may not be as simple as slower is cheaper. A high-drag aircraft with good STOL capability isn't the economical choice for long legs. A long time ago we discussed airliners and found the the largest aircraft were less economical than the medium-sized airliners.

So, here's another practical question: Say you want to move yourself and and three friends + baggage from Huntsville to Green Bay and you're in no hurry getting there -- what would be the most economical choice of aircraft?

[Tom Goodrick]

That is a very easy question to answer: I'd use a C182 Skylane. We might even have to stop twice, taking on fuel at one stop.

You can estimate a parameter that gives the clear answer in most cases: nautical miles per gallon of fuel or nmpg. You can simply get any aircraft in steady cruise with the payload of concern and then get the true airspeed and divide it by the gallons per hour or GPH. That division gives nmpg. I made a gauge that will do that some time ago. There's one for singels and one for twins. For jets I put the digital display on the panel between the throttle percentage values. Typical values for singles run 10 to 12 nmpg. For twins the values are down around 5 to 6 and for jets the values are around 2 to 3.

The more weight you carry th lower the nmpg. But the main thing that raises the cost is time. If you want to reduce the time for any trip it is going to cost you.

As for the cost of fuel, these days jet fuel costs about the same as avgas - on the order of $6/gallon in the US. But that may have changed recently. The cost of gas for cars dropped by 50% recently. The problem with avgas is it is specially refined in much smaller quantities than automotive gas. Jet A is specially treated in several ways and includes addatives to keep the fuel from freezing at high altitude. People were trying to use Jet A for the new Diesel-engined airplanes and found it does not work well. Exxon has released a warning to all distributers that they must get liability releases from all dealers to protect them in case of engine failure.

OK. I got the actual fuel prices at Green Bay, good within the past 30 days. Avgas - 100LL, is $4.80/gal. JetA is $3.99 per gal. That's for Full Service. (You watch them fill the tanks.) So now we know the costs are:

Baron 58P: $489.60
King Air C90 $726.18
Cessna Mustang $$997.50

[Tom Goodrick]

Well, the Skylane C182 did not work out. I decided to be comparable to the flights discussed above, The payload should be 200 for the pilot and 3x 180 for the passengers. The total baggage was 120. That makes a total payload of 860 lbs. When I checked that load in the C182, I had only 50% for fuel. I checked several otehrs. The bext seemed to eb the Bonanza A36 which had 77% fuel with that payload. That's what I flew from KHSV to KGRB. The same RW was used as in all the above flights.

I departed KHSV ta 10:30 am with 57 gal fuel. I climbed to 6,000 ft for the trip to KGRB via KHUF. When steady on course, I noted 16.99 gph and 177 knots ground speed for 10.4 nm/gal. I was busy watching a movie and missed making the landing at KHUF. The map showed KDNV near the route so I descended and landed there in VFR conditions. We bought 34.9 gallons of fuel and had lunch from vending machines. We landed at 12:35 and took off at 12:59. Finally we arrived at Green Bay, KGRB, at 14:32 with 31.2 gallons on arrival. We had used 25.6 gallons for a total fuel usage of 60.5 at a cost of $290.4.

Summary: Bonanza A36 4:02 using 60.5 gal costing $290.4

[hanspetter]

Even though the Cessna Skylane option was dropped, I assume that you were thinking of the RG version? What is the cost in terms of parasite drag / fuel consumption by choosing a fixed gear versus retractable gear version?

I'm a bit a surprised that sleeker and faster aircraft always seem to lose in the economy contest. I guess the extra drag doesn't matter much as long as you go slow.

Twins are gas guzzlers compared to single engine aircraft. That makes sense but only to some extent. Rather than doubling the horsepower I would assume that a twin would be fitted with two smaller engines that would give about the same power output as one bigger engine. Or, to get proper reduncancy one would choose two powerful engines, each one fully capable of propelling the aircraft. Even so, during normal operation both engines would share the workload and run well below their rated max -- hence, I would more or less expect two engines to suck the same amount of fuel as one larger engine for doing the same job.

[Allen Peterson]

I'm currently flying my Twin Comanche on the same route as Tom's in the A36. I'm on the way to KHUF at 8000 feet, 67% power getting 163 KTAS and burning 14.6 gallons per hour giving 11.25 NMPG.
I started off with 90% fuel and the same payload as Tom's.
I started the flight last night, and loaded Real Weather, but it is probably not the same as Tom's flight even though I set the date as 11/27. It was raining in Huntsville when I left, but I broke into the clear after about 15 minutes.
I'll post the results when I complete the flight.

[Tom Goodrick]

When I said the Skylane would be a good choice, I meant the fixed gear version. But I checked the fuel for the same payload in both fixed gear and retractable gear (RG) versions. The RG gets less fuel because the empty weight is more. Here's the comparison from the 1985 FLYING ANNUAL:

____________C182________C182RG
MTOW_______3100________3100
EW__________1733________1784
Useful________1377_________1328
Fuel Cap______88.0_________88.0
Cruise SPD____142__________156___(75% power 7500-8000ft)
Fuel Flow______12.67________13.17 gph
NMPG_________ 11.21_______11.845

The RG losses just a little useful load (49 lbs). But it is more efficient. If the payload is the same, the 49 lbs comes out of the fuel. Since this made the fuel margin lower, I did not like the airplne for this trip. Obviously the RG would be best for most trips. So why was it discontinued while the fixed gear version is manufactured to this day? The answer is insurance. Insurance rates on retractable gear aircraft have become much higher. Hence the advent of fast fixed-gear singles like the Cirrus and the Lancair or Cessna 300 and 400 of today.

Your question "Why does slow and draggy always win?" is answered negatively in this case. I chose the sleek and fast Bonanza A36 because it has a better fuel margin in addition to more speed!

For piston planes of today - no radial engines in ordinary use (except in agriculture where the company does its own maintenance), the most powerful engine in common use has 300 hp. Putting two 150 hp engines on a twin is hard to do though it has been tried. The extra structure to hold everything together makes the useful load very small and impractical. There have been 400 hp engines but they get tempermental, especially on starting.

You will find some interesting tradeoffs in turboprops between single high power and twin low power. For example compare the Pilatus PC-12 to the King Air C90. This can be done with turboprops for two reasons:
1) Turbopro engines of similar design have a constant fuel efficiency in pph per shp so the performance of a big single can be duplicated exactly by twin engines.
2) Turboprop engines can be flat rated where they maintain a high power through most of the rpm range. This gives small engines better performance in twins.

In the US, no twin can be certified unless it can maintain safe flight at a moderate altitude on one engine. This does not mean they can continue flight if over mountains. The single engine ceiling is always substantially less than the twin engine ceiling. But if an engine is lost in darkness or when over water, they can continue flight to a suitable airport. This is the main reason people buy them. Most twins are flown as business aircraft. The guy who authorizes the purchase is the old fat guy who sits in back with the money who knows very little about airplanes. he just wants to be safe and to get to the destination as fast as possible. Because a twin must be able to fly with one fan turning, when both are turning it can fly faster and climb better than any single.

Allen has the best piston twin flying on this trip as an example of an efficient twin. The Twin Comanche is essentially two Skyhawks hooked together. It can maintain flight on one engine but if one fails on takeoff its rate of climb is very poor. You'd better not have any bumps in the way. Also, it has a reputation as a killer because of its tendency to spin out when maneuvering with only one engine. But that reputation was earned because of previous FAA training requirements that a pilot being checked out must demonstrate a continued takeoff after engine failure.

Allen, just for comparison, I am sending you the RW file I used in my flights.

[Tom Goodrick]

Yes, it looks good. Was it bumpy at that time and altitude?

[Allen Peterson]

I took off from KHSV at 10:27 using your RW files. I climbed to 6000' and, like you said, it was bumpy. I then climbed to 8000', skimming along the top of the clouds, and it was much smoother. I could see the ground most of the time. I took the screen shot at that altitude.
As I got close to KHUF I noticed a thickening band of clouds ahead that seemed to be higher than my altitude. I descended to 5000', just under the cloud base, and flew until the cloud base started to lower. I let down to 3500' and by that time it was time to start my approach to KHUF. I got landing clearance for runway 5 and made a pretty good landing, 72 kts and -185 fpm.
I'm in the parking area at 12:26, not quite 2 hours for the flight. I used 26 gallons and have 54 left, so I probably won't refuel here. So now we're going to make a pit stop and grab a snack. Stay tuned.

[Allen Peterson]

Maybe I didn't do it right, but I like this better than the thumbnail.
Maybe I forgot to uncheck the "include details" box. When I linked the thumbnail and clicked on it I got the picture and some ads.

[Allen Peterson]

Jeez, time flies when you are having fun.
If anyone is still interested, I completed the flight from KHUF to Green Bay today.
I took off at 13:02 and landed at 15:00, again just under 2 hours. I had 25.34 gallons left so I used 54.6 gallons for the trip of a little over 4 hours and a fuel cost of $262.08, just a little less than the A36.
Tom says that the single engine climb rate on take-off for the Twin Comanche is poor, but I suspect it is better than an A36 when losing an engine on take-off.
Having said that , and, after reading the A36 article in the January issue of Flying, I must say that the A36 is probably a lot more comfortable to fly in and certainly a lot easier to get into and out of.
I may have to get me one of them.

[Tom Goodrick]

Consider this. Which would you rather fly across a big lake or a bunch of mountains? It may be a little more difficult for the two people in the back seat of the Twin Comanche to enter and impossible for two more people. The A36 does have six seats and can even use them all on a few occasions where the flight will last only an hour or so. But the pilot has to enter the A36 by the copilot or front passenger's door. That's not very convenient but it is the same door arrangement used on Baron's and other Piper twins. To carry six on occasion, you could fly a Seneca or an Aztec. The Aztec will carry six anytime with full fuel if the baggage allowance per person is moderate.

No matter how many are carried, they are probably all dead in a single if an engine is lost at night, over mountains* or over water.

The * is that twins with an engine out cannot maintain quite as high an altitude as with two engines working so sometimes the mountain thing doesn't work.

Don't mind me. I am just on a kick against single engine flight in the conditions where a dead stick landing probably won't work. I don't think losing an engine on takeoff is very probable. How many times have you lost a car engine getting out of the driveway? How many tmes have you lost one on a long drive? FS can be used to look at these problems. I have concluded a twin would be worth it in most cases.