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TB20 / Twin Commanche / Sportcruiser ?

10 GPH per engine probably equals a bit less than 50% of rated power (I don’t have the formula for the TSIO-550 at hand). Do you have any idea if operating it that way can be bad for the engine?

Mainz (EDFZ) & Egelsbach (EDFE), Germany

Yes, I agree, that is very low power. For the IO540, 10 GPH is about 50% of max power (depending on the actual RPM).

Flying so slowly will give you good MPG. The best range speed, still air, is slightly above Vbg and for the TB20 is probably about 110kt (Vbg is 95kt).

Whether it does harm, I think there are different views. I believe Deakin reckons it is not good for it, though I don’t know why.

Also whether it is the lowest cost per mile depends on how you do the accounting. Obviously, taking the most extreme one end of the scale, if you are renting per hour wet, nothing short of flying at 100% power makes economic sense And if you own the plane and pay a company 600 quid for a 50hr service, then flying at the best-MPG power setting cannot be the cheapest either because the 12 quid per hour (plus the other service stuff) shifts the best-economy point to a higher power setting (as does headwind).

Administrator
Shoreham EGKA, United Kingdom

Yes, but under Part 91, there is essentially nothing you have to “by hours”. Therefore, going slow tends to make sense.

Mainz (EDFZ) & Egelsbach (EDFE), Germany

As far as I remember, Deakin, Kromer and others are basically saying that our (non turbo) engines are designed to be flown with full open throttle to be most efficient. For a non turbo engine this would mean it will produce something >=75% power up to approximately 8000 ft and then lower accordingly. While I find this a bit old style American cheap fuel philosophy, it’s got some considerations speaking for it.

If I follow Bob Kromer’s recommendation for the O360, I would have to fly it in cruise at 2500 RPM, Full Throttle and leaned to either best power or best economy.Assuming a fuel price of €10/USG (€2.65 / Liter), for my plane, according to the tables produced in the POH this means, I’d fly it roughly at

5000 ft = 150 kt = 12 GPH = €120/hr = €0.80/NM
7500 ft = 144 kt = 11 GPH= €110/hr = €0.76/NM
10’000 ft = 140 kt = 10GPH=€100/hr = €.0.71/NM
15’000 ft = 140 kt = 8 GPH=€ 80/hr = € 0.57/NM

If I were to fly it on long range cruise, things look considerably different.

5000 ft = 132 kt = 8.7 GPH=€87/hr=€0.67/NM
7500 ft = 135 kt = 8.7 GPH=€87/hr=€0.64/NM
10’000 ft = 135 kt = 7.9 GPH=€78/hr=€0.58/NM
15’000 ft = 133 kt = 7.5 GPH=€75/hr=€0.56/NM

So the two extremes are a mere 24 cents per NM apart, which translates to €120 difference on a fictive 500 NM trip. It also shows that in the higher levels, values are almost identical but with max power you can get 5-7 kts more speed for relatively few money.

However, what needs to be taken into account is the fixed costs per hour. Calculating € 150 per hour, the results for a 500 NM trip overhead/overhead would be:
Max speed: 3:12 hours flight time=Fixed costs € 500 plus € 400 for fuel = € 900.-
Most economical: 3:45 hours flight time= Fixed costs €563 plus € 280 for fuel = € 843.-

While therefore it is still slightly cheaper to fly slowlier, the difference is not staggering. If the difference in speeds grow larger, flying fast can absolutely pay off, if the saving in time can outweigh the fuel costs. And of course, if I calculate the average, you get the usual 65% power which most of us fly at.

LSZH(work) LSZF (GA base), Switzerland

There is no such thing as “fixed costs per hour”. They are, well, fixed.

Mainz (EDFZ) & Egelsbach (EDFE), Germany

Philipp,

the fixed costs per hour in a calculation are the fixed costs divided by the budgeded hours, mostly calculated per year. I calculate mine over a year, all fixed costs divided by the amount of hours flown. This is the fixed cost per hour amount I budget for the following year.

Some of them are pretty much fixed indeed, others vary from year to year such as scheduled maintenance (unscheduled are variable) . e.g. if you budget 100 hours per year, you’d have to budget a 50 and 100 hour check, if you only fly < 60 you only need the 100 hour check. But that is relatively minor. In my last 4 years of ownership, the fixed costs have been pretty constant.

Of course, flying faster will get you more miles in between time related checks and into one TBO. If you want to play figures, you can calculate that in there as well, I did not as my engine has just had it’s overhaul and it is unlikely that i will manage to fly until it reaches the next one. Prop is calendar limited anyway (at least hartzell, who mandates the 6 year revision now even for private ops) so TBO does not really count anyway.

I am usually not one to crunch numbers to death, but I found that it can be helpful if you consider ownership to get a good idea of the costs involved. I’ve seen enough people buying something they found they could not afford and then sell with a loss after a short time, only because they never bothered to calculate out what it takes to own a plane. Well, I did the opposite (thanks to some very good advice) and therefore don’t have to worry about that. Good for the nerves, believe me.

Last Edited by Mooney_Driver at 26 Sep 19:26
LSZH(work) LSZF (GA base), Switzerland

For the original poster though, I would say the TB20 is the best bet of your options, and would be my choice.

A TwinCom will cost 4x the amount to run, operate, maintain. I am sure costs increase exponentially with a second engine. Insurance might also be an issue if you don’t have much twin time, but it is a great aeroplane I am sure.

The SportCruiser is in a different league, and an ideal Burger Run or short hop vehicle (I know some will disagree and say it is the best thing since sliced bread and they have been to the moon in it). It is great for Short Field stuff too and looks nice. However when it gets windy it gets bumpy, and I personally like something a bit heavier which is not knocked all over the place.

The TB20 is a great aircraft and a logical upgrade from a PA28. Costs are reasonable, fuel burn is reasonable (certainly sub 50 lph at 23/2300 @ 145kts TAS) and it shifts along nicely. I did Oxford to Edinburgh in one in 2hr 20 mins which point to point is quicker than using CAT.

Just my view!

EGHS

Of course I agree about the TB20, having had one since 2002.

It has no vices or dodgy behaviour and is an easy upgrade for anybody who is able to make the metal transition to flying at 140-150kt over 100kt (planning ahead, basically).

MPG-wise, it is about the same as any other IFR tourer with a similar cockpit volume. There is no free lunch in aerodynamics…

Maintenance is no problem. The airframe is conventional, but as with all airframes if you get one which has been long term neglected (a fairly common feature in GA “maintenance” everywhere) then you will pay for that because airframe parts tend to be manufacturer-specific and tend to be expensive no matter whose they are. The rest of the plane is American – engine and avionics are whatever they will be on a C182 or whatever of a similar era. Even a complete muppet can work on the engine. The landing gear is a simple and reliable mechanism but as with all retractables you don’t want to neglect it; it has to be kept greased.

If you can, get the post-2000 one (the GT) which has many small improvements.

Administrator
Shoreham EGKA, United Kingdom

If the OP is looking for numbers….I climb to say 10,000’ at 16.5GPH for about 20mins then cruise at ROP-80dF WOT / 2600rpm burning 10.8GPH for 160kts TAS then descend at 750fpm at up to 20" burning about 6,5GPH….I’ve never bothered with MPG calcs….

If you have a friend following in a TB20 you can be at the bar and halfway through a coldie waiting for them to turn up!

Last Edited by AnthonyQ at 27 Sep 12:22
YPJT, United Arab Emirates

Suggestions? Thoughts?

I would say, if you don’t have the money to purchase a “real” modern aircraft (Cirrus, Diamond etc), then the only viable option is a Cessna of some kind. All older types will be a waste of money just keeping them “air worthy”. That is unless it is Annex II or experimental (restored), or you have some other special interest in keeping the aircraft airworthy.

I have heard lots of bad things about the Sport Cruiser also. I don’t remember exactly what, but it was something about usable weight, C of G, fuel or something that makes it less desirable as an “all round” air craft with two on board. The Aquila A211 is apparently a vastly superior aircraft in every respect, and was chosen by a club here after considering all other similar aircraft. It’s also MTOW 750 kg and should be much more stable in windy conditions.

The elephant is the circulation
ENVA ENOP ENMO, Norway
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