1200 nm Every 2 wks.

[weilke]

PA-30-C Turbo has a cruise speed of 209 kts. (according to Risingup.com)

209 (IAS) @ 18,000 = 296 TAS = 4 hours.
Rate of Climb = 1290 fpm, therefore the climb to 18,000 from 6,000 would take 12 minutes.(12,000' / 1,000 fpm)​

​

Those numbers sound overly optimistic. VNE is 206kt IAS iirc.

 

[mn_voyageur]

What is "iirc"?

 

[Clark1961]

What is "iirc"?

if I recall correctly

As a I side note, it seems risingup reports TAS. I know for certain that the cruise speed they report for my turbo Dakota is the actual maximum level flight speed (TAS). No one can actually use that speed 'cause it'll cook the engine.

Use risingup with caution.

 

[weilke]

What is "iirc"?

Afaik, its internet lingo for 'if I remember correctly', bwthdik

 

[Ted]

Rising up is optimistic. Take those numbers with a grain of salt. Preferably with a pound of it. I would suspect the best you'll see is 200 KTAS, period, and I'd still suspect that to be optimistic. That's also at altitude with turbos.

So, the best you'd likely get would be 6 hours of flight time, which probably means more like 6.5 and about 7-7.5 hours with a stop.

Your rate of climb will probably be lower, and if you climb at best climb you may also find your CHTs cooking. I wouldn't climb with a turbo engine at full power unless I had reason good to - generally something like a mountain that I wanted to get over. So, let's say you do a cruise climb at 26", 2600 RPM, and whatever required mixture to keep heads cool, and do 800 fpm. So that'll be more like 25-30 minutes to get up to 17,000 ft heading eastbound, and then you're on O2 for the duration of your trip. That seems a bit more realistic to me.

So it's a full day, but I've done longer.

 

[flyingcheesehead]

So, you plan 157 kts @6000 18gph. Is this considered cruise speed? 75%? 65%?

I think that's 157 true at 6000, or about 140 indicated - That's actually where I started from with my numbers, adjusting 140 indicated for true airspeeds at various altitudes.

Bryon, is 18gph your actual burn in cruise? That number sounds higher than I've ever heard for a non-Miller Twinkie.

The reason for asking is that a turbo becomes a game changer on my 1200 nm hops. If we eliminate the wind component, does the following work?

157 (IAS) @ 6,000 = 7.6 (Probably longer, since this does not include the CFIT in WV)
157 (IAS) @ 12,000 = 197 TAS = 6.1
157 (IAS) @ 18,000 = 222 TAS = 5.4​

Start with the IAS of 140 (working backwards from the true of 157 at 6,000 as discussed earlier). You'd be looking at numbers more like 174 at 12,000 or 190 at 18,000.

So, now let's make assumptions: (I foresee some critical replies.)

PA-30-C Turbo has a cruise speed of 209 kts. (according to Risingup.com)
209 (IAS) @ 18,000 = 296 TAS = 4 hours.
Rate of Climb = 1290 fpm, therefore the climb to 18,000 from 6,000 would take 12 minutes.(12,000' / 1,000 fpm)​

I am certain that I am making a few beginner mistakes. I just want to know what they are.

Again, the Turbo gets 209 knots *true* at altitude. Vne is 230 mph or 200 knots indicated. (The "A" and B model PA-30's are mph airplanes, the PA-30C and PA-39 are knots airplanes.)

So, again, to get that 209 knots you'd need to be all the way up at FL250 assuming that 140 indicated number. With KLBB at about 3300 feet and KCPK pretty much at sea level, assuming an average climb of 1000 fpm at 120 knots you'd spend a hair under 22 minutes getting to altitude. Average descent of 500fpm and 180 knots would take 50 minutes. No-wind cruise would be 5 hours and 9 minutes for a total of 6 hours 21 minutes. Assuming 22gph for the climb and 16gph for cruise and descent, you'd burn 104 gallons - So you wouldn't need a fuel stop if you had a bird with tip tanks, which almost all of the turbo'd ones do.

An aside on tanks here: Normally-aspirated Twinkies came from the factory with a 90-gallon fuel system (60 mains, 30 aux), but there was an option for tip tanks to increase it to 120 gallons. Twinkies that came turbo'd from the factory had the tip tanks standard (tip tanks also raise your MGW by 125 lbs, but any weight over the standard 3600lb MGW must be fuel in the tips). There was also the option to add the turbos aftermarket, so you may find the unusual Turbo that does NOT have tip tanks if someone added turbos to one that was normally aspirated and did not have tip tanks from the factory.

For your use, you will want more than the 90-gallon fuel system. Most likely, you'll find a nice bird with the 120 gallon system with tip tanks. However, there have also been a number of tank STC's over the years. Here's a quick run-down of the possible tankage on a Twin Comanche:

* 60 gallon factory mains - On every Twin Comanche
* 30 gallon factory aux - On every Twin Comanche (optional on the PA24 singles)
* 30 gallon tip tanks - Factory option, later available aftermarket from Brittain, still available aftermarket today from J. L. Osborne.
* 38 gallon wet wings - J. W. Miller. No longer available today, like the rest of the Miller conversions, sadly.
* 20 gallon Nacelle tanks - Still available today from Webco Aircraft
* 40 gallon nacelle tanks - STC owned by "CAPCO" issued in 1993, but no sign of them on the web, so presumably no longer available.
* 20? gallon baggage compartment tank.

The most I've ever seen on one plane (not counting ferry tanks) was the factory + tips + Miller wet wings for 158 gallons or nearly 10 hours. Today, with the right amount of money, you could take a 90-gallon bird up to 140 gallons (Osborne tips + Webco nacelles). The most possible without ferry tanks is 218 (60 main, 30 aux, 30 tip, 38 Miller wet wing, 40 Capco nacelle, 20 baggage), but it's doubtful such a plane exists - The only reason to have one like that is if you want to fly it to Hawaii on a regular basis - Otherwise, there's no reason for a bird with a 13.6 hour endurance.

Back to the trip: Today, you'd have an average of a 66-knot tailwind at altitude, so your cruise would be reduced to 4 hours, 3 minutes for a total flight time of 6 hours, 15 minutes. In reality, I'd expect it to be a bit longer - I think that 209/214 speed number is a bit optimistic. Still, knock 10-15 knots off and you still have a pretty good door-to-door time eastbound.

Westbound, however... Plugging my numbers for cruise speed into ForeFlight (which doesn't account for time-to-climb or time-to-descend) you'd be looking at a flight time between 8:37 and 8:47 no matter what altitude you fly at, making it probably more efficient to stay low (less climb, less climb fuel burn!) in which case the turbos are kind of a waste - They ain't free to maintain by a long shot. You'd also need a fuel stop unless you have a plane with a lot of tanks and more tolerance for sitting in an airplane for one stretch than I've got!

That's all I've got for today.

 

[gismo]

I think that's 157 true at 6000, or about 140 indicated - That's actually where I started from with my numbers, adjusting 140 indicated for true airspeeds at various altitudes.

Bryon, is 18gph your actual burn in cruise? That number sounds higher than I've ever heard for a non-Miller Twinkie.



Start with the IAS of 140 (working backwards from the true of 157 at 6,000 as discussed earlier). You'd be looking at numbers more like 174 at 12,000 or 190 at 18,000.

That matches my expectations of a turbo twinkie, but I've never verified that myself (my only Twin Commanche time was in a NA version).

Back to the trip: Today, you'd have an average of a 66-knot tailwind at altitude, so your cruise would be reduced to 4 hours, 3 minutes for a total flight time of 6 hours, 15 minutes. In reality, I'd expect it to be a bit longer - I think that 209/214 speed number is a bit optimistic. Still, knock 10-15 knots off and you still have a pretty good door-to-door time eastbound.

Westbound, however... you'd be looking at a flight time between 8:37 and 8:47 no matter what altitude you fly at, making it probably more efficient to stay low (less climb, less climb fuel burn!) in which case the turbos are kind of a waste - They ain't free to maintain by a long shot. You'd also need a fuel stop unless you have a plane with a lot of tanks and more tolerance for sitting in an airplane for one stretch than I've got!

I think you'd need more than a tolerance for sitting 9 hours at a stretch. That kind of flight would be mind numbing and would likely seriously impair your ability to perform well, especially if there was any kind of weather along the way. If you started well rested it would be plausible but I'd hate to see someone do that on a regular basis without at least a quick stop along the way.

 

[Aztec Driver]

So, you plan 157 kts @6000 18gph. Is this considered cruise speed? 75%? 65%?

Since I would not fly at 6,000', do I adjust the 157 based upon TAS vs IAS?

The reason for asking is that a turbo becomes a game changer on my 1200 nm hops. If we eliminate the wind component, does the following work?

157 (IAS) @ 6,000 = 7.6 (Probably longer, since this does not include the CFIT in WV)
157 (IAS) @ 12,000 = 197 TAS = 6.1
157 (IAS) @ 18,000 = 222 TAS = 5.4​

So, now let's make assumptions: (I foresee some critical replies.)

PA-30-C Turbo has a cruise speed of 209 kts. (according to Risingup.com)
209 (IAS) @ 18,000 = 296 TAS = 4 hours.
Rate of Climb = 1290 fpm, therefore the climb to 18,000 from 6,000 would take 12 minutes.(12,000' / 1,000 fpm)​

I am certain that I am making a few beginner mistakes. I just want to know what they are.

MarkN

157 KTAS
Its actually closer to 17 gph at that altitude and speed. I tend to err on the rich side, although the new EGT gauges run pretty close to that. I tend to burn at the rich side of 65%, but at 75% I can eek out around 164 KTAS. That just burns more fuel and only saves a few minutes of time.

If it is only speed you are concerned with, and not payload, there are many faster single engine aircraft out there. Turboed Mooneys and Bonanzas would fit the bill nicely, but you wouldn't have much option of taking several people with you.
Plugging your flight into AOPA's flight planner with my profile nets a direct flight of 9:16 with 170 gallons used. I would need two stops for that for fuel and a gurney to wheel me into the emergency room for psychiatric observation at the destination.

 

[Aztec Driver]

I think that's 157 true at 6000, or about 140 indicated - That's actually where I started from with my numbers, adjusting 140 indicated for true airspeeds at various altitudes.

Bryon, is 18gph your actual burn in cruise? That number sounds higher than I've ever heard for a non-Miller Twinkie.

Its actually around 17, but I tend to keep it a little rich for cooling. My partner has the opposite tendency, and it tends to burn out exhaust valves. The new EGT gauges will help, I hope.

 

[TangoWhiskey]

While that trip would be fun occasionally, I would think it would turn into drudgery and certainly be a lot more expensive and time consuming than taking commercial. A flight of that length, considering engine reserves and maintenance reserves, would likely be 3 times the cost of a commercial flight, take at least 2 times the time of a commercial flight, and be exhausting by the time it is finished, especially if there is any weather issues to be dealt with. (this is the realist in me talking)
Now me? I am insane enough to do it, if I had the money to justify it. my Twinkie would do the job reasonably well, but I would definitely have to get an autopilot to ease the load. (Anybody have a spare 30K they want to get rid of?)

And that could make it tough to write the expenses off as a business expense, if the OP was planning to do so.

Once you've established that you're engaged in a trade or business, the next hurdle is convincing the IRS that your aircraft operating expenses are "ordinary and necessary." Never forget that if you take deductions for aircraft expenses, you have the burden of proving your entitlement to the deductions taken.

So how can you prove your aircraft expenses are "ordinary and necessary"? First, let's take a look at what qualifies under the law as an "ordinary" expense. Generally, the courts have held that an expense is ordinary if it involves a common and accepted business practice. In one decision, the court made it quite clear that they understood the use of private aircraft by executives to be a common practice, and therefore capable of qualifying as an ordinary expense. In this case, the court states that: "n this day and age, there is no doubt that the use of private airplanes by executives in charge of large projects is common practice." (See p.4, Marshall v. Commissioner of Internal Revenue, T.C. Memo 1992-65.)

A more difficult challenge is proving that your aircraft expenses are "necessary." The courts have said that an expense must be appropriate and helpful for your business in order to be deductible as a necessary expense. In order to show that your aircraft was "appropriate and helpful" you'll have to be able to show how it provides you with direct access to your destinations, flexible scheduling, fewer overnight stays, etc. Oftentimes, this will be the most critical test of your aircraft expenses deductibility.

<snip>

Finally, you must be prepared to defend against the IRS charge that your expenses were unreasonable. The IRS will often base this charge on comparisons between the cost of commercial airfare and the cost of using a private aircraft. Unfortunately, there is no hard and fast rule for determining whether your aircraft expenses are reasonable. Needless to say, it is enormously helpful to be able to show the economic benefit obtained from your use of a private aircraft. Again, that economic benefit can be measured in terms of time saved or economic gain from a particular trip in which you used a private aircraft. It is very important to note that in two recent cases the courts have made it clear that when determining whether aircraft expenses are ordinary and necessary, the IRS should not take into consideration any depreciation deductions. (See p.4, Marshall, and p.5, Noyce v. Commissioner, 97 T.C. No. 46 (1991). This is helpful in proving the reasonableness of your aircraft expenses, since depreciation is often a large part of your total deduction. Good record keeping for each business trip will go a long way in demonstrating how the use of a private aircraft helped to benefit your business by allowing for expanded customer contacts and flexibility in scheduling.

 

[mn_voyageur]

As for tax reasons, I'll leave that to my CPA. When most of your customers are calling you and asking if you can be on the next flight, having my own a/c makes the answer automatic.

All they have to do is look at how many times I am flying on the same day I purchased the ticket. (Or first flight out in the morning, if I can't make it to the airport.)

Last year, I was charged $1,500 for a one-way coach ticket. So, I can pay United $1,500 for a flight and write off the whole thing? I am certain that United likes that idea!

This may be a vicious rumor, but I was told that TSA was going to be tougher on people buying and flying on the same day. If that's true, then I am really going to get to know these guys!

MarkN

 

[weilke]

This may be a vicious rumor, but I was told that TSA was going to be tougher on people buying and flying on the same day. If that's true, then I am really going to get to know these guys!

It's not a vicious rumor, its official policy. Same-day cash purchase gets you a SSSSSSS on the margin of the boarding-pass which makes you a 'selectee' and as such subject to additional security theater (unless of course you have your underpants full of ignition cord, then you just get waved through.....).


One plane that crossed my mind that may work for you is a Columbia 300. Imho, they are a great value right now. They are relatively light (1100-1200lbs UL), carry 104gal of fuel, are fast and can be had for less than crazy amounts of money. Most of them still have the UpSat avionics and may require a 480 or 430W upgrade. It is basically a 350 with steam gauges + HSI + Stec55x. For some reason, they are actually faster (at least on paper) than the 350.

 

[Ted]

Westbound, however... Plugging my numbers for cruise speed into ForeFlight (which doesn't account for time-to-climb or time-to-descend) you'd be looking at a flight time between 8:37 and 8:47 no matter what altitude you fly at, making it probably more efficient to stay low (less climb, less climb fuel burn!) in which case the turbos are kind of a waste - They ain't free to maintain by a long shot. You'd also need a fuel stop unless you have a plane with a lot of tanks and more tolerance for sitting in an airplane for one stretch than I've got!

That's going to be the case with any turbo aircraft. On no wind or tailwind days, the turbos are a benefit. On headwind days, the likely won't be. But what the turbos give you is the option of going high and getting better TAS/tailwinds than you otherwise would. If you're doing long trips like that, it's worth it. I now wish I'd bought a turbo Aztec, after doing about 325 hours of cross-country flight in the past year.

 

[mn_voyageur]

When you look at the Winds Aloft I have always wondered at what point a turbo becomes cost effective.

Looking at the image of 12K, I have often wondered if it would be worth flying NW before heading West. (Working up and around the stronger winds.) When I flew the NA 182, I never thought of flying low since I had to climb over the mountains.

Also, below FL180 on an Instrument Flight Plan, I would be flying the Odd heading East and Even flying West. Once you pass FL180, is this still the same?

MarkN

 

[flyingcheesehead]

That's going to be the case with any turbo aircraft. On no wind or tailwind days, the turbos are a benefit. On headwind days, the likely won't be.

I think it depends on the aircraft. On a faster plane, say a 421, the typical headwinds will be less of a percentage of the true airspeeds the plane is capable of at those altitudes, thus making it more likely that the 421 would do better up high than the Twinkie.

 

[flyingcheesehead]

Also, below FL180 on an Instrument Flight Plan, I would be flying the Odd heading East and Even flying West. Once you pass FL180, is this still the same?

Yes, for the altitudes you'll be operating at:

(2) When operating at or above 18,000 feet MSL but below flight level 290, and—

(i) On a magnetic course of zero degrees through 179 degrees, any odd flight level (such as 190, 210, or 230); or

(ii) On a magnetic course of 180 degrees through 359 degrees, any even flight level (such as 180, 200, or 220).

Though the Turbo Twinkie can supposedly make it to 30,000 feet it'd take you forever to get there and there wouldn't be much benefit as your IAS and TAS would likely have dropped significantly by then. In addition, RVSM airspace starts at FL290 and the Twinkie won't be RVSM certified. So, the above rule applies as high has you'd actually fly the Turbo Twinkie.

 

[Ted]

I think it depends on the aircraft. On a faster plane, say a 421, the typical headwinds will be less of a percentage of the true airspeeds the plane is capable of at those altitudes, thus making it more likely that the 421 would do better up high than the Twinkie.

That makes sense for faster aircraft, but I seem to recall Tony saying the 421 was generally about a 200 kt airplane. If we're saying the Twinkie is a 200 kt airplane (which I still think is optimistic, but I'll go with it), then 200 kts is equal to 200 kts last I checked. But today is a Tuesday, and I never could get the hang of Tuesdays.

Now if you'd said Aerostar (doesn't the fastest one do somewhere in the mid 200s?) then that makes more sense. Of course it also depends on what the airspeed vs. altitude is, a data point that I don't have. I think the argument generally makes more sense when you get into the turbine aircraft where (at least per my understanding, which may be wrong) you not only go faster up high, but burn less fuel doing it. Zero turbine time here, so I don't know.

To me the bigger issue is one of pressurization. I don't know how much you really want to be sucking on O2 for hours straight in the Twinkie. It sure is nice to just have the environment around you conditioned to be more hospitable.

 

[mn_voyageur]

Without even asking, I get two answers. The bigger of the two was the advantage of a Meridian over a Mirage. I realized one was a turboprop, but did not realize they were more fuel efficient at altitude.

I have often wondered why Piper chose to name a plane an "optical illusion." (It looks like you are going REALLY fast, but you're not.)

Is there a point at which a turbo is beneficial? How long do turbos last, if they are properly fed and cared for? How much to overhaul?

MarkN

 

[Ted]

I have often wondered why Piper chose to name a plane an "optical illusion." (It looks like you are going REALLY fast, but you're not.)

Don't tell Andrew that.

Is there a point at which a turbo is beneficial? How long do turbos last, if they are properly fed and cared for? How much to overhaul?

I haven't done the math on it, but my SWAG is that if you routinely do trips of about 600 nm or more that turbos will give you an advantage for standard planes, or if you live in an environment where you need to operate routinely at altitudes above 10,000 ft. I say that because 10,000 ft seems to be the point where most naturally aspirated engines are really starting to gasp for more, and that when you're making trips of that distance it actually makes sense to climb high and take advantage of what the turbos will do for you, and take advantage of tailwinds.

Given the fact that you're looking at routine 1200 nm trips each way, you definitely qualify as someone who would benefit from turbos. For trips that distance I'd say you could justify a P-Baron, but whether or not you'd want to pay for one is another question.

 

[Areeda]

When you look at the Winds Aloft I have always wondered at what point a turbo becomes cost effective.

Here's a look at a flight from LBB to CPK in my NA SR22 at different altitudes with tonight's winds. Note that full fuel is 81 gal so even the most optimistic one would have one stop.

And the opposite direction:

 

[gprellwitz]

Y'know, given the above, I'd say to go ahead and get that TR182. It's familiar enough to keep you safe, but has enough additional capability to help you learn more. It's comfortable (essential on such long trips), capable, and shouldn't be too tough to insure since you've already got some 182 time. Use it for a year or two, fly the heck out of it, and then sell it to Grant and Leslie. They need one, even if they won't admit it to themselves.

I agree that the comfort factor is nothing to be sneezed at. 8 hours in a comfortable aircraft easily beats 6 hours in an uncomfortable one. And, as you know, the 182's are comfortable aircraft! And we freely admit that we want one and would use one. Just not that we need one, which is what would be required to make us go further into debt!

 

[Erice]

Here's a look at a flight from LBB to CPK in my NA SR22 at different altitudes with tonight's winds. Note that full fuel is 81 gal so even the most optimistic one would have one stop.

What software/website did you use to generate this Optimized Altitudes table? It looks very useful.

 

[Areeda]

What software/website did you use to generate this Optimized Altitudes table? It looks very useful.

That's Jepp FliteStar.

Stand alone prices are too high IMHO, but packaged with our CONUS JeppView for the MFD it is very reasonable.

Joe

 

[mn_voyageur]

I was going to ask the very same question. Currently, I use Aeroplanner.com and have to punch in different altitudes.

 

[TangoWhiskey]

I was going to ask the very same question. Currently, I use Aeroplanner.com and have to punch in different altitudes.

Try www.WeatherMeister.com; it does a great job, and shows the same info.

Works well on the iPhone, too (optimized for mobile if you browse to it from your phone).

 

[flyingcheesehead]

I haven't done the math on it, but my SWAG is that if you routinely do trips of about 600 nm or more that turbos will give you an advantage for standard planes, or if you live in an environment where you need to operate routinely at altitudes above 10,000 ft. I say that because 10,000 ft seems to be the point where most naturally aspirated engines are really starting to gasp for more, and that when you're making trips of that distance it actually makes sense to climb high and take advantage of what the turbos will do for you, and take advantage of tailwinds.

Given the fact that you're looking at routine 1200 nm trips each way, you definitely qualify as someone who would benefit from turbos. For trips that distance I'd say you could justify a P-Baron, but whether or not you'd want to pay for one is another question.

Ted,

What you say is spot-on for piston engines with turbonormalizers or turbochargers, but I got the impression from Mark's post that he was actually asking about turboprops, not turbocharged piston-powered planes (note the mention of the Meridian).

Mark: Turboprops (an entirely different beast, of course, basically a jet engine with a prop instead of a fan) are generally more expensive to purchase, guzzle fuel like you wouldn't believe, provide a lot more power, cost orders of magnitude more to overhaul but last twice as long, and are generally more reliable. But I've never owned one... Sigh.

 

[Ted]

Ted,

What you say is spot-on for piston engines with turbonormalizers or turbochargers, but I got the impression from Mark's post that he was actually asking about turboprops, not turbocharged piston-powered planes (note the mention of the Meridian).

Pretty sure he was talking about piston aircraft. The turbines were just a side discussion.

Mark: Turboprops (an entirely different beast, of course, basically a jet engine with a prop instead of a fan) are generally more expensive to purchase, guzzle fuel like you wouldn't believe, provide a lot more power, cost orders of magnitude more to overhaul but last twice as long, and are generally more reliable. But I've never owned one... Sigh.

The numbers get pretty interesting when you start looking at them for use over long term and high duty cycle. My instructor has a Navajo (PA-31-310) and he also flies a Cheyenne (PA-31T-620) for the guy who used to own my Aztec. Looking strictly at the engines, it's something like a $250,000 overhaul every 6000 hours for the PT-6s in the Cheyenne per side. The TIO-540-A2Cs are about $45,000/side on the Navajo, and that's every 1800 hours. So over the course of 6000 hours, you'll spend $500,000 on Cheyenne engines and $300,000 on Navajo engines.

But the Cheyenne files for 230 KTAS (and normally does a bit better than that) and the Navajo files for 180 KTAS (and normally does about that on the nose), and has easy access to a wider range of altitudes to take better advantage of winds on long trips. Ok, so the Cheyenne may still be a bit more per mile. But then compare that to a P-Navajo and it's pretty clear that $50,000 overhauls a side for the TIGO-541s every 1200 hours actually puts you behind the Cheyenne, since you're spending the same money and going slower. This doesn't even take into account any issues that occur on the way to putting all those hours in.

The big piston twins are interesting in that regard, as they're more affordable to purchase and operate in the short term, but in the long term probably end up costing you about the same if not more than a comparable turbine. The piston twins are also easier to get insurance on and have certain advantages depending on what you're doing. Plus I like pistons, so I'll keep on drooling over P-Navajos and 421s. I must be a glutton for punnishment. Then again, I think the Aztec is reliable.

 

[Trapper John]

All good points, but you also need to compare specific fuel consumption (lb/hp-hr) of turbines and pistons, factor in the difference in fuel cost, and get a cost per lb of thrust (or hp, if you like) to really complete the analysis.


Trapper John

 

[Ted]

All good points, but you also need to compare specific fuel consumption (lb/hp-hr) of turbines and pistons, factor in the difference in fuel cost, and get a cost per lb of thrust (or hp, if you like) to really complete the analysis.

Turbines will generally burn have a higher SFC than pistons (in fact virtually always), but compared to the bigger turbocharged engines, not as much as you'd think.

The Cheyenne burns about 70 gph going 230 KTAS (per my memory... I think at 230 it actually burns a bit less). The Navajo burns 40 gph going 180 KTAS. Then Jet A is a bit cheaper than 100LL in a lot of places, and if you pick your fuel stops well you can really get it pretty cheap in some places (although the same can be said for 100LL). Point is, it doesn't turn out to be as much more as it seems on the surface.

Now I'm waiting for the Cheyenne to pop up on FlightAware - it's coming home from Texas today. Looking at the winds, they should have some pretty impressive ground speeds.

 

[Trapper John]

Turbines will generally burn have a higher SFC than pistons (in fact virtually always), but compared to the bigger turbocharged engines, not as much as you'd think.

Yep, turbine fuel specifics are worse. Plus, the fuel unit weight is higher, so you get a double whammy there. Probably explains why Rutan's Voyager used pistons...

I think that's why the single engine turbine conversions don't pan out so well. The turbine engine weight savings is more than cancelled out by the required fuel (quantity and unit weight), so without a gross weight increase to account for the extra fuel, it's a losing proposition. Plus, having to climb to get the fuel burn down eats into the block speeds, so the net gain really isn't there.

But turbines are really cool, so sometimes that's reason enough right there...


Trapper John

 

[Ted]

Yep, turbine fuel specifics are worse. Plus, the fuel unit weight is higher, so you get a double whammy there. Probably explains why Rutan's Voyager used pistons...

I think that's why the single engine turbine conversions don't pan out so well. The turbine engine weight savings is more than cancelled out by the required fuel (quantity and unit weight), so without a gross weight increase to account for the extra fuel, it's a losing proposition. Plus, having to climb to get the fuel burn down eats into the block speeds, so the net gain really isn't there.

But turbines are really cool, so sometimes that's reason enough right there...

It seems to have worked out pretty well for the Malibus that got the PT-6 conversion, essentially making it a Meridian. That's been a very popular STC. The Bonanza and Lance turbines have been less popular. The Rolls Royce turbine in the P210 is also a very nice conversion, and the few times I've been to O&N they seem to have no shortage of business there. Their 340 turbine conversion looks pretty nice, too.

I agree that in general it can be a tough sell. However if done right, it can be a very attractive option. Those little Rolls Royce turbines can be pretty nifty for conversion.

 

[weilke]

Turbine cost tend to be lower if you listen to people who sell turbines :smile: The part they tend to omit are those little things in between, the nozzle-cleanings compressor washes, hot-sections, mandatory prop-overhauls at 15k a pop, the capital cost to finance 2 turbines and the fact that changing a lightbulb costs $5000 etc.

 

[Trapper John]

Good point on the Malibu conversions. Maybe the Malibu conversion works because it's already optimized for higher alititude?

The Rolls turbine is what used to be the Allison B-20, right?


Trapper John

 

[Ted]

Good point on the Malibu conversions. Maybe the Malibu conversion works because it's already optimized for higher alititude?

That's what I was trying to get at. Piston engines, turbocharged or not, are more efficient than turbines but tend to make less power, especially at altitude. Flying my Aztec around under 5,000 MSL is great, flying it at 10,000 MSL is not. The Navajo extends the good range up to around 15,000. From what I hear from people who fly pressurized piston twins, it seems that the low flight levels are the extent of the practical operating range. The airframe is still designed for high altitude flight. Add an engine that's happy at altitude and you have a nicer airframe, but then you have to convince people to dump that kind of money into an old plane that has now been modified from its original condition and may be more reliable for it, but then have less support. The fuel seems to be the biggest issue, since you want enough fuel to have a reasonable time up at that altitude you spent a while getting to.

The Rolls turbine is what used to be the Allison B-20, right?

Allison 250, I think. It's a nifty little unit - packs a lot of power in a small package. I think the TBOs are relatively low (compared to a PT-6), but I'm a piston guy, not a turbine guy. Getting between 450 and 715 hp out of a little 200 or 225 lb engine is hard to beat, though.

 

[gismo]

Yes, for the altitudes you'll be operating at:



Though the Turbo Twinkie can supposedly make it to 30,000 feet it'd take you forever to get there and there wouldn't be much benefit as your IAS and TAS would likely have dropped significantly by then. In addition, RVSM airspace starts at FL290 and the Twinkie won't be RVSM certified. So, the above rule applies as high has you'd actually fly the Turbo Twinkie.

IMO anyone would be absolutely nuts to regularly operate a Turbo Twin Comanche anywhere near that high. Even FL250 is dicey because if there's any issue with the O2 you're not likely to live through it. In a non-pressurized plane I wouldn't plan on flying very deep into the flight levels.

 

[Ted]

IMO anyone would be absolutely nuts to regularly operate a Turbo Twin Comanche anywhere near that high. Even FL250 is dicey because if there's any issue with the O2 you're not likely to live through it. In a non-pressurized plane I wouldn't plan on flying very deep into the flight levels.

+1...

 

[mn_voyageur]

I'll tell the wife to scratch turboprops off the list. (Since she's not here to defend herself!)

Flying my Aztec around under 5,000 MSL is great, flying it at 10,000 MSL is not. The Navajo extends the good range up to around 15,000. From what I hear from people who fly pressurized piston twins, it seems that the low flight levels are the extent of the practical operating range. The airframe is still designed for high altitude flight.

Does this mean that I should be looking at the P-Baron? (Or another pressurized piston.)

 

[gismo]

I'll tell the wife to scratch turboprops off the list. (Since she's not here to defend herself!)



Does this mean that I should be looking at the P-Baron? (Or another pressurized piston.)

If you want to cruise in the flight levels, yes. OTOH, you should be able to accomplish your cross Country requirements while staying below 18,000 MSL and there things aren't so human unfriendly. The problem with a pressurized airplane is that insurers typically want a fair amount of experience for that level of equipment.

 

[Areeda]

Mark,

I noted from an earlier post you have 230 hrs and working on your instrument rating. I didn't see anything about your purchase and operating budget.

Not to be a wet blanket here but it seems like we discussing options that may be outside your experience and budget.

If you have an unlimited budget and are willing to train extensively to get insurance, I have a whole hour in the left seat of my friend's Cessna Mustang. It would be perfect but frickin expensive.

Joe

 

[Ted]

I'll tell the wife to scratch turboprops off the list. (Since she's not here to defend herself!)

You aren't insurable in one at this point anyway, so it's really a non-issue.

Does this mean that I should be looking at the P-Baron? (Or another pressurized piston.)

Maybe once you get another couple hundred hours, preferably of multi time.

Right now, you are completely uninsurable in any pressurized aircraft, period. The insurance companies will laugh you out the door. Once you get your instrument rating, though, you will be insurable in one of the "lower end" twins. The Aztec, 310, Twinkie, Baron, all come to mind as planes that you would be insurable in but with probably about 25-50 hours of dual. And don't forget your multi rating (make it a commercial multi while you're at it).

I got insurance on my Aztec at 225 TT with 3 MEL and an instrument rating. I needed 25 hours of dual (which I got) and have been flying the thing ever since. Now, at 650 TT and 350 MEL, I'm at the point where I'm insurable in pressurized piston twins. I'd have to go to SimCom or Flight Safety for a week to get the training. I'm not sure how much dual I'd need.

I don't know what your operating budget is. I'm guessing here that you've got a sizable amount of money that you can spend on this. An Aztec costs about $200/hr to operate wet (at least mine does), and I'd suspect that the 310 and 55 Baron are pretty similar. A P-Baron or 340 seems to be more like $300-350/hr from what I can tell, and $400-500/hr when you get into the 414 and 421s (with the 414s being a bit cheaper). A P-Baron or 340 would do the job very well for you.

Get the training and get a light twin that you like (my pick would be a 55 Baron if it meets your capacity needs). The insurance mins I find are not a bad number of hours to get of dual before you solo the thing. Fly that for a couple hundred hours. If you feel the need to upgrade, then you'll be insurable in the upgraded plane. Only you know what your budget is, but make sure to plan accordingly. You can spend a lot of money on your plane the first year you have it, especially if you're like me and want everything working properly. Understand that this is normal, and the costs will go down after the first year.