Twin piston or single turboprop?
- Thread starter Insane
- Start date
JimNtexas
Pattern Altitude
- Joined
- Dec 21, 2006
- Messages
- 2,259
- Location
- Austin, Texas
- Display Name
Display name:
Jim - In Texas!
Wouldn't a single piston engine with a whole plane parachute be the best of all worlds?
OK, I'm sorry, I couldn't resist!
OK, I'm sorry, I couldn't resist!
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,019
- Display Name
Display name:
iFlyNothing
The interesting part with this question is that the two planes tend to handle different missions better. Turboprop singles are faster than piston twins. Meridian is what, 250 KTAS? TBM 300+? That's a lot faster than the 165-220 that you'll get from piston twins. The cabins on the turboprop singles are also better than a 310, worse than a 421.
Then there's the price. A nice 421C will run you $400k (you could get a KA90 within that price that will go about the same speed as the 421). The cheapest I've seen a used turboprop for is around $1M. That's a lot of capital difference for initial purchase.
I'm not sure that many people who are able to and interested in affording a turboprop single will really look into a piston twin in comparison unless their missions include shorter trips and need a bigger cabin. More likely would be looking at a turboprop single or turboprop twin.
FWIW, I would love a TBM if it was donated. 330 KTAS instead of the 185 we get now in the 310 would make my missions doable in one day instead of two. It would need the crew door option.
Then there's the price. A nice 421C will run you $400k (you could get a KA90 within that price that will go about the same speed as the 421). The cheapest I've seen a used turboprop for is around $1M. That's a lot of capital difference for initial purchase.
I'm not sure that many people who are able to and interested in affording a turboprop single will really look into a piston twin in comparison unless their missions include shorter trips and need a bigger cabin. More likely would be looking at a turboprop single or turboprop twin.
FWIW, I would love a TBM if it was donated. 330 KTAS instead of the 185 we get now in the 310 would make my missions doable in one day instead of two. It would need the crew door option.
flyingcheesehead
Taxi to Parking
Yep... And I'll do that for the purposes of practicing an emergency descent. But I would never do it with non-pilot pax because they have no idea if their ears can handle it, and they generally won't. They probably also don't think that the fact they had a cold last week is an issue until they experience their first ear block. That's not something I'm going to put passengers through, I want them to LIKE GA.
So, I plan all my descents at 500fpm and will not exceed 800 with non-pilot pax.
Wouldn't a single piston engine with a whole plane parachute be the best of all worlds?
OK, I'm sorry, I couldn't resist!
No, but it's not a bad median either.
Insane
Ejection Handle Pulled
- Joined
- Feb 26, 2014
- Messages
- 126
- Display Name
Display name:
Insane
Wouldn't a single piston engine with a whole plane parachute be the best of all worlds?
OK, I'm sorry, I couldn't resist!
Yes. Statistically a whole lot safer than a twin without all the hassle of the extra expense feeding and caring for that extra engine...
Insane
Ejection Handle Pulled
- Joined
- Feb 26, 2014
- Messages
- 126
- Display Name
Display name:
Insane
Why does that argument come up repeatedly? If you want to fly more than 200 nm in the south in summer COMFORTABLY you need a turbo because you need to be above 15,000 feet. That is high enough to be in really cool air, smooth air and high enough that you can dodge the buildups. Not high enough to fly above the weather but high enough to be able to maneuver around enough stuff. With a turbo and tubes up your nose you can comfortably fly in the high teens and have performance margin to be able to climb if needed comfortably (> 500 ft/min). Sure some NA planes can get up there, but I'm not personally going to any altitude where my best climb rate is only 100 ft/min.
If you think it is okay to bounce along sweating at 7k in your non-turbo, go ahead, enjoy, and good luck finding non-aviation minded passengers to go with you. I can't think of anything worse than a summer trip in a DA40 in the south. Been there done that. Slap a turbo on it and an oxygen system and maybe I'd consider it.
Well, in the 10 years I had my Travel Air, I came out ahead. Fuel was pretty much the same as my buddy in his 520 Bonanza, and since I had turbo normalizes, I could take advantage of altitude. The thing that tipped the scales was three times being able to precautionarily shut down an engine and fly back to an airport and execute a repair for a couple hundred dollars and continue on in a couple of hours. In a single engine plane these simple hose failures would have cost me an engine and an off airport landing, 2 survivable (although one would have been wet) and one probably not.
flyingcheesehead
Taxi to Parking
I don't think you really need to be that high. Example: Flying at 12,000 feet over Lufkin, TX in July with an OAT of 0ºC. Descending into Houston, somewhere between 4-5,000 the humidity came back with a vengeance... Yuck! But an OAT of 50-60ºF should be plenty low enough in cruise if your plane has adequate ventilation.
On the flip side, let's assume you're correct and anything below 15,000 is uncomfortable. On the Mooney, if I had a turbo I think I could probably get 1000 fpm climb average up through 15,000 while keeping the engine sufficiently cool. That'd be somewhere around 130 KIAS. It'd take about 38 nm to climb to altitude. I'm not going to descend any faster than 1000 fpm with pax (in reality, I plan on 500 and limit to 700 with non-pilot pax), and that's going to happen at 180 KIAS or greater even if I pull the power back a LOT prior to starting the descent. That means the descent is going to take 53nm. So, 90nm of our 200 is going to be spent climbing and descending. That leaves 110nm for cruise, which is going to go by in about 34 minutes at that altitude. So, we spend at least 30 minutes climbing and descending and at most 34 minutes in cruise, meaning the pax are gonna be uncomfortable for half the flight anyway.
Do the flight at 10,000 and there are plenty of normally aspirated birds that'll get there plenty fast. I can climb to 10,000 in under 10 minutes, and I would imagine that most of the planes in the ~300hp class can. If you're flying an Arrow or other 200hp-class airplane, a turbo would certainly help. But again, unless you're going far enough to make the climb worthwhile, the turbo is useless. If you're only going 100nm, even in the south in the summer a turbo isn't going to do you any good.
Sorry, I just had to laugh when I read those in the same sentence.
Someone was working on a supercharger STC for it a couple years ago. I'll have to see how that's doing. Unfortunately it still won't be able to go above the 16,300 foot ceiling Diamond placed on it, but it'll get there faster and cruise faster.
A better option for a DA40 in the south would be Premier's air conditioning STC.
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,019
- Display Name
Display name:
iFlyNothing
Dav8or
Final Approach
Just a point of reference in this debate- Fedex flies a fleet of 208 Caravans and not any type of piston twin. Obviously they find that cost of ownership, operation and safety superior. They also can haul more. Another point of reference is the ag business, where people have replaced their pistons with turbines. Clearly there must be a reliability/performance/economic equation that works in the turbine's favor.
As to the private pilot and twins vs. turbines, I think it all depends on the pilot. Is the pilot willing, or able to fly enough hours and go to enough recurrent training sessions to be safe and proficient in a twin? If the answer is no, then I would say that that pilot is better off in the single turbine. This is assuming the pilot had the means to afford either.
As to the private pilot and twins vs. turbines, I think it all depends on the pilot. Is the pilot willing, or able to fly enough hours and go to enough recurrent training sessions to be safe and proficient in a twin? If the answer is no, then I would say that that pilot is better off in the single turbine. This is assuming the pilot had the means to afford either.
Insane
Ejection Handle Pulled
- Joined
- Feb 26, 2014
- Messages
- 126
- Display Name
Display name:
Insane
Well Dave you bring up a good point. It appears that when a decision is made based purely on technical details and financial analysis then twin pistons are ruled out very rapidly. You have to WANT to fly a piston twin and make that decision based on your heart and not with your brain.
Dav8or
Final Approach
Well Dave you bring up a good point. It appears that when a decision is made based purely on technical details and financial analysis then twin pistons are ruled out very rapidly. You have to WANT to fly a piston twin and make that decision based on your heart and not with your brain.
Well, I don't know if I would go that far. There is a huge difference in cost between a piston twin and a turbine single. Many fly the twin because they can't possibly fly the turbine. For a great many private pilots, they don't fly the great numbers of hours that commercial operators do, so even though the twin may not be as cost effective in the high time, working environment, it is the best they can do and so fly it because if one can truly and honestly stay proficient, it does offer a certain degree of safety over the only other choice- the piston single that damn near all of us fly here on the bottom of the food chain.
flyingcheesehead
Taxi to Parking
That's the one. I wonder if they've sold any additional ones. There was a guy from the Diamond group who got the first one and whose airplane was used for the development and initial flight testing.
The only things I didn't like about it: 1) Can't push the throttle all the way in down low any more - Gotta be more careful on takeoffs and go-arounds, and 2) Still can't go higher than Diamond says. Because they couldn't get Diamond to cough up the data they needed to remove the ceiling limitation, they simply optimized the system for a lower altitude. It's useful for shorter flights that way too.
They are not. At this point, they still have such an advantage in capital expenditure over turbine singles that you have to fly many hours every year to make it worthwhile. The fedex 208s fly 5 nights/week several hours each night on cheap contract fuel, the equation for the individual owner who doesn't fly that much and doesn't buy enough contract fuel to make it worthwhile looks very different.
As I understand it that system wasn't able to measure up to the expectations created by the companies marketing.
There is a TAT turbonormalizer for the C177, it may be a challenge to squeeze this under the tight DA40 cowling, but it could transform that aircraft.
The best AC is a turbocharged engine and avoidance of towered airports.
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,019
- Display Name
Display name:
iFlyNothing
Keep in mind that no "modern" piston twin comes close to the size of a Caravan. You'd have to get into old radials for that.
That's what I've always said. If you don't fly a ton, keep the single.
Well Dave you bring up a good point. It appears that when a decision is made based purely on technical details and financial analysis then twin pistons are ruled out very rapidly. You have to WANT to fly a piston twin and make that decision based on your heart and not with your brain.
Incorrect. No piston singles do what most piston twins do. And turbine singles are so far out of budget and really fit a different mission that they don't make sense for many, either.
The careful throttle application is no different than for a turboprop, at least the ones I've flown. Firewall = massive overtorque. The service ceiling will be hard for an STC holder to change. I'm actually talking to him about a potential 310 application. I figure that we should be able to increase our cruise speed around 20 kts, which would be a significant time savings on our normal missions. Who knows if it will happen.
Any references or more detail regarding it not living up to expectations?
Got my plastic planes confused. There is afaik only one prototype of the DA40 with the blower and in 3 years they haven't gotten through the test program.
They sold a couple of kits in the SR22 market and the experience of the owners seems to be hit or miss. Over on beechtalk, some folks familiar with the SR22 experience posted data which elicited a lot of breathless fluffery from a representative of the vendor.
Dav8or
Final Approach
Fuel costs aside for a moment, do you believe that reliability of dispatch is equal, or greater and maintenance costs are lower for the piston twin? If that is so, could not FedEx buy 100LL on contract as well and save?
jonnyjetprop
Cleared for Takeoff
An interesting note on the FedEx caravans. While FedEx decided to go with new Cessna Caravans, UPS did not. FedEx owns their Caravans and leases them to operators who crew them and do line maintenance on them. UPS leaves it in the hands of the operators like Ameriflight to decide the best equipment for the job. Ameriflight chose Piper Navajos and older commuter twin turboprops like the Beech 99's, Beech 1900's, Metroliners, and Brasilias.
Dispatch reliability is probably lower, don't know about the per-mile-pound maintenance cost. Turbines tend to cost little maintenance wise until the day that they cost a lot. Other parcel haulers and couriers fly twins like Excalibur Queen Airs (e.g. Bemidji), Chieftains (a bunch of them), 310s (ProAire) Mu2s (a few) and metroliners (e.g. Martinaire). I imagine the access to capital that these companies have is different from the access that Fedex had when they bought their 250 Caravans.
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,019
- Display Name
Display name:
iFlyNothing
The SR22 setup is supposedly more complex, which I'd expect. What were they happy or disappointed with?
That all else being equal, the performance gain wasn't as transformative as other forced induction upgrades.
Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
- Messages
- 30,019
- Display Name
Display name:
iFlyNothing
I would expect as such. A properly designed and integrated turbo system has a number of advantages. It's a hard sell in my mind for an SR22 that has such a good turbo system available.
In the 310, there seem some benefits, at least for me. The inherent simplicity for one, the optimal altitudes for operation, etc. We'll see. Like I said, may not even happen.