Wife wants a twin, but does it exist?

Henning said:
Care to explain the difference in fixed cost?
Click to expand...

The difference is in the estimated annuals for each aircraft. C310/B55 = $7500, PA-30 = $5000. Difference = $208/month.

Although, after the horror stories I've been receiving through email and PMs and while reading through the forums, those estimates might need to be doubled!:yikes:
 
Henning said:
22 gph to do 180 in a 310, 18 to do 170 in a Twinkie. That is less than 4gph difference for the same distance.
Click to expand...

180 KTAS on 22 GPH in a 310 I believe. 18 GPH in a TC is ridiculous unless you're down low and very ROP. With my TC, at 10,000 ft I get 164 KTAS on less than 14 GPH, less than 13 GPH if I get everything just right with the mixtures. My best is actually 12.4 GPH total. I confirmed that by climbing to 10,000 ft on the mains, switched to the tip tanks, fly exactly one hour to the second by the clock, switch back to the mains and top of the tips when landing.

Block time you're looking at at least 7 and probably 8 GPH difference. Yes, the 310 is 15 kts faster so the TC would have to fly an extra few minutes, the difference is negligible though.
 
Banjo33 said:
The difference is in the estimated annuals for each aircraft. C310/B55 = $7500, PA-30 = $5000. Difference = $208/month.

Although, after the horror stories I've been receiving through email and PMs and while reading through the forums, those estimates might need to be doubled!:yikes:
Click to expand...


Or less than halved if you do owner assist annuals. I spent $7000 at my last annual cycle and that included $3000 of optional/upgrade stuff and $1000 of catch up left over from purchase, and that was me not involved and not a budget shop.
 
If the Twinkie will do the job, just buy Kens'. It's gotta be one of the cleanest planes in the western hemisphere. If I didn't already have two planes I'd give it a go and forget about my Aerostar passion.
 
That's a great deal on that rental Twinkie! We have a Seminole locally that rents for $160/hr dry plus 24gph at the local fuel rate (currently $5.58 = $294/hr + tax).
 
Banjo33 said:
The difference is in the estimated annuals for each aircraft. C310/B55 = $7500, PA-30 = $5000. Difference = $208/month.

Although, after the horror stories I've been receiving through email and PMs and while reading through the forums, those estimates might need to be doubled!:yikes:
Click to expand...

Depends on how much you spend on the airplane ip front and how good of a prebuy you get.

I'd say for a good B55 that $7500 is probably a reasonable rough estimate for annual Mx. Some years will be less and some a little more.

From my previous research talking to owners and A&Ps, the 310s ran a little higher on average (closer to $10k/year).

Any airplane can eat your lunch if you buy cheap up front and defer a lot, but if you buy well, your 'surprises' will be minimized.

I don't think you need to double your estimates, but you need to be prepared for occasional years that might be close to double your initial budget.

Let's face it, some items like fuel bladders can kick your butt if they catch you by surprise.
 
Ted DuPuis said:
..... A Malibu costs way more than a 310. A Saratoga is just... no.

Could go turboprop, but it would be much cheaper to get into a Cheyenne or an MU2 than a Meridian/JetProp or TBM.
Click to expand...


On the Malibu vs 310, how would you say that operating costs compare?
 
KLRDMD said:
And I wouldn't want a TC with Ray Jays either as down low (below 10,000 ft) they're slower since the turbos are always in the system making it less efficient.
Click to expand...

But isn't the wastegate going to be wide open down low, bypassing the turbos? How are they "always in the system"? It's very different than, say, a Seneca where they really are always in the system...
 
Henning said:
My 310 took up less space in the hangar than Av's Comanche. As for cam problems only coming from sitting, that isn't totally true. Even engines that see constant use have developed cam problems. Regardless, all things being equal, the difference in engine cost over lifespan will be about $5hr. IO-470s are not expensive engines and are very reliable.
Click to expand...

Most of the 310's take up more space than most of the Twin Comanches.

I didn't say that cam problems only come from sitting. That is, however, the major problem with cams in Lycomings. Anything in an engine can break for almost any reason, though rarely. Regardless, you statement that an IO-470 has the same cost of maintenance as an IO-320 is ridiculous.
 
flyingcheesehead said:
But isn't the wastegate going to be wide open down low, bypassing the turbos? How are they "always in the system"? It's very different than, say, a Seneca where they really are always in the system...
Click to expand...

A turbocharger presents some form of backpressure at all times to the exhaust flow, even in full bypass. There is a restriction in the throat of the wastegate that is still significantly smaller than the muffler of an NA plane. Plus, the turbine is always spinning in a turbocharger, and there is some amount of adiabatic delta to the incoming charge of air that is not usually present on a NA plane. The intake gasses literally pass through the vanes of the compressor which is driven at the other end of the turbine shaft, and no matter how you try, there is some thermal transfer from the turbine(hot) side to the compressor(cold) side when compared to the standard NA intake and exhaust system.

It's just a fact of life that a turbocharger is not a 'free' air system, even when it's in full bypass.
 
Henning said:
22 gph to do 180 in a 310, 18 to do 170 in a Twinkie. That is less than 4gph difference for the same distance. Drag is drag and requires x HP to overcome regardless of what engine you use. Even at $6 gal fuel it's about $20hr difference in fuel. However the amount of excess horsepower available in a OEI situation in a 310 is significantly greater than a Twinkie. If I got a Twinkie it would be a Miller with turbo normalized IO-360s.
Click to expand...

You are comparing a Twinkie at max cruise rich of peak with some reduced or LOP in the 310. How about the Twinkie doing 160 KTAS @ 14 gph. The numbers look a bit different when you get the Twin Comanche up to 11-12K where it likes to run.
 
cirrusmx said:
for what is worth. a lot of people here focus on fuel burn gph, which for a hobbyist/flight training/loitering makes sense. since you actually plan on going places i would look more into fuel economy and speed.
Click to expand...

With you so far - That's how I can consider the Mooney to be cheaper than a 172! :D

a lot of twins are the same. they seem, at the first glance, fuel guzzlers, but they have a better or the same fuel economy for higher speeds than a single. In addition, in a twin you get better payload, takeoff performance, and better weather flying capabilities.
Click to expand...

Whoa, now you lost me.

Give me a single twin that gets better fuel economy, higher speed, and better takeoff performance than a comparable single. The only way I can even come close is with a 17gph Cirrus vs. the 16gph Twinkie, and that's at the same speed (170 kts). And the Cirrus is a pig - The Mooney I fly will go as fast on 12gph.

The TwinStar gets great fuel economy, but only recently have they gotten it to go fast too. Even so, it's going to be out of the realm of affordable for at least another decade.
 
flyingcheesehead said:
But isn't the wastegate going to be wide open down low, bypassing the turbos? How are they "always in the system"? It's very different than, say, a Seneca where they really are always in the system...
Click to expand...

Yes, but the waste gates create back pressure. What Ken says is true.
 
docmirror said:
A turbocharger presents some form of backpressure at all times to the exhaust flow, even in full bypass. There is a restriction in the throat of the wastegate that is still significantly smaller than the muffler of an NA plane. Plus, the turbine is always spinning in a turbocharger, and there is some amount of adiabatic delta to the incoming charge of air that is not usually present on a NA plane. The intake gasses literally pass through the vanes of the compressor which is driven at the other end of the turbine shaft, and no matter how you try, there is some thermal transfer from the turbine(hot) side to the compressor(cold) side when compared to the standard NA intake and exhaust system.

It's just a fact of life that a turbocharger is not a 'free' air system, even when it's in full bypass.
Click to expand...

Agreed on all of the above, however, is it really significant? How big is the "throat" of the wastegate vs. the exhaust on an NA plane? How much warmer is the intake air, and does it cause significant hp loss?
 
flyingcheesehead said:
Agreed on all of the above, however, is it really significant? How big is the "throat" of the wastegate vs. the exhaust on an NA plane? How much warmer is the intake air, and does it cause significant hp loss?
Click to expand...

At sea level an NA Twin Comanche will climb a couple of hundred feet per minute faster and is 5-7 kts faster up until the turbo starts dialing in the boost to maintain 75%
 
flyingcheesehead said:
Agreed on all of the above, however, is it really significant? How big is the "throat" of the wastegate vs. the exhaust on an NA plane? How much warmer is the intake air, and does it cause significant hp loss?
Click to expand...

It's a difference. Some people call 0.5% significant, some call 5% significant. I don't know what you want to hear, but my guess is that it's a few percent different all other things being equal. Intercoolers were developed to handle the heating, but nothing can reduce the HP needed to drive the turbine even at full bypass.
 
Fearless Tower said:
Let's face it, some items like fuel bladders can kick your butt if they catch you by surprise.
Click to expand...

It's not the fuel bladder that kicks your butt. It's pulling out the old fuel bladder and finding a bunch of corrosion between the bladder and the surrounding wing :eek: .
 
comanchepilot said:
and - unless you get an aircraft that can maintain altitude on one engine above the rocks - there is no point to it. while an engine out in a single means you are not maintaining altitude, a twin that cannot hold its own is trouble waiting to happen and offers a very false sense of security since if you have say, a 160hp Apache or 180hp Seminole, you still need to operate it as if it were a single when it comes to overwater and similar -
Click to expand...

Not true, especially when it comes to overwater. I'd take *any* twin with an engine out over any single with an engine out at 10,000 feet over Lake Michigan! Even a Seminole with its worst-in-class SESC of 3800 feet will easily make it to an airport on one side or the other of the lake.

In fact, even in the mountains you're better off with a normally aspirated "trainer" twin than a single.

Keep in mind that SESC is where the plane can climb 50fpm on one engine at gross. That means you should be able to maintain an altitude higher than that, and if you're at a higher altitude yet, you'll simply drift down to the "maintain" altitude. With the Seminole example, my calculations indicate that altitude will be about 4800 feet. Up at 14,000 feet the drift-down rate will be a tad under 400 fpm, giving a "glide" ratio of about 22.8:1, so even that high you're still better than a single.

In the Twin Comanche with its 5800-foot SESC, the "maintain" altitude is a bit over 6900 and the drift-down at 14,000 would be about 275 fpm, equivalent to a "glide" ratio of about 33:1. I'd take that over any single, any day of the week.
 
flyingcheesehead said:
Keep in mind that SESC is where the plane can climb 50fpm on one engine at gross. That means you should be able to maintain an altitude higher than that, and if you're at a higher altitude yet, you'll simply drift down to the "maintain" altitude. With the Seminole example, my calculations indicate that altitude will be about 4800 feet. Up at 14,000 feet the drift-down rate will be a tad under 400 fpm, giving a "glide" ratio of about 22.8:1, so even that high you're still better than a single.

In the Twin Comanche with its 5800-foot SESC, the "maintain" altitude is a bit over 6900 and the drift-down at 14,000 would be about 275 fpm, equivalent to a "glide" ratio of about 33:1. I'd take that over any single, any day of the week.
Click to expand...

Someone has generated a drift-down map of the US with the places where you wouldn't be able to get out of the mountains on one engine in a B58 Baron. It was a small area, somewhere in eastern Idaho iirc.
 
stratobee said:
Well, the Aerostar will outfly all of these numbers. It will be faster and cheaper in fuel per nm compared to any twin except a Tecnam P2006T or a TwinStar. You can't beat low drag.
Click to expand...

Hmmm...

Aerostar, 220 KTAS at 32 gph = 6.9 nmpg
Twinkie, 165 KTAS at 16 gph = 10.3 nmpg

You're right, though, you can't beat low drag.
 
flyingcheesehead said:
Not true, especially when it comes to overwater. I'd take *any* twin with an engine out over any single with an engine out at 10,000 feet over Lake Michigan! Even a Seminole with its worst-in-class SESC of 3800 feet will easily make it to an airport on one side or the other of the lake.

In fact, even in the mountains you're better off with a normally aspirated "trainer" twin than a single.

Keep in mind that SESC is where the plane can climb 50fpm on one engine at gross. That means you should be able to maintain an altitude higher than that, and if you're at a higher altitude yet, you'll simply drift down to the "maintain" altitude. With the Seminole example, my calculations indicate that altitude will be about 4800 feet. Up at 14,000 feet the drift-down rate will be a tad under 400 fpm, giving a "glide" ratio of about 22.8:1, so even that high you're still better than a single.

In the Twin Comanche with its 5800-foot SESC, the "maintain" altitude is a bit over 6900 and the drift-down at 14,000 would be about 275 fpm, equivalent to a "glide" ratio of about 33:1. I'd take that over any single, any day of the week.
Click to expand...

Right! I worked all through this when deciding to get an NA Twinkie instead of a turbocharged one. I have been across the mountains from California to east of the Rockies dozens of times. My strategy on an engine failure is to turn down the nearest valley. The western mountains are a series of ridge lines generally. If you turn down a valley, the floor will likely be lower than my drift down ceiling and pretty much all valleys lead to an airport sooner or later. This merely requires knowing where you are. The iPad takes care of that.
 
flyingcheesehead said:
Give me a single twin that gets better fuel economy, higher speed, and better takeoff performance than a comparable single.
Click to expand...

When I compare a flight I routinely make, AVQ-SMO at 10,000 ft on the low altitude airways and plug in the typical profile of a previous Cessna 182 I owned and my current Twin Comanche, the twin both arrives earlier and burns less total fuel doing so. Of course the twin has a higher climb and cruise speed, better takeoff performance and much higher useful load and greater range too.
 
The reason a twin is faster is not just a speed calculation, it's avoiding a fuel stop while carrying a full load. Compare a 600 NM trip with a 40 knot headwind in a 140 knot 182 with a 190 knot Baron. 182 will take 6 hours flying, which means a fuel stop of 45 min. call it 6:45. The Baron takes 4 hours no stop. Increase the distance and the math gets worse for the 182. Assuming a normal 8 am departure arriving at noon to go grab lunch is great. Arriving at 2:45, in the bumps, starving, is not so nice.
 
KLRDMD said:
When I compare a flight I routinely make, AVQ-SMO at 10,000 ft on the low altitude airways and plug in the typical profile of a previous Cessna 182 I owned and my current Twin Comanche, the twin both arrives earlier and burns less total fuel doing so. Of course the twin has a higher climb and cruise speed, better takeoff performance and much higher useful load and greater range too.
Click to expand...

Alexb2000 said:
The reason a twin is faster is not just a speed calculation, it's avoiding a fuel stop while carrying a full load. Compare a 600 NM trip with a 40 knot headwind in a 140 knot 182 with a 190 knot Baron. 182 will take 6 hours flying, which means a fuel stop of 45 min. call it 6:45. The Baron takes 4 hours no stop. Increase the distance and the math gets worse for the 182. Assuming a normal 8 am departure arriving at noon to go grab lunch is great. Arriving at 2:45, in the bumps, starving, is not so nice.
Click to expand...

Note, I said "comparable". The 182 is not really like any twin. If I compare the Mooney to an Aztec, it's 15 knots faster than the twin and has an endurance an hour and a half longer and throws your whole argument out the window.

You want to see what two engines does for you, you need to compare things like the Lance and Seneca, Comanche and Twin Comanche, Bonanza and Baron, etc... Otherwise you're just comparing two types of airplanes, and there are airplane types available for every mission that perform well or not regardless of how many engines are hung on them.

While the twins will have a higher useful load, a good chunk of that load will be taken by the extra fuel needed to feed the second engine. In fact, sometimes the single has a higher payload...

So, define the mission, and find the airplane to fit the mission.
 
Kristin said:
You are comparing a Twinkie at max cruise rich of peak with some reduced or LOP in the 310. How about the Twinkie doing 160 KTAS @ 14 gph. The numbers look a bit different when you get the Twin Comanche up to 11-12K where it likes to run.
Click to expand...

If I want 160 I'll buy a Mooney or a Bonanza. I want 180, and that was an OP requirement as well, the Twinkie with 320s doesnt have the balls to do it, so I gave the closet numbers it would. The 310 does 180 loafing LOP like a Twinkie at 140. That's a 40 kt difference for 6 gph. I got the 310 down 12 gph at 127kts. We can play slow down all day, but that doesn't get you across the country in a day which 180kts will do. I don't really have anything against a Twinkie, but it's not the same animal in either size or ability on a single engine that a 310 does.
 
Henning said:
If I want 160 I'll buy a Mooney or a Bonanza. I want 180, and that was an OP requirement as well, the Twinkie with 320s doesnt have the balls to do it, so I gave the closet numbers it would. The 310 does 180 loafing LOP like a Twinkie at 140. That's a 40 kt difference for 6 gph.
Click to expand...

That's some funny math, Henning - You said 22 gph for the 310 to do 180. The Twinkie will do 160 on 14 gph, a difference of only 20 knots for a savings of 8 gph.
 
weilke said:
Someone has generated a drift-down map of the US with the places where you wouldn't be able to get out of the mountains on one engine in a B58 Baron. It was a small area, somewhere in eastern Idaho iirc.
Click to expand...

I'd love to see that!

However, I think you might be putting a couple things together - I googled for it and found a thread on BeechTalk where Larry Olson (who posts here) did an OEI test in his Baron and someone on that thread mentioned that some airline that operated in CO had a map like that.

Larry's results in the Baron: From 15K, it took 12 miles to get to 13K and about 44 miles to get down to 9K. He could maintain 9K indefinitely. (These results were hot and heavy, the worst case scenario.)

FWIW - Running the numbers like I was before with the B58's SESC of 7000 and MGW of 5400, I get 8000 as the neutral altitude. So, if Larry was really at gross and it was hot and he's got the 285hp bird, then the calculations have a somewhat conservative result.

FWIW, the calculation I was doing was to take the atmospheric pressure ratio at the SESC to determine max engine hp available, then using 50 fpm (definition of SESC) * MGW / 33000 to determine the number of excess hp available, subtracting from the max hp available to get the number of horsepower required to sustain level flight. That number can be divided by sea level HP to get a percent power required, and then you can determine the atmospheric pressure ratio and the altitude from there. Not perfect, but pretty good...
 
KLRDMD said:
Mine will do over 160 KTAS on less than 14 GPH, most or all of them will.

I've seen 160 KTAS on 12.3 GPH total.
Click to expand...

Just to make sure I've got it, you could fly the compass points and average up to 160 on 12.3 total?
 
Henning said:
The Twinkie does 140 on 14.
Click to expand...

Here's a post of mine from September that I sent to the Piper list:

I climbed on the main tanks, then once set up in cruise at 10,000 ft, full manifold pressure and 2450 RPM, I switched to the tip tanks that I had topped off yesterday. I flew EXACTLY (to the second, on my watch) 90 minutes on the tip tanks, then switched back to the mains. It was +13ºC outside air temperature. CHTs were between 350 and 380ºF.

My flight plan was for 165 KTAS and the IFR low altitude routing was projected by fltpln.com to take 2:32 showing an average 6 kt headwind along the route. I've made this trip a bunch of times and that is a very average number. It is 387 NM as filed.

I pulled the mixture well back in both climb and cruise, mostly in cruise. I was about 25º lean of peak (I didn't measure precisely) in cruise. My factory original analog fuel flow gauges were reading 7.5 GPH per engine. From taking the runway at AVQ until touchdown at SMO was 2:37 so I obviously lost some airspeed by running LOP.

If I take 2:32 and divide 2:37, (152/157 minutes) that's 96.8%. Multiply that by the 165 KTAS on the flight plan form that calculated the time en-route to be 2:32 and I get 159.75, cal it 160 KTAS.

Now, here's the amazing stuff. We know that the factory original fuel flow isn't all that accurate. But I had a known time frame and started with full tip tanks and topped them off immediately upon landing. The right one took 9.3 gallons and the left one took 9.2 gallons. Remember that's for a 90 minute cruise. That means I was only burning 12.3 GPH in cruise and getting 160 KTAS !!!!! I topped off the main tanks too and added 9.0 gal to the left and 8.7 gal to the right one.

In a 2:37 min flight, with a climb to 10,000 MSL, on a day well above standard temperature, I only burned 36.2 gallons. That's an average of 13.6 GPH for the entire flight !

When ATC brought me down to 6,000 ft I was burning 10.5 GPH per side (indicated, actual is less) and getting 180 kts across the ground with some degree of a headwind.
 
Henning said:
The Twinkie does 140 on 14.
Click to expand...

As far as I'm concerned, a twinCo flies slightly slower than the singleCo at the same gas. That puts it in the 150ish range, with the heavily modded ones on the upper scale. Not 140, but certainly not 160 either. As always, pics or it didn't happen;)
 
KLRDMD said:
Mine will do over 160 KTAS on less than 14 GPH, most or all of them will.

I've seen 160 KTAS on 12.3 GPH total.
Click to expand...


If I stop in Tucson on my way home from California, will you show me how that's done?
 
hindsight2020 said:
As far as I'm concerned, a twinCo flies slightly slower than the singleCo at the same gas. That puts it in the 150ish range, with the heavily modded ones on the upper scale. Not 140, but certainly not 160 either. As always, pics or it didn't happen;)
Click to expand...

The post above was AVQ-SMO, the photos are from the flight back, SMO-AVQ at 11,000 ft.

Airspeed & Altimeter

Calculation

Also, at 10,000 ft I was still climbing at 500 fpm:

Climb
 
Henning said:
Get a fuel flow and try it again and get real numbers.
Click to expand...

So first pictures or it didn't happen, then when I post pictures you still don't believe it. Amazing !

As I wrote earlier, my factory analog fuel flow gauges read high. When I top off after landing, I have proven that 8 GPH indicated is 6.2 GPH actual. I don't have digital fuel flow in my Twin Comanche, please forgive me.

Fuel Flow

Those are real numbers that actual owners of Twin Comanches will corroborate. My Twin Comanche is nothing special, there are others that are faster than mine on the same fuel flow.
 
You must log in or register to reply here.
Back
Top