BeechTalk - BT

Username Protected · **Posted:** 20 Jan 2014, 04:05

Username Protected wrote:

Even while a pilot is required, it's very little expense compared to the rest of the package.

But that's the point, the "rest of the package" is the problem. It's a quantum leap over the expense of a piston. You're used to it so you don't see it as a problem. Like a lot of people, I'd like a step up from a Cirrus-class airplane, and would expect to pay more for it, but proportionally more, not the order of magnitude more that certified turbines, even used ones, demand.

For those intrigued by the Evolution but want cabin class and more seats, consider the Epic Escape, a 92% (??) scale of the LT, which makes it similar in size to the Evolution (within a foot in span, length and height). One was built with a TPE-331 but came out with a CG issue. China got the rights in the bankruptcy and it's now on their website as the Primus 150 w/ a GE engine of 850 hp, lighter than a PT6, better sfc and cheaper lifecycle costs. First flight this year, they claim. AFAIK, China got the certified production rights but the current Epic retained the kit rights to all the designs.

Username Protected · **Posted:** 20 Jan 2014, 10:31

Username Protected wrote:

Even while a pilot is required, it's very little expense compared to the rest of the package.

One was built with a TPE-331 but came out with a CG issue. China got the rights in the bankruptcy and it's now on their website as the Primus 150 w/ a GE engine of 850 hp, lighter than a PT6, better sfc and cheaper lifecycle costs.

Username Protected · **Posted:** 20 Jan 2014, 11:17

Username Protected wrote:

If I'm not mistaken, the GE engines are a direct drive style turboprop right?

It was explained to me by an engineer that direct drive style turboprops are not ideal for single engine application. The reason being is that the direct drive will act as a gyro when you try to climb, thus it tries to spin the airplane.

That makes no sense. All TP try and spin the plane. Let alone the heavier wights of a gas engine spinning.

Tim

Username Protected · **Posted:** 20 Jan 2014, 11:48

Username Protected wrote:

If I'm not mistaken, the GE engines are a direct drive style turboprop right?

It was explained to me by an engineer that direct drive style turboprops are not ideal for single engine application. The reason being is that the direct drive will act as a gyro when you try to climb, thus it tries to spin the airplane.

That makes no sense. All TP try and spin the plane. Let alone the heavier wights of a gas engine spinning.

Tim

Username Protected · **Posted:** 20 Jan 2014, 12:06

Username Protected wrote:

That makes no sense. All TP try and spin the plane. Let alone the heavier wights of a gas engine spinning.

Tim

TP like a Pratt doesn't as much because there isn't a direct connection with the prop and the engine. That is why the fuel specifics are better on direct drive TP, because there is less loss from the engine output to the prop, thus there is more gyro effect.

As far as a gas engine goes, yes it also tries to spin the plane too, but nowhere near what a TP does. A gas engine only has the prop spinning that tries to turn the plane. A TP engine is spinning at tens of thousands of RMP's and then if you direct connect that to the prop, there is your gyro.

Username Protected · **Posted:** 20 Jan 2014, 12:13

Username Protected wrote:

TP like a Pratt doesn't as much because there isn't a direct connection with the prop and the engine. That is why the fuel specifics are better on direct drive TP, because there is less loss from the engine output to the prop, thus there is more gyro effect.

As far as a gas engine goes, yes it also tries to spin the plane too, but nowhere near what a TP does. A gas engine only has the prop spinning that tries to turn the plane. A TP engine is spinning at tens of thousands of RMP's and then if you direct connect that to the prop, there is your gyro.

Gerry,

This makes no sense. In a PT6 in the gas generator section and the compression sections you have spinning forces. From what I have learned about TurboProps, for efficiency reasons the majority of TurboProps alternate direction between each compression section. This means you have counter rotating props within the engine which reduce the torq produced to minimal amounts.

Just because the prop and the engine are connected does not make any sense to me in terms of producing a lot of torq on the airframe.

A gas engine has significantly heavier components spinning all in a single direction producing a lot of torq.

Tim

Username Protected · **Posted:** 20 Jan 2014, 12:31

Tim,

My brother is an engineer as well and this is what he had to say:

"The Walter or direct drive TP has a solid shaft running through the entire engine, so it makes sense that there could be more of a gyro effect. How much there is I do not know but it is possible. A Pratt is essentially two separate engines, so there is a softening effect that occurs. As far as a piston vs a TP, a TP engine is lighter and has to be pushed much further forward for weight reasons, thus giving the TP much greater leverage as well as having a larger prop area. This is why a TP would want to twist a plane much more than a piston."

Gerry

Username Protected · **Posted:** 20 Jan 2014, 13:19

Username Protected wrote:

Tim,

My brother is an engineer as well and this is what he had to say:

"The Walter or direct drive TP has a solid shaft running through the entire engine, so it makes sense that there could be more of a gyro effect. How much there is I do not know but it is possible. A Pratt is essentially two separate engines, so there is a softening effect that occurs. As far as a piston vs a TP, a TP engine is lighter and has to be pushed much further forward for weight reasons, thus giving the TP much greater leverage as well as having a larger prop area. This is why a TP would want to twist a plane much more than a piston."

Gerry

Gerry,

The position of the TP, resulting leverage and size of the prop makes a lot of sense. I just do not see much difference between a direct drive and free spinning TP. You are talking maybe one to two feet of a very light material used for a shaft to connect the two sections. :shrug:

Tim

Username Protected · **Posted:** 20 Jan 2014, 14:57

Username Protected wrote:

Tim,

My brother is an engineer as well and this is what he had to say:

"The Walter or direct drive TP has a solid shaft running through the entire engine, so it makes sense that there could be more of a gyro effect. How much there is I do not know but it is possible. A Pratt is essentially two separate engines, so there is a softening effect that occurs. As far as a piston vs a TP, a TP engine is lighter and has to be pushed much further forward for weight reasons, thus giving the TP much greater leverage as well as having a larger prop area. This is why a TP would want to twist a plane much more than a piston."

Gerry

Gerry,

The position of the TP, resulting leverage and size of the prop makes a lot of sense. I just do not see much difference between a direct drive and free spinning TP. You are talking maybe one to two feet of a very light material used for a shaft to connect the two sections. :shrug:

Tim

Username Protected · **Posted:** 20 Jan 2014, 15:16

I am pretty sure the GE H80 former Walter 601 is a two shaft, reverse flow, free turbine, and basically and eastern bloc copy of the PT-6. description below.

http://www.aviationweek.com/Portals/awe ... esign.html

The engine I think you are thinking of is the Garrett TPE-331 which is in fact a single spool engine where the gas generator and the power turbine share a common shaft.

http://www.cessnaconquest.net/30/21.html

There are some free turbine engines that have a common shaft like the Lycoming T-53 found in the Mohawk and the Huey copter. They have a one shaft but the gas generator spins on the power turbine shaft allow it to be a flow through instead of a reverse flow engine like the PT-6 and H-80/M-601...

BTW, there are several single engine Ag planes flying with TPE-331 as well as some converted Caravans, and others that will come to me later....

Username Protected · **Posted:** 20 Jan 2014, 20:33

Username Protected wrote:

Hmm, I was looking for info on Epics website on the Escape but there is none. What is the Chinese website?

http://www.caiga.cn/a/wangzhanyingwen/c ... nghang150/
http://www.geaviation.com/press/busines ... 21112.html
http://www.jeccomposites.com/news/compo ... light-year
Doug is correct, the GE engine is just like the PT6, reverse-flow free turbine so no issues there. GE bought Walter and updated the engine with their modern big-engine expertise. Compared to the PT6 it's lighter, better sfc, same 3600 hr TBO but no mid-life hot section inspection required. That's all good but I'm just pleased to see Pratt have some competition. Both the PT6 and 331 are early 60s designs. Since then, GA jet engines have gone through about 3 generations because "updating" wasn't enough, a new design was required to take advantage of advancing technology.

Username Protected · **Posted:** 20 Jan 2014, 21:56

So they are claiming a cruise of 350 kts for the Primus?

Max cruise: 652 k/hr

I see they have a Primus 150 and a Primus 100. There aren't very many differences between the two. I wonder why the two planes?

Username Protected · **Posted:** 20 Jan 2014, 22:40

Username Protected wrote:

I see they have a Primus 150 and a Primus 100. There aren't very many differences between the two. I wonder why the two planes?

The 100 is the Epic LT (1200 hp), the 150 is the Epic Escape, a 92% scale of the LT (notice 3 side windows instead of 4). I'm guessing Epic did the scale down for their SE jet but I don't really know. In any case, it let them compete both against the PC-12 (with the LT) and in the TBM/Meridian size market. And even with less power than the LT the smaller plane was faster. Note that the performance numbers on the Primus 150 website are still for the 331-10 which is about 10% more powerful than the GE engine.

Username Protected · **Posted:** 22 Jan 2014, 12:28

Username Protected wrote:

Hmm, I was looking for info on Epics website on the Escape but there is none. What is the Chinese website?

http://www.caiga.cn/a/wangzhanyingwen/c ... nghang150/
http://www.geaviation.com/press/busines ... 21112.html
http://www.jeccomposites.com/news/compo ... light-year
Doug is correct, the GE engine is just like the PT6, reverse-flow free turbine so no issues there. GE bought Walter and updated the engine with their modern big-engine expertise. Compared to the PT6 it's lighter, better sfc, same 3600 hr TBO but no mid-life hot section inspection required. That's all good but I'm just pleased to see Pratt have some competition. Both the PT6 and 331 are early 60s designs. Since then, GA jet engines have gone through about 3 generations because "updating" wasn't enough, a new design was required to take advantage of advancing technology.

Username Protected · **Posted:** 23 Jan 2014, 09:56

Username Protected wrote:

Hmm, I was looking for info on Epics website on the Escape but there is none. What is the Chinese website?

http://www.caiga.cn/a/wangzhanyingwen/c ... nghang150/
http://www.geaviation.com/press/busines ... 21112.html
http://www.jeccomposites.com/news/compo ... light-year
Doug is correct, the GE engine is just like the PT6, reverse-flow free turbine so no issues there. GE bought Walter and updated the engine with their modern big-engine expertise. Compared to the PT6 it's lighter, better sfc, same 3600 hr TBO but no mid-life hot section inspection required. That's all good but I'm just pleased to see Pratt have some competition. Both the PT6 and 331 are early 60s designs. Since then, GA jet engines have gone through about 3 generations because "updating" wasn't enough, a new design was required to take advantage of advancing technology.

OT: Lancair Evolution