Which model Lear?

Since I feel I was partly responsible for derailing thread:

The 5-blade MT props have been STC'd for the Mits, I saw. Does anybody know how much the conversion costs? Does it add any climb (doubt it will add top speed)? And is the STC available for all TPE331's or just -10's?

The turbocharged piston engine is perhaps losing a bit of efficiency as it goes higher due to turbocharger losses. Not a large amount, but some.


Yes, this is true.


The 45% power curve on the 421 starts to show that effect by starting to curve towards lesser range gain as altitude increases.

The 421C POH gives best glide speed of 122 KIAS at gross. The 45% power curve shows a true airspeed of 185 KTAS at FL250, which is 124 KIAS, so getting real close and the curve is almost vertical at the point.

This doesn't work on turboprops as you can see from the MU2 specific range chart I posted. The engine loses so much efficiency part throttle that you want to fly fast. Indeed, the specific range chart is pretty flat from 200 to 300 knots, so might as well fly 300 knots!


The key was the assumption of an engine (and prop or fan) which were uniformly efficient at varying power settings and conditions. This is not generally true. Spark ignition engines don't do that, they start to lose efficiency at partial throttle settings. Diesel engines suffer this less so. Turbine engines suffer this greatly. Props and fans work less well off their design set points.

So the most efficient speed is somewhat faster than best L/D since that optimizes the combination of the airframe, engine, and prop (or fan).

Flying at best L/D is mostly an academic exercise. GA planes are not typically designed around that operating point. Flying higher improves the operating efficiency since you can get more speed for less exceedance of L/D max speed.

Mike C.

About $100K/set.


http://www.mt-propellerusa.com/en/mtusa ... mu2b_1.htm

My assessment is that takeoff is improved on the order of 3-4% reduction in runway usage. Climb is improved on the order of 4%. Cruise is neutral or maybe hurt by 1 to 2 knots, very close.

Noise is reduced.

Super awesomeness factor is improved.

Engine start is maybe a touch quicker.


All engines on MU2s, -25AA, -1, -5, -6, -10AV, -10T, -10.

There may be only 1 or 2 -25AA MU2s left, and I doubt they would spend $100K for props (probably exceeds their hull value).

Air1st does most of this work.

Mike C.

Its Beechtalk...that's what we do here

BTW I always overfill my Aerostar for a long flight

Glenn

This was in reference to the 421C example.

Let me see if I can do this calc.

Let's pick 65% power, FL250, 227 KTAS. At ISA, this is 152 KIAS. The chart Cessna provided says range is 1165 nm (assuming 1404 lbs fuel, top axis).

At 1000 ft, 152 KIAS is 154 KTAS. At 1000 ft altitude, the range chart, interpolating, says range is 1150 nm (1404 lbs fuel). This corresponds to an engine power of 45%.

So an ever so slight reduction in range using the same KIAS if you fly low.

What this tells me is that the engine efficiency improves enough from 45% to 65% power that it covers any airplane loss of efficiency at the higher altitude AND the extra fuel to climb up there.

To say it another way, you can fly at 1000 ft and 154 KTAS or FL250 and 227 KTAS and get basically the SAME range, at the same 152 KIAS, and this includes the climb fuel.

I drew a line between the two operating points (can't assume any place in between, just the end points):

Mike C.

About $100K/set.Mike C.

But it's almost worth $90K to look as badass as this.

Quite all right. I got my answers way back. I'm learning a lot more interesting things now. Know yourself out!

Not its not. Please put me out of my misery if I even suggest spending 100AMUs on props...

Absolutely badass black! The props aren't bad either, especially, again, in badass black. I wonder if the owner wants to sell?

I like those props.

And apparently someone forgot to tell MT that more props are less efficient

Mike,

YES!

Max range can be had at any altitude in a piston.

Best,

I absolutely agree with you on most points. The piston engine does loose a little efficiency at altitude when you get excessively high intake air temps from working the turbos so hard, but if operated LOP the curve is pretty flat. You also hit the nail on the head in that partial power operations on a turbine kill the efficiency of the engine. The airframe may be operating at the optimum speed, but if the SFC of the engine is crap at that setting, your total MPG goes to pot. The most efficient operation of the engine and the most efficient operation of the airframe are quite often miles apart. As your 200-300 knot example points out, this is all academic and we almost all push the power to the limit in reality.

I enjoy the mental exercise of establishing max efficiency, but if I really wanted to set records for NM per gallon I would take my sailboat and leave the plane at home. By the way, my daily ride goes 135 knots at 65-70 GPH.

If you assume the engine is uniformly efficient at all power settings.

Alas, they are not.

Fly at high altitude means best L/D airspeed is at higher power, and the engine slightly more efficient.

But one has to use fuel to climb, which negates the effect to some degree.

The 421C case shows how close the results are sometimes.

Mike C.