Teach me why I listen to Turboprop drivers always discussing airspeed.

[hmmm]

Hey...

Someone please teach me why I listen to Turboprop drivers always discussing airspeed.

I have been flying on a King Air lately and hanging around the FBO's I keep hearing other KA pilots always seem to be discussing airspeed attained by their different aircraft configurations.

Now I have been around all sorts of airplanes forever. Worked on just about everything including being a jet and turboprop engine overhaul guy and inspector.

As a pilot I care about is my speed across the ground depending on the altitude in still air first then as affected by the winds compared to my fuel flow.

Speed across the ground is what matters to me and in the jets I was on (DC-8, CRJ & 737) the higher we got the faster we go across the ground... and lower the fuel flow.

As the airspeed dwindles as we go higher per profile.... who cares that the airspeed is lower.... we are going 460kts across the ground at maybe 275 kts indicated on most jets.

I hear guys on KA's more than once for example say "we usually run FL230 where we getting our best airspeed of about 272 kts.

I want to ask them what is there groundspeed at that FL and why do they care so much about airspeed in cruise compared to ground speed and what ground speed do they get if they climb higher which is what matters getting the burn per hour down and the ground speed per hour up.

I imagine their climb fpm is maybe much lower above FL230 so they don't want to sit there in climb but if climb fpm is 6 to 700 fpm I would want to get a little higher to at least 280 and stay out of RVSM if not capable.

But I am a new guy to this area of ops so I am keeping my mouth shut till the opportunity arises to ask, (not something I normally do, I usually ask right out) but this seems so simple I feel like I did when my ex girlfriend was talking about she can't understand why she is gaining weight while she is coming back from the kitchen with a second plate of food for herself.

She did though have nice legs and ti....oh never mind.....thread drift.

 

[Toolowflyer]

...i guess when they where talking about airspeed they mean TAS - because 272 IAS, would give around 370 TAS - there are quite some "tuning" kits around for KingAirs, but 370kts.....

FL230 - is just one of the faster Levels for KingAirs, for example the BE20 (200) is certivied FL350, but it´s about 30kts slower up there, cabin ALT above 10k...

 

[timeless]

Many guys can make it pretty far without a good understanding of TAS, GS and IAS.

I fly a Cargo Shorts 360 equipped with a big oxygen tank and decent masks so we can go above 10,000ft. The airplane is certified up to FL200, but is wasn't really intended to spend much time above 10,000 ft. It wasn't really intended for 4 hour legs either. Because of this there aren't very good cruise charts available for what we do. I had to plug the fairly basic performance data into excel for better analysis and put a detailed model into Flight Star to get a better understanding of all the variables that effect fuel burn and range. The better flightstar model automatically picks the best altitude accurately.

In a hypothetical still air situation 14000 offered the best TAS. 20000 offered the best range.

As for range regarding wind, Long Range Cruise offered better range than High Speed Cruise up to about a 50 knot headwind component. The value change slightly with altitude, weight and temp.

I've always found performance charts to be about 10 times more useful and about 100% more accurate than other pilots mathematically unsound recommendations. Spend some time studying and analyzing the performance charts. I don't have much turbine time, but knowing the charts better allowed me to back up my recommendations with solid data despite my limited experience.

 

[Diesel]

I think what you're missing out is that they are implying 0 wind or a tail wind.

 

[guido411]

Speed across the ground is what matters to me and in the jets I was on (DC-8, CRJ & 737) the higher we got the faster we go across the ground... and lower the fuel flow.

Not always true...

I think you may find the biggest difference is what you gain vs what you lose in both types of airplanes as you trade altitude for airspeed and fuel flow. Take, for example, the 2 airplanes I fly, one a jet and one a turboprop. In the jet our best TAS is attained around FL280 (~465 KTAS) because our engines are still making rated power and we are maxed out on allowable indicated airpspeed. But we gain so much more range by decreasing our fuel flows that going to FL370-FL390 is usually best even with the loss of TAS (~440 KTAS).

A tp doesn't usually have that much to gain by flying lots higher with respect to fuel burns and allowable altitudes so the typical best altitue is the highest altitude that you can still make 100 % of rated horsepower, that is if maximum TAS is your goal. There's a whole other discussion here about "flat-rating", or having an engine capable of producing a whole lot more horsepower at SL but de-rating it so it still produces max hp at higher altitudes.

You will most often see tp pilots flying at their FASTEST altitude unless they are really trying to stretch range. Most often you will see jet pilots fly at their most EFFICIENT altitudes, sometimes different due to winds aloft and again stretching range.

The groundspeed discussion is not valid in the remarks that the tp pilots you overhear are talking about. In short, there is a higher percentage gain available for jets to climb than there is for turboprops.

 

[hmmm]

thanks.... my goal has always been the farhest we can go with least burn (which equates to the highest ground speed compared to least burn per hour) and it seemed the higher we go within reason compare to trip length etc helps that in either turbine jet or tp taking into account time to climb or fpm to get there etc etc big picture.

It just seems like all they think about is airspeed airspeed airspeed because thats whats in front of there nose on the instrument panel and not paying attention to groundspeed.

 

[siouxicide]

I'm with Toolow. I don't know anyone who talks indicated airspeed, especially in the flight levels.

 

[caseyd]

thanks.... my goal has always been the farhest we can go with least burn (which equates to the highest ground speed compared to least burn per hour) and it seemed the higher we go within reason compare to trip length etc helps that in either turbine jet or tp taking into account time to climb or fpm to get there etc etc big picture.

It just seems like all they think about is airspeed airspeed airspeed because thats whats in front of there nose on the instrument panel and not paying attention to groundspeed.

The calculation you want to make is the "miles per pound" (or gallon). This calculation blends TAS and FF into meaningful information if what you're trying to do is maximize range. Ground speed is gonna be what it's gonna be.

caseyd

 

[timeless]

The calculation you want to make is the "miles per pound" (or gallon). This calculation blends TAS and FF into meaningful information if what you're trying to do is maximize range. Ground speed is gonna be what it's gonna be.

caseyd

This is called specific range. Weight, altitude, temp and wind all effect what power setting will give the best specific range specific range.

 

[ksu_aviator]

I'm going to second that the best altitude isn't always the highest you can get to.

The Metro I fly gets the best TAS at FL190 and FL200. I also get a huge fuel drop from 17,000 to FL190 but virtually no drop above FL200. I can go to FL300 (if I had RVSM) but I lose about 30 kTAS.

So, when you hear KA pilots talking airspeed (guessing its TAS) at certain altitudes, they are just comparing their best performance.