Heard on the air...

[0TreeLemur]

While flying Monday to eastern West Virginia on an IFR flight plan, I felt really happy with my 190 knot ground speed approaching intersection HOBOS thanks to 50 knot tailwinds at 9000 ft over Virginia.  I heard this exchange:

"Washington Center, Cessna 1234, do you have a read on my ground speed?"

"Cessna 1234, your groundspeed is 45 knots."

Cessna 1234:  "Thanks.  I wish I wasn't flying into the wind."

Isn't that just sometimes the sad fact.

 

 

[ArtVandelay]

Your CAS is 19 knots lower than your TAS?

[jaylw314]

23 minutes ago, ArtVandelay said:

Your CAS is 19 knots lower than your TAS?

At 9000' it would be?

[jaylw314]

1 hour ago, 0TreeLemur said:

While flying Monday to eastern West Virginia on an IFR flight plan, I felt really happy with my 190 knot ground speed approaching intersection HOBOS thanks to 50 knot tailwinds at 9000 ft over Virginia.  I heard this exchange:

"Washington Center, Cessna 1234, do you have a read on my ground speed?"

"Cessna 1234, your groundspeed is 45 knots."

Cessna 1234:  "Thanks.  I wish I wasn't flying into the wind."

Isn't that just sometimes the sad fact.

I recall doing some back-of-the-envelope calculations to figure out how fast to fly into a headwind to maximize range, and determined your range increases as you slow down all the way to the point your TAS is twice the headwind, which I thought was a pretty useless conclusion because nobody would ever fly that slow 

[Ragsf15e]

1 hour ago, ArtVandelay said:

Your CAS is 19 knots lower than your TAS?

Seems legit to me… were you thinking IAS?

[Bolter]

1 hour ago, ArtVandelay said:

Your CAS is 19 knots lower than your TAS?

CAS essentially the same as IAS, so at 9000' you would expect a large difference from KTAS.  The CAS value is in the POH, and in my experience, just 1-2 knots correction from IAS.  For the Ovation, IAS + 1 = CAS.  

[kortopates]

Yes, as every turbo pilot knows we get an additional 2 kts TAS for free with each thousand feet of density altitude. So at 9k, closer to 9.5 we would expect a 19 kt difference between IAS/CAS and TAS.


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[ArtVandelay]

Seems legit to me… were you thinking IAS?

Opps, my bad, yes I was.

[Hank]

1 hour ago, kortopates said:

Yes, as every turbo pilot knows we get an additional 2 kts TAS for free with each thousand feet of density altitude. So at 9k, closer to 9.5 we would expect a 19 kt difference between IAS/CAS and TAS.

My turbo-free C model loses 2% of IAS per thousand feet. So if I'm indicating 143 mph at 9000 msl, then TAS = 143 + (0.02 × 9 × 143) = 143 + 26 = 169 mph (147 KTAS).

[Pinecone]

On 10/21/2022 at 4:25 PM, kortopates said:

Yes, as every turbo pilot knows we get an additional 2 kts TAS for free with each thousand feet of density altitude. So at 9k, closer to 9.5 we would expect a 19 kt difference between IAS/CAS and TAS.

The last three days I spent a lot of hours at 15,000 and 16,000.

IAS around 134.  TAS - 173.

[Fly Boomer]

16 minutes ago, Pinecone said:

The last three days I spent a lot of hours at 15,000 and 16,000.

IAS around 134.  TAS - 173.

Love that turbo!

[Pinecone]

19 hours ago, Fly Boomer said:

Love that turbo!

Yeap.

And almost no traffic in the teens.  Most little guys are below 10K.  And the bigger and faster guys are above FL200.  In 13 hours of flying, in the cruise portion I had traffic called out twice.

[M20F]

2 hours ago, Pinecone said:

Yeap.

And almost no traffic in the teens.  Most little guys are below 10K.  And the bigger and faster guys are above FL200.  In 13 hours of flying, in the cruise portion I had traffic called out twice.

Fly over 10K and you don’t have to talk to approach generally ever either, just center.  Makes for a lot less frequency changes and chatter. 

[jlunseth]

I made it from KPIA to KFDK once in about 1:45, it is ordinarily around 3:45 without wind. And a similar flight from Williston ND to KFCM. I don’t remember the exact GS but it was close got 300 in both cases, in an aircraft that cruises up high at around 175 not counting wind. It was -54 at around 21k during that WIlliston flight, so cold that with the heat in the cabin up all the way, all the windows frosted over and we were cold in the cabin. On the other hand, there have been lots of flights into the wind. I usually go down as low as I can tolerate the bumps. 130 GS is about the slowest I have seen. Sometimes with AF passengers I will fly higher into more wind than I would experience at near ground level. The wind seems to increase with altitude at about the same rate as the TAS and lots of times more, so there is not much to gain going up except a smoother ride. On flights like the KPIA and Williston flights you have to be prepared to be assigned an Arrival, which they normally only assign to turbines and turboprops. Only flown a handful of those in the roughly 1800 hours I have had my Mooney.

One of my Angel Flight passengers once told me she had flown over 100 flights with AF but mine was the only jet she had flown in though. I explained the difference between a turbine and turbo piston engine just to remain honest. I have twice been asked to slow for the Citation ahead on approach.

I imagine the Acclaims and Ultras get treated as turbines on a regular basis.

Edited October 23, 2022 by jlunseth

[Pinecone]

5 hours ago, M20F said:

Fly over 10K and you don’t have to talk to approach generally ever either, just center.  Makes for a lot less frequency changes and chatter. 

I did have to talk to approach near Valdosta.  

Moody AFB is in the area with a lot of military flight training.  The MOAs go to 18,000.  So Approach has the airspace a bit higher there.

[M20F]

1 hour ago, Pinecone said:

I did have to talk to approach near Valdosta.  .

Hence my usage of the word “generally”…..

[Pinecone]

Agreed.  Was just saying.

Out of 13 hours, that was the only time at cruise that I talked to approach.

[A64Pilot]

On 10/21/2022 at 2:58 PM, jaylw314 said:

I recall doing some back-of-the-envelope calculations to figure out how fast to fly into a headwind to maximize range, and determined your range increases as you slow down all the way to the point your TAS is twice the headwind, which I thought was a pretty useless conclusion because nobody would ever fly that slow 

I’ve never understood why so many believe you can increase range in a headwind by speeding up, when about all you can really do is sit back and try not to keep looking at your ground speed.

[A64Pilot]

3 minutes ago, mike261 said:

So hypothetically if I'm carrying  20 gallons or two hours of fuel flying at 100 knots into a 100 knot headwind I fall out of the sky in two hours and get nowhere. 

If I increase my airspeed five knots and it burns all the fuel in one hour, I fall out of the sky in one hour - five miles from where I started. my range has certainly increased, but my endurance has decreased.

 

mike

What happens is your fuel burn does not go up linearly with speed, so to increase speed by say 5% will require much more than 5% increase in fuel consumption, so you will cut down the time to destination, but you will increase total fuel burned, even though your flying for less time, I’ve only hovered helicopters and rarely the Maule on approach, I’m bailing out long before your example.  Good thing though is if you can increase 10 kts, you get the whole 10 kts increase.

I know if I look down and see 120 kts airspeed I’m trying a different altitude and or often saying to hell with the fuel, I’m going to 100 ROP and pouring the coal to the thing, because 120 kts is just too slow, I just accept the higher fuel consumption. But I’m a sailor or was anyway, I got used to many days of not making sense to go and having to wait, so if big headwinds are forecasted I reschedule, cause I’m Retired.

”Time to spare, go by air”

If I see 100 kts, I may be looking for a place to land and give tomorrow morning a try, Wx permitting of course. But I don’t remember it being that bad yet, I did see 200 kts in the Maule so that was a 65kt tailwind at altitude, but just that once, made taxing after landing interesting though.

But those are personal decisions, I’ve known guys in Cubs just live with 30ish kt ground speeds, I couldn’t do that, it would drive me crazy.

[A64Pilot]

1 hour ago, mike261 said:

If range is what you want you generally speed up with a headwind and slow down with a tailwind. that is what my example illustrates. Drag is a factor, and my example is exaggerated for clarity, but it doesn't change the math.

 

I know that’s the generally accepted rule of thumb, to increase speed by 25% of the headwind component, the idea is yes your burning more fuel, but your burning it for less time.

But it falls apart in most of actual piston engine flying, reason is in order to get that extra speed the average GA airplane has to go to best power and abandon LOP, the decrease in BSFC wipes out the decrease in time aloft.

Only time it really matters is if your stuck over open water or similar and you MUST make your next fuel stop as it’s the only option, then it REALLY matters.

Now if your the guy that flies at normal cruise altitude with the power pulled back, then sure increase speed and stay LOP. However I most often fly mid altitudes say 6 to 10,000 ft and the throttle is wide open, to get more speed means ROP and that increase in speed cost fuel in excess of time saved.

I think I’m the average guy, who flies in my case usually 23 squared or whatever MP I can get and about 8 GPH LOP which gives me 8x15=120 HP, or 60% of my 200 available. If I could burn 10 GPH LOP, that would give me 75%, but I don’t think I can unless I get pretty low, haven’t tried to be honest, but think 10 GPH puts me into ROP territory at normal cruise altitudes

Most of us NA guys can carry 23” MP only roughly up to about 6,000 ft, some days higher but not by a whole lot, so many of us don’t have any extra MP to speed up

[A64Pilot]

39 minutes ago, mike261 said:

 It matters a lot, like the countless times pilots use a lower power setting to eliminate a fuel stop and go straight to destination because they have a tailwind. That is the converse of this.

Yes, but that’s not the topic, the topic is speeding up to save fuel.

If in a tailwind and range is the only consideration stay LOP and slow to best glide speed. But that’s not what you replied to.

The truth is, is it gets complicated often involving step climbs and different airspeeds as fuel is burned off, I’m sure the airlines have this down to a science, when able.

‘For us N/A piston guys higher up if winds are equal also plays into it, generally though 8,000 plus or minus some is the sweet spot, Turbos I’m sure it’s much higher, but don’t have a number.

I used to do a lot of ferrying down to Central and South America, but turbines and they are different, for them it’s high power and high altitude as a turbine part throttle fuel efficiency sux and your not leaning one out either. I assume a turbine and a turbo would be similar as in altitude is your friend as airframe drag drops off faster than engine power.

[jaylw314]

4 hours ago, mike261 said:

So hypothetically if I'm carrying  20 gallons or two hours of fuel flying at 100 knots into a 100 knot headwind I fall out of the sky in two hours and get nowhere. 

If I increase my airspeed five knots and it burns all the fuel in one hour, I fall out of the sky in one hour - five miles from where I started. my range has certainly increased, but my endurance has decreased.

 

mike

That was kind of my estimate, in a 100 knot headwind, you'd maximize you're range by going 200 knots or so.   Above that, your fuel use will increase faster than your groundspeed increases.

OTOH, if you're headwinds are <50 knots, you're not gonna want to fly around at 100 knots just to maximize your range

Granted, your range will still absolutely suck, but it will suck the least around that speed  

Edited October 25, 2022 by jaylw314

[Hank]

3 hours ago, A64Pilot said:

”Time to spare, go by air”

If I see 100 kts, I may be looking for a place to land and give tomorrow morning a try, Wx permitting of course. 

My level cruise groundspeed window, > 7500 msl, WOT- (for improved mixing in the carb), 2500, ROP is 68-183 knots. Theb63 knots flight was dodging cloud tops below freezing between GSP and TYS (high terrain for the East), and I'd already waited a day for PIREPS of enroute icing, then rerouted around it all. As my wife said that evening, "sure am glad I'm not flying a Cessna!"

[Fly Boomer]

6 hours ago, mike261 said:

So hypothetically if I'm carrying  20 gallons or two hours of fuel flying at 100 knots into a 100 knot headwind I fall out of the sky in two hours and get nowhere. 

If I increase my airspeed five knots and it burns all the fuel in one hour, I fall out of the sky in one hour - five miles from where I started. my range has certainly increased, but my endurance has decreased.

 

mike

Beat me to it.  Gotta love mathematics.

[A64Pilot]

6 minutes ago, mike261 said:

Since you are splitting hairs... the topic is speeding up to increase range. but i'm probably wrong on that  too. 

your right, save fuel thereby increasing range. I misspoke.

I’m not saying your wrong so much as I’m saying often that “best advice” given on the internet often is, like for instance to keep from losing any speed LOP, simply increase MP until your speed is recovered. Sounds good but often isn’t possible.

I’m flying WOT now, how do I increase MP?

Maybe it’s just me and the people I hang around, but when traveling, the throttle is opened on takeoff, and not touched until the let down at destination. Altitude reduces the throttle for me.