Book Speeds

Radar Contact

Radar Contact

Pattern Altitude
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I was just editing a video where I was explaining my power setting, altitude, temp, etc and mention my TAS of 181 kts. I just pulled out the book and saw that I was exactly 1 kt greater than the book speed for conditions. We always hear about tired old planes not making near book numbers and guess I was a little surprised. Just curious, how many others have done this recently and are ya'll getting close to book speeds, better or worse?

I was primarily capturing the data because I'm having her painted and VG's installed and wanted to see what, if any, impact it will have. I've heard people say with crappy old paint (especially double/triple coated) that they've picked up a couple knots. Anyone experience better speeds with fresh paint?
 
The probably forgot to put your antennas back on after the paint job.
 
Radar Contact said:
I was just editing a video where I was explaining my power setting, altitude, temp, etc and mention my TAS of 181 kts. I just pulled out the book and saw that I was exactly 1 kt greater than the book speed for conditions. We always hear about tired old planes not making near book numbers and guess I was a little surprised.
Click to expand...

Measuring accurate "air data" -- static and total pressure that are used to calculate altitude, airspeed, and rate-of-climb -- is one of the most difficult challenges in aircraft design. What was used in this case to determine TAS? If it was a GPS-derived value from a modern PFD like a G500 or Aspen, then that's probably pretty accurate. On the other hand, if TAS was being "calculated" by turning the conversion bezel on a pneumatic airspeed indicator, then errors are very likely. Airspeed indicators are based on a complicated system of springs and bellows that deform over time, and our 40-year old instruments typically read fast (sometimes, very fast). Also -- was the calibration correction out of the POH added to the indicated value? That has to be done to get TAS.

The other thing that has to be considered is what aircraft designers call "test day conditions". POH performance values are published for a specific weight and CG position and at a standard atmosphere. If the test day weight was lighter or the cg further aft, or if the ambient air was cooler or drier than standard atmosphere, then one should expect performance "better than book".

As pilots, we really aren't very good at determining accurate aircraft performance information.
 
Radar Contact said:
I was just editing a video where I was explaining my power setting, altitude, temp, etc and mention my TAS of 181 kts. I just pulled out the book and saw that I was exactly 1 kt greater than the book speed for conditions. We always hear about tired old planes not making near book numbers and guess I was a little surprised. Just curious, how many others have done this recently and are ya'll getting close to book speeds, better or worse?

I was primarily capturing the data because I'm having her painted and VG's installed and wanted to see what, if any, impact it will have. I've heard people say with crappy old paint (especially double/triple coated) that they've picked up a couple knots. Anyone experience better speeds with fresh paint?
Click to expand...
A few reasons you might be seeing a higher TAS than your POH specifies:

1. You were lighter than the weight the POH assumed to calculate the speed (a very rough rule of thumb is that you gain 1 kt for every 100 lb lighter for light piston utility planes like ours).

2. You were in an area of rising air, so you were in a slight aerodynamic dive relative to the airmass (even though your altitude wasn't changing).

3. Your tachometer and/or MP gauge was reading a bit low, so your engine was producing slightly more power than you thought.

4. You were at a higher density altitude than you thought (e.g. your thermometer was reading a bit low).

I'd say 1 or 2 is most likely.

And most people who say their planes don't make within 10 kt of POH numbers are the same ones who don't pay attention to their power-setting tables, and just always fly "24 squared" (or whatever) regardless of the density altitude they're cruising at.
 
X amount of fuel + y amount of air = z amount of power. There’s no age of engine variable in there. Granted poor rigging can slow you down some, as can a worn cam reduce x and y to some degree, it’s got to be pretty bad to move the numbers significantly.
 
Squirrelfury said:
Measuring accurate "air data" -- static and total pressure that are used to calculate altitude, airspeed, and rate-of-climb -- is one of the most difficult challenges in aircraft design. What was used in this case to determine TAS? If it was a GPS-derived value from a modern PFD like a G500 or Aspen, then that's probably pretty accurate. On the other hand, if TAS was being "calculated" by turning the conversion bezel on a pneumatic airspeed indicator, then errors are very likely. Airspeed indicators are based on a complicated system of springs and bellows that deform over time, and our 40-year old instruments typically read fast (sometimes, very fast). Also -- was the calibration correction out of the POH added to the indicated value? That has to be done to get TAS.

The other thing that has to be considered is what aircraft designers call "test day conditions". POH performance values are published for a specific weight and CG position and at a standard atmosphere. If the test day weight was lighter or the cg further aft, or if the ambient air was cooler or drier than standard atmosphere, then one should expect performance "better than book".

As pilots, we really aren't very good at determining accurate aircraft performance information.
Click to expand...
Thank you for your thoughts/information. I used my new ADC that displayed the data on the Avidyne IFD 550. It was installed in conjunction with the STEC 3100 and has to be very accurate as it is used to help control the envelope protection.

I did verify the conditions compared to what the book lists. I was a few hundred lbs lighter and that would make sense why I was doing a little better.

David Megginson said:
A few reasons you might be seeing a higher TAS than your POH specifies:

1. You were lighter than the weight the POH assumed to calculate the speed (a very rough rule of thumb is that you gain 1 kt for every 100 lb lighter for light piston utility planes like ours).

2. You were in an area of rising air, so you were in a slight aerodynamic dive relative to the airmass (even though your altitude wasn't changing).

3. Your tachometer and/or MP gauge was reading a bit low, so your engine was producing slightly more power than you thought.

4. You were at a higher density altitude than you thought (e.g. your thermometer was reading a bit low).

I'd say 1 or 2 is most likely.

And most people who say their planes don't make within 10 kt of POH numbers are the same ones who don't pay attention to their power-setting tables, and just always fly "24 squared" (or whatever) regardless of the density altitude they're cruising at.
Click to expand...
1. I was indeed a bit lighter and that makes sense
2. Maybe, seemed pretty stable
3. I have analogue and a separate Digital representation of these and they were both showing the same.
4. I have separate thermometers and verified them both

I think the primary reason I was slightly faster than book was the reduced weight and that makes sense. People regularly mention how hard book numbers/performance numbers in the POH are to obtain...."test pilot...perfect conditions...new motors...new props...no dents/perfect paint...etc", I guess I was just surprised my 40+ year old plane with mid-time engines, de-ice boots installed and really crappy paint would be right there with the book. I've also verified takeoff/landing distances and seem to be right there. Takeoff/landing numbers will improve slightly with the new VG's, hopefully cruise isn't impacted.
 
LOL, I use mph for airspeed..:lol::lol: Outer ring on ASI is mph. The Sport is underpowered with a draggy airframe. It is close to book numbers. Best speeds are a cold winter day were I get better than book numbers...:rolleyes:
 
Radar Contact said:
Thank you for your thoughts/information. I used my new ADC that displayed the data on the Avidyne IFD 550. It was installed in conjunction with the STEC 3100 and has to be very accurate as it is used to help control the envelope protection.
Click to expand...
I think the ADC still uses KIAS rather than KCAS. Does the book even list a KIAS vs KCAS difference at your speed/altitude?
 
James331 said:
Most planes I’ve flown hit book numbers.

Things seem to have to be a good bit out of whack to not hit book
Click to expand...

That has been my experience too. I have flown a few airplanes that were pretty bad but they were generally airplanes that had suffered major damage and were poorly repaired.

Personally, I think the old adage that airplanes won’t make book numbers was started by people, perhaps instructors, who aren’t disciplined enough to fly by book numbers. Every primary student I’ve had could meet the takeoff and landing distances listed in the flight manual, and every time TAS is checked it is within a knot of book numbers when the power is set appropriately.
 
Radar Contact said:
Takeoff/landing numbers will improve slightly with the new VG's, hopefully cruise isn't impacted.
Click to expand...

I'd be willing to bet you'll see a loss of cruise speed. I've flown several PA18s before and after vortex generator installation and like clockwork they all lost about 5mph. These were clean, well rigged airframes too, not some ratty POS.
 
Some say a dimpled surface is slicker through the air than a smooth one. I figure the more dents and dings I get, the faster I can go. :D
 
Radar Contact said:
Thank you for your thoughts/information. I used my new ADC that displayed the data on the Avidyne IFD 550. It was installed in conjunction with the STEC 3100 and has to be very accurate as it is used to help control the envelope protection.

I did verify the conditions compared to what the book lists. I was a few hundred lbs lighter and that would make sense why I was doing a little better.


1. I was indeed a bit lighter and that makes sense
2. Maybe, seemed pretty stable
3. I have analogue and a separate Digital representation of these and they were both showing the same.
4. I have separate thermometers and verified them both

I think the primary reason I was slightly faster than book was the reduced weight and that makes sense. People regularly mention how hard book numbers/performance numbers in the POH are to obtain...."test pilot...perfect conditions...new motors...new props...no dents/perfect paint...etc", I guess I was just surprised my 40+ year old plane with mid-time engines, de-ice boots installed and really crappy paint would be right there with the book. I've also verified takeoff/landing distances and seem to be right there. Takeoff/landing numbers will improve slightly with the new VG's, hopefully cruise isn't impacted.
Click to expand...
Piper made a big point in their ads in the early 1960s that they calculated their book numbers (for the Comanche, I think) under realistic conditions—full load, full panel, many types of weather, lots of antennas sticking out, etc. The implication was that other manufacturers didn't, but there was probably a lot of variation.

I imagine the impact of old paint, etc, would depend on things like your wing design. My PA-28-161, for example, isn't exactly a Mooney with its slick laminar wing, so a bit of roughness on the surface probably won't make me noticeably slower than I already am.
 
Radar Contact said:
I was just editing a video where I was explaining my power setting, altitude, temp, etc and mention my TAS of 181 kts. I just pulled out the book and saw that I was exactly 1 kt greater than the book speed for conditions. We always hear about tired old planes not making near book numbers and guess I was a little surprised. Just curious, how many others have done this recently and are ya'll getting close to book speeds, better or worse?

I was primarily capturing the data because I'm having her painted and VG's installed and wanted to see what, if any, impact it will have. I've heard people say with crappy old paint (especially double/triple coated) that they've picked up a couple knots. Anyone experience better speeds with fresh paint?
Click to expand...

Were you at the same weight as the book values?
 
Book speeds. When I throw a book out of my plane it accelerates at the same speed my physics teacher taught me it would.

I will show myself out.
 
Many certified aircraft have some static error making the TAS a bit optimistic. Run the aircraft through 3 90 degree headings and plug the data into this website. Don’t be surprised if your not as fast as you thought.
http://www.csgnetwork.com/tasgpscalc.html
 
Jeff767 said:
Many certified aircraft have some static error making the TAS a bit optimistic. Run the aircraft through 3 90 degree headings and plug the data into this website. Don’t be surprised if your not as fast as you thought.
http://www.csgnetwork.com/tasgpscalc.html
Click to expand...
... or just use the airspeed calibration table in your POH. For my PA-28-161, the ASI reads a few knots low around stall speed, about right near 55% power, and slightly high by 75% power.

The averaging of groundspeeds has its own problems, because it assumes the air has no vertical motion, which is rarely the case. If the air is rising slightly, you'll get a result that's too high; if the air is descending slightly (as it often is in nice, stable conditions), then you'll get a result that's too low.
 
AKBill said:
LOL, I use mph for airspeed..:lol::lol: Outer ring on ASI is mph. The Sport is underpowered with a draggy airframe. It is close to book numbers. Best speeds are a cold winter day were I get better than book numbers...:rolleyes:
Click to expand...
... unless you calculate your density altitude. :)
 
Just because an airplane is old doesn't necessarily make it slow, assuming it's maintained correctly and lovingly

many rental planes are slow because they're probably way out of rig and have underperforming engines with bad timing, low compressions, etc

But strictly speaking, age of an airplane should have nothing to do with its speed..

Was the Concorde any slower in 2004 than it was in 1970?

Late 70s and early 80s racing sailboats in the 40 ft range are still much faster than many of the newer beneteau out there, and can be had for less than $50,000
 
David Megginson said:
... or just use the airspeed calibration table in your POH. For my PA-28-161, the ASI reads a few knots low around stall speed, about right near 55% power, and slightly high by 75% power.

The averaging of groundspeeds has its own problems, because it assumes the air has no vertical motion, which is rarely the case. If the air is rising slightly, you'll get a result that's too high; if the air is descending slightly (as it often is in nice, stable conditions), then you'll get a result that's too low.
Click to expand...

just to be clear the website is not averaging airspeeds. That won’t provide a accurate TAS. The math is complicated and it solves it for you. It provides a check of your actual TAS and can help check for errors in your pitot static system.
 
Jeff767 said:
just to be clear the website is not averaging airspeeds. That won’t provide a accurate TAS. The math is complicated and it solves it for you. It provides a check of your actual TAS and can help check for errors in your pitot static system.
Click to expand...
It's not bad as a minor secondary check, I guess, but not in the same league as an actual pitot-static correlation check by a qualified instrument specialist with the proper equipment (which we have to do every 2 years in Canada, at least, if we fly IFR and/or in controlled airspace; not sure about US rules).

As I mentioned before, groundspeed readings can't take vertical motion of the air into account, no matter how "complicated" the math applied to them is, so any result could be accurate only at a time and place where the air had minimal vertical movement. And the user could still easily misinterpret its relationship to TAS if they hadn't calculated density altitude and power output correctly.
 
A pitot static check will not show static system errors that occur. The static side is after all static until you start moving the aircraft through the air rapidly. The above test is used by most test pilot schools. There is another check for a static system issue. You can set your altimeter to read zero altitude prior to takeoff or note the exact reading. You can then make a high speed low pass down the runway. If the altitude reads differently you have a speed induced static error.
 
asicer said:
I think the ADC still uses KIAS rather than KCAS. Does the book even list a KIAS vs KCAS difference at your speed/altitude?
Click to expand...
My ADC displays displays KCAS. The book does list the difference between KIAS and KCAS, at that speed it was less than 2 knots.

*edit to add the pic:
Screen Shot 2020-01-27 at 5.42.39 PM.png
 
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