Supercop0184

True airspeed not what book says

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Is your step and landing gear fully retracting? Just a quick thought.

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FWIW

Power problems show up in reduced climb rate. Rigging problems show up in reduced cruise speeds. The POH climb numbers are usually pretty close to reality.

Edited by N201MKTurbo
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On 1/7/2019 at 7:00 PM, gsxrpilot said:

We just did DRO to 84R which is 100 miles further, on 48 gal.

 I generally when traveling to Durango I'm flying relatively low due to head winds.  And if I'm flying low and I pass by an airport with cheap fuel (like KPVW), I'll stop. My wife appreciates the bath room break, I like having extra fuel reserves since the airports are further apart, and fuel is a bit pricey in the mountains.   On the way home, its almost always a non-stop trip and typically  17,000  or above.

My last trip home was right at 4 hours, and about 45 gallons.   --That said, I tend to go direct and over fly over 13,000 foot mountains.   In a "C" I might find a lower route, probably south, and then between  Santa Fe and Albuquerque.  --Though I believe there are some passes near KAXX if flying VFR

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5 hours ago, chrisk said:

 I generally when traveling to Durango I'm flying relatively low due to head winds.  And if I'm flying low and I pass by an airport with cheap fuel (like KPVW), I'll stop. My wife appreciates the bath room break, I like having extra fuel reserves since the airports are further apart, and fuel is a bit pricey in the mountains.   On the way home, its almost always a non-stop trip and typically  17,000  or above.

My last trip home was right at 4 hours, and about 45 gallons.   --That said, I tend to go direct and over fly over 13,000 foot mountains.   In a "C" I might find a lower route, probably south, and then between  Santa Fe and Albuquerque.  --Though I believe there are some passes near KAXX if flying VFR

Sounds like we take the exact route 

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7 hours ago, N201MKTurbo said:

FWIW

Power problems show up in reduced climb rate. Rigging problems show up in reduced cruise speeds. The POH climb numbers are usually pretty close to reality.

Here’s the issue - I’m getting good static MP on the ground and down the runway - but I looked at my POH, and I’m not getting anywhere near those climb rates -and I’m not even ever at gross -  POH SAYS I should still be getting 600 FPM at 10k. That does NOT HAPPEN. I’m doing good to get 500 ft a minute by5-6k feet. What’s happening?

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Don't forget a good wax job is worth @10kts  :-)

  • Haha 3

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3 hours ago, Supercop0184 said:

Here’s the issue - I’m getting good static MP on the ground and down the runway - but I looked at my POH, and I’m not getting anywhere near those climb rates -and I’m not even ever at gross -  POH SAYS I should still be getting 600 FPM at 10k. That does NOT HAPPEN. I’m doing good to get 500 ft a minute by5-6k feet. What’s happening?

Hard to say. MP just means the pistons are going up and down, so you can't use that as a gauge of engine health. If you think there is a power problem it comes down timing, compression and valve lift.

Has the airplane ever performed better? How long have you had it? How much time is on the engine? Are all your cylinders firing? 

 

Too bad our engines don't have gearboxes like the old radials. Then we would have a torque meter and a direct readout of power.

Edited by N201MKTurbo
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Just now, N201MKTurbo said:

Hard to say. MP just means the pistons are going up and down, so you can't use that as a gauge of engine health. If you think there is a power problem it comes down timing, compression and valve lift.

Has the airplane ever performed better? How long have you had it? How much time is on the engine? Are all your cylinders firing? 

All cylinders firing - compressions excellent - and I think he just reset timing when he removed and re installed one of the magnetos

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2 minutes ago, N201MKTurbo said:

Hard to say. MP just means the pistons are going up and down, so you can't use that as a gauge of engine health. If you think there is a power problem it comes down timing, compression and valve lift.

Has the airplane ever performed better? How long have you had it? How much time is on the engine? Are all your cylinders firing? 

And no I don’t feel that it has done better - I’ve owned it for three years - 1900 SMOH about 500 since top

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2 minutes ago, Supercop0184 said:

And no I don’t feel that it has done better - I’ve owned it for three years - 1900 SMOH about 500 since top

Hard to say, you could have a worn cam. They sneak up on you slowly. Oil analysis should show some metal if it is that bad.

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2 hours ago, Supercop0184 said:

Here’s the issue - I’m getting good static MP on the ground and down the runway - but I looked at my POH, and I’m not getting anywhere near those climb rates -and I’m not even ever at gross -  POH SAYS I should still be getting 600 FPM at 10k. That does NOT HAPPEN. I’m doing good to get 500 ft a minute by5-6k feet. What’s happening?

According to my Owners Manual, the climb at 10,000msl is 570 fpm with the following conditions:

  1. ISA atmosphere (i.e., 23°F) 
  2. Airspeed = Vy = 90 mph indicated
  3. Flaps 15° (Takeoff setting)
  4. WOT / 2700 / Full Rich
  5. Loaded to 2200 lb, or approximately:
  • Empty weight = 1670 (my plane, use your empty weight)
  • Full fuel = 312
  • Me on the left = 200 dressed (hah! Less than this now!  :) )
  • "Stuff" that lives in the plane = 20

That's 2202, pretty close to The Book's 2200 lb. Anything else will reduce climb rate on a straight-line basis to 370 fpm at gross (2575 lb).

Don't know ISA pressure at 10K, but in the summer when temps are pushing 60° instead of 23°, my climb rate is significantly reduced even with my 3-blade prop (reduced by ~50%).

Next time, record your loading (including fuel at departure), temps on the ground and aloft, MP aloft and whether you are using flaps. I almost never have flaps down for very long. Search for a thread from a couple of years back where we were timing our climbs, and think about having someone ride right seat and collect data every 1000 feet:  MP, OAT, elapsed time, Vertical Speed, Airspeed. I tried doing it myself and it's quite difficult.

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14 minutes ago, Hank said:

According to my Owners Manual, the climb at 10,000msl is 570 fpm with the following conditions:

  1. ISA atmosphere (i.e., 23°F) 
  2. Airspeed = Vy = 90 mph indicated
  3. Flaps 15° (Takeoff setting)
  4. WOT / 2700 / Full Rich
  5. Loaded to 2200 lb, or approximately:
  • Empty weight = 1670 (my plane, use your empty weight)
  • Full fuel = 312
  • Me on the left = 200 dressed (hah! Less than this now!  :) )
  • "Stuff" that lives in the plane = 20

That's 2202, pretty close to The Book's 2200 lb. Anything else will reduce climb rate on a straight-line basis to 370 fpm at gross (2575 lb).

Don't know ISA pressure at 10K, but in the summer when temps are pushing 60° instead of 23°, my climb rate is significantly reduced even with my 3-blade prop (reduced by ~50%).

Next time, record your loading (including fuel at departure), temps on the ground and aloft, MP aloft and whether you are using flaps. I almost never have flaps down for very long. Search for a thread from a couple of years back where we were timing our climbs, and think about having someone ride right seat and collect data every 1000 feet:  MP, OAT, elapsed time, Vertical Speed, Airspeed. I tried doing it myself and it's quite difficult.

Here’s a question - if the CAM lobes were spalled and that was causing a cylinder to not have full motion - would this affect cylinder head temps or any temps seen on an engine monitor?

 

seems to me that might affect the temperature of the affected cylinder - but I’m not sure how. 

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Here’s a question - if the CAM lobes were spalled and that was causing a cylinder to not have full motion - would this affect cylinder head temps or any temps seen on an engine monitor?
 
seems to me that might affect the temperature of the affected cylinder - but I’m not sure how. 

No, but it will affect Gami spread. A bad cam can cause cylinders to run rich (less fresh air).


Tom

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Adding to the methods of data collection...

i use the cloud ahoy app, with a WAAS/ sky radar as the data source...

Measuring T/O distance... is a great HP measuring tool...

less drag involved... a lot less...

Climb rate is also a great method of accounting for excess hp...Vx, Vy, Vz....

Best regards,

-a-

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11 hours ago, ArtVandelay said:


No, but it will affect Gami spread. A bad cam can cause cylinders to run rich (less fresh air).


Tom

What you say is true for a fuel injected engine. for a carbureted engine the mixture is made up before the air enters the cylinder.

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They exaggerate speeds in the book.  What a surprise!  I could have a heart attack from the surprise!

 

 

 

 

we need a special font for sarcasm

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A few things come to mind that can be checked without much effort/cost

  • Have you checked the accuracy of your air speed indicator? 
  • Temperature can have a massive impact on performance.  I'm assuming an accurate measurement and correction to density altitude.
  • Is your altimeter accurate at altitude?

Other items that may effect performance (and are a bit harder to check)

  • Is the W&B accurate for your plane?
  • Is the RPM indicated accurate?

 

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On ‎1‎/‎8‎/‎2019 at 1:57 AM, Hank said:

So if I did the math right, at 9500 msl:

144 + 19% = 171 mph

I spent several years working out whether my C model was doing ok or not. I always felt it was slow compared to the book.

Then I installed an Aspen which delivers TAS all the time. First thing I got was this:

Salzburg%20March%202015%20017.JPG

6500 ft, WOT, 2500 RPM and 9.8 GPH, leaned to 50°f ROP. Now that is not how I usually fly, my usual regime is WOT, 2300 RPM and LOP which gives me some 145 kts at this altitude.  

You can calculate, do math, most of the time our gauges are not accurate enough to really give proper TAS values. If at all, you need to have all parameters available and calculate using the E6B app or something like this, which most of the time is not ideal either. The Aspen (and other EFIS including an ADC) will deliver pretty straightforward TAS which is quite accurate.

Or you can do the 4 way ground speed test Bob Kromer used to do for the planes he tested for mooney. His M20C test is here.

In the end, what you need to do is "testfly" your particular airframe and note down the values regularly, then you can see how much it differs from the poh and update your flight planning app with correct figures. However, what I have found is that while the POH is quite optimistic in top speeds, it becomes much more realistic when you look at more normal values such as fixed percentage power (55/65/75%) which does take a bit of numbercrunching but it comes out not bad usually. Also you need to take into account that all speeds in the POH are ISA, which hardly ever exists. So you need to always know your DA as well to be able to say whether your plane is close to POH or not.

It is also interesting to calculate the sweet spots for your plane, that is where speed, range and economy deliver the best bang for buck. And to know the high-speed cruise, economy cruies, best range cruise parameters. These don't come in the POH listed as such, you need to read them out of the performance tables and figure them out. Lots of work but also lots of fun.

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What you say is true for a fuel injected engine. for a carbureted engine the mixture is made up before the air enters the cylinder.

Good point, so power is reduced but I don’t think that will substantially effect EGTs or CHTs, unless it gets really bad. CMIIW.

 

 

Tom

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20 hours ago, Supercop0184 said:

Here’s the issue - I’m getting good static MP on the ground and down the runway - but I looked at my POH, and I’m not getting anywhere near those climb rates -and I’m not even ever at gross -  POH SAYS I should still be getting 600 FPM at 10k. That does NOT HAPPEN. I’m doing good to get 500 ft a minute by5-6k feet. What’s happening?

Polished spinner or painted?

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2 hours ago, Urs_Wildermuth said:

I spent several years working out whether my C model was doing ok or not. I always felt it was slow compared to the book.

Then I installed an Aspen which delivers TAS all the time. First thing I got was this:

Salzburg%20March%202015%20017.JPG

6500 ft, WOT, 2500 RPM and 9.8 GPH, leaned to 50°f ROP. Now that is not how I usually fly, my usual regime is WOT, 2300 RPM and LOP which gives me some 145 kts at this altitude.  

You can calculate, do math, most of the time our gauges are not accurate enough to really give proper TAS values. If at all, you need to have all parameters available and calculate using the E6B app or something like this, which most of the time is not ideal either. The Aspen (and other EFIS including an ADC) will deliver pretty straightforward TAS which is quite accurate.

Or you can do the 4 way ground speed test Bob Kromer used to do for the planes he tested for mooney. His M20C test is here.

In the end, what you need to do is "testfly" your particular airframe and note down the values regularly, then you can see how much it differs from the poh and update your flight planning app with correct figures. However, what I have found is that while the POH is quite optimistic in top speeds, it becomes much more realistic when you look at more normal values such as fixed percentage power (55/65/75%) which does take a bit of numbercrunching but it comes out not bad usually. Also you need to take into account that all speeds in the POH are ISA, which hardly ever exists. So you need to always know your DA as well to be able to say whether your plane is close to POH or not.

It is also interesting to calculate the sweet spots for your plane, that is where speed, range and economy deliver the best bang for buck. And to know the high-speed cruise, economy cruies, best range cruise parameters. These don't come in the POH listed as such, you need to read them out of the performance tables and figure them out. Lots of work but also lots of fun.

Wow - that’s pretty substantial isn’t it - let me ask this? Have you done a test on your rate of climb / take off roll? Just curious. Thanks for the info! 

 

3 hours ago, chrisk said:

A few things come to mind that can be checked without much effort/cost

  • Have you checked the accuracy of your air speed indicator? 
  • Temperature can have a massive impact on performance.  I'm assuming an accurate measurement and correction to density altitude.
  • Is your altimeter accurate at altitude?

Other items that may effect performance (and are a bit harder to check)

  • Is the W&B accurate for your plane?
  • Is the RPM indicated accurate?

 

I have NOT tested RPM / airspeed indicator / next time I’m on the ground I’ll compare the OAT gauge to the reported temperature. Thanks for your input. 

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If you're not using it already, the CloudAhoy app for your iPad or phone is really good for evaluating takeoff roll, time to climb, landings, etc. Everything is done automatically and recorded. I also like that once started, it runs in the background and I can open and use a different app like ForeFlight.

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5 hours ago, chrisk said:

A few things come to mind that can be checked without much effort/cost

  • Have you checked the accuracy of your air speed indicator? 
  • Temperature can have a massive impact on performance.  I'm assuming an accurate measurement and correction to density altitude.
  • Is your altimeter accurate at altitude?

Other items that may effect performance (and are a bit harder to check)

  • Is the W&B accurate for your plane?
  • Is the RPM indicated accurate?

 

How does one check one’s airspeed indicator for accuracy?

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20 minutes ago, Aviationinfo said:

How does one check one’s airspeed indicator for accuracy?

An IFR pitot/static check is the gold standard on the ground.

In the air, you can make a functional check with your GPS.  There are a couple techniques posted elsewhere, but if you fly in different directions and average your GPS groundspeed, then convert to TAS, then IAS and compare that to your indicator

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12 minutes ago, jaylw314 said:

An IFR pitot/static check is the gold standard on the ground.

In the air, you can make a functional check with your GPS.  There are a couple techniques posted elsewhere, but if you fly in different directions and average your GPS groundspeed, then convert to TAS, then IAS and compare that to your indicator

I have never had my airspeed indicator checked for an IFR cert. They check your static system for leaks and your altimeter and encoder for accuracy and friction.

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