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Author Topic: Video: Fatal Take-Off  (Read 31309 times)
moto400ex
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« Reply #30 on: September 23, 2007, 01:00:52 PM »

Yea so much for following 91.103
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keith
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« Reply #31 on: September 25, 2007, 09:24:09 AM »

The NTSB report:

My comments -
Density altitude computes to at least 3800 ft.
Maximum TOGW at SL = 3650 lbs. His TOGW computes to 3638 lbs.
Max SL HP is 300. His max available TO HP computes to 285.
Due to the lower HP and air Density ratio combination, his max propeller thrust available was less than 90% of SL rated thrust.
In effect, his maximum rate of climb out of ground effect was NEGATIVE!



I too am confused by the conclusion you draw at the end of this.  What you're saying, then, is that given standard pressure and temperature, the plane would not have been able to climb beyond 3800' MSL, and I can't quite get my head around that.
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KSYR-pjr
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« Reply #32 on: September 27, 2007, 11:21:41 PM »

I too am confused by the conclusion you draw at the end of this.  What you're saying, then, is that given standard pressure and temperature, the plane would not have been able to climb beyond 3800' MSL, and I can't quite get my head around that.

Apparently the opportunity for both you and me to learn something new every day is not going to happen anytime soon?  I have been holding my breath for an explanation but have turned three shade of blue with no relief in sight.
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Regards, Peter
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Hollis
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« Reply #33 on: September 28, 2007, 03:26:33 AM »

Well OK, here goes:
Rate-of-climb is directly proportional to the Absolute temperature ratio.
Engine BHP (Brake HP) is proportional to the square root of the air density ratio.
Propeller efficiency is likewise proportional to the air density ratio.
Wing stall INDICATED airspeed is directly proportional to gross weight.
TRUE airspeed (i.e., ground speed) is a function of temperature. (Hence a longer take-off roll at higher temps).
Rate-of-climb is approximately 20% higher in ground effect than in free air.
Rate of climb decreases proportionally to the decrease in airspeed below the BROC speed (Typically about 20% above stall speed).

(Now, for my own 'amusement', I used Microsoft Flight Simulator and took the Cessna to Livermore, CA airport and tried a few take-off runs simulating the conditions of the accident. With a 10% reduction in TO power to duplicate the high temp effect of HP loss, I got airborne, but crashed in 4 out of 5 attempts. With an HP reduction of 8%, I managed to stay airborne, but could neither gain altitude or airspeed. Any attempt to turn resulted in a sink rate toward the ground).

For further enlightenment, read up on mountain flying!



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KSYR-pjr
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« Reply #34 on: October 02, 2007, 08:52:48 AM »

Rate of climb decreases proportionally to the decrease in airspeed below the BROC speed (Typically about 20% above stall speed).

So, what's the calculation that determines rate of climb?   I still don't understand how you are concluding that the aircraft in the video experienced a negative rate of climb using the ratio above, which you are saying is proportional (a decrease in one is tied directly to the decrease in the other).  Can't have a negative airspeed so you can't have a negative rate of climb unless there is something else not obvious.

You don't have to bother with explaining the above if it becomes too much work.  I will research it when I am ready to take a mountain flying course.

One question I have that you perhaps could answer:   What is the Absolute Temperature ratio?   Absolute temperature to me is temperature measured relative to absolute zero, typically expressed on the Kelvin scale.   







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Regards, Peter
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Hollis
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« Reply #35 on: October 02, 2007, 09:47:16 AM »

You are correct regarding absolute temperature being on the Kelvin scale. In this incident the ratio would be :
Standard S.L.  OAT + 273 (= 15+273), divided by observered OAT + 273 (=
42+273), or 0.91. In other words, his max HP available was only 91% of S.L. rated HP due to temperatiure alone.
A negative rate-of-climb is simply a rate of descent. It results from the thrust being less than the drag. The equation is:
(T - D)/W. You can't climb unless T is greater than D for a given weight.
And increased weight equals increased drag since a higher angle of attack is needed to generate the lift required to balance or overcome the weight.
And yes, it is a complex mathematical process.
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realscooter
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« Reply #36 on: October 11, 2007, 07:05:25 PM »


And yes, it is a complex mathematical process.

Which, I must say, you have explained so well, that even myself, who is useless in math, can understand.

I'm new to this forum, kinda stumbled in and got interested.
I'm no pilot except for MSFS, which I started using to overcome my fear of flying. It helps a lot, because I now better understand what happens and why tons of steel do fly.

I remember having been on an Aer Lingus flight from EDDL (Dusseldorf, Germany) to EIDW (Dublin, Ireland) on a very hot and humid summer day (temperatur was 36 Celsius, don't know how much that is in Fahrenheit but I expect it to be in the hundreds).

We used a good deal more of the runway than I usually witness there in the same type of aircraft, the initial climb out of the airport was unstable and rough - just what I don't like - until about 4.000 ft.  (taken into consideration my knowledge of the terrain, because I live in the aerea and the SID routes of the airport).
The guy next to me told me it was because of the heat. I assume this must have been "High Density"?!

Thanks for all the interesting information and the entertaining chatter between pilots, soon-to-be-pilots and other non-pilots like myself.

Martin
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Hollis
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« Reply #37 on: October 11, 2007, 07:25:08 PM »

Your 36C equates to 97F, which is still pretty warm/hot.
The relationship is: 9/5C+32 = F.
The higher temperature causes both a higher 'density altitude' and a 'true airspeed', which is why it requires a longer take-off run to reach the proper take-off 'indicated' airspeed. (As seen on the instrument).
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dmccabe79
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« Reply #38 on: October 30, 2007, 11:12:38 PM »

You 250 hour pilots are killing me.  NORDO is primarily an ATC used thing. 
Although when you squawk 7600 it shows "RDOF" on the datablock...go figure.
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moto400ex
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« Reply #39 on: October 30, 2007, 11:48:35 PM »

You 250 hour pilots are killing me.  NORDO is primarily an ATC used thing. 
Although when you squawk 7600 it shows "RDOF" on the datablock...go figure.

I think we have established that a long time ago.
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KSYR-pjr
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« Reply #40 on: October 31, 2007, 09:09:54 AM »

You 250 hour pilots are killing me.  NORDO is primarily an ATC used thing. 

Ah, sheesh, this again?   
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Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
RayZor
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« Reply #41 on: October 31, 2007, 06:38:38 PM »

NORDO!? What does THAT mean?!?!  wink
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cessna157
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« Reply #42 on: November 02, 2007, 12:04:11 AM »

NORDO!? What does THAT mean?!?!  wink

Nordo is simply someone's nickname.  Probably a friend of the controller.  Short for Norman?
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JBnut
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« Reply #43 on: November 26, 2007, 07:21:39 PM »

NORDO means that a pilot has no radio communications or radio has failed





JB

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KTUS
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« Reply #44 on: November 27, 2007, 09:02:16 PM »

This safety document explains density altitude pretty well and also includes a standard Koch chart on page 3. The Koch chart is not meant to be an absolute for every aircraft or to replace proper aircraft testing, but does give an indication for what kind of performance degradation might be expected. YMMV, etc...

http://www.gofir.com/aviation_accident_prevention_program/docs/pdf/density_altitude.pdf
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