VIDEO of managing drag during Approach

[Buzz313th 0]

I don't think your little experiment can shed any light on fuel efficiency. And oh, btw, you could repeat this experiment and observe the fuel flow - that should tell you the fuel efficiency story....

Well the experiment used idle thrust from 250 to 200 kias. So unless flight idle changes with aircraft weight, then fuel flow should be a constant.Correct me if I'm wrong, but in level flight both weight and lift are equal, so all we have left is thrust and drag. The heavy aircraft obviously shows less drag than the light aircraft as it decelerates at a slower rate. So in a steady state situation and in level flight does that mean that the heavy aircraft which has less drag requires less thrust to maintain a given airspeed? Less thrust would mean less fuel flow, wouldn't it?JB

[michal 44]

Well the experiment used idle thrust from 250 to 200 kias. So unless flight idle changes with aircraft weight, then fuel flow should be a constant.

Well, obviously using idle thrust doesn't give you anything, use the thrust to maintain a steady speed of your choice and then look at the fuel flow.

So in a steady state situation and in level flight does that mean that the heavy aircraft which has less drag requires less thrust to maintain a given airspeed?

In a steady state keeping the same chosen speed heavier (but otherwise identical) aircraft will need higher angle of attack, higher angle of attack means more induced drag, more drag means more thrust. Your "slowing down" scenario has nothing to do with steady state.

[Buzz313th 0]

Michal I think your missing the point. The deceleration experiment shows drag levels for a light and heavy NGX in the flight envelope at 10k feet between 200 and 250 kts. The experiment shows that regardless of induced drag, the flight model of the heavy aircraft takes longer to decelerate in level flight than the light aircraft. This means that the heavy aircraft in level flight has less drag than the lighter one. If you understand the 4 opposing forces of flight, which I believe you do, then you will know the opposing force of drag is thrust. Less drag means less thrust to maintain a given airspeed in level flight. I know you understand that with all other factors being the same, that less thrust means less fuel being used. The point here is that I am confused as to why the NGX does not seem to model the correct amount of induced drag caused by an increase in aoa from a heavier aircraft weight. Fuel flow in FSX can and has been customized through external programing to meet specific performance charts.Furthermore, It is my understanding, that other than the takeoff, climb, descent and the landing portion of a flight, the reason why every aircraft known to the public burns more fuel in cruise (level flight) when it's heavy, is because the increased weight increases aoa and higher aoa increases induced drag and higher drag means more thrust to maintain cruise flight at a given airspeed.JB

[michal 44]

This means that the heavy aircraft in level flight has less drag than the lighter one.

No, wrong conclusion.

The point here is that I am confused as to why the NGX does not seem to model the correct amount of induced drag

Because you are generally confused about aerodynamics. I end with this, this is rather complicated topic and you are trying to fit everything in a few "Buzz" words (pun intended!). Grab some textbook on aerodynamics.

[Buzz313th 0]

No, wrong conclusion. Because you are generally confused about aerodynamics. I end with this, this is rather complicated topic and you are trying to fit everything in a few "Buzz" words (pun intended!). Grab some textbook on aerodynamics.

Ok still sitting here trying to wrap my head around it and realized that my conclusion on drag from the test does not take into consideration momentum. So the test shows drag minus momentum or drag minus mass times velocity. So my conclusion is incorrect in thinking that the test represents the sum of nothing more than parasitic drag and induced drag. It also contains foreward momentum that I didn't consider.JB

[michal 44]

Ok still sitting here trying to wrap my head around it and realized that my conclusion on drag from the test does not take into consideration momentum.

You can think of the momentum if it helps but even just dealing with the mass should help explain everything.We have parasitic and induced drag. Induced drag goes up with a square of lift so induced drag will be much higher for a heavier aircraft. However in the range of speeds 200 to 250 kts parasitic drag will be dominant (we are on the right side of the power curve). Parasitic drag will be practically the same for both aircraft, in other words the extra drag due to induced drag for heavier aircraft will not be enough to compensate for its heavier mass hence deceleration of the heavier aircraft will be slower (as we know acceleration is force divided by mass).

[Bobby737 0]

It's all about the weight. How fast or slow You decelerate or descend depends on the gross weight. A 737-800 at 60 tons or above needs about one mile to loose 10 knots in level flight. The rate of descend with up speed is around 1100 fpm, speedbrakes aren't that efficient at slow speeds and give You around 1500 fpm. Your aim should be to have the glideslope alive at up speed to select Flaps 1. One dot below select Flaps 5 to be at flaps 5 speed when the GS is captured. If the slope is more than 3 degrees or if You experience tail wind, You can also try flaps 10 to put the leading edge devices in full extend, while having the same maneuvering speed. In our company it is mandatory to lower the gear at 2000 ft, which is quite conservative, but almost guarantees a stabilized approach at 1000 ft.

[Richard Sennett 2,499]

Great videos Jack thanks so much Buddy. Regards, Rich

[Jack_C 1]

No prob Rich. I sent you a pm back

[asc_airlimo 0]

Without starting an argument here but I've never heard of using flaps to slowdown an airplane. I have no problems slowing this plane down without the use of flaps on approach. I used the flaps but only as my speed decreases and I need more lift at the slower speeds. Pitch controls airspeed.

[Jack_C 1]

You can get a 130,000 pound 800 flying a 3.5 degree glideslope to slow down on an ILS or RNP approach without he use of flaps. Can you show a video? And keep in mind the ATC clearance maybe "maintain 210 until established".

[asc_airlimo 0]

3.5 is steep compared to most that are 3.0 and I always intercept at 180 kias and 5* of flaps but I'll try 210 for the challenge. I don't have any video making software, what do you recommend I get?

[Jack_C 1]

I think most ppl are using fraps. In the real thing once established on the glideslope and were asked to maintain 180 and the APP asks you to reduce to 160 by the FAF, you normally need flaps to slow you down. Or if you are doing the rnp into kelowna for example, you need flaps 10 to help you reduce speed unless you want to drop the gear 15 miles back but then it just makes a lot of wind noise.

[ahsmatt7 1,199]

you need flaps 10 to help you reduce speed unless you want to drop the gear 15 miles back but then it just makes a lot of wind noise.

Yeah but thats the best part!