Need help with some commercial maneuvers.

[shdw]

I was referring to when you were still carrying power. Gear down midfield, keep your speed up until abeam the touchdown point, then chop power. The faster you are at that point, the more airspeed you have to convert into altitude.

Easy. Since you seem technically minded, draw the induced drag curve and parasite drag curve. The speed of best glide is at the intersection. Now raise the parasite drag curve due to gear extension and see what happens to the best glide airspeed.

First, thanks for clearing that 120 up that was as shocking to me as the intern_mike with the 60 degrees transition to slip. You had me seriously scared sir!

As for the second thanks thats what I was thinking but was unsure if thats where you were going with that. Still no book value so I wonder how much it really is effected but the gear is 500 feet per minute so I would assume your right that it is pretty substancial. I will have to play around with that some next time I am in an Arrow. Thank you sir.

 

[tgrayson]

I would assume your right that it is pretty substantial.

I recall it making a very large difference. I'd usually shoot for about 95 mph. If you wanted to be very technical about it, you could go out to the practice area and record descent rates vs airspeed for a variety of configurations and go home and calculate your glide angle and drag.

sin(descent angle) = -Drag/Weight

 

[shdw]

I recall it making a very large difference. I'd usually shoot for about 95 mph. If you wanted to be very technical about it, you could go out to the practice area and record descent rates vs airspeed for a variety of configurations and go home and calculate your glide angle and drag.

sin(descent angle) = -Drag/Weight

That is exactly what I was referring to doing Now I just need a piper arrow and an hour of flight time. If i visit the college again I can take an engineer up to plug in his computer and make that much simpler. lol

 

[tgrayson]

That is exactly what I was referring to doing Now I just need a piper arrow and an hour of flight time. If i visit the college again I can take an engineer up to plug in his computer and make that much simpler. lol

You warm my heart. Don't forget to take into account your fuel burn when calculating aircraft weight.

 

[shdw]

You warm my heart. Don't forget to take into account your fuel burn when calculating aircraft weight.

Awww *non gay hug!* lol Will do thanks for the insight.

PS let me guess you agree we should have AoA indicators in all trainer aircraft? On top of that maybe AoA indicators incorperated into airspeed indicators to show increased stall speed from load factor! That'll be the day wahooo

 

[tgrayson]

PS let me guess you agree we should have AoA indicators in all trainer aircraft? On top of that maybe AoA indicators incorperated into airspeed indicators to show increased stall speed from load factor! That'll be the day wahooo

I'm ambivalent about it. I think people stall only when they aren't paying attention. At reasonable bank angles and normal handling of the aircraft, the airspeed indicator is a good measure of AoA. If you aren't paying attention to the airspeed indicator, it's unlikely you'd be paying much attention to an AoA indicator.

I do think having an AoA indicator would be a good educational tool in order to show the dependence of airspeed on AoA, which still escapes many people.

 

[shdw]

If you aren't paying attention to the airspeed indicator, it's unlikely you'd be paying much attention to an AoA indicator.

Valid point I agree.

I do think having an AoA indicator would be a good educational tool in order to show the dependence of airspeed on AoA, which still escapes many people.

Yes I was referring for trainer aircraft for the purposes of training.

 

[shdw]

sin(descent angle) = -Drag/Weight

Hey tgrayson I have a quick question for you in regards to this. When I first saw it I thought I remembered it from my flight dynamics notes but was unable to locate it. I did a quick example with an aircraft descending at 500 fpm (5.7 mph) with a forward speed of 75 mph. This came out to a 4.4 degree descent angle and assume the aircraft weights 2000 lbs.

The formula rewritten:

D = -(sin(DA)*W)
= -(sin(4.4)*2000)
= -(-1903)
D = 1903

Now I have 2 questions:
What are the Units?
Should the calculator be in radians or degrees?

Here is my thinking:
Weight is in pounds and drag, being the byproduct of AF and therefore a force itself would mean the units should be pounds. Force is generally in pounds/newtons so is it simply 1903 lbs of drag. Is this correct?

My thinking on the radians vs degrees is in degrees this answer would be -153 lbs which seems too small a force. However drag should act negative so I would expect a negative answer which leaves me confused with positive 1903 but what seems like a more sensible answer.

Thanks for the help.

 

[tgrayson]

D = -(sin(DA)*W)
= -(sin(4.4)*2000)
= -(-1903)
D = 1903

Now I have 2 questions:
What are the Units?
Should the calculator be in radians or degrees?

First, you made a slight math error calculating drag...I'm thinking you hit the cos button rather than sin button. D is equal to about 153 lbs. (A number so close to the weight of the aircraft should have been a red flag that something was amiss.)

As for the units, since the trigonometric ratios have no units, the units you end up with will be whatever you measure weight in. In this case, pounds. Normally you have to be very careful...in english units, velocity is normally measured in feet/second. Here it doesn't matter, since you're taking the ratio.

As for radians vs degrees, doesn't matter here, because you took the arcsin of a ratio and then immediately took the sin, so you ended up with what you started with.

 

[shdw]

D is equal to about 153 lbs.

Radians vs degrees is what did it then. See my later reply about the answer (if the calculator was in degrees) is -153 lbs. So drag acts negative and 153 is right that makes complete sense to me. Is that wrong?

I just did not think 153 was a large enough number seemed too low logically to me. Apparently I should just trust the math.

 

[tgrayson]

Radians vs degrees is what did it then.

Well, I assumed you were being consistent in your setting. If you did the arcsin and the sin on the same setting, it wouldn't matter. It looks like you did the arcsin in degrees, then changed to radians for the sin.

I just did not think 153 was a large enough number seemed too low logically to me. Apparently I should just trust the math.

No, no, wrong lesson. NEVER trust the math. You always need to do a "reasonability" check on any number you get. You did here, but just didn't know what was reasonable.

Consider: if the drag were really 1900 lbs, then in level flight, your propeller would have to be generating 1900 pounds of thrust. If it were capable of that, then you could almost hang by the propeller in an Arrow. Yet I'm sure you know you can't come anywhere close to that. 153 lbs of drag is very reasonable.

 

[shdw]

Well, I assumed you were being consistent in your setting. If you did the arcsin and the sin on the same setting, it wouldn't matter. It looks like you did the arcsin in degrees, then changed to radians for the sin.

Noooooo sir that is wayyyy to smart for me lol I definitely did degrees for arcsin to get a degree that made sense to me then back to radians for the 1903 number. whoops lol

Thanks hey where is the embarrassed face?

PS tgrayson check out my post on "What happened here and why?" I think you'll like it. It can get very aerodynamically technical