[COUPERS-FLYIN] Re: Glide ratio

[Jeffrey R. Lewis]

----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----

Just a slight correction to what somebody said about best glide speed.  To get the best glide angle, you do need to be at the best L/D ratio, but this is not the same configuration as what produces the highest coefficient of lift.  In fact, your plane is usually up to a pretty high drag when it's producing the most lift.

 

And just in case anyone wanted to know, to get the lowest descent rate, you want to fly at the maximum Cl^3/2 / Cd.

 

And finally, your best glide angle in the air won't necessarily cover the most distance over the ground.  If you're in a good headwind at say 80 mph, with nothing but mountains behind you, and your engine quits, you know you've got to fly forward to land.  The best glide speed in calm air might be 75 mph, but if you try that, you'll actually have a negative ground speed, and end up going back into the mountains.  You'll have to increase your glide speed enough to go forward with the headwind.  Even though you're descent rate will be higher, at least you're moving forward.  I don't know why anyone would actually try crossing mountains with an 80 mph headwind, but it makes for a good example.  This effect will be less at lower wind speeds, but it's still there.  But flying at L/D max is probably good except for extreme cases.

 

-Jeff

 

 

 

Ercoupe Hangar Flying <FlyIn@ercoupers.com> wrote:

----------------------------
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED], [EMAIL PROTECTED], flyin@ercoupers.com
Reply-To: [EMAIL PROTECTED]
Subject: Re: [COUPERS-FLYIN] Re Glide ratio

Now I should probably keep my mouth shut so I dont look stupid, but this is the way I understand it. There is a speed which is the maximum coeficiant of lift. This is the best glide speed. It is the speed that gives you the most lift for the least drag. A
Scott
N94428

---

Do you Yahoo!?
The New Yahoo! Search - Faster. Easier. Bingo.

==============================================================================
To leave this forum go to: http://ercoupers.com/lists.htm
Search the archives on http://escribe.com/aviation/coupers/