Aerodynamics of a nose-up glide

[Jodes]

Hello!

 

Apologies if this is in the wrong forum section, I couldn't see a better one, please let me know if there is! Most of my interest is in topics similar to this one :)

 

I'm a total beginner, just starting to read the classic pilot's beginner book, "Stick and Rudder" by Langewiesche. He says it's possible to glide nose-up. I think he's implying that a nose-up glide can actually maintain forward velocity. How is this possible? (Is it?)

 

As far as my understand goes, there is always drag, which acts to slow the aircraft. And there is lift, which when the aircraft is nose-up, will not have any forward component. So without any thrust, I cannot see how there is any force to counteract the forces that would slow the aircraft.

 

Pls can someone tell me what I am not understanding here?

 

Thanks! :-)

 

 

[Gentreau]

Hi Jodes, you have chosen an excellent book to read, but it can take some understanding.

 

Which chapter are you reading which is causing the confusion?

 

It may be that a later section explains it more clearly.

 

.

 

 

[Jodes]

Hi Gentreau, thanks for your response!

 

I'm confident that I understand the principle of angle of attack versus attitude. So for example in a normal glide, the angle of attack will be steeper than the attitude.

 

The statement in question is in chapter 2, (page 31 in my version), under the subheading "The Mushing Glide" he says:

 

"There isn't room here to explain why a clean airplane can glide slightly nose-high, but it seems worth stating that it can do so".

Having just read that again, I notice he says "slightly" which I thought might be the key.

 

I think I need to summarise some of his definitions in order to be precise about the aerodynamics of a nose-up glide; at least for me to refer to:

 

• "Chord is the line from the frontmost to the rearmost point of the wing section".
   
   
  
• Angle of attack is "the angle between the chord and the relative wind".
   
   
  
• Absolute angle of attack: "The angle that the no-lift line makes with the oncoming air".
   
   
  
• "[therefore] a wing can develop lift at zero or even at negative Angle of Attack".
   
   
  
• Angle of incidence is "the angle at which [the] wings are set with reference to the lengthwise axis of [the] airplane". (I don't know if this refers to the chord or the no-lift line".
   
   
  

 

 

 

So if I try to step through this problem:

 

1. Assume the aircraft is moving forwards. It will have drag opposing this motion.
    
    
   
2. For forward velocity to be constant, there must be a forward force opposite and equal to the horizontal drag force.
    
    
   
3. Assume that the fuselage and stabilisers and everything but the main wings create no forward force. (?)
    
    
   
4. Sub-conclusion: therefore, the wings must apply a forward force to the aircraft. (?)
    
    
   

 

 

I tried sketching a few diagrams of relative wind and lift. As per point (4), I conclude that the lift has to have a forward component.

 

If I then assume that lift is perpendicular to the no-lift line, then if the aircraft is nose-high (or even perfectly horizontal), I believe the lift would actually generate a negative horizontal component.

 

I'm digging a hole for myself here!!

 

If his statement about nose-up gliding is correct, and my arguments 1-4 are valid, then the lift is significantly forward of the no-lift perpendicular. Perhaps that's the quesiton I should be asking, but my brain is now stalled, this is going to need a lot of coffee to get my head round!!!

 

 

[aro]

So if I try to step through this problem:

 

1. Assume the aircraft is moving forwards. It will have drag opposing this motion.
    
    
   
2. For forward velocity to be constant, there must be a forward force opposite and equal to the horizontal drag force.
    
    
   
3. Assume that the fuselage and stabilisers and everything but the main wings create no forward force. (?)
    
    
   
4. Sub-conclusion: therefore, the wings must apply a forward force to the aircraft. (?)
    
    
   

In a glide, the direction of movement is not perfectly horizontal, you have a downward component as well.

 

Drag is opposite the direction of motion, so in a glide it is not horizontal, there is an upward component.

 

As the direction of movement has a downward component, gravity is partially acting in the direction of movement, and in opposition to the drag component.

 

 

[facthunter]

You are descending, so the mass of the plane acts vertically towards the ground and gives a forward component, relative to your flight path, Nev

 

 

[Tomo]

A light weight high drag aircraft needs a lot of nose down to glide... or even move forward without power.

 

Something a bit more streamline and weight will have less drag to keep forward motion going, so between the weight to pull you down which you then convert to forward speed and less drag you'll end up with a higher nose attitude to get best glide. If you keep the nose down, it will go to fast which will then increase drag and descent.

 

Put simply anyway!

 

 

[Hongie]

The way I understand it is this:

 

With a slightly higher nose, you may achieve minimum sink speed, which will leave you hanging around for longer, but not going as far.

 

Conversely, if you where to lower the nose and hit best glide speed, you will arrive at the crash site, umm, landing site of your choice, quicker, but having been able to travel further.

 

I'm happy for one of the more qualified souls here to correct me :)

 

 

[ben87r]

The "nose being high doesn't relate to the flight path of the aircraft. You would need the nose to be high to maintain a slow glide, it's more to do with airspeed then attitude. We adjust the attitude to produce the required performance of the aircraft but the attitude isn the performance itself.

 

 

[Sapphire]

A picture is worth a thousand words but here is less than thousand words. In straight and level flight lift is vertically up, weight is vertically down. Drag is opposite to thrust. To maintain straight a level flight at cruise speed you need an engine [thrust] Stop the engine and you have to get thrust from gravity. By pointing the nose down you produce a forward component of lift and your vertical component of lift decreases- hense you decend maintaining cruise speed. Cruise speed is not the speed for minimum sink, so you raise the nose to reduce speed to that which gives you minimum sink or longest time in the air. If you want to glide as far as possible you pick a speed which gives you best lift/drag [not calculating headwind or tail wind] So for longest time in the air or greatest glide distance you will raise the nose from cruise speed.

 

 

[Yenn]

I would assume that nose up means a higher angle of attack than normal glide, which really translates to a slow glide. I can do it on finals with no power and too high I pull the nose up to a very high angle of attack and get a very high sink rate, when back on the glide slope, just push the nose down, pick up speed and reduce the rate of descent.

 

Do not try this unless you are happy to possibly stall and have plenty of height to recover.