Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Debrody on March 03, 2011, 05:48:56 PM
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Some planes hold the energy well, some dont. I would like to know which factors are inportant in a good energy retention rate. Thank you :salute
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Be easy on the :joystick:
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lol you can pull a 152 as hard as you can and it will still remain fast, try the same in an earlyer 190...
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You asked.
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You mean which factors are important in the airframe for an aircraft to hold energy (from an engineering perspective)?
It primarily depends on the type of wing you have (and the wing loading). For example if you take a spitfire and accelerate it to ~500mph it will bleed off that energy quickly, but if you have it maneuver at ~300mph it will maintain it's energy a longer than most other planes (190 in this case will do the opposite).
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I believe the primary factor would be the thrust/weight ratio.
*edit See Bozon's post below, very informative! :old:
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Inertia is maintained better by high mass/drag ratio: drop a hollow plastic ball to the ground, then repeat the experiment with ball filled with water/sand. Guess things do not fall to the ground at the same speed like we heard in school... This is an important effect in holding straight line high speed gained after a dive. The mosquito is probably the highest mass/drag plane in AH set.
High thrust/drag ratio does not hold the energy, but instead replenish it giving a net effect of slower energy bleed. Spit 14, 109K, La7 are pretty good in this department.
Low wingload helps to lower the induced drag in a given turn (vs. the same turn with smaller wings on the plane). However, induced drag is important only in high angle of attacks and a larger wing will have more parasitic drag which dominated at high speed/low angles of attack. Lightly loaded planes will tend to hold E better in a turn, while high loaded planes will tend to hold E better in a high speed straight line after a dive.
Perhaps some other factors I forget.
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High aspect ratio wing has less induced drag.
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Inertia is maintained better by high mass/drag ratio: drop a hollow plastic ball to the ground, then repeat the experiment with ball filled with water/sand. Guess things do not fall to the ground at the same speed like we heard in school... This is an important effect in holding straight line high speed gained after a dive. The mosquito is probably the highest mass/drag plane in AH set.
High thrust/drag ratio does not hold the energy, but instead replenish it giving a net effect of slower energy bleed. Spit 14, 109K, La7 are pretty good in this department.
Low wingload helps to lower the induced drag in a given turn (vs. the same turn with smaller wings on the plane). However, induced drag is important only in high angle of attacks and a larger wing will have more parasitic drag which dominated at high speed/low angles of attack. Lightly loaded planes will tend to hold E better in a turn, while high loaded planes will tend to hold E better in a high speed straight line after a dive.
Perhaps some other factors I forget.
^ Pretty much nails it on the head. Energy retention has different meanings to different aircraft, as bozon describes above. Understanding how an aircraft retains its energy is crucial in a dogfight.
I like to think that energy fighting is a lot like manipulating an aircraft's momentum. Like a pendulum swinging from one spot to the next. It's a dance of trading speed and altitude back and forth in order to shoot down your opponent.
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Some planes hold the energy well, some dont. I would like to know which factors are inportant in a good energy retention rate. Thank you :salute
Maybe two discussions - one is 'retaining/maintaining energy once gained' which is a discussion more about drag, and except for high CL (and Induced Drag) is about Parasite Drag and Viscous drag due to Lift. All things being equal an a/c which has a higher Aspect ratio will have less Induced Drag
Two is 'regaining energy once lost' which is a discussion invloving several factors. To name a few is thrust to weight ratio, zoom climb characteristics (which is a combination of CL and drag and W/S)
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Inertia is maintained better by high mass/drag ratio: drop a hollow plastic ball to the ground, then repeat the experiment with ball filled with water/sand. Guess things do not fall to the ground at the same speed like we heard in school... This is an important effect in holding straight line high speed gained after a dive. The mosquito is probably the highest mass/drag plane in AH set.
High thrust/drag ratio does not hold the energy, but instead replenish it giving a net effect of slower energy bleed. Spit 14, 109K, La7 are pretty good in this department.
Low wingload helps to lower the induced drag in a given turn (vs. the same turn with smaller wings on the plane). However, induced drag is important only in high angle of attacks and a larger wing will have more parasitic drag which dominated at high speed/low angles of attack. Lightly loaded planes will tend to hold E better in a turn, while high loaded planes will tend to hold E better in a high speed straight line after a dive.
Perhaps some other factors I forget.
Very informative. :aok
The theory that everything falls at the same speed only applies to objects in a total vaccuum.
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Very informative. :aok
The theory that everything falls at the same speed only applies to objects in a total vaccuum.
Yup.
http://www.youtube.com/watch?v=MJyUDpm9Kvk (http://www.youtube.com/watch?v=MJyUDpm9Kvk)
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High aspect ratio wing has less induced drag.
In level flight.... Your trying to use a blanket statement for all conditions and this is incorrect.
The lower the aspect ratio of a wing the higher the angle of attack the wing stalls at.
Higher aspect ratio wings will reverse any benefit if the airfoil is asked to perform at a high angle of attack. Stalling the airfoil induces drag.
The question should be as follows. "What plane holds its energy better under certain maneuvers?"
The best example I can come up with to address both issues would be the f-14. It can change its aspect ratio by simple changing its wingspan. It adjusts its aspect ratio to the best configuration for any type of maneuver.
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I just try to remember which planes jug will catch in zoom--spit is goner..F4...D9...not so much
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In level flight.... Your trying to use a blanket statement for all conditions and this is incorrect.
The lower the aspect ratio of a wing the higher the angle of attack the wing stalls at.
Higher aspect ratio wings will reverse any benefit if the airfoil is asked to perform at a high angle of attack. Stalling the airfoil induces drag.
The question should be as follows. "What plane holds its energy better under certain maneuvers?"
The best example I can come up with to address both issues would be the f-14. It can change its aspect ratio by simple changing its wingspan. It adjusts its aspect ratio to the best configuration for any type of maneuver.
Debrody mentioned that pitching up in a Ta152 doesn't bleed energy like a FW190 in reference to his original question about holding vs losing energy. Why do you think that is? Is it because high aspect wings have less induced drag?
Your point seems to be that a wing has more drag after it stalls. Thank you for explaining that.
Edit: Also Bozon had mentioned leaving something out. :D
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Thank you for answering sirs :salute
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In level flight.... Your trying to use a blanket statement for all conditions and this is incorrect.
The lower the aspect ratio of a wing the higher the angle of attack the wing stalls at.
You just replaced one blanket statement with another.
High aspect ratio lower the inefficiency caused by wingtip turbulence. These turbulence increase with angle of attack, so a rough statement that high aspect ratio lowers induced drag is justified. Also, the effect will be felt in low speeds and turns where angle of attack is higher than in level high speed flight. Planes that want to fly high use high aspect ratios because the IAS (as opposed to TAS), which is what matters for aerodynamics is quite low and close to the stall speed.
Also, the effects aspect ratio are a bit hard to compare because you cannot keep all the other variables constant. If you keep the area constant it means shorter cord. To then keep the cross section proportional, the wing must be thinner. Then due to the overall down-scaling of the profile you also need to increase the speed to keep the Reynolds number constant - but then the total parasitic drag on a constant area wing will increase...
I think broad statements are justified in this case.
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In level flight.... Your trying to use a blanket statement for all conditions and this is incorrect.
The lower the aspect ratio of a wing the higher the angle of attack the wing stalls at.
At zero lift, there is no difference but as the aspect ratio Increases, the slope of the CL to alpha increases and drag coefficents decrease with increasing AR. Reducing AR is desirable for high speed as Cdo dominates but in high CL (like turning and climbing) the higher the aspect ratio the better.
If you have a copy of Abbot and VonDoenhoff you could review this on pages 2-8.
As you know there is no induced drag for a 2-D airfoil (i.e 'infinite' AR, and maximum CDi for AR =1 (or less). Consider which airframe stalls the fastest with increasing AoA - an F-104 or a U-2?
Higher aspect ratio wings will reverse any benefit if the airfoil is asked to perform at a high angle of attack. Stalling the airfoil induces drag.
For the same airfoil and all other factors being equal, the lower AR will have higher CDi. This was certainly a factor in Oswald's studies as he pondered the differences in differences between various configuration types in context of total added components of viscous drag.
The question should be as follows. "What plane holds its energy better under certain maneuvers?"
The best example I can come up with to address both issues would be the f-14. It can change its aspect ratio by simple changing its wingspan. It adjusts its aspect ratio to the best configuration for any type of maneuver.
But the F-14 sweeps its wing back to reduce high speed drag effects, and sweep forward to increase Lift and lower CDi for low speed manuevers..
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You just replaced one blanket statement with another.
High aspect ratio lower the inefficiency caused by wingtip turbulence. These turbulence increase with angle of attack, so a rough statement that high aspect ratio lowers induced drag is justified. Also, the effect will be felt in low speeds and turns where angle of attack is higher than in level high speed flight. Planes that want to fly high use high aspect ratios because the IAS (as opposed to TAS), which is what matters for aerodynamics is quite low and close to the stall speed.
Also, the effects aspect ratio are a bit hard to compare because you cannot keep all the other variables constant. If you keep the area constant it means shorter cord. To then keep the cross section proportional, the wing must be thinner. Then due to the overall down-scaling of the profile you also need to increase the speed to keep the Reynolds number constant - but then the total parasitic drag on a constant area wing will increase...
I think broad statements are justified in this case.
So what you are saying is the lift factor is actually changing the effects of the angle of attack, or actually canceling them out with a higher A/R? I can see this.
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Aspect ratio is important when considering the difference between the Ta152 and the FW190 but when you're talking about the F-14 the sweep wing is optimizing supersonic flight vs subsonic handling and it's not the same issue.
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So what you are saying is the lift factor is actually changing the effects of the angle of attack, or actually canceling them out with a higher A/R? I can see this.
You'll have to explain what do you mean by "lift factor" and "A/R". I apologize if these are standard terms, but I am not familiar with them in English.
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Aspect ratio is important when considering the difference between the Ta152 and the FW190 but when you're talking about the F-14 the sweep wing is optimizing supersonic flight vs subsonic handling and it's not the same issue.
Strictly speaking Aspect Ratio is Span>>2/Wing Area.
When the F-14 extends its wings, both the wing span and AR increases. The swept wing a.) increases the 1/4 chord angle to the Free Stream Velocity vector, optimizing transonic drag rise versus the unswept wing - and b.) decreases parasite drag - but it also reduces AR and increases Induced Drag.
When the wing extends, it decreases the CDi, it increases max CL and optimizes for subsonic manueverability and lowers landing speed dramatically.
It is exactly the same 'thing'
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I didn't say it was a different "thing". I said it was a different issue than the thread topic of why different WW2 aircraft bled energy at different rates.
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I didn't say it was a different "thing". I said it was a different issue than the thread topic of why different WW2 aircraft bled energy at different rates.
Fair 'nuff
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Fair 'nuff
I'm often overly concise. I appreciate the input.