Author Topic: Serious question about the La7  (Read 2486 times)

Offline Angus

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Serious question about the La7
« Reply #45 on: October 31, 2005, 05:07:21 PM »
Are you all clear about the fact that induced drag means LIFT induced drag.

The same wing with higher loading at the same speed will for instance require more power for the job to keep it there.

The same wing with higher loading at the same thrust setting will create more induced drag resulting in the aircraft being slower for total drag will be more.

But anyway since it's going on about banking what's the effect on chord and span?
It was very interesting to carry out the flight trials at Rechlin with the Spitfire and the Hurricane. Both types are very simple to fly compared to our aircraft, and childishly easy to take-off and land. (Werner Mölders)

Offline Tilt

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Serious question about the La7
« Reply #46 on: October 31, 2005, 06:19:22 PM »
So ...because I am slow at this...........

Example A

I have 2 planes both able to generate the same thrust (engine prop etc). Both with the same control and lift surfaces, both of the same weight.

But one has less pure (or parasitic) drag than the other.

What performance differences would you expect to see?

Sustained  rate of turn?
Top speed
Climb rate
acceleration
de acceleration
zoom


Example B

I have 2 planes both with the same top speed abilities and climb rates. Both with the same control and lift surfaces, both of the same weight.

But one has greater thrust and pure(parasitic) drag than the other.

What performance differences would you expect to see?

Sustained  rate of turn?
acceleration
de acceleration
zoom
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Offline Crumpp

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Serious question about the La7
« Reply #47 on: October 31, 2005, 06:21:16 PM »
Quote
Are you all clear about the fact that induced drag means LIFT induced drag.


Lift stays constant.

Quote
In the case of lift, the lift force is (by its definition) perpendicular to the relative wind, so there is no such thing as dissipation due to lift.


People seem to confuse the CD(i) with the FORCE and POWER of induced drag.

While the CD(i) and the FORCE appear to go up gradually acting as a steady pull:

Quote
At higher angles of attack (approaching or exceeding the critical angle of attack) the basic-model approximations break down. The coefficient of parasite drag will rapidly become quite large, and the induced drag will probably be quite large also


http://www.av8n.com/how/htm/4forces.html#fig-coeff-ias

http://www.av8n.com/how/htm/4forces.html#fig-force-ias

However the POWER or force application if very different:

Quote
Figure 4.15 shows the amount of dissipation due to drag, for the various types of drag. Dissipation is a form of power, i.e. energy per unit time.


http://www.av8n.com/how/htm/4forces.html#fig-power-ias

The mushing realm is where induced drag becomes a wall and the power increases dramatically.  Before then it is hardly a factor.


Tilt,

Your doing pretty much the same effect in both cases AFAIK.  The lowering the drag increases thrust.

Everything would go up or perform better.

Quote
Hitech says:

What you realy want to compare is E loss per G of turn. I.E. When 2 planes are doing the same turn. Who is loosing E the quickest.


Depends on the turn doesn't it?  As long as an aircraft does not drop off the backside of the lift polar beyond CLmax, it would not be in the mushing realm were the power of induced drag becomes a factor in dissipation.

Any aircraft which does this will experience dissipation due to drag not just high wingloaded aircraft.

Notice too that force of parasitic drag increases dramatically in the mushing realm.  This is due to the aircraft having to present more surface to the relative wind as it increases AoA, correct?  Wouldn't the larger wing surface present more parasitic drag?

All the best,

Crumpp
« Last Edit: October 31, 2005, 07:24:09 PM by Crumpp »

Offline MANDO

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Serious question about the La7
« Reply #48 on: October 31, 2005, 06:44:08 PM »
Are AH planes considering the viscosity drag? Not sure about the correct term in english, but it is related to the drag generated by the air flowing in contact with ANY surface. So, for two planes with exact flat area (lets say frontal area section opposing the air flow in a forward movement), the one with wider wings will suffer more viscosity drag. This is, in fact, the second component of parasite drag.

Offline Knegel

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Serious question about the La7
« Reply #49 on: November 01, 2005, 01:10:13 AM »
Hi,

Quote
Originally posted by Bonzon

quote:
--------------------------------------------------------------------------------
but more inertia = less E-bleed.
--------------------------------------------------------------------------------


By that logic you'd want to load your plane with lead to make it turn better - more inertia. But I see that arguing here is pointless.

Enjoy AH.
Bozon


I dont talk about the most tight turn!

But actually exact thats what most nations did! Of course there is a edge where the heavy liftload of a plane get to be a handycap, but as long as a plane can turn with high G it dont make sence to use bigger wings, cause bigger wings have more drag as result.  
The japanese HQ did follow your logic, the result we know.
A A6M2 couldnt follow a P40 in a highspeed turn, not cause the stiffness off the elevator, but cause it did bleed energy while that.  VS later US planes the different was even bigger. As result, although much to late, they cutted the wingarea of the Zero and Ki43 down, but not enough.
The wing had to be as smal as possible, but it must have been possible to pull high G´s at normal combatspeed. Since the normal combatspeed increase with more power, the wing´s could get smaler(or the weight more big).  

Quote
Originally posted by hitech
Hi Knegel.

 
While this statment is absolutly true. It is also meaning less when considering turning of any sort.

What you realy want to compare is E loss per G of turn. I.E. When 2 planes are doing the same turn. Who is loosing E the quickest.

In your case you are comparing when 2 planes are both doing there max turns at the same speed. But 1 plane could be a 10g turn and the other 2 Gs.


HiTech


If a 109G2 and a 109F4 make a decelerating turn, with same G-force and same power, at a given speed both planes will bleed same energy! As faster the planes as more the inertia help to keep energy, as slower the plane as more the more weight will be a handycap.
The 109F will need less AoA to pull the same G, therfor it will cause less drag, but the 109G2 have more inertia(swing). With same power the E-bleed get determined by the dragload, while a decelerating turn the inertia often get forgotten. The higher drag of the 109G2 get evened out by the higher inertia, depending to the speed.

While a sustained turn, no inertia into flightdirection work, therfor in this case the 109G2(if same power) will lose, but the 109G2 had more power, therfor i doubt that it would lose while a turn with same G-load. At least the climbratio of the 109G2 with combatpower was better than that of the 109F4, this indicate that the more power did overcome the more induced drag.


Greetings, Knegel

Offline bozon

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Serious question about the La7
« Reply #50 on: November 01, 2005, 03:25:27 AM »
Quote
Originally posted by Tilt
Example A

I have 2 planes both able to generate the same thrust (engine prop etc). Both with the same control and lift surfaces, both of the same weight.

But one has less pure (or parasitic) drag than the other.

What performance differences would you expect to see?

Sustained  rate of turn?
Top speed
Climb rate
acceleration
de acceleration
zoom
 

Your example is two identical planes, one has its airbreaks sticking out. they create nothing but turbulance (drag).

Sustained  rate of turn - The same, provided the plane with the excess drag can sustain the same speed in the turn.

Top speed - here parasitic drag rules over induced drag, less of it - more speed. THIS is the reason planes got smaller smaller wings, for less parasitic drag at high speeds at the cost of more induced drag at lower speeds / manuvering.

Climb rate - potential energy storing rate. Drag is the sink that burns you energy, therefor higher drag means that your burned fuel is used to stirr the air instead of making you climb and increase potential energy.

acceleration - prop pulling forward, drag pulling backward. less net forward force, less acceleration.

zoom - pure zoom climb is done at zero G so parasitic drag is all the drag there is - you don't even need wings and they are just more surface area to create drag.  Lets consider powerless zoom climb - this is ballistics. Try throwing a pingpong ball straight up. Now try a metal ball of the same dimention. Which can you throw higher?
Here what counts is drag/mass ratio. If you want to make a plane zoom well FROM HIGH SPEEDS you want it heavy and you can use relatively small wings. sounds familiar? P47! YES mamma! This is the only case where your weight works for you and not against you (and the inverse case - 0 G dive).

Bozon
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Click!>> "So, you want to fly the wooden wonder" - <<click!
the almost incomplete and not entirely inaccurate guide to the AH Mosquito.
https://www.youtube.com/watch?v=RGOWswdzGQs

Offline Tilt

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Serious question about the La7
« Reply #51 on: November 01, 2005, 05:11:48 AM »
Thanks Bozon

Example A is a comparison between the La7 and the La5FN.

Basically (aerodynamically) the La7 is an La5FN with reduced parasitic drag and a very minor increase in thrust. (plus a weight saving of 120 kg in 3360)

Example B was me scratching for the ramifications of increasing both thrust and parasitic drag (in the FM) to achieve the same top speed and climb rates.

Instinctively I beleived that by increasing thrust and parasitic drag proportionally the result would be

Greater accel at low speeds.
Lesser accel at high speeds.
Lesser accel and final top speed in dive.
Slightly reduced zoom.
Greater de accel when throttling back at all speeds.
Lesser endurance at optimum cruise setting.
« Last Edit: November 01, 2005, 05:25:52 AM by Tilt »
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Offline glacey145

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Serious question about the La7
« Reply #52 on: December 21, 2005, 05:32:00 AM »
Could this be relevant to the original post?

http://www.simhq.com/_air/air_015a.html

Offline Kev367th

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Serious question about the La7
« Reply #53 on: December 21, 2005, 10:24:19 PM »
Serious, and La7 in the same sentence, your having a laugh.
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