Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: thrila on March 03, 2002, 09:35:04 PM
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Flew a la7 at 13k and it reached 400mph @13k with 50% fuel (no WEP). I thought this was a tad faster than it oughta be so i checked the charts- apparently it should only be doing about 390mph. Shave a few mph off the la7 plse HT cause i hate 'em:p
P.S. perk the la7:D
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Hey thrila...nice cat and mouse in those 262s...was fun. :)
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Thrila, all posted speeds are for 100% internal fuel. Test it that way and check your results.
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Awww you gotta be kidding me verm........ahwell back to the drawing board for me.
Raub, that was the most fun i've had in ages dogfighting in the 262 with you. I didn't even see you on my 6 until about 1.5k and i crapped myself hehehe. Luckily i got you to overshoot after your first pass and i thought you would be my first 262 kill in a 262.:D
I only had about 40 rounds of 30mm left so i was waiting for the perfect shot. Fortunately for you, you weren't staying still or slow for very long and doing some nice evasives. I thought i was gonna die when you dragged me to the depot but the ack wasn't up hehe- i was soooo lucky.:D You then dragged me to that furball and a p51 tried to get on my 6 but i was too fast for him. I was low on fuel so i had to rtb and home i went hoping my fuel would last out. About 12 miles out my engines died so i had to glide the rest, i got there with a bit of speed so it wasn't too bad. Aaaarrgh!!! i bled to much speed when circling and touchedown short of the runway, luckily for me i rolled just onto the tarmac and landed perfectly......well almost.:D
Musta been my lucky day yesterday.:)
Raub, some nice flying yesterday i had lots of fun.
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Verm, does more fuel imply more drag or less Hp?? AFAIK, more weight imply less acceleration in level flight, but same top level speed. If top speed is depending on internal fuel load, then there is something I cant understand in AH.
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Originally posted by MANDOBLE
Verm, does more fuel imply more drag or less Hp?? AFAIK, more weight imply less acceleration in level flight, but same top level speed. If top speed is depending on internal fuel load, then there is something I cant understand in AH.
dont whine, is just a 4% difference so it is okay.
(aproximate answer I got in this same forum when I posted info and charts on the Fw190A5 being 10mph slower than what it should at Sea Level. It was never corrected, btw.)
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Mandoble:
More fuel will cause more drag.
Hooligan
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RAM, 4% is not ok, but a brutal difference when we are talking about plane types whose top speeds differences are between 5% and 10%.
Hooligan, are u able to explain why?
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Originally posted by MANDOBLE
RAM, 4% is not ok, but a brutal difference when we are talking about plane types whose top speeds differences are between 5% and 10%.
Mandoble, I know. I was being sarcastic about the matter. As I said, I once came with some focke-wulf factory charts about 190A5's SL speed some time ago, being it around 345-348mph@SL in the chart while at AH its 335mph@SL.
Answers to an official focke-wulf chart showing AH's 190A5 being 10mph too low met several answers saying that "it isjust a 4% difference in the topspeed, so it is ok"
So I hope you understand the big ammount of sarcasm involved in my previous post in this thread.
Hooligan, are u able to explain why?
More weight needs more lift from the wing to compensate. More lift provided by the wing means more drag. More drag means reduced top speed.
However a 50%-100% fuel weight difference shouldn't cause a 10mph speed difference. Its too big a difference.
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Give your ground crew a case of vodka for polishing, taking out any imperfections , super tuning the engine,........ your a/c.
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that kind of drag at these speeds should affect minimaly top speed. U are well above stall speed, in fact u need to be trimmed nose down to dont start gaining alt. At these speeds you are not fighting against your weight, just the contrary, you are fighting against your lift to keep level flight.
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Ok, i went and tested the la7 speed offline. Went to a 15k field took off and dove down to 13k and levelled out. Went and ate my lunch and when i got back 10mins later the la7's speed was 399mph (the 400mph white line was almost completely covered).
So in my view the la7 is too fast at 13k. Gonna try at different alts 15k, 17k, 20k later on and see what i get.
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Mandoble, like Hooligan said total weight has an effect on top speed. Its not as much as you would think, but it does have an effect.
In this case I'm guessing probably about 3-5 mph.
Thrilla, no offense buddy, but if you can read those itty bitty analog gauges to a tolerance of 1 mph, you have eyes better than mine. From my experience, its hard to get an accurate reading within a plus or minus 5 mph tolerance.
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use auto-trim for angle in conjonction with the .speed command...
exemple : you set auto-climb angle and next you type .speed 400
if it climb you are fastest than 400
if it dive you are lower than 400
and it's better than reading gauges ...
btw you would be better to set the fuelBurnrate (spelling?) (*) to 0
(*) it's an arena parameter.
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Verm, I need a rational explanation of that.
At 15k, at your top speed, lift will be greater than weight, so, to compensate, you'll need to trim your nose down. If you are lighter, you will need to compensate even more, so your trim tabs, or entire elevators will generate more drag than if you were heavier (less overcompensation needed to keep level flight).
Basically, heavier or lighter you are tending to climb and we are talking about level top speed, not climb rate.
Where am I wrong?
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RAM, would it be possible for you to send me some charts that you have? I am desperatly trying to find such things but without luck.
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MANDOBLE,
if you are heavier, you need more lift to keep you in level flight. more lift means greater angle-of-attack, that means more drag for the same speed. at top speed, the effective (actually trasfered through the prop) power of the engine equals the rate of consumed energy by the drag. hence, max speed is lower.
Bozon
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Where the weight is can also effect top speed.
The more nose heavy a plane ,the slower it is.
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LA7 at 13k chart shows 393, chart can't be read this accuratly but the number we put in is 393.
Just ran the test at 13k full fuel, we hit 392
Zoom in on the gauge you will see it's very slightly below 400.
To make a long story short it's correct.
Btw thanks for the testing. If you wish to tests speeds the best way is with the .speed command
HiTech
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>analog gauges to a tolerance of 1 mph, you have eyes better than mine. From my experience, its hard to get an accurate reading within a plus or minus 5 mph tolerance.
A "debug" digital speed (etc) indicator would be a nice adition for end user, i think.
Greetings
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Hitech, could you maybe, sometime in the future implant a Digital speed meter for offline use only? Just something to have in a corner of the picture, same thing with rate of climb and such, would make testing easier, and IF we find some misstakes, it would benifit everybody. Allso, people would do more testing and you'd hear less whining.
Btw, do you know which engine you have modelled for the Ta152? :)
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.speed command....didn't know that cool!!!
Alright i'll give it a go with that HT.
For a moment i almost cancelled my whisky bribe to you HT;)
While you're in this thread HT, what engines have you modelled for the mossie fbVI? 21's? 25's? ......oh and ......errrr....any plans for any other mossie varients in the future.
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At stall speeds induced drag is a greater part of the total drag force than parasitic drag but at max speeds induced drag is negligible and most of the total drag force comes from parasitic drag. The slight increase in AoA needed for the additional lift to balance the weight of 100% fuel vs 50% fuel at max speeds would add a little induced drag to the negligible induced drag component of the total drag.
In other words, you shouldn't see any significant speed difference at max level speed comparing 50% and 100% fuel loads.
If you use the .speed command keep in mind that it sets the IAS not TAS.
--)-FLS----
Musketeers
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^ What him say?
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Originally posted by Apache
^ What him say?
him say more fuel not affect top speed.
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Just to be accurate
Him say 50% fuel will not effect top speed by a lot.
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Hi everyone,
Actually, more fuel might even make a fighter faster.
Design angle of incidence would typically be selected for top speed at full pressure altitude. Below this altitude, the fighter probably flies with a nose-down attitude, meaning that the fuselage is not optimally aligned with the airflow. More fuel and more weight means that the same lift is achieved at a higher angle of attack, which is equivalent to a less pronounced nose-down attitude of the fuselage and less parasitic drag.
If the decrease of parasitic drag is greater than the increase of induced drag, the heavier aircraft will be faster.
Regards,
Henning (HoHun)
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Exactly HoHun.
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Too much aerodynamic information must stop reading threads must must.................
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henning i believe you are on crack. your statements make no sense. fly at a higher angle of attack for the same lift? huh?
hitech is correct however asssuming aces high models trim drag. does it? the more stable a plane is (the greater the static margin) for a given airframe and weight the tail will have more required downfore to maintain zero pitching moment for cruise. i do not know if aces high calculates trim drag tho.
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"Well, Whoop dee doo, What does it all mean Basil?"
:confused:
:D
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Originally posted by Zigrat
henning i believe you are on crack. your statements make no sense. fly at a higher angle of attack for the same lift? huh?
Not for the same lift, but to keep aircraft flying level at its maximum level speed, where lift will be greater than weight u will need different "nose" angles depending on your weight to keep the aircraft flying at level. And most probably than not, the lighter aircraft will need to overcompensate with a slight more nose down attitude than the heavier one.
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I am just curious if there are not a few things you oversee.
Location of the fuel tanks will have influence to, cause if the tanks are far way from the CG, the plane needs more trimming to compensate for that away from CG weight.
Also i think reduced weight will generally increase speed, cause you get a better power to weight ration, also accel, climb and turning will be better.
I have an FW document that includes a comparrison calculation for the D9 at 3500kg (normal take-off weight 4270kg), the plane achieved a max speed of 698 km/h at its climb and combat power setting.
A normally loaded D9 managed speeds equal to that only with Special Emergency Power.
The difference in PS output looks like this:
SWEP: 2100 PS
Climb&Combat: 1680 PS
I think considering weight differences the power-weight-ratio effect is much larger than the drag effect through a little change in the angle of attack.
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Naudet, all this is considering no variations in the CG due fuel load. It is true that some planes have the tanks "far" from the CG, but, for example, this is not the case with 190A5 and D9. No idea about La7 fuel tank placement.
The extra weight will affect climb and acceleration negatively, but not top speed at level.
When u are flying level at your max speed u need to:
1 - Fight the extra lift with a nose down attitude. At these speeds your aircraft will tend to climb and you want to keep at level. More weight implies less overcompensation to keep flying at level.
2 - Fight the drag with your engine power.
Think that at these speeds u are fighting your lift to fly at level, not your weight, your weight will help u to keep at level with less compensation (nose down trim), just the opposite than at slow speeds.
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Hi Zigrat,
>fly at a higher angle of attack for the same lift?
I meant to say "the same equilibrium".
Regards,
Henning (HoHun)
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Zigrat, Might be a different use of terms, i would call trim drag the addition drag created by the trim tab to move the control surface where other wise you would generate this force from the stick, This we do not model, it realy would be a very small effect.
Now if you using Trim drag to meen with a more forward CG the horizontal stab must produce more down force, and the wing must produce more lift to compensate for this extra down force. and hence more drag, yes we do.
HoHun
As to the faster with while being heaver, would have to do some big analisis to be sure, but would find it hard to belive that the reduction in profile drag would be greater than the increase in induced drag. The only way I could see this is with a very thick/high lift wing.
HiTech
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A few comments:
1) Rather than all this discussion about whether or not an La-7 with full fuel should be faster, just measure it ferchrissakes.
2) As stated before, measure it with the autotrim method and realize that this is only accurate to within a one or two mph.
3) Take a close look at the chart. Eyeballing the 10k speed as being 390 is not that accurate. I enlarged the chart and printed it out. The first thing to notice is that the speed lines are about 2-3mph thick so there will necessarily be some uncertainty in the figure you get off the chart. When I used a ruler to measure the speed off the enlarged chart I got a speed range of 394-397 for the La-7 at 10k.
Hooligan
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There's no noticable difference in speed or AoA between 25% fuel and 100% fuel in the AH La-7. I'm guessing 50% fuel would be the same too.
If you want to debate the affect of weight changes on maximun level speed in RL you have to keep in mind the affect of speed on lift and drag. Changing the CG is a seperate issue.
--)-FLS----
Musketeers
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Why did you guys have to hijack my whine thread into a science lesson?:( :D :p :eek: ;) :)
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Hitech
can u give me a short defeniton what is induced and what is profile drag?
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RAM - Lame of you.
Naudet - http://www.grc.nasa.gov/WWW/K-12/airplane/drag1.html
And http://wright.grc.nasa.gov/WWW/Wright/airplane/drageq.html
What HT calls Profile Drag is called Form Drag in those explanations.
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Drag?......did someone say drag, you mean this sort of drag?
(http://www.somethingawful.com/cliff/ihateyou/page-153-03.jpg)
Oh wait that's not drag:eek: it's a real ugly chickl:eek:
Also, can someone help me out with this, i'm having a hard time calculating it's aerodynamic properties- (http://www.somethingawful.com/cliff/ihateyou/page-201-03.jpg)
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Originally posted by MANDOBLE
No idea about La7 fuel tank placement.
La 7 had a three tank set ......2 in the inner wing areas and one on the same axis in the fuselage. Fuel was therfore held on a nuetral axis re nose / tail heavy.
Nose / tail heavy trim adjustment apart........... weight has to be over come by lift and so induces drag.
I suppose it is plausable that an AC could be so badly designed as to require such trim correction at lesser weights for level flight as to induce such drag.
Obviously such a plane would be a useless fighter aircraft for one it would never be able to successfully "unload"
Tilt
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Hi Hitech,
>As to the faster with while being heaver, would have to do some big analisis to be sure, but would find it hard to belive that the reduction in profile drag would be greater than the increase in induced drag. The only way I could see this is with a very thick/high lift wing.
I'm afraid my explanation wasn't as accurate as I'd hoped :-)
It's not the wing by itself that causes the effect, it's the fuselage. Angle of incidence is (for example) selected for best level speed at full pressure altitude, so below that altitude, the fuselage has a nose-down attitude at top speed in level flight. Adding weight will require more lift and a greater angle of attack, decreasing the nose-down attitude, aligning the fuselage with the airstream and decreasing parasitic drag.
I don't think the effect has a big impact, but it's interesting for the impact being opposite of what one would normally expect.
Regards,
Henning (HoHun)
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The heavier a plane is, the more power required by the
engine to maintain x mph. Since the max power of the
engine is finite, any weight added at max power would either
slow the plane or cause it to lose alt. Or we can say lose
E where E is energy which is some function of altitude
airspeed and weight of the plane. Those of u who have
mastered vector calculus should easily see this.
At any fixed thrust, any weight added to any part of the
plane bleeds e. If the alt is fixed AND the thrust is fixed
(for ex. full throttle and 1 inch above the ground) any additional
weight, even a bird poop on the window, will slow the plane
down a bit. So, to the guy who cant understand why a
couple hundred pounds of fuel has no effect on top speed of a
plane, rest assured, it does.
Next, I am going to learn to use those faces to the left.
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HoHun, I understood your post perfectly. The resone I said a thick/high lift wing is because with a high lift wing, the zero lift aoa is in the large - direction, hence getting into the steaper part of a normal profile drag curves, hence the profile drage would change more with a small aoa change than the induced drag would.
I agree it can theoreticly be the case, just doubt if it is the norm, you could also make a configuration where adding the first 1000 lb increased speed the next 1000lb slowed it down.
White Hawk , the only resone weight will effect top speed either increase or decrease is do to a change in drag. The over all e state i.e. (v^2 + Alt) * mass would most likly be higher for a heavier plane in level flight at a given altitude.
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True, true. The increase drag (frction) due to the increase in the Angle of attack of the aircraft necesary to maintain the the alt.
Prolly one dozen of one and a half of the other, but, if the
angle of attack were fixed as wel as the alt and the thrust, and the weithgt were added in such a way that drag profile was
not changed, (internally), I would say the plane would slow,
in accordance w the E equation. (increasing M would
reduce V for all values M>0 until V=0).
But since I didnt have the E equation proior to this debate
NOR did expect anybody else to have it, I can only say that
this is my humble, yet correct, opinion :)
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So tyhe cute faces change to cute faces AFTER the reply is
submitted. AHAAAAAA!
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Hi Hitech,
>I agree it can theoreticly be the case, just doubt if it is the norm, [...]
I'd expect it to be the norm: If the angle of incidence is selected for full pressure altitude at design weight, the aircraft will have a nose down attitude at all lower altitudes for the same weight.
As many later fighter versions received more powerful engines without angle of incidence being changed, too, this effect probably was even more pronounced with the late-war fighters.
>[...] you could also make a configuration where adding the first 1000 lb increased speed the next 1000lb slowed it down.
Exactly, there's actually an optimum weight for each altitude (below design altitude), higher than the design weight.
Regards,
Henning (HoHun)
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Wow, I'm always learning something new here. I almost wish I were a little better at all that math stuff :)
Charon