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Old May 31, 2009, 06:25 AM
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Why would a small increase in model weight change the angle of attack??

Fact is there is a Mirage flying at our field that weighs 2.5kg or more, and it flies exactly the same as mine does at 2.2kg with almost identical speed, (both running the same fan speed & watts) only difference is it does not have as much vertical climb rate as mine does for obvious reasons.

If I went to the Lander fan & 5000mah pack I would end up at 2.4kg AUW, and I would have around 2.7kg thrust.

I would expect the Mirage to be faster because the eflux will be higher due to the more powerful setup.

As for landing, its doubtful Kambalunga has flown any of these models, it takes experience to discover that small changes in weight make very little difference to these large jets, the surface area means oz per sq inch loading hardly changes if you add 200 grams to the model.
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Old May 31, 2009, 03:21 PM
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Quote:
Originally Posted by Kambalunga
Bring this any increase in the T/W-factor? More weight need more AoA and produce therefore more drag and caused less max speed and higher landing speed!
Not quite. The landing speed will possibly increase, yes. But adding 200g to a jet this large in negligible. And it will not be slower.

My jet is 3.5kg and fast. The FlyFly Mirage tends to pitch up quite a bit as it gathers speed. During full throttle passes I struggle to keep the nose down and fly straight and level across the deck. You can solve this by adjusting the balance forward, But then you have a jet that pitches down at slow speeds, which is bad for takeoff and landing.

I think you could fly the RC Lander 90mm with the included motor on 6 high discharge 4000mAh cells. It looks like in their test, it pulled 85 amps out of 2 4500mAh 25c 3s packs.
Old May 31, 2009, 06:19 PM
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Quote:
Originally Posted by Extreme_RC
Why would a small increase in model weight change the angle of attack??

Fact is there is a Mirage flying at our field that weighs 2.5kg or more, and it flies exactly the same as mine does at 2.2kg with almost identical speed, (both running the same fan speed & watts) only difference is it does not have as much vertical climb rate as mine does for obvious reasons.

If I went to the Lander fan & 5000mah pack I would end up at 2.4kg AUW, and I would have around 2.7kg thrust.

I would expect the Mirage to be faster because the eflux will be higher due to the more powerful setup.

As for landing, its doubtful Kambalunga has flown any of these models, it takes experience to discover that small changes in weight make very little difference to these large jets, the surface area means oz per sq inch loading hardly changes if you add 200 grams to the model.
For produce more lift to compensate more weigth need you always more AoA. More AOA caused more drag or you are a wizard and all aerospace engineers like me are all morons. A delta like the Mirage caused more aileron down force in the neutral point or you need relaxed stability like the orginal Mirage 2000! (fly anybody it's modell Mirage tail-heavy?). In fact I have fly the Mirage 2000 in orginal and have a Jepe FastFoam. So what? I think the glased Jepe Mirage is a little bit faster as the orginal FlyFly.

PS. A 3.5kg FlyFly Mirage is bakestone and fly like a bakestone only through power.
Old May 31, 2009, 06:54 PM
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Quote:
Originally Posted by Kambalunga
For produce more lift to compensate more weigth need you always more AoA. More AOA caused more drag or you are a wizard and all aerospace engineers like me are all morons.

PS. A 3.5kg FlyFly Mirage is bakestone and fly like a bakestone only through power.
Agreed. I am a wizard to get this giant foamie to fly.
Old May 31, 2009, 07:02 PM
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Quote:
Originally Posted by Kambalunga
For produce more lift to compensate more weigth need you always more AoA. More AOA caused more drag or you are a wizard and all aerospace engineers like me are all morons.
An airfoil will stall at the same AOA regardless of wing loading. Maximum L/D will be attained at the same AOA regardless of wing loading. Maximum endurance will be attained at the same AOA regardless of wing loading. What does change with wing loading is the airspeed associated with any specific AOA.

Quote:
Originally Posted by Kambalunga
A delta like the Mirage caused more aileron down force in the neutral point or you need relaxed stability like the orginal Mirage 2000! (fly anybody it's modell Mirage tail-heavy?). In fact I have fly the Mirage 2000 in orginal and have a Jepe FastFoam. So what? I think the glased Jepe Mirage is a little bit faster as the orginal FlyFly.
Hard to understand what you are saying here but it appears to be related to reflex and COG position?

The flyfly Mirage runs no reflex in the control surfaces unlike most smaller Mirages (Gaui &Guanli are two I have personally flown) so has less drag anyway. My mirage has maybe 0.5mm of reflex as does the heavier version I mentioned. The flyfly Mirage is quite tolerant of changes in COG and does not appear to suffer from the pitch instability that some smaller versions suffer from.
Old Jun 01, 2009, 02:19 AM
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I just wrote a long response using the lift formula etc, but short answer Kambalunga is right when talking about unaccelerated level flight, ie constant speed, level flight. So for two aircraft at the same speed, the heavier will be at a higher AOA, which increases lift but also increases drag so more thrust is required. All to get back to lift = weight and thrust = drag.
Old Jun 01, 2009, 03:38 AM
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Quote:
Originally Posted by twang
I just wrote a long response using the lift formula etc, but short answer Kambalunga is right when talking about unaccelerated level flight, ie constant speed, level flight. So for two aircraft at the same speed, the heavier will be at a higher AOA, which increases lift but also increases drag so more thrust is required. All to get back to lift = weight and thrust = drag.
Your own argument can be used against you here. I understand that at any given speed, in order to maintain altitude, the AOA will increase with increasing weight. However, we are talking about a jet with significantly more thrust than stock. Therefore it can fly faster, requiring a lower AOA, producing less drag.

The statement that "More weight need more AOA and produce therefore more drag and caused less max speed and higher landing speed!" is only correct in that landing speed will increase, in the case of 200g, were talking about maybe 1.5 kph. More weight does not mean a lower top speed because we aren't simply adding lead weights here. The increase in weight is met with a substantial increase in thrust. In some cases doubling the thrust vs stock.

I'd like to hear that RC Lander fan in a Mirage. It's not going to give two craps about AOA when it's flying straight up.
Old Jun 01, 2009, 12:48 PM
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I have a HET 600-32 in a 90MM Hoeya (or Hoya) fan. Will it fly the mirage on 5s ok or would it be lame? I don't have any numbers in terms of amps as I don't have a 5s lipo. I do have 6s but assume that would toast it.

I got a couple of these cheap so not sure where to put them, I was going to use them in the mig-29 but went with medusas on 6s instead.

Thanks guys!
Old Jun 01, 2009, 12:51 PM
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I have been running a 6s on that same motor with a CC HV85 and it is still running strong. Only consideration I have had is that it melted the motor mount in my first one. When I built my 2nd one I added a heatsink and some other options to keep this from happening again. See my build info at https://www.rcgroups.com/forums/showthread.php?t=975062
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Old Jun 01, 2009, 12:54 PM
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Quote:
Originally Posted by techspy
I have been running a 6s on that same motor with a CC HV85 and it is still running strong. Only consideration I have had is that it melted the motor mount in my first one. When I built my 2nd one I added a heatsink and some other options to keep this from happening again. See my build info at https://www.rcgroups.com/forums/showthread.php?t=975062
You're on a midifan right? From my understanding the hoyas are high pitched, which means lower RPM and a better sound, but it also means more amps.
Old Jun 01, 2009, 01:06 PM
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I am not sure about the Hoya pitch but I know the stock blade is much higher pitch than the midifan. If the Hoya does have a lot more pitch, then I wouldn't try 6s on that motor. Unless you are really concerned about noise, I would go with a midifan and aluminum spinner like I have. I have been very happy with that setup.
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Old Jun 01, 2009, 01:38 PM
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How many flights do you have on the 6s? Do you know the amps it pulls with a midi?
Old Jun 01, 2009, 01:43 PM
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Max amps about 85, and I have approx 25 flights on it.
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Old Jun 02, 2009, 09:34 AM
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what size of lipo did you go with, I will be on 5s since my fans suck more amps. I am thinking 3000 Mah?

EDIT: How about 5000 mAH, too big?
Last edited by skydve76; Jun 02, 2009 at 09:40 AM.
Old Jun 02, 2009, 10:00 AM
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I am using 5000mah and it works fine. You just have to make sure the cog is correct.
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