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Old Jul 19, 2011, 11:12 AM
You win again gravity!
SMorrisRC's Avatar
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Low pressure on the underside would cause suction, the same as on the upper surface of the wing, which would cause the nose to rise under power, not fall. Then, power off would be a nose down. That's why I'm struggling to get my head round it, as the explanations given so far dont follow scientific logic.
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Old Jul 19, 2011, 11:14 AM
You win again gravity!
SMorrisRC's Avatar
UK
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Originally Posted by pavcon View Post
ok morris you know better than a pilot... What can i say
Given that I'm an aeronautical engineer for a large aircraft manufacturer, I'd tend to agree with you pav! Since when did pilots understand aerodynamics?
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Old Jul 19, 2011, 11:18 AM
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whatevr deans... Covering the cheater hole solved the problem for many pilots if that says something to you. Anw.. Im just happy that my plane flies great .. i know what i did to make it work. And since its your job you should know that it needs testing to esolve something because not all cheater holes have the same effect.. This cheater hole is actually causing some sucking. Somehow . I was explaned how but i only know what i was told. And since it was solved by covering it it says a lot to me
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Old Jul 19, 2011, 11:24 AM
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Hmmm

Perhaps the airflow in from the cheater hole is bouncing off the top of the thrust tube and exiting in a downward motion like vectored thrust. This would pitch the nose down. Again, just like too much downthrust on a propeller driven aircraft.
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Old Jul 19, 2011, 11:41 AM
You win again gravity!
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Originally Posted by jpflyer View Post
Perhaps the airflow in from the cheater hole is bouncing off the top of the thrust tube and exiting in a downward motion like vectored thrust. This would pitch the nose down. Again, just like too much downthrust on a propeller driven aircraft.
Quite possibly. If the air is being sucked up into the cheater, it could be leaving a bit of a 'void' in the air behind it, which the efflux is then falling down into, effectively giving a downthrust with the cheater open. It certainly explains the phenomena logically, obeying the laws of physics......which is a bonus.
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Old Jul 19, 2011, 11:47 AM
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Originally Posted by jpflyer View Post
Perhaps the airflow in from the cheater hole is bouncing off the top of the thrust tube and exiting in a downward motion like vectored thrust. This would pitch the nose down. Again, just like too much downthrust on a propeller driven aircraft.
Sounds possible, certainly think it is more of a thrust line problem than anything else. Looking at my Panther, covering the cheater will almost certainly reduce the thrust which would make any ballooning effect less noticeable anyway. I will run it up tomorrow and see what effect the cheater has on the thrust line between being open/closed.
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Old Jul 19, 2011, 12:11 PM
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anw.. Im just happy mine flies great.. Now, is the stock cg of the cougar correct??
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Old Jul 19, 2011, 12:12 PM
FLY IY, BREAK IT, FIX IT,
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Originally Posted by pavcon View Post
anw.. Im just happy mine flies great.. Now, is the stock cg of the cougar correct??
tell me when you find out - I am about to build one!
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Old Jul 19, 2011, 12:54 PM
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cheater hole

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Originally Posted by BRIARCROFT View Post
Sounds possible, certainly think it is more of a thrust line problem than anything else. Looking at my Panther, covering the cheater will almost certainly reduce the thrust which would make any ballooning effect less noticeable anyway. I will run it up tomorrow and see what effect the cheater has on the thrust line between being open/closed.
What I have seen is that with the cheater hole open is quicker acceleration but less top speed. When the hole is covered acceleration suffers a bit, but I pick up a little more top end.
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Old Jul 19, 2011, 01:07 PM
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Originally Posted by jpflyer View Post
What I have seen is that with the cheater hole open is quicker acceleration but less top speed. When the hole is covered acceleration suffers a bit, but I pick up a little more top end.
I noticed this also on my Cougar. When the hole was covered no ballooning remove it and it was back. I fly a pretty tight course, so I enjoy the bottom end performance of the open hole, I pretty much mixed it out with throttle to elevator with regard to the ballooning.

If this one bites the dust, I'll have to check out Pav's elevator mod on my next build. I like this plane enough that I'd get it again. Just wish the da heat would let up.
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Old Jul 19, 2011, 01:18 PM
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tell me when you find out - I am about to build one!
hahhahahaa.. Man.. Are you waiting for me to crash mine first??? Loool
Btw if the servo retracts wont work im going to install the 7 dollar hobbyking ones with the rclander struts. The retacts mechanism is exaaaactly the same

Again its going to be 4s with the 68mm dps and thrust tube

Btw a friend got some footage of my panther.. But hes a lame cameraguy still hes going to upload whatever he got on sunday evening after recording sundays flights too
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Old Jul 19, 2011, 01:27 PM
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Cougar CG

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Originally Posted by Impailer View Post
tell me when you find out - I am about to build one!
I test flew mine about 10mm ahead of the manual CG based on the Panther flights. However, the Cougar was extremely noseheavy. I ran out of elevator on landing and it landed very hot. I would start out at the recommended CG.
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Old Jul 19, 2011, 10:25 PM
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Originally Posted by SMorrisRC View Post
I don't need to. It's simple physics. Air going in the front and coming out the bottom is a change in momentum downward. As every action has an equal an opposite reaction, this pushes the back of the plane up. It's why rockets, with all the gases coming out the bottom, go up, not down.
Anyway, like I mentioned earlier, why wouldn't the air just come out the tail????
I'm looking at a lander panther now, and I still think its a cg / thrustline issue because it only happens when you throttle off. It's such a short coupled plane, its incredibly pitch sensitive.
Either way, as long as its not ballooning anymore, its all good. But please, stop landing deadstick. :P
not CG related at all just buy one and then you will see what we mean, but it looks like you already know it all haha
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Old Jul 19, 2011, 11:03 PM
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anw.. Im just happy mine flies great.. Now, is the stock cg of the cougar correct??
I fly mine at stock CG No Problem. Front wheel barely has enough weight to stay down while taxiing. But shel lands nicely with no flaps at all.
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Old Jul 20, 2011, 04:42 AM
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maghull , merseyside
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Originally Posted by Adrian_M View Post
not CG related at all just buy one and then you will see what we mean, but it looks like you already know it all haha
What part of " I am looking at one right now " means he has to buy one and you will see what we mean. I think you will find he has one, the cougar too. And as he is one of the leading aerodynamics engineers at major aircraft manufacturer, he probably does know a little bit more than you - haha.
Ok, done simple thrust line tests with cover on/off. There is no perceivable change in thrust line between both states. What I did find is that there is less suck through the cheater holes than I would have thought. Mind you I have the hand launched version so no servos ( or servo mounts ) in the intakes to get in the way. I like to fly slightly nose heavy and have reduced the throws from the manual " recommended throws", simply because I could not get the elevator to travel plus or minus 18mm. Has anybody flown this with 18mm of travel on the elevator ?
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