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Why is my Mosquito so 'balloony?'

Old 03-04-2011, 01:11 AM
  #1  
mclarkson
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Default Why is my Mosquito so 'balloony?'

Just got the new Parkzone UM Mosquito and I'm having a problem with it.

Weather's bad, so I only had two short flights but, man, does it want its nose in the air. It's similar to my PZ Radian in this respect.

I was flying it around in sorta-high alpha mode: nose in the air, tons of down elevator. It's ridonculous.

What usually causes this kind of behavior? Is it just tail heavy? Down angle on the props looks good. Everything is straight and fresh from the box. Where should I look?
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Old 03-04-2011, 01:25 AM
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AirmanAirhead
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I don't have that plane, but the place to begin is to check your CG (Center of Gravity). Somewhere in the instructions it should indicate where on the wing the balance for the CG is. It sounds indeed that it is tail heavy. At least begin there. Also, what happens when you cut the power, how does it glide? If it tends to drop rather then glide in, that also would indicate a tail heavy situation.
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Old 03-04-2011, 01:47 AM
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SHADY
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Got any pics of the tail feathers and control links?
I'm curious to see how it's configured....

One of my Champs came with up elevator set way up...
All it wanted to do was back flips....
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Old 03-04-2011, 01:49 AM
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Nitro Blast
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If it is touchy, add expo if your radio allows, that can often help in the 'balloon' feeling when you make it softer in the middle.
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Old 03-04-2011, 01:56 AM
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kenchiroalpha
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Hi
Install the flight battery and do a check for CG 38mm rearwards from the leading edge of the wing at the fuselage.
Adjust CG by moving flight battery
Taken from the manual
Take care
Yours Hank
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Old 03-04-2011, 02:56 AM
  #6  
mclarkson
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Yep. I checked the CG pre-flight, and it looked to be pretty close with the battery all the way forward. (I won't pretend to be able to measure with sub-mm accuracy.)

If it's actually tail heavy, I'ma have to add weight to the nose. I'd be surprised, as my previous PZ planes have all been pretty much right on, straight out of the box.

It's not so much that it's 'touchy' as that it wants to pitch up drastically under power. Again, if you've ever flown a Radian glider, you're familiar with what I was seeing on my test flight: the more throttle, the more the nose went upwards.

Sitting on the ground with power on, there's a visible amount of down elevator from the trims, and it's not enough to fly level.
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Old 03-04-2011, 03:28 AM
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mclarkson
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Just took some snapshots of the plane. I have trouble using the CG machine on my tiny planes, so I took the pads off and just placed the plane on the ball, after making a tiny mark at 38mm. You can't tell exactly from the photos, but it's very close to level here, and is balancing unsupported.

Also took some snapshots of the tail controls.
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Old 03-04-2011, 05:17 AM
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Lol it's a twin engine vapor!
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Old 03-04-2011, 06:10 AM
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con244
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On another forum jbc says to try changing the props to MAS 9x7x3 if using 3s lipos. He was having all sorts of probs until he changed over. Might be worth a try!
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Old 03-04-2011, 06:48 AM
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mclarkson
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I'm using the stock 1S 250 mAh battery that came with the plane. A 3S? Really?
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Old 03-04-2011, 08:07 AM
  #11  
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Con224, I think you're thinking of a different plane.... This one only has a 20.5 inch wingspan... I can't imagine using two 9 inch props on it!
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Old 03-04-2011, 09:10 AM
  #12  
JetPlaneFlyer
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Sounds like it needs more downthrust to me.. If it pitches up only when power is added then it's not caused by the CG being too far back (too far forward might compound the problem though)

If possible I'd add more downthrust. Reversing the prop rotation (swap motors and gearbox from one side to other) might also help as that should create upwash rather than donwash on the tail helping to 'lift' the tail.

Steve
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Old 03-04-2011, 09:15 AM
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eye4wings
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Hi mc,
My much larger O/D Mosquito did exactly that on the first flight.
It was cured by increasing the power available over several succeeding flights.
To be honest it doesn't sound to me like your model is tail heavy. If it was it would porpoise as the centre of lift wandered fore and aft of the CofG with speed variation.
My feeling is that the tailplane doesn't have the authority it needs to adequately control the pitch of the plane at the speed it can get.

The suggestion to change the props may be a good first stop in your quest for a solution. Can you get a pair of props with a bit more pitch? That should not present too much of a risk of burning out your ESCs so long as you don't run it at full throttle static for more than a second or two.

How did the speed seem to you?

An alternative would be to ask about whether the battery has enough current availability to give full power, because if not, throttle full forward will just cause the battery volts to be pulled low so that full power is not obtained.

Do you have a WattMeter to check this with?
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Old 03-04-2011, 10:37 AM
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mclarkson
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How would CG too far forward exacerbate the problem? I can't move the battery farther forward, but I could push it back. It just seemed perfectly balanced where it is (38mm).

I'm also not sure I understand how insufficient power would cause it to balloon up.

Speed seemed okay. Down angle looks right on. The elevator seemed to have sufficient authority. I could fly, do loops, etc.

I don't have a wattmeter I can use.

If the wind dies down, I'll try another flight or two and take better notes (maybe a video.)

I'm reluctant to mess with the props, etc., etc. just yet. It just came out of the box.
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Old 03-04-2011, 10:59 AM
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CHELLIE
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Originally Posted by mclarkson View Post
How would CG too far forward exacerbate the problem? I can't move the battery farther forward, but I could push it back. It just seemed perfectly balanced where it is (38mm).

I'm also not sure I understand how insufficient power would cause it to balloon up.

Speed seemed okay. Down angle looks right on. The elevator seemed to have sufficient authority. I could fly, do loops, etc.

I don't have a wattmeter I can use.

If the wind dies down, I'll try another flight or two and take better notes (maybe a video.)

I'm reluctant to mess with the props, etc., etc. just yet. It just came out of the box.

Add a little more weight to the nose, most RTF planes are balanced tail heavy, and try that by making it a little more nose heavy, it looks like you have pleanty of down thrust, and check the incidence of the main wing and stabilizer, set it to 0 - 0 incidence, some brush planes come with pos incidence, because of a lack of motor power, is your plane Brush or brushless
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Old 03-04-2011, 11:01 AM
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eye4wings
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I don't think I or anyone was suggesting your Cof G was too far forward.
The only time that could be a problem would be if it was so far forward that the tailplane couldn't cope.
I think you've got us scratching our heads as to what the problem might be.

If as you say everything is 'straight out of the box' then it ought to be fine.

If you have enough power to do loops (of any decent size) then you clearly have enough power and can safely ignore my earlier suggestions.

Although you say 'the down angle looks right', which I assume means the amount of downthrust on the motors, the increasing tendency to climb under increased throttle is the classic symptom suggesting that the motors could use more downthrust.
I don't know how they are fixed in that model. Can you get at them to alter the mountings?
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Old 03-04-2011, 11:05 AM
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CHELLIE
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set the CG to 1/4 of the wings width at closest to the fuselage, or 25% of the main wing cord, check to see that there is no slop in the linkages, if that does not fix it, then you might need more down thrust, does the plane feel that it has enough power to pull itself well
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Old 03-04-2011, 11:20 AM
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eye4wings
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Good grief Chellie! Is that the amount of downthrust those things are supplied with?

Can't want MORE can it?

I assume that was your model? Or was it your model after you added more downthrust?
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Old 03-04-2011, 11:26 AM
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CHELLIE
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Originally Posted by eye4wings View Post
Good grief Chellie! Is that the amount of downthrust those things are supplied with?

Can't want MORE can it?

I assume that was your model? Or was it your model after you added more downthrust?

Have you seen the down thrust on some micro planes gee those thing must have 10 degrees of down thrust stock The pic belongs to mclarkson, i just blew it up , sometimes you have to try different things untill you find the sweet Spot as they say Take care and have fun, Chellie

http://www.rcgroups.com/forums/showthread.php?t=701562


An unusual amount of down thrust in the propulsion system.

Last edited by CHELLIE; 03-04-2011 at 11:44 AM.
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Old 03-04-2011, 12:15 PM
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JetPlaneFlyer
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Originally Posted by mclarkson View Post
How would CG too far forward exacerbate the problem?.....
A forward CG makes the plane more stable.. A stable plane when trimmed wants to fly at only one airspeed, the more stable the plane is the more 'determined' it becomes to stick to it's trimmed airspeed. Decrease the airspeed and the plane dives, increase the airspeed and the plane climbs. This is normal behaviour for a stable plane and is desirable to a degree, but too much stability means that the plane climbs excessively whenever you apply power and/or dives excessively whenever you throttle back.

To be honest though I suspect in this case, as the model is properly balances as per manual, that the problem is more to do with downthrust. Twin engine planes often need very large downthrust angles due to the props being close coupled around the CG. As I mentioned before, reversing prop rotation direction so that the blades move upward as they pass the fuselage might also help.

From reading online it seems that everyone has the same nose up pitching problems with this model.

Steve
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Old 03-04-2011, 12:20 PM
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eye4wings
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Phew! I'm glad that amount of downthrust is 'unusual'!
I have to admit that I have not had anything to do with models that were that far removed from 'real' aeroplanes... I guess that if that's what it takes to hold a feather down to the Earth that's what you have to do!

Having for years been busily engaged in designing my models' structures light enough to fly at scale speed it comes as a bit of a culture shock to find that actually adding weight might prove to be the answer... seems definitely counter-intuitive somehow - and certainly not logical to have to devote that much power to holding a model down!

So might the answer also equally well be to REDUCE the power available so the model doesn't balloon?
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Old 03-04-2011, 12:27 PM
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CHELLIE
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Originally Posted by JetPlaneFlyer View Post
A forward CG makes the plane more stable.. A stable plane when trimmed wants to fly at only one airspeed, the more stable the plane is the more 'determined' it becomes to stick to it's trimmed airspeed. Decrease the airspeed and the plane dives, increase the airspeed and the plane climbs. This is normal behaviour for a stable plane and is desirable to a degree, but too much stability means that the plane climbs excessively whenever you apply power and/or dives excessively whenever you throttle back.

To be honest though I suspect in this case, as the model is properly balances as per manual, that the problem is more to do with downthrust. Twin engine planes often need very large downthrust angles due to the props being close coupled around the CG. As I mentioned before, reversing prop rotation direction so that the blades move upward as they pass the fuselage might also help.

From reading online it seems that everyone has the same nose up pitching problems with this model.

Steve
Yes I agree with JPF Also, the Mosquito has a blunt nose, and a more foward CG will help with the pitching up as will more down thrust, just try a little forward CG, it that does not help, remove the weight and add more down thrust, also small micro plane dont fly as well as larger planes do, so you might have to settle for good enough some where along the line Hope that helps, Chellie
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Old 03-04-2011, 12:33 PM
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Originally Posted by eye4wings View Post
Phew! I'm glad that amount of downthrust is 'unusual'!
I have to admit that I have not had anything to do with models that were that far removed from 'real' aeroplanes... I guess that if that's what it takes to hold a feather down to the Earth that's what you have to do!

Having for years been busily engaged in designing my models' structures light enough to fly at scale speed it comes as a bit of a culture shock to find that actually adding weight might prove to be the answer... seems definitely counter-intuitive somehow - and certainly not logical to have to devote that much power to holding a model down!

So might the answer also equally well be to REDUCE the power available so the model doesn't balloon?
more power help to remove the ballooning affect with down thrust, because you are putting more of a load on the wing to Stabilize it, and flat wings need to be loaded to fly right, here is a pic of my Mavrick, it has 5 degrees of down thrust, with that amount of down thrust, it loads the wing so that i am able to fly in 25 MPH wind.





[media]http://www.youtube.com/watch?v=wz5ilV8jQRM&feature=player_embedded[/media]
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Old 03-04-2011, 01:26 PM
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SHADY
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I hope you post it up when you figure it out, I really want a Mossy....
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Old 03-04-2011, 02:10 PM
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eye4wings
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There are plenty of Mosquitos out there SHADY, especially if you are up to building your own. As has been stated many times 'the bigger they are the nicer they fly' - and without downthrust too!

PND does a nice little one about half way between my own and the PZ offering.
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