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Old Mar 31, 2012, 01:48 PM
Mike
United Kingdom, England, Thurstonfield
Joined Feb 2012
80 Posts
Help!
Dynam EZ hawksky "Porpoises"

I am very new to this hobby and I am learning myself to fly. I am not doing to badly using the EZ which was a xmas present. At First I naively thought that the plane would fly "straight" at full throttle but the beginners thread put me right on that and now I can achieve good level flight at at 1/2 throttle. However I am finding it difficult to prevent the plane from porpoising when I give it more than 1/2 throttle the nose goes up then down then up then down and so on. With very careful control of the throttle I can stop this and achieve level flight again. consequently I am frightened to fly to low for obvious reasons so I am limited to going round in circles at high altitude. I have checked and re-checked the COG by adjusting the battery position but this does not seem to help. I was led to believe that this plane was very easy to fly but this has me beat. With the throttle off the plane does glide straight and fast and landing is not a big problem. The plane is standard out of the box 2.4ghz 4 channel tx but only 3 channel on the plane, throttle, airelon, elevator.
i am sure I have everything trimmed ok having checked all control surfaces carefully.

Thanks for any advice anyone might have

Mike
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Old Mar 31, 2012, 02:25 PM
'tis nothing
shunyata's Avatar
United States, CA, Napa
Joined Dec 2011
941 Posts
Here's a related thread on RC Universe. It's old but doesn't matter.

http://www.rcuniverse.com/forum/m_28...tm.htm#2879523

I have an interest in this also as my Sky Surfer/Bixler suffers from a bit of this. Could also be the nature of a pusher to some degree.

???
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Old Mar 31, 2012, 02:54 PM
Old Fogey-ish
United States, WA, Vancouver
Joined Aug 2010
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If it glides well with the throttle off then you're CG and trim should be OK . If the problem only occurs with thrust , try adjusting the thrust angle . I don't have that plane , but you might be able to loosen the motor pod , put a shim or washer under the front ( to make the thrust go DOWN ) and then tightening the pod back down . Or if it's easier , loosen the motor from the pod , put a shim or washer on top ( to make the thrust go DOWN ) and then tightening the motor back down .
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Old Mar 31, 2012, 03:43 PM
Registered User
USA, IL, Wheaton
Joined Oct 2010
463 Posts
Watch out when adjusting thrust line with a Pusher! If you're looking from the back of the plane, you need to put the washer under a bottom mounting screw to get the motor to point up a couple degrees and make the thrust line go down towards the front the same amount. Put a ruler along side the plane and point the front of it down to see what I mean. I've built a push panther so have had to figure it out. Go to the EZ Star thread on Foamies(Kits) to get more info on this.
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Old Mar 31, 2012, 06:53 PM
Old Fogey-ish
United States, WA, Vancouver
Joined Aug 2010
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Yeah , it's gonna be a trial and error thing to get the proper up/down thrust , but the goal is to not have the nose go up when increasing the throttle .
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Old Mar 31, 2012, 10:53 PM
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Moab, Utah, USA
Joined Apr 2003
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Mike,

Since this is a ready to fly airplane I seriously doubt that it is a balance or thrust angle problem. There is basically no way to adjust the thrust angle and the battery compartment is such a tight fit that the center of gravity cannot be shifted very far. Any position of the battery will probably have the center of gravity within the acceptable range for this aircraft.

A little more information would be helpful here. When you say the airplane is porpoising at full throttle, is that with or without any elevator input by you? If it is with elevator input it sounds like you are overcontroling for which there are fixes. If it is without elevator input then it is a trim problem which can also be resolved. Please get back to us and try to give us a more descriptive narration of the problem and let us know what control inputs you are you are adding, if any. Hopefully we can then diagnose your problem more accurately.

Larry
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Old Apr 01, 2012, 01:19 AM
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Gerry__'s Avatar
United Kingdom, London
Joined Jan 2005
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Quote:
Originally Posted by METATRON12 View Post
I am very new to this hobby and I am learning myself to fly. I am not doing to badly using the EZ which was a xmas present. At First I naively thought that the plane would fly "straight" at full throttle but the beginners thread put me right on that and now I can achieve good level flight at at 1/2 throttle. However I am finding it difficult to prevent the plane from porpoising when I give it more than 1/2 throttle the nose goes up then down then up then down and so on. With very careful control of the throttle I can stop this and achieve level flight again. consequently I am frightened to fly to low for obvious reasons so I am limited to going round in circles at high altitude. I have checked and re-checked the COG by adjusting the battery position but this does not seem to help. I was led to believe that this plane was very easy to fly but this has me beat. With the throttle off the plane does glide straight and fast and landing is not a big problem. The plane is standard out of the box 2.4ghz 4 channel tx but only 3 channel on the plane, throttle, airelon, elevator.
i am sure I have everything trimmed ok having checked all control surfaces carefully.

Thanks for any advice anyone might have

Mike
The porpoising is a pilot-induced oscillation.
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Old Apr 01, 2012, 06:10 AM
Mike
United Kingdom, England, Thurstonfield
Joined Feb 2012
80 Posts
Thanks a lot shunyata you may be right about the pusher thing at the moment I am not sure if it is a plane or pilot error
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Old Apr 01, 2012, 06:26 AM
Mike
United Kingdom, England, Thurstonfield
Joined Feb 2012
80 Posts
Since this is a ready to fly airplane I seriously doubt that it is a balance or thrust angle problem. There is basically no way to adjust the thrust angle and the battery compartment is such a tight fit that the center of gravity cannot be shifted very far. Any position of the battery will probably have the center of gravity within the acceptable range for this aircraft.

A little more information would be helpful here. When you say the airplane is porpoising at full throttle, is that with or without any elevator input by you? If it is with elevator input it sounds like you are overcontroling for which there are fixes. If it is without elevator input then it is a trim problem which can also be resolved. Please get back to us and try to give us a more descriptive narration of the problem and let us know what control inputs you are you are adding, if any. Hopefully we can then diagnose your problem more accurately.

Larry[/QUOTE]

LARRY

I think you may be right I was out this morning dead calm and I got a bad dose of this porpoise problem. The plane seemed to get into a cyclic routine and was very difficult to control. I eventually gave it full throttle and gained height ok I then managed to stabilise the plane with very careful adjustment of the throttle.
To answer your question I do not think I was using elevator , only throttle but I did reduce the throttle from nearly full to half very quickly which is what I think initiated the porpoise. I assume this is what you mean by over control ( Would overcontrol of the throttle have the same effect as to much elevator?). What bothers me is that once the plane gets into this cycle it is difficult to get out of it.
If it is pilot error then the plane may be ok which is good.

Mike
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Old Apr 01, 2012, 06:32 AM
Mike
United Kingdom, England, Thurstonfield
Joined Feb 2012
80 Posts
Quote:
Originally Posted by balsa or carbon View Post
If it glides well with the throttle off then you're CG and trim should be OK . If the problem only occurs with thrust , try adjusting the thrust angle . I don't have that plane , but you might be able to loosen the motor pod , put a shim or washer under the front ( to make the thrust go DOWN ) and then tightening the pod back down . Or if it's easier , loosen the motor from the pod , put a shim or washer on top ( to make the thrust go DOWN ) and then tightening the motor back down .
Thanks a lot the plane really does head for the heights with full throttle, this may be normal and I have learned to go easy on the throttle. To get straight level flight
I have to use approx 40% throttle. It would be easy to shim the motor as you suggest but being a newbie I would like to rule out pilot error 1st

Thanks a lot

Mike
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Old Apr 01, 2012, 06:34 AM
Mike
United Kingdom, England, Thurstonfield
Joined Feb 2012
80 Posts
Quote:
Originally Posted by DuPageJoe View Post
Watch out when adjusting thrust line with a Pusher! If you're looking from the back of the plane, you need to put the washer under a bottom mounting screw to get the motor to point up a couple degrees and make the thrust line go down towards the front the same amount. Put a ruler along side the plane and point the front of it down to see what I mean. I've built a push panther so have had to figure it out. Go to the EZ Star thread on Foamies(Kits) to get more info on this.
Thanks a lot for the link I will check that out

Mike
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Old Apr 01, 2012, 06:42 AM
Mike
United Kingdom, England, Thurstonfield
Joined Feb 2012
80 Posts
Quote:
Originally Posted by Gerry__ View Post
The porpoising is a pilot-induced oscillation.
Thanks for the input Gerry I have a feeling you are right, but as a newbie I assumed the EZ hawksky was a very easy to fly plane, just surprised I am falling into this trap so often with this plane, but I suppose what seems difficult at first becomes easy with experience. I only have about 5 hours flying time experience

Thanks again

Mike
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Old Apr 01, 2012, 06:49 AM
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Gerry__'s Avatar
United Kingdom, London
Joined Jan 2005
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Quote:
Originally Posted by METATRON12 View Post
Thanks for the input Gerry I have a feeling you are right, but as a newbie I assumed the EZ hawksky was a very easy to fly plane, just surprised I am falling into this trap so often with this plane, but I suppose what seems difficult at first becomes easy with experience. I only have about 5 hours flying time experience

Thanks again

Mike
Fly it as a glider and you'll be fine. Use the motor to climb only. When setup properly for gilding you should only need to nudge the stick, while flying around under power, the more power you use the more hands on you will need to be.
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Old Apr 01, 2012, 06:57 AM
Mike
United Kingdom, England, Thurstonfield
Joined Feb 2012
80 Posts
Quote:
Originally Posted by Gerry__ View Post
Fly it as a glider and you'll be fine. Use the motor to climb only. When setup properly for gilding you should only need to nudge the stick, while flying around under power, the more power you use the more hands on you will need to be.
Thanks for the advice Gerry I will do this whilst I am still "learning"

Mike
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Old Apr 01, 2012, 08:09 AM
'tis nothing
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United States, CA, Napa
Joined Dec 2011
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Mike, I'd try some of the suggestions regarding expo on the elevator if your transmitter can manage that. My son, who is also a general aviation pilot, was explaining to me that this issue is related to the plane's basic design. Not the porpoising problem, as that seems to be a control issue if the plane is set up well. But, these things want to climb fast under very little throttle, more so than all the other planes we have here.

I think Gerry has it right. It's a powered glider, just a little more forward speed results in a lot of lift, thereby challenging the pilot to manage its trim, so we end up chasing the plane's behavior with the controls instead of being "ahead of it."

That said, this is what I was working on yesterday. Running an 8" prop on it now and lower Kv. Plus, I can play with the thrust angle.
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