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  #1  
Old 05-28-2014, 12:06 PM
richrfl richrfl is offline
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Unstable plane

I need some help here.
I want to simulate a Hawk airplane and I used the models
Hawk (Red Arrow) Improved_AV http://www.knifeedge.com/forums/down...d=777&act=down and
Hawk(Red Arrow)_EA http://www.knifeedge.com/forums/down...d=739&act=down.
However, the my plane is quite unstable in flight tending to roll towards the right side very randomly. My design is in the attached file, and hopefully some one with better knowledge than me will be able to help.
From the above files the EA is physically a trainer, and the modified advance is rather a more realistic airplane but with few unrealistic tricks to flight.
Because my objective is to use this model as a real simulator for the actual model, I do not want to use tricks to make it flight. I think though, that I am making something wrong in the setup that makes the plane to behave "funny" at all times.
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  #2  
Old 05-29-2014, 03:54 AM
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Maj. Numbskully Maj. Numbskully is offline
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if you've never flown the real thing ..how did you determine the swap file flys
"funny"
many take great pains to have an accurate flight model after taking the time to make a model for RF ....
maybe it really flies that way ??
how do you know whats realistic?
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  #3  
Old 05-29-2014, 08:00 AM
richrfl richrfl is offline
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Maj.
I did not flew the real thing, but I saw other people's flying it, and unless they use gyros, which I doubt, the plane flights like any other jet plane.
Well, yes it seems is takes a great pain to simulate a RC. However, I simulated other planes (propeller driven) and found no weir things on them. They just flight like the real thing.
Also, if you took your time to do some tests, you can see that the "improved" model is quite stable, and there are three differences with my model: The scale (he uses 200%, I use 100%). I tried initially at 200%, and did not work; The engine (he uses a jet, I use an EDF) and the location of the engine. (he installed it in the nose, I installed it in its real place). As test, I also moved the engine to the front, to no avail. Otherwise, sizes are the same, surfaces are located in the same place, wing profiles are the same. Because a logical reasoning, weights are different, as required by the engine type.
With realistic, I mean dimensions and components weight, size and location as per the physical model.
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Old 05-29-2014, 03:18 PM
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csgill75 csgill75 is offline
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What RC model are you trying to replicate? Is it a foamie, balsa or fiberglass model? I can replicate the exact physics of the RC model once it is at the correct size and weight and the equipment is in the right place. RF7 does a excellent job of reproducing accurate physics provided the correct parameters are input. Give the make and model of the real world RC aircraft and then we can go from there.
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  #5  
Old 05-30-2014, 05:16 AM
richrfl richrfl is offline
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csgill85,
The fuselage material is fiberglass. It includes the vertical fin. Wings and horizontal tail are balsa film covered.
I may have the plane weights written down before assembly, but regardless, by using a ballast I adjusted the weight to the actual weight, that is 7.5 lb. At this time I am verifying the motor and battery, because I have done some runs in the field and the real seems to run faster than the simulated. One other issue I have is that the actual DF runs 12 blades and G5 allows max 6. I am not an expert, but I think that may be the reason for a difference. Once I get the motor issue, I will play with the propeller pitch and see if I can compensate for the "missing" blades.
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  #6  
Old 05-30-2014, 06:41 AM
richrfl richrfl is offline
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I fixed the issue with the engine and battery, the random rolling still there. I have a new RFX.
Attached Files
File Type: rfx BAE Hawk 6 ch_AV.RFX (24.8 KB, 7 views)
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  #7  
Old 05-31-2014, 12:12 PM
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Maj. Numbskully Maj. Numbskully is offline
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Quote:
Originally Posted by richrfl View Post
Maj.
if you took your time to do some tests, you can see that the "improved" model is quite stable, and there are three differences with my model: The scale (he uses 200%, I use 100%). I tried initially at 200%, and did not work; .
LOL, ,well you didn't say THAT!
You could even Have stopped there ........but then it goes down hill from there doesn't it ..
Nuff said

But you do see my point in initially being skeptical...right ?
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Last edited by Maj. Numbskully; 05-31-2014 at 12:28 PM.
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  #8  
Old 06-01-2014, 10:07 AM
richrfl richrfl is offline
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Maj,
You made a good point about the scale and probably you missed the engine issue. Now, you seem to be as smart as the picture that identifies you, and way above my league. However, I have not seen any suggestion from you on how the explain the random rolling tendency. Neither the scaling proved to be the reason for the flying behavior, as I also mentioned. As an engineer the use of reverse testing is mandatory to verify this type of inconsistencies between two models, and that was the first thing I did.
In summary, besides expressing your skepticism, do you have any practical suggestion?
Thanks a lot for your help in advance.
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  #9  
Old 06-04-2014, 02:16 PM
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Quote:
Originally Posted by richrfl View Post
I fixed the issue with the engine and battery, the random rolling still there. I have a new RFX.
I see 3 things wrong with your AV.

1. The Rudder servo is reversed. pushing the stick right makes the aircraft go left. Remove the Servo reversing on the rudder

2. you have Flaps on the same switch as dual rates. When switching dual rates, the flaps deploy 100%. move the control of the flaps to either the knob or the 3-pos switch.

3. the CG is 1 inch to low. raise the CG 1 inch on the z axis. When the aircraft is rescaled, or shrunk down, sometimes this is necessary to make it act like it should in the simulator since the aircraft appeared to be rolling on a axis that was a few inches below the actual aircraft. This would account for the random rolling issues as it is being balanced above where the CG actually should be. now it rolls where it should instead of above it.

by resolving all these problems I have a perfectly flying aircraft and goes where i want it. I have no random rolling issues or wayward flying aircraft.

Last edited by csgill75; 06-05-2014 at 01:58 PM.
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  #10  
Old 06-05-2014, 04:17 PM
richrfl richrfl is offline
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Csgill75,
Thank you for your advices. I will run the modifications you suggested. I actually made a trial with the location of the CG, but I moved it downwards!!!!. I assumed it would be more stable if it was under the Center of Lift (I guess it is pretty close to the wing).
I will try it this week end and report.
Thanks a lot!!
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  #11  
Old 06-11-2014, 11:53 AM
richrfl richrfl is offline
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Csgill75,
You hit the nail. With your modifications I got a stable flight. Thanks a lot.
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  #12  
Old 06-12-2014, 09:52 PM
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  #13  
Old 06-22-2014, 09:00 AM
richrfl richrfl is offline
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Cagill75,
I have another question for you, as I am not familiar with the ~CS stuff. When selecting the airplane, I get an alert, saying that ~CS_RMHS and ~CS_LMHS are missing. The question is: although the plane is configured for horizontal tail plus elevator, if the physics will act as per the configuration of the airframe or the configuration of the ~CS components or both. I am not quite sure the ~CS components are not considered in the physics.
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  #14  
Old 06-22-2014, 12:55 PM
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Quote:
Originally Posted by richrfl View Post
Cagill75,
I have another question for you, as I am not familiar with the ~CS stuff. When selecting the airplane, I get an alert, saying that ~CS_RMHS and ~CS_LMHS are missing. The question is: although the plane is configured for horizontal tail plus elevator, if the physics will act as per the configuration of the airframe or the configuration of the ~CS components or both. I am not quite sure the ~CS components are not considered in the physics.
The ~CS components are overridden by how the plane is actually set up in RF...otherwise you would not be able to add working components after the fact
keep in mind you can add spoilers in the RF Aircraft editor that will effect the physics as if the model did indeed have them ....but you wont see the spoilers in the sim .......as there is no ~CS '' for them

look at the model in "wire frame' in the editor that will show you what Control Surface Components are actually working/effecting the physics regardless of the visual model
If it moves in the wire frame it is effecting the physics


a person could model what looks like a cinder block brick in RF but still have wings, stabs ailerons flaps and everything else a conventional plane has to fly when viewed in wire frame
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Last edited by Maj. Numbskully; 06-22-2014 at 01:13 PM.
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  #15  
Old 06-22-2014, 04:23 PM
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Maj sums it up pretty nicely. the 2 errors you are seeing is because there are elevators in the Physics model, but the visual model has the entire stabilizer moving with no elevators. just disregard the errors.
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