Question Aerodynamic troubles during a test flight with a Kitfox3

[ChrisKitfox]

Hi to Everybody,

I just acquired a Kitfox3 from 1991. The previous owner is dead, I do not have all the history of the device. I reviewed the Rotax582 which works well. This week test flight in calm conditions, 2 pers on board, after take-off, initial climb and wind cross branch without worries, during the branch wind back in level with 60Knt, departure in fluetter of the whole cell. Phenomenon strong enough that required an emergency. During this maneuver, in base and tight final, the response to the controls is uncertain with a tendency of the plane to dive on the left that it was necessary to counter strongly to compensate during all the final and the posed one. No finding of particular problem on the controls, the shutters, the control surfaces nor other elements. Unable to identify the cause, we are now investigating to solve the problem and fix it. Another clue, we found an unexplained rear centering which implied a thrust of the stick to stitch to hold the machine level ..
I would be very enjoy to make fly good this kitfox after all the work I made on!!
Thanks all for your help
Good flights

Chris

[CoClimber]

You should probably post this in the general discussion area along with photos of your airplane. Do you know which control surface was fluttering? Are the weights on the flapperons? Is there any play in the flapperon mixer? Same with the elevator.

[ChrisKitfox]

You should probably post this in the general discussion area along with photos of your airplane. Do you know which control surface was fluttering? Are the weights on the flapperons? Is there any play in the flapperon mixer? Same with the elevator.

Hello,
thank you very much for your answer. I will actually put the message in the topic.
The flutter was very strong at the cell and felt strongly in the cockpit. Not a priori in flight orders.
The elevator was in neutral the phenomenon was amplified when we tried to slightly out.
There was no fuel in the wings. The weights are, a priori, on the flappers. No play in the flapperon mixer but we will check again. I attach photos.
2334423345


Best regards

[avidflyer]

The only time I ever had flutter in one of these planes was when the adjustable trim tab cable broke, and the tab started flopping up and down. That made the joystick jerk from front to back. What do you mean when you say the flutter was at the cell? What is the cell? Also, which way did the joystick move? JImChuk

PS that was on my Avid Flyer MK IV. Not the same exactly as the Kitfox 3, but very similar.

[Av8r_Sed]

I would pull out the seat pan and go through the controls carefully, comaparing against the Model III diagrams. You're looking for free play, binding, friction, reversed linkages. Originally mine had some binding and I found one of the rod ends bent and soon to fail. The goal is to get it to operate smoothly, with as little play as possible from the control stick through to the flaperons and elevator. Pay particular attention to how the flap hand interacts and make sure it can't move unless you move it. Most people install some sort of stop on the flap handle movement.

[ChrisKitfox]

The only time I ever had flutter in one of these planes was when the adjustable trim tab cable broke, and the tab started flopping up and down. That made the joystick jerk from front to back. What do you mean when you say the flutter was at the cell? What is the cell? Also, which way did the joystick move? JImChuk

PS that was on my Avid Flyer MK IV. Not the same exactly as the Kitfox 3, but very similar.

Hi,
Thank you for your answer.
In our case, no cable break, but can actually be a little play in the flappers. One of the causes of the beginning in fluttering.
I mean cellule (all the part exept wings). But the pilot with me told me that the wings had flutted also. The joystick did not move to be effective during
the fluttering but it was very hard to control the plane to land. Even with very experienced test pilot on the command (a friend, not me !!)
During the landing, out of tight corner very short the aircraft had a tendency to want to dive left, it was necessary to find a compromise
of flight with the handle very left and a weak response of the controls We also found after the flight that the joystick must be very forward on neutral position and the elevator lowered to stay level.
So there is a problem of back centering that we do not explain.
Best regards

[ChrisKitfox]

I would pull out the seat pan and go through the controls carefully, comaparing against the Model III diagrams. You're looking for free play, binding, friction, reversed linkages. Originally mine had some binding and I found one of the rod ends bent and soon to fail. The goal is to get it to operate smoothly, with as little play as possible from the control stick through to the flaperons and elevator. Pay particular attention to how the flap hand interacts and make sure it can't move unless you move it. Most people install some sort of stop on the flap handle movement.

Thanks Paul for your answer and solutions,
I do not have the pattern and diagram of model 3, can you tell me where to find them.I unfortunately did not have much information with this device.
We will follow your advice and review the orders to achieve this minimum free play.
An idea also on the problem of centering or balance when no element has been modified and weight displaced?

An other question: what is approximatly the take off length with the Rotax582 on clean grass track?
If we success to make fly this machine correctly, I would like to use it on track of 400meter (1200ft). Our take-off test seemed longer.

Best regards,

[CoClimber]

Did you check your weight and balance? If your center of gravity is too far back, your airplane will be uncontrollable. If you are pushing the stick forward to stay level, I suspect the cg is too far back and that you are lucky to have landed.

[ChrisKitfox]

Exatly! We know it and we will do it. But no change one the originale machine. Did not allow us to imagine a problem of centering.

[avidflyer]

I'm not sure if the Kitfox 3 is the same, but a Kitfox 4 has different bolt holes on the front of the horizontal stabilizer for setting the incidence on the stabilizer. I would check that out as well if you have to use a lot of forward or rear stick to stay in level flight. Here is a picture of my Kitfox 4 project horizontal stabilizer forward mounting point. JImChuk

[ChrisKitfox]

I'm not sure if the Kitfox 3 is the same, but a Kitfox 4 has different bolt holes on the front of the horizontal stabilizer for setting the incidence on the stabilizer. I would check that out as well if you have to use a lot of forward or rear stick to stay in level flight. Here is a picture of my Kitfox 4 project horizontal stabilizer forward mounting point. JImChuk

Thank you JImChuk for these iformations and the photo, I will check it.
I am looking for the manual of Kitfox3, where can I find these technical data?

Best regards

[ChrisKitfox]

I'm not sure if the Kitfox 3 is the same, but a Kitfox 4 has different bolt holes on the front of the horizontal stabilizer for setting the incidence on the stabilizer. I would check that out as well if you have to use a lot of forward or rear stick to stay in level flight. Here is a picture of my Kitfox 4 project horizontal stabilizer forward mounting point. JImChuk

Hi JImChuk,

Sorry but I don't sse on the photo the bolt holes you talk. Could you please show it more precisely?
Other, do you know were I could find kitfox3 technical manual?

Best regards

[avidflyer]

Here is another picture of the Kitfox 4 fuselage, laying on it's side. The 4 holes show fairly well on the front horizontal stabilizer attachment fitting. That fitting is the triangle shaped fitting below and to the front of the verticle stabilizer when the fuselage is sitting right side up. JImChuk

[Av8r_Sed]

Thanks Paul for your answer and solutions,
I do not have the pattern and diagram of model 3, can you tell me where to find them.I unfortunately did not have much information with this device.
We will follow your advice and review the orders to achieve this minimum free play.
An idea also on the problem of centering or balance when no element has been modified and weight displaced?

An other question: what is approximatly the take off length with the Rotax582 on clean grass track?
If we success to make fly this machine correctly, I would like to use it on track of 400meter (1200ft). Our take-off test seemed longer.


Here is a section from the build manual covering the controls. I believe everyone who owns one of these planes would benefit greatly from having a full copy of the build manual.

Takeoff distance is a function of weight and your engine/prop combination. For what you're doing now, I would recommend flying lighter with no passenger and only a safe amount of fuel. My empty weight is around 575 pounds. Solo, I take off of turf in less than 300 feet. Landing is then a function of your approach speed. There's no need to push the envelope while you're getting used to the plane, so make sure you have plenty of field to work with. What is your empty weight?

[ChrisKitfox]

Here is another picture of the Kitfox 4 fuselage, laying on it's side. The 4 holes show fairly well on the front horizontal stabilizer attachment fitting. That fitting is the triangle shaped fitting below and to the front of the verticle stabilizer when the fuselage is sitting right side up. JImChuk

Ok, Isee now,
In what position is yours set? Which hole?
Do you have the technical manual, I have no documents or manuals?
Thanks,

[avidflyer]

I looked in my manual, and see that the builder drills these holes. (read step 3) My plane is still a project, so I can't tell you what hole it should be in. Maybe someone else can chime in on what their location is. Also, remember, this is for a Kitfox 4, and may not apply to a Kitfox 3. I don't have a manual for a Kitfox 3 to compare. JImChuk

[ChrisKitfox]

I looked in my manual, and see that the builder drills these holes. (read step 3) My plane is still a project, so I can't tell you what hole it should be in. Maybe someone else can chime in on what their location is. Also, remember, this is for a Kitfox 4, and may not apply to a Kitfox 3. I don't have a manual for a Kitfox 3 to compare. JImChuk

Thanks JIm for these informations.

[ChrisKitfox]

Here is a section from the build manual covering the controls. I believe everyone who owns one of these planes would benefit greatly from having a full copy of the build manual.

Takeoff distance is a function of weight and your engine/prop combination. For what you're doing now, I would recommend flying lighter with no passenger and only a safe amount of fuel. My empty weight is around 575 pounds. Solo, I take off of turf in less than 300 feet. Landing is then a function of your approach speed. There's no need to push the envelope while you're getting used to the plane, so make sure you have plenty of field to work with. What is your empty weight?

Thanks for this answer and all the informations you give. Which weight are you talking about?
I am 80kg and the other pilot 62kg.
Do you know where I could find Technical information and manuel about Kitfox3?

[Xengineguy]

Hi,
Thank you for your answer.
In our case, no cable break, but can actually be a little play in the flappers. One of the causes of the beginning in fluttering.
I mean cellule (all the part exept wings). But the pilot with me told me that the wings had flutted also. The joystick did not move to be effective during
the fluttering but it was very hard to control the plane to land. Even with very experienced test pilot on the command (a friend, not me !!)
During the landing, out of tight corner very short the aircraft had a tendency to want to dive left, it was necessary to find a compromise
of flight with the handle very left and a weak response of the controls We also found after the flight that the joystick must be very forward on neutral position and the elevator lowered to stay level.
So there is a problem of back centering that we do not explain.
Best regards

Did the builder install the nylon blocks in the turtle deck area? They support the inner flaperons
where they pass thru. If they are not there I would guess you might end up with flight problems like you describe.

[ChrisKitfox]

Did the builder install the nylon blocks in the turtle deck area? They support the inner flaperons
where they pass thru. If they are not there I would guess you might end up with flight problems like you describe.

Hi,

Thanks for your answer. I don't understand what do you mean by: " in the turtle deck area?" Would you please send me the photon or a draw of this part?
Best regards