First flight follies

22 posts in this topic

Posted

Hi you knowledgeable folks.....at last I have put my avid into the sky..

I have a question about horizontal stab rigging....but first I'll explain what happened..

A couple of big surprises for me!!!

1. Water take off is crazy quick and short......6 seconds and hardly any time on the step....rate of climb about 1300fpm.....all that caught me by surprise as I wanted to perfect my step taxi before flight.....

2. after take off I had to input a lot of pitch down to level off. I used all the trim I had and that just positioned my elevator down enough to fly level. Now in that configuration my stick position is way to far forward and I will not get the required 17 degrees down. I did at altitude some slow flight and stall, it's all well, it stalls straight ahead with no bad habit.

Now the question...obviously this craft has a tendency to have a rear C of G. Now for my flight with with only me on board (I am light) I was within the C of G range but positioned  just before the rear limit (@ 16.8 in) and weighing 1000Lbs.

Do you guys have to maximum trim the aircraft at rear C of G? How much incidence does forward c of g vs rear c of g have on your trim?

I guess I will have to adjust the horizontal stabilizer incidence to correct the pitching moment and get my stick back towards the center....??? Any input and experiences are greatly appreciated.

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Posted (edited)

Hi you knowledgeable folks.....at last I have put my avid into the sky..

I have a question about horizontal stab rigging....but first I'll explain what happened..

A couple of big surprises for me!!!

1. Water take off is crazy quick and short......6 seconds and hardly any time on the step....rate of climb about 1300fpm.....all that caught me by surprise as I wanted to perfect my step taxi before flight.....

2. after take off I had to input a lot of pitch down to level off. I used all the trim I had and that just positioned my elevator down enough to fly level. Now in that configuration my stick position is way to far forward and I will not get the required 17 degrees down. I did at altitude some slow flight and stall, it's all well, it stalls straight ahead with no bad habit.

Now the question...obviously this craft has a tendency to have a rear C of G. Now for my flight with with only me on board (I am light) I was within the C of G range but positioned  just before the rear limit (@ 16.8 in) and weighing 1000Lbs.

Do you guys have to maximum trim the aircraft at rear C of G? How much incidence does forward c of g vs rear c of g have on your trim?

I guess I will have to adjust the horizontal stabilizer incidence to correct the pitching moment and get my stick back towards the center....??? Any input and experiences are greatly appreciated.

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Stabilizer adjustment should help - You didn't mention using the flaperons to trim - they should give you some nose down.    Congrats - Nice bird.   EDMO

Edited by EDMO

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Posted

sure looks like you had a nice day for flying.

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Posted

I played around with the cg on my MKIV and found that about 16.5" is perfect. I think all Avids have the same wing chord but different wing spans.  If this is true then your plane should be balanced just right. Look at your moment arm for adding a passenger, because it looks as though pilot and passenger are in front of the cg. If this is so, then when you add a passenger, the plane won't require so much down trim, if any at all.  I would recommend you perform flight test by adding 30 or 50 lb. sand bags to the passenger seat, one at a time, to see how the aircraft responds to the cg change. Do this gradually.  And make sure to secure the bags. I would do this before adjusting the horizontal stab because if you change the stab incidence to make it fly level with no trim and just you in it,and if you then fly with a passenger, you will possibly not have enough up elevator to land at your normal solo landing speed. With a passenger, You might have to touch down at a much higher airspeed to have enough elevator authority all the way through the flare. And this might be too high of speed for the airframe. She is a beauty for sure! Good luck, Bryce

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Posted

How much pitch change are you getting with throttle settings?  if your carrying half a stick of down to fly lever where are your flaperons set at?  pull on a bit of flaperon to trim the nose down and see how it is.

:BC:

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Posted

Hi everyone, tanks for your inputs. Here a few answers to your questions....

1. Ref throttle settings.....I had a real hard time to keep it from going over Vne (100Mph). The most power I could set with a relatively fine pitch was 5250Rpm. Anything above (more pitch or more Rpm) made me go over red line. At that "cruise" setting I had to set the maximum trim "nose dwn". When reducing power from there I had to give a little more nose down using stick but really not much (maybe 3/4 in movement fwd on stick)...

2. I did try flaperons...from full reflexed to full down it does have som incidence but not even enough to re-trim the elevator....still had to keep trimmed full nose down.

I think I will plan two other flights before doing anything with stab incidence (ANYONE KNOW WHAT IT SHOULD BE??) .....one with 100Lbs on the front seat and another one with elevator gap seals installed. Any reply from all very much appreciated.

P.s I also will check my flaperon rigging again to make sure...

 

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Posted

there must be huge difference in the Catalina versus the other avids.  When I pull on flaps I have to use a lot of up elevator to get the nose us, it will really pitch the nose down.  I would check the stab incidence just for grins. 

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Posted

I can't tell from the pics but do you have the ribs on the bottom of the stab?

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Posted

yes, the stab has all the ribbs.

I guess the Catalina being longer (2ft) than the avid MK4 means that different flaps settings has less influence on attitude than the MK4....not sure but my 2 cents.

Cheeeeers from BC

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Posted

To all the amphibian/Catalina flyers out there :

 

Has no one flown the catalina being at or close to the rear C of G ?????? Could you tell me how much nose down trim you need on your bird to fly level please...

Thanks

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Posted

When flying my Catalina at aft CG, I run out of nose-down trim at my cruise speed of about 75MPH.   I'd test the full CG range before you make any changes though.  With a heavy passenger and minimum fuel, the CG is at the forward limit, and I'm glad I have every bit of that hstab incidence :).  

I think the flaperons have much less pitch effect than on the other avid birds.  I can't imagine trying to trim out my Catalina using just the flaperons.   I think the CG range tends to be a lot bigger with the Catalina, and the trim forces much larger.  

Anyway, your performance numbers look amazing.  I'm about 1050# solo and get 75MPH cruise at 600fpm climb on a good day.  What's your motor?  Obviously something a little more fit than my tired 582.

 

 

 

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Posted

Hey Cowlove,

your response was exactly what I was after...thank you so much.

My Catalina has a rotax 912 originally 80 hp but this one is fitted with the Xtra piston kit supposed to produce 95 Hp. Also I have an inflight adjustable propeller. On take-off i have about 5700Rpm giving me best power.

My empty weight is 776Lbs. The good thing is that I am slightly underfed and weigh in at 130Lbs....

Cheers and all my wishes

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Posted

PS- I also added vortex generators to the underside of the hstab to try and get a little more pitch up authority in the forward-CG limit.   It's right at the barely-acceptable limit with the power at idle.  

So as it stands, going from solo minimum fuel to dual minimum fuel takes me from one extreme end of the CG envelope to the other, and luckily the controls, rigging and trim are just within their limits in both cases.  

Running out of nose-down trim and the fwd stick location is more annoying on a daily basis, but I think running out of up elevator authority in the flare of an engine-out landing with a buddy on board would be more consequential :).   I'd rig to solve the latter case, and use workarounds and creativity to deal with the former problem.  I believe Jack down in TX made a little weight bracket on the floorboard that he can slip a 25# weight plate onto.    I'm considering a bigger foam core/fiberglass trim tab.  (Lighter and more aerodynamic while I'm at it.)

 

 

  

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Posted (edited)

PS- I also added vortex generators to the underside of the hstab to try and get a little more pitch up authority in the forward-CG limit.   It's right at the barely-acceptable limit with the power at idle.  

So as it stands, going from solo minimum fuel to dual minimum fuel takes me from one extreme end of the CG envelope to the other, and luckily the controls, rigging and trim are just within their limits in both cases.  

Running out of nose-down trim and the fwd stick location is more annoying on a daily basis, but I think running out of up elevator authority in the flare of an engine-out landing with a buddy on board would be more consequential :).   I'd rig to solve the latter case, and use workarounds and creativity to deal with the former problem.  I believe Jack down in TX made a little weight bracket on the floorboard that he can slip a 25# weight plate onto.    I'm considering a bigger foam core/fiberglass trim tab.  (Lighter and more aerodynamic while I'm at it.)

 

 

  

Please excuse me, as one who barely knows what a Catalina looks like from seeing photos, for asking a couple of questions:  How big is your trim tab now?  Do you think enlarging this will make enough difference in trim without making the elevator larger?    I can check my design book again, but I believe it says that a tab that controls another surface needs to be about 10% of the area of the surface (elevator) that it controls, the same way that an aileron needs to be 10% of the wing area that it controls.

My plans, after converting Kitfox flaperons into separate flaps and ailerons, is to have two trim tabs - one trim tab working automaticly when flaps are deployed to reduce stick pressures, and the trim tab on the other side of the elevator manually or electricly adjusted by the pilot.   EDMO 

Edited by EDMO

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Posted

So you went and did it?  Congratulations!  At your weight, I can imagine that it would fly off pretty quickly.  I weigh 195 and, as mentioned, I attach a 25 pound barbell weight to the floor on the passenger side of the plane to give me more forward CG when I fly solo.  When I have a  passenger, I can remove it. It's nothing more than a pipe flange, a short nipple, and a cap. The pipe flange stays, and really isn't in the way.

My first flight had the stick pretty far forward as well, I just adjusted it back a bit. And, yes, with all that wing and lift, first takeoff surprised me too!  I hardly use any trim at all, don't really need it.  I worked through the weight regime by flying with Mr. Sandman.. a waterproof duffelbag with first one, then two 50 pound sacks of sand, augmented by additional barbell weights along the way. I do find that the forward CG positions (at gross) do tend to become hard to perform a full power-on stall, but have little issue with power-off. And, if you want to practice engine-outs, what better place to do it than over a large, empty body of water?  I did one BFR in the catalina, and when the instructor asked about engine outs, I demonstrated one.  I believe it was the first time she'd aver done a *real* engine out...

If you change the horizontal stabilizer, do it one washer at a time- a little bit of change goes a LONG way!

While the other is an earlier picture, you can see on zooming in on the trim tab that it's just barely deflected upwards- I do not trim for landings, I prefer to hold pressure, and not mess with re-configuring if I need to go around.

 

Have fun!

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Posted

Hey Avidjack..

that is a nice catalina you have. Thanks for the info. As it stands now I have "bent" back my stick a little to give me a better position when flying aft c of g. Also I added elevator gap seals for more authority.

I am not changing stabilizer incidence as I don't want to run out of elevator when flying forward c of g (thanks cowlove)

As soon as the weather's good I am going up again with a little ballast up front and check how that goes.

I see you have lots of HP on your cat.....what is your cruising speed? How fast did you dare go flying level?

I also see that you took away your water rudder....any problems with turning when windy?

Cheers from BC, Laurent

 

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Posted (edited)

Where did Jack's two photos go?  All I see now is an X and the image # where the pictures used to be, and cant bring them up now.   That's a nice plane and good photos.  EDMO

Wednesday morning and the photos are back - I don't understand these "puters"!    EDMO

Edited by EDMO

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Posted

I never installed my water rudder, but have found the plane always has excellent rudder authority with a little bit of power.  It's practically vectored thrust with the tail right behind the prop like that :)   I have nickle leading edges and don't worry too much about prop abuse, so in a pinch I can add more power.   If I'm in close quarters or feel like I need a ton of control, I extend the landing gear, which act as a very effective water brake and allows the safe application of even more power, and also moves the center of hydrodynamic pressure a little aft, helping the plane turn away from the wind.   With full flaps, there's also quite a bit of adverse yaw in the beneficial direction when hold your ailerons into the wind.  

If all this didn't get the plane under control, I am guessing the water rudder wouldn't be any additional help.  

These tricks are a little unconventional, but I've found the Catalina's water handling to be amazing.   More jet-ski than airplane. 

 

 

 

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Posted

EDMO, Re: trim tab sizing. 

I'd heard that rule of thumb too, and I'm pretty sure the trim tab is currently a little on the small size, with plenty of room to meddle before the thing becomes too inefficient or looses additional effectiveness.   I'll take exact measurements of the relative area next time I'm at the plane. 

With the current design, the piano hinge is on the lower side, meaning upward motion of the tab is fairly limited by binding.   The most improvement from making a new tab may be just rearranging the hinge or the tab shape to allow more symmetric range.  

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Posted

 

I am not changing stabilizer incidence as I don't want to run out of elevator when flying forward c of g (thanks cowlove)

 

Changing stabilizer incidence may be just what you need- I was just advocating flying and testing your most fwd CG first, and always making sure you have that case covered.   Trim, CG and elevator/rudder authority are very, very intricate in this plane, all profoundly affected by the off-axis thrust and the prop sitting *right* upstream of the tail fins.  Love it!  There's a noticeable difference between power on, power off, and even prop windmilling or stopped    Test all these conditions and make sure you have ample control.  

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Posted

EDMO, Re: trim tab sizing. 

I'd heard that rule of thumb too, and I'm pretty sure the trim tab is currently a little on the small size, with plenty of room to meddle before the thing becomes too inefficient or looses additional effectiveness.   I'll take exact measurements of the relative area next time I'm at the plane. 

With the current design, the piano hinge is on the lower side, meaning upward motion of the tab is fairly limited by binding.   The most improvement from making a new tab may be just rearranging the hinge or the tab shape to allow more symmetric range.  

Agree - most homebuilts have the piano hinge on the lower side of the tab, not giving any "up" motion to the trim tab from neutral position - the idea being that most don't need any help on the "nose-down" trimming - maybe this plane is the exception to that?   EDMO

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Posted

Cruising speed is still around 75, but I can push it on up to 90+ straight and level.. and burn lotsa fuel.  I have a fuel flow gauge, and try to keep it down around 5.5 gph in cruise, full throttle is more like 11. There's a LOT of drag in the design, especially as you push it faster.  I do use the water rudder when it's windy, it's hard to turn against the wind without it, even dragging an outboard sponson isn't enough at times.  I don't hook up the control rod from the tail unless it's windy (that picture was an early one- the rudder is now installed).  Of course, landing will be rough when it's windy.. go for the lee.  I have nickle edges on my prop as well, but was shocked at the amount of water going through the prop in rough water plow taxis (camera footage), so avoid that whenever possible when rough. It was even taking the paint off- my tips are no longer painted. One note of caution, it's possible  to bring up the rudder and have it on the outside of the control rod, which then limits your rudder travel.  If it doesn't come up right (takes extra oomph to try and seat it), drop it back down, center your rudder, and try again. 

If  you're really far forward CG (you've seen my W&B), you might cast some lead into a split shape that might easily fasten onto those handles at the rear when needed... a little lead that far back goes a long weigh (some pun intended)?

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