Mike Noin

I have to fly with what seems to me to be alot of down trim in my 8' Unionville Beaver. I have just bought the plane. What is the best way to correct this so that the elevator is not out of line with the stabilizer? Should I use a trim tab? If so how do I go about making one and where do I mount it? Is there a better way than a trim tab? I can't move the stab now and it seems to be in the correct position. The whole plane is true and straight. I have looked at the amount of down thrust on the engine and it seems to be about 1-2 degrees, should I put in more? The plane does not climb with the addition of power once I have trimmed it out with the amount of down trim mentioned above. I just don't like the look of the tail with all that down trim when its on the ground. It also limits the amount of down elevator I have at my disposal. Not that I need alot for a Beaver, hardly an aerobatic plane.

bla bla

quote: "It's not an aerobatic aeroplane"

Yep and it's not a high speed aeroplane.
Your doing nothing more than driving to fast, come back on the throttle...a lot!
If you want to burn up the sky, don't use a beaver or mix some down elevator with throttle... even then it'll get stroppy with speed.

Kicks from this aeroplane? Sharp/steep side slipped handings... you can't find a better aeroplane to perfect your technique.
Enjoy.

BillHarris

You might also check the wing incidence. Relative to the stab, it shouldn't be more than a "couple of degrees" positive.

I assume that you have to use the excessive down-trim for a cruising throttle.

A couple of degrees of engine down-thrust would be adequate for this plane.

And check the balance. Tail-heavy may require down-trim to lift the tail, in addition to making the flight a tad squirrely.

Mike Noin

Thanks for the replies guys.

The balance is bang on where the plan calls for it to be and the incidence looks about right, although I do not have an incidence meter to measure exact degrees. The excessive down trim is at half throttle and the plane does not require more down trim as I increase throttle. It seems that once I get it trimmed out for straight and level flight it does not need to be changed for different throttle positions. Once the trim is in the plane flies like a dream, I just don't like the look of the elevator. What about a trim tab? To change the incidence now would require major rework of the wing mounts or the tail feathers.

Walter D

My Feedback: (16)

Is there any play on the wings, that might cause wing incidence change?, loose covering that might lift up when the wind pressure runs over it? even a minor thing can cause this behavior.

On another note, the Beaver has a very high lift wing, you'd better check the wing incidence and its relation with engine and stab, all that wing should be at around 1 to 1 1/2 deg. positive, as mentioned above, never more than 2, if you can't change anything at this time, you could increase its down thrust (engine) by another deg. or so.

Flypaper 2

I don't know how the wing is held on your fuse but is there any you can shim up the back of the wing a 16th of an inch at a time to see if it helps.

Mike Noin

The wing bolts onto the side of the fuse with 3 bolts and also has 2 or 3 dowels that slip into holes that have been drilled into the side of the fuse the same size as the dowel for a snug fit. The stab is glued to the fuse as usual. I could move the mounting holes for the wing but its a little more rework than I wanted to do, I may have no choice. I see no one has commented on the trim tab idea, I will assume then that its a bad idea.

All covering is tight and the plane is quite clean aerodynamically for a Beaver.

Flyfalcons

No need for a trim tab, it won't do much. Try balancing the plane a little more nose heavy. On the full size Beav we are often using nearly full down elevator trim to fly level with an aft CG near full gross.

Mike Noin

Thanks flyfalcons, I will give that a try as well. Moving the cg a little forward is easy enough and a fairly safe thing to try. Now if the damn wind would co-operate I might be able to put this to the test...lol.

Flypaper 2

Mike:
Another thing you might try is raising the ailerons a bit. Would act like lower incidence, also act like washout which ain't bad. Try an eight of an inch and see what happens. let us know.

Mike Noin

They are forecasting 5 km/h winds for my area today so maybe I can get out and try some of these suggestions. I will post the results if I can get out to fly today.

Thanks again

ScaleRules

My Feedback: (5)

Mike,

Do you know what kit this was built from?

Why are you upset about the amount of down trim? You can't see this while flying. Do you want a hanger queeen or something to fly?

I agree with another post about rying to shim trailing edge to lower incedence.

JMHO!

Mike Noin

Yeah, this is a Unionville Hobbies Kit 8' span. I am going to try the suggestions made here as soon as the wind goes and plays in someone else's backyard. I just don't like the look of the elevator when the plane is on the ground, and it also limits the amount of down elevator I have at my disposal should I need it. I'm talking allot of down trim, probably 3/8" from neutral. Makes inverted flight REALLY hard. Just kidding I would not do that with this plane.

ScaleRules

My Feedback: (5)

WOW!!! 3/8" that is a lot!

Are you sure the CG is correct? Or the incedence has to be off!

As you are in Toronto have you tried ti contact Joe Murray at Unnionville? He may have some suggestions.

ScaleRules

My Feedback: (5)

Mike,

What club do you belong to?

I am with the OMFC, Oakville Model Flying Club!

Mike Noin

Okay, I got out to fly today and here is how it went. I have added some down thrust to the engine and now the plane requires much less down trim for level flight. I will be adding a little nose weight and see how that affects flight performance. Overall I was pleased with the performance of this plane today, however this is my first plane larger than a 40 size and I am finding it requires much more finesse than the smaller aircraft. It has to be flown like a full size airplane and not like a toy, if you know what I mean. I am also having a hard time slowing this thing down for landing. I use full flaps and I still find it floats like a glider in ground affect. I have an O.S. 91 fs on it with a 16' 8 prop on it. I was thinking of adding a on-board plug ignitor that is automatically turned on at less than 1/4 throttle to help lower the idle speed and ensure that it keeps running. The engine is mounted inverted and I was told that can sometimes create an unreliable idle therefore you have to increase you idle speed to keep it from stalling. My idle is pretty low now but it will sometimes stall on me. I have also found that there is a heck of allot of torc from this engine prop combo. I have to gently ease the throttle forward on take off or the plane does violent turns and I can barely keep it straight. I find this plane gets my heart going much more than my Cap does. My Cap goes where you point it and doesn't change until you tell it to, not this thing it requires your full attention, especially in a little breeze.

Flyfalcons

A 16x8 prop on a 91 four stroke? Sounds like a lot to me. Try something with less pitch, like a 14x6 or 15x4. That should help you slow down.

Edwin

My Feedback: (2)

Was thinking the same thing. Thats a big prop. I assume this is the 4-stroke .90. Had a similar problem with an extra that wouldnt slow enough on landing. Same engine as you. When I bought it used, it had a 12x8 on it. I switched to a 14x6 and made all the difference in the world. A whole different plane.
Edwin

Mike Noin

Sorry the prop is a 16x6 not a 16x8. When I bought this plane it had a 14x6 on it. The guy told me he had trouble slowing it down enough to land so I thought by using a larger diameter prop that would slow the rpm's down and thus help slow the plane down for landing. Is my problem that the plane doesn't slow down or just that it floats forever in ground effect? Guess it will be hard to tell if you haven't seen it fly.