propbuster

My Feedback: (1)

I've got a Hanger 9 Extra Easy .40 size with a big, flat bottomed airfoil wing. I've got a ton of down trim dialed in and this plane still wants to climb at 1/2 throttle. I'm thinking of either raising the wing TE to decrease the wing incidence or adding more down thrust to the engine. What do you guys think? Thanks

alan0899

G'day Mate,
I would try both solutions, trailing edge first, a small piece of ply or balsa is easy to add, & if it doesn't work, easy to remove.

BMatthews

Shimming the trailing edge is the right way if it's already got a heap of downthrust. If the model they tries to dive in the glide then shift the CG back to restore the glide.

dignlivn

propbuster

I had the same experience yesterday with my Instructor. He said
"throttle contols Altitude" .

Bob

DaveyWA

Some instructor you've got there.

Unless your model is 2 channels, throttle + rudder or something similar, then no, throttle does not control altitude, if it does, the wing incidence is incorrect as stated above

wellss

Hmm,

You have down trim dialed in? Is the elevator actually angled down? If so, the CG is too far back. These planes can fly with the CG at 50% chord, but it should really be closer to 25%.

pimmnz

Throttle controls altitude, elevator controls speed, even in the real world. You model is doing what it should, climb with power, throttle back to maintain, and close the throttle to descend. All full size pilots will tell you that, and so should your instructor. If your model does this, then it's pretty close to how it should be.
Evan, WB#12.

meaden

My guess would be tail heavy. I'd check the CG before you messed with the wing. If the CG is right then I would try adding some down thrust on the engine by adding a couple of washers behind the engine mount. After that mess with the wing...

pimmnz and dignlivn are right throttle controls altitude...try it DaveyWA I guarantee your landings will improve.

propbuster

My Feedback: (1)

Yes, throttle does control attitude to a point and elevator controls angle of attack. Too much of both and you stall the wing. We do it all the time flying full scale practicing power on stalls. The CG is at the manufacture's suggested point and it does have some downthrust already built in. This big flat bottomed wing is just doing what it's designed to do, create lift. Just a little too much in my opinion I think I'll try shimming the engine for a little more down thrust and see how she does. After that, a semi-symetrical wing build may be in the future for it!! It has plenty of power with the Evolution .46 in the nose and might be a nice aerobatic trainer with a better airfoil profile Thanks Guys

Jim Thomerson

Having the CG too far forward will make the airplane climb when it should be flying level. I would suggest moving the CG back maybe 1/4 inch and giving it a try. I spent an interesting afternoon with a free flight model and a roll of solder seeing how CG placement affects flight.

BMatthews

I hate to bust in but dignlivn's instructor is right. Other than on an aerobatic model throttle is supposed to control climb angle and elevator controls speed. This is the way it works in full sized aviation and with our trainers it's the same.... or rather it can be the same unless we trim this tendency out of the model using rearward CG locations, smaller decalage angles and downthrust. So really the instructor and you are both right but only from widely different perspectives.

rainedave

My Feedback: (1)

If your wing is attached with rubber bands then use more rubber bands. I have witnessed the LE of trainer wings raise up as speed increases or heading into the wind when not using enough rubber bands. It will cause your plane to climb drastically. No amount of elevator trim or down thrust will overcome this.

David

propbuster

My Feedback: (1)

Changing the wing incidence helped out a bit and got me thinking about checking the decalage. I ran a long straitedge along the wing saddle and checked the horizontal stab in reference to that line. Seems that in the 7" length of the horz stab it's angled down 1/4". I guess herein lies the problem. I've decided to go ahead and make a new wing for it, using a NACA 2415 semi symetrical airfoil. When I cut the wing saddle for the airfoil profile, I'll change the wing incidence to 0 degrees and see how that works out.

franciscan

Hi
I have been through this recently with my Super Sixty(40 power). I had to reduce the wing incidence and move the cg forward a little to make it fly reasonably. Flight path was only comfortable at the mid range throttle setting and in fairly calm conditions.
However I finally decided to use a spare symetrical wing I had and modified the fuselage and set the wing at 1 deg incidence. I added 2deg downthrust and moved the cg a little forward from the theoretical position. This machine is now much better and flies really well, even in windy conditions and is much more responsive. No elevator trim neccessary.
Hope your mods are as successfull.

propbuster

My Feedback: (1)

franciscan, I'm going to take out the positive decalage by changing the angle that the horz stab is at right now, and cut the new wing saddle at 0 deg. This bird has a bunch of down thrust already built into it and I'm wondering if I ought to get rid of that too!??

da Rock

Sometimes an engine with down thrust has enough power to pull the airframe straight where the prop disc is pointing. On a high wing, the drag of the wing will "pull back" and the two (the thrust and the drag) finally balance out with the wing cranked up at a higher Angle Of Attack. What does that usually do? Causes the airplane to climb.

If your engine mount is one that bolts to the firewall, it's quite simple to place a couple of washers behind the lower mounting bolts. That reduces the downthrust. You don't need to cut anything on the airframe to try it out.

Very few successful models have over a couple of degrees of downthrust.

alfredbmor

Incidences are real altitude controllers.

pimmnz

Oh, no, sir. Incidence controls airspeed, throttle controls altitude.
Evan, with respect.

da Rock

Actually guys, incidence controls what angle the rest of the airplane flies at when the wing has assumed whatever angle of attack it needs to resolve the pilot's input.

It's written in stone. The words are chiseled into the stone tablets where the aerodynamic words are writ.

We often see models act in ways that seem to refute those words, but what we see is often a temporary response that'll balance out if we give it time. For example, an airplane with lots of downthrust and a powerful engine often will climb with increased throttle. If only throttle is changed and there is no further pilot input, that airplane will level out at a higher altitude when the drag and thrust balance out. And the airplane's pitch will be very slightly changed by the new AOA the wing will have assumed.

The increase in engine power will have given an increased altitude and the change in speed will cause the wing to assume a flatter AOA.

We see our models' immediate response and make assumptions. They may be right, but often are not.

da Rock

This spin off topic is often hard for modelers to believe for a simple reason. Modelers have little chance to know the exact speed the airplane settles into. And have little chance to know the AOA of the airplane. We can't see the difference between 90mph and 100mph, much less 45 and 46. And can't see AOA angles worth spit.

When we're buzzing around at WOT the airplane looks to us like it is flying at the same top speed no matter how high it is. And it looks to us like it's flying just as flat at 400' as it is when we bring it by on a lowlevel pass. And just as flat at 2/3 throttle as at WOT.

da Rock

We can momentarily change the AOA with elevator. Do nothing but pull a bit of elevator and what happens? The AOA is pitched and the wing will give more lift. And more drag. And the airplane will climb. Yes, we have momentarily gotten elevation with AOA. BUT..... keep holding that same elevator setting and the airplane slows down because of the increased drag from the entire airplane (wing included) and it quits climbing and will very slowly begin balance out all it's aerodynamic problems. And will settle back into a lower altitude. Will most modelers have the time and vision to see all this? Most probably, you will have run out of room at your field and are in a turn to keep sight of the sucker before almost anything has balanced out.

So we think elevator controls altitude.

What modelers actually SEE most often is the result of another aerodynamic truth. You can trade energy for altitude, and altitude for energy.

That little nugget overlaps all the others. And the others overlap it. And we can't actually see the details of the trade offs worth spit.

propbuster

My Feedback: (1)

Gotta agree with da Rock. In full scale, you add throttle to climb and then re-trim evevator to maintain. It's so funny that I have no problem flying full scale, where I can see and feel every thing from the cockpit but have a hard time sometimes, looking up at my models from the ground. For me, controlling an RC model is harder I went ahead and reworked the horz stab on the model and it's now at 0 degrees decalage. Weather permitting, I'll give her a try tommorow and report back on the change.
The pics are of the re-worked horz stab saddle and another fuse (a spare) in it's original state for comparison.
And, the ribs for the new semi-symetrical wing in the works.

BMatthews

Keep in mind that along with the decalage change you'll most likely need to move the CG back to see the improvement. Otherwise if you leave the CG where it was you'll have to add up trim to achieve normal flight and the effective stabilizer angle will end up right back where it was and you'll still have the strong climbing tendency.

It's the CG location that is the real culprit in all this. You COULD have just moved it and added down trim to effectively do the same thing as cutting and gluing the stabilizer on at the new angle.

propbuster

My Feedback: (1)

Bruce, I'll be sure to bring some lead with me to the field to adjust the CG and see how she does. Thanks Tim

propbuster

My Feedback: (1)

Update on the Degalage modification................ 0 degrees decalage= One great flying plane now! It flys strait and level at 1/2 throttle with one click of UP trim, and still climbs out fantastic with added power. No change in the CG was needed either. It still floats forever on final and you have to fly it down to the runway, but, I'm sure that the new semi-symetrical wing will take out a bunch of that. Thanks for all the help and advice on this one guys, and I'll post back on this forum when I get the new wing done with a flight report. Tim