Trim question - ship seems to hop as it comes around a corner

[Dennis Toth]

Guys,
I've been flying my Stuka and started to notice that as I come off a corner the ship appears to hop around it. The ship is stable and smooth through the rounds although it can snap coming around the bottom of the insides if you pull them tight, takes lots of concentration to keep it smooth. Ship is CG balance is about 20% back of leading edge, leadouts are about 3/8" back of CG Any thoughts what might need to be adjusted?

Best,   DennisT

[Perry Rose]

I set my leadouts so the fuselage is nose down 3/8" for every foot of fuselage length. I use a line level on the nose while hanging by the leadouts to set that. It could be stalling too.

[Dave_Trible]

Dennis it's hard when you can't see it in person but it sounds like a classic case of the airplane being too nose heavy.  To some the hop or gallop looks like its tail heavy, in fact the opposite is true and requires too much elevator travel AND time to work the handle and then get back to neutral and since going so far in handle travel it's harder to find neutral again with accuracy.  Some days it may look much better than others depending how quick your responses are that day.  To find out start moving the CG back in small increments then narrow your handle line spacing in small amounts if the controls speed up too much for you and see if the gallop goes away.  As you go back with the CG your lead out adjustment will also walk back equally with it- they work directly together.   Should solve it.  If not you can go right back to square one with the adjustments. This was much more common in earlier days before we understood adjustable handles.  We just poured lead in the nose until our 2-3" bellcranks and 4-5 Hot Rock or Easy Just handles felt comfortable- and we galloped along like the Lone Ranger and Tonto.

Dave

Dave

[Brett Buck]

Guys,
I've been flying my Stuka and started to notice that as I come off a corner the ship appears to hop around it. The ship is stable and smooth through the rounds although it can snap coming around the bottom of the insides if you pull them tight, takes lots of concentration to keep it smooth. Ship is CG balance is about 20% back of leading edge, leadouts are about 3/8" back of CG Any thoughts what might need to be adjusted?

         Dave probably has it, having the CG too far forward will tend to cause that. The other possibility is that you don't have enough flap travel or area compared to the elevator.

     Brett

     

[Steve Helmick]

"Still's Stuka", or another Stuka? Is it all setup and bench trimmed per the plans? The 20% sounds about right for a Classic design. The 3/8"> LO position sounds pretty shy. I would suggest a close inspection of all hinges to make sure some aren't loose. Steve

[Randy Cuberly]

One other thing that I haven't seen mentioned is pushrod or control horn flex.  Either can cause something like this to happen...especially a flexible flap horn or flaps.  I would suggest holding the flaps down and pushing on the elevator to check flex.  They should be stiff and resist a reasonable force on the elevator or flaps.  Any significant flexing especially in the flap horn can cause exactly what you are experiencing.

Randy Cuberly

[Dennis Toth]

OK, checked through the control system, all is stiff with no flexing in the rods. I was thinking the flap/elevator adjustment was off so cause the outsides are softer then the insides so adjusted to give a little more flap on up elevator. Hingers are all good and sealed hinge line. Since it is electric (now, has had three other setups - Fox 35, PAW 19, OS 20 FS) it is easy to do short test to get the CG and leadouts right. Will fly soon.

Best,   DennisT

[Dennis Toth]

Got to fly yesterday. Had gone out one and a half turns giving more flap on up elevator. This worked very well and helped smooth out the inside turns and also helped the outside get a little tighter. I think I need maybe one more turn it is very close.

Best,    DennisT

[Steve Helmick]

It sounds like you're dialing in more down elevator at neutral flaps? Is that correct? It kinda sorta sounds like you're changing the flap/elevator ratio, but I'm easily confused...  Steve

[Dennis Toth]

Steve,
Actually, I'm adding more up elevator at neutral flaps. This gives more flap deflection for a given up elevator deflection. Having more flap deflection slows the inside turn rate (also will reduce flap deflection for a given down deflection which increase the outside turn rate).

Today I added one more turn and flew the ship. The turn rates are now both as equal as I can feel and is very smooth.

Best,   DennisT

[Steve Helmick]

Equal turns inside/outside and a decent groove in level flight is a great start. Which "Stuka" is this? Don Still's design?

Many years ago, Jerry Day asked me to fly his Brodak Cardinal when it had just a few flights on it. I did one loop and flew it out level. Put a half turn of down elevator in it, and it was like a light switch...went from scary to fun to fly. Still needed a flap tweek, but it was night & day. I'm happy that you found the problem and encourage you to keep tuning on it!  Steve

[Dennis Toth]

Steve,
Its a Don Still Stuka. I've been flying this ship since about 1993. It has had a Fox 35, OS 20FS, PAW 19 now it is E power. I have had more fun with this ship. Over the years it has won its share of contest hardware. A great ship and very steady flyer.

Best,    DennisT

[Steve Helmick]

Electrics need the CG much farther forward than IC, only partly because of the non-changing fuel load's affect on the CG during the flight. Ted Fancher has written than 18% CG is a good (safe) starting place for IC powered Classics (because of their small tail volume). So, having the CG at 20% for an electrified Classic probably isn't optimal.

The up elevator trim requirement (assuming that the plane turned equal insides/outsides when IC powered) tells me that you've got some thrustline error, like probably a bunch of downthrust. A little downthrust will give awesome outside turns, and a little upthrust will give awesome inside turns, but unfortunately, the opposite turn is just terrible. Getting equal turning response is critical to a model's long life!   Steve  

[john e. holliday]

Was this Don Still Stuka built from the original plans or a kit.   I competed with the Ambroid kit version and have both sets of plans.   If you lay a straight edge on the original plans you will see the engine, wing and stab/elevator are lined up with each other but not the fuselage.  Don even wrote that in his original article that I have with the plans buried in the shop.  When I get energetic  enough, I may have to dig them out.

[Dennis Toth]

Steve and John,
The ship is a Still Stuka from plans. I adjust the CG to get the ship stable and to turn well. I find that yes the ECL ships can have the CG a little further forward the IC ships but you need to adjust to your feel. Adjusting the flap/elevator alignment is a pain on the ship so for the longest time I just put up with it. Now that I finally made the adjustment its the best its every flown. Lesson learned - don't be lazy.

Best,   DennisT