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Extra 260 (SD-models) trim question

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Extra 260 (SD-models) trim question

Old 12-05-2007, 08:42 PM
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nonstoprc
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Default Extra 260 (SD-models) trim question

My 30% Extra 260 has the following "problems":

1. requiring 4 clicks up elevators to hold it level (upright);
2. flying toward the belly on a 45 degree inverted upline. The line curves up. Ideally it should follow a 45 degree up-line and then comes down;
3. When cutting down the power to idle during a level flight, it likes to fly upward. To maintain the level line, I need to apply down elevator.


So far, I have tried seveal ideas: 0.5 degree up-thrust and 0.5 degree wing incidence. The improvement is marginal. The CG is set at the recommnded spot.

Just wonder if there are any trimming tricks I should try.

Old 12-05-2007, 08:51 PM
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altavillan
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Default RE: Extra 260 (SD-models) trim question

Put a long straight edge along the side and see if the pins are all parallel. If the plane doesn't change pitch when accelerating then it has to be stab to wing incedence out of alignment or a weight/ballance thing. If it changes pitch going from idle to full throttle then it a thrust issue.
Old 12-05-2007, 09:07 PM
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Al Lewis
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Default RE: Extra 260 (SD-models) trim question

That's exactly what mine did and I had to put up thrust in it. Now it flies level at all throttle settings and is neutral either inverted or right way up. The down thrust caused it to pull down under throttle and work against the flight surfaces. BTW My CG ended up at 6" back which, as you know, is not where they say it should be.
Old 12-05-2007, 09:51 PM
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Bob Pastorello
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Default RE: Extra 260 (SD-models) trim question

Definitely, the "stock" CG is too far aft. Your description sounds like it could be other things, but mainly, it sounds like "tail heavy".
Old 12-06-2007, 05:32 PM
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KWJ48
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Default RE: Extra 260 (SD-models) trim question

I've also ended up adjusting the engine thrust up some to mine, and have been moving batteries forward. I just stuck in 1 fender washer behind each of the 2 bottom standoffs. I may put in 1 more? I'm not sure where my cg is at, but it keeps getting better.
Old 12-06-2007, 09:14 PM
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Default RE: Extra 260 (SD-models) trim question

I once moved CG forward and the problem did not go away. Since the 20oz fuel tank is located before the wing socket, the actual CG, when the tank is full, shouold be less than 6".

Another fact is that perfect stall turn is relatively hard to perform with CG at 6.5" (the recommended spot), this is a sign the plane is actually nose-heavy.

Could it be a design flaw? From side-view, the engine is positioned well above the wing center-line. The engine can be installed lower, but then it will not align with the cowl.

Old 12-07-2007, 12:45 AM
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Default RE: Extra 260 (SD-models) trim question

This plane definitely needs up thrust on the engine. I've got a standard thickness 1/4-20 washer plus a thin one under the lower standoffs. Looks like about 1.5 degrees of up thrust. What you describe is classic engine thrust issue and has little to do with CG. Go full throttle in level flight and chop the throttle. If it balloons then you need more up on the engine. If it dives then down thrust. Before I adjusted mine, when I put it into an inverted 45deg upline it would just go to verticle. Now it stays on line. That means the cg is pretty far back but not enough to adversely affect most flight. My cg does make it tuck a bit to the belly on knife-edge.

Bob, I've been reading your posts for a long time and I respect your research and opinion, but you must really dislike the way this plane handles on the recommended cg. What is your plane doing? To me, if the plane is stable and doesn't "hunt" (won't stay level hands off) the cg is not too far back. Maybe thrust is your real issue? BTW, why did you remove you Extra from your web page? I miss it.
Old 12-07-2007, 12:48 AM
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Al Lewis
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Default RE: Extra 260 (SD-models) trim question

I came to the same conclusions and used the same fix. One thick and one thin washer under each bottom stand-off and it took it right out. Thing flies like a dream now. Nail the throttle in level flight and it just speeds up and stays level. Here's a video of my last trim flight.

http://media.putfile.com/Final-Trim-Flight
Old 12-07-2007, 06:03 PM
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Default RE: Extra 260 (SD-models) trim question

I found another problem with the Extra yesterday: the stab tube did not align perfectly wit the wing tube (left lower than the right). See picture 1.


I ended up removing the stab tube socket, rolled a new fiber-glass one with 2oz cloth. See picture 2.


Then I adjusted the mounting hole on the left fuze, and installed the new socket. The stab tube is perfectly aligned now. See picture 3.


Will try more up-thrust idea and report back.

BTW, the alum stab stub is 1.4 oz in weight. If replaced with a lighter carbon fiber one, some nose weight (if any) can be removed.










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Old 12-07-2007, 06:43 PM
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Jake Ruddy
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Default RE: Extra 260 (SD-models) trim question

#3 on your list is all thrust.. until that is right I would leave the CG in the recommended position.

Since you have made a change to the tail I would go over the whole plane with an incidence meter.
Old 12-07-2007, 08:26 PM
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Bob Pastorello
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Default RE: Extra 260 (SD-models) trim question


ORIGINAL: h82crash

This plane definitely needs up thrust on the engine. I've got a standard thickness 1/4-20 washer plus a thin one under the lower standoffs. Looks like about 1.5 degrees of up thrust. What you describe is classic engine thrust issue and has little to do with CG. Go full throttle in level flight and chop the throttle. If it balloons then you need more up on the engine. If it dives then down thrust. Before I adjusted mine, when I put it into an inverted 45deg upline it would just go to verticle. Now it stays on line. That means the cg is pretty far back but not enough to adversely affect most flight. My cg does make it tuck a bit to the belly on knife-edge.

Bob, I've been reading your posts for a long time and I respect your research and opinion, but you must really dislike the way this plane handles on the recommended cg. What is your plane doing? To me, if the plane is stable and doesn't "hunt" (won't stay level hands off) the cg is not too far back. Maybe thrust is your real issue? BTW, why did you remove you Extra from your web page? I miss it.
h82crash - I sold mine in the summer before I finished trimming it. You know, there are some you "connect" with, and some you don't. This was the latter. Great plane, flew a little fast for my taste, but flew very well. I agree that thrust ultimately would have needed some changing, but mine definitely was tail-heavy with the batteries at the cowling bulkhead. It acted tail-heavy, but not real bad.

I've ended up needing up thrust on the SD Yak, the SD Extra, the GP Cap, GP Wagstaff Extra, the GP Ultimate, but NOT the Wildhare Extra 300, or the EF Yak. No pattern to it.... some need it, some don't, and I think ultimately it's probably interrelationships of wing/stab angles PLUS the thrust line.
Old 12-07-2007, 08:46 PM
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Default RE: Extra 260 (SD-models) trim question

Personally I have yet to fly a plane that didnt need thrust correction. For those of you reading this thread for info or to learn its important to understand if you plan on flying any precision IMAC type flying chances are your plane will need thrust correction. This is why there are a number of good step by step trim charts out there.

The reason for this is simple... it is impossible for a designer to know what engine, or what prop you are going to use. It's important to understand that changing props will effect your trim. Find a prop that you like for your plane and then do the trim steps.. I mean you can test CG of course.. but fine tuning should be done once you select a prop. Every prop effects your thrust lines differently.

Trim can be difficult to understand sometimes and sometimes hard to pin point exactly what needs to be changed.. but do a search for a trim chart and follow it step by step.. in the end your plane will fly better and you will be happier with the out come.
Old 12-07-2007, 08:56 PM
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Default RE: Extra 260 (SD-models) trim question

For any interested, there is a very good trim chart on my website, collaborated with Mike Chipchase and Verne Koester a few years' back and tweaked it a bit....it's good reading!
http://www.rcaerobats.net/trim_chart.htm
Ours is a little down the page; we gave Chip top billing....
Old 12-25-2007, 11:18 AM
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Default RE: Extra 260 (SD-models) trim question

Flew the extra 260 this week after the following mods:

1. aligned the stabs with wings
2. added about 0.5 degree more up-thrust
3. added 2 oz of nose-weight

IT REALLY FLIES TRUE now. It flies perfectly level with elevators at 0 degree, which is incredible. When it slows down, the nose will not pitch up.
Stall-turn also easy to do and looks good. The 45 degree test shows no bad sign.

Old 12-25-2007, 05:31 PM
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Default RE: Extra 260 (SD-models) trim question

I found another problem with the Extra yesterday: the stab tube did not align perfectly wit the wing tube (left lower than the right). See picture 1.


I ended up removing the stab tube socket, rolled a new fiber-glass one with 2oz cloth. See picture 2.


Then I adjusted the mounting hole on the left fuze, and installed the new socket. The stab tube is perfectly aligned now.
nonstop, You just gave me the motivation to fix my misaligned stab tube on a Rich Model 30% Yak. I have the same problem and it's been buggin' the heck out of me. A couple of questions. I assume you used the aluminum tube (mine's carbon fiber) for a "plug"(?) to "roll your own socket" and if so what did you use to cleanly release the plug from your newly made fiberglass socket. Saran Wrap or similar?? How many wraps of fiberglass cloth around the tube and what type of resin did you use. Finally, how did you remove the old socket from the fuse? Thanks in advance for any info.
Old 12-26-2007, 12:25 AM
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Default RE: Extra 260 (SD-models) trim question

Goog questions, bass1.

yes, the new socket is rolled using the alum tube. The release agent is one roll of thin clear plastic wrap (to cover food with) over the tube. I cut the wrap the length of the socket plus extra half inch at each side. Use office tape over the extra half inch to secure the wrap. Notice I just used one roll over the tube and allow it a tiny bit of overlap.

The thickness of the socket is measured out of the old socket. Translate that to the number of wraps based on the thickness of the fiber cloth. On mine, I recall it is about 3.5 wraps using 2 oz cloth. Epoxy is applied on to the cut cloth and firmly roll it over the tube covered with plastic wrap. Remove excess epoxy with tower paper when done.

The release of the socket is by gently pushing the alum tube through a hole on a wood block that is the exact OD of the stab tube. Use 2X4 wood block to tap the tube and socket will be pushed to one side of the tube. Then pull the stab tube over from the other side.

The old socket is removed using Dremel tool and hobby knife. First, the socket is cut through about 1/8" from the inside of the fuze. Do it from both side. This is to cut the socket into about 3 sections. The middle one should fall by itself. The two remaining sections hanging on the fuse sides are removed by Dremel tool through grinding. Be careful not to grind the fuse itself.


After the adjustment to the socket mounting hole is done, push the new socket over and trace the cuting lines from the fuse. Cut the new socket to length, sand for a perfect fit and glue it back. On SD Extra 260, there is an access door at the tail and I applied thick epoxy through the door to where the socket joins the fuze (inside).


Hope this explains the process.
Old 12-26-2007, 01:23 AM
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Default RE: Extra 260 (SD-models) trim question

Thanks nonstop, I'll assume you used 30 minute epoxy? I may thin it a bit with alcohol. My plane has been fine for tumbling around but has been a little disapointing as far as just trying to fly basic and sportsman Imac sequences. Although it has given me some insight on how to fly a "catywompus" airframe
Old 12-26-2007, 09:46 AM
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Default RE: Extra 260 (SD-models) trim question

Sure, thinned 30min epoxy should work fine. Finish Cure epoxy will work as good.

For IMAC, the fix is definitely worth while.

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