Loss of tension above 45 degrees....

I know we have discussed this before. I'm loosing almost all line tension above 45 degrees especially in the overheads and V8. Level line tension is good. Here's my set up on the Harbinger:
625 sq
52 oz
SSW ASP 53
BE 2 blade W 12 1/5 x 4.2 launched at 8900
lap time 5.2 to 5.3
wings level upright and inverted
1 3/4 to 2 oz tip weight
airplane checked for trueness and stab tilt
63 foot eye to eye .018 lines
3/4 longer inboard wing V outboard wing
outboard flap area is about 2% larger in area V inboard flap
moving the LO all over the place doesn't seem to help a lot
cg at about 24 to 25%
I used a fixed adjustable rudder with little help then hooked up a Rabe rudder. It gives no left rudder on the insides but gives good right rudder on the outsides. When I do the O8, the inside line tension is very soft, but the outside line tension is good.

Any ideas that I could try?

Thanks in advance,

Crist,

Try some out thrust on your motor.

If you are getting a soft inside and strong outside then your RRudder is setup to move to much. It is supposed to even up the tension. Your plane may need just a bit of rt rudder all the time jsut to keep it out there.

I would try just a bit of outward thrust. Also as BB has said many times I would start with the center of the LOs at 1" behind the CG and go from there. I would resort to this setting if I were getting no where with LO adjustment like you are. I would set them there and leave them until I got something to cause a change in tension.

Then you will know what is going on and you can adjust from there

You mention the amount of tip weight you have added, but what really needs to be known is how much the outboard tip weighs in relation to the inboard. With an assymetrical wing, you have already added more mass to the inboard wing. Then you have leadouts and leadout guide to add more weight, plus any unknowns in the weight of the wood.

If you have a digital scale, hold the plane upside down by the prop and the tail wheel with the outboard wingtip on the scale. Now, weighing this, you know what the difference (or effective tip weight) is. I would add tip weight until the outboard wing flies low both upright and inverted, then back it off a bit. You still may have some "banging" in the corners which will mean more needs to be removed or more flap area added outboard, but the more tip weight you can stand, the better will be your total tension.

Still, the problem that you have described is one of a loss of tension overhead. I am not a fan of offset thrust, but you don't want to have any inthrust. Make sure your engine is at least straight ahead or "slightly" aimed outboard. If you have too much outthrust it will mess you up.

As Doug says, there is a starting point for your leadouts. After that, and after making sure you have enough tip weight to at least fly level, check your tension in level flight and at 45 degrees. The tension should be about the same both ways. If it is lighter on top move the leadouts forward slightly until the level and 45 degree points are approximately equal. You will lose some level tension this way and trade off for more overhead tension.

The prop you are using is small for the engine and you can use a little more airplane speed. If you go to a 3-blade prop and up the pitch to about 5.5 (We tried this engine with a variety of props, but a little more pitch and a little more blade helps--the one we liked was a 13 inch 3-blade) you will get more "pull" from the engine. Speeding up the plane a bit helps and then you can go to longer lines with more tension. We were using lines about 66 to 67 feet in length. Overhead tension was not a problem.

>Still, the problem that you have described is one of a loss
>of tension overhead. I am not a fan of offset thrust, but
>you don't want to have any inthrust. Make sure your engine
>is at least straight ahead or "slightly" aimed outboard. If
>you have too much outthrust it will mess you up.

That is exactly what I meant. I just wasnt that clear. You want just enough so that you know for sure it isnt inward.

I fought a plane once for a month before I noticed it was just a tad in. Then once I figured out I had the nose ring on there slanted inward I aligned the motor properly and it came alive.

Crist,

Rabe style rudders are very, very touchy. There is definately a "sweet spot". I also have added a Rabe rudder to my new plane, but for a different reason. While the plane flew pretty well and I had zero line tension problems with pretty much equal tension both inside and outside, it had a wicked yaw on hard, outside corners. So much so that it even attrached Brett Buck's attention from the other side of an adjacent circle at the NW Regionals. It was determined that the plane just didn't have enough side area aft of the CG to dampen the yaw tendency. I tried putting in a adjustable rudder without much success. So I tried setting up a Rabe style rudder. While this pretty much fixed the yaw problem it had the bad grace to add a new problem. It now has a pronounced tendency to roll toward me on hard, outside control. Doesn't seem to do it if I hit the controls more softly and do an easy corner. It's fine on insides, even very hard ones. My rudder barely moves on inside control so this new problem is likely being caused by too much rudder movement on outside control. So I just put on a larger rudder horn to slow the movement down a bit and will try it again tomorrow. I may have to go longer yet. We'll see, but at least it doesn't yaw anymore.

I suspect I'll find the "sweet spot" where the yaw problems is sufficiently dampened but it doesn't roll either. I can hope, anyway.

LAST EDITED ON Jul-03-04 AT 10:40 AM (CDT)
 
Do you have Wheel pants? If you do are they lined up to the vertical CG? Take them off and see what happens!.....if you have them

Now I see a PHOTO.....Hum....prop

Scott

More wing weight usually cures this one for me. I don't have an explanation, simple or otherwise.

I looked at a picture of your plane that you posted earlier. Nice looking plane.

It's hard to tell from the pictures but it appears to have a long nose and a relatively short tail moment. From your description of the CG location would it be fair to say that it is located about where the white is between the red and blue trim strips next to the fuselage?

The aft lateral area of the fuselage and rudder seems relatively small for a plane this size and the forward most leadout location appears to be about an inch or so behind the CG.

Overhead, the nose of plane may be hinging down because the CG is ahead of the leadouts (which is normal) but there isn't adequate lateral fuselage area behind the CG to hold the nose up. Seeems to me that the fact that the Rabe rudder helps tension when it kicks right seems to validate my "theory".

Maybe moving the CG back a bit and/or a bigger rudder and/or set up the rudder to have right rudder offset at neutral might help.

LAST EDITED ON Jul-03-04 AT 10:29 AM (CDT)
 
Guys,
Thanks for the replies. Last night I rechecked the airframe. I found out the there is a difference in the hinge lines on my 26 inch stab of less than 2mm tip to tip from the flap hinge line and the stab has a small tilt to it of less than 1/16 with the inboard high. We checked for warps and such and found none.

Doug,
We checked the thrustline and it has about 1/4 difference between tips of a 12.5 diameter prop pointing outboard.

Len,
I'll try a bigger prop and faster speed. I see no reason that this airplane can't have line tension with a 12.5 prop. I'll launch at a higher rpm and see how that works.

Randy,
When the Rabe rudder does its thing the plane shows no yawing or rolling or anything. It does prove that it does help in the outside portion of the O8.

Dick,
The picture is deceiving. The NM is 9.2 and the TM is 17.3. There is ample depth aft of the CG. The tailpost height is 4 inches.

I'll do some flying this weekend and let all know what I find out.

>Len,
>I'll try a bigger prop and faster speed. I see no reason
>that this airplane can't have line tension with a 12.5 prop.
> I'll launch at a higher rpm and see how that works.

This engine is very prop friendly (meaning you can use a wide variety of props on it and it will still be happy.) We ran it all the way from 12-13 inch 2-blade, 11-13 inch 3-blade, and 12 inch 4-blade, with the bigger 3 and 4 blade props providing the most "pull" on the lines. We did run higher pitch with the larger props, and went to higher speeds on the plane, but with longer lines to keep the same 5.2 to 5.3 second lap times.

>I know we have discussed this before. I'm loosing almost
>all line tension above 45 degrees especially in the
>overheads and V8. Level line tension is good. Here's my set
>up on the Harbinger:
>625 sq
>52 oz
>SSW ASP 53
>BE 2 blade W 12 1/5 x 4.2 launched at 8900
>lap time 5.2 to 5.3
>wings level upright and inverted
>1 3/4 to 2 oz tip weight
>airplane checked for trueness and stab tilt
>63 foot eye to eye .018 lines
>3/4 longer inboard wing V outboard wing
>outboard flap area is about 2% larger in area V inboard flap
>moving the LO all over the place doesn't seem to help a lot
>cg at about 24 to 25%

OK. Sounds pretty good.

1. Accurately measure your CG point. ACCURATELY. Use a CG Machine or something similar. Measure this point from the hingeline. Measure forward at the tip from the hingeline and mark this point with a ren written on a piece of clear tape. Cover this tape with a another piece (it is fuelproof now and can be removed later).
2. Move the leadouts to 1.25" behind this point.
3. Add another 3/4 oz of tip weight. Making the total 2.5 oz (Paul Walker would kill me). You may not realize how much tip weight will be required if the outboard flap is LARGER than the inboard. Especially with these new high thrust engines. I think the larger outboard flap is mostly required when airplanes slows in the corner a lot. Most of the new engines slow much less. The four cycle almost does not slow down at all.
4. Look for hinging in the hard bottom corners (obviously that is a lot of tip weight). Hit some hard corner bottoms.

Look for line tension up top. You should see a noticable increase.

Look for "lurching" (Al Rabe word--love it). That is when the airplane does not turn where you tell it too. It turns late and "slides" before it turns.

Both hinging and lurching are symptoms of too much tip weight. If neither are present ADD MORE TIP WEIGHT.

Hinging is the most severe symptom of excessive tip weight. Hinging will require 1/4 oz removed or more.

If lurching is present but not hinging, remove little "chips" of lead at a time, it won't take much to hit the spot where the lurching stops.

Once this is done and the airplane is somewhat satisfactory (the overhead tension should be adequate). Move the leadouts forward 1/8" of an inch at a time. The overhead tension should maximize at some point between 1.25" and 3/4" behind the CG.

Also the corner entry will "clean up" some.

Do not be tempted to move the leadouts too far forward to get a lot of overhead tension. Foward leadouts can cause a lot of weird "funnies" especially in the wind.

>I used a fixed adjustable rudder with little help then
>hooked up a Rabe rudder. It gives no left rudder on the
>insides but gives good right rudder on the outsides. When I
>do the O8, the inside line tension is very soft, but the
>outside line tension is good.
>
>Any ideas that I could try?

Set the rudder fixed and nuetral for all of the above. You can hook it back up when you are through with the above process and use it to optimize again.

Brad,
Thanks for the detailed info. I'm printing this out and will give it a try. Right now we have a slight drizzle but later I'm hoping to get out. Certainly before I leave Wednesday for the WC and NATS. See you there.

>Brad,
>Thanks for the detailed info. I'm printing this out and
>will give it a try. Right now we have a slight drizzle but
>later I'm hoping to get out. Certainly before I leave
>Wednesday for the WC and NATS. See you there.

See you Thursday!

Crist:

Having watched your Harbinger both at Pewaukee and and Sig I can tell you that it's just not giving any real VISUAL cues as to what's wrong. I was surprized when you got blown out at Pewaukee because from the ground it looks stable and very, very solid. Granted, in that gentle zephyr you were tilting about 40 degrees just to stay stnding (a problem those of us with built in ballast don't have!), and the trees were leaning the other way about 30 degrees so maybe the model just couldn't figure out where it should be!

Seriously, at Sig, although the ship appeared in good trim, I wondered if you might be fighting it a bit up high, even in the perfect conditions we had there.

Two thoughts come to mind. Is it just possible that that is WAY too much tip weight? I've never even come close to having that much, but I haven't used the bigger engines either. The Tempest was almost the same size,also weighed 52, had the heavy K & B muffler on the inside plus a longer inboard wing and still only took 7/8 oz after you got me to add more while we were trimming a year ago at Sig. It was hauling .015's rather than .018's but that shouldn't be that big a difference.

Second: Back in the late 60's I had a Gieseke Nobler that floated above 45deg. Lot's of things made it worse but nothing helped. It did everything you asked if you had enough faith in it, and taught me how to fly without line tension (as at Pewaukee), but it took several hundred flights to find the real answer. The fuselage had a slight "bow" in it, kind of following the radius of the circle. I never fixed it but both it and the Merco .35 Redhead in it did better than 1,000 flights. I let a couple of others fly it and it scared the heck out of them.

Anyway, I'm still recovering from the "Great Sig Shootout"....and I didn't even fly Classic!

Hope to see you up here in August.

Jeff W.

LAST EDITED ON Jul-03-04 AT 11:19 PM (CDT)
 
Jeff,
Thanks for the reply. If this thing has a bow in it, i'll be darned. It does have a little "right fin", in other words the fin LE is slightly to the left of center. this does give me some right "rudder". I do this as more of being sure the fin isn't giving left. Like I raise the stab LE up .5 degrees and build in a little downthrust to be sure I'm not down at the stab LE and not up with the engine.

Yes the plane flys very steady and there are no visual clues as to what might be going on. There is no hinging, no yawing, no rolling either. I watched very closely at the eight intersections and the plane just reverses itself rock solid. Just not much line tension above 45 and especially in the overhead 8 and the top of the vertical 8.

I like some line tension in the overheads because it helps me point the plane where I want it to go. With very little or no line tension it just sorta floats through the stunts. Not what we want.

Rained off and on all day. No flying today so tomorrow we'll see.

>Yes the plane flys very steady and there are no visual clues
>as to what might be going on. There is no hinging, no
>yawing, no rolling either. I watched very closely at the
>eight intersections and the plane just reverses itself rock
>solid. Just not much line tension above 45 and especially
>in the overhead 8 and the top of the vertical 8.

Then there IS NO WAY YOU HAVE TOO MUCH TIPWEIGHT.

You most likely do not have enough.

Windy carries 3+ oz in the MA 2, and I hear it is a dream to fly. Al's Sea Fury carried 3+ oz also. It takes what it takes.

LAST EDITED ON Jul-04-04 AT 02:37 PM (CDT)
 
Crist,

Much the same with my plane. Flies pretty well, no obvious roll problem at all. But where you are having line tension issues above 45 degrees, mine is fine. Plenty of tension above 45 degrees, great in the overheads , vertical eight, and hourglass. Just a wicked yaw (without any roll) on hard outside control. I'm told it is really obvious from outside the circle. But the plane flies fine. The Rabe rudder will hopefully fix that, but we'll have to see. Initial test show that the yaw is gone with use of the Rabe fixture, but I now have roll problem that will have to be trimmed out.

Interesting comment on the tip weight. When I'm trying to figure out that sort of thing, I tend to go big to see if the thing I'm trying to trim has any real effect on the problem. So with tip weight, I tend to put in a lot to see if it has any effect. If it does, then I just back off on successive flights until I get what I want. If the big load of tip weight has no effect on the problem I'm dealing with, I put it back where it was and go to something else.

Just a thought.