Author Topic: More line tension at the top! (Read 3101 times)

Curare · « **on:** August 19, 2012, 08:26:05 PM »

Hey all, forgive me for splattering the forums with seemingly random questions, but I need some help.

I pulled out some balsa on the weekend and knocked up a little 1/2a buzz bomb, not dissimilar to a skyray, but running a surestart on suction with a slack balloon tank instead of a tin one. The engine was swinging a top flite 5x3 but after the last wingover I didn't get tension back in time and it broke the prop, now I'm back to a MAS 5.5x4 cut down to 4.75. thinking a little more speed may help as well.

Now it's fine (when it's running right that is), It'll loop, and fly inverted happily with reasonable line tension, but if I try anything a bit more upwards in the hemisphere it gets a bit tricky. Wing overs can be completed at about 70° but any higher and I get draped in my own lines over the top. Obviously this puts most of the overhead manevures out of business, and I'm not game enough to try a vertical 8.

So, what can I do to keep line tension on the top?

I was running a low fin canted to give me some offset (as opposed to a rudder), it's a relatively deep fuselage (around 2 1/4" deep) and I'm running about 5° engine offset as well. I've sanded the fin's trailing edge outboard so as to give me some more airfoil effect, and shifted my leadouts back.

Anything else I can do? Oh and I forgot to say, I'm flying on about 42' of spectra lines. Should I shorten them a little?

Larry Renger · « **Reply #1 on:** August 19, 2012, 09:50:44 PM »

I love Spectra lines, but they are really draggy and need the leadout position pretty far back. Also what are the area and weight of your model? Also what size spectra lines are you using, they come in everything from "can't see it" to "raise the anchor Popeye".

Curare · « **Reply #2 on:** August 19, 2012, 10:29:23 PM »

Larry, It's a shade under 5 oz with about 100 sq's of area.

I'm using (I think) 20lb fire line. too much?

George · « **Reply #3 on:** August 19, 2012, 10:34:10 PM »

You may have too much canting and it's working against you. Try moving the leadouts forward. You might want to fly high but not a wingover until your problem is solved.

I would also take the offset out of the fin.

What you are shooting for is to have close to the same tension no matter where you are in the hemisphere.

George

Curare · « **Reply #4 on:** August 19, 2012, 10:53:43 PM »

Sorry, canting?

The leadout initially was a bit far forward, having a slight nose out tendency when hung from the leadout. Not much, maybe a a degree. I've shifted this back about 1/4" or so.

ray copeland · « **Reply #5 on:** August 20, 2012, 03:57:20 AM »

Tip weight?

kenneth cook · « **Reply #6 on:** August 20, 2012, 05:37:05 AM »

I certainly agree with your last statement concerning line length. Although I've managed to fly some models on 42' lines using Cox engines it certainly seems to be in the upper limit for reed valved engines. Try shortening the lines 2' at a time. The Surestart does have the capability. I've removed the spraybar and drilled the venturi open to increase the intake. Using a nitro content of 35% will also gain you some more power. I'm not familiar with the plane. If it is a flat wing like the Skyray, a sheeted wing can be made to work it's just not as effective as a built up. The 4 pitch prop may gain you speed in level flight, it also may just load the engine in maneuvers. The prop choice you originally tried in my opinion is one I would try and stick with. Try different brands. The APC 5x3 works quite well and will allow the engine to turn up. Ken

Larry Renger · « **Reply #7 on:** August 20, 2012, 10:20:05 AM »

I generally use 5 lb or at most 10 lb fireline. Even that is pretty draggy compared to .008 wire. But it is tough as nails and highly visible on the ground (the yellow stuff, that is). I use Powerline brand now, as it still specifies that it is Spectra.

Jim Thomerson · « **Reply #8 on:** August 20, 2012, 02:51:28 PM »

As a general rule the cure to loss of tension up high is to move the leadouts forward. I fly 1/2A on 008s so I have no idea where "forward" is for Spectra lines, and your airplane. When you move your leadouts, move them a small distance, mo more than 1/8 inch, at a time. I run 1/2A leadouts out one hole, as an 1/2 inch separation, for example, will give a noticeable yaw when maneuvering.

Tim Wescott · « **Reply #9 on:** August 20, 2012, 03:34:11 PM »

I'm no expert, but I've had good luck with an APC 6-2 on a Cox reedie. It lets the engine turn up, limits the speed in the level, and doesn't let the plane slow down very much on the verticals.

When you're feeling the plane out to see if it'll do a wingover, don't just commit to a straight wingover and hope for the best. Instead, pull up 40 degrees and hold neutral controls until you level off. Then try 50, then 60, then 70, etc., until you're either going straight overhead or the airplane has informed you that it does not feel up to doing a wingover.

George · « **Reply #10 on:** August 20, 2012, 05:26:47 PM »

Quote from: Curare on August 19, 2012, 10:53:43 PM

Sorry, canting?

The leadout initially was a bit far forward, having a slight nose out tendency when hung from the leadout. Not much, maybe a a degree. I've shifted this back about 1/4" or so.

OK. It may be that your airplane is flying with the nose pointed out too much. By adjusting leadout position, line diameter and length as folks suggest you should get it to fly tangent to the circle imposed by the lines. That is usually the ideal position.

George

Curare · « **Reply #11 on:** August 20, 2012, 05:32:20 PM »

Cheers guys, I'll get some thinner spectra for a start, and see if I can find some better props. Unfortunately where I am, most LHS's don't even know that props exist below 10", so it may be a while before I get something that works.

Then again, if it was simple, everyone would do it!

Larry Renger · « **Reply #12 on:** August 20, 2012, 10:33:04 PM »

Tower handles just about any APC prop you could desire.

Curare · « **Reply #13 on:** August 20, 2012, 11:09:41 PM »

Correct, and shipping isn't all that slow.

I have however pledged to go 'halvies' in a shipment from tower with a friend. I may just go nuts on teeny props, a complete about face for me as usually my props are 18-19"!

Steve Helmick · « **Reply #14 on:** August 22, 2012, 12:15:37 AM »

Fireline is rather "fuzzy" and would probably be draggier than PowerBraid, Tuff-Line, or Suffix 832. I'm a fisherman, but not really hip to all the "super lines". I really haven't enjoyed using most that I've tried for fishing. Partly because I don't like the noise as it goes through the guides on the rod. I would be inclined to suggest .008" braid. It's pretty delicate stuff and doesn't like being trampled on, but maybe you would try it anyway.

What George said about yaw...it doesn't do anything good, but slows the plane and thus reduces line tension. It's an old wives tale about engine offset and rudder offset increasing line tension. What a little engine offset does is to help get the lines tight again, quicker. Fly level, then at 45 degrees, then higher and higher, and see if the tension stays relatively the same. The 2012 book says that if it doesn't, you move the LO's forward, not back. Weird, eh?

Steve

Wayne Collier · « **Reply #15 on:** August 24, 2012, 05:46:30 PM »

I currently have two sets of 1/2 a lines; 35' and 42' and have only used them with an older reed valve Cox engine. I use braided spiderwire (20lb test but the same diameter as 8lb mono). The Golden Hawk I had until recently worked really well on the 42' lines but I never tried a wing over. Flew it many times before the crash I did not feel like repairing. (It was repairable, I just used the crash as an excuse for new plane.) When I got back into 1/2a a few years ago, I designed my own plane. It was a little heavy but had a good TD .049. It would scream around in level flight but slow down on even slight climbs. It only lasted a day. I have become convinced it was a trim issue.

I would keep getting trim advice until you solve the issue.

About props, one thing that helped me understand prop dynamics was realizing that for stunting I kinda needed "crop duster" performance. More of a "climb" prop and less of a "cruise" prop.

Curare · « **Reply #16 on:** August 24, 2012, 06:56:52 PM »

Well guys, it's a fine saturday morning here, and during the week I've gone for slightly shorter (35'), slightly thinner spectra lines, so we'll see if that makes a difference.

I've also gone back through all of my props and pulled out a few that I think might work, there's a cox yellow 5x3, a balck 5x3 and a cut-down 5.5x4 that's now about 4.75x4, so we'll see what that does.

I also have a big bottle of ZAP with me. Needs must as the devil drives!

Curare · « **Reply #17 on:** August 26, 2012, 10:40:20 PM »

Okay, weekend's been and gone and the poor little ukie has more grit and finger skin glued to it.

After shortening the lines about 5 feet (to 35') and messing around with props I don't really appear to be making much difference.

It's still falling in on overheads which can be exciting and tends to get very loose at the top of loops or when swapping to inverted flight.

What now? shorten the lines again?

kenneth cook · « **Reply #18 on:** August 27, 2012, 03:47:59 AM »

Your now at the minimum line length you should be flying at. At 100 squares, you certainly don't have a whole lot of wing area. The plane is going to need to fly fast. I believe the Baby RIngmaster is roughly at 150 squares and it's no prize when it comes to clean maneuvers. It doesn't do bad but the Baby Flite Streak will run circle around it and it has 150 squares. The design of the wing on the Streak is thicker. It sounds as if the wing is stalling when you go from level flight to upright as the speed just quickly falls off. Ken

George · « **Reply #19 on:** August 27, 2012, 08:00:32 PM »

Curare,

Do you suppose you could post some pics of your plane? Other than that, I would suggest trying a 6x3 prop. You may be under propping it.

George

Curare · « **Reply #20 on:** August 28, 2012, 06:09:41 PM »

okay guys, just yanked it off the wall and snapped a quicky with my phone, so apologies for the mess, and the poor quality of the shot, but I'm currently remodelling (HA!) the workshop in preparation for my new F3A ship to come in.

Here 'tis.

George · « **Reply #21 on:** August 28, 2012, 08:24:49 PM »

Curare,

Nice plane. I would suggest a pushrod guide just below the "1". A "U" of wire CA'd into the fuselage should work.

It's hard to tell from the pic but how is the alignment? The elevator hinge line should be perpendicular to the fuselage and the stab/elevator should be parallel to the wing.

Good luck with it.

George

Curare · « **Reply #22 on:** August 28, 2012, 10:11:52 PM »

It does look a little wonky in that pic doesn't it, probably because of the TE taper I think.

Tail is square to fuse, and aligned with wing, which is also square to the fuselage. It has no assymetry so all dimensions are equal port to starboard.

I don't like wonky models, and the smaller they are the less I like 'wonks'

Bill Little · « **Reply #23 on:** August 30, 2012, 07:13:56 PM »

HI Greg,

Believe it or not, more wing tip weight is recommended to help with overhead line tension. On the engine side, is it turning up pretty fast? If the plane is flying too slow, it will show symptoms like you describe.

As far as overhead line tension, the plane needs to be flying tangent to the circle. This means very very little engine offset or rudder offset. If the model is yawing out while flying, it slows down too much in overheads and even loops. Also, hitting the controls too hard will slow the model down.

Lots of fun trying to get a 1/2A trimmed out to fly well!

BIG Bear
RNMM/AMM

Curare · « **Reply #24 on:** August 31, 2012, 06:55:09 PM »

It's fairly honking around the circle, but if it's not on song it'll barely loop, so tuning is something I spend a bit of time on every time I fly.

I'll try adding some more wing tip weight, just to see.

When I initially started I had about 5-8˚ of out thrust, but with each consecutive nose rebuild, that's been reduced, I'm now running about 2-3˚. I run more on my RC aircraft!

Speaking of RC, I'm trying to keep momentum where I can buy entering wingovers softly, and exiting hard, waiting for the speed to build up, then jumping into more maneuvres.

Wayne Collier · « **Reply #25 on:** September 01, 2012, 05:08:02 AM »

Are you sure it isn't tail heavy? Looking at you're picture, it just seems that there is a lot of airplane aft of the leading edge and you've got a really light engine. Also, beware of excess elevator travel. The elevator can become an airbrake fairly quickly.

George · « **Reply #26 on:** September 01, 2012, 05:25:40 PM »

Quote from: Curare on August 31, 2012, 06:55:09 PM

Speaking of RC, I'm trying to keep momentum where I can buy entering wingovers softly, and exiting hard, waiting for the speed to build up, then jumping into more maneuvres.

Did you try a 6x3 prop? If that does not help try a 6x2 or 5.7x3. I don't think a 4" pitch prop will help maintain constant speed.

George

Bill Adair · « **Reply #27 on:** September 02, 2012, 04:23:16 PM »

I may be mistaken, but that engine sure looks like a Product engine, and not the more powerful Sure Start? Sure Starts have a choke tube, and better porting in the cylinder.

If that is a Product engine, 42 foot lines may be pushing your luck.

Bill

George · « **Reply #28 on:** September 02, 2012, 09:28:48 PM »

Quote from: Bill Adair on September 02, 2012, 04:23:16 PM

I may be mistaken, but that engine sure looks like a Product engine, and not the more powerful Sure Start? Sure Starts have a choke tube, and better porting in the cylinder.

If that is a Product engine, 42 foot lines may be pushing your luck.

Bill

Good catch Bill. I thought Sure Starts were #290's with a choke tube. I did not know about the better porting.

BTW, Sure Starts WERE used as product engines near the last. I have some of those Star Wars "Naboo Fighters" with Sure Starts in them.

George