Tail Heavy Four * Sixty
11-20-2002, 11:10 AM
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Tail Heavy Four * Sixty
I have just completed a Sig Four Star 60 and was surprised to learn that it is definitely tail heavy.
I am balancing it by holding it upside down with one finger under each main spar (with a partner).
Anyway it clearly is tail heavy which surprises me because I am using a Magnum 91 four stroke, which if anything, is mounted slightly forward on its mounts. Plus, I have the battery and the receiver as far forward as they can go.
So, should I be worried or should I just put some weight in the front and forget about it?
Thanks,
JPF
I am balancing it by holding it upside down with one finger under each main spar (with a partner).
Anyway it clearly is tail heavy which surprises me because I am using a Magnum 91 four stroke, which if anything, is mounted slightly forward on its mounts. Plus, I have the battery and the receiver as far forward as they can go.
So, should I be worried or should I just put some weight in the front and forget about it?
Thanks,
JPF
11-20-2002, 02:48 PM
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Tail Heavy Four * Sixty
ALWAYS balance a plane on the reccomended CG with an empty tank. You're better off with a plane that is slightly nose heavy than tail heavy. In most cases, the main spar is a good starting point. (You typically ballance at 25 - 33% of chord from the LE, but thre are exceptions...)
You have plans, and it should indicate the balance point/range. If you've built it per the instructions, all should be OK, with what you're saying.. were there any mods you made?
One thing does pop into my head though.. Are you balancing it with a finger at each wing tip? that will definitely give you wrong info. You want to balance it with your 'points' as close to the fuselage as possible.
You are best not to use fingers, as you'll 'roll them' to balance the plane. the easiest thing to do is build yourself a balancing jig: Head to the lumber yard, and get a block of wood, 1" x 4" x12". Get a dowel, 1/4" dia should be fine. Drill two 1/4" holes in the block, centered along the length, and as far enough apart to fit the fuse. Make sure the holes are perpendicular to the block! (Well, get them as close as possible!!) chop the dowel into two equal lengthed pieces; about 12" long, and stick them in the holes. You should have a block of wood, with two sticks poking out of it. Clamp it to a table, and place yopur plane on the sticks at the balance points. Use a bit of masking tape on each side of the fuse to indicate where to balance. Also, sand/round the tips of the stick so you don't wreck your covering jog. Pencils with rubber tip erasers are a good substitue!
Hope that helps!
You have plans, and it should indicate the balance point/range. If you've built it per the instructions, all should be OK, with what you're saying.. were there any mods you made?
One thing does pop into my head though.. Are you balancing it with a finger at each wing tip? that will definitely give you wrong info. You want to balance it with your 'points' as close to the fuselage as possible.
You are best not to use fingers, as you'll 'roll them' to balance the plane. the easiest thing to do is build yourself a balancing jig: Head to the lumber yard, and get a block of wood, 1" x 4" x12". Get a dowel, 1/4" dia should be fine. Drill two 1/4" holes in the block, centered along the length, and as far enough apart to fit the fuse. Make sure the holes are perpendicular to the block! (Well, get them as close as possible!!) chop the dowel into two equal lengthed pieces; about 12" long, and stick them in the holes. You should have a block of wood, with two sticks poking out of it. Clamp it to a table, and place yopur plane on the sticks at the balance points. Use a bit of masking tape on each side of the fuse to indicate where to balance. Also, sand/round the tips of the stick so you don't wreck your covering jog. Pencils with rubber tip erasers are a good substitue!
Hope that helps!
11-20-2002, 03:13 PM
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Tail Heavy Four * Sixty
The .91 four strokes, with muffler, tend to be lighter than a .61 BB ABC without muffler. Its not suprizing you need some nose weight.
I had a 1.25 oz in the spinner type noseweight on my 4*60 with a O.S. .91 FS. I also had retracts, adding a BUNCH of weight, and the plane's performance didn't suffer at all. (was a little smoother in turbulance than other 4*60's that have been at our field...)
Add the nedd weight and don;t worry. It'll fly GREAT! (Just don't have a dead-stick when in vertical climb-out 20 ft up from a touch-n-go... it'll trash the plane. [img]i/expressions/face-icon-small-sad.gif[/img] )
I had a 1.25 oz in the spinner type noseweight on my 4*60 with a O.S. .91 FS. I also had retracts, adding a BUNCH of weight, and the plane's performance didn't suffer at all. (was a little smoother in turbulance than other 4*60's that have been at our field...)
Add the nedd weight and don;t worry. It'll fly GREAT! (Just don't have a dead-stick when in vertical climb-out 20 ft up from a touch-n-go... it'll trash the plane. [img]i/expressions/face-icon-small-sad.gif[/img] )
11-21-2002, 07:06 PM
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Tail Heavy Four * Sixty
Mine too was very tail heavy with a Saito 91. Had to completely cover the fuselage bottom underneath the engine with lead. But it flys nice.
11-21-2002, 09:58 PM
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Tail Heavy Four * Sixty
Spinner weight, heavy brass acorn prop-nut... bolt the lead to the engine mounts. ANYTHING but plastering lead on behind the firewall.
The further forward the weight is, the less you need.
The further forward the weight is, the less you need.
11-22-2002, 05:22 PM
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There is an "engine cavity" with plenty of room below the engine and in front of the fire wall.
I was planning on just epoxying some hobby store lead in that general area.
Sound OK?
JPF
I was planning on just epoxying some hobby store lead in that general area.
Sound OK?
JPF
11-22-2002, 05:36 PM
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Hmmm, well I suppose, but it is already about 1/4 forward of where the plans suggested it should be.
I would rather go with a little lead up there.
Hey, I'm trying to post a pic of it, but, I'm having trouble attaching the image. Is there some secret??
JPF
I would rather go with a little lead up there.
Hey, I'm trying to post a pic of it, but, I'm having trouble attaching the image. Is there some secret??
JPF
11-22-2002, 05:38 PM
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Tail Heavy Four * Sixty
Hi,
This plane looks a lot like my Super Sportster. It was extremely tail heavy with a OS 90 FS. Someone before me tried to add nearly 3 lbs to the front end. NO GOOD, I watched it nearly crash.
Then I bought it, removed the weights, removed the covering and cut out lots of bulsa in the fuse and tail feathers, Now i have only about 1 1/5 lbs in the front, recovered.. it flies beautifully, it is my favorate flyer at the moment. WIth the 90 it has all the power to do anything i want, **So I don't like adding more and more weight , find out why it is tail heavy and do it right, You don't want to loose a good plane. Happy Flying
This plane looks a lot like my Super Sportster. It was extremely tail heavy with a OS 90 FS. Someone before me tried to add nearly 3 lbs to the front end. NO GOOD, I watched it nearly crash.
Then I bought it, removed the weights, removed the covering and cut out lots of bulsa in the fuse and tail feathers, Now i have only about 1 1/5 lbs in the front, recovered.. it flies beautifully, it is my favorate flyer at the moment. WIth the 90 it has all the power to do anything i want, **So I don't like adding more and more weight , find out why it is tail heavy and do it right, You don't want to loose a good plane. Happy Flying
11-22-2002, 06:03 PM
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Well, that's sort of the challenge isn't it? Why is it tail heavy? It is built exactly according to the plans with no mods.
I don't think it's going to take much weight forward to correct it. Certainly only a few ounces, not POUNDS!!
The pic on the avatar is my first four star which my son "re-kitted". I'm trying to post a pic of the new one on this thread but haven't had any luck yet. The covering on the new one is much cooler.
JPF
I don't think it's going to take much weight forward to correct it. Certainly only a few ounces, not POUNDS!!
The pic on the avatar is my first four star which my son "re-kitted". I'm trying to post a pic of the new one on this thread but haven't had any luck yet. The covering on the new one is much cooler.
JPF
11-23-2002, 11:54 AM
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Tail Heavy Four * Sixty
The DuBro aluminum rounded safety prop nut, and a Parma weight for mounting n the crankshaft with the prop have the same outer dia. A standard prop nut (not the one that has the slotted jam nut the 4-strokes normally come with now) fits inside a depression in the weight, which replaces the original prop washer. The result looks VERY nice. No spinner required. [img]i/expressions/face-icon-small-wink.gif[/img]
You've got the bennefit of the weight for ballancing the plane, a nice appearance, and no plastic spinner to get ground up by the electric starter. (The electric starter rubber insert will have to be flipped, and will wear a bit to get a depression to grab the DuBro safety nut. Takes about 3 starts to get the depression.)
BTW... I'm NOT going to buy plastic spinners EVER again. In crashes of 2-stroke models, they tend to collapse and rip the carb off the engine. The aluminum safety nuts look good, and don't have that problem. Costs as much to relace a couple of carbs as to buy an engine. (and sometimes the carb rips part of the engine case out...)
You've got the bennefit of the weight for ballancing the plane, a nice appearance, and no plastic spinner to get ground up by the electric starter. (The electric starter rubber insert will have to be flipped, and will wear a bit to get a depression to grab the DuBro safety nut. Takes about 3 starts to get the depression.)
BTW... I'm NOT going to buy plastic spinners EVER again. In crashes of 2-stroke models, they tend to collapse and rip the carb off the engine. The aluminum safety nuts look good, and don't have that problem. Costs as much to relace a couple of carbs as to buy an engine. (and sometimes the carb rips part of the engine case out...)
11-23-2002, 05:10 PM
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Tail Heavy Four * Sixty
Maybe I am driving this point in the ground, but I have 7 planes in the shop right now and have built
maybe 20 others and have never put lead in one. The benefites in flight are tremendous with a lighter bird.
Now I don't know what kind of flying you do, but any kind off aerobatics will be better on a lighter airframe.
Your airplane dosn't have anything behind the spinner anyway so why not move the engine out.
Try an expierament if you have time. Zip tie enough lead to the motor mount to get the correct C.G.
Then put five flights on it. Then cut off the lead and slid the motor out. Put five more flights on it.
Then post a thank you because I think you will like it that much better.
later daveo
maybe 20 others and have never put lead in one. The benefites in flight are tremendous with a lighter bird.
Now I don't know what kind of flying you do, but any kind off aerobatics will be better on a lighter airframe.
Your airplane dosn't have anything behind the spinner anyway so why not move the engine out.
Try an expierament if you have time. Zip tie enough lead to the motor mount to get the correct C.G.
Then put five flights on it. Then cut off the lead and slid the motor out. Put five more flights on it.
Then post a thank you because I think you will like it that much better.
later daveo
11-23-2002, 08:51 PM
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I'll agree... IF possible, move stuff to not have to add lead, or any other dead weight.
On the 4*60... a 1 oz on the prop shaft weight is so insignificant... you won't see a difference between that and moving the engine forward.
first choice is always avoid lead. Seond choice, put the weight where it does the most good... ALL the way in front of the prop. (where 1 oz changes the CG almost as much as 4 oz just behind the firewall...)
My 4*60 came out several ounces heavier than any other I've seen... because I put in retracts. The .91 FS gave it bette performance than any other that I've seen... because it gave better power than the .61 2-strokes they were using. I don't expect you'll have ANY problem, and the weight may add wind penetration and stability in turbulance. (you CAN have your 4* too light. Thats one reason many people clip the wings.)
On the 4*60... a 1 oz on the prop shaft weight is so insignificant... you won't see a difference between that and moving the engine forward.
first choice is always avoid lead. Seond choice, put the weight where it does the most good... ALL the way in front of the prop. (where 1 oz changes the CG almost as much as 4 oz just behind the firewall...)
My 4*60 came out several ounces heavier than any other I've seen... because I put in retracts. The .91 FS gave it bette performance than any other that I've seen... because it gave better power than the .61 2-strokes they were using. I don't expect you'll have ANY problem, and the weight may add wind penetration and stability in turbulance. (you CAN have your 4* too light. Thats one reason many people clip the wings.)
11-25-2002, 11:37 AM
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I may have inadvertantly exagerated the CG problem. Although it was "clearly" tail heavy, it was not "outrageously" tail heavy. I was able to balance it perfectly with just 1 1/4 oz lead in the front of the engine cavity. That's the good news.
The bad news is that on the plane's first flight on Sunday, after a smooth take off and a few perfect laps, rolls and loops, the plane fell out of the sky (fortunately, it is repairable). At first we thought radio failure but the radio/servos worked fine even after the crash.
Best guess is that the wing partially separated in flight. Based on the damage, I think the wing separated at the leading edge (one of the blocks holding the dowel was completely torn out of the wing). I think as the leading edge separated, the wing pinched together at the trailing edge causing the ailerons to pinch against the fuse, thereby preventing any movement.
In the autopsy, some of the guys commented that the dihedral brace, which came completely out of one wing half, was not adhered to the wing properly. For you 4* builders: it seems that this brace is designed to adhere to the top and bottom of the main spar, but there isn't anything (other than the two ribs it crosses) fore and aft to adhere it too. Anyway the guys at the club suggested design failure or building failure. Whatever . . . . I have an idea to reconstruct the wing with a hardwood brace that is as wide as the main spar.
The bad news is that on the plane's first flight on Sunday, after a smooth take off and a few perfect laps, rolls and loops, the plane fell out of the sky (fortunately, it is repairable). At first we thought radio failure but the radio/servos worked fine even after the crash.
Best guess is that the wing partially separated in flight. Based on the damage, I think the wing separated at the leading edge (one of the blocks holding the dowel was completely torn out of the wing). I think as the leading edge separated, the wing pinched together at the trailing edge causing the ailerons to pinch against the fuse, thereby preventing any movement.
In the autopsy, some of the guys commented that the dihedral brace, which came completely out of one wing half, was not adhered to the wing properly. For you 4* builders: it seems that this brace is designed to adhere to the top and bottom of the main spar, but there isn't anything (other than the two ribs it crosses) fore and aft to adhere it too. Anyway the guys at the club suggested design failure or building failure. Whatever . . . . I have an idea to reconstruct the wing with a hardwood brace that is as wide as the main spar.
11-25-2002, 12:37 PM
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Building error if the dihedral btrace wasn't epoxied in, using 2 hour epoxy, coating the spars and dihedral brace, then sliding the brace in. The brace should have ripped chunks out of the spars rather than pulling free from them.
Definitely not design error... My 4*60 went in HARD. 9 inches of fuselage turned into sawdust. Crushed the center LE of the wing back almost to the spar, and the spar held, no sign of wing deformation aft of the spar. (dead stick in vertical climb from a touch-n-go, before any real airspeed aquired out of the SHARP pull up.)
Definitely not design error... My 4*60 went in HARD. 9 inches of fuselage turned into sawdust. Crushed the center LE of the wing back almost to the spar, and the spar held, no sign of wing deformation aft of the spar. (dead stick in vertical climb from a touch-n-go, before any real airspeed aquired out of the SHARP pull up.)
11-25-2002, 12:41 PM
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Tail Heavy Four * Sixty
What did you use to glue the dehidral braces in with? It should have been epoxy.. and goop'd in pretty thick Mine is!)
Was the center joint to be taped? I can't remeber..
Mine had a fatal fall as well, but the most damage I got was a busted wing tip, and a pushed-in fire wall.. and this was a 'dive' form about 20 feet.
Was the center joint to be taped? I can't remeber..
Mine had a fatal fall as well, but the most damage I got was a busted wing tip, and a pushed-in fire wall.. and this was a 'dive' form about 20 feet.
11-25-2002, 01:16 PM
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I used 30 minute epoxy. The brace did go in quite hard. The post crash observation was that, except for the top and bottom main spars, there just isn't enough material for the brace to adhere to (ie, nothing fore and aft of the brace except the two ribs it passes through.
I know all the evidence points to "builder error". I can accept that, but I would feel more comfortable if it was more clear what exactly I did wrong.
JPF
I know all the evidence points to "builder error". I can accept that, but I would feel more comfortable if it was more clear what exactly I did wrong.
JPF
11-25-2002, 03:27 PM
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Hmm... Gonna look in my manual tonight, to get a better idea of the process. It's been a few years since mine when together..
Let's start a discussion..
Although most manuals don't tell you, epoxy should be applided to both surfaces being glued. With that said, epoxy should have been applied to the bottom and top spar, as well as the dehidral brace. This will ensure both surfaces are glued, and will bond to each other, filling any voids. Extra should have been dripped on the joint, to ensure a 'glue fillet' between the spar and the dehidral brace.
When you glued the two wing halves together, you used epoxy as well? and lathered it on nice and thick? thick enough that excess oozed out when you clamped the two halves? again, 'buttering' both wing halves? Then checking it later on , to see that glue has remained in the joint? (Sometimes, with long set time epoxy, the glue can run out of the joint before it cures.. Sometimes, you can add a strip of tape to the underside on the wing joint to prevent this..
And the obvious, you had a nice snug fit between the dehidral brace, and the spar, and with the two wing halves mating surfaces (everything was square, no big gaps?)
Let's start a discussion..
Although most manuals don't tell you, epoxy should be applided to both surfaces being glued. With that said, epoxy should have been applied to the bottom and top spar, as well as the dehidral brace. This will ensure both surfaces are glued, and will bond to each other, filling any voids. Extra should have been dripped on the joint, to ensure a 'glue fillet' between the spar and the dehidral brace.
When you glued the two wing halves together, you used epoxy as well? and lathered it on nice and thick? thick enough that excess oozed out when you clamped the two halves? again, 'buttering' both wing halves? Then checking it later on , to see that glue has remained in the joint? (Sometimes, with long set time epoxy, the glue can run out of the joint before it cures.. Sometimes, you can add a strip of tape to the underside on the wing joint to prevent this..
And the obvious, you had a nice snug fit between the dehidral brace, and the spar, and with the two wing halves mating surfaces (everything was square, no big gaps?)
11-26-2002, 11:06 AM
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Ironically, I remember being pleased with the manner in which the two wing halves came together while I was building it. I had gotten the dihedral angle just right and the two sides mated flush. I used gobs of 30 minute epoxy on both sides and wiped off the excess with alcohol as it oozed out.
In hindsight, there is one aspect of that assembly that seems less than perfect. The brace is a tight, tight squeeze into the inboard ribs and between the top and bottom main spar. There is no way to get epoxy to the spars prior to squeezing in the brace ( I suppose you could drizzle it in, but there is no way to be certain where it will go).
So, all you can do is butter up the brace and jam it in, but much of the epoxy actually scrapes off on the way . . . .
Oh, well, I must have done something wrong, but it also seems like this part of the assembly has some room for improvement.
I got a basswood block the same width as the main spars from which I am going to fashion a new (and structurally superior) dihedral brace. I have to custom build new inner ribs so I am going to make the opening for the brace the same width at the spars and the new brace. In my head, it looks like it will work perfectly. We'll see how it turns out on the workbench.
JPF
In hindsight, there is one aspect of that assembly that seems less than perfect. The brace is a tight, tight squeeze into the inboard ribs and between the top and bottom main spar. There is no way to get epoxy to the spars prior to squeezing in the brace ( I suppose you could drizzle it in, but there is no way to be certain where it will go).
So, all you can do is butter up the brace and jam it in, but much of the epoxy actually scrapes off on the way . . . .
Oh, well, I must have done something wrong, but it also seems like this part of the assembly has some room for improvement.
I got a basswood block the same width as the main spars from which I am going to fashion a new (and structurally superior) dihedral brace. I have to custom build new inner ribs so I am going to make the opening for the brace the same width at the spars and the new brace. In my head, it looks like it will work perfectly. We'll see how it turns out on the workbench.
JPF
11-26-2002, 12:56 PM
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I flipped though my manual last night.. (always save the manuals and plans!!)
Holes were cut in the sheeting to run the servo leads. If memory serves me, I used these holes to 'goop in' the epoxy. You can also use these holes to see that the dehidral brace is properly seated on the spars.
The next step was to tape [with fiberglass cloth] the joint. You never mentioned taping, so that would be my next question. And you hinted that is was a clean break along the wing joint. How did the tape look? how did you glue it on?
Go with ply for your brace. It is much stronger than a solid block of wood. With the layered wood, you get a much stronger peice for the size, having the wood grain run in two directions, as opposed to just one. Midwest make a few styles..
Holes were cut in the sheeting to run the servo leads. If memory serves me, I used these holes to 'goop in' the epoxy. You can also use these holes to see that the dehidral brace is properly seated on the spars.
The next step was to tape [with fiberglass cloth] the joint. You never mentioned taping, so that would be my next question. And you hinted that is was a clean break along the wing joint. How did the tape look? how did you glue it on?
Go with ply for your brace. It is much stronger than a solid block of wood. With the layered wood, you get a much stronger peice for the size, having the wood grain run in two directions, as opposed to just one. Midwest make a few styles..
11-26-2002, 03:56 PM
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I almost always depart frm the instruction order with regard to sheeting the center bottom of the wing. I join the wing first. I can then run a continuous piece of balsa sheet across the lower dihedral joint. (wet balsa makes the bend allmost every time.) The added bennefit of access to ensure I can coat the dihedral brace contact area doesn't hurt. [img]i/expressions/face-icon-small-wink.gif[/img]
30 min epoxy doesn't soak into the wood like 2 hour type does. The bond strength of the 2 hour is FAR superior. (I'll let a certain newbie's error tell you why not to use 5 min to install the dihedral brace... sawing the brace out when the epoxy set with the wing halves 1/2 inch apart wasn't fun.)
Wiping excess epoxy off the dihedral jont with alcohol?!?! [img]i/expressions/face-icon-small-shocked.gif[/img] NEVER! The alcohol can prevent a solid joint from forming. (Don't mix alcohol with epoxy even to coat the firewall... porous epoxy is NOT fuelproof.) Alcohol can leave the epoxy porous and gummy with NO strength at all.
30 min epoxy doesn't soak into the wood like 2 hour type does. The bond strength of the 2 hour is FAR superior. (I'll let a certain newbie's error tell you why not to use 5 min to install the dihedral brace... sawing the brace out when the epoxy set with the wing halves 1/2 inch apart wasn't fun.)
Wiping excess epoxy off the dihedral jont with alcohol?!?! [img]i/expressions/face-icon-small-shocked.gif[/img] NEVER! The alcohol can prevent a solid joint from forming. (Don't mix alcohol with epoxy even to coat the firewall... porous epoxy is NOT fuelproof.) Alcohol can leave the epoxy porous and gummy with NO strength at all.
11-26-2002, 05:36 PM
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I did tape the joint with fiberglass tape, coated with CA. The tape was split right down the middle with the wing. It seems like the tape would be more effective if the grain of the tape was perpendicular to the seam. Has anybody done that?
Good suggestion on a ply brace and sheeting the bottom after the thing is joined.
Never thought about the alcohol weakening the epoxy. I'm sure I've seen the tip about mixing alcohol and epoxy for fuel proofing about 1,000 times . . . . .
Good suggestion on a ply brace and sheeting the bottom after the thing is joined.
Never thought about the alcohol weakening the epoxy. I'm sure I've seen the tip about mixing alcohol and epoxy for fuel proofing about 1,000 times . . . . .
