CG Adjustments/Problems
05-24-2005, 04:46 PM
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CG Adjustments/Problems
I recently completed a Superstar 40 and rough checked the CG (pointy finger method) according to the directions. My choice of engine was an OS .46AX. The fuel tank was empty and my measurement markings were right on (3 5/8" from leading edge). The battery and receiver placement were also according to directions. The aircraft appears to be aggressively nose heavy. Obviously my choice of engine is having an impact. Almost 3 oz of weight placed (temporarily) near the tail is starting to bring it level. I have several questions:
1) Is 3 oz or more weight excessive (when does the plane become too heavy)? What point do I stop counterweighting and start to move batteries and/or receivers instead?
2) Due to a long lever arm, the farther back I place my weights in the fuselage, the less I have to use. Does anyone have any techniques to cut into the rear portion of the fuselage and place weights there?
Any suggestions will be much appreciated. If I can crack this problem, I can "maiden flight" the aircraft as soon as the weather breaks!
Cheers,
S&L Flt
1) Is 3 oz or more weight excessive (when does the plane become too heavy)? What point do I stop counterweighting and start to move batteries and/or receivers instead?
2) Due to a long lever arm, the farther back I place my weights in the fuselage, the less I have to use. Does anyone have any techniques to cut into the rear portion of the fuselage and place weights there?
Any suggestions will be much appreciated. If I can crack this problem, I can "maiden flight" the aircraft as soon as the weather breaks!
Cheers,
S&L Flt
05-24-2005, 04:55 PM
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RE: CG Adjustments/Problems
ORIGINAL: SLFlt
I recently completed a Superstar 40 and rough checked the CG (pointy finger method) according to the directions. My choice of engine was an OS .46AX. The fuel tank was empty and my measurement markings were right on (3 5/8" from leading edge). The battery and receiver placement were also according to directions. The aircraft appears to be aggressively nose heavy. Obviously my choice of engine is having an impact. Almost 3 oz of weight placed (temporarily) near the tail is starting to bring it level. I have several questions:
1) Is 3 oz or more weight excessive (when does the plane become too heavy)? What point do I stop counterweighting and start to move batteries and/or receivers instead?
2) Due to a long lever arm, the farther back I place my weights in the fuselage, the less I have to use. Does anyone have any techniques to cut into the rear portion of the fuselage and place weights there?
Any suggestions will be much appreciated. If I can crack this problem, I can "maiden flight" the aircraft as soon as the weather breaks!
Cheers,
S&L Flt
I recently completed a Superstar 40 and rough checked the CG (pointy finger method) according to the directions. My choice of engine was an OS .46AX. The fuel tank was empty and my measurement markings were right on (3 5/8" from leading edge). The battery and receiver placement were also according to directions. The aircraft appears to be aggressively nose heavy. Obviously my choice of engine is having an impact. Almost 3 oz of weight placed (temporarily) near the tail is starting to bring it level. I have several questions:
1) Is 3 oz or more weight excessive (when does the plane become too heavy)? What point do I stop counterweighting and start to move batteries and/or receivers instead?
2) Due to a long lever arm, the farther back I place my weights in the fuselage, the less I have to use. Does anyone have any techniques to cut into the rear portion of the fuselage and place weights there?
Any suggestions will be much appreciated. If I can crack this problem, I can "maiden flight" the aircraft as soon as the weather breaks!
Cheers,
S&L Flt
When you get the hatch cut off, glue the lead onto the bottom of the horizontal stabilizer or the fuselage sides. Recheck your CG before gluing the hatch back on. After gluing the hatch back on, you can leave it as is, or get some scrap covering from somebody and recover the seam.
Go Fly
Don
05-24-2005, 04:56 PM
#3
RE: CG Adjustments/Problems
ORIGINAL: SLFlt
I recently completed a Superstar 40 and rough checked the CG (pointy finger method) according to the directions. My choice of engine was an OS .46AX. The fuel tank was empty and my measurement markings were right on (3 5/8" from leading edge). The battery and receiver placement were also according to directions. The aircraft appears to be aggressively nose heavy. Obviously my choice of engine is having an impact. Almost 3 oz of weight placed (temporarily) near the tail is starting to bring it level. I have several questions:
1) Is 3 oz or more weight excessive (when does the plane become too heavy)? What point do I stop counterweighting and start to move batteries and/or receivers instead?
2) Due to a long lever arm, the farther back I place my weights in the fuselage, the less I have to use. Does anyone have any techniques to cut into the rear portion of the fuselage and place weights there?
Any suggestions will be much appreciated. If I can crack this problem, I can "maiden flight" the aircraft as soon as the weather breaks!
Cheers,
S&L Flt
I recently completed a Superstar 40 and rough checked the CG (pointy finger method) according to the directions. My choice of engine was an OS .46AX. The fuel tank was empty and my measurement markings were right on (3 5/8" from leading edge). The battery and receiver placement were also according to directions. The aircraft appears to be aggressively nose heavy. Obviously my choice of engine is having an impact. Almost 3 oz of weight placed (temporarily) near the tail is starting to bring it level. I have several questions:
1) Is 3 oz or more weight excessive (when does the plane become too heavy)? What point do I stop counterweighting and start to move batteries and/or receivers instead?
2) Due to a long lever arm, the farther back I place my weights in the fuselage, the less I have to use. Does anyone have any techniques to cut into the rear portion of the fuselage and place weights there?
Any suggestions will be much appreciated. If I can crack this problem, I can "maiden flight" the aircraft as soon as the weather breaks!
Cheers,
S&L Flt
The first thing you want to try it to move the battery. Disconnect it and take it out. Now put the wing back on and look at the balance. Now place the battery on the fuselage and check the balance again. Keep moving the battery until you find that it does balance. If you get all the way to where the battery will no longer go the stop there and add weight further back.
Unless it's really extreme, you can usually use the battery to get the balance right on or at least help elimate dead weight.
3oz on that plane would not be excessive
You are correct, the longer the lever, the less weight is needed
I'll elt someone else explain how to cut in a hatch.
05-24-2005, 07:07 PM
#4
RE: CG Adjustments/Problems
Do as Bubbagates said for the battery to balance the plane.
Now if you don't want to cut the "shiny new covering",
Get some industrial strength velcro. Cut 2 pieces about 2" long. Peel the backing ON ONE SIDE and adhere it to the tape wrapping the foam on the battery. You should have 2 pieces of velcro adhered to the battery.
Next, slide the battery to the proper position needed to balance the plane and make a mark so you know where it goes. Pull the battery out, add a servo extension if needed, remove the backing from the other side of the velcro and put in place and press it in place. To be certain the velcro will not come loose from the balsa, use some THIN CA (I suggest a piece of micro tubing in the tip of a bottle so you can control the amount of CA and get precise placement of the CA) and put a few drops on each adhered strip. If you ever want to remove the battery, reach in and grab it and pull it loose. I have had batteries attached this way stay in place even after a "lawn darting".
Now if you don't want to cut the "shiny new covering",
Get some industrial strength velcro. Cut 2 pieces about 2" long. Peel the backing ON ONE SIDE and adhere it to the tape wrapping the foam on the battery. You should have 2 pieces of velcro adhered to the battery.
Next, slide the battery to the proper position needed to balance the plane and make a mark so you know where it goes. Pull the battery out, add a servo extension if needed, remove the backing from the other side of the velcro and put in place and press it in place. To be certain the velcro will not come loose from the balsa, use some THIN CA (I suggest a piece of micro tubing in the tip of a bottle so you can control the amount of CA and get precise placement of the CA) and put a few drops on each adhered strip. If you ever want to remove the battery, reach in and grab it and pull it loose. I have had batteries attached this way stay in place even after a "lawn darting".
05-24-2005, 08:03 PM
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RE: CG Adjustments/Problems
First off, thank you for your quick replies. You got me thinking. I have two votes for "move the battery" and one vote for cut a hatch and add weight. The battery method is appealing because not adding weight does not decrease performance. Unfortunately, the kit had the battery velcroed with the receiver forward of the servo tray. The space behind the servo tray is blocked by a control tube brace and I'm not confident moving the battery there will be sufficient. Hattend's suggestion to cut out the hatch and install it under the horizontal stab just might work. Besides, I've needed an excuse to go buy a Dremel tool which would do the cutting quite nicely. I will get some help from the instructor from my club who will help be balance and fly the aircraft. I'll keep you posted...
Cheers,
S&L Flt
Cheers,
S&L Flt
05-24-2005, 09:34 PM
#6
RE: CG Adjustments/Problems
I vote to move the battery. Never add weight if you don't have to!!!! Take your time and see if you can relocate something to get your CG. I've relocated servo trays etc. and redone control rods etc. rather then add weight. ENJOY!!! RED
05-25-2005, 05:53 AM
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RE: CG Adjustments/Problems
SLFlt,
If the battery relocation isn't feasible and you have to add weight at the tail, you don't have to cut a hatch for this. Merely drill a 1/4" hole close to the rear on the underside. Generously coat small fishing weights with epoxy and drop into hole with the plane pointed up to allow the weight to drop rearward. I use the bullet shaped weights with a hole drilled through the center. (3/8 ounce works well)
You'll need to know how many weights will balance the plane before you start dropping them through the hole. Take into account the weight of the epoxy as well.
When the epoxy has cured, check the balance, and place a small patch over the 1/4" hole.
If the battery relocation isn't feasible and you have to add weight at the tail, you don't have to cut a hatch for this. Merely drill a 1/4" hole close to the rear on the underside. Generously coat small fishing weights with epoxy and drop into hole with the plane pointed up to allow the weight to drop rearward. I use the bullet shaped weights with a hole drilled through the center. (3/8 ounce works well)
You'll need to know how many weights will balance the plane before you start dropping them through the hole. Take into account the weight of the epoxy as well.
When the epoxy has cured, check the balance, and place a small patch over the 1/4" hole.
05-25-2005, 08:33 AM
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RE: CG Adjustments/Problems
I have a couple of modified Superstars with TT .46 Pro's in them (similar in weight to your engine). I cut a hatch in the top of the fuselage behind the wing & built a battery compartment there, above the pushrods. It works well & is not an aesthetic problem.
05-25-2005, 11:21 AM
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RE: CG Adjustments/Problems
Britbrat,
Good idea to build the battery hatch behind the wing. After flying the aircraft for a season I plan on doing a tailwheel conversion, remove the dihedral and converting it to a nylon bolt wing (assuming the I don't lawn dart the aircraft). That would be a good time to move the battery aft and remove the tail weight. Press on....
Cheers,
S&L Flt
Good idea to build the battery hatch behind the wing. After flying the aircraft for a season I plan on doing a tailwheel conversion, remove the dihedral and converting it to a nylon bolt wing (assuming the I don't lawn dart the aircraft). That would be a good time to move the battery aft and remove the tail weight. Press on....
Cheers,
S&L Flt
05-25-2005, 12:06 PM
#10
RE: CG Adjustments/Problems
Move the battery NOW. Keep the weight down and the plane will fly better. Extra weight is a last resort. Fishing weights or lead shot like used in reloading shotgun shells are both OK for the "Hole in the tail" method but I would rather see the battery hatch behind the wing. Weight removed from in front of the CG and added behind the CG is the best way to move the balance point with no weight gain. Can you move the engine back any?
05-25-2005, 08:46 PM
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RE: CG Adjustments/Problems
There is little to no space behind the engine as the fuel lines run through the engine mount to the muffler and carb. I could maybe get a milimeter or two. I doubt it would have any effect.
Regards,
S&L Flt
Regards,
S&L Flt
05-26-2005, 07:24 AM
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RE: CG Adjustments/Problems
I am going to let this thread wither on the vine as I solved my CG problem and this horse is quite dead. I know many of you felt stongly about moving the battery. This being a trainer and my first aircraft; and my work time being as limited as it is, I elected to go the "Frankenstein route" and cut a hatch under the horizontal stab. I added just over 3 oz of weight and re-checked the CG. This brought the nose level. With all the work that was going to be involved moving the battery, it would have set my maiden flight back a week or more. Today I do engine runs/break in and maiden flight this weekend. Fly safe everyone...
Cheers,
S&L Flt
Cheers,
S&L Flt
05-26-2005, 09:51 AM
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RE: CG Adjustments/Problems
I am a bit worried about the amount of lead required -- 3 oz is a lot more than I ever had to add to a Superstar to balance it with a BB 46 up front. Make absolutely sure that you aren't tail-heavy -- hiding the lead in the stab will make it a pain to get at if you need to remove some.
