Potted Nose Weight

[Mark9]

This is my first time to try the lead shot potted in with epoxy method of balancing a glider in a confined volume. The pictures below show my installation. I hope to use the area around my tow release first to pot in the primary nose weight. But, I’m not sure how much to pour in or mix up. Not being a math wiz calculating the amount of shot required is out of the question…how many balls fit in a cylinder? YIKES!

The first shot shows the area around the barrel of the tow release I plan to fill. This glider according to my research can have the CG up to about 5 mm aft of stock. I need to get about 18.5 oz. in the nose to achieve that. Behind of the open cylinder that the tow release is installed in are some open bays which I may need to use for overflow and initial ballast to get to the recommended factory CG. Any comments on how to best do this, ideas or pit falls to avoid will be appreciated.

[ljsoarinson]

One tip I'll offer is to pot less than you think you will need. Especially if the model is unflown. It is far easier to add more weight than to remove what is epoxied in.

But if worst comes to worst and it comes out nose heavy, only a small amount of weight (by comparison) needs to be added to the tail.

I will set the model up on it's balance point, then add lead shot to a paper cup taped on the nose. Remember, the weight of the epoxy should be considered too.

[ARUP]

Yes... put less than you need. If you have room then pour the lead/epoxy mix around an empty plastic bottle. I used a small squeeze bottle that had a screw cap. The bottom of the bottle was cut off and the near bottom section of the sides were split apart and flared/ roughened to give some 'tooth' to the epoxy mix surrounding it. Then, lead could be added/removed as needed by the simple expedient of removing the cap! My current build has a space in the fuselage behind plywood covering (yet to be glued) for lead to be placed. This will get done at final assembly.

[Mark9]

Thanks for the comments guys. I really don't have enough room for a plastic bottle in the nose area. Besides the tow release would need to go through the center of the bottle. I am hoping to make most of the required ballast permanent and have some be removable for trimming. This final process of CG'ing a new unflown airplane is probably my least favorite of getting an airplane ready to fly. It's necessary and it does get one aware of how serviceable their installation is though.

[Mark9]

Here's a follow up pic of what I did for the permanent nose weight. All of the shot was mixed with epoxy and the a sealing coat was applied. The last time I had it on the balance rig I estimated I will have about 3-4 oz. of removable ballast bolted to the cockpit hatch. That should allow me to move the CG aft if desired.

[ARUP]

The sealing coat looks stout and thick enough! What sailplane is it? Are you going to post some pics so we can see it? Please!

[Mark9]

ARUP, sorry I didn't see your comment till this morning, just saw the notification. Also, I have had some health issues the last few days and have been slowed a bit. Out of the very concerned status now, but still not great yet and more Dr. visits to go. Stay out of the emergency room if you can! What a zoo with all the flu cases.

It's a Phoenix Model Ka-8b 3.5 meter, about 1/4 scale. Small, but I needed an aero tow ship that I could thermal while I work on repairs for my Blanik. A long time sailplane buddy and one of the tow pilots at the Mickey Sullivan last year recommended it to me. Also, one of the guys that I fly tow with in Greenville, TX also has one and he really likes it. Since my only other tow glider is a 1/5 Fox and the kit price was attractive, I said why not.

I have taken a few pictures of some of my modifications along the assembly process, but do not have any with it completed. Right now the weather sucks, plus I've heard it's bad karma to take a picture before it's maidened...don't really believe that though. I will try to get some when the weather clears since it's now ready for a maiden, other than putting on the registration numbers.

The kit is a dual use design, electric and tow, but mine will be strictly tow. Haven't weighed it, but I think it will be about the same weight as my Fox...around 7 lbs. Should thermal well and if the winds come up, get out the Fox. Some of my modifications are:

Horizontal incidence change to about -2 degrees, many say the stock incidence makes for funky handling. As I measured it stock was around -5.
Custom fabricated tow release, there are some posts of it here on this site.
Electric spoilers, everybody on the web says once it hits the boundary layer "it keeps going and going like the energizer bunny".
The nose ballast installation. I finished it last week and three ounces of it is removable for trim changes if desired. It took about 1.5 lbs to balance at the stock recommended CG.

[ARUP]

No worries about getting pics posted! Hope you get feeling better soon! The Ka8 is a great looking model! I always take pictures of my models before they've maidened because you may never see them whole again! In over 40 years of building and flying only two didn't make it... both flying wings of sorts... the ARUP and Charlotte II.