Espritmodel.com Telemetry Radio
Reply
Thread Tools
Old Jan 27, 2012, 12:18 AM
I DS slower than I build!
Cory's Avatar
Idaho Falls
Joined Jul 2006
2,345 Posts
Build Log
Victor Models America3

Is it worth it to vacuum bag an keel with a foiled cross section for my Victor Models America3? Will the foiled keel make a noticeable difference in performance? The actual work of making such a keel won't be that hard. I vacuum bag my own glider wings.

If it's worth it, my next question is what is a good foil? I'm assuming a fairly thin one, but what percent of chord?
Cory is offline Find More Posts by Cory
Last edited by Cory; Feb 03, 2012 at 04:32 PM. Reason: Might as well make these questions the start of my build log.
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 27, 2012, 06:05 AM
Don't lie to my dog.
Gregg28's Avatar
United States, DE, Wilmington
Joined Jun 2005
3,071 Posts
Quote:
Originally Posted by Cory View Post
Is it worth it to vacuum bag an keel with a foiled cross section for my Victor Models America3? Will the foiled keel make a noticeable difference in performance? The actual work of making such a keel won't be that hard. I vacuum bag my own glider wings.

If it's worth it, my next question is what is a good foil? I'm assuming a fairly thin one, but what percent of chord?
When building a sail boat, you want to get the center of gravity as low as possible. A vacuum bagged keel would be somewhat lighter than a molded keel, but it is already low in the boat. So yes, a vacuum bagged keel would be marginally better. It is not worth it for most of us, but if you are set up for it than it probably is.
Perhaps more importantly, if you have a way to cut good, true foam cores, the fidelity of the shape would be a big plus.
In answer to your last question, the foil shape is really not that important. Given the low speed, short cord and high density and viscosity that we operate in, the Reynolds number is very low and it is difficult to detach flow over the keel. A regular NACA section would be fine. It wants to be as thin as possible, but thick enough to make the fin strong enough to support the bulb. Something in the 4 to 5mm range should do it.
Gregg28 is online now Find More Posts by Gregg28
Reply With Quote
Old Jan 27, 2012, 08:30 AM
Registered User
seefest's Avatar
United States, MA, Bristol
Joined Sep 2009
1,561 Posts
Quote:
Originally Posted by Cory View Post
Is it worth it to vacuum bag an keel with a foiled cross section for my Victor Models America3? Will the foiled keel make a noticeable difference in performance? The actual work of making such a keel won't be that hard. I vacuum bag my own glider wings.

If it's worth it, my next question is what is a good foil? I'm assuming a fairly thin one, but what percent of chord?
A proper foil, bulb and rudder on an America3 makes a huge difference.

The stock bulb(plastic filled with shot) is terrible and way too much wetted surface. Ditto the low aspect ratio stock plywood fin.

I put a Talon II (hi-tech US1M) fin and bulb on an America3 along with a proper elliptical rudder. I also had proper panelled sails. What a difference it made.
The America3 could never point with a CR 914, and was slower pretty much on all points of sail. With new foils and new sails, it was as fast or faster(when the wind came up)

Later, I also modified it with taller carbon rig, and a fat head mainsail. Wow, now it was way faster than a CR914, especially in the light, but did tend to bury the bow too soon in the heavy.
seefest is offline Find More Posts by seefest
Reply With Quote
Old Jan 27, 2012, 10:46 PM
Registered User
Joined Sep 2009
170 Posts
Hay Cory I would love to see the boat when it done. Thanks Mike
m.g. is offline Find More Posts by m.g.
Reply With Quote
Old Jan 28, 2012, 12:03 AM
I DS slower than I build!
Cory's Avatar
Idaho Falls
Joined Jul 2006
2,345 Posts
I'll do a build thread. I have two reasons to do so. First is that since this is my first boat I'm I could use pointers from those who are experienced. Second is that this sailboat forum is fairly sparse on build threads - at least compared to the Slope and Dynamic Soaring forums where I usually hang out, and it would be good for new boaters like me to have more to help them.

Seefest, you said that the low AR of the stock keel is bad. What would be considered a good AR? I would guess that you would recommend keeping the same root chord and lengthening the span (is that what you would call it? I'm used to wings).

As far as thickness goes, the stock keel has a root chord of 107mm and a tip chord of 75mm. A 5mm root thickness would make for 4.67% max thickness. That would be hard to make strong enough with that big gob of lead on the bottom. I could build in a carbon spar, but it would not be easy to make it strong enough. In the slope glider world a 6% lead sled wing is pretty thin, but that would have a longer root chord that this keel so the resulting max thickness would be much easier to work with. It would be much easier to build one at 7 or 8%. If you guys know techniques to get a strong bagged keel that is that thick, let me know.

I've attached a comparison of several sections at Re 150,000 which is what the root would see at just under 5 mph and Re 300,000 which would be what the root of this keel would see at just under 10 mph. In all three cases the 4 and 6 percent sections outperform the thicker ones at a Cl of less than 3-4. At Cls above that the thicker sections shine. Since I'm new to sailboats I have no idea what kind of force needs to be generated by the keel but I would expect that it would be fairly high when tacking in stronger winds. Any advice on this?

Seefest, you also mentioned that you don't like the bulb. What do you do? Cast a solid lead bulb that is longer and thinner?
Cory is offline Find More Posts by Cory
Reply With Quote
Old Jan 28, 2012, 05:49 AM
Don't lie to my dog.
Gregg28's Avatar
United States, DE, Wilmington
Joined Jun 2005
3,071 Posts
Quote:
Originally Posted by Cory View Post
As far as thickness goes, the stock keel has a root chord of 107mm and a tip chord of 75mm. A 5mm root thickness would make for 4.67% max thickness. That would be hard to make strong enough with that big gob of lead on the bottom. I could build in a carbon spar, but it would not be easy to make it strong enough. In the slope glider world a 6% lead sled wing is pretty thin, but that would have a longer root chord that this keel so the resulting max thickness would be much easier to work with. It would be much easier to build one at 7 or 8%. If you guys know techniques to get a strong bagged keel that is that thick, let me know.
5mm is not too hard to achieve. A good Marblehead fin, which is 20" deep and supports a 7lb bulb. You do need a fair amount of carbon fiber in there. I used to use 4 layers of 20oz bi-directional weave on each side. Plenty of strength.
Gregg28 is online now Find More Posts by Gregg28
Reply With Quote
Old Jan 28, 2012, 07:32 AM
Registered User
seefest's Avatar
United States, MA, Bristol
Joined Sep 2009
1,561 Posts
Stock VS hi tech fin

Here is a pic of the stock VS carbon US1M keel fin and bulb. Please note, The stock keel is 11" deep and carbon keel is max legal US1M 14" deep.

The carbon fin is balsa core with one layer of 1" wide uni-directional carbon on each side, covered by one layer of 5oz carbon weave on each side.
The bulb is 4 lbs. Thickness is exactly 5 mm.

Obviously, I had to modify the keel trunk on America3 to accept the new fin and bulb.

Higher aspect ratio, more righting moment, less wetted surface = better pointing and speed.
seefest is offline Find More Posts by seefest
Reply With Quote
Old Feb 03, 2012, 04:43 PM
I DS slower than I build!
Cory's Avatar
Idaho Falls
Joined Jul 2006
2,345 Posts
Well, I'm not into racing and couldn't be if I wanted to. I don't have a club around here. In fact I have never seen a radio controlled sailboat here in Idaho in the 34 years I've lived here. I'm building this sailboat as a daddy/daughter build and learn to sail project. My girls are 4 and 8 and will be helping with the build as much as they can. Because of that, I'm going to stick with the stock keel for now. Later I'll probably make a higher AR keel. It will be interesting to actually experience the difference. I'll just make it fit the stock keel trunk.

I do appreciate the tips, guys.
Cory is offline Find More Posts by Cory
Reply With Quote
Old Feb 04, 2012, 03:37 AM
I DS slower than I build!
Cory's Avatar
Idaho Falls
Joined Jul 2006
2,345 Posts
I bought this sail boat because everything I saw here on RCGroups about Victor Models was very positive. So far my impressions of this boat are mixed. Much of the kit is good quality, but there are some glaring problems. For starters I did not get a keel blank, mast base, keel trunk sides, or vang assembly and clevis in the kit.

The mast is also very warped. I called Victor Models and they promptly sent the parts out...sort of. They sent everything except a replacement mast. They also sent an extra set of Bowsie blanks. I already had those.

The quality of the wood parts is mixed. The 3/16" x 1 1/4" square keel trunk filler really isn't 3/16". It's considerably thicker than the 3/16" square x 6" trunk filler piece. That's easily fixable with sanding, but poor quality control. Also, the two sides of the keel trunk are different thicknesses and different types of plywood. It won't really matter in this case, but once again is not impressive quality control. I'm really not hard to please, but in 23 years of RC planes I've never had a kit with this many problems. Not getting a straight mast, even after calling them, really ticks me off.

Enough of my rant. I have a question before I get started. The instructions say to waterproof the wood of the keel trunk with CA. Does this work really well, or would I be better off using West Systems epoxy? I have often heard that CA isn't totally waterproof, but according to this thread it's good enough. http://www.rcgroups.com/forums/showthread.php?t=1477514 Having both CA and a good laminating epoxy available, which would you use?
Cory is offline Find More Posts by Cory
Last edited by Cory; Feb 04, 2012 at 04:44 AM.
Reply With Quote
Old Feb 04, 2012, 10:54 AM
Registered Billy
Louisville, KY
Joined Dec 2003
334 Posts
I don't have any evidence to support my opinion but I would use epoxy if you have it on hand. As far as the mast goes, aluminum or carbon arrows are a lightweight and straight replacement for the crooked wood mast. Happy building.

Brian
bkopke is offline Find More Posts by bkopke
Reply With Quote
Old Feb 04, 2012, 12:07 PM
I DS slower than I build!
Cory's Avatar
Idaho Falls
Joined Jul 2006
2,345 Posts
My assumption is that since West Systems is designed for building real boats, using it can't be wrong.

As far as using an aluminum or carbon mast goes, how does one attach the hardware to the mast? This kit comes with a bunch of screw eyes with threading for wood. Do you use machine threaded screw eyes and run them all the way through? I don't think I've seen those at my local hardware store, at least not in the small size required.

My plan is to try to save the mast by wetting it with a 50/50 ammonia/water solution and clamping it into a piece of angle metal until dry. I'm hoping that will straighten it enough to make it usable.
Cory is offline Find More Posts by Cory
Reply With Quote
Old Feb 04, 2012, 01:05 PM
Useful Idiot
Asturias, Spain
Joined Mar 2001
3,545 Posts
Quote:
Originally Posted by Cory View Post
...
As far as using an aluminum or carbon mast goes, how does one attach the hardware to the mast? This kit comes with a bunch of screw eyes with threading for wood. Do you use machine threaded screw eyes and run them all the way through? I don't think I've seen those at my local hardware store, at least not in the small size required.

...
I've never liked the idea of drilling carbon fibre tube, so I usually whip swivels etc. on to the mast using Spectra wetted afterwards with CA.
martin richards is offline Find More Posts by martin richards
Reply With Quote
Old Feb 04, 2012, 01:19 PM
I DS slower than I build!
Cory's Avatar
Idaho Falls
Joined Jul 2006
2,345 Posts
Thanks again for the tips. I didn't like the idea of drilling into carbon either. Those photos really help. I have some fly tying kevlar thread and some 1k carbon tow that I could use to attach the vang, cotter pins, etc. if I end up scrapping the wood mast.
Cory is offline Find More Posts by Cory
Reply With Quote
Old Feb 04, 2012, 02:32 PM
Registered User
seefest's Avatar
United States, MA, Bristol
Joined Sep 2009
1,561 Posts
Quote:
Originally Posted by Cory View Post
My assumption is that since West Systems is designed for building real boats, using it can't be wrong.

As far as using an aluminum or carbon mast goes, how does one attach the hardware to the mast? This kit comes with a bunch of screw eyes with threading for wood. Do you use machine threaded screw eyes and run them all the way through? I don't think I've seen those at my local hardware store, at least not in the small size required.

My plan is to try to save the mast by wetting it with a 50/50 ammonia/water solution and clamping it into a piece of angle metal until dry. I'm hoping that will straighten it enough to make it usable.
West System is definately the way to go.

Bummer about the mast. The one I got originally with my kit was warped as well. Was your's in two peices and had to be scarfed together? Mine was, but I built that boat over 10 years ago. I did the same as you and it straghtened it OK.

I drill carbon tube all the time. I get pultruded graphite tubes from a kite supply shop.
I never wrap it in line as I don't like the way it looks and I have found it unecessary.
A great way to attach shrouds to a mast is using internal tangs. Drill a hole where you want the shroud to go, Take an extra long peice of rigging wire, and thread it into the hole and up to the top of the mast.(before crane goes on). Then take a wire crimp and crimp the end of the wire. Now pull it back into the mast and the crimp keeps the wire from pulling out. Nice clean way to attach shrouds.
seefest is offline Find More Posts by seefest
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
New Product Techone 39'' Airfoiled Wing EPP SU-31 From EPPHOBBY.com Get Real 3D Foamies 364 Nov 18, 2013 07:21 AM
Discussion Fancy Foam EPP Yak 55 and Yak 54 - flat and airfoiled wings adreher 3D Foamies 18 Jan 10, 2013 07:49 PM
Discussion Is There a Way to Calculate Keel Weight? daddyrabbit1954 Sailboats 9 Dec 14, 2011 08:49 AM
Discussion Keel Fin and Keel (fishing lead sinker) attachment? FalconXman Sailboats 9 Aug 26, 2009 07:14 AM
Fanfold Full airfoiled Yak 54.... Thomas Manson 3D Flying 8 May 04, 2008 08:39 AM