canardlover

Alasdair, is there any possibility to get more info/pics on the North Star twin (in post #338 above) made by your friend John Campbell...?!?!...Cheers/Harald

drumduan

Sorry to restart this thread....

I have just aquired a kit from balsa usa and am thinking of going brushless with it. The combined weight of brushless and LiFe is more than a .46 and fuel however as I can place the battery in the nose I hope to come in under the weight or on it. Thinking of the weight where on a brushless version could/should I save weight as compared to the glow plans?

In addition I intend to place the elevator servo in the motor pod, the throttle cable obviously wont be a concern!

I want to use a 13" prop and as such need to increase the height of the motor pod. By doing this the moment arm will be increased thereby exaggerating the tendancy to nose down with throttle inputs. Will this be a problem? If so should I increase the downthrust to compensate? Or reduce the distance from the LE of the motor pod to the TE of the wing in an effort to reduce the moment/torque applied by the motor?

Thanks

senrak

drumduan,
I have found that weight and it's distribution on this airplane are very critical. It must be kept as light as posssible. I have found that that an OS46 is just barely enough power if you are at or even below the called out building weight. A OS55 would be better, so unless your electric system has got lots of power and low weight I would rethink going that way. Adding any weight to the tail only makes the problem worse and I am told that raising the pod causes all kind of problems. It's probably better to put a relief in the top of the wing for prop clearance. The best way to improve the problems that arise with this plane may be in finding a way to move the engine forward, thus achieving balance with less weight.
Good Luck
DW

drumduan

I intend to use a brushless OS equivelant to a 55. The weight of a LiFe, the OS 55 BRUSHLESS equivelant and nose weight is less than the weight of fuel, .55 and weight in the nose (I wont need to add weight to the nose because the LiFe will go in the nose). Basically because i wont use nose lead the brushless power system comes out lighter.

I will actually be reducing the weight in the tail because the elevator servo weighs less than 8oz of fuel.

Because it will be electric and not glow where should/would i save weight? I.e. lightening holes.

Regarding a relief hole in the wing, I have packed the plans away for the moment, I assume that the relief slot is infront of the TE wing spar?

senrak

The weight of fuel is not considered when balancing this plane. Balance is measured with an EMPTY fuel tank. I would estimate the weight of an empty fuel tank at about the weight of a servo. So you are good there. When you put your battery in then nose you are in fact ahead of the game because it can take the place of the dead weight that you would otherwise need to put there. Your speed control, taking the place of another servo. Also a plus. I would think that lightening holes in the tail pieces would be a plus, also in the pod, as it will not have the stress of carrying the weight of fuel, only the motor. Wherever you can save weight on this plane, do it. Mine was built according to plans with a .46, and it flys like a lead sled.

Also, there is no prop relief on the plans. You would have to make modifications where interference would otherwise occur between the larger prop and the wing surface. But, that shouldn't be very hard to do.

Goldenduff

I will look at the plans sometime re prop relief slot.

Yak Dude

All great ideas about keeping it light. Becarefull about how much you lighten up the tail. Lots of stress just behind the wing on the fuse area. I put a hole in the vertical tale plywood for my servo wires to go up to the pod. Used 4 wires, Pos, Neg, signal for elevator and signal for throttle. Yours will be easier. I have had great succsess iwith the balance aft about one inch from the plans.
Mine is the Coast Guard plane with the OS .55. 6 & 1/2 lbs. Please see pic's and notes on the pod, to sum it up, the pod is raised about 1" and prop line is 1" forward of stock, same thrust angle. This gives room for a 12 & 1/2 prop. I'm flying with a 12 x 6. So plenty of room. I haven't had any issues with pulling or pitching with power changes. I have logged over 50 flights, all off water. Altitudes from 500 ft to almost 7000 ft at Big Bear Lake in CA. Low altitude landings are really fun. Keep it off the water about a foot and keep feeding in the up all the way, slowly add in a little power, do it just rite and the plane will almost stop and plop onto the water. It is close to almost hovering, stall and plop kind of thing. I have it on vidio, just need to figure how to put it on YouTube from the camera. The picture is a normal nose high angle at landing. Wes.

Goldenduff

I've made the foamy Polaris and am hooked! 

Yak Dude

I think you will be just fine with an electic .55 motor. You will save about 2 oz in the pod with no tank and the motor might or is lighter than the .55 engine. My pic's start on page 5 and go through 8 and once in a while after that. I also fly many sizes of electric T-Rex helicopters. The 550 uses a pretty heavy 6 cell, 5000 battery. So your battery idea up front is much better than the pound of shot lead in the front. I would build a test stand and run all the wires needed, distance wise of the battery, speed control and all the other stuff to make sure you don't get interferance and/or power drop to the motor due to distance of speed control to motor. The other thing, you really need to seal up everything even better so water doesn't get to it under the canopy or any other covers you make. My engine does stay pretty dry. So your motor should be good, just pick nicer days to fly off the water where the chop is kept down. Keep updating as you go along, I'm intrested in seeing how this comes out.

Goldenduff

Hello 

LADDIE

drumduan
When I designed the N.S. about 25 years ago it was for plain bearing OS.35 I had. Since then me and other modellers installed all kind of glow engines up to the 120 four stroke. In 2006 I built the N.S. for AXI 4120/18 electric motor. I was happy with the performance. It was not as fast as the one powered by .46 glow engine, but still fast enough. If you want to read more about my electric N.S. go to this thread. When I designed the N.S. about 25 years ago it was for plain bearing OS.35 I had. Since then me and other modellers installed all kind of glow engines up to the 120 four stroke. In 2006 I built the N.S. for AXI 4120/18 electric motor. I was happy with the performance. It was not as fast as the one powered by .46 glow engine, but still fast enough. If you want to read more about my electric N.S. go to this thread and read the posts 395 to 408. http://www.rcuniverse.com/forum/fb.asp?m=5123547
Laddie

Goldenduff

Fantastic Laddy! No disrespect, that's Scottish for man and what I always think when reading the manual etc!

Yak Dude

Wow, that electric one of Laddy's is very nice. I really like the looks of the cleaned up pod. With the fuel tank eleminated, there is lots of room for speed control and elevator servo for direct pushrod.

Goldenduff

Esc should go near the battery not the motor.... I think

LADDIE

You are right. Since these pictures were taken I changed the wiring so the speed controller is close to the battery.

Bob93447

Isn't the motor mount the best place to save weight when converting the Northstar from glow to electric?

Goldenduff

Hello Bob- do you mean the motor mount and or pod? 

Bob93447

I was taking the global view. Everything that attaches to the vertical fin I consider part of the motor mount.

Bob

skywagn180

Northstar owners, I need some advise. I picked up a twenty year old brick of a Northstar for cheap. It looks to be built without any mods. The previous owner only flew it a few times and couldn't get it to perform well. I took on the challenge to revive it. It is heavy but not unreasonably so. I strapped on a .46 fx with the biggest three blade I could get to clear the wing. I flew it on wheels, and after experimenting with CG all day, I found the sweet spot where wing rock is minimal and stability is at its best...about an inch in front of the step. It flew okay, but not great in my oppinion. I then took the gear off and took it to the water. I have it set up with elevator and elevons. It flies best at all speeds in that configuration. The first flight was on choppy water. It took just a little forward pressure to get on step. Rotation took forever even as the chop was assisting it. Later in the day it would not lift off glassy water at all no matter what I tried. I was finding that as the plane got up on step, or what little there is, the rudder would lose effectiveness. A tip float would then touch and create drag bringing the plane off step and pulling to its respective side. As it came off step I would regain rudder control as the stub below the rudder made contact with the water. The process then started all over again. I realized I needed a longer water rudder first of all. Second on my list was more step on the fuse. I used a broken propeller from the unfortunate guy next to me to fabricate a taped on exaggerated step. That actually was very effective and the aiplane planed at very slow speeds. Unforntunately, as the hull rose further out of the water, the tipping tendency toward the tip floats was exaggerated and directional control was almost impossible at speed. The next issue is that when you do get to flying speed and start to rotate, the back of the tip floats dig in and create instant drag slowing the airplane below flying speed again. I was finally able to bounce the airplane off a small buoy and get it airborne, but it was the sketchiest takeoff I have ever been a part of. I had to regain forward flight from the hover it ended up in. It took some fancy stick movements and even a little body english to pull it off. The crowd went wild and I finally got my five minutes of 90 mph passed out of my system. Landings are a non issue, but could be improved with a v-hull design. I don't want to hurt any feelings here, but knowing what little I know about aerodynamics, hull performance, and float design, I feel like the Northstar is kind of poorly thought out. I think the designer made many mistakes that are causing me and others a lot of problems. I know the fans are going to hate that statement, but I think even they know it is true after reading a bunch of related forums. I do understand that my overweight model is amplifying the issues, but the point is this model is not that out of line for weight and should still fly well for what these kits cost back in the day. If I were building a new one, I would address all of these issues in my build. Here is my list:

1. Poor engine placement/prop clearance.
2. Nose too short/engine too far aft for balanced CG in stock configuration.
3. Hull step too far aft of CG and not pronounced enough.
4. No step on tip floats.
5. No means of directional stability on hull or tip floats (v bottom, strakes, etc.)
6. Not enough water rudder depth.
7. Rudder not large enough.
8. Wing angle of attack to shallow on land and water for reasonable rotation speeds.
9. Ailerons/elevons not large enough.
10. Wing rock and whatever causes it should have been addressed and eliminated aerodynamically.

I know there is a lot of information out there about mods to these things, but it would take forever to get to them all. I will live with all the issues except getting this thing off the water. I would appreciate any and all suggestions both proven and unproven that will help me get this contraption to takeoff from smooth water. However crazy the idea, I'm listening and probably have the tools and materials here to do it. I'm even considering a three point hydofoill system. Obviously the simpler the better though. Thanks for your time and thoughts in advance.

Goldenduff

A .55ax might make all the problems go away! What weight is the plane, 8lbs is on heavy ish side. Is the step sharp? Are te rear edges of floats sharp? What 3 blade are you using? The ns is awesome if built properly- any additional weight in the tail requires 3 times as much added to the nose. Is the nose weight in a hollowed pi nose come or in the fuse?All the best

Cougar429

My Feedback: (3)

The NS has been out successfully for far too long to be a dog, (and in fact is still in production. Something that cannot be said for a majority of kits).

Having said that, I have built some wonky examples, one in particular the Parkinson glass and foam model that had rounded fuse/bottom intersections and an improperly designed step that NEVER got off the water. One of my first, ( also back in the 80's) had air retracts and gear doors. Ended up far too heavy to show any performance.

Yes, there are improvements that can be made and I will hopefully incorporate a few into the next one on the build table. For now I intend to have too much fun with the Polaris Ultra and current NS to plan another any time soon.

skywagn180

Thanks Goldenduff. I thought of more power too, but I don't have a .55 and don't plan on ever buying anymore nitro motors as I have moved to gas. This plane was covered in solartex and painted with automotive paints by the builder. Obviously not ideal, but it looks too nice and I don't have the heart to strip it. I don't have a scale, but it is between 8.5 and 9 lbs dry going by comparison with items of known weight. The edges of the step and rear of the tip floats are not sharp by any means. That could be improved with some aluminum sheet I guess. I was thinking of temporarily taping aluminum strips to all three edges bent down a little like a boat trim tab. I still think the tip floats may create too much drag during rotation if I do that. i also thought about cutting big steps into the tip blocks, but that would require a lot of work considering the covering and paint situation. I'm using a Graupner 10x7 three blade prop. Thrust and speed is more than adequate in the air. Wheeled flights are acceptable as far as takeoff and landing. The 12 ozs of lead required to balance the plane is way up in the nose cone.

Goldenduff

Hmm, doesn't sound too bad- you got the prop on the right way round (lol). 

Cougar429

My Feedback: (3)

Solartex and auto paint sounds like a heavy combo.

Sharp edges to the fuse/side intersection and step are almost mandatory to break suction. Another mod I posted earlier involved reverse angling the aft edge of the tip floats. Reduces both aqua and air drag in flight.

One trick we used years ago was to add perforated sides angling rearward up from the aft bottom of the step. Basically wedge shaped side plates with holes to promote aeration behind the step. Sorry, I do not know how to add graphics for this here.

One other thing to note is, not accounting for the fact they look cool, I have never had much luck with 3-blade props on 2-stroke motors. Even with the proper conversion static thrust usually ended up drastically reduced, on the order of 30%. On that note your 46 should likely run a 10/7 2-blade. Using the conversion you would need to work with a 9/7 or 10/5 to 10/6 3-blade, (always reduce 1 number in pitch or diameter). From my own experience I would guess your motor would be hard pressed to reach peak RPM, perhaps lugging down below the nominal power band. This has a major effect on performance, especially water ops where you need to get out of displacement quickly.

LADDIE

Too bad that you are having all these issues with the NS. I am not surprised that you NS is dog.
You said that it is flying brick. At 9 Lbs and powered with .46, no wonder that it underperforms.
Out of 10 points you are wrong on 9. Only on number 6 you are right when there is a cross wind the rudder could use more area under the water. The size of rudder above the water is fine.
It is unfortunate that who ever built your model did not followed proper building sequence. There is no way that this model would come to 9 Lbs.
Personally, I do not think you have too many options outside of putting in larger engine.

Before slamming the design, it would have been nicer from you to go on the Internet and find the NS site. Read and ask what could be done to your model.
I designed model in 1984-1985. Since then the construction articles were published in USA (RCM), France (MRA), Czech Republic (Modelar) and in UK.
The Balsa USA started making the kits between 1987-1988 and still making them. Thousands were built and flying.
Personally I am all for improving the design. What you proposing is not improving basic design, but to cover for poorly built model.
I am sorry for being harsh, but I am proud for what I created in the North Star.