|
|
Post by iflyforfun on Aug 25, 2010 2:10:53 GMT 1
Hi Everyone, I have learned so much from this club and thought it was about time I join and get more involved.
I have a Super Cub LP and have done a Aileron,Battery Box and some other small upgrades like larger wheels ext. I have found the 20 part upgrade series on youtube by "NeCubFlyer" to be fantastic. Following his instructions my aileron mod came out great and looks like a factory job.The Cub fly's great and I'm getting about 25 to 30 minutes of flight time with a Turnigy 2200-20c battery. I also have a Dx6i that I have been using for quite a while and just bought a AR6110E receiver.
I have been studying for a few weeks all the threads relating to brushless upgrades and I have narrowed it down to a Turnigy 35-36 1100KV motor.
If my understanding is correct, I could get away with a 40 amp esc but I don't see any reason why I should not just order a 60 amp ESC to play it safe. Is there a good reason why a person should not go with a larger amp ESC like a Turnigy Plush 60A I have in mind.
This is how I worked it out:
2200mah20c = 20 x 2.2 = 44amps.
Using this calculation, Is it true that I can pull up to 44 amps without over stressing my Lipos?
Turnigy 35-36 1100KV is rated for 400watts@11.1V = 36Amps
All my calculations above have been picked up from different threads and I am just trying to put it all together in a package that I can fully understand.
So, on to Motor Mounts. I really like the Motor Mount that Dillzio bought on ebay. It looks great and The only thing that needs to be done to the Cub is to open up the hole in the cowl to 1". I have searched for quite a while for an alternative that is cheaper but also has the correct thrust angle built in or is adjustable. I have also been considering a stick mount. I have not found many threads on motor mounts and thought some of you out there could talk about what you have used and the pros & cons of the different types.
Thanks for all the help!!!
PS. I have a couple of videos on youtube. Search "mcintosh1964" :-)
|
|
|
|
Post by flydiver on Aug 25, 2010 3:54:50 GMT 1
If my understanding is correct, I could get away with a 40 amp esc but I don't see any reason why I should not just order a 60 amp ESC to play it safe. Is there a good reason why a person should not go with a larger amp ESC like a Turnigy Plush 60A I have in mind. This is how I worked it out: 2200mah20c = 20 x 2.2 = 44amps. Using this calculation, Is it true that I can pull up to 44 amps without over stressing my Lipos? Turnigy 35-36 1100KV is rated for 400watts@11.1V = 36Amps Welcome! ESC - somewhat larger is necessary. A LOT larger is not necessarily safer (you can fry other components just fine) but it is larger (may not fit some spaces), more expensive, and heavier. Battery - you've done your homework. The part you may have missed is that the Chinese specs are sadly optimistic a good portion of the time. They can claim anything they want and feel no compulsion to back it up. It's MUCH safer to whack 20% off ALL specs unless proven otherwise. Read this-excellent advice from a smart man: www.rcgroups.com/forums/showpost.php?p=11476940&postcount=4341Without having done it I think a stick mount in the Cub would be a pain to put in correctly, more difficult to mount that motor, and not as secure when dealing with that many amps. With ingenuity, and good glue many things are possible though. I'd just go for the prefab mount. You'll be glad you did unless you get a kick out of fabricating things. |
|
|
|
Post by ginginho on Aug 25, 2010 10:11:59 GMT 1
I've mentioned it before to others who have suggested this motor, and believe that it is well over-powered for the SC. I have one spinning an APCe 10x5 on a MPX Gemini and the performance is way beyond what the SC requires. To get to the 400w mark you'd need to spin a something like a 12x6. The Gem (similar weight to the SC) goes vertical infinitely as it is, and is nearly capable of prop hanging on the smaller prop. The SC doesn't need or is suited to this sort of power. 200-250w is more than enough for the SC to become very lively. Obviously this is only my opinion, you can ignore it if you like. As to the other points raised, the power draw calculation is a bit optimistic as you've not factored in voltage drop under load, which many if not all Lipo's will suffer from. A safer calculation would be for 10v meaning a draw of 40A, which is fairly accurate for reasonable quality packs. Mystery (or other E-Bay type) packs will probably perform worse than this, mates who use these packs often suffer from puffing whereas a similar sized LoongMax used in the same application comes down cool and unaffected. That said, the 35-36 in the Gem is hung off of a 40A HobbyWing ESC and has been reliable, although as stated before, I've not propped it for maximum performance but it does pull in the order of 33Amps. The other thing that you should consider if you go with this setup is the weight. You may well struggle to balance it out with this motor (100g+), a suitable mount and the ESC mounted in the cowl (recommended especially if you are going to to be maxing out the power). Your SC will be seriously nose heavy if you mount your pack just behind the CoG, i.e. in and around the battery box, so you may have to design a pretty unique way of mount your packs. Remember, a heavier plane will be more stable in the wind (advantage) but will have a higher stall speed and hence landing speed (disadvantage). If you can grease your landings on a regular basis and have a nice strip to fly from, this will not be a problem. If not, you'll be repairing your cub constantly due to damage caused during this (rather important) flight phase. Each repair will add weight and hence exasperate the situation. One last thing, I wouldn't trust a stick mount with a 400w+ motor hanging off the end. A motor with spec similar to this would give you enjoyable performance (and probably not noticably any different to the bigger one due to the draggy airframe) without the problems that the weight of the heavier one introduces. A 40A ESC would suit nicely, assuming it has a 2A switched BEC. |
|
|
|
Post by iflyforfun on Aug 25, 2010 12:37:49 GMT 1
Hi Ginginho,
Thanks for all the info. I am aware that the 35-36c will be extremely overpowered for the Cub and am also very concerned about weigh and balance. ( I also fly real planes and am a former weight and balance agent for Pan Am before they went bankrupt). Let's just say I like lots of power and I am doing this more as an experiment than anything else.
Ok, we agree on the power issue! I don't fully understand why you say the Cub will me extremely nose heavy with this setup.
The stock motor with mount weighs 139.8 Grams
The 35-36C motor and Dillzio mount from eBay comes in at 129 grams.
Turnigy plush 40A BEC comes in at. 33 Grams
Remove 139.8
Add. 129.0 forward of the firewall
Add. 33.0 on fire wall or under wing balance.
Am I missing something???
Does the BEC need to be mounted for cooling or can I use it in the receiver compartment.
Also, the stock receiver/bec combo that comes with the Super Cub LP is very heavy. I have not weighed it yet but will do so tonight. The new AR6110e is tiny and only weighs 3grams. I have a feeling that I will be under the original weight after confirming the receiver weight tonight.
Please let me know if I'm missing some critical info..
I have also calculated the wing loading with this new setup and come out with a stall speed of around 18 MPH. That's a littler higher than normal but feel it will be ok for the Cub.
|
|
|
|
Post by ginginho on Aug 25, 2010 14:27:58 GMT 1
Hi Ginginho, Thanks for all the info. I am aware that the 35-36c will be extremely overpowered for the Cub and am also very concerned about weigh and balance. ( I also fly real planes and am a former weight and balance agent for Pan Am before they went bankrupt). Let's just say I like lots of power and I am doing this more as an experiment than anything else. Ok, we agree on the power issue! I don't fully understand why you say the Cub will me extremely nose heavy with this setup. The stock motor with mount weighs 139.8 Grams The 35-36C motor and Dillzio mount from eBay comes in at 129 grams. Turnigy plush 40A BEC comes in at. 33 Grams Remove 139.8 Add. 129.0 forward of the firewall Add. 33.0 on fire wall or under wing balance. Am I missing something??? Does the BEC need to be mounted for cooling or can I use it in the receiver compartment. Also, the stock receiver/bec combo that comes with the Super Cub LP is very heavy. I have not weighed it yet but will do so tonight. The new AR6110e is tiny and only weighs 3grams. I have a feeling that I will be under the original weight after confirming the receiver weight tonight. Please let me know if I'm missing some critical info.. I have also calculated the wing loading with this new setup and come out with a stall speed of around 18 MPH. That's a littler higher than normal but feel it will be ok for the Cub. I don't think you are missing anything really but there are a few other factors apart from the actual weight to consider: The Stock motor is mounted pretty near the firewall and hence near the CoG. The B/L motor with that mount is mounted a fair bit out from the firewall and hence from the CoG. Therefore it's effect of the balance will be increased, by how much I couldn't be sure. To know for certain you'll need to work out the weight distribution over distance from the CoG for each. It's all about the cantilever action of a weight at a distance from the (in this case ideal) balancing point. You may well get away with putting the ESC in the cabin, it would certainly move a fair amount of weight to near (or just behind) the CoG, which may make it easier to balance. Whether the airflow through that area is sufficient to keep it cool, again I can't say as I put my ESC in the cowl to ensure a good airflow. As you say, the stock ESC/Rx is a heavy beasty when compared to a Spekky RX, not sure by how much, a fair bit I'd guess. However the original is mounted just around the CoG (slightly behind if anything) so putting a lighter one in (unless you move it a long way back) will actually add to the nose heavy characteristics. Don't get me wrong, it's possible to do and will probably be flyable even if horribly nose heavy. I actually have mine set quite a bit more than perhaps it should be but I like the way it flies in that it gives better wind penetration and sits nicer (in my view) in the air. It does also mean faster landings, and a greater tendancy to nose over. I'm impressed that you've worked out the wing loading, do you have a figure for a stock SC as I don't think I've ever seen one? |
|
|
|
Post by leisureshoot on Aug 25, 2010 15:32:03 GMT 1
So, on to Motor Mounts. I really like the Motor Mount that Dillzio bought on ebay. It looks great and The only thing that needs to be done to the Cub is to open up the hole in the cowl to 1". I have searched for quite a while for an alternative that is cheaper but also has the correct thrust angle built in or is adjustable. I have also been considering a stick mount. I have not found many threads on motor mounts and thought some of you out there could talk about what you have used and the pros & cons of the different types. I made a motor mount last night based on something I saw on RCUniverse. I used the original, black geat box/motor frame as a starting point. My preference would be to buy one, but I didn't want to wait a week. The base that screws to the SC firewall is the base of my mount. I cut off everything that extended past that flat base. This leave a mount with 4 screw holes to screw into the firewall, and a nice flat forward portion to mount a scratch-built base to. In my instance, I used 3 pieces of cabinet grade 1/2 inch plywood laminated together with White Gorilla glue. I attached the wood to the front of the black base, with 3 screws into the back of the wood from the back side of the base. Now, you have the black base, with a block of wood solidly attached to the front of the base. This maintains the thrust angles from the original design. And, importantly, it can be mounted and removed using the original screws/screw holes on the firewall. My motor has a rear cylinder that extends approx 1/8 inch, so I drilled out a hole where the rear of the motor seats, and this allowed the motor mount to attach to the front of the plywood. I came out just a little too far forward with my motor front, so I am going to have to sand my plywood, or the back portion of the black base to remove 1/16-1/18 inch, as the front of the motor rubs the cowl slightly. I'm at work. I'll try to post pics tonight. It was very straight-forward and required nothing more than a sheet of coarse sand paper, and a Dremel, although a good knife and/or Xuron cut-off pliers would have worked, instead of the Dremel. |
|
|
|
Post by iflyforfun on Aug 25, 2010 18:40:53 GMT 1
I agree with Ginginho. Nose heavy is better. I calculated the optimum CG as 1.250 from LE. After mounting my camera underneath and right behind the cowl I was at 1.387 from the LE. This is nose heavy and can be good or bad depending on how you fly. I have my DX6i flap switch programed to give me 25% up elevator when activated. So about 30 seconds before landing I flip the switch and reduce throttle to a little under half. I let the cub settle and it just slows down to a really nice angle of attack. I now use( not always successful) just throttle for altitude and a little up elevator for flaring.
I left the CG at 1.387 from LE and I love the flying characteristics.
I forgot to mention that my stock RX is mounted on end across the fuselage right in front of the servos. This required making a small notch on each side of the fuselage to allow the RX to slide down. No Velcro is needed and the RX is held in by the wing.
I will post the wing loading data tonight when I get home.(US east coast)
I will also weigh the stock RX. Just about the only thing I have never weighed on the Cub.
If you want to know your wing loading, you must have a accurate total flying weight of your Cub and the total square inches of wing surface.
47.7 inches X 7.?.. At work and don't have the measurements with me but I'm sure you get the drift.
I will confirm this later but in think it's around 330 sq inches.
My SC flying weight with camera, aileron mod and 2200 lip is 28.5 oz or 8 grams.
I think I will just go with the mount off eBay.
Thanks Ginginho, I forgot about the brushless being so much farther forward that the stock motor and mount. I will have to do some new calculations. :-(
|
|
|
|
Post by iflyforfun on Aug 25, 2010 19:56:59 GMT 1
@ GinGinho I did miss some vital info that you made me aware of. I have read over and over that the specifications of most motors and batteries are overrated. I never thought about using more (real world ) numbers in my calculations. Again, thanks for the help!! leisureshootVery interesting, this motor mount that your working on! Do you have any pics? I read and re-read youngest and I'm a little confused at how you bolt then motor to your mount. What are you using between the new ply firewall and the motor? I understand that the ply is screwed to the old mount. What type of motor are you running? Thanks |
|
|
|
Post by leisureshoot on Aug 26, 2010 3:34:02 GMT 1
I should have cut a separate, forward-most piece of plywood, with the "ears" for the upper two motor mounts. I originally thought I was going to be using a 3/32 plywood piece on the front (between the motor and 1/2 inch ply). But it turned out that I didn't have as much room as I initially measured, once I put it all together. I Gorilla glued and and clamped them on, followed up with pinning them from the sides with an 18 gauge nail from my one of my pneumatic pin nailers. I did it by drilling a very small hole, and filling with Gorilla Glue by pushing it in with a wire. I then pushed the pin nails in with a pair of needle nosed pliers. I had to sand the front and back of the plywood block, and sand the front and back of the black plastic gearbox to move the motor back 1/8 inch so it didn't touch the inside front of the cowl. In one or two pics, you can just see one of the silver screws inside the black mount the face forward, and attach the plywood block to the black gearbox. The motor hole was a bit difficult to locate. I mounted the black gearbox and the plywood, then placed the cowl onto the fuse, and used a marker to approximate center. I drilled a small drill bit into the center I just located, and pulled off the cowl, and put the bit back into the hole to check that it was perpendicular to the plywood face in all directions. I then drilled out a large hole 3/8 inch(?), then used a stepped enlarging bit to get a nice, clean hole of the desired diameter, to recess the rear of the motor into. You can find these at Harbor Freight for under $5 and they work well for small hobby projects. I used a Dremel with a wood rasp bit to carve away a nice smooth recess to route the wires out from behind the motor. And also for a recess for the set screw that holds the motor mount collar to the back of the motor. The screws hoding the motor mount to the wood were pre-drilled very close to screw size, so as not to split the two ears. Once again, using a front piece of plywood with the ears included would eliminate this issue. It looks like the picture below shows a split in the plywood, but it is just a dark piece of wood along the edge of two layers of plywood. The wood in the holes had thin CA added for strength.       |
|
|
|
Post by iflyforfun on Aug 26, 2010 3:52:25 GMT 1
@ leisureshoot
Did you ever weigh the block of wood? very cool idea. Looks simple.
thanks for the pics.
|
|
|
|
Post by iflyforfun on Aug 26, 2010 4:00:26 GMT 1
How and why I always Calculate Wing Loading
1) Convert the area to square feet. There are 144 (12 x 12) square inches in a square foot.
SC has 317 in2 of wing area. This is with 3 inches subtracted for the cabin.
317 in2 ÷ 144 = 2.20 ft2
2) stock SC LP weight. = 25.2oz published
3) Divide the weight by the area:
25.2 oz ÷ 2.20 ft2 = 11.45 oz./ft2
A stock SC LP has a wing loading of 11.45 oz/ft2
My SC with mods has a wing loading of 12.95 oz/ft2 a stall speed of 17.6MPH
If you know your stall speed you have a general idea of how fast you have to fly to have a nice landing. Fly to fast you bounce or break something. Fly to slow and no matter how much up elevator you give it plows into the ground.(no flare). My video on youtube( go to youtube and search "iflyforfun") and you'll see a result of me landing with a high wing loading. Its the last 5 seconds of the "hight altitude into clouds video" I had full up elevator and not enough power.
I have flown my SC with a total weight of 37.5 Oz. That was a wing loading of 17.04 oz/ft2
and a stall speed of about 20 Mph.
Ya, it sounds crazy but it flew. Like a rock I must say.
11 to 15 oz per sqft are managable, flys slow without stall at the low end, flys fast at the high end tends to stall when slowed down, so glides and landings are fast. Above 15 oz/ft2 needs a long area for landing approch.
So thats how I use to figure out how to mod my glow planes and what weight they can carry. Now I’ve turned to electric. But the calculations are the same.
I enjoy carrying stuff on my planes. Im not a precision flyer or like to do much more than fly inverted sometimes. But I love strapping my 9 Oz sony HD digital video camera to my plane and shooting video at extreem altitudes.
So in a nutshell, why not a 35-36C. Over powered yes, but I will strap my video camera to it and climb to 1000 feet and hope I dont have a midair collision with a real plane.
I think i got a little more in depth than I wanted to but only touched on a tiny bit of aircraft weight and balance. I hope someone out there will find this info usefull and if so, someone should start a thread in the correct area called “Weight & Balance”. I’ll be happy to answer any questions as long as I dont get blamed for you plane crashing. :-)
|
|
|
|
Post by leisureshoot on Aug 26, 2010 4:08:33 GMT 1
@ leisureshoot Did you ever weigh the block of wood? very cool idea. Looks simple. thanks for the pics. No - I really need a scale. I did compare the assembly to the original motor. It probably weighs only half the weight of the orig motor. If you look at the middle, head-on picture, you can see 3 holes in the corners of the firewall. I put a 2 inch drywall/woodscrew with metal nuts around it into the firewall for weight. I think, I'll probably mount metal weight to the bottom of the wood mount to get it further forward. So, there are two easy options. |
|
|
|
Post by ginginho on Aug 26, 2010 11:00:27 GMT 1
Hmm, I'm not sure your numbers add up (quotes): "stock SC LP weight. = 25.2oz published" I assume this is with the stock lipo (1300mAh?). "My SC flying weight with camera, aileron mod and 2200 lip is 28.5 oz " bigger lipo so heavier, plus camera. "my 9 Oz sony HD digital video camera" I assume this is the same camera mentioned in the previous quote. Therefore a stock cub = 25.2oz Camera = 9oz --------------------------------------- Total 34.2oz Your pack being bigger will be heavier, so your SC with ailerons, 2200 pack and camera has got to weigh more than this, unless you've shed a fair amount of weight elsewhere. You've stated that you've flown it at 37.5oz, would this be the weight of it with the camera? Swapping the motor out for something more meaty (but for arguments sake let's say the motor/mount/esc combo weigh the same as the stock) won't change the way it flys, it'll still be a brick, just a brick with more power. Additionally if you make it more nose heavy (which I think is likely) it's going to be worst in a glide, harder to maintain inverted flight and have a greater tendancy to nose over during a landing. I can't find what the actual CoG is, IIRC it was somewhere around the 2"- 2.5" back from the LE (search function on this site seems to have stopped working), but this is quite a bit different that what you've quoted for yours. I bet rolls are quite barrelly (is that a word???)  FWIW, I think mine is set a fraction behind the 2" mark, and this has a nose heavy attitude. As previously intimated, I'm not trying to scupper your plans, just trying to make you aware of how your SC will perform with your selected hardware. |
|
|
|
Post by Dillzio on Aug 26, 2010 11:03:17 GMT 1
|
|
|
|
Post by leisureshoot on Aug 26, 2010 13:40:48 GMT 1
Nice find. Thanks. I wish I were nose heavy at this point. The wood is much lighter than the motor it replaced. I've attached several metal nuts to the side and bottom of the mount for now. I've got it just about right. |
|
FWIW, I think mine is set a fraction behind the 2" mark, and this has a nose heavy attitude.