CG on an old Piper Cub ?
I have recently converted an old Piper Cub , Balsa wood from nitro .46 to an electric . G46 400kv from Value hobby with an 80amp ESC. I have figured out the CG as I do for all my planes. Between 1/4 and 1/3 back from the leading edge as a starting point. But if anyone out there knows the correct CG for this plane I would appreciate any info before my maiden voyage. I have never flown this plane before. It was given to me by someone who had it sitting around for 30 years amnd he doesn't remember anything.
Also , I am going with the biggest prop I can fit and that's a 14-8 prop. powered with 6s power. Before the conversion it was 7 1/2 pounds and its now 7 pounds AUW. The wing is 77 " long 10 3/4" wide Any tips or help would be greatly appreciated. Thank you Bob |
Oh man that will be a super sonic turtle of a Cub. :) :) I would say way more power than needed. But hey, there is always the left stick.
A good guess would be on the spar. Front side or back, but on or very near the spar. Buzz. |
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Originally Posted by blvdbuzzard
(Post 12344465)
Oh man that will be a super sonic turtle of a Cub. :) :) I would say way more power than needed. But hey, there is always the left stick.
A good guess would be on the spar. Front side or back, but on or very near the spar. Buzz. |
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All of my cubs, some five or more, all flew best with a CG slightly more forward than most CG calculators suggest. Also make sure you have some toe in on the landing gear to minimize the tendency to ground loop on take off.
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Originally Posted by Rodney
(Post 12344578)
All of my cubs, some five or more, all flew best with a CG slightly more forward than most CG calculators suggest. .
Also when balancing never balance with the nose slightly down for "mother and country" always balance with the fuselage Level. If you do that you have not balanced at you target point but instead at some unknown point forward. John |
Ok so here is my dilemma. General consensus is 25% back from leading edge. And also it should be at or near the spar. If the wing measures 10 3/4" inches , then 25% back from the leading edge should be at 2.687 (2 11/16") " But here is the conflict. The spar is 3 3/4" to the front edge of the spar and 4 1/8" to the back edge of the spar which is even more then 1/3 back . Even if I went 1/3 back , that doesn't even reach the spar. So do I say the heck with the spar and just set my CG 1/4 back ?
any help is appreciated thank you bob |
Bob go with 25% if you want the sweet flying airplane that Cubs are supposed to be famous for, only go for 30% and beyond if three D flight is the goal and the airplane is plane is intended for the vast majority of its flight time to be prop hanging a current catch phrase for that type of flight is sometimes called high alpha.
The spar reference is only because it been traditional to express that way for newbies and of course its only a crude reference and every design can an will vary in that regard. John |
I have a Tacon 46, 60 amp ESC, 5s battery swinging a 13x6 prop and it will hover a 7 pound plane. I would guess your plane will fly at about 1/4 throttle or less. Or you could enter the pylon race and see how fast it goes and how far back you can get those wings to flex backwards :) :) :)
If you fly it with floats, you will have plenty of power to fly off the water. Buzz. |
I truly appreciate all this good info. I will for sure start out with 25% on the CG. And I guess I have way to much power for this plane. I will start out with the 6s , but it sound like I will be able to go down to probably 4s or 5 s. . I always believe its better to have to much power then not enough. So I guess that what I have.
Thanks again , and I will probably be flying this within a week. So I report in and tell you how I made out. Bob |
Originally Posted by schomper42
(Post 12344446)
. Before t
Also , I am going with the biggest prop I can fit and that's a 14-8 prop. Any tips or help would be greatly appreciated. Bob The old saw that states shoot you can always just pull the power back may not be such good advice when you are dealing with an out of control takeoff and fighting the temptation to rip it off the ground far to early as you are running off the side of the runway. John |
To compare your Cub, I flew my very over weight Goldberg Cub with an O.S. 48Fs engine. I would hazard a guess that is about the same power as a Tacon 25 with a 3s battery and a 12x6 prop. Might I suggest, run a 12x6 prop, 5s or even a 4s battery. If you find you do need more power, setup up to a 13x6.
Here is a tool you may well need. It will tell you how much power you really have. A watt meter will help you decide how your setup will preform. Plus it will help you to keep the magic smoke in. So your plane is 7 pounds, so if you get 800-850 or so watts, you should be good. If you test and you have 1500, you know you can step down a bit and still be safe. https://hobbyking.com/en_us/turnigy-...-analyzer.html https://www.amazon.com/Power-Analyze...=RC+watt+meter Let us know how she flies and pictures would be great. Buzz. |
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Well i need to figure out how to attach a picture of the plane
Ok , so the long awaited report on my first flight with this converted Piper Cub. I took your advise and sent the bird up in the air with a 12x8 prop ( only 12" prop I has on hand) still with 6s power. It took off ok , but I needed to give the plane full throttle the entire time. It was severely under powered. I brought along a 13x6 prop and tried that. What a difference ! The plane flew great at half throttle, just the way I like it. Giving me reserve power if I ever needed it. No doubt this type of plane is a slow flyer and it was. But it flew beautiful. It is by far the largest and heaviest plane I have ever flown so I was a little nervous. Take off and landings were a little different , just something I need to get used to. I will now try to come up with something for cowling. Oh by the way, I did set the CG for 25% back off the leading edge and it was perfect. So a plane that's been sitting around unused for about 30 years is flying again, but now with electric power. Thanks again for all the advise from everyone, it is much appreciated. Bob |
Well i need to figure out how to attach a picture of the plane
Ok , so the long awaited report on my first flight with this converted Piper Cub. I took your advise and sent the bird up in the air with a 12x8 prop ( only 12" prop I has on hand) still with 6s power. It took off ok , but I needed to give the plane full throttle the entire time. It was severely under powered. I brought along a 13x6 prop and tried that. What a difference ! The plane flew great at half throttle, just the way I like it. Giving me reserve power if I ever needed it. No doubt this type of plane is a slow flyer and it was. But it flew beautiful. It is by far the largest and heaviest plane I have ever flown so I was a little nervous. Take off and landings were a little different , just something I need to get used to. I will now try to come up with something for cowling. Oh by the way, I did set the CG for 25% back off the leading edge and it was perfect. So a plane that's been sitting around unused for about 30 years is flying again, but now with electric power. Thanks again for all the advise from everyone, it is much appreciated. Bob |
I tried to attach a photo in the post and that didn't work out very well. So I added a picture of the plane in my gallery
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Post images by going to "Go Advanced" next to "Post Quick Reply". You'll will see a paper clip in the header. Click on that. Dan.
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trying to clip a picture ....
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Thanks Dan , that worked
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Glad things worked out for you,, add some pitch and you'll make better use of that motor's power,,, 13-8 or 13-10 and you'll be cruising around at more like 1/4 throttle I bet,,
Good luck. p.s. Contact Callie Graphics for some numbers for the wing ;) https://callie-graphics.com/collections/piper-cub |
I will give a 13x8 a try , and thanks for the graphics link !
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Glad you had a successful flight. See you can teach old planes new tricks.
You might be able to find the cowl here. Goldberg Anniversary Piper Cub 40 Kit Parts Listing Cowling & Accessories for Kits Buzz. |
Piper Cub Cowl
I have recently made a cowl for the plane. But thanks for those links. I'll take a picture of what it looks like with the cowl.
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