Appropriate engine for a restored Piper Cub
09-29-2011, 01:22 AM
#1
Thread Starter
Appropriate engine for a restored Piper Cub
Hello,
I just restored a Piper Cub that I got for free from the guy who crushed it. I believe the airplane is 40 size, it's wingspan is 183 cm. After restore the airplane weight with electronics was 2800 grams. I installed on the plane an OS 46fx engine which added 490 grams and in order to get the CG correct I had to add 350 grams in the front because the airplane was very tail heavy. yesterday I took it for a test flight and got it to the air after a very long run on the runway. The takeoff was very slow, long and flat. It took only a little bit of trimmin and the cub seemed blanced and controlable. The thing was that it felt underpowered in compare to what I'm used too. Gaining altitude wasn't easy and in general the behaviour was very scaly I think. Throttle was at maximum or very close to it most of the time. Landing was good and I think I can declare the flight test was successful. One thing that keeps bugging me is the thought that maybe the airplane was designed for a bigger engine. I own a 20cc gas engine which weigh 800 grams with it's ignition. Now, the dilemma is whether I should install the gas engine and gain more power without gaining more weight or should I keep the same setting and get used to this real airplane behaviour. Is there a "correct" decision here?
That's all. I hope I posted in the right forum, after all it's a rebuiled case.
Everyone is welcomed to offer his comments or insights.
Thanks.
Liron
I just restored a Piper Cub that I got for free from the guy who crushed it. I believe the airplane is 40 size, it's wingspan is 183 cm. After restore the airplane weight with electronics was 2800 grams. I installed on the plane an OS 46fx engine which added 490 grams and in order to get the CG correct I had to add 350 grams in the front because the airplane was very tail heavy. yesterday I took it for a test flight and got it to the air after a very long run on the runway. The takeoff was very slow, long and flat. It took only a little bit of trimmin and the cub seemed blanced and controlable. The thing was that it felt underpowered in compare to what I'm used too. Gaining altitude wasn't easy and in general the behaviour was very scaly I think. Throttle was at maximum or very close to it most of the time. Landing was good and I think I can declare the flight test was successful. One thing that keeps bugging me is the thought that maybe the airplane was designed for a bigger engine. I own a 20cc gas engine which weigh 800 grams with it's ignition. Now, the dilemma is whether I should install the gas engine and gain more power without gaining more weight or should I keep the same setting and get used to this real airplane behaviour. Is there a "correct" decision here?
That's all. I hope I posted in the right forum, after all it's a rebuiled case.
Everyone is welcomed to offer his comments or insights.
Thanks.
Liron
09-29-2011, 11:01 AM
#2
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RE: Appropriate engine for a restored Piper Cub
If it is, indeed, a 40-size then the OS 46 is sufficient. The Cub is not meant to be a fast (or aerobatic) flyer. Adding the gasser (and removing the extra weight added to the front) will give you more power, you might also consider a .52 or .70 four-stroke...more power and more scale sound. I had a 40-size Cub that with a .52 four-stroke that flew very scale-like and was easy to handle.
09-29-2011, 02:25 PM
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RE: Appropriate engine for a restored Piper Cub
Congratulations on the restore.
Sounds like you have a truly scale flying model
As to the question as to if there is a truly correct decision?
There are many truly correct ones available to you.
1 - Leave it as is and fly "Scale".
2 - Remove the existing engine (and ballast) and replace it with the higher powered option
3 - Go somewhere in between 1 & 2
All are corect decisions, only you can decide what you prefer.
If you like doing Aerobatics, go for more power. If you want to learn about scale flying - leave it as is.
If it was mine, I would be looking to see if there was anything I could relocate forward (or change) to reduce the tail heaviness first. That would have the benefit of reducing the wing loading. If there is nothing that could be done practically, I would go for the DLE20 that you have as you can then also do things such as run a smaller fuel tank and an IBEC and "perhaps" end up with a (very slightly) lower overal weight.
Sounds like you have a truly scale flying model
As to the question as to if there is a truly correct decision?
There are many truly correct ones available to you.
1 - Leave it as is and fly "Scale".
2 - Remove the existing engine (and ballast) and replace it with the higher powered option
3 - Go somewhere in between 1 & 2
All are corect decisions, only you can decide what you prefer.
If you like doing Aerobatics, go for more power. If you want to learn about scale flying - leave it as is.
If it was mine, I would be looking to see if there was anything I could relocate forward (or change) to reduce the tail heaviness first. That would have the benefit of reducing the wing loading. If there is nothing that could be done practically, I would go for the DLE20 that you have as you can then also do things such as run a smaller fuel tank and an IBEC and "perhaps" end up with a (very slightly) lower overal weight.
09-30-2011, 04:31 AM
#4
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RE: Appropriate engine for a restored Piper Cub
In this situation, I would do my best to remove that dead weight set in the nose, by pushing everything as forward as I could.
Move the servo tray, battery pack, fuel tank and even the receiver to the most forward place possible. Remember that moment is a magnitude that takes ARM and WEIGHT, so moving the heavier parts to the farthest spots is more effective. By this, I mean you should take at first, probably the battery pack (the heavyer unit) to the most forward point (most times, next to the firewall, aside of the fuel tank), maybe using an extension. Than the servo tray, this move may be painful, you might need to re-do or modify the pushrods, and so on.
In my humble opinion, adding dead weight to any aircraft is heresy. It raises the weight (obviously), but also the dinamic moment. Heavy crafts tend to fly much more "on th engine" than "on the wings", because them need a lot of thrust to overcome the big drag generated by a "diving" wing, and this seems to be you case, when you tell you must be at almost full throttle, on a OS 46FX, installed on a 1,8m wingspam cub.
Another simple but effective tip is to change the tailwheel. Saving 10g on the back may save 50g on the front and by doing this you just saved 60g total.
Move the servo tray, battery pack, fuel tank and even the receiver to the most forward place possible. Remember that moment is a magnitude that takes ARM and WEIGHT, so moving the heavier parts to the farthest spots is more effective. By this, I mean you should take at first, probably the battery pack (the heavyer unit) to the most forward point (most times, next to the firewall, aside of the fuel tank), maybe using an extension. Than the servo tray, this move may be painful, you might need to re-do or modify the pushrods, and so on.
In my humble opinion, adding dead weight to any aircraft is heresy. It raises the weight (obviously), but also the dinamic moment. Heavy crafts tend to fly much more "on th engine" than "on the wings", because them need a lot of thrust to overcome the big drag generated by a "diving" wing, and this seems to be you case, when you tell you must be at almost full throttle, on a OS 46FX, installed on a 1,8m wingspam cub.
Another simple but effective tip is to change the tailwheel. Saving 10g on the back may save 50g on the front and by doing this you just saved 60g total.
10-01-2011, 10:20 AM
#5
My Feedback: (2)
RE: Appropriate engine for a restored Piper Cub
If I may put my $.02 in here, I have a H9 1/5 Scale Cub with a Saito .82 in it. The Cub is very overpowered. I only installed the .82 because I will be flying off of floats, and someone recommended that engine for the extra power I'd need for taking off from water.
Bob
Bob
