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Maiden and preflight characteristics questions

quorneng

Active member
#21
20" span is small and Paracodespode said a C pack motor has far too much power and weight for it.

Just to give you an idea this is my P51 (ish) plane that is made up from crashed bits.
Complete1.JPG
Considerably bigger at 38" span yet it uses a smaller lighter motor (46 g against 70 g for the C pack) and it still has more than sufficient thrust.
 

FDS

Active member
#23
Lift calculations were more complicated than I expected (I am famously stupid at maths.) I would start with the all up weight, that way you can calculate the thrust required from your motor and prop. For example if your airframe weight is 700g and the max thrust your motor can generate is 600g then you might have problems.
NASA has the lift calculation if you want to explore it, there’s also calculators for it once you find the values to add to the equation.
I think priority is still to get an idea of weight and CG to either try a test flight with some nose weight added and the bare airframe or to get everything in. Use the link for calculating the wing cord and CG first, then go from there.
 

FDS

Active member
#25
Fluid dynamics will bend your head inside out!
Apparently that feeling indicates you are doing real maths, not just mechanical calculations.
 
#26
Update! I finished my scratch built trainer ( Simple Starter ) and hopefully can find a time and place to maiden today. School starts back up tomorrow and I would like to not have to wait another week to fly. Sadly winds are supposed to be bad today. If anyone knows of any open indoor places to fly, please let me know ASAP. If it comes to it, I think I may try to just take off outside, It´s got quite a bit of power to it.
 

Merv

Well-known member
#27
aerodynamics is just too confusing!
12-15 oz per square foot is a good wing loading for a plane the size of the Storch. But a smaller indoor plane is going to be 1-2 oz per sqft. A ten fold change.

To get some idea of what works, look at a store bought plane of similar size to your plane. Look at wing loading and power requirements. They have already done the hard core aerodynamics for you, no use reinvent the wheel.
 
#28
Update! So, the trainer didn't get off the ground in our maiden test. I was really anxious to get it in the air, so I threw a random prop onto my C pack motor. I also didn't know if the prop was balanced but assumed that it was because it came off a Seawind, which is a prebuilt RC plane I had. I went to a large gym and tried to take off off the ground. My landing gear was not the best because I threw it together, once again anxious to get into the air. Eventually, I got tired of trying to take off and tried hand launching. The motor was really shaky, but I launched anyway. The plane went into a dive-ish, probably because I'm bad at hand launching, and had nobody to do it for me. It nit the ground nose first and the prop broke. This time I'm ordering a new prop that fits that motor, and probably a new motor. But, since I do have a powerful motor on my hands, I had another plane design in mind. If you would like to hear about it please to say. I know I'm new, and while this plane may be big, it's pretty simple. I think I can pull it off. Thanks!
 

quorneng

Active member
#29
As you have found out "anxious to get into the air" is not really the best approach. ;)
Despite the relative simplicity of a quick foam build any plane is still quite highly stressed, it has to be to fly so it pays to make sure everything is "as good as you can make it" and fully tested before any attempt at flight. :)
Knowing what is likely to be good enough or not is all part of the scratch build learning experience.
Keep posting!
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#30
If you are anxious to get into the air try building or buying a plane that has already been proven to be capable of flying! Learn to fly it and then when you are able to fly properly you can experiment with your own designs and start having success, IT IS NOT THAT HARD!

If you have never flown an RC model successfully there are just too many variables and success will continue to elude you!

Just a thought!

Have fun!
 
#31
@quorneng sad I had to learn it the hard way but differently leaned! @Hai-Lee, I had a Sports Cub S for a while, and I already have the materials for a scratch build. Plus I don't want to spend a lot on a pre-built when I can learn to build one myself. I think I might get an FT kit since I know they fly and I get to build.
 
#32
Well, can anyone suggest an FT plane that runs off a C pack that would be a good start? The cheaper the better, but when it comes to scratch building, anything is worth it. Or would it be better to get completely new electronics? Currently, I have 5 5g servos, an A pack ESC running the C pack motor, a 2s, and a 4 channel receiver. I ruined me A pack motor a while back. I just need a good solid foundation.
 

quorneng

Active member
#33
Land Shark
Running a C pack motor from a A pack ESC is not a good idea. To run the C pack motor at anything like its full power will just "fry" that A pack 12 A ESC.
So either get another A pack motor with a suitable prop and build a A pack sized plane or get a C pack 30A ESC to use with you C pack motor and build a bigger C pack sized plane. It is also likely to need a 3s battery.
A note of caution, your 5 g servos are bit on the small size for a big C pack sized plane.
 

FDS

Active member
#35
The Tiny Trainer is excellent, it can run off a 2s and 5g servos.
A 30 A esc is under $10 or a smaller motor for the TT is the same sort of price. I got an 1806 2300kv off Hobbyking for $6 and run a 6x4 prop.