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Help! Flying Rc Car

#1
Hi! I am thinking about trying a project to fly my rc car. I have a power pack C for propulsion and was planning on building the airframe around the rc car so that I could still drive. The car weighs a little less than 6 lbs, and I think the power pack C weights a little over a pound. I think it will give me around 2.5 lbs of thrust. So with the right wing, is it possible to fly 7lbs with 2.5lbs of thrust?
 

Hondo76251

Legendary member
#3
The very minimum size of wing required for this would be probably 6' or better. The power required for a wing of that size alone, without the car, would be more than a c pack. Typlically for rc flying models the closer to a 1:1 power to weight ratio the better. Many far exceed that.

Check out the FliteTest episode where they parachute a car from a plane to see what size of a craft is required to lift a decent sized RC car...
 

JasonK

Master member
#4
the 'minimum' thrust to weight ratio would be that to maintain an air speed greater then the stall speed of your wing(s) with what ever drag your craft creates at that speed in the air or the thrust needed to accelerate to that speed (on the ground/air/etc) and then a bit more so you have climbing ability.

I know that that can be less then 1:1 thrust to weight for real aircraft.

a glider's WCL is under 4, so lets use that for a target and 10lb AUW given the numbers you have given already. (which would be thrust:weight of 0.25:1)
gliders have an aspect ratio of 8-12:1

a 10ft x 1ft wing (10:1 aspect ratio) runs a WCL of 5.1
a 10ft x 1.5ft wing (6.67 aspect ratio) runs a WCL of 2.8
a 12ft x1ft wing (12:1 aspect ratio) runs a WCL of 3.8
(also for drag/lift, I think a wider wing is better, but 10ft is already going to be creating structural challenges)

a 10ft x 15in (easy math range for the above measurements) would be 6 sheets of DTFB + your wing spar @ 120g each => is 1.58lb if you don't take off the internal paper (which would probably be a good idea) and then you still need the spar. So the 10lb range looks at least theoretically achievable based on your stated numbers.

a quick google gives this: which shows a 747 at a thrust to weight of 0.27:1. so you might need a bit better then 0.25:1 that we came up with before, but at least puts us at a 'theoretically' possible level based on actually flying aircraft.

if I was going to try this, i would look at a 12ft x 1ft wing with a carbon fiber rod reinforced spar (probably 2 light spars separated by foam vertically) with an appropate airfoil shape (look at some of the smooth curve wings over the FT standard angled one). you would also need a big runway to get up to speed.
 
#5
Thank you very much for your help.
For me I don’t think I have the space to use more than a 6 foot wing and don’t have any carbon fiber parts. Would it give me a similar effect if I did a bi-plane design and stacked two 6x1 wings? Also, would I need flaps to get this size of a plane/car in the air? Because I only have one Y lead and need it for the ailerons...
 

Hondo76251

Legendary member
#6
Flying with a WCL over 15 is perfectly doable if you are heavy lifting but it requires a lot of power.

My "smart duck" (FT Sea Duck with long range gear) has an estimated WCL of about 17! It weighs over 5lbs loaded and flys reasonably well with twin C packs.

What you are proposing is feasible but it will require more than a c pack...
 

JasonK

Master member
#7
a biplane's effective lift is less then that of a single wing of the same surface area (the wings impact each other). I don't know the the exact level of impact. Also the aspect ratio (why the wing would be so wide) has to do with lift to drag ratios.
 

JasonK

Master member
#8
Flying with a WCL over 15 is perfectly doable if you are heavy lifting but it requires a lot of power.

My "smart duck" (FT Sea Duck with long range gear) has an estimated WCL of about 17! It weighs over 5lbs loaded and flys reasonably well with twin C packs.

What you are proposing is feasible but it will require more than a c pack...
why I pointed out getting a very low WCL is specifically to allow a weaker engine. if you have high enough thrust your plane becomes a missile and your control surfaces are just guides.

while your correct, Thrust:weight of 1:1 definitely makes flying easier, it isn't required.
 

JasonK

Master member
#9
Thank you very much for your help.
For me I don’t think I have the space to use more than a 6 foot wing and don’t have any carbon fiber parts. Would it give me a similar effect if I did a bi-plane design and stacked two 6x1 wings? Also, would I need flaps to get this size of a plane/car in the air? Because I only have one Y lead and need it for the ailerons...
now we have went from 'can this be done' to 'can this be done with my limited supplies', and we are heading toward no, because to make this work your going to have to build something a bit more extreme in structural design then the normal foam board plane.

one thing that the bi-plane could get you, is extra structural strength to your wing for the given weight... you could definitely try your idea out, nothing says it can't work [except physics - you do have to be able to make more lift then your weight and more thrust then your drag at the required speed for that lift], but if your going to go down to 0.25:1 thrust to weight ratio, your going to want everything in your favor to make it happen.
 

JasonK

Master member
#10
So to clarify -> which of these is what your asking? (or where between these 2 extremes are you? how much $ and time are you willing to put into this?)
  • is there a way to get an aircraft to fly with a thrust:weight ratio of 0.25:1 given plenty of access to tools/materials and lots of time trying different things?
  • Can I get something to fly at a thrust:weight ratio of 0.25:1, just by slapping some random bits together and hoping it works?
 

Hondo76251

Legendary member
#11
There was a thread some time ago where we were talking about doing a challenge like this. The idea was to see who could lift the most weight with a c pack motor. I was kind of excited about it, might be worth re-visiting! I think ill work on setting that up soon.
 
#12
I have never built anything bigger than a standard sized plane and am not sure if I have the skill for this project. Also, knowing now how low my chances are of getting it to work, I think might wait and revisit the subject if I ever get a better power setup like a C twin pack. Thank you all very much for you comments they were very helpful and I learned a lot. :)
 

Hondo76251

Legendary member
#14
I forgot all about that one!

Looks like twin c's and a very light truck. He also must have disconnected the motor on the rear tires at some point because you can see it freewheeling as it flies...
 

JasonK

Master member
#15
yah, I have seen it done (probably that one above)... you could also keep the car drive train working, if you linked the control with your plane controls so that you could use that motor for ground control.