• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.
Pumpkin drop event

Episode suggestion - Gravity vs Lift challenge

Do you like the idea of a Gravity vs Lift challenge


  • Total voters
    6
#1
Like a lot of the Flitetest community, my interest in RC remained dormant for many years after my introduction at an early age. When I discovered FT in September 2014, I had a new Apprentice in my hands within 48 hours and had taught myself to fly within a week (after Apprentice no. 2 was ordered. Apprentice no. 1 spent 6 weeks at the top of a 70ft Ash tree...). Since then the house has become littered with white foam aeroplanes, quad and tri-copters and I have started an aerial filming business and have a commercial UAV licence and an Inspire 1! And it is all your fault, Flitetest. I used to be considered normal.

Sorry for the long intro. I have been starting to get more into modifying designs and coming up with my own designs both in foam and paper. The paper aeroplane designing led me to this suggestion for a show.

With a paper aeroplane, if all the forces on the plane are not in correct balance it just won't fly. So you can't just add power or control surface travel to sort out an inherent problem. This got me thinking about the, not particularly generally understood, principle of balancing centre of gravity and centre of lift. In a paper plane, this is effectively the propulsion method. Using the couple between C of G and C of L to angle the plane down at the ideal angle to have a controlled descent without stalling. It seemed to me that this would be a useful concept to teach people getting into the foam plane design journey. At the moment we are usually given an ideal C of G point and we try to get the plane a bit nose down. But how is the ideal C of G point decided and that has to have a lot to do with the C of L.

It occurred to me that one way of getting this across would be with a graphic demonstration and a bit of a challenge. This all rests on my assumption (and I have no idea if it is correct) that the C of L does not move with forward speed. I thought the episode could start with a description of C of G and C of L including clips of tail heavy aeroplanes. Then it could go onto a challenge where Peter or someone has designed a frame to hang a variety of FT planes beneath (well beneath - out of the prop wash) a heavy lifting multi-rotor. The multi-rotor would lift the test subject which would be in full flying trim with power to the electronics but not motor to a reasonable height and then drop it straight down. The pilot of the test plane would then wait a second or two to demonstrate the attitude the plane would adopt then try to gain control of the plane and glide it in for a landing. My theory is that as the plane drops, if the C of G is forward of the C of L, the plane would nose down, gain speed and start flying. If the C of G is aft of the C of L, the plane would nose up, go into an uncontrolled tail slide and provide entertainment as the pilot tried to regain control of it. This could be done with a few different planes and pilots or the same plane with the C of G moved around and different pilots trying to catch it.

Just a thought! You can take the man out of engineering (I trained as a mechanical engineer but run an IT business) but you can't take engineering out of the man!

Love the shows, podcasts, forum, articles etc. I just wish I was closer to Ohio or any group of like minded individuals. I fly mostly on my own as I live in the middle of Exmoor in the UK...
 
#2
Demonstrating various stability principles in a fun way might make for a good episode. It could also be quite a challenging thing to do well given the time the FT guys might have to put into it.

You are speaking mostly of pitch stability, but there is also spiral stability, lateral stability, etc.

A more practical technique might be to start with a simple foam board plane and add a flight controller, like the Guardian or similar. You then fly it with the FC turned on and then turn off the FC in mid flight and see if you can keep it in the air.

Start with a good flying basic airplane, and then make it very tail heavy, then make it very nose heavy, then fly it with a wing with a lot of dihedral, then a lot of anhedral, then slice off chunks of the vertical stabalizer, etc.

Since the aircraft will at times be very hard to fly, or unflyable, and then crash, it lends itself to a fun episode with lots of carnage, but it also gives a chance to see what happens and hear the descriptions of how the plane flies, along with practical explanations of why.

It might not be text book classroom accurate, and it might not explore all the combinations of issues, but it could be fun. As a somewhat accidental byproduct it would also demonstrate to what degree a flight controller like the Guardian can make a marginal plane fly much better, or at least flyable.
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#3
You can do all this in a game called Kerbal Space Program. You learn pretty quickly how CG and CL work. You also learn to ensure CG remains forward of CL after all the fuel is consumed so your balanced craft doesn't suddenly flip on you and plummet tail first into the ocean. :black_eyed:

The cool part of KSP is that you can build planes and rockets and see how the same principles impact different vehicles simply due to angle of attack and drag.

Could be a cool episode. If it never happens and if you are geeky enough, check out KSP! :)