Thanks for this video. Regarding your point at 12:47, does this also apply to modifications where the RC plane (a flying wing) is extended in length (at the tail end) but no changes to the wing surfaces? Does the CG point move? Or just moving weight around to maintain the original CG should suffice? Thanks.
If you added a tail onto a flying wing, the weight of the tail would move the CG towards the back. The location of lift on the wing would not change. So, you would need to add weight to the front to get it to balance near the centre of lift.
i would suggest that, in the future, you use a high-wing model as a visual aid; and begin with an explanation of why a high-wing config is the most stable. hint: it's because the center of mass is Lower in the airframe.
That's a good thought. However, it is more complex than that. At the end I discuss how the movement of the centre of lift during a stall moves behind the CG, and that having the CG below the wing reduces the tendency of the plane to pitch nose down in that situation. We needed the background to explain that. Having the CG low does also help the plane to level itself out regarding roll in normal flight, but a low wing aircraft often has more dihedral, which can give it more or less equivalent stability that way.
6:38 information the science of aircraft design tells us that the two, chord-wise values (cg and center of lift locations) Should be coincident; at/near thirty percent of chord or mac. conclusion: the design of a main wing Should include a contiguous load-bearing main spar, at thirty percent. d
Yes, and 30% is pretty well in the middle of the 25% to 33% range. And because that is the centre of the force acting on the wing, it makes sense to locate the main spar there.
While I can appreciate the work and effort you put into this presentation, The Knowledge is mostly un used in the world of Buy a chunk of Packaging material shaped like a Plane. Then, go and fly/crash it . Then if you're a gluten, Do it all over again. I watched the whole thing and even understand it but I just want a cheap toy Plane to PLAY with.
That's great unless your toy plane crashes because it wasn't configured properly. None-the-less, at times I do get carried away with trying to understand every little thing about our hobby. For me there's a lot of interest in working out the details of how things work, and how we can make them better.
Yes, guilty of rambling a bit, but on topic. Flaps change the location of the centre of lift on the wing. That's what we have been discussing. This explains why the nose typically will lift when flaps are added without also adding down elevator.
What I didn't ramble about was what happens when one wing stalls before the other. The dynamics that we have been discussing explain why that leads to a spin. I'll ramble on about that another day, but it makes sense, and the basic principles in this video explain why.
When I was learning to fly full size aircraft, I had one instructor teaching me to fly a Piper Super Crusier. It didn't have flaps, and we did power off landing approaches, using a sideslip to get the plane down in the right place at the right airspeed. Around that time I had another instructor that was teaching me to fly a Cessna 150 with flaps. He wanted me to do power on approaches using flaps, because that was what was needed in the larger aircraft. Both work.
Thanks for this video. Regarding your point at 12:47, does this also apply to modifications where the RC plane (a flying wing) is extended in length (at the tail end) but no changes to the wing surfaces? Does the CG point move? Or just moving weight around to maintain the original CG should suffice? Thanks.
If you added a tail onto a flying wing, the weight of the tail would move the CG towards the back. The location of lift on the wing would not change. So, you would need to add weight to the front to get it to balance near the centre of lift.
@@RCJim Thanks for your response/clarification.
Glad to help!
No worries.
i would suggest that, in the future, you use a high-wing model as a visual aid; and begin with an explanation of why a high-wing config is the most stable. hint: it's because the center of mass is Lower in the airframe.
That's a good thought. However, it is more complex than that. At the end I discuss how the movement of the centre of lift during a stall moves behind the CG, and that having the CG below the wing reduces the tendency of the plane to pitch nose down in that situation. We needed the background to explain that. Having the CG low does also help the plane to level itself out regarding roll in normal flight, but a low wing aircraft often has more dihedral, which can give it more or less equivalent stability that way.
6:38 information the science of aircraft design tells us that the two, chord-wise values (cg and center of lift locations) Should be coincident; at/near thirty percent of chord or mac.
conclusion: the design of a main wing Should include a contiguous load-bearing main spar, at thirty percent. d
Yes, and 30% is pretty well in the middle of the 25% to 33% range. And because that is the centre of the force acting on the wing, it makes sense to locate the main spar there.
6:58 c-m , not cg, is forward of the center of lift.
Thanks for your feedback, David.
While I can appreciate the work and effort you put into this presentation, The Knowledge is mostly un used in the world of Buy a chunk of Packaging material shaped like a Plane. Then, go and fly/crash it . Then if you're a gluten, Do it all over again.
I watched the whole thing and even understand it but I just want a cheap toy Plane to PLAY with.
That's great unless your toy plane crashes because it wasn't configured properly. None-the-less, at times I do get carried away with trying to understand every little thing about our hobby. For me there's a lot of interest in working out the details of how things work, and how we can make them better.
10:10 off-topic rambling about flaps
Yes, guilty of rambling a bit, but on topic. Flaps change the location of the centre of lift on the wing. That's what we have been discussing. This explains why the nose typically will lift when flaps are added without also adding down elevator.
What I didn't ramble about was what happens when one wing stalls before the other. The dynamics that we have been discussing explain why that leads to a spin. I'll ramble on about that another day, but it makes sense, and the basic principles in this video explain why.
David, thank you for your interaction. I'm not the source of all truth, and I do appreciate other people sharing their own opinions and ideas.
9:32 flaps flaps flaps bleh
When I was learning to fly full size aircraft, I had one instructor teaching me to fly a Piper Super Crusier. It didn't have flaps, and we did power off landing approaches, using a sideslip to get the plane down in the right place at the right airspeed. Around that time I had another instructor that was teaching me to fly a Cessna 150 with flaps. He wanted me to do power on approaches using flaps, because that was what was needed in the larger aircraft. Both work.
7:22 saying cg when you should be saying c-m.
Thanks for your feedback, David.
gaaawd 11:53 it's CENTER of MASS (c-m)
Thanks for your feedback, David.
7:42 HUH? fail
Pass, as far as I can see.