Theory of flight - model airplanes

beatsal

Joined Jan 21, 2018
394
Trying to understand the theory of flight. Hence, got a few balsa wood rubber-band kits and a trying to fly the, not much luck. They tend to nose dive. Any help/suggestions appreciated.

Ya’akov

Joined Jan 27, 2019
9,117
This lecture is excellent, worth watching.

MrChips

Joined Oct 2, 2009
30,792

An airplane wing has to supply lift. To do this it has to have camber profile, i.e. curvature in the wing's profile.
Experiment with various paper or balsa wood designs.

Testing
1) Without any push, the plane should have a smooth downward glide.
2) With just a moderate push before letting go, the plane should maintain a longer glide. If it climbs up initially it has too much lift.
3) You need to balance, lift, CG (centre of gravity) balance and elevator trim.

Papabravo

Joined Feb 24, 2006
21,225
If the model goes nose down in flight, it is likely the the CG (Center of Gravity) is in front of the CL (Center of Lift). Try moving the CL forward of the CG. As the nose pitches up, the wing will have a greater angle of attack and generate more lift.

beatsal

Joined Jan 21, 2018
394
Thanks. Here are 2 pics

Attachments

• 22.5 KB Views: 13
• 208.1 KB Views: 12

MrChips

Joined Oct 2, 2009
30,792
Thanks. Here are 2 pics
Experiment first without the propeller and rubber band.
The important thing is to get the lift and balance correct.

Joined Jul 18, 2013
28,673
If I recall correctly from my modeling days, the typical CofG is about 1/3 of the wing cord from the front edge..
A simple balance test proves it.

Wendy

Joined Mar 24, 2008
23,420
My dad once bet a friend that with enough power anything can fly he proved this by bending a sheet of aluminum into an airfoil in attaching a really large model aircraft engine onto it and then flew it as a you control.

DaviBrons

Joined Jan 18, 2022
5
Trying to understand the theory of flight. Hence, got a few balsa wood rubber-band kits and a trying to fly the, not much luck. They tend to nose dive. Any help/suggestions appreciated.
Hello. It is normal that they tend to nose dive (if no too much of course).
Look: it takes off not in a straight line, like from cannons, but in tacks. At the same time, at each turn, the elastic is again stretched due to the inertia of the airframe. The idea is that the glider serpentine rises higher and higher, and the elastic band remains stretched, about the possibility of having a dynamo start. The main thing is to choose a soft enough rubber so that the overclocked model can stretch it again.
If the problem still persists then try this: maybe the elevons are too small for the profile you have chosen. They need to be made 3-4 times larger in area in order to be able, by lifting them slightly up, to give the profile the desired S shape to ensure longitudinal balancing. Most likely, the center of gravity of your airplane wing is much ahead of the focus (the center of application of the lifting force). Therefore, the wing lowers the nose. To ensure balance (so that the nose does not fall), an S-shaped profile is used on the wings, or this S-shaped profile is created due to raised elevons, the length of which is the entire trailing edge, and the width of which increases from the center to the tips. The simplest solution is to fix the existing elevons and attach new ones, for example from balsa. And recalculate the position of the CG again, for new sizes.

Alec_t

Joined Sep 17, 2013
14,312
To do this is has to have camber profile, i.e. curvature in the wing's profile.
Actually, it doesn't. A perfectly flat wing at a positive angle of attack will provide lift; albeit not as efficently as a cambered one.

drjohsmith

Joined Dec 13, 2021
852
Hello. It is normal that they tend to nose dive (if no too much of course).
Look: it takes off not in a straight line, like from cannons, but in tacks. At the same time, at each turn, the elastic is again stretched due to the inertia of the airframe. The idea is that the glider serpentine rises higher and higher, and the elastic band remains stretched, about the possibility of having a dynamo start. The main thing is to choose a soft enough rubber so that the overclocked model can stretch it again.
If the problem still persists then try this: maybe the elevons are too small for the profile you have chosen. They need to be made 3-4 times larger in area in order to be able, by lifting them slightly up, to give the profile the desired S shape to ensure longitudinal balancing. Most likely, the center of gravity of your airplane wing is much ahead of the focus (the center of application of the lifting force). Therefore, the wing lowers the nose. To ensure balance (so that the nose does not fall), an S-shaped profile is used on the wings, or this S-shaped profile is created due to raised elevons, the length of which is the entire trailing edge, and the width of which increases from the center to the tips. The simplest solution is to fix the existing elevons and attach new ones, for example from balsa. And recalculate the position of the CG again, for new sizes.
Can you show a video of this working
sounds almost like perpetual motion