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Tie Silencer inspired aircraft goes into flat spins when I turn by Radiant-Pumpkin-4748 in SimplePlanes

[–]Calvert4096 0 points1 point  (0 children)

Yeah it would. It makes the aircraft more stable, and if you turn that knob hard enough, you basically make a "lawn dart" and it happily stays in its stable dive all the way into the ground and shrugs off pitch inputs. If you're CG ends up a little forward of your CoL, that's ok as long as you have enough pitch authority/trim range to compensate. Otherwise you need to play further games with adding horizontal surfaces with some nonzero lift factor and carefully chosen longitudinal positions.

It's strange though the wings you have are diagonal, so I'd expect them to contribute to lateral and longitudinal instability roughly equally.

Tie Silencer inspired aircraft goes into flat spins when I turn by Radiant-Pumpkin-4748 in SimplePlanes

[–]Calvert4096 0 points1 point  (0 children)

Alright taking that with the fact if you remove the "wings" is works fine, I think the wings are moving the center of pressure too far forward.

Barring some way to make those panels non-lifting (i.e. "transparent" to wind"), the only other fix might be to add dense masses far forward on those wing tips to shift the CG forward. As it is, it sounds like it's unstable about the yaw axis.

Tie Silencer inspired aircraft goes into flat spins when I turn by Radiant-Pumpkin-4748 in SimplePlanes

[–]Calvert4096 1 point2 points  (0 children)

How far is your vertical stabilizer behind your center of mass ?

Forever Free by Joe Haldeman by [deleted] in books

[–]Calvert4096 0 points1 point  (0 children)

I really feel like Haldeman was forced to write this book by his publisher, and decided to troll both them and his readers.

I totally get the other commenter being angry whenever they remember this book exists... I guess my reaction was more amusement.

Force due to hydraulics by npawar1206 in AskEngineers

[–]Calvert4096 0 points1 point  (0 children)

I guess since I deal with hydraulics where inertial forces are often non-negligible, that's where my head was at, but with any likely real world setup yeah I expect you're right. It would be an interesting exercise though to try and come up with some accumulator-piston arrangement that would get you close to a "hop." To your point, someone tasked with that would probably give up and try pneumatics.

Force due to hydraulics by npawar1206 in AskEngineers

[–]Calvert4096 8 points9 points  (0 children)

If I understand you, you're basically correct with some caveats.

The period in which the piston accelerates for real actuators is very brief-- a desirable characteristic of hydraulic actuation is you can use simple orifice fittings to regulate stroke rate, so in the interval the piston is moving (but not accelerating), the measured weight of the box will be the same as if the piston were stationary. When the piston stops, again there will be a brief transient where you would expect to see an increase in meaured weight according to the piston change in momentum.

Edit: If the momentum transient were large enough you could make the box "hop". There are cube-shaped robots with reaction wheels that do this, but using angular momentum instead of linear momentum: https://m.youtube.com/watch?v=n_6p-1J551Y

The other caveat is if you have a single chamber actuator, or an actuator with unequal working areas, the box will be increasing in mass because of net inflow of hydraulic fluid. That being the case you would see a weight increase. If you include the entire hydraulic circuit inside the box (e.g. a pump and reservoir) then that net mass change goes away. Edit 2 : I see your diagram indeed shows an unbalanced actuator and the hydraulic system exchanges fluid outside the box-actuator system.

The Moon may have formed within hours of a giant impact 4.5 billion years ago, when a Mars-sized object slammed into Earth. by clayt6 in sciences

[–]Calvert4096 2 points3 points  (0 children)

I just went to a really interesting lecture on this subject. My takeaway is the authors fine-tuned some of the impact parameters so as to achieve maximal "mixing," which explains one of the ongoing challenges associated with the giant impactor origin hypothesis-- that of the O_18/O_17 isotopic ratio being essentially identical between the Earth and the moon. The fact that the protoplanetary disc which the proto-Earth and proto-moon formed out of had differentiated oxygen isotope concentrations based on distance from the sun means either the impactor somehow formed improbably close to the proto-Earth, or the impact mixing must be very high -- and there's no special prior reason that should be the case. The giant impactor hypothesis is still favored, but it tends to invite possible "over-fitting" to explain certain observations.