Sunday, May 06, 2012

Somewhat puzzeling data...

I've now flown the canard finned nose cone, three times...



On the first flight I had the accelerometer sensitivity too high, but the roll sensitivity was fine.
In all hte following plots roll is red, and vertical acceleration is blue.  Flown with a CTI L800 blue





We had ever increasing roll as the flight progressed, no evidence of any control

So I changed the acceleration scale  and removed the fins, leaving everything else unchanged...
(Slightly differnt motor  CTI L820 Skidmark)


The roll was in the same direction and of lower magnitude than the controlled attempt....

Then I re flew with the fins attached and the mechanical throw increased about 50%.
Again with a CTI L820 Skidmark.)


This flight almost looks like it worked, ad the roll was controlled during the early boost phase of the flight.
Either I have weird aerodynamics or I need a lot more control authority. 
Its possible this last flight worked as designed until it got close to Mach 1 and saw shock wave issues.
The altimeter reported a maximum velocity of 1150 ft/sec or right near Mach 1. 

Got to think about this one a bit more...





12 comments:

ian said...

Paul, do you have fin angle data? Do a phase plot of fin angle vs angular acceleration (differentiate the angular rate from the roll gyro). You should get close to a line. Actually, the slope of the line should change for different dynamic pressure, so... also do it for different velocity ranges, in case the slope changed (which it should). If you want to get fancy divide by the estimated dynamic pressure to get Cll. *Then* you should get close to a line.

I find these plots very telling of what's going on.

schoasblodan said...

Hey Paul,

why you thrown your four fin design away? Don't you get the hoped benefit?

Anonymous said...

The work reported here concluded that canards were ineffective due to canard-tail interference: http://www.feretich.com/Rocketry/TotallyStable/index.html

Paul Breed said...
This comment has been removed by the author.
Paul Breed said...

Yeah I've commented on Canards not working supersonic, so yea I know this is a dead end. Just trying to use it as a test bed for some electronics. Probably should bith the bullet and make moveable rear fins.



Paul

Nathan Bergey said...

Like the earlier comment suggested: the canard-tail fin interaction can ruin the usefulness of the canards for roll. I think their report sums it up perfectly, "Canard Deflection actually changes Angle of Attack for the rear fins causing lift in the opposite direction"

But note that this is NOT just a supersonic effect! It's true at all speeds.

-Nathan
PSAS

Anonymous said...

It's not that the fins don't work supersonic; it's the interaction with the rear fins that will cancel, or even negate the forces of the canards.

Canard lift is very predictable through the Mach transition (many papers on this), but the lift mechanism for a delta wing is very different than an airfoil.

Hence, canard-main fin interaction is a big problem.

Andy said...

Did you estimate the torque requirements? Does the servo have enough torque?

sworkeld said...

Paul,

You may want to contact Italian grad student Adriano Arcadipane to find out about the canard roll controller for rockets he created for his thesis. The video he has posted is worth watching.

This page lists a dozen missiles that use canards, so it's obviously possible. (Disclosure: Some use dual-control mechanisms. Not sure how many.)

You may also want to try rollerons.

In 1976 the US Army published The Effectiveness of Canards for Roll Control that lists the same problem discussed here.

NASA also has a 1986 report out worth reading, A Look at Handling Qualities of
Canard Configurations
.

FWIW,
Thom

Angular Acceleration said...

Angular speed and angular acceleration both are necessary to learn when we are designing the circular moving objects.

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