Offset or off-axis nose weight?

[KenECoyote]

Hi!

Have any of you tried off-center nose weight to adjust or affect flight trajectory?

This was something I thought of trying after having flown winged rockets (ex. Dynastar Foxfire & Lexxjet, X-15) and noticing a tendency for the rocket to arc up towards the top of the nose cone cockpit bulge. I had figured that the extra bulge was causing more drag on that side.

 

[KenECoyote]

I had started to experiment with this on my Radical Rocketry F-104 Starfighter build.

On the first launch, it arced a bit over my head:


This is normally not any great issue, however the club I attend has a line of trees and a river behind the spectator area and having rockets launch over there can spell their doom.

 

[KenECoyote]

After I painted the Starfighter, I wanted to try something to make the flight straighter and out to where I point it.

I thought that maybe offsetting the clay nose weight would help because having one side of the rocket heavier will cause it to arc more to the heavier side, right?

So I adjusted the clay in this way:


And on the next flight (same motor, but windier), it flew very straight!

View attachment 20230422_113052_1.mp4

Thoughts? Experiences?

 

[KenECoyote]

I should add that if the rocket has any tendency to rotate during boost or coast, this would probably be bad to try.

 

[KenECoyote]

Also wind direction may be a factor since the rocket can weathercock. I haven't done further testing since I don't have a good local field to launch at.

 

[sr205347d]

There is likely more offset drag from the tail than from the cockpit. The cockpit and tail would also add weight to the top side. But the wings seem to be angled down (anhedral) which would counter the cockpit and tail weight/drag. You could check the weight offset by hanging it with a string from the tip of the nose cone. Your weight adjustment seems to have fixed things though.

 

[lakeroadster]

Also wind direction may be a factor since the rocket can weathercock. I haven't done further testing since I don't have a good local field to launch at.

Only way to really know what's going on would be in a wind tunnel...

My mindsim thinks that offset in nose weight had almost nothing to do with the different flight pattern.

 

[David Schwantz]

Yes, on the grain bin, 16" dia, I tried offsetting the nose weight due to 1 pound in the cap for the chute cannon. Never saw a difference.

 

[Daddyisabar]

Yes. Lots of mindsiming until the Grinchy puzzler was sore. Worry, worry, worry. I know CP-CG. What is the LCP-LCG thing they are talking about? Asymmetric drag? Thrust centerline? CALGON, TAKE ME AWAY!

Like the First Order storm troopers in R.O.S, "they fly now?"

It has to be balanced both ways?

You have to be crazy to fly silly airplane oddrocs. 3-4FNC is so much easier! Oh no! Here comes the dreaded RSO table. What's my story this time? Blind them with science. It worked! It flew good a few times!

 

[Pem Tech]

View attachment 577088
Yes. Lots of mindsiming until the Grinchy puzzler was sore. Worry, worry, worry. I know CP-CG. What is the LCP-LCG thing they are talking about? Asymmetric drag? Thrust centerline? CALGON, TAKE ME AWAY!

Like the First Order storm troopers in R.O.S, "they fly now?"

It has to be balanced both ways?

You have to be crazy to fly silly airplane oddrocs. 3-4FNC is so much easier! Oh no! Here comes the dreaded RSO table. What's my story this time? Blind them with science. It worked! It flew good a few times!

I Want This! Is there a build thread?

 

[Daddyisabar]

I Want This! Is there a build thread?

Yes. B58 Hustler on TRF. Never figured out how to post link on fancy phone.

 

[Blast it Tom!]

View attachment 577088
Yes. Lots of mindsiming until the Grinchy puzzler was sore. Worry, worry, worry. I know CP-CG. What is the LCP-LCG thing they are talking about? Asymmetric drag? Thrust centerline? CALGON, TAKE ME AWAY!

Like the First Order storm troopers in R.O.S, "they fly now?"

It has to be balanced both ways?

You have to be crazy to fly silly airplane oddrocs. 3-4FNC is so much easier! Oh no! Here comes the dreaded RSO table. What's my story this time? Blind them with science. It worked! It flew good a few times!

Beautiful! But I've seen enough of your challenging, interesting and original oddroc builds to start making me wonder - do you try to fly rockets like airplanes? Little wheeled art rolling down the runway... ( I KEED, I KEED!).

But yes, absolutely if you have an off-center CG or CP, you create a moment (torque, or twisting force) and it will turn the vehicle. My beloved Pigasus arcs every time.

 

[KenECoyote]

There is likely more offset drag from the tail than from the cockpit.

Yes, however, the cockpit is at the tip, so there's a greater effect on trajectory given that (angular momentum ? Lever effect?). This is why fins at the top effect the flight dramatically more than on the middle or rear.

The cockpit and tail would also add weight to the top side. But the wings seem to be angled down (anhedral) which would counter the cockpit and tail weight/drag. You could check the weight offset by hanging it with a string from the tip of the nose cone. Your weight adjustment seems to have fixed things though.

Yes! Same observations about the raised tail having more drag topside, yet countered or reduced by the anhedral.

Great advice on checking the weight offset. I had planned to, but hadn't gotten around to it. However, I think suspending it from the motor end may make more sense in this case.

Very tough getting good steady pics, but I tried my best.

Without the nose cone, balance appears close to neutral/in-line:



With the nose cone on (with more clay on the bottom of the cockpit), it looks like weight is more biased to the bottom:


I tried to keep the string in line with one of the door edges in the photos.

 

[Daddyisabar]

Beautiful! But I've seen enough of your challenging, interesting and original oddroc builds to start making me wonder - do you try to fly rockets like airplanes? Little wheeled art rolling down the runway... ( I KEED, I KEED!).

But yes, absolutely if you have an off-center CG or CP, you create a moment (torque, or twisting force) and it will turn the vehicle. My beloved Pigasus arcs every time.

Our old RSO only allowed rockets, no airplanes. Must be a vertical launch, fly straight up with little arc. Must recover safety under adequate chute. No airplane like flights, nothing horizontal, no sky writing. Like NASA, failure was not an option. Prestigious University Engineering standards placed on all, especially Liberal Arts History majors. Strict review, inquisition expected. Those days were hard but fun.


Yes sir Mr. RSO. The B58 utilizes POOR BOY DUAL DEPLOY from fuselage. One D123 and one D125. Both cones weighted with their own chutes.

 

[sr205347d]

Is the motor centered with the body tube? It looks offset. Is the thrust line parallel with the body? It looks like it might be angled to give the rocket a pitch up moment.

 

[Blast it Tom!]

Our old RSO only allowed rockets, no airplanes. Must be a vertical launch, fly straight up with little arc. Must recover safety under adequate chute. No airplane like flights, nothing horizontal, no sky writing. Like NASA, failure was not an option. Prestigious University Engineering standards placed on all, especially Liberal Arts History majors. Strict review, inquisition expected. Those days were hard but fun.

(slight threadjack for humor's sake) - But I thought maybe you'd take your rockets to an RC Airplane field...

 

[KenECoyote]

Is the motor centered with the body tube? It looks offset. Is the thrust line parallel with the body? It looks like it might be angled to give the rocket a pitch up moment.

Great point. On the F104 it's 3D printed motor tube, so maybe @BigMacDaddy can answer?

My Dynastar Foxfire and other winged rockets had the motor centered in the bt.

 

[Daddyisabar]

(slight threadjack for humor's sake) - But I thought maybe you'd take your rockets to an RC Airlane field...

Back in the day I took my newly completed Blackburn Triplane to my buddy's RC club. They thought it was cool but became frightened beyond all means of rational thought when they discovered it was rocket powered with no active control.

It was awesome watching them take off the WWI warbirds with those ridiculously small and ineffective rudders. Major flying skills to even get in the air!

 

[Daddyisabar]

Lopping the clay nose weight to one side of the cone might help a little bit (any help is good,) but canting a motor will make a whole lot more difference...SCARY STUFF. Canted motors rule!

Yes Mr. RSO, asymmetric rocket airplanes are fun!

 

[sr205347d]

If the CG is not on the thrust line, any pitching due to that would be only be apparent during boost. Pitching due to asymmetric drag would be most apparent at max speed, right after motor burnout.

 

[Daddyisabar]

If the CG is not on the thrust line, any pitching due to that would be only be apparent during boost. Pitching due to asymmetric drag would be most apparent at max speed, right after motor burnout.

Any pitching immediately after leaving the rod or rail and things can go horizontal and "airplane" like very quickly...very badly.
Hey guys, did you see the Park Ranger and Sheriff just showed up to see the first flight of your Beech Staggerwing? Cool, Right?

 

[Daddyisabar]

Experience: On the B58 I was going to lop the nose weight on the bottom side of the cockpit cone. But then, after loading the motors and balancing on finger (very hard to do) the CG and LCG were still off the precise mind simmed locations. I also wanted to fly on E motors (before the worst of the CATO batches) and that caused even more fear. 6 X of additional E motor weight on the back end, very bad! So I went with mighty D's to lessen the amount of sin. In the end all the space in the cones was filled with clay and BBs. The windscreen was heavy expoxy clay but the rest of the rear cockpits were super light balsa. Balancing is a bitch. Despirate for recovery room. Trying to mindsim centerline thrust and asymmetric drag. Why? Why does one fly silly airplane rockets?

The F104 makes a great rocket. Old, pre WWII warbirds, not so much.

What silly things can I do to make it work? Who are a few friends that can help in these desperate times? Base drag? Canted thrust? More power and nose weight? GDS? Tractor motors? Kite tails? Gear down? Tungsten nose weight? Spin stabilization? Pop out fins? Rear eject? ...Etc.etc.etc...

By far the most frightening thing on the Hustler was the chrome paint job. Looked nice for a couple weeks before the first launch.

 

[Pem Tech]

Our old RSO only allowed rockets, no airplanes. Must be a vertical launch, fly straight up with little arc. Must recover safety under adequate chute. No airplane like flights, nothing horizontal, no sky writing. Like NASA, failure was not an option. Prestigious University Engineering standards placed on all, especially Liberal Arts History majors. Strict review, inquisition expected. Those days were hard but fun.

View attachment 577100
Yes sir Mr. RSO. The B58 utilizes POOR BOY DUAL DEPLOY from fuselage. One D123 and one D125. Both cones weighted with their own chutes.

Needs about three more chutes...

 

[Daddyisabar]

Needs more about three more chutes...

Total of Eight chutes tighty packed into every nook and cranny of internal space. Typical oddroc: desperate to get as much drag on the descent as possible, twisting and flopping coming down. Cockpit nose cone on seperate chute after poor boy dual deploy. Upon witnessing the launch at Tripoli Colorado the wife of one of the high power Top Men said "Was it supposed to do that?" OH the horror. Parachute duration champions watching cheap Estes chutes tangling with each other and only partially deploying. BUT NO ROD WHIP BABY! It was stable and went straight up like a model rocket should. The down part not so pretty but it worked.

 

[lakeroadster]

.... Upon witnessing the launch at Tripoli Colorado the wife of one of the high power Top Men said "Was it supposed to do that?" ...

And the answer to that is always: "Why, Yes. Yes Indeed... just ask my wife, Morgan Fairchild".

 

[BigMacDaddy]

Great point. On the F104 it's 3D printed motor tube, so maybe @BigMacDaddy can answer?

My Dynastar Foxfire and other winged rockets had the motor centered in the bt.

Very interesting experiments / hypotheses.

Main motor is not canted but is off-center / shifted upwards since the tail is an oblique cone. I thought this would partially offset the tendency of plane-style rockets to arch up due to the tail (I did not really think about the canopy drag effect but have seen something like that in other rockets). In my experience (not a huge sample size due to so many changes in versions), the F-104 rocket arched over the top more with a C5-3 than with a D12-3 but this is without controls for wind or other variables.

F-104 on C5-3

F-104 on D12-3

F-104 w/ D12-5 + 2nd canted A-10 motor (I think it got a little hung up on the rail due to canted A-10 igniting faster than D12)

 

[David Schwantz]

I know it is not a rocket but look at the down thrust on the turbine. This is needed for straight and level flight. I 'm sure yours will act the same.

https://www.bing.com/images/search?...uuQFkmn5sFBDT-Y21e6EwHaEU&vt=0&sim=11&iss=VSI

 

[Daddyisabar]

And the answer to that is always: "Why, Yes. Yes Indeed... just ask my wife, Morgan Fairchild".

Great fantasy but I don't think you could get a classy lady like Morgan out to the old gravel pit and Bison ranch by Hartsel Colorado. Phone into the Broadmoor Hotel in Colorado Springs...maybe.

Just lots of old dudes out there flying asymmetric rockets.

 

[lakeroadster]

Great fantasy but I don't think you could get a classy lady like Morgan out to the old gravel pit and Bison ranch by Hartsel Colorado. Phone into the Broadmoor Hotel in Colorado Springs...maybe.

Just lots of old dudes out there flying asymmetric rockets.
View attachment 577757

That's the joke... she's not there... and she's not you're wife.

 

[Daddyisabar]

That's the joke... she's not there... and she's not you're wife.

I have not seen that sketch for years! But nothing can beat flying your clustered oddroc. "I once flew a three tractor motored Mercury Redstone Capsule...gonna fly a cluster, four Staged Saturn V, yeah that's the ticket!" Thats neither fib nor fantasy!

Aaaah, you like flying unevenly weighted oddrocs do you? NUDGE NUDGE SAY NO MORE!