Pivot point...
I think I would have placed it further back on the canard to reduce the force required to operate the canards under full aerodynamic stress. But that's just me....
LOHAN in FIGHT to DEATH with brace of cantankerous canards
Our plucky Playmonaut is back in his seat in the Vulture 2 spaceplane following the recent servo meltdown which had prompted his rapid exit from the vehicle. The miniature emergency required a servo swap-out, and while we were about it, we decided to upgrade the linkages to the canards, and bolt the cantankerous forewings to …
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Friday 20th June 2014 10:59 GMT SuperTim
Re: Pivot point...
It is quite far forward of the centre of aerodynamic force at the moment, meaning you need to really press hard to deflect it in the air stream. moving it back a bit will make that easier. Move the pivot too far back and you actively have to manage the canard to keep it where it is as the air flow will try and force the canard to one extreme or the other. I think it should go back a bit to ease the strain on the servo, but still maintain enough force for the canard to self level back to the neutral point should the link snap.
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Friday 20th June 2014 17:19 GMT G R Goslin
Re: Pivot point...
A couple of points. The canard will not return to a neutral point if a link snaps. It will move to a point of least drag, relative to the direction the rest of the aircaft is travelling. Of course the two will vey quickly be the same as the craft goes into a vertical dive. The second point relates to the wing bushes. They are far too short. Length over diameter is the rule for shaft bearings. Or you could have fitted three bushes. One in the centre of the craft and common to both canards and one adjacent to each wing root. If these two bushes were internally threaded , to fit the threaded shaft, the end location of the wing would have been achieved without binding or looseness.You simply arrange that at the maximum deflection of the wing, there is still an air gap between it and the fuselage. The small increase in air gap at the other extreme is insignificant. So no rubbing of the wing against the fuselage. Even under stress
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Friday 20th June 2014 08:12 GMT Michael H.F. Wilkinson
Teflon is just wonderful stuff
I have used it so often in building telescope mounts, and it just gives a thrill to see things suddenly move smoothly, without wobble or stiction. Not surprised it got the canards sorted. Smoke from servos and sticky canards don't mix, unlike smoke from apple wood and marinated magret de canard.
\
Darn, hunrgy now
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Friday 20th June 2014 10:10 GMT imanidiot
Threadlocker
I hope you have used it on those grub screws. Those tiny little screws tend to easily shake loose, allowing the rod to slide. Which will probabably put you into a spin pretty fast.
PS: Something I just thought of, since this already a project of epic proportions with massive amounts of gadget-o-gasms and it will be known where LOHAN comes down. How about filming the launch and landing from the air with one of them quad/hex/octo-copters? That should give some pretty cool footage.
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Friday 20th June 2014 13:34 GMT Holtsmark
Re: Threadlocker
Looking at the way the canards are fixed to the fuselage, I am a bit worried about how the forces from the canards are introduced into the aircraft structure. At the very least, a lifting force will introduce severely increased friction loads on the surfaces that work as glide bearings.
If you were to introduce a shaft that could transfer bending moments (but not torque) from the right canard to the left canard, then the bearings would only have to deal with the lift generated by the canards, and not the bending loads (Assuming both canards are moved in the same direction). If the canards are used as ailerons, then the bending loads would be reduced by a factor close to 10 (using the width of the fuselage rather than the width of one glide bearing sleeve to offload the canard..
oh.. and IAAAE :P
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Friday 20th June 2014 10:46 GMT dsdetective
Sorry if I missed this in a previous update, but have you guys thought about centre of gravity? It's no good having working control surfaces if the aircraft is massively tail heavy (was looking at pic with all those batteries in the back). The COG ideally needs to be at the point of lift from the wings so that the control surfaces are just pivoting around it. Unless of course you're deliberately making it "relaxed stability" like the Eurofighter for maximum turn-and-burn performance?!
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Friday 20th June 2014 16:32 GMT WalterAlter
Re: Lockdown
If weight saving is an issue, wondering why steel washers and nuts when aluminum or nylon would do. What sorts of hideous forces do you expect to have ripping this RC apart other than acceleration when the rocket motor smokes the tires?
Will LOHAN plummet to earth like a cormorant after a mid afternoon snack or do you plan a spiraling descent?
Are you expecting vicious cross winds or strange unaccountable up and down wind shears that might flip the intrepid craft on its back? Is you ground pilot prepared for such?
What sorts of launch time weather data will you be accessing? Might you launch your own weather balloon before LOHAN to get the straight and immediate skinny on LOCAL atmospherics?
If this has all been sorted in previous conversations then curse me for a novice.
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Friday 20th June 2014 16:40 GMT Lester Haines
Re: Re: Lockdown
Weight is an issue - without getting too excessive. The Vulture's got to have a bit of healthy mass (optimum already calculated, and we're prtty well right on the button), otherwise it'll just get blown around.
A spiralling descent is the plan, by autopilot control. The actual path depends on where the plane lucnhes in relation to the return point.
We use flight prediction to work out the balloon track. That pretty accurately shows the wind conditions at altitude. We'll have other resources available to complement that information.
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Friday 20th June 2014 22:23 GMT WalterAlter
Re: Lockdown
>>A spiralling descent is the plan, by autopilot control. The actual path depends on where the plane lucnhes in relation to the return point.
Mkay, but read up on inverted spin recovery and such. What speeds will be attained during rocket launch? Have you done wind tunnel testing at expected speeds vs. air density, etc.? If turbulence is periodic up there, you may get amplifying pendulum motion and loss of laminar flow. How fast does your autopilot react, hundredths of a second? But I'm chiming with my usual day late, dollar short methodology.
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Sunday 22nd June 2014 04:27 GMT Don Jefe
Re: Lockdown
For small fasteners it's pretty much impossible to top cyanoacrylate (CA) glue for thread locking purposes. Specialty liquid thread locking products are perfectly fine, but CA delivers the same benefits plus you can glue stuff together with it and use it anywhere you'd use a bandaid for minor first aid purposes as well as harmless but annoying ouchies like hangnails, cigarette burns, small stab wounds and paper cuts.
Liquid thread lock acts as a wedge that prevents fasteners from moving around due to vibration. CA does the same thing but it also bonds to the fastener and any parts the fastener threads into, which most safe for garage rocket project thread lockers don't do (the ones that do are actually CA's, but that's often not printed on the container). The CA family of adhesives also greatly outperform regular liquid thread lockers in their capillary action; the stuff really gets into every possible bit of open space. CA has very low sheer strength as well, so the fasteners are easy to remove without damaging the engagement surfaces of the fastener (just clean the parts if you have to take them apart).
The CA's have a proven track record in extreme demand applications. We use them in the multimillion dollar machines we build for manufacturing and CA is basically what holds satellites and F1 cars together. It's great stuff, and it's dirt cheap.
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Sunday 22nd June 2014 18:52 GMT Don Jefe
Re: Lockdown
Here in the US the stuff from BSI (Bob Smith Industries, yes, that's really the name) is the dominant provider for non-industrial CA. There's no difference between the consumer and commercial products other than the packaging. The BSI stuff comes in small bottles with consumer tolerant lids and applicator nozzle. The commercial stuff comes in everything from 1-pint bottles to 53' tanker trailer sizes. The stuff is somewhat age sensitive, so it's a waste to buy large quantities unless you're using huge quantities.
The 1oz bottle has enough glue to put on every fastener in the craft and will leave you with enough glue to encase the pilot in a crystal coffin as a memorial to his bravery tshould something unfortunate happen and you're able to recover his body. Like Lenin, but with 100% less Commie.
Either of the 'Insta-Cure' products (link below) are perfectly acceptable, but I like the Insta-Cure+ as it's a bit thicker and less likely to get where you don't want it.
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Saturday 21st June 2014 08:21 GMT Morrie Wyatt
Alternate control method.
From the "makes sense to me" school of engineering, I would probably have opted to use the pivot purely as a pivot point, and moved the control horn forward of backward along the canard through a suitably sized slot in the body. Drive the system via an L shaped link to convert the horizontal movement of the servo control movement to a vertical movement of the control arm of the canard protruding through the slot. This would take the control torque away from the threaded rod of the pivot.
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Saturday 21st June 2014 09:04 GMT Markus Imhof
Re: Alternate control method.
_That_ was what was bothering me with this setup. Locking nuts, high performance glue, massive linkages - all well and good, but in the end, you still got a round hole on a round bolt trying to transfer torque. In most R/C applications I've seen so far where torque is actually an issue, you either use a flattened bolt with a respectively shaped hole or, if torque really is an issue, the round hole with the round bolt for the bearing and a steering horn somewhere else on the outside of the control surface to transfer the torque.
As for the twisting, warping and subsequently blocking under load: yes, same fears here. If you can do a test flight (or even better a wind tunnel test - might ask your university chaps) under close-to-real conditions to see whether the canards will still work under high speed wind load, then for the better. But it's still not too late to change your setup:
- push a full length tube through the hull instead of those two small bearings
- cut out maybe 10 mm in the middle after securing the tube basically everywhere else
- push through the canard axles and secure with a retaining ring (will need some rework on the canards, maybe even a new set of canards at the most)
- screw a rudder horn on the canard (I'd suggest upside near the trailing edge)
- cut a slot for the linkage into the fuselage
Of course, this will make the pilot's compartment somewhat drafty.
Oh, and in hindsight, a nylon or ptfe washer around the axle would probably have worked as well as the full size coating.
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Saturday 21st June 2014 19:54 GMT Bronek Kozicki
Re: Alternate control method.
Ah yes, there is distinct lack of bearings around the axle mounting the wing. However, given the temperature in which this has to function (some -60 Celsius) I am not sure that this is a bad thing. Low temperature grease is the most important thing here, and forcing it inside bearings (to avoid any trace of water which would freeze) might be difficult.
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Saturday 21st June 2014 22:28 GMT PC Paul
Has anyone ever heard of the KISS principle
It's nice to see all the gadgetry on show and the details of the engineering decisions, but it also feels like the KISS principle went out of the window a long time ago.
There are lots of things in this project that would make a substantial research task for an experienced hobbyist on their own.. I just hope it all works out in the end.
When is the end anyway? Is there a planned launch date?
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