Experts suspiciously eye LOHAN's cantankerous canards

As ever, we're grateful for our reader experts' feedback on the Low Orbit Helium Assisted Navigator (LOHAN) mission, and today we have a round-up of your comments on the Vulture 2 spaceplane's cantankerous canards. As we reported last month, the aircraft's forewings have finally been tamed, and here they are attached to the …

[Lionel Baden]

Interior Feed

Would it not be sensible to have a interior camera, in case of catastrophic failure / pilot error / Space madness ?

I had asked earlier but i was too late to the comments

[Lester Haines]

Re: Interior Feed

I don't know if we've got room, but we'll look into it.

[Benchops]

Re: Interior Feed

interior camera... we'll look into it... just me?

['s water music]

discrete != discreet

Quietly ridding the world of homonyms one at a time

[phuzz]

Re: discrete != discreet

I'd never realised that they were separate words. Curse you dyslexia! Or damn the English language, or possibly both.

[VinceH]

Re: discrete != discreet

"I'd never realised that they were separate words. Curse you dyslexia! Or damn the English language, or possibly both."

It's easy to remember:

discreet - adjective: Careful and prudent in one's speech or actions, especially in order to keep something confidential or to avoid embarrassment.

Versus:

discrete - verb: To make negative or derogatory comments about a Greek island.

Mine's the one with the dictionary in the pocket.

[JonW]

Canard Loading

SuperTim raises a valid point - where is the Centre of Pressure on that thing? I'm assuming it was modelled to death in the design phase, but 2 things occur to me and I cba to go back through the archives to see if they were addressed:

1. The air's very thin up there. Relative airspeed will be low, so large control deflections will be required to control the vehicle. The force needed to move the control surfaces will be correspondingly reduced, so rather than gear down (as it looks at the moment), I'd consider gearing up. In a previous life, I used to fly pointy things for the Queen; my aerodynamics are a bit rusty now, but I still remember wallowing around at over 40K feet, full throttle with a stupidly high ground speed and being only a few Kts (Indicated) above the stall...

2. That shape of aerofoil is going to result in drastic shifting of the CoP if it moves far, so the pivot point needs to be biased (imo) to the high load / high deflection position.

My 2p

[Lester Haines]

Re: Canard Loading

All valid points, but the design chaps did do the maths and the necessary calculations. Let's see how that works out in practice...

[JonW]

Re: Canard Loading

Given my Math, that's probably a good plan :) You able to log the demanded servo deflections when in flight?

[Lester Haines]

Re: Re: Canard Loading

We should be able to log just about everything for the whole flight.

[Benchops]

> Let's see how that works out in practice...

Oldie but a goodie:

What's the difference between theory and practice?

Well, in theory there is no difference, but...

[toxicdragon]

Re: > Let's see how that works out in practice...

Theory is when you know why something should work but it doesn't, practice is where something works and you don't know why. Where I work we combine both.

[Martin Budden]

Re: > Let's see how that works out in practice...

Where I work we combine both.

It doesn't work and you don't know why? I used to work there too.

[Pookietoo]

Re: the design chaps did do the maths

Including the loading on those bearings?

[Anonymous Coward]

Re: Canard Loading

One thought I had for dealing with the lack of indicated air speed is directed thrust. At least for the boost stage. A bit late now though.

An achievable tweak for reducing the strain on the aircraft body would be to extend the bolts to the middle of the craft and anchor them there. Would be better than nothing.

[Lester Haines]

Re: Re: Canard Loading

Vectored thrust? We've spent god knows how long getting the rocket motor to light without worrying about where the gases are going.

Actually, the idea is sound, if impossible to realise on this scale and within weight constraints.

[Anonymous Coward]

I told you so...

Because no matter how well you plan ahead, there's always something that can, and will, go wrong, and someone will at least partially hinted at it.

[Lester Haines]

Re: I told you so...

Of course. Good to see you got your "I told you so" in early.

[SuperTim]

Re: I told you so...

I personally think that the efforts all have put in have been laudable. I wish I was more local to the project as I would love to have hands-on participation* to this small piece of space history. Kudos to all involved! The I-told-you-so lot may have one or two aspects right, but wrangling all of the technologies required for this groundbreaking project is always going to be tough. You may wind up designing by committee and end up trying to launch an Austin Allegro into orbit.

*I have no formal qualifications to claim any entitlement at all, but an active interest in all things space and 5 years working with delta-canard flight-sim games gives me some perspective at least. Also, I think I could bring much needed Bacon Sandwich expertise to a team that clearly craves it!

[Lester Haines]

Re: Re: I told you so...

The input from all concerned - readers included - has indeed been laudable. Award yourselves beer and bacon sarnies.

[Peter Simpson 1]

Re: I told you so...

^^^ He's AC because his real name is Murphy.

// Capt. Murphy to you

[Camilla Smythe]

In words..

This will probably be too complicated for you to bother trying to implement it...

Mount the canards on two rods that extend almost across the width of the fuselage. Arrange the rods so that one slides inside the other forming its bearing surface. Support the external rod internal to and either side of the fuselage with two mounting posts forming its bearing surface. Leave space either end to thread and glue on some large diameter cogs, teeth on face rather than circumferance. Drive the cogs with motors fitted with worm gears. Loads of support, loads of torque and unlikely to slip about the place.

[Lester Haines]

Re: In words..

"Probably" = "certainly" in this case. It's a cunning plan, though.

[Camilla Smythe]

Re: In words..

You are too kind. The previous cunning plan involving my nostrils was rejected as well. I shall now remove the pencils from my ears and discard this one as well.

[Ugotta B. Kiddingme]

something you probably already thought of...

...but I don't recall reading in the details thus far. It hadn't previously occurred to me but as JonW pointed out, "The air's very thin up there. Relative airspeed will be low, so large control deflections will be required to control the vehicle. The force needed to move the control surfaces will be correspondingly reduced."

Of course, as you descend through ever thicker air, the opposite becomes true. The servos are sufficiently beefy to handle the extra force required, but I am wondering about the deflection. Too little up high or too much down low and you've got a serious control problem. If your receiver can switch to servo half-rate on the fly, then perhaps program that to kick in at a certain altitude. Seems to me that would be the simplest way to deal with changing requirements during descent. If your current receiver can't switch servo rates in flight, then it should be simple and relatively inexpensive to replace the receiver.

If you've already thought of and/or resolved this, then I withdraw my suggestion and will return to admiring your progress from a safe drinking distance. In any case, smashing job thus far and best of luck.

[Lester Haines]

Re: something you probably already thought of...

The servo deflection issue is on our list. We know the specified max/min deflection angles for various altitudes as per the design calculations.

It's a matter for the Pixhawk, whose mighty brain is about to be probed and tweaked by an international team of experts. Details in due course...

[Johndoe888]

I don't like the pivot point, I would rather see approx 25% of the canard area in front of the pivot point for aerodynamic balancing. Where the pivot point actually is and the moment arm of the canards equals a very high load on the servo :(

I know your stuck with what you have, but I would rather have the pivot on axis with the canards at 25% of cord.

No plan can be cunning unless it involves a Turnip :)

Why no turnip icon ?

[VeganVegan]

Will you be using asymmetric canard control?

If not, and the canards deflect in parallel, then in your current setup, you can still tie the two sides together to alleviate the torque loads. Maybe it's as simple as connecting them using a rod with both ends threaded, threading the ends into your existing "A" lock nuts on either side. In he same vein, you could perhaps tie the pushrods together as well.

If your control circuitry is fancy enough to use asymmetric (independent) canard movements, then please ignore the above.

[Lester Haines]

Re: Will you be using asymmetric canard control?

We do have asymmetric canard control, hence the two servos.

[Faye B]

Re: Will you be using asymmetric canard control?

I think he meant asymmetric as in a canard will deflect more in one direction than the other. You may find that you need more control in one direction than the other with canards. Especially swept wing ones.

[Lester Haines]

Re: Re: Will you be using asymmetric canard control?

Aha, I see. Well, they go up and they go down, independently.

[cortland]

It's done, then?

And that's your base canard, right? (ducking)

[Faye B]

Give us a lift

I think the pivot point may be correct as it looks like it is just forward of the centre of lift, which will provide better control stability. Air pressure will sort out the canard travel problem (i.e. it will be easy at high altitudes giving full swing, and reduced at low altitude by drag). The bearings do look a bit weak though but I assume you are not going to try and pull some high G acrobatics while flying it so it should stand it for one flight.

[Faye B]

Test flights

I still think you should give it a few test flights by gliding it down a slope. Find a nice soft meadow on a hill and hand launch it. Even a short flight will give you an idea of how the controls are going to respond.