Miscellaneous questions

[dynamite dean]

I do hope someone can aid me with the following questions....

1. What is so special about canards? having a dicussion with a student about these and if there are so good why don't they fit them to more aircraft?

2. I know what a MLS is and a GPS but how do I answer this question..."what are the advantages of a MLS over a GPS - I'm puzzled any takers?

3.I have a sim ride coming up soon in a jet and am trying to source a simple crew briefing ; I am only a piston pilot at present so I am not used to icluding terms V1 Vr V2 in my patter - could someone suggest a SIMPLE punchy crew brief what airline pilots say - thanks dynamite:)

[Fresca]

1. The vertical stabilisers produce negative lift, that is they are basically inverted wing. What this means is that the lift the wing has to produce must be equal to the weight of the aircraft (in unacelerated flight) + the negative lift of the stabiliser.

The canard however produces positive lift and therefore the wing does not have to porduce as much lift.

Canard is also helpful in stalls, because it can be made to stall before the wing, the aircraft then drops it's nose and picks up speed again.

2. Don't know much about MLS exsept I know it i aproved for precission approaches which the GPS isn't at the moment. It works very like an ILS.

3. Not sure what you are asking here. Can you be more specific?

[Dave Incognito]

As mentioned above MLS is a precision approach aid (azimuth & glideslope) whereas GPS approaches are currently non-precision (azimuth guidance only).

The biggest advantages with a MLS is that it allows curved approaches as well as a wide range of glide slopes.

[Mad (Flt) Scientist]

Why don't all aircraft have them? Well they're noisy, they make a hell of a mess, quack all the time,...:)

Stupid remarks aside, the benefits of canards are not as cut and dried as Fresca states. There are a number of factors which reduce their attractiveness:

1. Canard produces lift, while h-stab produces "anti-lift" i.e. downforce.
True up to a point, but of course the ideal situation for cruise is no trim lift force at all, because the wing is the most efficient lifting surface. And there's no reason why I can't have true lift on the aft surface, if I'm prepared to consider active controls (to cope with aft c.g. movement), which are common on canards of a certain kind anyway. Even without active controls I may have an aft enough c.g. that the h-stab generates lift.

2. Canard behaviour in stalls/high lift regime. Well, here we certainly see a down force on the aft surface, so the h-stab is losing lift, while the canard is adding lift. Unfortunately, the surfaces do not act in isolation. All the lift generated by the canard (or any other surface) will manifest as downwash; this will reduce the effective angle of attack on any further aft surfaces, which will reduce lift. Additionally, this downwash field will be concentrated over the inboard wing, assuming it's a canard-wing configuration and not two wings, and so either you have to account for significant variation in the flow between inboard and outboard wings, or accept a non-optimal flow for the wing. The whole canard/wing interference can seriously mess with the apparent trim lift gains of the canard configuration.

Regarding the pitching moment behaviour - the same can be achieved through good wing design and/or systems devices.

One thing canards are good for is flexibility in placing surfaces around the aircraft. If the aerodynmaic effect for lift is neutral, then I can choose the configuration which is better for drag. Canards, especially canard-deltas, lend themselves naturally to a good area distribution, while the aft-tailed configuration struggles to achieve as good results. That's an important consideration for the European latest generation fighters.

Basically canards are just another configuration; there are benefits and disadvantages to them (just as with things like FSW). Some design requirements are best met by them, some are not.

[*Lancer*]

MLS will not have the advantage for long...

GPS is presently being evaluated to CAT III Autoland standards with complete curved lateral and vertical guidance. The ground augmentation required is vastly cheaper than an ILS or MLS, and very little additions (if any) are needed in the cockpit.

Within 10 years it will allow CAT III Precision Approaches to almost any airport!

Lancer

[flyingdream]

Dynamite

Just wait a little while and I will try to provide you with a briefing.

fd

[Miserlou]

A common misconception but, although most conventional aircraft have negative lift, ie downforce, at the tail, this is not a requirement.
The canard configuration is a lifting tail taken to it's logical extreme .

Our briefing goes something like this:-

"This will be a left/right seat take-off with weight at xxxkgs, speeds set V1-x, Vr-y, V2-z.

Any failures before V1, either crew member state the failure and (Captain) will decide to stop or continue.

Departure is Bla bla 2c that way, this way (waypoints or radials) climbing (cleared level) with minimum rate (if specified (noise abatement procedure)).

Failure after V1 check max power (perhaps uptrim + autofeather on a turboprop) and in case of fire silence the Master Warning.

Otherwise, no action below acceleration at (4-500'agl) except on (Your or my) command. (Captain has the last say).

Contingency procedure, perhaps and/or obstacles in departure area.

Any questions?"

There's a start for you.

[Onan the Clumsy]

what are the advantages of a MLS over a GPS

You can cook a TV dinner on the approach with an MLS - but you'd better not have to go around or it might get overdone.:p

Sorry I don't have any real answers, but I think at least part of airplane design is still marketing. Some prospective buyers are used to seeing certain configurations and would be worried by radical designs, whereas others are looking specifically for such things.

I've seen a 182 with canards and it looked really odd.

[m&v]

years ago the industry was offered the option of MLS as an answer to freq'congestion,fm interference and installation (terrain)concerns .It had been developed for the military,and was free of interfernce.Several installations around the country(Canada) proved their potential in Mountainous areas
UNfortunately the transition to MLS usage required the industry to equipe their fleets with both.side by side,until the whole of the industry was converted.Alongside this was the main selling point of cost(the MLS was to be far less than the ILS installation)this did not prove to be the case.So the industry retained ILS(with FM shielding) to the CAT3 standard that you see today.with the US gov' releasing the use of GPS to the industry,MLS was forgotten(several installations remain in the US)...:rolleyes:

[RadarContact]

The main advantage of the MLS over GPS is, as for the ILS, that it's ground based.
So the nearer you get to the transmitter (i.e. ground), the more accurate the signal and thus your guidance becomes. This is specifically not true for GPS.
Plus, there still ist the (substantial?) fear of a global NAV-System being controlled by one single government, which can anytime switch it of at will.