Newbe question Are any Canards suitable for Grass fields ?

[saabpilot]

Sorry for the dumb newbe question.

I quite like the idea of my own canard but i fly mostly to grass airfields.

[Jon Matcho]

Not a dumb question, but one typically answered with "no".

 

However, there is the Bateleur from www.rmtaviation.com, which is promoted as being able to fly from unimproved strips.

 

 

Steve Wright designed his StaggerEZ the option to fly from grass strips as well, but that's a one-off design and not available as a kit.

 

Reasons against are:

• The pusher configuration exerts a nose-down force
• The grass further compounds the issue, hindering the nose from lifting
• The nose gear and/or main landing gear can throw "stuff" into the propellor
• Canards generally require higher speeds and longer takeoff and landing rolls

So again, in general, canards are not a good match for unimproved runways. Professionally maintained golfing fairways is another story.

[saabpilot]

Thank you Jon

for a quick reply.

steve's bird looks nice and i hope he gets the remaining bug ironed out soon.

My local "field" is a CAA licenced grass areodrome aka ex WW2 so its not a unmaintained grass stip.

Same cos i think the Cozy is cute. The tandum Bateleur may be my best hope, they say it can land on a beach -wow ! (if it ever gets approved in the Euro/JAR world) and (if the dynosaurs in the PFA actually pass it for flying in the UK). I think it only took them about 5yrs to do the Cozy4, as a 2 seater only.

An EAA in the UK would scare the pants off the autorities here, although i and many many others would welcome it. Some are trying to get very small light UL's deregulated but that another story.

[Nathan Gifford]

I think whatever pusher aircraft you select, debris in the prop is going to be a problem. Further the standard techniques for rough field departure and landings puts the prop more in harm's way. Still I have read several posts from Cozy and EZ pilots that perform flight ops from good soft strips.

 

The other issue are the higher takeoff and landing speeds.

 

As far as 2-seat versions of the Cozy go, no problem. It means you can haul a helluva lot of baggage. That's the way a lot of people fly the plane anyway.

[kumaros]

snipped ...

The tandum Bateleur may be my best hope, they say it can land on a beach -wow ! (if it ever gets approved in the Euro/JAR world) and (if the dynosaurs in the PFA actually pass it for flying in the UK). I think it only took them about 5yrs to do the Cozy4, as a 2 seater only.

snipped...

 

The Bateleur is also available as a kit built experimental. If you think this is the plane for you, try contacting the factory. Their site mentions various versions available or planned: UL, VL, LSA, Experimental etc. Find out what suits your needs best.

Kumaros

It's all Greek to me

[saabpilot]

Thanks Kumaros

 

but untill the manufacturer can get the plane appoved for use in the UK I would never be allowed to fly it here .

even then i would have to put in a few hours approved instuction before being able to solo it. - but the plane is new and i've still got to get my hours up for my NPPL so maybe next year or the year after.

[H.Zwakenberg]

Reasons against are:

 

The pusher configuration exerts a nose-down force

 

I've heard this argument before, but consider this:

 

Any prop with a thrust line above the landing wheels axis excerts a nose down force. Since this definition might very well include all prop aircraft (exceptions anyone ? ) it's most likely reasonable to claim that all propeller configurations excert a nose down force on the nose gear...

 

Now, what is true, is that pusher configs very often have somewhat higher thrustlines, which is causing a somewhat higher moment around the main gear axis, which in return results in a somewhat higher down force on the nose gear.

 

bye

Hans

[H.Zwakenberg]

I think whatever pusher aircraft you select, debris in the prop is going to be a problem.

This is not a problem with Bataleur, as the prop turns above the main wing in front of the main wing's trailing edge. It's pretty well protected up there.

 

bye

Hans

[Jon Matcho]

This is not a problem with Bataleur, as the prop turns above the main wing in front of the main wing's trailing edge. It's pretty well protected up there.

Hans, yes, that would do it, but looking at their Web site, you can see pictures where the prop is behind and below the main wing's trailing edge. I wrote to them about it, and got a response that they only have one model, and then asked a question about the different pictures and haven't received a response. I gave up my research after that, so if you know anything I don't, please share.

[H.Zwakenberg]

Hans, yes, that would do it, but looking at their Web site, you can see pictures where the prop is behind and below the main wing's trailing edge. I wrote to them about it, and got a response that they only have one model, and then asked a question about the different pictures and haven't received a response. I gave up my research after that, so if you know anything I don't, please share.

 

Hi Jon,

 

please check out this picture of Bataleur dismantled on a trailer:

 

 

also see this picture, showing Bataleur from the side:

 

 

Notice that the propeller plane is in front of the trailing edge of the main wing (which, by the looks of it, sports a NACA 23112 similar section....).

I do admire the compactness of the trailerable Bataleur a lot.

 

take care,

Hans

[Jon Matcho]

It certainly is a nice looking plane and design, but how about the 2nd picture down on the right of this page. It appears that the prop is behind and below the trailing edge.

 

http://www.rmtaviation.com/manufacture.html

 

[kumaros]

I have the Flieger Magazin January 2001 issue with an extensive report on the Bateleur and several big and detailed photos. The prop is definitely above the delta wing and is totally protected by it from flying object damage.

Kumaros

It's all Greek to me

[H.Zwakenberg]

Hi Kumaros,

 

somewhere in one of those many cardboard boxes that didn't get emptied just yet (I moved mid August....) I have that same issue.

 

On three occasions, I've tried to get some more information about this design, once per mail, twice on some webform on that site. No joy on either of the three.

 

Marketing this design seems to be stone dead, at least, that's my perspective on it. Also note that no further articles appeared in a German magazine since the one you're referencing: not in Aerokurier, no follow up in Flieger Magazine, nothing. Until new info comes up, I consider Bataleur dead...

 

bye

Hans

[deuskid]

I've heard this argument before, but consider this:

 

Any prop with a thrust line above the landing wheels axis excerts a nose down force. Since this definition might very well include all prop aircraft (exceptions anyone ? ) it's most likely reasonable to claim that all propeller configurations excert a nose down force on the nose gear...

 

Now, what is true, is that pusher configs very often have somewhat higher thrustlines, which is causing a somewhat higher moment around the main gear axis, which in return results in a somewhat higher down force on the nose gear.

 

bye

Hans

 

I'm as dumb as a rock newbie... but would this not be true of a tail dragger? The engine would be 'lifing' away from the field not 'driving' down into the field.

 

The one additional item I wished a canard could do was use unimproved fields. The little bit of research I've been able to accomplish indicates that even tricycle gear BD-4s have more problems [and unless 'modified' can't use grass fields] unlike trail draggers.

 

Merry Christmas,

 

John

[Jon Matcho]

Wow, I just learned something. I couldn't believe Hans' statement until I drew up a simple vector diagram on a napkin. I'm now convinced that pushers exert no more nose-down force than tractors (both with 0 degree thrust lines).

 

However, as John points out, tail draggers are different. They still exert some nose-down force, but not as much since the thrust line is NOT at 0 degrees. That changes when the tail lifts up, but at that point flight will soon happen.

 

Thanks for the enlightenment.

[deuskid]

Wow, I just learned something. I couldn't believe Hans' statement until I drew up a simple vector diagram on a napkin. I'm now convinced that pushers exert no more nose-down force than tractors (both with 0 degree thrust lines).

 

However, as John points out, tail draggers are different. They still exert some nose-down force, but not as much since the thrust line is NOT at 0 degrees. That changes when the tail lifts up, but at that point flight will soon happen.

 

Thanks for the enlightenment.

 

wouldn't the debris problem still be greater for a pusher than a tractor tho?

[Jon Matcho]

wouldn't the debris problem still be greater for a pusher than a tractor tho?

Only for those pushers that (a) have their props exposed to potential debris, and (b) have wheels in front of the prop (most all canards). The Bateleur seems to have this figured out.

 

Marketing this design seems to be stone dead, at least, that's my perspective on it. Also note that no further articles appeared in a German magazine since the one you're referencing: not in Aerokurier, no follow up in Flieger Magazine, nothing. Until new info comes up, I consider Bataleur dead...

Given that I managed to exchange e-mails with Andre von Shoenenbeck, their CEO, two weeks ago, I certainly wouldn't consider them 'dead'. Sure, not marketing enough, but let's not kill them before they've had a chance -- I would love to see one of these at a fly-in here in the U.S.

[cncdoc]

Hi Guys! (and Gals)

 

The main drawback IMHO to grass field / soft field operations with a canard design such as the Rutan derived ones, is more of a wing shape issue. The wings are designed for high speed operation with little drag whereas the aircraft design with the wing that gets greater lift at lower speeds does not allow for higher speeds because of the drag associated with that shape. The way to get around the "cake and eat it too" is to change the shape of the wing during flight (flaps, slots, etc.). This works well but doesn't come stock with many (if any) canard designs for amatuer building.

In any case, the drag from the wheels has to be overcome to produce speed (drag from the air and other things) and then speed produces lift at which point the wheels' drag decreases until it isn't a factor, either in the overturning moment or the speed resisting drag of friction.

Herein lies the rub Tractor aircraft has better leverage from the lifting standpoint. The thrust only has to be used to provide flow for one lifting surface to overcome drag. The canard design has to provide sufficient flow for two lifting bodies. The secondary lifting body (canard) is in the same rotational plane as the drag from the landing wheels and once relative wind exceeds the canard's optimal lift angle in either direction, it becomes a weather vane until it is again placed in the "sweet spot" a feat which is almost impossible. The lift from the canard is necessary but has to be matched to the wing. If the main wing lifted before the canard, it would scoot along until it ran out of runway. Too much lift and it would wheelie until something got scraped off

An elevator in conventional aircraft works with gravity during take off and takes advantage of the relative wind in angling the prop (and the main lifting body) lessening the wheel friction drag which increases speed, so, (although the wing faces higher angle of incidence) the thrust stays aligned with the wing angle and the pressure on the upper side of the wing continues to lower (producing more lift)). The canard has to patiently wait intil VR to overcome wheel friction entirely, as the canard has to lift the weight of the aircraft from the center of balance forward and wait until the main lifting body overcomes all of the other drag.

The wheel drag on a grass strip is much greater than a solid surface strip. To attempt to get an idea of the difference, ride a bicycle on the street. Now, ride it on your lawn.

Although the drag on both aircraft lessens as it approaches VR, the tractor type, especially tail-draggers, will lessen the drag of the wheels more efficiently and more quickly than it's canardian cousin.

The issue of prop debris can be lessened by altering the gear to a wider stance and taking off with the belly board down.

I am going to use taller than normal wheels which should cut down drag a little.

 

My 2 cents worth...

[Marc Zeitlin]

Where to start.......

 

The main drawback IMHO to grass field / soft field operations with a canard design such as the Rutan derived ones, is more of a wing shape issue.

Not so much. As we've discussed before, The biggest problem with Rutan derivative canard aircraft operating from soft fields is the geometry/deflection of the nose gear due to drag on the small nose wheel. You allude to this somewhat below, but you miss the point that this is the single largest issue.

 

Landing on grass/soft fields is not much of a problem, as long as they're smooth, but takeoffs are a big problem due to nose-down deflection of the nose gear.

 

The wings are designed for high speed operation .....

This is a very minor issue WRT operating from soft fields. Short fields are a different issue, but that's not what you're addressing.

 

Tractor aircraft has better leverage from the lifting standpoint......

As an Aeronautical Engineer, I tried real hard to figure out what you're attempting to say here, but I failed. It makes no sense to me whatsoever.

 

An elevator in conventional aircraft works with gravity ......

Hmmm, same issue as above - no clue what you're on about.

 

The wheel drag on a grass strip is much greater than a solid surface strip.

Now THAT'S true, especially on the nose wheel, since it's so small, and it's the single largest reason for problems with soft fields, as I mentioned previously.

 

Although the drag on both aircraft lessens as it approaches VR, the tractor type, especially tail-draggers, will lessen the drag of the wheels more efficiently and more quickly than it's canardian cousin.

Actually, it has little to do with where the propeller is, and more to do with the ground incidence angles and nose wheel geometry. It would be easy to design a canard aircraft that sat with a 10 degree nose up incidence angle, and had nose gear that didn't REDUCE the incidence angle as drag was applied to the nose wheel. But there would be other problems, such as a VERY long nose strut, and poor prop clearance (or very tall main gear, as well). But IF the canard aircraft were built that way, it would perform about as well as the tractor/taildragger aircraft.

[saabpilot]

Thank you all.

For a very interesting set of answers and questions.

It would appear that this thread has started ot take on a life of its own. hayho thats what forums are about.

 

Hi Jon

I took on board the comment about pushers applying a downward presure on the noise wheel and did like you, i did a simple force vector diagram and i can see the point; that the rear wheels would act as the fulcum point so any force behind that point would apply a turning moment at the nose end, thus forcing the nose down harder than if the nose was being pulled (ie tractor arrangement). In that model the nose wheel would act as a falcrum point and the turning moment whould apply less presure to the rear wheels relative to the nose, but the nose would not dig-in as its being pulled.

however now i'm

[cncdoc]

Thanks Marc,

I was mainly trying to point out the weight and balance issues of the different type of aircraft during take off roll. The tractor with tricycle gear can take advantage of a change in the AOA of the main wing during takeoff run that the canard can't and can use flaps. The thrust angle from the prop also can change to pull up as well as forward in tractor type aircraft although taildraggers actually change from an angled to a parallel thrust during the latter part of take off roll (except in short/soft field take off). The canard wing AOA doesn't change much if at all leaving the drag high until the canard can provide lift sufficient to pull up the aircraft in front of CG or rotates the axis around the main wheels lifting the nose wheel as well.

Since there aren't any (plans) flaps, there isn't much lift from the main wings at slower speeds, so any ground effect in conjuction with the packing effect from a higher AOA would be minimized whereas the tractor type especially low wing with flaps can take advantage of this to take more weight off of the wheels, and this from a slower speed than the canard wing will begin to lift weight from it's wheels (all 3 since the nose wheel will still be in contact with the ground). This is a sizeable advantage during take off roll in soft field.

Also (more "leverage") the elevator has more authority than the canard. It doesn't "stall" as easily as the canard if run to it's limits during ground roll and is more effective at slower than flying speeds.

 

In soft field and short field, it's all about getting off the ground sooner.

 

Short field: To get into the air to lessen drag to build up speed to fly/climb/fly over obstacles.

 

Soft field: To get into the air sooner to lessen drag to build up speed to reach flying speed.

 

There isn't a "get into the air sooner" option for canards. Yet. Unless the air brake helps to lift at slow speeds.

 

Does that make more sense?

[Jon Matcho]

...thus forcing the nose down harder than if the nose was being pulled (ie tractor arrangement).

It's been a while, and I'm not the best with this, but here's where I think your thinking is off. A pulling force is the SAME as a pushing force on a beam (the fuselage, and baring tensile strength; assuming a "perfect beam").

 

Not that this particular discussion really matters to the subject at hand though. Marc pointed out that the real issue with Rutan canard derivatives is the nose wheel geometry, which does not fair well in grass.

 

Other canards, such as the Velocity, have different nose wheels, but the Velocity is also not recommended for grass fields.

[H.Zwakenberg]

Only for those pushers that (a) have their props exposed to potential debris, and (b) have wheels in front of the prop (most all canards). The Bateleur seems to have this figured out.

 

Given that I managed to exchange e-mails with Andre von Shoenenbeck, their CEO, two weeks ago, I certainly wouldn't consider them 'dead'. Sure, not marketing enough, but let's not kill them before they've had a chance -- I would love to see one of these at a fly-in here in the U.S.

I've tried to get in contact with them on a number of occasions, through their web feedback form. None of those attempts was succesful... However, like you, I'd like to see them spread...

 

bye

Hans