Nose weight - how much is too much

[Ken Culbertson]

I have been slowly moving the CG forward on my Canard.  As I learn more about it I am finding that the plane really flys better nose heavy.  The plane has about 100 flights on it now and the more I fly it the more I like it.  It is large - 710sq" and has a 175sq" stab and 50 sq" Canard which I am told adds to the wing area for our purposes.  It started life at 66oz which is not bad for that area but as I have been creeping the CG forward I am now up to 71 oz.  So far there are no issues with stalling anywhere in the pattern with F2B like corners but, with 5oz of lead in the nose it still wants to float on landing.  What are the signs that adding more weight to get a better CG is going in the wrong direction.

Ken

[Dan McEntee]

  For that airplane and it's configuration, I would say you are on your own here!! Usually too much nose weight results in a vary slow, wider radius turn, especially in a wing over or square corner. Just keep following your nose and flying different set ups. I think the model will tell you.

[Paul Walker]

Too much stick force...

[Ken Culbertson]

Too much stick force...

Good point.  Then I guess I am not quite there.  The Canard really reduces stick force.  Maybe that is why I am able to hold a tight corner even as the CG moves forward.  I should be moving the leadouts forward.

Ken 

[Paul Taylor]

Is there a picture of this plane?

[Perry Rose]

For me too much nose weight is when the nose drops when the engine stops. Canards are a different duck all together.

Pun intended.

[john e. holliday]

Yes canards are a different breed of plane.  I have had two real canards.   One I still have has moving elevators on trailing edge of the wing and landing gear forward more than normal plane as it wants to nose over on take off until some speed is obtained.  The one that I crashed because the LA 25 decided to be a speed engine had no moving elevator.   The wheels were as far forward as I could get them   They were ahead of the prop like in very early days of rat racing.  The balance point on both were well ahead of the leading edge of the wing.  Both planes would do the pattern if every thing was right.   Both needed a decent pilot.

[EricV]

I have been slowly moving the CG forward on my Canard.  As I learn more about it I am finding that the plane really flys better nose heavy.  The plane has about 100 flights on it now and the more I fly it the more I like it.  It is large - 710sq" and has a 175sq" stab and 50 sq" Canard which I am told adds to the wing area for our purposes.  It started life at 66oz which is not bad for that area but as I have been creeping the CG forward I am now up to 71 oz.  So far there are no issues with stalling anywhere in the pattern with F2B like corners but, with 5oz of lead in the nose it still wants to float on landing.  What are the signs that adding more weight to get a better CG is going in the wrong direction.

Ken

Just be glad you didn't scale down a Kyūshū J7W Shinden with a rear engine pusher setup. An old buddy did that with an LA46. By the time he was done trimming he had a solid lead plate in the nose that weighted more than the weight of the engine (LA46). Even at that, it was only capable of scale-like flight, not a pattern capable ship. 
EricV

[Ken Culbertson]

Yes canards are a different breed of plane.  I have had two real canards.   One I still have has moving elevators on trailing edge of the wing and landing gear forward more than normal plane as it wants to nose over on take off until some speed is obtained.  The one that I crashed because the LA 25 decided to be a speed engine had no moving elevator.   The wheels were as far forward as I could get them   They were ahead of the prop like in very early days of rat racing.  The balance point on both were well ahead of the leading edge of the wing.  Both planes would do the pattern if every thing was right.   Both needed a decent pilot.

Good to know.  I am starting to believe that the Canard has as much, if not more, affect than the elevator.  Maybe I am as far forward as I need to be and I just need to learn how to land it.  Watching a 70oz plane float for a half a lap in the ground effect is hilarious.

Ken

[Dave_Trible]

Ken I've never worked with a canard except in 1/2A as a kid but my thinking is that by the time you get enough nose weight on the plane to tame the landing float it will be too heavy and out of balance to be a very effective stunter.    You may just have to deal with the float and not kill the performance for the rest of the flight.   In the end you may decide to decrease the size of the canard to resolve the issue.   It may become more cosmetic than functional at that point but otherwise you may be the dog chasing it's own tail on this one.   Experimenting with new things is fun-but not always totally successful.

Dave

[Paul Taylor]

Is there a picture of this plane?

Ok I think I found it.
Are you talking your Endgame?

I was looking for a bat wing🤣

[Brett Buck]

Ken I've never worked with a canard except in 1/2A as a kid but my thinking is that by the time you get enough nose weight on the plane to tame the landing float it will be too heavy and out of balance to be a very effective stunter.    You may just have to deal with the float and not kill the performance for the rest of the flight.   In the end you may decide to decrease the size of the canard to resolve the issue.   It may become more cosmetic than functional at that point but otherwise you may be the dog chasing it's own tail on this one.   Experimenting with new things is fun-but not always totally successful.

Dave

   There's a few discussions about canards and how they don't work particularly well for stunt purposes. Ken's case is a gray area, since he has a more-or-less conventional airplane with an additional canard right behind the engine. There is a long thread about this specific configuration, the "conclusion" being "we don't know", because a pure canard is a net negative, but his may have other effects that may make it less of a liability or a net positive.

    I note that the key difference is whether the canard has enough thrust vectoring capability to offset the loss of lift from the wing or having to run the CG forward to keep it stable.  I note the question here is in the glide - where there is no thrust to vector, thus it "floats".

      Brett

p.s. https://stunthanger.com/smf/stunt-design/three-surface-stunter/

[Brett Buck]

It is large - 710sq" and has a 175sq" stab and 50 sq" Canard which I am told adds to the wing area for our purposes. 

  Huh? If anything, you lose overall lift with a canard, so I wouldn't think that it "adds to the wing area". Maybe "subtracts from tail area", which is why you need the CG further forward.

    Brett

p.s. Paul cut to the solution - keep putting on nose weight until something bad (like excess control loading) happens.

     

[Ken Culbertson]

  Huh? If anything, you lose overall lift with a canard, so I wouldn't think that it "adds to the wing area". Maybe "subtracts from tail area", which is why you need the CG further forward.

    Brett

     

All I know is the extensive reading before starting this project told me that it increased lift.  Can you enlighten further, you know far more than I do on this subject.

Ken

Missed your first post.  You have properly described what I may be experiencing.  The thrust vectoring may explain why it is giving me mixed signals for the CG.  The twin (Endgame 4) that I have nearly completed may answer that question.  The Canard is identical to the one on III but it is ahead of the twin props in clean air.  I can see how deflecting the thrust before passing over the wing might affect wing lift but wouldn't that same thrust passing over the canard create lift?  Keep in mind that the Canard is not a hinged "stab/elevator" but a symmetrical airfoiled "wing" and only deflects about 10 degrees.

[Brett Buck]

All I know is the extensive reading before starting this project told me that it increased lift.  Can you enlighten further, you know far more than I do on this subject.

Ken

  Check the other thread, that's about the degree to which I have thought it through. Quick summary is:

   canard destabilizes the airplane
   you have to move the CG forward to restore the stability
   moving the CG forward moves it away from the CP of the wing
   having a large separation between the CG and the CP means you can't tolerate as much lift from the wing,
   The lost lift must be made up for by the canard, leading to an expectation of inordinate CL from the canard
    The presence of the canard also disrupts the flow of the wing with unknown degree of negative effect
   Maybe,  and only maybe, the canard vectoring the thrust makes up for the lost efficiency and lift of the wing
    maybe , and only maybe this makes the high effective CL possible

    That's the experiment you are doing. That it is OK during powered flight, and floats in the glide is 100% consistent with the reasoning above, the thrust vectoring is offsetting some of the stability loss, but on the glide there is none, so your CG is not far enough forward to stabilize the system.

       Brett
   

[Ken Culbertson]

Ok I think I found it.
Are you talking your Endgame?

I was looking for a bat wing🤣

Endgame III

[Ken Culbertson]

[/color]

  Check the other thread - do you know what that thread was called?

   canard destabilizes the airplane - true until you get the CG in range.  I had to move it nearly 2" after the 1st flight BUT the plane was stable under power, very stable.
   you have to move the CG forward to restore the stability
   moving the CG forward moves it away from the CP of the wing - agreed
       Brett

It may be that I have reached the forward CG point.  On the last flight after adding another ounce I did notice that my fingers were feeling some increased pressure on the outside corners, and I used some wrist on the 4th corner of the hourglass.  All of which are what Paul cited as reaching the right CG.  Maybe I should just move the leadouts forward a tad to lessen the pull and figure out how to land it. At least the twin has tricycle training wheels!

A word on the whole concept.  My goal was to make the plane more stable and relieve stick pressure.  It does both and has the side benefits of having never stalled and blinding corners.  Having said that does it grove better than a Bear - no.  Does it out turn a Shark - no.   BUT, is does both as well as they do.  For any progress to be made in PA design you must first be able to equal the state of the art.  I may never be able to prove the worth of the canard and that is fine, I am having fun trying and that is what is most important in a hobby.  But what if I do?  I guess I will know that I am succeeding when the comments are "but they are ugly".

Ken

[Brett Buck]

[/color]It may be that I have reached the forward CG point.  On the last flight after adding another ounce I did notice that my fingers were feeling some increased pressure on the outside corners, and I used some wrist on the 4th corner of the hourglass.  All of which are what Paul cited as reaching the right CG.  Maybe I should just move the leadouts forward a tad to lessen the pull and figure out how to land it. At least the twin has tricycle training wheels!

A word on the whole concept.  My goal was to make the plane more stable and relieve stick pressure.  It does both and has the side benefits of having never stalled and blinding corners.  Having said that does it grove better than a Bear - no.  Does it out turn a Shark - no.   BUT, is does both as well as they do.  For any progress to be made in PA design you must first be able to equal the state of the art.  I may never be able to prove the worth of the canard and that is fine, I am having fun trying and that is what is most important in a hobby.  But what if I do?  I guess I will know that I am succeeding when the comments are "but they are ugly".

Ken

   First and foremost, please do not infer than I am trying to shoot down the idea, I freely admit I am unsure about whether your canard will help or hurt. I am just trying to help explain the results. So far, I think you are more-or-less seeing exactly what everyone expected.  The question remains, is it better than the same or similar airplane without the canard? 

    Brett

[Dan McEntee]

    Well, the Wright brothers and a few others first flew in the early 1900's, and many used canards for pitch control. I think Glenn Curtiss and the Wrights eliminated it at about the same time. As aviation progressed through the years, the canard never made it back into main stream aircraft design. There were experimental designs during WW-II such as the Curtiss XP-55 Ascender and the Japanese Shinden already mentioned, and you don't see it again until the XB-70 Valkyrie. The Saab Draken makes use of one and may be the design that has been produced in the greatest numbers as a fighter. And we can't forget Burt Rutan and his extensive use of canards in his designs. I don't think there has even been a dedicated aerobatic aircraft design that uses a canard. The Vari-Eze and like designs can loop and roll but I don't think anyone does an airshow routine in one. The Draken fits the bill but being jet powered and rear end thrust, does that help to make it maneuverable enough to be a successful fighter? I don't think any major airplane uses any aircraft that employ a canard, with the Beech Starship coming the closest  but more or less failing. But on the other hand, the Piaggio Avanti seems to be quite successful where the Starship wasn't?? Simply put, I think the biggest reason for the configuration to exist is to simply reduce tendency for the airplane to stall and computer enhanced controls probably have those bases all covered.

[Reptoid]

Is the Canard "full flying" or fixed with hinged surface?

If it's "full flying", where's the pivot point?

If it's fixed with hinged surface what % is movable?

The addition of the canard itself moves the C/L forward making controls lighter and more sensitive with the original CG (since CG is now closer to C/L)

[Ken Culbertson]

   First and foremost, please do not infer than I am trying to shoot down the idea, I freely admit I am unsure about whether your canard will help or hurt. I am just trying to help explain the results. So far, I think you are more-or-less seeing exactly what everyone expected.  The question remains, is it better than the same or similar airplane without the canard? 

    Brett

Brett, I never interpreted anything you offered as negative.  Fortunately, I made the canard removable.  The plane has been flown without it and it did not perform as well without the canard.   That was done before the latest canard winglets were put on.  I have been through three sets and the last set was not removable so I can't repeat the exercise.  I am open to anything that anybody has to offer advise wise.  I noticed that you added the link to the older thread.  I am off to find my reading glasses!

Ken

[Ken Culbertson]

Is the Canard "full flying" or fixed with hinged surface?

If it's "full flying", where's the pivot point? 30% of root

If it's fixed with hinged surface what % is movable?

The addition of the canard itself moves the C/L forward making controls lighter and more sensitive with the original CG (since CG is now closer to C/L)

Here is a picture.  There are others in another thread, but it might be useful here.  I reread the earlier thread which was my inspiration for this plane.  All that is being said here has me thinking that I have stumbled onto what Brett pointed out in the earlier thread that using the canard to vector thrust may be a net positive.  I am coming to the conclusion that it is, and I need to start focusing on how to optimize it. 

Regarding your last comment, the controls are much lighter.  It pulls like a mule.  I am guessing in the 8-10lb range with very little loss overhead.  Without the canard I would be forced to use wrist to do corners and at that pull I can guarantee wiggly bottoms after about three flights.  What surprised me was the lack of sensitivity.  When it is in trim it groves with the best of them and even on the first couple of flights with the CG about 1 1/2" too far back it barely hunted at all. 

[Brett Buck]

Regarding your last comment, the controls are much lighter.  It pulls like a mule.  I am guessing in the 8-10lb range with very little loss overhead.  Without the canard I would be forced to use wrist to do corners and at that pull I can guarantee wiggly bottoms after about three flights.  What surprised me was the lack of sensitivity.  When it is in trim it groves with the best of them and even on the first couple of flights with the CG about 1 1/2" too far back it barely hunted at all.

   Hunting is not caused by an aft CG, aside from very unusual cases.

   The combination of lots of tension and very light sensitivity is maybe not what you want. If the control forces are very light, you normally want light to moderate line tension, so you are not having to hold on for dear life and at the same time with the same muscles. feather the controls. The simplest way to proceed is to slow it down and probably move the CG further forward, the effect will be to lighten the tension but keep the same control loads, so they are more compatible with each other.

    Brett

[Ken Culbertson]

   The combination of lots of tension and very light sensitivity is maybe not what you want.
    Brett

I see your point but it may not apply to the way I grip the handle.  I use a superlight thin hardpoint.  It pretty much seats itself along my second knuckle.  As a result I don't have to squeeze the handle to hold it.  No holding on for dear life.  This allows me to totally control the plane with my fingers.  Very little wrist and no elbow.  I let the plane's pull be the force I use on the controls.  By relaxing my lower fingers I get Up and visa versa.  Corners get a little squeeze from the other fingers.  After you get used to this method it feels like you are directly connected to the bellcrank. I wish I had discovered this when I was in my 40's and still had the vision and reflexes to do something with it.  I am sure others use this method or something similar.  Sorry, a little long-winded explanation of why I don't mind line pull but like low stick pressure.  Low mind you, not very light which I agree does not end well.

Ken

That 8-10 reading came from a digital fishing scale hooked up to a "Y" yoke hooked to my handle and pulling till it "felt" like what I get flying.  Repeated the exercise today and got roughly the same thing, probably closer to 8 than 10.  How in the world do we accurately measure line pull short of the math formula which doesn't take into account half of the variables we encounter.  SWAG seems to rule.

[Steve Helmick]

It occurred to me that your floaty glide might be cured by setting the flaps/elevator neutrals closer to zero/zero. But then I don't know if you have any difference between them...do you? And are you sure?  Steve

Edit: Thinking about it a little more, adding a moving canard into it mixes that into the problem, but maybe adjusting the various neutrals is the fix.

[Ken Culbertson]

It occurred to me that your floaty glide might be cured by setting the flaps/elevator neutrals closer to zero/zero. But then I don't know if you have any difference between them...do you? And are you sure?  Steve

Edit: Thinking about it a little more, adding a moving canard into it mixes that into the problem, but maybe adjusting the various neutrals is the fix.

It has a conventional layout.  Stab is above the wing and so is the canard.  So, like most it needs a touch of stab incidence.  I have 1/16" down elevator at flying neutral.  Flaps and canard are at zero.  Brett, perhaps unintentionally, spotted the cause and there is no acceptable solution.  In a nutshell, under power the canard is a thrust vectoring device, without power it is a lifting wing.  Trimming it to land easily will destroy the pattern trim so I just have to figure out a glide path that doesn't have me much over stall speed when I hit the ground effect.  Roughly 3-4"

Ken

[Steve Helmick]

Maybe deploy a spoiler when the motor shuts off?  Steve

[Brett Buck]

Maybe deploy a spoiler when the motor shuts off?  Steve

    The issue is that the CG is too far aft - light control pressures relative to the line tension,  and floats in the glide.  So, maybe have a spring shove the battery forward when the motor stops.

     Brett

[EricV]

    The issue is that the CG is too far aft - light control pressures relative to the line tension,  and floats in the glide.  So, maybe have a spring shove the battery forward when the motor stops.

     Brett

Doorbell chimes will run on 10 to 24v right? 🤣 I would SO want to hear it ding when deployed! Kidding aside, a landing gear servo would probably be a lot stronger and more reliable, heh.
EricV

[Ken Culbertson]

To both Brett and Eric - I have considered some gizmo like that.  A battery box on rails powered by a servo.  Might just work as long as it is all in the nose.  I would much rather have heavy gizmos that sheet lead!  Have to check the rules.  Servos for LG are legal but it may be worded so that only LG is legal.  You folks do realize that none of this tinkering is intended for competition.  Some things I like to do just to see if I can but I try and restrict them to what will pass the rules just in case.

Ken

Well after checking the rules it appears that a servo actuated battery box slider is either allowed or not allowed depending on how you read the first sentence of the rule.  It appears that the intent of the rule is to only ban control surface actuation, but the wording may restrict it to the landing gear.   If I actually try this I will get those that write the rules to weigh in.  Your idea has implications for old fashioned stunters without canards as well.  Taking off and landing nose heavy with normal CG for the rest - not a bad thing.

[Dave_Trible]

That rule is about the pilot actuating things from the ground.   It's not about something programmed into the electronic controls that would trigger a servo to perform a function ( ie. shifting the cg when the motor cuts off).   If that were the case accelerometer governed motor controls wouldn't be allowed.

Dave

I think if I were to attempt to do try this (i'm not) I would use a weighted pendulum that was spring loaded,  then released by a servo.  It could be built internally under your battery I would think.

[Ken Culbertson]

That rule is about the pilot actuating things from the ground.   It's not about something programmed into the electronic controls that would trigger a servo to perform a function ( ie. shifting the cg when the motor cuts off).   If that were the case accelerometer governed motor controls wouldn't be allowed.

Dave

I think if I were to attempt to do try this (i'm not) I would use a weighted pendulum that was spring loaded,  then released by a servo.  It could be built internally under your battery I would think.

I agree 100% that the spirit of the rules allows it but it is not the spirit I am worried about.  I seriously doubt that I will try this either, but it is fun designing stuff and Brett's idea has merit.  Some real airplanes adjust their CG in the air by shifting fuel around.  Why not the toys!  There are 70-80 free points in the pattern if you work at it.  Takeoff & landing.  A floater isn't going to get a 35+ even if it doesn't bounce.

IC's take off with 6oz of fuel in the nose and land with zero.  On every lap they get more tail heavy.  Rounds are easier and squares have a more realistic CG and by the time you get to the hourglass it starts to get tail heavy which is nice.  Electric is a one CG fits all.  We say that is good but is it really better or just different? 

I have 4oz of lead in the nose of Endgame III.  One to make the rounds easier and another 3 simply to kill the float.  I am using more control as a result.  Shifting a 10oz battery 1" or so would have the same effect and it is going to be there anyway.  That is red meat to a tinkerer.

Ken

[Dave_Trible]

Not sure.  After seeing a battery ejected from a flying airplane during practice at the Worlds I'd have second thoughts about anything but a solidly mounted,  immobile battery.  I don't play in that world and have no experience with it but........

Dave

[Steve Helmick]

Folding the canard surfaces or having them deflect to negative incidence when the motor stops would be another solution. I'm surprised that Brett didn't suggest that.  Steve

[Howard Rush]

If you can avoid the destabilizing effect of the canard, you won’t have to move the CG forward.  I can think of three ways to keep canard lift while reducing or eliminating the destabilizing effect.  The first is using a really low aspect ratio canard (Google Helmbold equation).  Second is the moustache canard used on the Tu-144.  It only works in one direction, but maybe Wes Dick can figure out how to make it work both ways.  My favorite is the floating canard, where the canard is free to pivot like a weathervane and is driven by an attached flap or—better yet— stabilator. Fuddy-duddies at work rejected this idea because they feared it would flutter. I think the Shinden canard floated.

Below is a picture of an airplane with a floating canard in a museum in Poland. Jive Combat Team Research travels the world to bring you stunt and combat intel.

[Dave Hull]

Is that an anti-servo tab on the spade? That would at least make it a trimmable floater?

[Ken Culbertson]

Folding the canard surfaces or having them deflect to negative incidence when the motor stops would be another solution. I'm surprised that Brett didn't suggest that.  Steve

That would work but as hard as I try, I cannot come up with a mechanical only way of doing it.  The sliding battery box or weight, servo driven connect to the landing gear circuit of a timer is worth looking at.

Ken

[Howard Rush]

Is that an anti-servo tab on the spade? That would at least make it a trimmable floater?

Could be. It’s kinda big for a trim tab only.