ltc

My Feedback: (3)

Would the implementation be to remove the rudder and drill/install lead into the top of the vertical stab from the hinge line side?
Is this something that other planes need to do?

serious power

Hi,
Why not just lift the battery pack position, looks like 5mm would do the job. It is easy to work out using the actual data.
Can be moved back as well to achieve same net effect - at a guess I'd say 30mm, but again it is easy to work out from your data.
It is just levers and moments !
You have the weight of the added lead and the height above/ distance from the current CG.

Brian

serious power

Hi,
Why not just lift the battery pack position, looks like 5mm would do the job. It is easy to work out using the actual data.
Can be moved back as well to achieve same net effect - at a guess I'd say 30mm, but again it is easy to work out from your data.
It is just levers and moments !
You have the weight of the added lead and the height above/ distance from the current CG.

Brian

flyintexan

My Feedback: (1)

Brian,

I most certainly move the main battery pack. As I mentioned though, at this point I am still testing and confirming cause and effects. Final pack location requires commitment to altering some heavily attached items in the battery area.


Regards,
Mark

serious power

Hi Mark,
Yes, I understand - you are fact finding.

I was responding to ; ' remove the rudder and drill/install lead into the top of the vertical stab from the hinge line side? '

A light foam pad or set of pads with different thickness's to go under the pack might be a good way to do tests !!?
Best of luck with the process.

Brian

Sorry for the double post above !!???

flyncajun

Hey Guys,
Not trying to get into a debate , Just experience sharing.

I`ve been down this road it`s fun to test but it the end you will find there is no such thing as a " vertical C/G" on a Pattern plane.
all forces (within reason) are aero related. I would call that plane with in reason.

I`ll save you some trouble and effort.
if you weighed the weight you moved as a percent of total weight above the thrust line you will finds it`s miniscule. Also
the moment arm is negligible. and if you put that weight on the bottom of the tail it will give you the same results. it`s a pendulum effect that`s all. Add different air / Flight conditions and your fix. caused three other problems

Just two clicks of elevator trim or 2 tenths of a degree of engine thrust or even 2 tenths of a degree of wing miss alignment is 5 times more powerful.

stay focused there!

Bryan

serious power

Brian

serious power

Hi Mark,
One advantage I've found with electrics is the relative ease we have when it comes to CG adjustment.
The pack is between 20% and 25% of the total mass. So being able to move this to do tests is great. I use it to set longitudinal, lateral and vertical CG.
I found, generally speaking for most current designs, that for Monos it needs to go as low down in the Fuz as possible and quite high in bipes.
On my current bipe I have it as high as possible with the formers etc that are there.
For the monos with belly pans (a few years ago now) the under-slung pack in the belly pan was easiest and best. Of course those models were designed for a YS installed inverted with headers, pipes and mounting brackets also under-slung.

Yes it makes a difference ;
All forces acting on our planes do so through the GC.
Take thrust line for example ;
Thrust line height = the distance between the thrust line and the CG (vertical).
In most models there is a range of say 100mm for battery placement, height wise. Not to be sneezed at !! This represents a 20mm thrust line height adjustment, approximately.
Thrust line height feeds into down thrust and so on.

However Bryan is correct in saying ; 'if you weighed the weight you moved as a percent of total weight above the thrust line you will finds it`s miniscule.'
I estimate that it's equivalent to lifting the pack say 5mm which = a 1mm increase in vertical CG and a 1mm reduction in thrust line height (I'm guessing that's 20 to 25g of lead).
You have moved the CG back quite a bit, maybe 5 or 6mm.

Vertical CG also matters , some, for rolls etc - as CG affects everything.

You can do no harm doing some testing - it's all good fun.

Brian

Malcolm H

I've got to say I agree with Bryan on this one. I'm inclined to think the change in pitch to the wheels was down to moving the CG back rather than changing its vertical position.

Easily checked by moving the same amount of weight from the top of the fin to underneath it but in the same position fore and aft.

Malcolm

serious power

Hi Malcolm,

' I've got to say I agree with Bryan on this one. ' Which bit ??

Your suggestion is good though.

Btw I did say in my post ;

' However Bryan is correct in saying ; 'if you weighed the weight you moved as a percent of total weight above the thrust line you will finds it`s miniscule.'
I estimate that it's equivalent to lifting the pack say 5mm which = a 1mm increase in vertical CG and a 1mm reduction in thrust line height (I'm guessing that's 20 to 25g of lead).
You have moved the CG back quite a bit, maybe 5 or 6mm. '

Brian

Malcolm H

Brian,

Where Bryan points out that the change in moment about the CG (and its potential effect) is minuscule with the fuselage in a vertical position.

Malcolm

serious power

Hi Malcolm,

Yes, me too

Brian

flyintexan

My Feedback: (1)

Hmmm. I apologize as I failed to mention in my original post that the tailweight started out that day taped alongside the tailwheel.

I have room to move the batteries up about 27mm and back perhaps the about the same. Will require some surgery if further testing confirms.

Thank you all for all the valuable input, it is appreciated and encouraged.

(Please note: older pic..the Rx battery is no longer located there)

Best Regards,
Mark

serious power

Hi Malcolm,
Just for the fun of it I've done a couple of 'back of the envelope' calculations ;

So assume the prop is 600mm from the CG.
Rotate the shaft to give 1 degree of downthrust.
Extend the shaft centreline back past the CG.
The change in the height of this line as it passes over the CG is 10.47mm (effective thrust line height change)
Therefore for a 0.1 degree change in down thrust the change to the effective thrust line height, above the CG, is a mere 1.047mm

If I've got this right then 5mm of pack height = 0.1* of thrust line. So 50mm = 1* (while going vertical) - Now that's a surprise !!??

Brian

serious power

Hi Mark,
Thanks for the clarification.
Keep up the good work.

Brian

flyncajun

Hey Guys

I also said within reason

I`m not saying it has no effect ,but it`s the wrong approach. What I`m trying to demonstrate is that moving a wing .1 of a degree or correcting a warped or misaligned stab will potentially fix and adjust more than moving a large battery around even a couple inches. There is no such thing as vertical cg. The cg does not lift, it enables the airfoil to work properly within its designed tolerance.
The CG is the GC of the wing nothing more.

The reason it works on a foamy is because there is no airfoil on the wing.

Yes, you may fix one problem by moving weight around. A fix to me, is make a change and fix 3-4 problems some you did not even realize that you had. There is no fix when trimming an airplane that fixes just one problem When you think you found that fix , I can assure you ,you messed up three other things.

Aero forces Trump All other forces Fix them first.
if that won`t fix it , work on fixing the design next.
Bryan.

serious power

Hi Bryan,
Like you said earlier ' not trying to get into a debate '.
Just trying to make constructive suggestions to Mark.

However to say ' There is no such thing as vertical cg '​ Is to claim that the aeroplane is 2 dimensional, permanently in the horizontal and has a vertical height of 0.
Sounds like something out of Tron or something. Maybe a new concept for a foamy

Joking aside, maybe you might have a suggestion for Mark ?

Brian

flyncajun

Hi Brian
I hear ya !
I guess we`re all a little bored of winter.

But so far on trimming and design ,I've been right ,continually... , so I`m working with good equity
There is still the miss belief that the wings are not under loads ( or flying in a vertical plane ) so I have to crack that barrier first with these debates or everything else is mute.

As for as suggestions I know Mark very well! he has my drawings LOL because he did them in Cad for me I`m not trying to be a smart ^^% he knows he can always just pick up the phone and call me.
As for here,I gave the suggestion in the last two sentences of my previous post! I also don't want to sound like a trim bully.

If I were to give all the answers, it would hurt the feelings of many folks, and factory's too so I save the answers for guys who fly my designs. For other designs , I debate the questions leadingly, so everyone else may discover them for themselves..
In todays Market ,Today you cannot accidentally design a Real Pattern plane. and A top shelf Pattern plane is even Harder.
slapping wings an a Bipe with a pretty paint scheme will only get you so far (I`m not talking about Marks Plane) I `m talking about just giving the answers out here for Bipes in general. It takes Knowledge pedigree and dedication. not art or magic add on`s.

If you piece together every thing I have written here on rcu you can discover the answers they are usually hidden in the arguing Uhh debates lol if you dismiss it as all wrong you can never discover the answer , if you take it pieces at a time ,the same result. It is not mystery or aero magic, 90% is cause and effect, and common sense. where we get off track , is trying to put some mystical blame of building, designing or trimming areas. I have taken the time and effort to figure this stuff out, without any help, I`m offering some help and direction, so it should not be that hard. But one thing is for sure ,we will not find the answers arguing here ,or in a text book, only the questions. The answers, they are at the field and the setup table


Bryan

serious power

Bryan,

' The answers, they are at the field and the setup table '

I could not agree more.

' The CG is the GC of the wing nothing more. ' .

For a mono yes - if one wants to look at it that way, and in the wing is the best place for it.
A bipe, as we all know, has 2 wings. It has only 1 CG !!
To seek to find the best location, in all 3 dimensions, is a good aspiration and worthy of some trials.

Our big old battery packs may have some use after all

Brian

flyncajun

Hey Brian

You can take it or leave it but Cg placement on the Bipe is no different than a Mono
But, Efficiency loading, and wing / c/g placement is a whole other issue though.

I`ll share a discovery there are 5 places where cg will fool you and you think it`s the correct spot and it may be for a given design because of that designs limitations , but all 5 have side effects elsewhere. Some can be corrected on the design and some are needed because of the design . These side effects come from the c.g placement and wing incidence. you ready? Here they are exactly.

20% 23% 25% 27% 30% now anywhere in between these numbers and the airplane is difficult to fly perfectly. On those numbers you can make It work ,but each number has a distribution of it`s own trim issues. each attributed to the particular wing incidence, cg placement. and engine thrust.

Remember for mixes (purity) and the ability to guide the airplane accurately , is why we move the cg and incidence.
This holds true; Wing incidence and loading is the only thing that affects where the GC is placed. If the design limits you , you can`t blame that on the vertical up line weight distribution issues.

So now, all that being said, if you trim up elevator in your airplane , what do you think will happen in the up lines chew on that for a few.
I think your smart enough to figure out what I`m saying with out me spilling the beans.

Bryan

flyncajun

Hey Brian

You can take it or leave it but Cg placement on the Bipe is no different than a Mono
But, Efficiency loading, and wing / c/g placement is a whole other issue though.

I`ll share a discovery there are 5 places where cg will fool you and you think it`s the correct spot and it may be for a given design because of that designs limitations , but all 5 have side effects elsewhere. Some can be corrected on the design and some are needed because of the design . These side effects come from the c.g placement and wing incidence. you ready? Here they are exactly.

20% 23% 25% 27% 30% now anywhere in between these numbers and the airplane is difficult to fly perfectly. On those numbers you can make It work ,but each number has a distribution of it`s own trim issues. each attributed to the particular wing incidence, cg placement. and engine thrust.

Remember for mixes (purity) and the ability to guide the airplane accurately , is why we move the cg and incidence.
This holds true; Wing incidence and loading is the only thing that affects where the GC is placed. If the design limits you , you can`t blame that on the vertical up line weight distribution issues.

So now, all that being said, if you trim up elevator in your airplane , what do you think will happen in the up lines chew on that for a few.
I think your smart enough to figure out what I`m saying with out me spilling the beans.

Bryan

DagTheElder

Guys,
Sorry to jump into this discussion��
All forces must go through the CG. Anything else and you have a trim issue. The CG may be somwhere Close to the standard measure at 25% but this will be found out after trim flights. It may be that the tail is flying to low so increase the incidence and this will lift the tail!!!!!!

Regards

PS.
Take look at my posts in Pattern flying page 3 I think and maybe you find some answers. DS

Malcolm H

20% 23% 25% 27% 30% now anywhere in between these numbers and the airplane is difficult to fly perfectly. On those numbers you can make It work ,but each number has a distribution of it`s own trim issues. each attributed to the particular wing incidence, cg placement. and engine thrust.

So Bryan,
Are you saying that on those numbers it's possible to obtain a satisfactory trim setup on some designs but between them say at 24% it isn't?

Let us take one aspect of trimming, pitching in knife edge flight and further let us limit this discussion to monos because I know you value your IP when it comes to bipes. Your Triangulation Trimming method suggests that if a model pitches towards the belly it is tail heavy and vice versa. Given what you have stated above what should one do with an apparently tail heavy model that pitches to the belly and has a measured CG around say 23%?

Malcolm

flyncajun

Yes Malcolm

I really don`t want to hijack this thread,,but.

Yes in between those numbers and things are not as perfect that why I was specific .For mixing reduction and over all flying some designs require those forward numbers to fly the best such as bipes, and even my Valiant design like 25-27% as you read above it depends on wing efficiency.
A forward cg increases rudder and elevator power and decreases finesse or ease of application like fine inputs for reversal rolls,spin entry, and small changes on knife edge flight. But the power under use goes through the roof. However the auto wind correct gets too aggressive with a forward cg as well. I use it as an indicator of the cg limits.


On your other problem you need to read this carefully I explain the problem here.
http://www.ckaero.net/blog/2015/02/1...-differential/
All reverse belly pitch is a result of stab or elevator miss alignment or , warps . if one knife edge goes to the belly and the other don`t , the stabs are not set the same. (yes the spiral slip stream is not to blame again this time)
I think if you are flying a mono with the cg that far forward you will appreciate the above article. If its a Bipe , you will really appreciate it

I would like to continue this but we need to move it to it`s own thread and not trample this one.

serious power

Hi,
Back to Mark !

' I have room to move the batteries up about 27mm '

That will move the CG up by approx 5mm - significant considering the effect of the lead.
Though you may have reduced the drag some low down at the tail and increased it some high up at the tail (and or a small aero effect - at the extreme of such a long lever ??) !??

I did a little doodling in 'Paint' (something to refer to in conversation perhaps) ;
Not to scale though - just an approximation.
However already some stuff is apparent !

Brian