protectedpilot

I entered the red herrings, because that was the types of technology he was referring to, without knowing it. For instance, alternators(generators) on cars are AC devices; we used bridge rectifiers to convert to DC. (that's what fails when you try to jump start a car reversed polarity) The stuff about motor braking is just WRONG. Speed control, without feedback (i.e. tachometers) IS vector control. Counter EMF in motors IS a wound field motor. Where in a permanent magnet motor would you measure counter EMF that induced braking?

I operate large generators, and when sync'd up to the grid, they WILL motor if we push too lightly. Bad deal. Again, AC devices. Wound field devices. ESC motors do not brake. Propellers may brake, but motors do not. It is confusing to see everything claimed to be true about electrics, and does not propel me in that direction when all I read is verifiably wrong. Yes, PM motors on voltage control exhibit constant speed. Yes, slowing the motor down will slow the plane, through slowing the prop.

But guys, describe the effects, and leave the techno mumbo jumbo to the people with the facts. It really screws up people with more expertise. Half the time, I'm trying to figure out exactly WHAT the point is, and the flying effects get lost. If I were to try electrics, based upon the information here sometimes, I would certainly fry every bit of equipment I purchased.

brian

rmh

Thank you for exhibiting your vast font of knowledge
by the way - older cars used generators not alternators -

Lnewqban

Thank you very much for the detailed explanation, Bryan.

I will need some time to understand every bit.

What I don't understand are your references to Dick's school of trimming.
I guess I would need to be familiar with previous discussions between both of you, especially in the precision aerobatics forum.

This brings a question to my mind, regarding your previous reference to models and aerobatics of the 70's:
Dick Hanson successfully designed and flew pattern planes in the 70's.
Then, his trimming methods must have worked for such models and maneuvers.
Are the modern designs so different from the 70's models that the trimming approach has changed much?
Are materials or aerodynamics what limits a 70's model to compete and win nowadays contests?

If you don't mind, I may come back with more questions after I study your post and the triangulation method.

Again, thanks.[sm=thumbs_up.gif]

[Edited for spelling]

rmh

To clarify: DC PM motors used in slot racing DO use shorting for braking -VERY effective
The motors we use in our planes are typically outrunner and a few inrunner types (common terminology)
Thes are not shorted for braking but the ESC can be programmed in many of them to enable braking
It is also quite effective.
(Too much mumbo jumbo?)

rmh

This is for those who wanted clarification

Mastertech

My Feedback: (31)

Having used all the above methods over the years, Bryan's is the one that has consistently worked for me. The others............... Not so much.

I built two Prolines a few years ago, outfitted exactly the same. I set #1 to Byran's spec's on the board and it flew near perfect off the board with only having to adjust the stab to get the small amount of elev trim out of it and a slight move forward of the CG (10mm).

The second airplane I didn't move anything except got it close on the cg. I left everything as set by the factory, which was 0-0-.5. This one gave me a fit from the first flight. I then started to move things (With out measuring) until it flew like #1.

At the time I didn't know how to figure the MAC to get the % for the CG, later I found the formula on the NSRCA website and checked them and found I was at 27% moved from about 32%.

Then I measured the airplane and it was EXACTLY like #1 only trim issue I have on both was a slight pull to the canopy on the down line.

I'm a firm believer in Bryan's methods.

Tim

MTK

The pattern models of yesterday versus the models of today......yes there are several differences, keys among them are speed and size. Another key, wing vertical location on the fuse.

Current pattern designs are 30-40% larger than those of the 70's-80's and are designed to fly 30% slower (80 versus 120). Today's models are much closer to mid wing configuration requiring only a couple degrees of dihedral

Yesterday's model flying 120 and set-up all zeros, would fly as straight as the schedule demanded back then. There was practically no extended knife edge (including looping elements) required. A 4 point was about all we had to contend with with the occasional brave Masters soul who added an 8 pt for kicks to his schedule.

As schedules got more complex and required more performance in knife edge flight, designers attempted to produce more pure response from their models when flying knife edge flight. The speed was much slower and the models much larger, so the was little buffering available from pure speed. Trim in knife edge became the most important key to a well trimmed model. Do that right and I'd say you are 90% of way home.

That's the reason Bryan and I have been as adamant about KE trim. It is most important..... it was much simpler flight enevlope in yesterday's models.

Hope that answers...

ytell

Suppose Bryan's method is adopted as described. What flying qualities will you gain? Is it just pros without cons?

I can think of at least one big issue, at least for me, as a result of a quite a bit of forward CG which means that your inverted flying will no longer be close to a trimmed (hands-off) flight as upright.

So I'm thinking if it would not be wise to follow other trimming methods which are more tolerated to an aft CG and when you're close enough just mix out the remaining problems with your radio.

Do you see any flaw with this approach?

Yoav

Lnewqban

It answers very well!,......and dissipates the myth over modern pattern planes.

Thanks, Matt.

rmh

Sure -try it
Basically the trimsetup depends on the model and how YOU like to fly
In 1980 - I did a model dubbed the Hippo Tipo
I made it with a huge fuselage and intended it for slower flying in close
A friend in Ohio Dean Koger did a similar thing as did Steve Rojecki (long time friend and TOC winner and director)
The idea really never caught on and the fast models prevailed till the 1990's.
The trimming of ALL of these remained the same - get the model as light as possible - get it as straight as possible ,then fix any tendencies to corkscrew in looping and balance to get the best compromise of upright/ inverted flight handling.
The knife edge thing was typically a balance thing and again we went for the best compromise
It was always obvious that the best setup was the most predictable setup -which meant - -go for the most forward CG which allowed the rest of the stuff to be easily flown.
When we did IMAC TOC designs - all the same held true
Basically we started with zero angles all around - THEN as needs be tweaked if necessary
Some designs simply needed help from mixing and the new mix radios really helped.
What we found along the way was that the basics - get it as light as possible - as straight as possible -as overpowered as possible and as zero in all relative lines as possible was the best starting point.
Not surprisingly - some basic setups were seen to work differently than some others -especially in scale aerobats .
It is all compromise -and when we found that some setups were simply easier to fly and allow for wind etc., with mix we added the mix.
PS with far more power on tap -holding constant speed fixed a LOT of other problems such as speed losses when maneuvering thru snaps etc.. as reserve power instantly put the model back to desired (read that TRIMMED) speed.
I don't have any trimming secrets never have - just did what seemed to work the best.

MTK

There is little problem with this approach. You can try to get a model as pure responding as possible but in the end, if you have it very close but still need, say, a couple percent of mix somewhere, fine.

Inverted flight will be heavier feeling with the very forward cg that cures the various problems of knife edge trim. If you prefer a lighter feel to the forestick in inverted, make the required CG change but make sure you don't change it back to where it was.

Pattern models will tolerate very aft CG's, beyond 35% MAC, but that doesn't mean they will fly quite as well as they can, set-up like that.

At the end of the day, great flying skill will trump a bad set-up....that's the bottom line

rmh

35%?
Ouch!
We played witha lot of foamy setups and pushed cg to - ready ? 75% back!
IF you kept throttle input to minimums you could stagger around and flip n flop
At 35% things got flyable but stability at speed sucked
around 30% was best compromise for these little flip n flop designs

UStik

Oh well, don't ask how screwed up I am.

May I fill you guys in on some facts...ah...figures on electric drives? I'll leave the interpretation to you. The diagrams are for a typical F3A drive made by AXI (including 20x13 prop). May be not quite exact but you get the idea. Better to look at a whole drive than at the motor alone, isn't it? And better to have the characteristics depending on speed.

The second diagram goes to show that thrust is reverse-proportional to speed (except at low speed due to some blade stall). You may lay out a stiff or an elastic drive, but it's not nearly constant speed. It's simply better than an IC drive. Static thrust/weight ratio is 1.85 and lets the model go up vertically at 50 mph after all. You just need a more powerful IC drive for that.

You may notice that maximum (zero-thrust) speed is about 54 m/s what is 120 mph. That's exactly the top speed of a Hanno Special drive with a 12x12 prop. I reckon the ballistic pattern ships flew at 90 mph maximum and 65 mph maneuver speed, and the modern ships do about the same. (Their wing loading is about the same). It just looks slower due to size.

The old pattern ships might even have been nearer to a mid-wing configuration than the modern ones, simply due to flatter fuselage.

Thanks for all insights (as far as I could get them, still waiting for the rationale...).

rmh

The point being that thrust is greatest at zero airspeed and least at maximum (top speed?) A "constant speed" model -at least those I know of - fly at a desired speed and can maintain that speed up/down whatever.
They are NOT flying at WOT at anytime typically except in vertical climb and then perhaps only after multi snap sequences -or any maneuver which saps speed.
The only IC models I have had which remotely come to this level of performance, were extremely light - had tuned exhausts and swang (past perfect) BIG props. My tuned exhaust ZDZ80 powered 540 was very good at accelerating straight up this setup turned 6600 on the ground
But - in electrics this was not an uncommon setup .
For an example my ERATIX: a 3.75 lb model with a EFlite 32 and a 14.7 prop and A123 batteries (actually beat the best LiPos!)
Acceleration was instantaneous-on a WOT take off - you had better be pointed exactly where you wanted it to go.

UStik

I don't object, on the contrary. As you and others have said as well, there has to be some control for constant speed, manual or automatic. An electric drive is not constant speed per se.

MTK

Not true!! I don't remember seeing any model back then (Arrow, Curare, Atlas, Dirty Birdy and several other American designs, and several Japanese) that used less dihedral angle than the present day crop of models. Doesn't make much difference whether a fuse is flat box or rounded box.

About the only one I can recall was the Laser which was a true mid wing requiring zero dihedral, but that came in the late 80's I think.

Location of most present day wings is just slightly below the true reference line of the model, making these closer to true mid wing designs. They require very little dihedral in the wing

UStik

Of course you know better, but how about Brushfire and Integral? Yes, Brushfire has more dihedral even though it's more mid-wing. I'm just missing tangible quantitative details. And I'd prefer to have the steam vented out of this thread.

protectedpilot

To clarify: You are wrong. The motors in the cars use external power sources and controllers which are, in essence, rheostat controlled. Shorting the windings provides an infinite loop, which does not brake. Period. What you are describing is the EFFECT, not the mechanism. The friction alone provides the braking. You short the leads on the slot to provide infinite loop in the motor, that's all. Incidentally, this turns them into brushed motors.

ESC's do not brake. Period. That would require reverse biasing capabilities, which is HEAVY. Slowing the motor allows the propeller to brake the airplane, which on electric models, is less than in a glow engine...... it has a greater pitch. The edge here goes to glow. Larger rotating mass of motor, more friction and less pitch in the prop.

And yes, it is too much mumbo jumbo, which is why I clarify. You cannot claim electric motors will solve everything that is wrong with model power plants with the simple explanation that the "just do it all." They don't, it is a lot more complicated. It is easy to make up a fact to fit a known outcome, but the next time the supposed fact might not fit. What then? Do we simply go back and re-edit our prior posts to once again appear correct? [shame on the guys doing that here, it is less than honest and I see it ] Knowing the truth about ESC/motor combinations and how they work allows us to make proper application of the technology. Otherwise, we are confined to buying the combinations that Tower Hobbies lists in the catalog. You won't win many pattern contests that way, but you will have an excellent sporting experience. I fly to win; and I stretch my setup, knowledge and skill by gathering all of the expert help I can.

Brian

protectedpilot

Yes, Yoav; crosswind flying. Ask people I fly with, crosswind flying is my forte. Trimming is most important in the wind.

Brian

protectedpilot

Very good point, well spoken. We do have a tendency to defend our opinions, don't we? Thanks for being a voice of reason; it really is about helping each other and not "being right". I, for one, appreciate the suggestion and will heed it. Starting now.

Brian

rmh

amazing - check out a slot car setup - I have a lot of it and had a room full of trophies for it years back Al;so read the setup page for ALIGN ESC - as well as others and fly the results
I would go into detail but I see no reason for it as the slotcar motor setup is so simple (it is a simple brushed three armature segment two pMmagnet setup)the braking thru shorting is common knowledge even to very young boys
The ALIGN ESC- read one of the instructions for setup seperate settings for brake or non brake setup - common even on powered gliders/helicopters . Most other ESC are the same
My car esc even have reversing on brushless setups

MTK

It's a matter of where the wing is located relative to the fuse reference line. The true mid wing has the wing centerline going through the reference

What about the Brushfire and Integral? The integral is more of a low wing. It needs to carry more dihedral to fly knife edge with no roll couple than the mfr put in the kits. Raise the wing about 1/2" (if you keep the same wing) and the problem goes away. Never seen a Brushfire so I can't comment further on that one.

Sure anyone can find a specific example of anything that counters the trend. My point was and is that most of yesterday's models were low wing configs where most of today's are closer to mid wings

No real point in debating that point any further, yes?

rmh

Brushfire was Steve Rojecki's design about 1976 we both were in Cincinnati then
Most of my own stuf had the thrustline slightly above the wing saddle except the ZLINS
funny thing they flew almost the same as the dihedral was optomised for it

MTK

How old is Libby now?

RCFlyerDan

My Feedback: (54)

I haven't read anyone mentioning balance. Balance is EXTREMELY important when trimming. The plane will talk to you, if you are willing to listen. Some tucking towards the canopy on verticles, or flying up side down, is actually too nose heavy of a plane. Because in level flight at a given power setting, there is up trim to hold the nose up in flight, flip the plane over, and now that up becomes down. Move some weight aft to remove the up trim, so now the elevator is more neutral in flight, whether the plane is upside right or up side down. Just something to think about too. Balance prior to changing incedences and thrust lines.