Tricky Flight, not much control

[Allen Eshleman]

Today, I gave the Akromaster listed in my other post it's first flight.  I couldn't keep it in the air.  I am seasoned enough that this problem had to be extreme.     I had to ride the up line and didn't have much up or down control.  I think the surfaces are aligned.  Could severe over weight in the nose or tail have caused this?   

The CG was around the front line.

[Allen Eshleman]

I'm going to try again.  When I finished that flight I noticed that my clips were not closed.  The CG is where it is supposed to be per the plans. 

[Tim Wescott]

Allen, as I said in your build thread, you've left out the elevator pushrod support.  I'm including the picture that I'm looking at to know.  Without support it is free to bend when you give it "up".  The z-bend in the middle doesn't help, either.

I'd replace that with a straight pushrod, and support it in the middle of its run.  You don't need much -- just something that'll keep it from moving up or down.

[Allen Eshleman]

I will do the suggested fix with the control rod first and see what happens.  This kit does not come made for flaps.  That's a modification I tried to do as others have done.  I didn't know which rod goes on top.   Thanks for the ideas. 

[Bill Little]

Hi Allen,

I would agree with Tim on the push rod situation.  Plus, the push rod looks mighty thin.  What is it, 1/16th"?  If so, it really needs a fairlead somewhere near the middle.  I would go with 3/32nd" from the flap horn to the elev. horn.

If the C/G is where recommended, everything is "equal", then you should have control.  How far are the lines spread on your handle?

Good Luck!

BIG Bear
RNMM/AMM

[john e. holliday]

I probably not say this, but I have several planes in which the pushrods are not in the usual position at the flap horn.  In fact on one I use ball links and have the rods working in the same hole at the flap.    The preceding is to get more elevator than flap movement.

I do say you need a support at least one half way on the pushrod to the elevator.   I use cotter keys from the local hardware store.

[Brett Buck]

I probably not say this, but I have several planes in which the pushrods are not in the usual position at the flap horn.  In fact on one I use ball links and have the rods working in the same hole at the flap.    The preceding is to get more elevator than flap movement.

I do say you need a support at least one half way on the pushrod to the elevator.   I use cotter keys from the local hardware store.

   Old "Luxon" clips, cut in half, also work nicely. Sure don't want to use them on the lines.

    Brett

[Allen Eshleman]

I'm making a new push rod out of carbon fiber.  That shouldn't bend!  I am in the process of putting that together.

[Tim Wescott]

I'm making a new push rod out of carbon fiber.  That shouldn't bend!  I am in the process of putting that together.

I was toying with suggesting that, but didn't want you to feel inundated by suggestions.  I use arrow shafts, because there's an archery place across town that sells used ones for $1.00 apiece.  Just make sure that you do a good job attaching the ends to the shaft and it should work great.

[Allen Eshleman]

I bought this from a hobby store and used the major part of it.  That's a great suggestion - going to an archery store.

Question.  Does having the bellcrank pushrod connection on the control horn (flap horn) and the elevator pushrod below it cause more elevator movement than flap movement? 

[Tim Wescott]

Question.  Does having the bellcrank pushrod connection on the control horn (flap horn) and the elevator pushrod below it cause more elevator movement than flap movement?  

Not necessarily.  What causes more elevator than flap movement is having a shorter hing-to-pushrod distance on the elevator than on the flap.  Having the long arm on the flap side just means you need a longer arm on the elevator.

What you are causing there is more flap motion compared to your bellcrank motion.  It takes surprisingly little motion at the flap and elevator to do a satisfactory pattern.  I'd set the bellcrank-to-flap linkage up so that when you move the bellcrank from stop to stop you're getting about twenty degrees of flap motion in each direction.  Then I'd set up the flap-to-elevator link to give you about 50% more, or even twice as much movement at the elevator.  That should give you a flyable plane which you can then tune more as you go.

(Edited to fix error in comment about flap-elevator ratio).

[Allen Eshleman]

I have always thought that if there is a difference in movement between the flaps and the elevator that more elevator movement is preferred.

[Tim Wescott]

I have always thought that if there is a difference in movement between the flaps and the elevator that more elevator movement is preferred.

I usually get these things right when I'm actually doing them.  Honest.  It's just when I'm stating them that I mess up.  Regularly.

[Steve Helmick]

I usually get these things right when I'm actually doing them.  Honest.  It's just when I'm stating them that I mess up.  Regularly.

Tim...How's about going back into that post and just fixing it, please? You don't want to leave mistrakes like that on the 'net, or somebody will quote you and ignore all else!

On the KISS!, I soon realized that the wing loading justified 1:1 controls, which was easy enough to accomplish. I was not ready for the huge change in response and feel that also resulted (besides a better corner). A simple series of round loops became a climbing spiral...too weird. I had to reduce line spacing at the handle to 2.5", and then gradually widen the spacing back out (about 3.25"?), where some sort of precision was again possible.  The sooner you get the ratios dialed in, the less trouble you'll have getting used to the upgrade, I bet.  Steve

[Brett Buck]

I have always thought that if there is a difference in movement between the flaps and the elevator that more elevator movement is preferred.

   That depends entirely on the other parameters. In this case I wouldn't venture a guess - wing loading is going to be extremely high for this size airplane, suggesting more flap, but the tail volume is minimal suggesting that flap movement be minimized. If it was me, I would start with relatively little flap movement, then work up the the point that it was obvious that the lack of pitch authority was inhibiting the turn. Presumably this is the point at which you could no longer stall it with full hand motion.

     Brett

[Tim Wescott]

If it was me, I would start with relatively little flap movement, then work up the the point that it was obvious that the lack of pitch authority was inhibiting the turn. Presumably this is the point at which you could no longer stall it with full hand motion.

That's what I would suggest.  You know it works with all elevator and no flap, because that's how the thing is designed.  So that's the worst you can do, and if what folks say about the Acromaster is true, that ain't bad.

[Dick Pacini]

Bob Hunt recently told me never to have the line spacing at the handle inside your grip.  I pointed out that most hard point handles arms have clip attachment holes that bring the adjustments closer together.  His reply was flip the arms upside down.  He said to adjust control sensitivity at the airplane, not the handle.

[Brett Buck]

Bob Hunt recently told me never to have the line spacing at the handle inside your grip.  I pointed out that most hard point handles arms have clip attachment holes that bring the adjustments closer together.  His reply was flip the arms upside down.  He said to adjust control sensitivity at the airplane, not the handle.

   Have to pretty strongly disagree with that one. Several of us have won an awful lot of hardware doing just the opposite. Adjust the airplane so it flies properly, then adjust the handle (however it needs to be) to make it suit your needs.

     I speculate that you are misinterpreting the comments. In fact you probably want the controls in the airplane as slow as they can be and still provide the proper sensitivity which means a lot of spacing. What you don't want is really narrow spacing to compensate for the really fast controls. That's because with fast controls and slow handle you end up with reduced margin over the Netzeband wall.

     The limitation is that if you build it with a small bellcrank, at some point you can't make it move any further. So altering the rest of the ratios doesn't matter.

   Problem is, one you have built the airplane you frequently can't change the control ratios without cutting into it. Certainly you can't make the bellcrank bigger and usually you can't change the bellcrank-to-flap motion. So you want to use a big bellcrank, usually as big as will conveniently fit, and that will allow you to have reasonable spacing and decent control margin.

   So, once you have built it and set the control ratios, you no longer have much control over it, you need to select the handle spacing that works. What you absolutely do not want to do, unless you can't avoid it, is compensate for control sensitivity with nose weight or tail weight. Back in the dark ages, you would build the airplane however it was, use whatever handle you happened to like, and if it was too twitchy put on nose weight and too sluggish, put on tail weight, regardless of whether the airplane was happy.

    Brett

[Dick Pacini]

Perhaps Bob will drop in and comment.

[Brett Buck]

Perhaps Bob will drop in and comment.

  He might be otherwise occupied this week...

   Brett

[jim gilmore]

First off, Hold the flaps level and push on the elevator. If your getting major push rod deflection with very little effort you got a problem.

[Tim Wescott]

  He might be otherwise occupied this week...

All the heavy hitters seem to be distracted this week.  Some coincidence.  Go figger.

[john e. holliday]

You forget this is NATS week for control line.   They are busy trying to do the best they can with the flying and conditions.   Also there is the socializing of an evening.   

[Allen Eshleman]

Well, flight number 2, not much better but I had some up control.   

Changes I made:     1.carbon fiber push rod.    2.   flipping rods on flap horn   3.  weighted nose cone for easier starting - ie electric finger.

The nose cone moved the CG forward.   This time I made it through the whole flight but fought to keep the front end up.

My next move is to add a bit of weight to the back.

Question:  does anyone know of a way or something that could could be bought like a threaded coupler to put in an already existing control rod.  I would like to lengthen the rod coming out of the bellcrank without doing surgery.

There is a bit of binding somewhere when I pull up - it might be the flap hinges or the bellcrank.  I'm doing some testing.

[Allen Eshleman]

P.S. to above:  It landed like a nose heavy plane

[john e. holliday]

With heavy nose cone it probably is nose heavy.   At least you are making progress.

[Balsa Butcher]

I think the problem may be more involved than just a nose heavy condition. When up is applied the flap goes down. Although this increases lift it also acts like down elevator, causing the airplane to pivot around the center of lift which causes the tail to go up, nose to go down. It is normally compensated for by up elevator. In this case however, the elevator is too small to be effective hence the nose heavy feel, especially in the glide.

Best bet is to just go with elevator only as designed. If you still want to experiment reduce the flap area by cutting them down by 1/3. Outer 1/3 to be stationary, inner 2/3 functional. Limiting flap movement is still a good idea as is making them narrower. Flaps are not always your friend however it is fun to experiment.

[Bill Little]

Hi Allen,

Get rid of the "binding" for sure.  It can really play havoc in trying to control a model.

BIG Bear
RNMM/AMM

[Brett Buck]

I think the problem may be more involved than just a nose heavy condition. When up is applied the flap goes down. Although this increases lift it also acts like down elevator, causing the airplane to pivot around the center of lift which causes the tail to go up, nose to go down. It is normally compensated for by up elevator. In this case however, the elevator is too small to be effective hence the nose heavy feel, especially in the glide.

   That's essentially right, and why I suggested starting with as little flap movement as possible. Moving the CG aft will accomplish a similar purpose in terms of pitching moment - it actually pivots around the CG, not the CL  so moving the CG aft reduces the pitching moment from the flap substantially and hardly effects the elevator. It's not quite the same because moving the CG aft is pretty dangerous on these sorts of airplanes, because with a tiny tail volume it can easily become unstable, or you can jump from way to nose-heavy to way too tail-heavy with only a tiny change in the CG. In any case, you still have to be able to generate enough control torque to move the controls, and even if the pitching moment is reduced when moving the CG aft, you still have to deflect the flap just as much into the same airstream, with very likely less line tension.

  Bear in mind also that the leadouts are fixed, so moving the CG aft moves the leadouts forward. Whether that might help or hurt, hard to tell.

    Reducing the flap/elevator ratio will also reduce the flap pitching moment without reducing the stability very much and without losing much if any line tension. I would have set it up to start with the flap fixed, then only add it in small increments instead of jumping right to full movement, but making it 3:1 elevator/flap will certainly change it and make it obvious if that's the problem, or something else.

   Brett

[jim gilmore]

one think nobody has seemed to mention is the gap on your flaps.
Clean the bottom side of the aircraft and run a length of tape to seal that gap.

[Allen Eshleman]

Thanks for the many suggestions.

I was able to free up the controls by cutting some of the Kolar Kote hinges.

I added some weight in the back to counter balance the nose cone.

I changed the control rod setting by putting the bellcrank rod just a bit above the control rod and also drilled a new hole a bit further back on the flap horn for the control rod.  This gave me more elevator travel.

The result:   This time I had a controllable plane.  Still a bit of down draft when the lines went a bit slack.  Howevr, I did one large loop. 

I did two flights tonight.  But I had engine woes.  The engine needed to be tightened to the fuselage after the first flight.  Then, at the end of the second flight - Pow!   Look what caused it on the the third picture below1

[john e. holliday]

I've never had that happen to a McCoy before.   Guess you must have forgot to check the tightness of the head bolts.   Also using Monokote hinges I have found them to also be stiff until I got a couple of flights on them.   Better keep an eye on the hinges now.

[Allen Eshleman]

I can't seem to get the head and piston sleeve to go all the way down over the piston.  Is it alright if I twist it.   My brother tightened the head bolts about 7 runs ago.

[john e. holliday]

Some times you have to twist the cylinder to get it to slide down over the piston.   Be gentle.   You did make sure no burrs in the exhaust ports or intake either.

[Jim Kraft]

Also make sure the wristpin is not sliding out into one of the ports as that will keep it from going on. And don't let the wristpin pads fall out. It should slide right on if you take out the plug.

[Ted Fancher]

I can't seem to get the head and piston sleeve to go all the way down over the piston.  Is it alright if I twist it.   My brother tightened the head bolts about 7 runs ago.

Did you remove the glow plug before trying to slide them together??  Compression you know!

[Allen Eshleman]

I didn't remove it the first time.  Then I removed it.  I still had trouble but eventually with some twisting, it went on.  With several flips, and the use of the starter, it is getting better.  It has good compression.  Haven't tried to run it yet.