Removable Controls

[Ken Culbertson]

With the switch to logarithmic controls an opportunity arose to make them removable and therefore easy to modify/replace.  This tray holds the entire flap control system developed by Mark Wood.  What makes it removable is the connection to the flaps which as a side benefit makes them adjustable therefore no more tabs or tweaking.

Ken

[Curare]

One would assume that you'd need a reasonably large access hatch to get that assembly out, correct?

If I recall correctly the logarithmic bellcrank is fitted aft of the wing, correct?

Are you adding any additional structure to offset the fuselage weakness created by cutting in a hatch?

[Ken Culbertson]

One would assume that you'd need a reasonably large access hatch to get that assembly out, correct?

Huge in fact.  The entire bottom of the plane to the end of the flaps is a hatch.

If I recall correctly the logarithmic bellcrank is fitted aft of the wing, correct?

Normally yes but mine is mounted 2" into the wing.  The wing was designed with this indent and reinforced with CF Tubes.

Are you adding any additional structure to offset the fuselage weakness created by cutting in a hatch?

The hatches are structural. They fit into the fuselage tongue and grove and are held in place by 4-40 flat head bolts and blind nuts.  Actually stronger than a glue joint.  I must have take a hundred pictures of the plane during construction.  How many were of the bottom? - 1.  I highlighted the hatches and mounting hardware.

We typically build with everything accessible from the top then we cover it up.  I have always thought that doing everything through the bottom would be better.  Want to change the bellcrank flap pushrod hole on a typical build and you are in for some refinishing.  That oblong hole on the build picture lets me do that at the field if I want. 

This plane is a test bed.  No effort put into a "Nats" quality finish but if you take care in building hatches that really fit and use panel lines you can make them part of the finish.  Personally, I will never build another PA plane that does not have a full bottom access hatch.  This setup is probably a bit heavier than normal construction, but it is worth it to me.  Part of the reason I built a new control box was the weight of the old one.  This one is a 1/2 oz lighter. The other reason was to remove slop.  The horns are printed with some pretty stout material but after about 20 flights on the plane I started to get some slop in the flaps.  Turns out that the pivot holes needed bushing.  Slop gone, life is good.


Ken

[Jim Svitko]

Does this level of complexity really make any difference?  I doubt I could notice any difference over a conventional system.  At least, not enough for me to take the risk of all those extra components providing more possible failure points.

[Ken Culbertson]

Does this level of complexity really make any difference?

No it doesn't and it is not intended to.  It is a test bed to try out different ratio's and ways to make trimming easier.  For example the split flap horns allow both "level wing" trimming with no need for a tab ( That is not a new idea, just an implementation.) ,and individual range ala Palmer but I do not plan to implement that.  The logarithmic has the same number of moving parts as Igor's, it is just made removable so that I can change them as I find out more how they interact with the canard, which is going to be on all of my planes going forward.  The positioning of the control box is to move the weight closer to the CG.

It will be 2 years before I am able to take my act to the Nats and what I take will be the end product of what I am learning.  I like to tinker but you are right, a competition plane needs to be as simple as possible.

Ken 

[Claudio Chacon]

Dear Mr. Culbertson.
The entire removable system looks pretty strong, with the following exception:
The ball link that connects the flap horn to the stab horn!

I urge you to PLEASE replace it with some other STRONGER link!
THE ONE YOU SHOW IN THE PIC WILL FAIL EVENTUALLY (sooner than later...)! 

I hope this non solicited advice doesn´t bother you.

Kind regards,
Claudio.

[Lauri Malila]

Ken,

I think you sacrifice quite a lot of fuselage rigidity for this rather unnecessary accessibility. Perhaps you have to adjust so many things because of some weird flexing caused by the huge access hatch right where the forces are the greatest..?
A more efficient solution, if you want a full access, would be a removable fuselage tail part a'la Yatsenko's. Split line at flap hinge line. L

[Ken Culbertson]

Ken,

I think you sacrifice quite a lot of fuselage rigidity for this rather unnecessary accessibility.

You are forgetting that this is a test bed.  The controls are in and out of the plane all the time.  There is no loss of rigidity.  Like I said earlier, the lower hatch is structural and held on by 4-40 machine screws through the side.  The control box is on 1/2" balsa/bass and the CF tray which is a sung fit is bolted to the rails.  It spans the wing from 1 1/2" in front of the TE to 3 behind.  The stab has virtually no wiggle. It is no less rigid than a removable would be.

Ken

[Ken Culbertson]

Dear Mr. Culbertson.
The entire removable system looks pretty strong, with the following exception:
The ball link that connects the flap horn to the stab horn!

 I urge you to PLEASE replace it with some other STRONGER link!
THE ONE YOU SHOW IN THE PIC WILL FAIL EVENTUALLY (sooner than later...)! 

I hope this non solicited advice doesn´t bother you.

Kind regards,
Claudio.

No bother, I am looking for comments.  This is a test project, so I need the good and the bad.  Not sure which link you are talking about.  The stab is driven by the top half of the forward logarithmic horn (the picture is the bottom).  It is the one that you can barely see.  It is a Dubro heavy duty, same as all of the others.  If you are talking about the Clevis's driving the flaps, I have used those for years and never had one fail.  There is no choice but to make that connection with a clevis.  Ball links won't fit.  I am in the process of re-doing the aft pushrod.  It is rubbing on the base of the canopy after repositioning the control box.  There were a lot of little things wrong that needed to be fixed if the canard was successful.  It is and then some, so now I am going about fixing them!  Thanks for the input.

Ken

[Mark wood]

I've been out of the model building phase for quite some time working on full size projects. I'm coming to the point where my 4/4 work for other people is about finished. Then I'll be back to building models.

Ken this is looking pretty good. The real question is in how the system performs. As was pointed out, this is really just an adjustable version of Igors flap control. The intent is to be able to modify the movement ratio between the flaps and elevator. The adjustable links allow for trimming.

True for some the complexity is excessive and unreasonable. For others it allows for experimenting. No, it is necessary at all. If the goal of the pilot is to win the nationals or world championships, time and energy is better spent flying and not developing. If you are an innovator, like myself, Pushing the boundaries and creating new things is what we do.

Ken, I think what Claudio has concern with is the push rod coming off of the input lever. I could add a feature to mount a proper ball link there fairly simply.

[Claudio Chacon]

No bother, I am looking for comments.  This is a test project, so I need the good and the bad.  Not sure which link you are talking about.  The stab is driven by the top half of the forward logarithmic horn (the picture is the bottom).  It is the one that you can barely see.  It is a Dubro heavy duty, same as all of the others.  If you are talking about the Clevis's driving the flaps, I have used those for years and never had one fail.  There is no choice but to make that connection with a clevis.  Ball links won't fit.  I am in the process of re-doing the aft pushrod.  It is rubbing on the base of the canopy after repositioning the control box.  There were a lot of little things wrong that needed to be fixed if the canard was successful.  It is and then some, so now I am going about fixing them!  Thanks for the input.

Ken

Ken,
This is the ball link I was referring to...

Claudio.

[Ken Culbertson]

Ken,
This is the ball link I was referring to...

Claudio.

That is the line that drives the CAM rudder (yes, I am a tinker addict). It is very low pressure and like the clevis, I needed to have it attach via a "ball & post".  If that were a control surface, I would have already crashed!  Thanks for noting it because I think I need a bigger ball!

Ken

[Ken Culbertson]

Ken,
This is the ball link I was referring to...

Claudio.

You were right.  That link failed.  Actually it failed before I ever flew it.  The hole is too large and the threads don't hold worth a *&%.  Fixed that along with the other stuff.  Thanks for pointing it out!

Ken

[Claudio Chacon]

You were right.  That link failed.  Actually it failed before I ever flew it.  The hole is too large and the threads don't hold worth a *&%.  Fixed that along with the other stuff.  Thanks for pointing it out!

Ken

You're welcome, Ken.
That was, by far, the weakest link on your control system chain...
I'm glad that it happended at home and not while flying!

Regards,
Claudio.

[Ken Culbertson]

You're welcome, Ken.
That was, by far, the weakest link on your control system chain...
I'm glad that it happended at home and not while flying!

Regards,
Claudio.

All it would have done was disconnect the CAM rudder but why go to the trouble of having one if it is disconnected!

Ken

[Vitalis Pilkionis]

Igors logaritmic controls removable version...