I am planning on scratch building an 80" Cap based on the Midwest kit plans. Outlines will be the same, but everything will be lighter (based on discussion with Dick Hanson). I would also like to lower the horizontal stab some to reduce the pitch and roll coupling with rudder. My questions are:

1) How much to lower the stab? I am thinking maybe 1-1.5". Any more than that and it will start to look goofy and decidedly non-scale. Can much of the pitch couple be trimmed out with CofG changes as well? I don't need perfection, but less is always better and easier to mix out with no weird side effects.

2) The roll couple should be manageable with a change in dihedral (I think). Any guesses on how much to take out?

3) I would like some recommendations for aftermarket landing gear (carbon fiber preferred) and a fiberglass cowl to keep the weight down and quality up. I plan to use a two piece wing with carbon joiner tube, so I might as well continue the carbon theme.

I will be using sheeted foam core wings and stab and a built up balsa fuse. My target is less than 12lb with a ST2300 or OS160 for power. Any other tips/things to note about this aircraft or the Midwest plans?


Thanks,
Mark

You may want to take a look at some pics of a Carden 40% Cap and see where they placed the stab. If I am not mistaken, GP has a .40 size cap kit and in the instructions they stated that the dihidral was more than scale and not to change it as it would adversly effect roll coupling. A chat with Peter Goldsmith may prove useful as well.


Shawn

FWIW the Cap stab -in the scale location works extremely well -the lowered stabs are easier to do structurally and I have done them in various positions for that reason. but the benifits of lowering it for any real performance gain -- in my book -- extremely questionable - read that horse sh-it
some excellent full scale aerobats have relatively high stabs -the Zlin 50 for example .
in order of importance - weight then power then weight then power then weight then power .

If the standard location works well then I will not deviate far from that. I am awaiting the plans to see what else I feel the need to tinker with.

Thanks for the input, Dick, it's been a great help.


Mark

Lowering the stab on many CAP 232's significantly reduces the push to the belly in Knife-edge. In turn that means that you need much less rudder-to-elevator computer mix. Done this on three Cap's in the past and the latest 79" GP Cap 232 has it done already. That GP CAP pictured, KE'd very well as supplied with only a few % of mix.

Regards,

Eric.

Upload not working.

That was my question, because I have seen it mentioned in numerous places that the Cap 232 has significant pitch coupling in knife edge flight. Does the GP Cap still pull to the belly in KE? Do you have a dimension for how much below the thrust line it is placed? Did you notice any effect on stall or snapping and spinning manuevers with the lowered stab on the ones you have done? I have also seen roll coupling mentioned as well, but to me that is almost strictly a dihedral issue. To the point of a small mix eliminating it, anyways.

Has anyone had direct experience with the Midwest kit and it's characteristics in KE?


Thanks,
Mark

OK...this is an honest question..
I do not know much about aero or plane design... sadly,, I am one of the ARF masses.... and I have not owned a CAP...

but the comments state that moving the stab made a difference...

forgive me, but my question is this... unless you fly the EXACT same model with the stab in two different places.... how can you really tell if it is making a difference.. as two models of the same plane can fly quite differently due to the several hundred other things that could be a hare of here, a scosh there??

Honest question... how do you "KNOW" it made a difference?

I can then add the testing methodology to my quiver of knowledge...

Thanks

Very fair question. And the answer is that any number of good builders will produce the same model that flies virtually identical every time when building from the same kit. I have seen the pitch couple mentioned numerous places related to a number of different kits and/or plans of the Cap. And the root cause of a pitch towards the belly on KE flight is that the stab is too high relative to the fuse and/or thrust line (I'm not sure which, exactly, and they are intertwined somewhat) and needs to be lowered. On many pattern planes, adjustable wings and stabs mean that you can trim the plane with different incidence settings to make the tail fly higher or lower in level flight, essentially moving the stab up or down relative to thrust and achieve the neutral KE performance I want. Go through a trim chart to set up a good aerobatic design and you will find that they are very sensitive to changes and a different stab location will make a very noticeable difference in KE pitch coupling. Moving the CofG 1/2" makes a detectable difference in pitch coupling and inverted behavior as well. So if Eric says it improved his models, I don't doubt that it did.

The differences between airframes you ask about are real, since no one can exactly duplicate another airframe, but those differences are small between good builders. If you had Eric build one and Dick Hanson build another, one might need 4% mix to trim out a couple and the other 6%. But it won't be 2% and 20%, which is what we are talking about by relocating the stab.


Mark

Gentlemen,

Thank you for the input, it is now time to get over to the shop and do something with it. Going from this, I will definitely be lowering the stab for both structural and aero reasons. I will have to wing it on the dihedral and see what happens.

If anybody has a recommendation for landing gear or cowls, please let me know.


Thanks,
Mark

Ref.

"forgive me, but my question is this... unless you fly the EXACT same model with the stab in two different places.... how can you really tell if it is making a difference.. as two models of the same plane can fly quite differently due to the several hundred other things that could be a hare of here, a scosh there??

Honest question... how do you "KNOW" it made a difference? "

The way I found out about this condition was flying my CAP's, including a 321 EX. They all exhibited a wicked push to the canopy in four-point rolls and knife-edges. When a plane does not "work", out comes the knife or saw.

For roll-couple I used to increase or decrease the dihedral. For elevator problems the rule of thumb was lower the stab for a push and raise for a pull. How much is a guessing came of trial and error. Also it is not a simple action and result because other things can be made worse such as pulling or pushing to the canopy in up and down lines. After 50 years of modeling you get good at guessing!

As regards the Great Planes CAP 232, mine only needed a few % of up and no roll correction. It was by far the best CAP I have ever flown in many departments. Also I have never built an ARF as good as this one. Said another way, I didn't modify it. Usually I do something. Not on this one. I did fit a soft-mount but that's another story.

Regards,

Eric.

OK, now that you have put that out there, how much dihedral did it have?


Mark

pictures are not working - will try later...

Thanks all... I get it...

I was out of town for the weekend so sorry for the delayed response

No problems, it is all a learning experience.

It doesn't have to stay that way. Just get a kit to start with and start hacking. None of us knew anything at the beginning and just pushed at it until we did...[8D]


Mark

FWIW--
the CG setups will change how the CAPS and any other bird handles
But -- the stock CAP 232 setup - will do absolutely flawless four points extended slow rolls -etc.. setup correctly with very little mix
The reasons why a lowered stab helps have been listed many times -by others also. frankly I can't buy into it .
Having built many CAPS with large/small / high/ low stabs - there is some difference but other than structural - none I would bother with.
making the stab larger makes for far greater differences in how the model performs
check out your own setup -- likely the horizontal tail has been fudged a fair bit .
.

Very true. I noted that CofG affects inverted behavior and pitch coupling back a few posts, too. How did you set yours up with the high stab to get very little coupling? Were you at hands off inverted (and upright, of course) level flight or did you keep a bit of forward stick for inverted? If necessary, one can also raise or lower the ailerons a turn or two (at the clevis) to adjust the trim. As Eric noted, vertical uplines and down lines also become involved. Complicated thing, this perfection in flying...

On your lightweight ones what did you use for dihedral? Straight in line with only the taper creating dihedral, flat top of wing or somewhere in between these two?


Mark

Here are some pictures of the Great Planes 79" CAP 232 that illustrates the much lowered position of their stab.

I don't want to get into a brawl with Dick Hanson over this stuff. Dick is a well known designer and builder. Please take my information more as a data report for you to do with as you see fit.


Regards,

Eric.

Thanks for the pics, Eric. I had a look through their site as well and it is apparent that the stab is much lower than any other 232 I have seen.

I don't want a brawl, either. I'm just trying to get the best flying Cap 232 I can. I respect Dick's resume and advice and yours as well. What I do with it is up to me. As mentioned, CofG and many other set up items can influence this, even a particular flyer's choices and preferences for control throws and style of flying. There is no magic bullet for this stuff and it takes trial and error and some compromise in the end. From this discussion and other reports and comments I have seen, I will be lowering the stab some, for an easier/better structural arrangement and to reduce coupling. If it goes wrong, I will have no one to blame but myself...

Did you ever notice the amount of dihedral used on the GP version?


Thanks to all for the help,
Mark

I have avoided the dihedral question because it is a hard one to answer.

The thicknes of the wing-rib at the root and the wing-rib at the tip means that the wing tapers a lot in thickness. Your dimensions would influence the resultant flight behavior, which I can't predict. My CAP is now in the hands of a less experienced flyer and he is doing very well with it. That also means that I can't easily measure it for you either.

Regards,

Eric.

C'mon, chicken. I understand the thickness/taper problems and mostly was just wondering if the dihedral was only from taper (that is, the centerline of the root and tip ribs were level) or if the wing was built upside down with the top surfaces flat. From what I see and have heard, the flat top would be pretty good or maybe a touch too much dihedral and the taper only would not be enough. Many pattern planes are like this, but they are mid-wing designs and don't need any dihedral to yaw properly. Ah well, I will just go with what looks about right (and I will see what the Midwest plans say) and see what happens.

Since the Cap is a low wing design, for a two piece wing would you go with a tube joiner and bolt the joined wing to the fuse or keep the tube in the fuse and slide a wing panel on from each side (as is typical on most 2M pattern ships right now)? I am leaning towards joining the wing, then bolting it on with 4 bolts myself, but that is with no experience on a plane this size so far. Which is the lighter set up? Dick, can you comment on this as well?


Mark

I have done this exact same size --both ways and the tube joined wing model was lightest - however that is because the entire model was -piece by piece -lighter -lighter cowl and canopy also
typically the CAPS I did this size are 10lobs with a YS140 and 13 with a ZDZ40 and can
I also flew the H9 80 " setup with a ZDZ50 and a in cowl setup I designed - very good flyer but almost 3 lbs heavier
The dihedral was close enough with the 10% tip and 12% root - and flat along top high point
Note in the interior shot --the forward fuselage ass'yis an I beam --on it's side - this is incredibly stiff and light made from laminated balsa and spruce longerons .

So it's pretty much a wash between the two methods? I would be very happy with a 12lb model using a ST2300, 10lbs is simply amazing.

So it shall be.

I'm not sure I have this right. Are you referring to what looks like the fuse floor? It appears to be spruce longerons on each side with an end grain shear web in between, is that correct? Then you simply have a framework to support the covering and form the exterior bottom of the fuse? At least that is the way it looks in the fuse shot from the tail forward.

Many thanks for the 3 view and pics.


Mark

I showed the fuselage on it's side - - --Imagine an I beam-the sides are top and bottom -the floor in centre is the upright
Each side is laminated balsa -light stock - bonded at 90 degrees .
the bulkhead is als laminated
The spruce carries the load fore/aft - the floor does two things: It makes the fuselage absolutely rigid against any "racking"
secondly the exhaust system is below - isolated from anything else.
Frankly I think the current structures used by many ARFS - is simply archaic--

Got it. I understand the I-beam concept, was just trying to understand which piece was doing what in your pic.

This very similar to the Insight pattern plane by Mark Hunt. He used 1/8 balsa sides with a vertical grain 1/16" balsa doubler in the wing tube area. He said it has been working well and is very light.

I have used formers that were 1/16" balsa laminated at 90 degrees and they worked well. Sounds like the same thing.

Lots to think about, thanks Dick. Anything I can do to get it to 12lb or less is very appreciated. Did you find the 10lb ones at all "floaty" or touchy in windy conditions? That is extremely light for that much wing area.


Mark