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Author Topic: Cardinal weight  (Read 1869 times)

Offline harold hogan

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Cardinal weight
« on: March 11, 2022, 03:34:35 PM »
For you guys that have built a profile Cardinal,  what final weight should I be targeting? I'm going to use a 46LA and probably a 4 1/2 ounce tank. Thanks

Offline Dan McEntee

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Re: Cardinal weight
« Reply #1 on: March 11, 2022, 03:47:07 PM »
For you guys that have built a profile Cardinal,  what final weight should I be targeting? I'm going to use a 46LA and probably a 4 1/2 ounce tank. Thanks

      If you are building a kit, you won't have much control over finished weight unless you have a good stock of wood to replace what's in the kit. It's a largish model so could tolerate a bit more than expected. If it's anything under 48 ounces, I think you will find a LA.40 easier to tune and still have plenty of power. If it comes out over 50, then go with the .46. I have a profile Cardinal that I got second hand and I'm much happier with the .40 after experimenting with the .46.
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Offline Ken Culbertson

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Re: Cardinal weight
« Reply #2 on: March 11, 2022, 04:06:11 PM »
For you guys that have built a profile Cardinal,  what final weight should I be targeting? I'm going to use a 46LA and probably a 4 1/2 ounce tank. Thanks
Mine (highly modified) was a beast with the LA46 at 52.  I tried it with the LA40 and changed back immediately.  The 46 is just easier to live with.

Ken
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If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline harold hogan

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Re: Cardinal weight
« Reply #3 on: March 12, 2022, 05:58:45 PM »
Thanks guys, I'm going with the 46LA because that's what I already have. I'm at 35 ounces right now before covering and dope. That's weighing everything individually before assembly, including the motor.

Offline Motorman

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Re: Cardinal weight
« Reply #4 on: March 12, 2022, 09:23:34 PM »
LA 46 will be awesome on a Cardinal. What's the fuselage look like between the wing and tail? Is it hollowed out like the ARF. The reason I ask because, the flexibility of that area will be the difference between a great flying airplane and one that's hard to control. If you add weight there with 1.6 oz fiberglass cloth on the bias put on with 2 coats of Zap Zpoxy, it will be weight well spent on stiffness.

Motorman :(

Offline Ken Culbertson

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Re: Cardinal weight
« Reply #5 on: March 12, 2022, 10:44:33 PM »
LA 46 will be awesome on a Cardinal. What's the fuselage look like between the wing and tail? Is it hollowed out like the ARF. The reason I ask because, the flexibility of that area will be the difference between a great flying airplane and one that's hard to control. If you add weight there with 1.6 oz fiberglass cloth on the bias put on with 2 coats of Zap Zpoxy, it will be weight well spent on stiffness.

Motorman :(
He is right about the tail whip.  I put arrow shafts on the top and bottom.  Almost zero twist in the tail.

Ken
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If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline harold hogan

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Re: Cardinal weight
« Reply #6 on: March 13, 2022, 09:11:56 AM »
The fuselage is standard 1/2 inch balsa..its not hollow. I plan on covering the fuselage with light silkspan and dope to strengthen it some. Should that be adequate?

Offline Ken Culbertson

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Re: Cardinal weight
« Reply #7 on: March 13, 2022, 10:09:02 AM »
The fuselage is standard 1/2 inch balsa..its not hollow. I plan on covering the fuselage with light silkspan and dope to strengthen it some. Should that be adequate?
Much of that depends on how you are going to use it.  The tail flopping around, which it will even with silkspan covering will hurt the quality of maneuvers, not your ability to do them.  If you are planning on competition, then you need to stiffen it better.  Any one of several methods will do it and I will leave them to those that use them.  My favorite is to dig a trench in the top and bottom of the fuselage from mid wing to the tail and imbed 2 thin wall arrow shafts.  I would also take out about 1/2 of the balsa in the center and replace it with an "X" pattern 1/2 x 1/16 stiff balsa web and sheet over the top with medium 1/32.  Some use 1/64 plywood. Then cover with silkspan.  You have 3/4" width to play with.

Good luck - Ken
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline Brett Buck

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Re: Cardinal weight
« Reply #8 on: March 13, 2022, 03:37:36 PM »
The fuselage is standard 1/2 inch balsa..its not hollow. I plan on covering the fuselage with light silkspan and dope to strengthen it some. Should that be adequate?

   While there may be value in some of the suggestions, don't take extraordinary measures to stiffen it up. Depending on your experience level, you could replace the silkspan and dope with 1/2 ounce/square yard fiberglass with finishing epoxy - in addition to stiffening it up, it also seals it from fuel, and gives an excellent base for the finish.

  Most of the flexibility comes around the stabilizer/fuselage joint. Make sure you use a good-sized epoxy filler fillet (SuperFil, Aeropoxy Light, or Epoxolite) to beef up that connection. On my airplanes, I use hard-balsa doublers with the grain running vertically, but those are in the inside since my fuselage is built-up.

    The one performance change I would recommend is to build it with a single flap hinge pin on each side, so you can remove the flaps later. The most serious design flaw with the airplane is that the stock flap dimensions are *far too large* for good control response. On airplanes with fixed (not-removable) flaps, the usual fix is to remove 1/2" - 3/4" from the trailing edge. With the flaps removable, you can just pull the pins, remove the flap seals, and put on alternate flaps of different size. That way you can try it stock, try it with, say, smaller flaps, and not have to cut anything. Put it back if you don't like it.

   The corollary caution is to *make sure the leading edge is rounded off as much as you can practically manage without going through the sheeting*. The plans probably show the LE coming to a point, or very close, but you want it to be as blunt as you can make it. Make it a pure radius from the upper to lower surface of the sheeting, starting where the sheeting goes over the rear edge of the 1/4 square LE wood, that will be good enough.

     Brett

Offline harold hogan

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Re: Cardinal weight
« Reply #9 on: March 14, 2022, 02:44:18 PM »
Thanks guys......Brett, excuse my ignorance....I'm just getting back into control line after over fifty years but I like your suggestion about making the flaps removable. Could you give me instructions on how to do that please?

Offline Brett Buck

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Re: Cardinal weight
« Reply #10 on: March 16, 2022, 09:58:13 PM »
Thanks guys......Brett, excuse my ignorance....I'm just getting back into control line after over fifty years but I like your suggestion about making the flaps removable. Could you give me instructions on how to do that please?

     Remove all the pins on the hinges, and replace them with a single really long hinge pin that goes through all of the hinges. Normally on the large hinge, the pin is 1/32 in diameter, use a 1/32 wire to install them, then, once the glue is set, replace the pin with a .025 diameter pin for flight. Put a bend in the end and use clear tape it to the wingtip to keep it from falling out. If you want to alter the flaps, remove the tape, pull out the pin, then make a new flap using the current hinge positions.

  Note that the hole where the flap horn goes into the flap can't be glued, otherwise, you can't get it off. Just make it a tight slip fit.

   I show mine in this thread:

https://stunthanger.com/smf/building-techniques/removable-flaps/msg630594/#msg630594

    The reason is that this is a pretty simple modification (as opposed to some of the re-engineering ideas that might have some merit but are much more complex) that allows you to address the issue with the excessively large flaps without having to cut up the airplane. Note that I am pretty much 100% certain, having dealt with this issue on several occasions, that the flaps are much too large for the airplane. This allows you to fix it without taking a knife to a completed airplane. We have had to do this several times, including to the 2006 Senior National Champion Paul Ferrell - we cut 3/4" off the flap chord about a week before the NATs, it immediately fixed all the problems he had, and he won against some real competition. 

   Of course, building it as shown, then cutting it if necessary, is still an option. But the removable flap thing is so easy and so convenient for a variety of reasons that it seems like a good modification to do in any case.

    BTW, the idea behind the large flap is that it gives you "more lift". I think it has more to do with the noiproblem with the excessive flap is that it inhibits the pitching motion of the airplane. The tail is extremely large to overcome this effect. The combination has the effect of requiring a lot of control force to get the turn started, but when you reach some amount of deflection, the turn suddenly tightens up. The results is a sort of "explosion" corner that can be very difficult to control.

    Cutting the flaps down, or using smaller flaps, greatly reduces this effect (and not coincidentally makes the arrangement much more like other more successful stunt planes) and makes it much more predictable and take much less effort to fly.

     Brett

Offline harold hogan

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Re: Cardinal weight
« Reply #11 on: March 18, 2022, 07:04:32 AM »
Thanks Brett, I'm at the stage in the build where I may either narrow the flaps about a half inch or go ahead and make the flaps removable like youaresuggesting....not sure yet what I will do. I was wondering about sources for 1/32 and .25 wire....thanks again for your advice.

Offline Ken Culbertson

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Re: Cardinal weight
« Reply #12 on: March 18, 2022, 07:52:35 AM »
Thanks Brett, I'm at the stage in the build where I may either narrow the flaps about a half inch or go ahead and make the flaps removable like youaresuggesting....not sure yet what I will do. I was wondering about sources for 1/32 and .25 wire....thanks again for your advice.
Do both.  My experience with the Cardinal, and others around here as well, is that the flaps are too large.  Having them removable using Brett's method is no more difficult than having them fixed.  In many ways it is easier.

Good luck - Ken
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline Dan McEntee

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Re: Cardinal weight /Flaps Too Large
« Reply #13 on: March 18, 2022, 08:33:00 AM »
    I think that this may be a good time to point out just what to look for in flying traits that would indicate flaps too large? I and of the opinion that on a lot of models that the flaps could be smaller or simply reduce the throw in the thought that they would make more lift and less drag. I built my Dusty profile scale/stunt model using a Twister wing as a base, added a rib bay to each end of the wing to get a higher aspect ratio, and in order to make the flaps look more like the real aircraft flaps and ailerons, I made the flaps just a narrow strip. When it came time to do flight trimming, I was surprised at hw well it turned. The purpose of the airplane was not to be a world beater stunt model, just something to ease into scale with and also have it be capable of flight the patter reasonably well. In looking at other more recent design stunt models I have seen others out there that use a more constant chord width. I have a profile Cardinal that I bought from another modeler selling off his stuff, and as far as I can tell, flies reasonably well. I would like to get it back down off the wall and experiment with the flaps a bit if I can learn what I should be looking for. I'll put in a good , long flying session in it's current state just to get a good understanding of where it is now.  This may be a good comparison also with the non-flapped models out there like the Primary Force and the Sakitumi, of which I have an example of each.
  Type at you later,
   Dan McEntee
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Offline Brett Buck

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Re: Cardinal weight
« Reply #14 on: March 18, 2022, 02:28:01 PM »
Thanks Brett, I'm at the stage in the build where I may either narrow the flaps about a half inch or go ahead and make the flaps removable like youaresuggesting....not sure yet what I will do. I was wondering about sources for 1/32 and .25 wire....thanks again for your advice.

  Both are available in the usual K&S display with the cardboard tubes.

     If you are going to cut them down, start with 1/2". I like the removable flaps (and elevators, normally), because it makes it very easy to finish around the trailing edge, easy to put the seal on, and I have had to remove them to fix various issues over the years. And, if nothing else, to clean out the hinge line, which tends to get a little grungy over time.

      Brett

Offline harold hogan

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Re: Cardinal weight
« Reply #15 on: March 19, 2022, 02:50:30 PM »
Thanks for the great advice, I would prefer to start out with the full size flaps just to see the flying characteristics of the Cardinal, but after spending all that time finishing the plane with all the sanding, applying several coats of dope, more sanding, filler coats, color coats then clearcoat only to discover that the flaps are too big and needed to be cut down and refinished again, I would prefer to go ahead and narrow them down now before I start applying the finish on the plane. I'm probably going to cut them down by a half inch.

Offline Brett Buck

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Re: Cardinal weight
« Reply #16 on: March 19, 2022, 04:07:25 PM »
Thanks for the great advice, I would prefer to start out with the full size flaps just to see the flying characteristics of the Cardinal, but after spending all that time finishing the plane with all the sanding, applying several coats of dope, more sanding, filler coats, color coats then clearcoat only to discover that the flaps are too big and needed to be cut down and refinished again, I would prefer to go ahead and narrow them down now before I start applying the finish on the plane. I'm probably going to cut them down by a half inch.

  Do as you wish, of course, but it's no harder to install the hinges with a single pin than 6 individual pins, and it allows you to try it and then change your mind. I have used it for exactly that purpose on multiple occasions. One airplane, I have 3 separate sets of flaps for, the current airplane, two.

   1/2" inch is the reduction to build in, if you are going to. Note that this is about control feel/control consistency, so it might be hard to do any better without a reference (either a normal airplane that already flies well, or some expert help).

    Brett


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