Brodak ARF Cardinal trimming issue

[Jared Hays]

Ok so I have been working on trimming this plane out.  My dad and I assembled it a few years back we never liked how it flew so we hung it up and moved on.  Well there is a profile contest in Denver coming up quick so I decided eh what the heck I'll give it another go.  First flew flights kinda feeling it out and it seems like it wants to turn a hard corner but like its fighting itself.  

First thing I know that is wrong with it is that wing has a degree or two of up angle of attack as the fuse must not have been cut out quite straight from Brodak.  So when the plane is flying, it actually kinda looks like a B-52 with nose down attitude while flying level.  It's not terrible but its there.

Well I noticed the leading edge is very sharp like my Strega was.  So I did surgery and rounded off the leading edge.  That helped but not as much as a difference as it did to the Strega.  Then I checked CG.  WOW, was way up on the leading edge.  I added 2 1/4 oz of tail weight to get it to CG properly.  Went out tonight and boy will it turn a corner now.  But when making a hard corner the outboard wing comes up both right side up and upside down.  So I started adding tip weight.  Started the day with only a 1/4 oz.  Went to 3/4 oz.  seemed maybe a tad better.  went to 1 1/4 oz.  seemed about same as far as wing popping up in corners but started losing line tension in maneuvers went to 2oz and outboard wing still pops up in hard corners and losing all line tension in the corners now.

So, for now I went back to 3/4 oz and thinking I need to move lead-outs ahead and try again?  I know I read somewhere that people were saying there is too much flap on this plane and to cut off a full inch in length of the flap.  Is that what I am experiencing, just the flaps are creating to much lift and lifting the wing in hard corners?
 

[Brett Buck]

Ok so I have been working on trimming this plane out.  My dad and I assembled it a few years back we never liked how it flew so we hung it up and moved on.  Well there is a profile contest in Denver coming up quick so I decided eh what the heck I'll give it another go.  First flew flights kinda feeling it out and it seems like it wants to turn a hard corner but like its fighting itself.  

First thing I know that is wrong with it is that wing has a degree or two of up angle of attack as the fuse must not have been cut out quite straight from Brodak.  So when the plane is flying, it actually kinda looks like a B-52 with nose down attitude while flying level.  It's not terrible but its there.

Well I noticed the leading edge is very sharp like my Strega was.  So I did surgery and rounded off the leading edge.  That helped but not as much as a difference as it did to the Strega.  Then I checked CG.  WOW, was way up on the leading edge.  I added 2 1/4 oz of tail weight to get it to CG properly.  Went out tonight and boy will it turn a corner now.  But when making a hard corner the outboard wing comes up both right side up and upside down.  So I started adding tip weight.  Started the day with only a 1/4 oz.  Went to 3/4 oz.  seemed maybe a tad better.  went to 1 1/4 oz.  seemed about same as far as wing popping up in corners but started losing line tension in maneuvers went to 2oz and outboard wing still pops up in hard corners and losing all line tension in the corners now.

So, for now I went back to 3/4 oz and thinking I need to move lead-outs ahead and try again?  I know I read somewhere that people were saying there is too much flap on this plane and to cut off a full inch in length of the flap.  Is that what I am experiencing, just the flaps are creating to much lift and lifting the wing in hard corners?
 

   I think the flaps are way too big, but that's not the cause of your hinging problem. You just need more tip weight, put it in until it rolls away from you, then remove the last bit you added. Since it has equal-span wings, I think, it might take a lot of it to get it right.

 If the wing has positive incidence with respect to the fuselage, you probably can't fix the nose-down look. I it is turning significantly better inside than outside, you can put in down elevator at neutral flap.

     Brett

[Jared Hays]

That's what I thought but it seemed the more tip weight I put in the worse my line tension got and no change with the hinging problem...or do I just keep going with the tip weight.  My strega took like 3 1/2 oz and that to me seems like a brick out in that box haha.  Seems to turn the same inside and outside. The nose down look doesn't bother me, the worst part is it likes to shotgun takeoff because of it.

[Randy Cuberly]

Of course Brett is right about the tip weight.  However I would add one more thing that can seriously affect this situation, and that is flap hinge line sealing.  I know Brett didn't mention it because normally if the problem is caused by one flap being more effective than the other (outboard in this case) the condition will reverse in inverted flight, and the other wing will come up.  However, I have seen a couple of situations where the flaps were not properly sealed and also had a curved warp in one flap that made that flap very effective in one direction and not very effective in the other and coupled with a lack of properly sealed hinge line, caused the exact same problem you're experiencing.  Also, you said that the wing has positive incidence relative to the fuselage.  What is the Stab incidence relative to the wing and the flap neutral relative to the elevator neutral.  The relative incidence of win to stab is probably more important than the effective downthrust in the engine that you likely have if the fuselage seems to be pointing down as you mentioned.  More than a dergree or two of down thrust could be very detrimental, but about a half to 1 degree can actually be an aid to stability and tracking in maneuvers, 
Are the elevators both in the same plane.  Large elevators like the ones typically found on Stunt Planes can have an aileron effect if a couple of degrees out of plane to each other.

I've had two Brodak Cardinals but built from kits not ARF versions, and there are considerable differences.
The kit version, built with, smaller flaps (1/2 inch trimmed from each flap) is and excellent flier.  It does also have a somewhat different airfoil than the ARF version.

It really doesn't make any sense to me that adding tip weight decreases line tension and something else must be going on there.  Perhaps a warp in the wing or flap!

Try moving the line slider to a position about 1/2 inch behind the CG ( center point between the lines) as a starting position.  You mentioned that you moved the CG back significantly...What about the line slider position?  Did you move that also?

Randy Cuberly

[Jared Hays]

No I  did not move the lead-outs, thats what I planned on trying next they are pretty far forward already.  The stab seems level with the fuse.  The elevator is down just a tad when flaps are neutral so maybe I need to extend the push-rod.  None of the hinge lines are taped.  Yea didn't make sense to me either that I'm losing line tension by adding tip weight with this problem, that has helped on every other plane that has done what this one is doing and this one seems opposite.

[Brett Buck]

No I  did not move the lead-outs, thats what I planned on trying next they are pretty far forward already.  The stab seems level with the fuse.  The elevator is down just a tad when flaps are neutral so maybe I need to extend the push-rod.  None of the hinge lines are taped. 

   D'OH!   Go back, seal the hinge lines, then start over. It's particularly important on ARFs where the construction is haphazard at best. The chances that the hinge lines are not even or even throughout the travel.

    Brett

[Jared Hays]

what is the best material to seal hinge lines with?  I was thinking about trying clear monokote? Just make a strip and iron it on over the hinge line?

[Brett Buck]

what is the best material to seal hinge lines with?  I was thinking about trying clear monokote? Just make a strip and iron it on over the hinge line?

   Scotch Crystal Clear tape (sometimes called Multi-Task Tape) is what I use. For the technique, search the archive. Done properly there is negligible extra control load.

    I would also note that we all learned that it was valuable from one of Denny Adamisin's construction article in FM.

    Brett

[Rick Henry]

I haven't flown in a couple of seasons but I still like to read the posts from time to time.  I flew an LA 46 powered kit built Brodak Cardinal for three years and I can tell you mine flew better after I cut about a half inch off of the trailing edge of the flaps.  I remember reading somewhere that several people had cut down the flaps on the Cardinal. 

Rick Henry

[Dan McEntee]

  Do I understand that you cut 1/2" off the trailing edge of the flap, the whole length of the flap? Just want to be clear and log this if I ever get around to assembling the one I have stashed.
  Type at you later,
  Dan McEntee

[Brett Buck]

  Do I understand that you cut 1/2" off the trailing edge of the flap, the whole length of the flap? Just want to be clear and log this if I ever get around to assembling the one I have stashed.
  Type at you later,
  Dan McEntee

As I recall, it was 3/4" on Paul Ferrel's kit profile cardinal to win the 2006 NATs. I suggest starting with 1/2". You can always remove more later.

   Brett

[Rick Henry]

Yes that is right. I cut 1/2 inch off of the trailing edge of both flaps the entire length of the flap.  I know it seems like a lot but that is exactly what I did.

Rick Henry

[Tim Wescott]

And make sure you're not just trying for too sharp a corner.  After you fix the hinge lines.

If you're a PAMPA member, grab the last three issues of Stunt News, and read Paul Walker's instruction for trimming in his "Flying" column.

[Howard Rush]

As I recall, it was 3/4" on Paul Ferrel's kit profile cardinal to win the 2006 NATs. I suggest starting with 1/2". You can always remove more later.

Be careful not to let Brett near your airplane if he is carrying any sharp tools.  He has this flap-trimming obsession.

[Jared Hays]

Be careful not to let Brett near your airplane if he is carrying any sharp tools.  He has this flap-trimming obsession.

 

[Brett Buck]

   I would get it trimmed as designed first, then see if it is unacceptable. That way, if you end up needing some flap differential, you can trim one side 1/2 and the other 7/16.

    Brett

[Tim Wescott]

And make sure you're not just trying for too sharp a corner.

Let me expand on this:

I recently had a problem with the plane I'm flying with too much tip weight and really hammering the corners.  It'd go slack on the tops of the square maneuvers, disproportionately, it seemed, to what it was doing anywhere else.  I don't know if it's your problem, but read on:

After reading Paul's first article, and paying close attention to what I was doing in the turn, it became evident that on the square corners I'd hammer the turn to high level flight.  The plane had too much tip weight, so it'd roll out.  The problem was that then it'd be rolled so far out that it'd immediately roll back, overshoot level on the lines, and as a consequence go slack.

I'm pretty sure that I had gotten myself into that situation by adding tip weight to mask problems with leadout position in the overheads, but it may have been simple stupidity.

The answer was to first, stop turning so dang tight, second, take tip weight OUT until it was behaving nicer in the square corners, and then third, learn just how tightly I could turn my overweight Twister on the squares (the answer was -- tighter than before I took out tip weight).

Try all the simple things first -- but sometimes a problem seems complicated because it really is complicated.

[donchandler]

After about 35 yrs of Carrier and Scale and assorted odd ball WAM events I started to get alittle serious about Stunt And last seaon was asked to move up to intermedaite. Last contest, about two weeks a go, I finally got a half way decent score, for me, and am getting a lot more comfortable with squares etc. Point is, I have 3 Cardinals and that is all I have been flying at the 4 or 5 contests I have gone to and Brett and Ted Fancher both advised me to trim 1/2" from the trailing edge of the flaps and it does make a difference. I also added 1/2 ounce of tip weight after several flights and the last flight was nice and stable.

Just my 2 cents worth.

Don

[Jared Hays]

I appreciate the help guys...I just completed taping the hinge lines.  I wont cut the flaps until I get it flying better like Brett said.  I like to only make 1 change at a time put and then put couple oz. of fuel in and try it.  So hopefully the weather holds well tomorrow and I can get a couple more flights on it before I head to Denver on Friday.  Wish I had a few more nights of flying time but don't we all lol.

[Ted Fancher]

I appreciate the help guys...I just completed taping the hinge lines.  I wont cut the flaps until I get it flying better like Brett said.  I like to only make 1 change at a time put and then put couple oz. of fuel in and try it.  So hopefully the weather holds well tomorrow and I can get a couple more flights on it before I head to Denver on Friday.  Wish I had a few more nights of flying time but don't we all lol.

Jared,

Just saw this thread and wanted to comment.  I saw nothing about exactly where on the average chord of the wing the CG was...either before or after adding (the equivalent of) a small airplane   to the tail end.  Nor was there any comment about the leadout position RELATIVE TO THE CG before and after the big CG change...the failure to adjust the latter after so big a change in the former begs for re-assessment!  The leadouts pretty much had to be grossly incorrect for one CG location or the other...or maybe both...too far aft before the added weight and/or too far forward afterwards.

Also, you also more or less raved about the quick turns after adding the tail weight and, in my experience, really quick turns with a Cardinal with stock flaps pretty much pleads guilty to a too far aft CG.   The airplane with the flap trailing edge  trimmed as others have suggested turns a very nice corner with modest control effort.  With the large flaps and the CG in an appropriate location it will turn but only (IMHO) with excessive input requirements.  If it does "flick" corners with the big flaps it is almost certainly tail heavy with respect to the idea location. (I'm a big proponent of no greater flap chord than necessary, by the way...which is far from a generally accepted opinion so keep that in mind)

I'd encourage you to search for a good thread on bench trimming of a stunt ship.  Brett had probably the best one I can recall and can probably provide the link to it.  With just a bit of education it is possible to trim a straight, well powered stunt ship at a reasonable weight to fly close to correctly right off the board, requiring only small adjustments (a little harder to learn as the changes then become pretty subtle once the basic trim is established) to get it close to contest worthy (oh, and by the way, 2.25 ounces on the tail of a pretty long airplane doesn't qualify as subtle!  Part of the bench trimming process would have been to get your Cardinal to balance in the vicinity of 20% aft of the leading edge AT the AVERAGE chord before ever putting fuel in the tank...with the anticipation that corners would still not be crisp and flight trimming would be expected to suggest moving the CG a bit aft of that location...in small increments).

I wrote an column in Model Aviation years ago on bench trimming (might be somewhat dated) that is probably available through AMA's web site.  Brett's was,IIRC, much more up to date...and almost certainly more accurate!

Ted

[Robert Zambelli]

Since I have considerable experience with the Cardinal ARF, I would like to contribute to this thread.
I was visiting John when the first two prototype ARF Cardinals arrived from the factory in China.
One was slightly damaged, the other perfect.
We assembled the intact model and installed John's personal Brodak 40 (the FIRST Brodak 40) along with a four ounce non-uniflow tank, an 11-4 Top Flite wood prop and a two-inch plastic spinner. We positioned the leadouts by guess.
In that configuration, we made the first few flights. The prototype had no tip weight. As Brett correctly stated, it needed it badly. A few flights confirmed that 1 1/2 ounce was perfect.

Here are some particulars:
Weight: 45 ounces.
Balance point: 3 1/2 inches aft of leading edge edge at wing root (we DID NOT add tail weight)
Tip weight: 1 ½ ounces.
Front leadout: 1 3/4 back from leading edge. 2 3/8 inches spacing.
Rudder offset: Approximately ½ inch at rudder T/E.
Engine offset: zero.
We DID NOT round off the leading edge.
We DID NOT seal the hinge lines.

As we were quite pleased with the results, we gave the factory the go-ahead to start production.

At one of the Brodak Fly-Ins, they had an ARF stunt event. Four of us entered in the expert class. Gary Tultz, who had NEVER flown the plane, won first. I cannot remember the exact order but we all finished in the top five.

I loaned the plane to a fellow and he flew it to a first place in beginner stunt at KOI. He then splattered it and returned it to me in two shopping bags. I wrote a repair article while rebuilding the plane and published it -Stunt News, as I recall. After the repair, there were no detectable changes in flight characteristics. It gained less the one ounce.

I brought the plane to just about every event I attended, as well as trips to the local flying fields. I let anyone fly it and of course, solicited comments. For the most part, comments were positive. Besides myself, many people entered it in completion and it garnered quite a few trophies.
When it finally met its demise in 2008, it had around 600 flights, most of which were with the Brodak 40. I did experiment with a four-stroke engine, the OS Non-Surpass 40, and the results were quite good. At many of the Fly-Ins, we flew it at night, towing lights and having silly fun. Phil Spillman even killed a bat with it!
In closing, I should mention that I do not know if the factory made any changes from the prototype configuration, as they were told not to. There may have been some different materials used but I cannot confirm this. I have never flown another ARF Cardinal except for the prototype.
I hope this information is helpful.
Bob Z.

[Randy Cuberly]

Since I have considerable experience with the Cardinal ARF, I would like to contribute to this thread.
I was visiting John when the first two prototype ARF Cardinals arrived from the factory in China.
One was slightly damaged, the other perfect.
We assembled the intact model and installed John's personal Brodak 40 (the FIRST Brodak 40) along with a four ounce non-uniflow tank, an 11-4 Top Flite wood prop and a two-inch plastic spinner. We positioned the leadouts by guess.
In that configuration, we made the first few flights. The prototype had no tip weight. As Brett correctly stated, it needed it badly. A few flights confirmed that 1 1/2 ounce was perfect.

Here are some particulars:
Weight: 45 ounces.
Balance point: 3 1/2 inches aft of trailing edge at wing root (we DID NOT add tail weight)
Tip weight: 1 ½ ounces.
Front leadout: 1 3/4 back from leading edge. 2 3/8 inches spacing.
Rudder offset: Approximately ½ inch at rudder T/E.
Engine offset: zero.
We DID NOT round off the leading edge.
We DID NOT seal the hinge lines.

Hi Bob,
I'm sure it is just a typo but being basically a SmartXXs, I have to point it out.
I seriously doubt that the CG was 3 1/2 inches AFT of the TRAILING edge...likely you meant Leading edge but some poor beginner might get seriously confused!

I wouldn't want to try to fly any CL airplane with a CG in that position! 

Gotcha!!!

Randy Cuberly

[Robert Zambelli]

YIKES did I goof.
Now that would need some trimming!!!

  Sorry for the goof - it's corrected.

   Thanks for pointing it out, Randy.

      Bob Z.

[Mike_Ostella]

I remember flying Windys prototype ARF. It flew just as you described. You had to fight it to get to turn, and fight just as hard to get it to stop turning.

blunting the leading edge fixed that plane, but on windy days the back of the fuse was so twisty the plane had a mind of it's own.

Not a problem with the Brodak P40 ARF
Cheers
Mike Ostella

[Brett Buck]

I remember flying Windys prototype ARF. It flew just as you described. You had to fight it to get to turn, and fight just as hard to get it to stop turning.

   Exactly. Rounding off the LE and then reducing the flap size pretty well cures this.

   Brett

[Robert Zambelli]

"I remember flying Windys prototype ARF. It flew just as you described. You had to fight it to get to turn, and fight just as hard to get it to stop turning."

Mike: I'm not sure to which prototype you're referring but I was at John's when we opened the first two pre-production units that were sent from China. John stated that these were indeed the first prototypes and they were sent for evaluation. As I mentioned in my August 31 post, we assembled one of them and used it for testing. In that post, I also mentioned some of the other specs of the original.
Here are two more particulars from my notes:
Flap width at root: 2 7/8 inches. At tip, 1 3/4 inches.

Was the one you flew the prototype FOR the ARF? Before the specs were sent to China?

After we flew the ARF for a while, the factory sent me a wing for the ARC version, which I still have. Tony stated that it was identical to the ARF but of course, not covered. The photo shows the shape of the leading edge, as traced from the ARC prototype wing. Note that it is not sharp.

Again, I hope this helps.

Bob Z.

[Jared Hays]

Okay so before I added tailweight the CG was right on the LE of the wing.  My LE was very sharp.  Even sharper than the ARF Strega I have.  After tail weight was added the CG is about where the balsa sheeting ends on the front of the wing.  So pretty much at the thickest part of the wing.  I have been playing with the Leadouts some I havn't measured exactly where they are but they are fairly far forward.  I have gotten the plane to fly a lot better, I placed 3rd with it out in Denver at their Labor Day weekend contest.  The biggest problem it still has is when you try to turn a hard corner the outside wing hinges up then down, doesnt matter if right side up or inverted, it hinges up then hinges down, but Im not losing line tension like I was before.