Bouncing at the stooge

[Dave Moritz]

My SIG Skyray does this to a remarkable degree, so much so that I fear damage to the empennage. I can control it with weight, but might the bouncing indicate other problems with the plane? By the way, it flies very poorly and am working hard to get it trimmed properly.

Dave Mo...

[Gerald Arana]

Bouncing? Can you explain that a bit more please?

Thank you, Jerry

PS: Brett will have the right answer for you I sure!

[Ken Culbertson]

With the motor running full tilt and the plane restrained at the tail with the nose pointed up some it is going to try and take off and most of our modern motors are producing thrust  in excess of our model's weight.    That will cause the wheels to bounce. I tried to keep the plane as close to level as possible.  Have you tried a string "Wrap around the stab" release instead of a tail hook?  I use a 3" wire soldered to the tail wheel wire with a loop at the end.   That kept the tail well clear of the stooge and also made it easier to hook the plane in.  They also make nice wall hanger mounts.

Ken

[Dave Moritz]

Hmm…, the bouncing of the tail occurs when the engine is at takeoff speed. The tail is restrained by a 3” wire with a loop on the end. At first I thought it was some kind of harmonic tuned to an unstable engine run. Changed tank, got a much better run, but still bouncing. I could live with it though Ken’s suggestion sounds like it’ll do the job in place of the weight.

Flight characteristics are more problematic (discussion perhaps to follow when this is ironed out).

Thanks.

Dave

[John Park]

It sounds as though the anchor point of the stooge might be too low.  The one I use (home-made, of course) is arranged so as to restrain the model in a level attitude, and I've never experienced the problem you mention.

[Dan McEntee]

  This is why you need to use a double upright or goal post style stooge that restrains the model at the horizontal stab. It's noty much different than your flying buddy holding the model and releasing it. The tail wheel hook holds the back end down and on release, it tends to spring upwards. If your stooge is constructed in a way that has the tail wheel roll over any part of the structure, that affects how smoot the release is also.
  Type at you later,
  Dan McEntee

[peabody]

Just as juming rope when you were a kid, it's best you start timing your jumps to match while a foot or so away.
When you feel comfortable that you are in sync, slowly hop toward the plane. When about an inch away, take a BIG forward ieap.
You ought to be able to crush it in a single try.

[Steve Dwyer]

Dan,

I have a friend that uses the goal post style stooge. He's not happy with it because it tends to lift the tail as the elevator leading edge moving forward rides up the goal post as the post swings forward and down. If the grass is a bit high, or you have a large prop the prop will occasionally strike the ground. We thought if the post was spring loaded and it snapped forward faster than the elevator moved forward this could be eliminated.

Steve

[Steve Dwyer]

https://stunthanger.com/smf/open-forum/bouncing-at-the-stooge/#:~:text=By%20the%20way%2C%20it%20flies%20very%20poorly%20and%20am%20working%20hard%20to%20get%20it%20trimmed%20properly.

I'm anxious to see the comments on the Skyay's performance issues. I built one last year and was disappointed with it. I know this topic has been kicked around at length previously.

Steve

[Dave Moritz]

Gents:

Well at least I now know that the problem is in the stooge. I did have a dual post stooge at one time and it was great for larger models, but lousy for the little ones. Might reconsider.

Peabody’s advice sounds tempting. I built this model from the kit and had trouble with a crooked spar. The suggested balsa replacements saved saved the bird in two crashes. Can’t praise that idea enough.

The plane is slow in loops and turns in. Will try engine offset today before bad weather sets in.

Dave...

[Brett Buck]

The plane is slow in loops and turns in. Will try engine offset today before bad weather sets in.

  What engine, what prop, what RPM? "Slow in loops" sounds like an engine problem.

    Brett

[Dan McEntee]

Dan,

I have a friend that uses the goal post style stooge. He's not happy with it because it tends to lift the tail as the elevator leading edge moving forward rides up the goal post as the post swings forward and down. If the grass is a bit high, or you have a large prop the prop will occasionally strike the ground. We thought if the post was spring loaded and it snapped forward faster than the elevator moved forward this could be eliminated.

Steve

   There has to be a problem with the hinges in the uprights, or the up rights are too slick and they allow the stab to slide up. I have never witnessed that myself on mine or anyone else's stooge. With the engine running and creating pressure against the uprights, they should jump forward on their own. I have some pipe insulation on mine and maybe that cushion provides some spring action. Having the uprights tilted back a bit will give some extra oomph to kick the uprights out of the way.

    Dave;
  Have you got any experienced help near you? Sounds like the engine isn't running fast enough, but still, loops shouldn't be too fast if you are making them large enough. You need to be closer to 5 seconds for a lap to get what you need.  We need to know more about your operating parameters.
  Type at you later,
  Dan McEntee

[john e. holliday]

I fly off of grass and have not had that bouncing while engine is running while I go to the handle.  Does the plane bounce while you are at it?   Also the upright armed stooge is used mainly for my trike geared planes which are twin engined.   

[Ken Culbertson]

I think all of us (me included) are coming up with solutions to what WE think your bouncing looks like.  I am also pretty sure that if we knew what it looked like someone will quickly recognize the problem and give you the fix.  I will ask one more question anyway.  Are your controls free.  In other words, will the elevator self-center just from the prop wash?  It is not necessary that you be able to smoothly operate your controls by moving the elevator.  Mine are slily smooth when powered by the bellcrank but not so much if you try and use the elevator pushrod to move them.  On a simple wire loop stooge connection combined with an elevator pointed down you are going to get a spring effect and the tail will "bounce" until you get to the handle and put tension on the leadouts.

Keep in mind that this is just another "SWAG" until we know what it looks like, but it is still dark here and I thought I would take another shot!

Ken

[Dave Moritz]

Hello Good Gents:

Such generosity here!

Ken: Yes, the elevator droops downward when it's unimpeded. I can live with that and the possibility of having to construct another dual post stooge. Thanks.

The bigger problem is the model's lack of performance. Brett: I'm running an OS 20FP (steel version) BBTU, 9x4 prop, launch tach speed of 11,800 on 59 feet of Spectra lines. Last time I checked, laps were 5.2 seconds and still likely close to that. Model weight is 32 ozzies (as the Divot would say). I swapped the motor for another OS 20FP and did no better. The large loops end up about three feet above the ground. I've got an OS 25 FP that'll fit the front end but will hold off on that a bit. The OS motor did such a good job on my Cartier RST that I thought it would do as well here. No dice. This sport does indeed have its mysteries!

Per Dan, a related problem is not having anyone around to help me figure this stuff out. Closest help would be a club near Milwaukee. I hope one of their members sees this and can PM me.

Thanks all!

Dave Mo...

[Dave Moritz]

Oops, a follow up concerning the BBTU. Both motors are the RC versions converted to CL. Both have large NVAs and large venturis (correct size from what I can tell).

Dave Mo...

[rich gorrill]

Dave if your skyray wont loop, check the balance, sounds like it might be very nose heavy. Dan is right about the pipe insulation on the goal post stooge, i have it on mine and the stab never rides up. Good luck

[Steve Helmick]

It would help a lot if you could post a picture of your model hooked to the stooge.

I am wondering if the tailskid or tailwheel strut is too flexible, or the stooge pulls up or down on said strut.

Do the math on the effective throat area of these .20FP's. I'm wondering if your launch rpm is maxed out, resulting in the engine sagging lean during maneuvers.  Steve 

[Ken Culbertson]

A 5.2 on 59' lines is barely adequate flying speed.  I have never owned a Skyray but I have had numerous small profiles that are similar.  They do like to fly fast and trim is impossible until you have enough speed.  Some quick math says you are flying at around 48mph.  Do what you have to do to get to a 4.5 or so. I would say 50-55mph minimum.  Maybe Brett can guide you on airspeed.  He is known to have flown a few of them.

Check the flexing issue too.  Steve is right about flexible tail wheels.  Personally, I like them because of the way I land so I mount my stooge hookup well above the tail wheel to minimize the spring when it is released.

Ken

[Dan McEntee]

     Now we are getting a few more pieces of the puzzle. This difficult to do with being able to lay eyeballs on things.  A Skyray .35 on 59 foot lines flying a 5.2 second lap or there abouts should be able to do a nice loop. They Skyrays I have and have flown of others handle quite well at that speed as long as they have enough thrust. The parameters you are quoting are in the realm of what Brett usually quotes. The only thing we can't see is how you are attempting your loops. most beginners just give an up yanks for all that are worth thinking that is what the trick calls for. This just stalls the airplane, slows it down and it tends to drop. The first thing to make sure you are aware of is where the wind is blowing and you want to be dead down wind when you do a loop. You have the whole sky to loop in, even right over and behind your head, so fly the airplane all the way through the loop. The old fashioned way is to start with wingovers, and you start with those by pulling straight up when up wind, and let the model go up and over and pull out on the other side. If your airplane will do a wing over, it will loop. When you start to close up the wing over into a loop, move things more down wing. Just do two or three loops and then stop so your lines don't get too twisted. Repeat on subsequent flights. When you are getting them to about 45 degrees or a bit more at the top and pulling out 5 or 6 feet above the ground consistently, and you are not loosing any speed doing it, you are getting there. Time to go read the "How to Fly Inverted Thread" and get that mastered so you can get ready to do outside loops to unwind your lines.!!
  Type at you later,
   Dan McEntee

[Brett Buck]

Oops, a follow up concerning the BBTU. Both motors are the RC versions converted to CL. Both have large NVAs and large venturis (correct size from what I can tell).

Dave Mo...

   Do you have a way to measure them to within a few thousandths? "Large NVA" makes me uncomfortable, because the stock units are pretty small. The symptoms sound as if you are down on power, or setting it so lean that it is going "over the top" lean in the maneuvers.

     Are you setting it as described - start, peak out lean, then back off until you get a distinct drop in RPM (about 6 clicks on the stock needle)? 

     BTW, 5.2 on 59 foot lines is pretty slow, mine was much faster, but if otherwise in trim, should be enough to do loops. Note also that unlike a lot of "classic" airplanes, you need the elevator motion to go as far as it goes, +-45 with full handle motion. The difference is that the tail moment is much longer than old designs, arguably too long.

     Brett

   

[Dave Moritz]

Gentlemen:

Lots to digest and respond to here. Many thanks. For the time being, I'll concentrate on Brett's good question concerning the engine(s).

With a digital caliper and drill bits, I've got confidence in these numbers (inches):
Engine Number One - NV tube is .138, venturi is .253
Engine Number Two - NV tube is .158, venturi is .283

Dave Mo...

[Brett Buck]

Gentlemen:

Lots to digest and respond to here. Many thanks. For the time being, I'll concentrate on Brett's good question concerning the engine(s).

With a digital caliper and drill bits, I've got confidence in these numbers (inches):
Engine Number One - NV tube is .138, venturi is .253
Engine Number Two - NV tube is .158, venturi is .283

Dave Mo...

   Thats about right, the first is probably the stock (3.5mm) spraybar with a slightly small venturi, the second is a ST copy or the older OS type from the 35-S (4mm). .253 is a bit on the small side, but probably OK. The other one is too large (probably a 9/32 drill).

   Engine #1 ought to be close enough and should have plenty of power, certainly faster than 5.2 seconds.  Engine #2, the venturi is excessive and will probably tend to go "over the top" due to inadequate fuel suction.

     I have little experience with steel-liner 20FPs but those who have (like David F.) tells me it runs about the same as long as you use enough oil.  What fuel and nitro are you running?  How is the engine running in level flight - hard 2? Medium 2? Does it ever hit a 4-stroke?

    Brett

[dave siegler]

Dave, check your PM.  The Milwaukee club can help you out, but its getting cold, windy and dark here. 
Next meeting is Saturday Nov 5.  if its nice we will fly if not we go to the nearby library.  Expecting a stunt clinic at that meeting as well.  please consider coming down.

Also I have flown skyray on a weak enya .19  or Fox 25 but had to shorten up the lines a little.  They would loop and to all the tricks.  So if your engine is in reasonable shape it ought to do it. 

IMHO is usually a prop, or tank fuel feed issue(vibration).  We can help out. 

[Dave Moritz]

Wowza, did I just hit paydirt here with Dave’s message! Will definitely follow up with him.

Again, many thanks to all those here who really put in the thought and time to help me suss this out. And yes, the cold North wind is a blowin’ round these parts. I’ll issue a progress report concerning the stooge and plane, likely during Spring.

Best to you all!

Dave Mo…

[Dave Moritz]

Good Gents:

Success at last this afternoon! In short, the problem was operator malfunction all along. Yes, I was giving the elevator way too much input and stalling, Dan. Thanks to Brett and Ken, I got the lap time to exactly 4.5 seconds. I had to monkey with the needle a bit more than the 6 clicks suggested as it was a cool 60 degrees outside. But did she ever fly well and stay out on the lines on the wingovers. By the way, I'm running home brew fuel of 8-24 (half and half). Seems to work well.

I've got a stooge modification to work on. I didn't know that a release rod that is too low could cause such troubles. Thanks for that pointer!

So, I'm off to meet and greet the Milwaukee club folks this weekend.

All the best to you and the rest,
Dave Mo...

[Brett Buck]

Good Gents:

Success at last this afternoon! In short, the problem was operator malfunction all along. Yes, I was giving the elevator way too much input and stalling, Dan.

    That's very interesting. Glad you got your engine run right. A lot of people just can't bring themselves to crank it up enough, after decades of equating "2-stroke" with "burn up!". Not a chance with this engine, look at how RC guys run them.

    If you are stalling and have an otherwise stock model, yes, cutting down on the throw is one possible solution. But there's no way that this should be possible with the stock elevator and even pretty large throw. It makes me wonder where your CG might be - in particular, is it too far aft. Could you balance it and tell us how far behind the LE it is?

    Brett

[Steve Dwyer]

I built a Skyray two years back to use as a beater to work on the pattern. After reading other's experiences I eliminated the plywood ribs using 3/16" balsa and covered it with silk with Napa grey primer prior to shooting it with a one color Butyrate finish. I never weighed it, unusual for me but I never bothered and chances are it was probably running a little heavier than I would have preferred. It definitely was tail heavy with the CG coming in about mid wing chord using a LA 25 and 2.5 oz tank, plastic spinner and APC 9x4. I added 1.0 oz nose weight and threw on an old heavy VECO 2.5" wheel to help move the balance forward. Still disappointed I decided to chop 2.5" off the tail. This resulted in less nose weight down to .5 oz to reach a CG about 1" behind the LE.

It flies ok with the LA 25 running fine at about a 4.6 lap but still seems doggy coming out of tight turns. I just not impressed with the Skyray, it's performs similar to the many flapless older design OTS models out there that have to be babied. I had expected it to be similar to the comparative size and length Flite Streak powered with the same engine and we all know the results there.

Steve

[Brett Buck]

I built a Skyray two years back to use as a beater to work on the pattern. After reading other's experiences I eliminated the plywood ribs using 3/16" balsa and covered it with silk with Napa grey primer prior to shooting it with a one color Butyrate finish. I never weighed it, unusual for me but I never bothered and chances are it was probably running a little heavier than I would have preferred. It definitely was tail heavy with the CG coming in about mid wing chord using a LA 25 and 2.5 oz tank, plastic spinner and APC 9x4. I added 1.0 oz nose weight and threw on an old heavy VECO 2.5" wheel to help move the balance forward. Still disappointed I decided to chop 2.5" off the tail. This resulted in less nose weight down to .5 oz to reach a CG about 1" behind the LE.

It flies ok with the LA 25 running fine at about a 4.6 lap but still seems doggy coming out of tight turns. I just not impressed with the Skyray, it's performs similar to the many flapless older design OTS models out there that have to be babied. I had expected it to be similar to the comparative size and length Flite Streak powered with the same engine and we all know the results there.

Steve

   One big difference is that the Skyray has a significantly longer tail moment than a Flite Streak, almost too long, as it inhibits the turn.

   You are more-or-less right, it is not a significantly better airplane. What is *does* have that is a overwhelming advantage for almost everyone likely to read this, is that it is *easy to build and trim*. You set the CG, use the leadout position I recommended, tweak the wings to get them level, and adjust the tipweight.

    So, anyone, even those without extraordinary trim skills, can get it nearly to ultimate performance. Use a proper engine, and trimmed to near 100%, it flies *much much* better than most people's "better" airplanes. It's the same idea as behind the Doctor/Medic  - airplane with good performance but *easy to trim* and uses reliable modern power.

   This is such an overwhelming advantage that it trumps all other issues, as far as I am concerned. Because I can tell you right now, most people's "better" airplanes are not nearly as good and very difficult to fly, even for me.

   
    Brett

[Dave Moritz]

Brett et al:

Here are the full specs on my Skyray as presently set up:
1) CG 1-7/16" behind LE
2) Leadouts centered 1-3/4" behind LE
3) Tip weight .7 oz.
4) Fuel tank 3 oz. standard metal stunt tank on muffler pressure (intake 1-7/8" from fuse)
5) Elevator motion 45 degrees both directions
6) An additional 1/2" (front to aft) added to stock elevator.

Dave Mo...

[Dan McEntee]

Brett et al:

Here are the full specs on my Skyray as presently set up:
1) CG 1-7/16" behind LE
2) Leadouts centered 1-3/4" behind LE
3) Tip weight .7 oz.
4) Fuel tank 3 oz. standard metal stunt tank on muffler pressure (intake 1-7/8" from fuse)
5) Elevator motion 45 degrees both directions
6) An additional 1/2" (front to aft) added to stock elevator.

Dave Mo...

   What you have posted here is for sure in the ball park. I think you should just keep flying it, and fine tune things as you get more time on the airplane and more handle time yourself. Getting hooked up with the Piston Poppers will most definitely be a plus also. Lots of experience and just a lot more fun t fly with a group. I think that is what most of this thing called "stunt" is about!!

  Type at you later,
   Dan McEntee

[Ken Culbertson]

 Lots of experience and just a lot more fun t fly with a group. I think that is what most of this thing called "stunt" is about!!

  Type at you later,
   Dan McEntee

What Dan says is Sooo true.  I don't fly alone anymore unless I absolutely have(need) to.  Question, why the extra elevator?  Have you flown it before adding the extra?  I have added elevator to several profiles but always by lengthening the span, not the chord.

Ken

[Dave Moritz]

Ken:

I read it somewhere on the Interwebs. Figured it would be easy to remove should I have been led down the primrose path. Thanks to you and Dan for the good comments.

Dave Mo...

[Brett Buck]

Brett et al:

Here are the full specs on my Skyray as presently set up:
1) CG 1-7/16" behind LE
2) Leadouts centered 1-3/4" behind LE
3) Tip weight .7 oz.
4) Fuel tank 3 oz. standard metal stunt tank on muffler pressure (intake 1-7/8" from fuse)
5) Elevator motion 45 degrees both directions
6) An additional 1/2" (front to aft) added to stock elevator.

Dave Mo...

   I think your leadouts are too far forward, move them back about 3/8" next time. 

      Brett

[Dave Moritz]

Brett and others:

I forgot to mention that the ship has one degree of engine offset. Will move leadouts accordingly next flight.

Thanks.

Dave Mo...

[Brett Buck]

Brett and others:

I forgot to mention that the ship has one degree of engine offset. Will move leadouts accordingly next flight.

Thanks.

Dave Mo...

   I am curious about how "fast" your controls are - not how far it moves, total, how far it moves for a given leadout movement. For instance, assuming the leadout ends are next to each other at nuetral, how far does the elevator move when you give them 1" of differential? Average it out for either direction to null out differential movement. Also, what kind of handle spacing do you have?

   Some of the discussion above makes me think that it might be on the fast side.

    Brett

[Dan McEntee]

   I am curious about how "fast" your controls are - not how far it moves, total, how far it moves for a given leadout movement. For instance, assuming the leadout ends are next to each other at nuetral, how far does the elevator move when you give them 1" of differential? Average it out for either direction to null out differential movement. Also, what kind of handle spacing do you have?

   Some of the discussion above makes me think that it might be on the fast side.

    Brett

    On the Skyrays I have flown, I have put longer control horns to slow them down, just like on a Ringmaster. I think I used a 7/16" dimension from the bell crank pivot to the pushrod hole in an effort to slow then down right from the beginning, but after test flying I found them still too fast at the time. This was a long time ago , so not really sure. Both models have been put through the ringer, using them for all sorts of events like balloon bust, racing and such. I always thought that they flew a respectable pattern at the time. These were both Fox powered. The biggest flaw I remember was that on a hard corner they tended to roll so I must have too much tip weight in them.  I need to build a new one with a OS FP, LA .25 or FP.20 in the nose as a strictly stunt model some day.
    Type at you later,
    Dan McEntee

[dave siegler]

the weather here looks good for Saturday. 

We will help get is sorted out.  But if the controls a a little to fast, and the airplane is a little fast, it will still fly reliability.  When it loops flies level both upright and inverted, then we can fine tune it.  Then you can go to the steps outlined above to slow the controls and bring the lap speed in line. 

I always start too fast, a little nose heavy, a little shorter lines and extra control throw and back off to fine tune it.   

[Steve Helmick]

With a sidewinder engine and tank, I'd think .7 oz tipweight might be more than ideal. But I would also start with too much tipweight, rather than too little. It's hard to improve the trim on a basket case.  Steve

[Brett Buck]

With a sidewinder engine and tank, I'd think .7 oz tipweight might be more than ideal. But I would also start with too much tipweight, rather than too little. It's hard to improve the trim on a basket case.  Steve

   Maybe, but can't really estimate it that way, because you don't know how much lateral imbalance it has just built into the airframe.

   The only reasonable way to compare tipweight is to use the counterbalance method; that is, with the airplane in flight condition, just stack loose weight on the inboard tip until it is balanced. The weight required to balance the airplane level is the effective tipweight.

In any case, you have to adjust it by observation - fly it, look for hinging, adjust accordingly. And you generally want to start with too much and reduce it in small increments until you go too far.

    Brett
   
   

[Dave Moritz]

Brett:

The latest stats:

Handle spacing is 3.5"
One-inch differential for up is 28 degrees
One-inch differential for down is 32 degrees

Dave Mo...

[Brett Buck]

Brett:

The latest stats:

Handle spacing is 3.5"
One-inch differential for up is 28 degrees
One-inch differential for down is 32 degrees

Dave Mo...

   That seems pretty quick to me. I might suggest flying it "as is", then narrowing the handle spacing by 1/2", and seeing if that is a step in the right direction.

    This is not quite applicable, but for reference, I run a 3.875" handle spacing on my big airplane, and the differential for 38 degrees is about *3 1/2"*. Not that this is a standard to shoot for, since that is a full-up piped 60 sized stunt plane, and you have a Skyray, but, the travel rate is about 3x slower.

   With slightly slower rate on my former Skyray, I think I was running about 2 1/2" of spacing.

    Brett

[Dan McEntee]

Brett:

The latest stats:

Handle spacing is 3.5"
One-inch differential for up is 28 degrees
One-inch differential for down is 32 degrees

Dave Mo...

     You probably have a 3" bell crank, so you might be happiest the closer you get to 3" line spacing. I put longer control horns on the elevator on the Skyrays I have to help out with sensitivity so I don't have to go really narrow on line spacing. You can even just make up an "extension" out of a strip of brass stock and bolt it to the stock horn. The push yod is probably out about an inch from the elevator and if you put in enough holes to go from 3/4" to 1 1/4" you should find your "sweet spot" for the control speed. The airplanes have still been plenty responsive.
    Type at you later,
    Dan McEntee