Jetco Sabre Stunt

[Dennis Leonhardi]

I've admired that design since it came out (which makes a statement about age).  Looking at the plans last night, I noticed the stabilizer is to be sanded to a "lifting" airfoil ...  Word on the street has been that the airplane doesn't turn outsides well.  Is that airfoil supposed to help?

If you had or have one, please share your experience & thoughts - just for kicks.

Dennis

[Dan McEntee]

  The Jetco Sabre Stunt has an interesting history, if I am remembering all that I had learned about it. I think it was originally designed as The Wicked Witch?  Or maybe something similar, and as far as performance, you may want to build the original as it has a better airfoil. The Sabre Stunt was another victim of a design being altered to fit in a standard kit box. My flying buddy Mark Hughes built one years ago to take to VSC. He had only built a few models prior to that and had just started doing the full AMA pattern. Mark is a good builder even in his early days and did a nice job on it. I forget the weight and don't know if he even still has the model or not, I will find out. We built up a hot rod Fox .35 to power it using all the tricks I had at my disposal for it and it flew quite nice, I think. On his first flight in the contest, in front of Bill Zimmer and another good judge whose name escapes me now, Mark got a decent score in the upper 450's . In his second flight I think he was improving on that but got blown out of the clover a bit and almost lost it, but made a good recovery and managed to complete the trick with the Fox.35 really chugging away to pull the model straight up from a near stall at the bottom of the last loop, but it made it up and over the top like it should! I would have to check out a kit plan to be really clear on what you are referring to, but Mark's model seemed to fly well at that time for a guy who was probably an intermediate level pilot. Mark definitely improved as on his next appearance at VSC I think hew surprised everyone with a 3rd place finish in Classic against some pretty formidable competition!
    Type at you later,
    Dan McEntee

[jfv]

Dan:

Do you know where to get the airfoil for the original?

[Dennis Leonhardi]

  The Jetco Sabre Stunt has an interesting history, if I am remembering all that I had learned about it. I think it was originally designed as The Wicked Witch?  Or maybe something similar, and as far as performance, you may want to build the original as it has a better airfoil. The Sabre Stunt was another victim of a design being altered to fit in a standard kit box. My flying buddy Mark Hughes built one years ago to take to VSC. He had only built a few models prior to that and had just started doing the full AMA pattern. Mark is a good builder even in his early days and did a nice job on it. I forget the weight and don't know if he even still has the model or not, I will find out. We built up a hot rod Fox .35 to power it using all the tricks I had at my disposal for it and it flew quite nice, I think. On his first flight in the contest, in front of Bill Zimmer and another good judge whose name escapes me now, Mark got a decent score in the upper 450's . In his second flight I think he was improving on that but got blown out of the clover a bit and almost lost it, but made a good recovery and managed to complete the trick with the Fox.35 really chugging away to pull the model straight up from a near stall at the bottom of the last loop, but it made it up and over the top like it should! I would have to check out a kit plan to be really clear on what you are referring to, but Mark's model seemed to fly well at that time for a guy who was probably an intermediate level pilot. Mark definitely improved as on his next appearance at VSC I think hew surprised everyone with a 3rd place finish in Classic against some pretty formidable competition!
    Type at you later,
    Dan McEntee

Lots of interesting - and intertwining - history here. 

Don Hoag's Wicked Witch is an entirely different design, published in the November 1955 Air Trails.  At that time the magazines teased us with hints of the next issue's contents - my good friend Tom and I anxiously awaited the appearance of the "F-86 Sabre like" Wicked Witch.  Meanwhile, we went to watch a major contest here in September of that year and were startled to find indeed a "F-86 Sabre like" beauty.  So of course we asked the flyer if it was the Wicked Witch.

But no, it was Lloyd Curtis with his "Pink Ecstasy", published in the November 1956 issue of Young Men as the Curtis Special.  I got to know Lloyd later when I enrolled in Air Force ROTC at the University of Minnesota - great guy!

The Wicked Witch has a pretty significant difference in span between the inboard and outboard sides - enough that Bill Little advised it really affected the performance.  But it sure looks classy - Air Trails described it as "our nomination for best looking control line stunt plane".

Jose Sadurni designed the Sabre Stunt kitted by Jetco.  He placed 2nd in Open Stunt at our '55 Nats after winning the Mexican Nationals in '52, '53 and '54.

I have plans for both the Sabre Stunt and the Wicked Witch if anyone wants them.

Dennis

[Don Jenkins]

I have a Jetco Sabre Stunt kit and the plans do show a "lifting airfoil" for the flaps and stabilizer/elevators. Doesn't seem to be a good set up for stunt!

Don

[Dennis Leonhardi]

That's what got my attention Don!   

And the plans clearly instruct the builder to make it so.

Note on the Wicked Witch by Don Hoag: Inboard wing is 3" longer.  Ain't that a bit much?

Dennis

[Dan McEntee]

   I had never noticed the stab on Mark's plan, and that was along tie ago. There may be a simple explanation. One of the details for setting up a newly constructed model that I have learned from an article Bob Whitely did for Stunt News was to install the horizontal stabilizer with a tiny bit of positive incidence, about 1 degree or so. This was to counter an airplanes natural tendency to climb or pitch up when under power. I think that is the way the Bob explained it, but I found that it works, and the title of the article was "Things that always work" if I remember correctly. Free flight designs quite frequently use a lifting stabilizer to help keep the nose of the model down when ion glide mode. I think you would be very hard pressed to find any decent free flight design, powered model or glide (which they all tend to be) that doesn't have a lifting stab. This might have been the designer's way of achieving the same affect that Whitely was doing with the positive incidence. The effect is supposed to be very subtle. From what see in the photos it is a very small profile and I believe it would also be very subtle in it's effect. Knowing what I know now about model flight trim in general, I probably would try it, and just be as careful on the elevator/flap installation as I normally would be. I don't think it would cause the problems you think it might.  If there is a shortcoming to the design, it would be the thin airfoil, like there was on a lot of kit designs back then.
  Type at you later,
   Dan McEntee

[Dave_Trible]

I’ve admired the looks of the airplane but never had one.  One reason is that high- mounted stab.  My experience with that,  mostly with V- tailed stabs is that when turning outside the down wash off the wing and flaps blanket or disturb the airflow to the stab that it becomes pretty ineffective.  You can only try to compensate for it.  I’d try to fly with the CG as far back as it will tolerate and narrow the ‘up’ line spacing to compensate for that.  The ‘down’ you will need more of,  biasing the hand adjustments in that way.  Be sure you can get full down travel to a max of about 45 degrees.  You won’t need much ‘up’.  You should be able to find a useful trim to get the inside/ outside feel at the handle balanced.

Dave

[Chuck_Smith]

The tribal knowledge on stunt designs here never ceases to amaze me!

Cool read.


Chuck

[wwwarbird]

 The simple fix? Ignore the plan, sand and shape them as normal without the "airfoil".

 Given the overall Sabre Stunt design, if anyone was to claim they could actually tell a difference between the two shapes in flight they're FOS.

[Dave_Trible]

Hi Wayne.  I'd shape the stab and flaps normally too-but that doesn't fix anything here.  It seems the lifting airfoils were an attempt to fix what is really a design flaw (for a stunt airplane) flown as we do.  The hope I think was that it would generate a little more lift in the desired direction.  It would never make enough difference here to make a difference but they took a stab at it (pun intended).  This was a product of it's time period where all the 'rules' hadn't been written yet.  You could come forward to Bob Lampione's F 86 for an example of what had to be changed to become a true stunt model F 86.  This one could be fun though I'm sure.

Dave

[Dennis Adamisin]

There is a school of modern stunt design that promotes that the otherwise symmetrical  stab have a small positive incidence angle, i.e., a lifting stab. Positive incidence in the stab was also a feature of Al Rabe's designs.

Maybe the Jetco SS was just decades ahead of its time???

[Dave_Trible]

Gee Denny I wish I'd have thought of that! 
This brought to mind a few other designs of that era that also suffered not turning outside very well for similar reasons, mostly mounting the wing too low in relation to the thrust line.  I built both sizes of the Ambroid Whipsaw combat-stunt airplane which could only turn outside VERY large.  The Sterling p-51 profile was a popular airplane but flew quite large outside maneuvers.  I think they had another similar design that escapes me right now.  They also had a couple .19 size profiles, a p-40 I built and ......that didn't do outsides very well.  Scale looks seemed to be more important than stunt flying ability.

Dave

[wwwarbird]

Hi Wayne.  I'd shape the stab and flaps normally too-but that doesn't fix anything here.  It seems the lifting airfoils were an attempt to fix what is really a design flaw (for a stunt airplane) flown as we do.  The hope I think was that it would generate a little more lift in the desired direction.  It would never make enough difference here to make a difference but they took a stab at it (pun intended).  This was a product of it's time period where all the 'rules' hadn't been written yet.  You could come forward to Bob Lampione's F 86 for an example of what had to be changed to become a true stunt model F 86.  This one could be fun though I'm sure.

Dave

 Yep Dave, I think you and most of us here realize we're not talking about a highly competitive design with the 'ol Sabre Stunt, even for it's day. I've always considered it a cool "period" design though. I've got a perfect NIB one on my shelf I'd like to build someday. If I ever get to it I think I'd stretch the fuse 2 or 3 inches for a longer tail moment, just 'cuz. Not that it would be a world beater at that point but it would probably fly and track much better than a stock one.