1/12 Scale Reiher Sailplane foam

[OZPAF]

I feel that the primary problem may be lack of rudder authority - possibly stemming from the small scale size of the fin/rudder and accentuated by the low flying speed due to the very low wing loading.

The corresponding low roll rate would also make it more susceptible to gusts as you have noticed.

I would suggest that you try adding extensions to your fin and rudder.

As a last resort it may be necessary to add some ballast to the model.

many years ago our club had a contest to see who could make the slowest flying RC glider. The limiting factor was the wing loading - flying slow was not the problem - lack of control was the limiting factor!

John

[bcarter1234]

John,

Thanks for the helpful observations. I'll add temporary extensions to the fin and rudder. If that works making larger replacements won't take long. I'll also make a pocket for ballast to see how much higher glide speed helps.

Your comments are echoed in the 99 year old technical document that contained the La Pruvo drawings I'm using for the next 36" towline glider.

"N.A.C.A. Technical Memorandum No. 471

Performances and Properties of School and Training Gliders

Despite their simple construction, the school and training
gliders made very good flight records. Long soaring flights
were made by the more skillful pilots with the school glider,
even at wind velocities of less than 6m (19.7ft.) per second.
Gliders of both classes showed a marked superiority as regards
maneuverability, over many earlier performance gliders. This
is all the more noteworthy, because satisfactory rudder effect
has always been difficult to obtain at the low speeds attained
by the lightly loaded gliders of this class."

[OZPAF]

It's interesting and almost strange to think that the fin/rudder area can cause problems - as it rarely appears.

One of the most surprising issues I had was with a small semi scale jet  catapult catapult glider. On launching it was OK at speed but on slowing it started spinning around the CG on the yaw axis. Completely puzzled I tried extra dihedral, CG shifts - all to no avail.

Finally out of desperation I extended the fin and the problem was solved. I was more than a little amazed.!

Good luck with the alterations.

John

[Lastwoodsman]

1/12 Scale Reiher Sailplane foam

Hi bcarter1234.           Tues March 31 2026

   Thanks for the builds.   You have me interested ....   I am considering building another high start towline glider for my next model.    The tow hook  was/is,   a big deal for me to get right.

   I am interested in that tow hook that you and John are talking about?    Would you please post a pic,  or even better,  a pic of your sketch,  of your tow hook?    Thanks for your help.   

     And also some help from John on this:   " the CG can go back till under the CG.  (?)     However I would suggest that you make the position adjustable "  and a nice hand drawn diagram from John too.    Oh,  and a pic of the adjustable tow hook please.    Thanks.

My apologies for the newbie questions ...

Lastwoodsman
Richard

[bcarter1234]

Richard,

Your questions are welcome, nothing I have would fly if people hadn't answered a lot of questions for me.

Keep in mind my fuselages are foam so adding and moving a tow hook is simply a matter of cutting a thin slot in the bottom of the fuselage and inserting the hook shown below into it. The hook is held in place with two strips of tape in front and behind the vertical leg of the hook. Tape is sufficient for my application because the loads om these light planes is very low. Once I find the best location I may glue them in. The hooks are bent from a paper clip.

The hook is placed somewhere between 15 and 45 degrees in front of the CG location at the bottom of the wing. Make sure the rear of the hook diverges from the bottom of the wing a little bit. Otherwise the tow line may not release when you want it to.

[Konrad]

I think a lot of these control issues can be traced to what the fin area (aft of the CG) is actually doing. I like to think of what the fin is doing when it comes to directional control and spiral instability. These are often at odds with each other. I like to keep in mind that as we slow down the aerodynamic forces from our control surfaces drops by the square of the speed. But the mass stays the same. Generally, the slower I design a model to fly the larger I make the aft vertical area.

[OZPAF]

This is the type of straight tow hook I have used on every thing from Tow Line FF models to F3B winch launched models.

The hook is a screw in "L" shaped or straightened cup hook. It is screwed into a piece of ply (section of glass fibre on F3B models) and adjustment just requires drilling and tapping new holes.

The hook shown is 1.5mm dia and the F36B models used 3mm or slightly more.

John

[Lastwoodsman]

1/12 Scale Reiher Sailplane foam

Hi bcarter1234 and John :              Tues March 31 2026

    I was always wondering how to move the tow hook to a new position,  after you glued it in place.    Thanks for the pics and tips John and bcarter.    Now I understand them.

      I only had three types of tow hooks, Pics 1  to 3,  and I only had flying sucess with the 20" Osprey from Vintage Model Co.    The cheap store bought  'ready to throw'  foamy glider,  and the balsa builtup Mystery Man "Vulture Glider",  were both 37".    I never got the foamy to fly,  and the Vulture Glider broke right up upon hitting earth,  for reasons I do not yet know why  -  it was flimsy,  I suspect,  because of the cheap double covering I used,  of cheap,  present-wrapping tissue ?   

    Anyways,  those are good ideas for the tow hook -  I can see your threaded screw into a plate,  John,  and I can see your tape-it-in-place  "sandwich"  slot also,  bcarter1234.    Which ones to use  depends on if my next model glider will have a flat fuse bottom,  or a skid on the fuse bottom  ....

Pic #1    2212
Pic #2    2212 expanded snip
Pic #3    2213

Lastwoodsman
Richard

[OZPAF]

I like to keep in mind that as we slow down the aerodynamic forces from our control surfaces drops by the square of the speed. But the mass stays the same. Generally, the slower I design a model to fly the larger I make the aft vertical area.

 Yes I agree. The large old rudder/elevator floaters such as the Paragon and Drifter with 100" wing spans and low wing loadings had large fin/rudders with a lot of movement compared to current models.

John