The Jekyll or Hyde

Of course airliners and the like use very complex area increasing slotted flaps but this is forced on them as they want to fly very fast as well with cruise speeds 4x the landing speed.
At model sizes simple hinged flaps work well as any 'slot' has to be relatively very big to allow a significant air flow through and this then largely negates any benefit the slot effect has to control airflow over the flap's upper surface.
The same also applies to leading edge slats/slots although a simple 'drooping' leading edge in conjunction with simple flaps works by effectively increasing the wing's under camber.

If you look carefully at some of those big super light indoor scale planes many use no lower wing skin aft of the spar at all resulting in a very pronounced high lift under camber wing section. Notice they do not fly fast. They simply can't, too much drag. :woohoo:

Also it is practical if you have the thrust to use extreme flap angles, 80 degrees or more. The lift remains more or less constant beyond 45 degrees but the air brake effect rises dramatically so 'multi step' movement is required. I actually like to control such flaps with a knob rather than a multi position switch.

My own definition of STOL is to achieve at least a 3 times max to min speed differential whilst maintaining a level fuselage attitude so no 'prop hanging'.

This my own STOL twin.

2 section flaps over 2/3 of the trailing edge and a push/pull arrangement with counter rotating props to eliminate torque when flying at very slow speed. An important issue as the ailerons get less and less effective as the speed comes down.

Thanks for the info Simon. That's given me plenty to think about!
New foam is here so decided to try it this morning & cut half the wing & the center joiner. It cuts nice, just needs a bit of power (6 amps) & you can't rush it. Sanding definitely requires a lot more elbow grease! The best thing is it doesn't crumble !
Now I am going have to copy Phil's bacon slicer to cut down some of the sheets, as it only comes in 50 mm.

I got quite a bit done today & the Jekyll is slowly taking shape. Fixings for the removable wing are done. 5 mm studs at the front, with plastic tube inserts all the way through to stop the foam crushing. The studs are in rivet nuts on a 60 X 5 mm spar nearly the width of the fuz & glued 60 mm down in a solid foam block. This is repeated at the back, only using set screws rather than studs. I will probably set in plastic plates on the top to spread the load, but it's already pretty solid. Aileron & flaps fitted to the first wing half. I deliberately took the aileron right to the tip of the wing, gives me the option of adding extra wing tips at a later date if necessary. I wasn't happy with the battery box cover, so I'm making another with the new foam, which is "SO" much better. I did a few paint tests on it, acrylic gloss sticks beautifully without the need for primer.
Laid out what I have so far.

looks good crash! is that a type of insulation foam?

paul d wrote: looks good crash! is that a type of insulation foam?

Thanks Paul. Yes it is insulation foam. The difference is that it's extruded rather than expanded, which makes it slightly more dense, but much easier to cut and sand as it doesn't crumble. It cost me about £80 for a pack of eight, 50 X 600 X 1250 sheets. 50 mm is the thinnest they make, so I'm going to slice some down. From what I have seen on some of the off cuts I would think down to 2mm is achievable.

sounds like you've bought a lifetimes supply!
Foam is really not my thing but it does sound a interesting material.
The only thing that concerns me is the potentially harmful fumes it may give off when being cut.

I think it will last a while ! I would definitely wear a good charcoal filter mask when cutting, hydrogen cyanide to name but one gas ! :ohmy: If you use it don't take any chances !

That looks impressive.
However for foam the terms "dense" and "solid" are not attributes I particularly favour for wing construction.
One or the other, no problem, but both?

Quorneng wrote: That looks impressive.
However for foam the terms "dense" and "solid" are not attributes I particularly favour for wing construction.
One or the other, no problem, but both?

When I say "solid", I was referring to the fixings Simon.

After doing my bit for climate change this morning ( more logs for the wood burner) I decided to get on with the Jekyll undercarriage. It's far from finished but I think you can get the idea. Loosely based on the Fieseler Storch. The miniature shocks I bought are rubbish,to weak & not enough travel. I am going to replace them with my own design built into the strut, then I can try different springs to get the pre-loading & travel I want. Anyway I bolted it together to test the principle & it seems to work.
Still waiting for the balloon wheels to turn up!

That looks pretty sturdy.
With such a 'tall' undercarriage the base width of the 'A' frame will be the limiting strength factor as the front strut is likely to pull out of the fuselage under tension long before the rear strut collapses in compression.

My advice is to give it as soft and long travel as you dare. Ultimately a broken prop may be a small price to pay compared to the damage caused from a ripped out or worse still a part ripped out undercarriage.

Undercarriage now assembled & in primer. Pre- load will be adjusted by selecting the right springs when the model is finished. Theoretically I should have around 30 - 40 mm of travel. I recon with 5" balloon tyres this should be sufficient.

Very neat but I do worry about the base width of that "A" frame.

This is a still from a video of a restored Storch.

Note the fore and aft distance of the fuselage A frame mountings.
Another thing that I had not realised until studying this picture was the smaller A frame used to locate the bottom of the top strut above the oleo to allow the oleo to move almost vertically rather than at an increasing angle as it compressed.

Looking at Crash's photos - what is stopping the little bracket the stub axle will be mounted on - from rotating outwards so the wheel can either tuck under or be propped up, so the metalwork touches down?
Also - as I mentioned earlier, there is very little support stopping the legs from moving aft on touchdown/arrival.
Picture a slightly nose-down impact - or a big tuft of hard grass - the wheels are going to be pushed backwards.

Yes I see what you mean. I suppose I could always add struts from the front of the A frame brace forward to a fixing center fuselage. That would add considerable torsion strength for very little extra weight ?
I'm not worried about the angle of the oleo's, they work fine. I will have to have some negative camber on the wheels ( when hanging) as this will become positive under compression.