Mad Hatter - F3-RES

Apologies, but this almost a duplicate posting of that on the MF forum. Hope you dont mind but I want to share what we are doing to a large audience and I am also interested in any comments that you may have here. I suspect that I may get more interaction here than anywhere else..

This is a new glider class that will be adopted by BARCS as a postal event in 2017. Hopefully, it will develop into a full blown class.

F3-RES is a class that is very well supported in the USA and Germany. Although intended for Newbies, the interesting rules have made it fun for the experts as well. Consequently, events are well supported.

(RES = Rudder Elevator Spoiler, Ailerons or flaps not allowed)

Rules are quite simple, limited use of high res(tech) materials (but not totally excluded), prevent expensive moulded aircraft from being used. Wings must be built up and predominantly wooden although carbon can be used for spars. The boom can be carbon but high tech materials for fuselages must not proceed forward than mid chord of the wing. Max 2m projected span.

For the postal event, a reduced length bungee and towline will be mandated, using a HK rubber tube bungee and towline with a minimum line thickness making it an ideal small field glider class

There are kits available and even ARTFs from Germany if you are that way inclined. However, I wanted to fly my own creation. This is about as high tech as the rules allow and could be simplified with a wooden fuselage and spruce spars if needed. Target weight for the RTF model needs to be about 400gms - i.e. light

Designing iteratively from the ground up, there are not many published designs to steal ideas from..

I chose to use Mark Dresla's excellent series of AG airfoils as used on the Bubble Dancer. To keep the Re as high as possible necessitated a large chord and therefore quite a low aspect ratio.



The finished design looks mainly like this:



And has the following glider stability parameters.



I am happy to try and explain these further if needed but they are mainly about how a glider behaves in a tight thermal turn.

So, with that, the DXF files for the wing ribs have been sent for laser cutting, the carbon ordered (and received) from Hyperflight and a start on the tail surfaces has been made.

Plans printed selectively to a tile print

The tailplane has been simplified from the plan to reduce the amount of glue required > less weight.




and more or less completed




The tailplane is all flying and supported by a C/F mount from a Blaster DLG - from Hyperflight.





Local C/F reinforcement where the tailplane is supported. The tailplane at this stage weighs 8.4g




The mount from underneath that will loop over the rear boom

The fin is fairly simple as well. Light wood used to keep the weight down





The tail surfaces will be covered in 5 micron Mylar. As I have to apply adhesive to the surface to glue the covering down it will hopefully make the covering easier

Progress on this will be fairly slow as I am working on 2 other builds at the moment.

Feel free to ask any questions.

More to come

Martyn

No apologies needed Marty
A very interesting and well written post, I am sure you will get feedback on such an interesting subject

Garry

Thanks Garry



and



Lots of colour and variety..

just realised that in my OP I used the term High Res which due to lack of engaging brain with finger should really have read Hi-Tech..

Firstly, yes you are eligible. For the postal, there are no hard and fast rules except a model and towline assembly must comply. You time your own flights and if you cheat and come first, you don't get a prize. You also don't get a prize if you win by not cheating. There is nothing to gain or lose except your own self esteem. A 'postal' event has been running for several years for F3K and mosquito and the system works well. What happens is there are 26 x 2 week windows through the year. You simply submit your best times in the form of a post on the BARCS forum. You don't need to be a BARCS member but obviously we hope that guilt gets better of you and you join.. Not mandated though. For F3-RES, we are going to have a league as well to encourage poor scores to be submitted. This will be normalised using standard normalising techniques. The league winner at the end of the year doesn't get a prize either Gets heaps of admiration from fellow competitors though.

In a proper event, there will be a spot landing bonus. So learn not to land out.. These new breed of models, despite being very light have very efficient low drag airfoils, so they penetrate well. Far better than you would imagine. Have a look at some DLG videos on You tube to get an indication on how they perform

The calculations are formed from an adaption of 2 spreadsheets. The final table is mine and the 3 parameters determine pitch, yaw and spiral stability.

A low Vh - horizontal stability parameter - determined by tail, wing area and moment arm will make a model twitchy and force a forward CG. This means the wing will need to fly at a higher AoA which means more drag. ideally you want the wing to fly at a lower AoA (not too low obviously) with a more rearward CG which means the tail can be smaller and do less work. However any change in elevator causes a big move in the total CP which can make the model totally unstable in pitch. My solution with this model is a small tail and a long moment and reasonably high stability margin

Vv - Vertical tail stability parameter- determined by the Fin moment arm, Fin area , wing area and wing span. It determines the Yaw stability. Too much and the model will spiral, too small and it will wander - wont hold a heading. Why the span? The reason is that the wing span also has an effect on the yaw performance. A high aspect ratio is more reluctant to turn

B - Blaine Rawdon Parameter, This determines a models spiral stability. A R/E model has to be more spirally stable than an aileron model and is measured accordingly. This incorporates the amount of dihedral - calculated from panel length and the amount of dihedral (in degrees) on each panel. My model is a 5/6 panel wing. Technically a 5 panel but would be known as a 6 panel if the inner panels had dihedral. The multiple panels are positioned to emulate the shape of an ellipse (when looking from the front) which is the optimum wing shape for dihedral. The B parameter determines whether a model will be inclined to spiral in a tight thermal turn. It shouldn't

For more info and a precis of how difficult it was to get the German rules translated see the BARCS forum here:
www.barcs.co.uk/forums/topic/6248-2m-competitions-in-the-uk/

Please ask more questions

Very informative Martyn, and I even understood some of it sounds like you have your bases covered, this model is bound to be a corker, well done

Cheers
Danny

Thanks Danny. I just have to get it built and trimmed by 31/12.. And complete 2 Kwik Fli 40s by then as well..May have over committed this time.

And get on with a certain Chipmunk that is languishing on Bench 2 saying 'take me, take me now'

The Chipmunks were never going to be quick builds, but the Kwik Flis, you can churn those out in your sleep

Only the Puppetteer has taken longer than the Chippie - that was 5 years, but for 4 years and 9 months it was in the loft.. Need to get on with it. I want to attend some Scale events. next year

Hi Eric. Yes that can be a problem. I tend yo get to the field early when flying gliders when I am by myself or it's quiet. My full size bungee is about 150m long when stretched but I try and position it so it blows off the strip and Pilots area when it detaches. It is a pain. Same when
I am flying my F5J electric soarer. We just get in each other's way so for the same reason I tend to fly early at weekends when I have the time and space to myself. It's very therapeutic flying gliders. Something very satisfying watching it disappear into cloud in a big thermal. Or perhaps not


Sent from my iPhone using Tapatalk

What a fascinating and informative thread Martyn, thanks for posting.

Here's a couple of questions:

- I used to use a surgical rubber bungee which is now rotten. I'd like to replace it. Do they still exist, and if so, where would I get one?

- Is there now a better alternative to surgical rubber?

- Can a releasable tow-hook be fitted to F3-RES, operated off, say, the elevator servo on full down?

- Are the spoilers mandatory?

No eBay APP ID and/or Cert ID defined in Kunena configurationHi Andy
The bungee that has been specified for the postal (and the main events if they happen) is from HobbyKing

2x #RLT-6x4-10m/50932 HobbyKing® ™ 6mm Silicon Rubber Bungee Hi-Start Cord

I think that it is 6mm o/d, 1mm wall thickness and mine was red. However, that maybe a bit too heavy for 36" high start F/F class which I guess is what you need your for.

This may be OK though:



Eric we are just within the ATZ for Manchester. Sometimes gets a bit worrying when an A380 overflies us. Its still probably 3000' up but a good glider (or even a bad one) in a thermal can easily top that (I know from experience)

Hi Andy

Sorry - your other questions.

I think surgical/silicone rubber is still in vogue. It would be interesting to try something like 6 or more strands of 3mm Tan II though - although it would be expensive

No - spoilers are not mandatory

I dont think there is anything preventing a releasable towhook, I would have to check. I can see advantages to that. A good question