Converting C/L model to RC

[Peter Miller]

Funny, My Moondancer doesn't show any strange characteristics like that.

Perhaps I am not a very good pilot.

[Andy Stephenson]

Posted by PatMc on 04/04/2020 22:56:38:

Posted by Andy Stephenson on 04/04/2020 16:47:02:

CL models usually have zero dihedral to allow the control wires a straight run to the elevator bell-crank. If converting to one to R/C you might find significant adverse roll on application of rudder without adding a commensurate amount of dihedral to the wing.

A.

Care to explain why ?

Pat,

I can explain why this is the case. The application of rudder not only tends to create yaw it also acts like a kind of aileron causing a rolling effect. With right rudder applied it tends to roll the plane to the left. We all know that on a rudder steered plane you need a fair amount of dihedral to induce a turn because the rudder yaws the plane then the forward going wing presents more air resistance which rolls it into the turn. There is a point at which if just the right amount of dihedral is applied the adverse roll effect of the rudder is cancelled out by turning effect. This why pattern ship designers always strive to get this just right to create the most neutral flying characteristics.

Andy.

[Bob Cotsford]

Andy, wouldn't yaw/roll couple depend on a lot of factors, let's see if I can list a few. Fuselage depth, vertical position of the fin and rudder relative to the centres of mass and drag, vertical position of the tailplane, degree of aerodynamic blanking of the inboard wing when sideslipping and finally the dihedral. For reference you can look at any thread discussing mods to the Acrowot design, it was once a hot topic for debates. edit - nearly forgot the vertical angle of the rudder hinge line and dihedral/anhedral/sweep on the tailplane!

A second point - for most people yaw/roll couple isn't a real issues as ailerons are the primary turning control and coupling only gets discussed for precision aerobatics. Converting a c/l design would hardly come under that banner!

Edited By Bob Cotsford on 05/04/2020 11:04:35

[Keith England 1]

Posted by Andy Stephenson on 05/04/2020 10:26:19:

Posted by PatMc on 04/04/2020 22:56:38:

Posted by Andy Stephenson on 04/04/2020 16:47:02:

CL models usually have zero dihedral to allow the control wires a straight run to the elevator bell-crank. If converting to one to R/C you might find significant adverse roll on application of rudder without adding a commensurate amount of dihedral to the wing.

A.

Care to explain why ?

Pat,

With right rudder applied it tends to roll the plane to the left. We all know that on a rudder steered plane you need a fair amount of dihedral to induce a turn because the rudder yaws the plane then the forward going wing presents more air resistance which rolls it into the turn.

I’m sorry but that is really not true at all, i have only ever flown one aeroplane, full size or model, that did not roll right if right rudder was applied - and that was the Excitation I mentioned above. it depends upon a lot of things but mostly where the vertical C of G is with respect to the centre of drag and diihedral. I got to fly a Taylorcraft plus D army observation plane and the pilot used to grip the stick between his legs and fly it completely on rudder leaving his hands free to operate the radio. it actually banked much better using rudder than it did using ailerons. Using rudder causes the outboard wing to move faster than the inboard and generate more lift, Hence banking the plane. it takes a very low wing without dihedral to counter that - which would be the case with some CL types - but certainly not if it was shoulder wing or higher.

But it is not so much rudder, as instability,  if a low wing CL plane is flown as an R/C without some dihedral it will be unstable in roll and only really comfortable to fly inverted.

Edited By Keith England 1 on 05/04/2020 12:16:13

[Andy Stephenson]

My explanation comes from several decades of model building and flying experience,

While aerodynamics is a complicated subject all I can say is I have actually seen these effects occur.

If you are not bothered about trimming for best performance then have at it.

A.

[Erfolg]

My reduced scale Nobler, just flies like any other RC model I have, other than the poor roll rate when undertaking a full roll.

The only other issue is the ineffectiveness of the rudder, needs a lot of deflection to skid (yaw) the model. I put that down to the relatively small rudder chord, relative to the fin.

As a model, that is generally benign, it is fine, as a RC stunter my model is no great shakes. Although more power recently did help a lot, with response and climbing and even rolling. Power is what you need.

[Mike Etheridge 1]

I bought a Spectre kit from Heset Model Supplies in South Croydon when the owners were selling off the stock in the 1970's. I also bought a Veron Mini Concord, an Enya 09, an OS 10 RC a KK Marquis plus one other plane. As time would tell I was a pretty hopeless CL flyer, but my nephew Nigel was an expert and acquired the CL models. I helped him finish the Spectre and of course can remember that the wings were asymmetric,one wing being larger in span than the other. So an RC version would need the wings to be modified. Nigel may still have the Spectre but when I last spoke to him he said his old shed had partially collapsed squashing some of his old models. I still have the engines but the part complete fuselage of the Mini Concord was stolen from a garage.

[PatMc]

Posted by Andy Stephenson on 05/04/2020 10:26:19:

Posted by PatMc on 04/04/2020 22:56:38:

Posted by Andy Stephenson on 04/04/2020 16:47:02:

CL models usually have zero dihedral to allow the control wires a straight run to the elevator bell-crank. If converting to one to R/C you might find significant adverse roll on application of rudder without adding a commensurate amount of dihedral to the wing.

A.

Care to explain why ?

Pat,

I can explain why this is the case. The application of rudder not only tends to create yaw it also acts like a kind of aileron causing a rolling effect. With right rudder applied it tends to roll the plane to the left. We all know that on a rudder steered plane you need a fair amount of dihedral to induce a turn because the rudder yaws the plane then the forward going wing presents more air resistance which rolls it into the turn. There is a point at which if just the right amount of dihedral is applied the adverse roll effect of the rudder is cancelled out by turning effect. This why pattern ship designers always strive to get this just right to create the most neutral flying characteristics.

Andy.

Sorry Andy, I don't think that is a credible explanation. The leverage of the tallest fin/rudder would cause very little roll effect even on a zero dihedral low wing model. Apart from any other consideration, the small potential for "adverse" roll caused by the rudder would be completely negated by the fuselage blanking the slipstream over the inner part of the lagging wing as the model yawed, which would assist roll in the desired direction.

[Erfolg]

I changed one other important aspect, that was the thickness of the wing. The original was 18% NACA, no doubt to limit acceleration, and allowing smooth flight at high AoA. or the jargon of today, high alpha.

Having limited power, and being aware of the need to penetrate, I reduced the section to 10% NACA. It has little effect I am guessing on the stall characteristics. This is probably due to my efforts to keep the wing loading light.

Edited By Erfolg on 06/04/2020 11:44:10

Edited By Erfolg on 06/04/2020 11:45:06

[alex nicol]

My thinking is to keep it simple. The construction will probably change quite a bit from the plan but the basic outline will stay the same as the Spectre apart from the fuselage wing/tail moment which will be increased somewhere in the region of 150 - 175% of current then the whole lot will be scaled up to about 140%ish. the fuselage may need to widened to accommodate the engine/tank set up ( probably going to be ic 46 - 53 size)

Erfolg makes a good point about the thickness of the wing section which I'll give some thought to, once I see what it looks like

I've got a couple of projects I need to get finished first then here goes ............

[Erfolg]

Alex

If going the IC route, power issues probably do not apply as critically. People tell me that a modern glow is far more powerful than they were 15 or so years back.

[Trevor]

I had completely forgotten about this thread but it has clearly been working away in my subconscious because I now find myself gazing at an enlarged version of the plan for the Spectre, contemplating an R/C version for my winter build. If I can try and summarise the points made so far about this conversion prospect:

 

i) Build both wings the same size, leave off the tip weight and rudder offset

ii) Increase the tail moment and possibly the fin/rudder area

iii) Add a bit of dihedral

iv) Increase the chord of the flaps (now ailerons) towards the tip

v) Thin the wing section a bit

 

What have I missed?

 

I'll post details of my particular project as and when it gets underway but the idea is that, as well as flying it as a sport aerobat, it should also be able to serve as a glider tug. To that end, the plan has been scaled to 175% giving a span of around 72in (depending on which wing panel you work from!). It will be electric powered, probably using a 6s x 4000mah battery, target weight of about 6lb.

 

Essentially, this would be a nostalgia trip - like others have said, the Spectre was one of the C/L models that I lusted after as a schoolboy so, now that I'm well into my second childhood, why not?!?

[Rich Griff]

Interestingly the vintage model company have advertised an RC Radian, I have an untouched kit of this cl model in the loft.

[Nigel Grant 1]

I realise this is a nostalgia project and looking to be fairly sizeable, 72".  But another plan to have a look at if you have it is Mike Bell's Monkey Hangar. There are a few threads on here and the plan was a giveaway in the October 16 RCM&E. Mike designed it from scratch but said the design brief was "intended to be reminiscent of vintage control line stunter's , the KK Spectre being a favourite". It certainly does have some resemblance to the Spectre, helped by his colour scheme, and is reported to be a good flyer. Reference to the plan could help with the proportions for your scaled up Spectre.

[Trevor]

Thanks Nigel, I’ll look into that. However, being a print subscriber, this means I’ll have to delve into my magazine archive (‘pile’ might be a better description!). 

I may be some time. . . .

 

[GrumpyGnome]

@Rich GriffI could only see a C/L one.....

[Trevor]

Okay, I've managed to dig out the plans and article for the Monkey Hangar and the comparison has indeed been helpful in making sure that I don't miss something vital in the C/L to R/C conversion of the Spectre.

 

I've been thinking more about the wing section/thickness discussion. On the Spectre, like most of the C/L models of its day, the flaps are simple flat plates hinged on to the trailing edge of the wing. Whilst some fun fly R/C models have flat plate ailerons added in this way, we more often nowadays build the  ailerons into the wing section.

 

So my question is, should I stick with the 'add-on' flat plate ailerons and make the wing thinner or keep the absolute thickness of the wing as is, and stretch it chordwise to include the ailerons, as is done on the Monkey Hangar and indeed on the near contemporary Astro Hog?

 

[Rich Griff]

Been looking for the vintage model company advert for the RC Radian, I know I have seen it some where, but did come across the vmc advert for the Phantom cl design to RC...

 

First of a series it says...

 

Will continue the hunt for my own interest and post when found...

[Nigel Grant 1]

I would tend go for built up ailerons, "barn door style" out near the wingtips as on an RC model you want the ailerons to roll the aircraft. Flat plates, especially large size on 72"plane could also warp or twist over time which is difficult to fix. Also the flaps on the Spectre have most of their area inboard as they were intended to assist the pitch of the craft. On a larger model you might want to go for outboard built up ailerons and also do flaps inboard.

[Trevor]

Thanks Nigel. It's reassuring to know that we are thinking along similar lines. Or, to put it another way, if it all goes wrong there's someone else to share the blame ?

[Trevor]

The first monthly diary entry for my K. K. Spectre C/L to R/C conversion and enlargement project is now online:

http://www.bartonhewsons.uk/home/modelflying/sport/spectrediary.html#September