Kwik Fli 40

[Martyn K]

Hi all

Kwik Fli 4-40 Plans now available for download (as a zip file).

HERE

Laser cut parts can be ordered from Dylan at LaserCraft. PM him from this website please

(Edit - Laser cut parts are Wing ribs, Fuselage ply formers and Wing ply parts - not ply fuselage doublers)

Dylan Reynolds LaserCraft Services

DXF files are available on request

KF3-40 plans to follow soon.

Best wishes

 

Martyn

 

Edited By Martyn K on 11/01/2017 14:04:06

[Braddock, VC]

Martyn, a quick query. I looked at the ic fuselage and see you "used" an OS 35AX and fitted the slec 9 ounce tank.

Is that tank a bit on the large size, I ask because I'm using an Irvine 36 in a wot 4 which would seem to be a similar source of drag etc and had 3, 5 minute flights [fingers get cold this time of year] with a third of a tank left from the slec 6 ounce tank.

I have another irv 36 and thought about building a kwik-fli around that.

[Martyn K]

Very good point. I had no experience of the 35AX before this model was unsure just how big a tank I needed. As it stands and without the engine being fully run in it will give a comfortable 15mins flight time.

You could comfortably drop down a tank size if you wished. I certainly would if I did it again. I wish my OS61RV was that economical - even pro rata

[Martyn K]

Apologies all. Just realised that the cut parts drawings were missing from the original zipped plans set I linked to above

Try this Set

Kwik Fli IV - 40 Plans v2a ZIP

Regards

 

Martyn

 

Edited By Martyn K on 13/01/2017 10:03:27

[Braddock, VC]

Thanks, martyn. I run my 36s on 15% nitro so I guess if I dropped down to 5 or 10% the fuel would go even further.

[Martyn K]

Belatedly, here are the Kwik Fli III 40 plans

kwik-fli-III-40-v2.zip

Please let me know if you find any problems or have any difficulties with either of the plans

Dylan at Lasercraft has the DXF files if you want a parts kit cutting. The embedded file: kwik-fli-3-40-laser-parts.pdf shows the parts that comprise a parts kit. You will need to let Dylan know if you want the Electric or IC version.

Good luck

Martyn

[Martyn K]

A brief update

I went out with the KF4-40 (E) at the weekend. I had 3 flights with the revised 11x8 prop (was 12x6) and it has transformed the model. Not unlimited vertical or anything uncharacteristically silly but comfortable 100m diameter loops and large sky filling cubans. An absolute delight to fly. Still getting the rates/EPA settings correct but its nearly there.

With the power setup I have used I am getting 6 minutes on a %age throttle setting - about 9-10 minutes of real flight time. If I was buying again, I would opt for a 3500 or 4000 4S LiPo. It would help the CG as well which may be a bit back for some.

Only problem I have found so far is a reluctance to stall turn away from the wind.. Maybe a KF peculiarity,,

Martyn

[Lucas Hofman]

Hi Martyn,

Where do you get an 11x8 propeller for electro. I use often an APC 11x7E with 4S setups and a 800kv motor. Works fine but I would like to try a bit higher pitch. Regrettably APC does not do 11x8E, only 13x8.

Regards, Lucas

[Martyn K]

Hi Lucas

I bought them off an eBay Seller. I also have an 11x10 to test as well but I probably wont bother as I don't want to stress the system. It still easily out performs my 60 sized Kwik Fli 4

Martyn

[Lucas Hofman]

Thanks Martyn. APC does make 11x8E (if these are not copies...). I ordered one. Lucas

[TIM Shaw]

Just so you know your work is appreciated Martyn, heres a couple of pics of my KF 4 40, powered by OS35 AX and 10x7 APC prop. Flies really nicely, although I've also noticed it is reluctant to stall turn away from the wind and the rudder is a bit lacking in authority in knife edge.

Built from your drawings and a real pleasure to do. Added the wing fillets in a bid to avoid the tail wag and I am pleased to say she hows no sign of it.

[Martyn K]

That looks lovely Tim. Very nice and your canopy looks far sleeker than mine.

Interesting about the stall turn. When the model is flying it should have no idea which way the wind is blowing..

I think there is plenty of rudder authority, its lack of fuselage depth is the problem. Try a 80 degree knife edge. You may be surprised

Thanks for building it, I really appreciate it.

[Lucas Hofman]

Martyn,

Reacting on your comment that the model does not know which way the wind is blowing, which is true. However:

- on a vertical with cross wind the fuselage is already pointing slightly into the wind, making it more difficult to stall turn away from the wind compared to into it.

- many models turn into the wind on verticals or when entering loops. I think that is because of the wind gradient (the wind blowing harder with increasing height). Thereby the model is accelerated sideways by wind and that will blow away the tail, making the nose turning towards the wind.

regards, Lucas.

ps. they look lovely. Maybe I should build one next vinter!

[Martyn K]

Fair point Lucas. I was assuming that the upline track was vertical and not leaning, however, you are correct that its a likely reason for the problem. I'll check mine again and watch a bit more closely

Thanks

[TIM Shaw]

All good points.

If I fly straight into wind there is no issue with the stall turn, but very rarely is this actually the case - particularly if trying a figure M. And if there is any component of side wind, as Lucas says, it tends to blow the tail away and the model weathercocks into wind - don't forget, at the point of a stall turn it has no forward movement either, so has no idea where it is!

We shouldn't be surprised at that really, as surely this is the function of the fin?

I know exactly what you mean about an 80 degree "cheat" knife - I can do a very nice version of my Wall of Death ( christened on the slope, as it looks so wrong....) with it, which is a knife edge, outside, 360 degree outside turn.

But in pure knife edge I feel a bit more rudder would be a good thing, I may be able to solve it with upping the movement a bit but have yet to get into fine tuning - I like flying it so much!

[TIM Shaw]

Just for a cheap laugh you might notice the second pic does not have the U/C fitted. I prefer fuz mounted, tail draggers for ruggedness - probably overly cautious since our field has been improved so much in the last 30 years, but old habits and all that.

Originally, I made the legs too long and it looked daft - and I will admit, this model would look much better as a trike - so I removed the legs, cut the axles off, re- bent new ones and bolted the legs back on.

Only then did I realise I had made a small mistake....

The canopy is simply carved from blue foam (well, it was my fourth attempt, tbh) until it looked right, then covered with glass cloth and eazykote. Its got a bit marked by handling issues but it looks fine in the air.

[TIM Shaw]

Posted by Martyn K on 07/07/2017 13:03:29:

That looks lovely Tim. Very nice and your canopy looks far sleeker than mine.

Interesting about the stall turn. When the model is flying it should have no idea which way the wind is blowing..

I think there is plenty of rudder authority, its lack of fuselage depth is the problem. Try a 80 degree knife edge. You may be surprised

Thanks for building it, I really appreciate it.

Ok So now I know what you are saying about the side area.

Was a beautiful day today, and I had a great flight with it. Then my throttle servo died and my good friend Jim insisted I had a flight with his Sebart Nuance 110, on 6s electrics ( the work of beelzebub in my view)

Yes. Something of an eye opener tbh, but somehow, nowhere near as much fun as a classic..

But applying the sort of rudder I need to hold the KFs nose up in knife edge resulted in a fairly spectacular (totally unintended) knife edge loop

Know which I prefer tot fly though, - and it involves smoke,oil, mess and noise!

[TIM Shaw]

Oops - sorry - that Nuance is a BJ Craft model, as is the Fantasista 110 he made me fly yesterday

[Nigel R]

Tim, the KwikFli looks great - nice one. I like the colour scheme.

What's the AUW?

[TIM Shaw]

Hi Nigel

Its just under 4 lbs mate.

Wing is a little unual because I didn't have any big enough bits of foam, and previous attempt at sticking bits of foam together were not entirely successful as the glue tends to snag the wire..

So I built a 1/8" balsa framework of the planform, stuck strips of blue foam to either side of it for the D box, ribs and TE, then hot wired the section, and then sheeted that with 1/16" balsa.

[Nigel R]

Must go nicely at that weight on the AX.

So you've got (sort of) blue foam ribs, and LE + TE sheet, plus caps I guess. Are there any spars or webs in there?

As a regular foam wing cutter (and here comes the usual question) how do you find yours compare? I'm thinking particularly with the foaming PU type glues around.

It always used to be accepted wisdom a foamie would turn out heavier than a built up, and the only reason I can every come to is the large surface area that needs glueing...

At one point I wrote a spreadsheet to calculate built-up structure weight, it always came out that the internal elements of a balsa wing weighed very close to the cut white foam; the sheeting was a no score draw, leaving only the glue to add a bit of extra weight to the foam wing.

[TIM Shaw]

So I tried to post a few pics showing the process - seem to have come out a bit backwards, and the editing features on her are not compatible with my thought processes...

Was hoping to take it to the Retford meet, but I am in the middle of a Radiotherapy course and not at my best, so that might not happen

So I hope you got the idea. Agree absolutely about the glue, even if when I cut a normal core I cut holes in it and avoid putting glue there to save weight

Edited By TIM Shaw on 14/07/2017 22:56:08

[TIM Shaw]

So I didn't fancy the drive to Retford today, but did make it up to the local field this afternoon.

With a new throttle servo fitted and the engine finally breaking in nicely I was really enjoying myself.

I had increased the rudder throw considerably and it will now hold true knife edge both ways very nicely, although you still have to watch any crosswind to get the stall turn correct.

Unfortunately, pulling out of a half cuban 8 there was a clearly audible crack, loud enough to be heard by everyone on the field, and although nothing was visibly amiss it seemed to have developed either a bit of up trim or a rearward CG, so I landed it before anything nasty happened.

Casual inspection showed nothing wrong, to the extent that one club member suggested it could have been a motorbike backfiring as it passed our gate, but it seems the Tailplane (which was 1/4" sheet balsa, sorry Martin) has cracked across the middle as a result of in-flight loads.

Not quite sure yet as surgery will be required, but anyone planning a similar build might like to consider a spruce spar in the tail.

[Nigel R]

"but it seems the Tailplane (which was 1/4" sheet balsa, sorry Martin) has cracked across the middle as a result of in-flight loads."

Seems a surprising thing to happen during a regular loops & rolls type maneuver. Maybe the sheet was weak to begin with? I would have thought a plank of 1/4" was more than up to the job for a 4lb model.

[kc]

I agree with Nigel that 1/4 is usually quite OK for 4 pound models or more and for many flights too.

Worth careful investigation and particularly looking to see if when trimming the covering film back that the balsa may have been slightly incised too causing a weak spot. ( Years ago I examined a clubmates Wot4 that had a tailplane break in half during flight. Some good flying by the instructor landed the model nicely despite only half tailplane so careful examination was possible - verdict the tailplane failed exactly where the film had been trimmed and the 'nick' in the balsa was still just about visible so was the cause of failure. )