Whiz Kid builders

[Chris Reid]

Hi Steve.

Good luck with your build. Don't worry about the lack of side/down thrust, I rarely use either as they usually aren't necessary; minor torque effects can be trimmed out. As you will find, Whizkid climbs vertically on half power, so down thrust wouldn't work too well anyway!

Chris

[Steve Kenney]

Many thanks for feedback, Chris.... Will let you know how it goes

cheers, Steve

[John Roberts 9]

Hello

I intend to start my own build sometime next week and I will post a few photos as I go along.

I might omit the wing dihedral to make construction even simpler. I note that Chris refers to this being OK in the RCM&E article (June 2013 edition).

Also, the plan suggests that the aileron torque rods, which drop down into the fuselage cavity, look at though they might get pretty close to the wing mounting plate. Has this proven to be an issue in practice? I guess that it would be possible to install the servo the other way up and have the aileron pushrods on top of the wing instead. A more elegant solution would be to relieve the ply mounting plate either side of the captive nut in order to allow an extra millimetre or two of torque rod movement. I can't imagine that the model will require huge aileron deflections.

Cheers,

John

[Chris Reid]

Leaving the dihedral out will be ok, and will simplify wing construction. Similarly, relieving the ply plate to make more room for the aileron torque arms will probably be necessary; it was on mine. The alternative wing fixing with dowels and rubber bands would get over that issue. I've also had the odd confliction between aileron and elevator links. I got over this eventually by removing a bit from the elevator servo mounts to drop the servo down a little. I guess I should have left a little more space for everything, but I was going for the smallest possible build around the components I had. Now everything works fine, and I keep my Whixkid permanently rigged ready to fly.

I hope this helps.

chris

[John Roberts 9]

Hi Chris,

Thanks for your input and clarification

I think I will just get stuck into the build, see how it goes and them make some decisions once I have some partly constructed balsa in front of me!

Cheers,

John

[John Roberts 9]

Hello

Well here is my finished model:

Completed weight, including a 3s 800mah Gens Ace Lipo is 13 ounces.

I also found the model to be a little nose heavy and I have ended up with a carbon boom that measures 20 inches from the rear of the fuselage up to the leading edge of the tail feathers.

I used a cheapo Hobby King motor D2826-10 (under £7) which is rated at 200 watts on 3s with a 7 x 4 prop. Link

To simplify the build I omitted the dihedral and I also mounted the aileron servo on top of the wing. This solution isn't nearly as elegant as Chris's but made for simpler construction and avoided having the torque rods hanging down into the cramped fuselage compartment where they would almost certainly conflict with the rear wing mounting plate.

Lots more photos in my album for anyone who might be interested.

Thanks to Chris for a nice design and a fun build.

Just waiting for a nice calm day now for the maiden.

Cheers,

John

[Chris Reid]

Looks great John. I like the purple and white. Take care with the throttle first time out, Whiz Kid can easily get out of hand at full chat. I still enjoy mine, and have discovered that it will soar if the lift is good.

Have fun.

Chris

[Steve Kenney]

Good selection of pics there John. Got the wings completed on mine and now started on fuz. Let us know how the maiden goes! Looks like weather better for weekend, so get those lipos charged!

[John Roberts 9]

Thanks Chris & Steve

The forecast up here in "sunny" Scotland suggests it might be a little breezy over the weekend but after that it looks like light winds for several days so I will report back on the maiden early next week.

The purple covering is just what I had left over from repairs to a damaged PA Addiction generously given to me by a friend a few weeks ago.

Cheers,

John

[Caveman]

Just by coincidence I finished my Whiz Kid today!

Mine uses a 3S 1300 driving a 120W motor and uses only bits and pieces I had in stock. The distance from the back of the fuselage to the front of the tail is 340mm.

All up weight, including battery, is 17oz. Somewhat more than others seem to achieve, but it still feels pretty light to me. I would have thought that 120W would be quite adequate for decent performance.

Here's the finished (almost) model:

You will notice the lack of cowl and folding prop. As I don't have a folding prop in stock I can't make a suitable cowl - this will have to wait until I need to order some more bits and pieces.

In the meantime we'll see how it flies, given some decent weather and low winds.

I'll report back - GDB

[Chris Reid]

Nice one GDB . Smart colour scheme. You seem to have hidden the aileron servo somehow too. Great to see so many Whiz Kids coming together

Enjoy your flying.

Chris

[John Roberts 9]

Looks great Caveman .

So how did you manage to completely hide the servo? Very neat!

It certainly looks more attractive than my solution with the servo, rods & horns externally mounted on top of the wing.

Cheers,

John

[Caveman]

I mounted the servo on the underside of the wing centre panel, which allowed just enough depth for the servo body to sit inside the wing without protruding through the top sheet.

If necessary the servo mout could have been packed to reduce the amount of servo body in the wing cavity - the aileron torque rods are not particularly, within reason, at what angle the pushrods meet them and there's plenty of depth in the body to accommodate it all.

GDB

[Caveman]

Just to report that the Whiz Kid was maidened this morning. It flew from hand beautifully and glided quite well, but was a touch tail heavy.

Removed a bit of weight from the tail (I had to add some as it was a little nose heavy) and that improved matters.

The downside was the lack of downthrust on the motor. It ballooned alarmingly with any more than minimal power.

I'll place a couple of washers under the motor mount and try again. All in all looks very promising.

When I've got a folding prop, I'll finish the cowl, adjust the downthrust and fly again - weather permitting!

GDB

Edited By Caveman on 21/09/2013 18:45:19

[John Roberts 9]

Thanks for the report back on your maiden flight.

Mine will get its first run out on Monday or Tuesday.

Your thoughts on downthrust are particularly interesting especially as my build is both lighter (13 ounces) and more powerful (200 watts) than yours. I am clearly going to have to exercise some throttle control !!

I will report back next week.

Cheers,

John

[Caveman]

John, I've just put a strip of 1/16th ply under both of the top motor mount holes, which gives about 3.75deg of downthrust. Now ready to try again.

I'll let you know how I get on, but not sure I'll be able to fly for a few days.

GDB

[Chris Reid]

See my earlier notes on down thrust guys. I don't use it. The model is seriously overpowered and needs elevator trim in the climb. You can easily hold it in, or mix it if your TX has the facility. You need very little power for level flight. It is a glider after all.

Chris

[Steve Kenney]

Thanks for clarifying downthrust point again, Chris. Will experiment with a little throttle/elevator mix. Build coming on fine, if a little slow and enjoying it....

Appreciate your feedback re this

Cheers, Steve

[Jonnor]

I'm getting hold of a back copy to get the plan..........but the c/f tube looks very thin - and whippy - should I get a stouter one rather than the indicated dimensions in the plan?

[Chris Reid]

Hi Jonnor,

the plan is misleading in that the drawing of the boom is correct, but the written dimension wrong. The carbon tube needs to be 7 mm in diameter, with a 1mm wall thickness. Other folk have used thinner tube as per the written dimension and run in to CG issues as the boom is then too light and the models comes out nose heavy, or the boom far too long. Don't worry about rigidity, the carbon tube is incredibly stiff.

sorry about the plan glitch. I didn't spot the error in boom dimension when doing a check of RCM&E 's drawing.

Hope this helps.

Chris

[Jonnor]

Many thanks Chris -- much appreciated.

[John Roberts 9]

Mine had a successful maiden flight today .

 

The weather here was rather murky with low cloud & poor visibility so I could really only pootle around. It needed just a couple of clicks of trim to get it flying straight and level.

 

Perhaps surprisingly it didn't seem overpowered and showed no tendencies to "balloon" when opening the throttle. I would speculate that the longer boom on mine (20 inches) perhaps makes it less sensitive to throttle application?

 

It also has a nice gentle sink rate and can be very slowly floated in for a landing requiring only a tiny whiff of elevator to achieve a gentle touch down.

 

I only got one flight due to the poor weather but after 7 minutes of tootling around my 3s 800mah battery had 65% remaining. With more altitude I imagine that 20 minute flights will be easily achievable.

 

Cheers,

John

 

 

Edited By John Roberts 9 on 23/09/2013 15:06:06

[Caveman]

Had chance to have another fly with the Whiz Kid today.

I've added a piece of 1/16th ply behind the top motor mount screws, which gives a downthrust of 3.75deg. The model still ballooned quite a lot on application of throttle, indeed full throttle causes it to loop with neutral elevator!

So, I packed the back of the wing with a short piece of dried nettle stem (didn't have my usual flight kit with me, just tx, 2 batteries and a screwdriver so had to inovate!).

Launched the model again. This time the ballooning was reduced and the model flew quite well - glided nicely too.

Then increased the diameter of the nettle stem with a few self-adhesive packing tickets to lift the back of the wing even further. The model flew OK but didn't have quite the same stability .

I've since checked the wing incidence to see what values were, wing chord relative to the horizontal stabiliser of 0deg :-

Unpacked wing +4.5deg

Nettle stem packed +3deg

Nettle stem plus tickets +2deg

I've looked at glider, and other, plans on Outerzone and lower values appear to be more common, and generally the plane of the bottom of a flat-bottomed section at 0deg to the horiz stab.

Anybody any thoughts on this?

I have to say that it's a nice, fun model to fly and I'm even contemplating building another, but with more conventional rear fuselage and a rudder.

The comments ref. the carbon fibre boom noted. Mine is 6mm od and although slightly whippy it seems to be sufficiently rigid.

GDB

[Chris Reid]

Hi Caveman. You and others are having the odd problem with the excess power. The model cannot really be trimmed to fly level on full power as it is going too fast. It can be trimmed to fly level on approx half power, after that the only way is up. It will of course then loop and go on doing so unless you hold in some down elevator. Using down elevator, the climb can be managed to be as steep as you like - it's what the competition guys go for, and it's not for long.

Take care with reducing wing incidence in an effort to reduce the climb. All my models are designed with 2.5 degrees of incidence to give some longitudinal stability. If you reduce it too much you will lose stability and down elevator may make the model bunt uncontrollably.

Chris

[John Roberts 9]

Hello

I have had a chance to fly mine a few more times now and very pleasant it is too!

Oddly the only area of slight disappointment is the modest amount of power. The 28mm HK motor is supposed to deliver 205 watts on a 3s battery on a 7 x 4 prop and, although I havent checked it on a watt meter yet, it feels as though its only delivering half this amount at best. The model doesn't balloon, it really struggles to do a lazy loop and it has nothing like unlimited vertical so something is amiss in the power delivery department for sure.

My suspicion is that the GensAce battery (800mah 3s 30C), which uses tiny little 2mm gold bullet connectors, is struggling to provide sufficient current when I open the throttle wide.

I need to make up some connector adapters later today so that I can do a power test with my watt meter (the meter uses 4mm connectors hence the need for adapters so that I can hook it up to the 2mm battery connectors).

Cheers,

John