Peter Millers Harlequin Build Blog (electric conversion)

[Geoff Bradley]

Thanks for that Peter - will do.

KC - if you look just to the right of the former that the battery passes through you will see a strip of velcro (black and white) which secures it to the lipo holder. Also I've added an end piece to front of the liop holder (not on the earlier picture) to stop any forward movement.

[kc]

Actually Geoff I thought that was a velcro strap but I was also thinking about the back end of the Lipo where it looks like just a lap joint in balsa holds quite a heavy battery which otherwise might smash into & dislodge the Rx wires. I wonder whether a liteply cross piece to the fus sides would be even more secure?

My apologies but I always think it better to raise such matters even if my concerns are unfounded, rather than keep quiet & have someone find the problem later at the autopsy!

[Geoff Bradley]

That's a good point KC - I'll take your advice.

No need to apologise - you may have just saved me a lot of woe - thanks.

[Jimbo565]

Cracking job Geoff,just waiting for some decent weather to give mine a wizz

JIm

[Jimbo565]

Geoff

Just for future reference a fellow forumite, Tim@modelmarkings does some nice artwork for the Harlequin

Cheap as chips as well

[Geoff Bradley]

Thanks for that - I've just mailed him.

[Quantumsquid]

Beautiful build Geoff, just read the links from the start..

Good luck with the first flight.

I'm just starting the IC version and I was wondering if you built any side and down thrust to your motor mount, there isn't any indicated on the plans.

Keith

[Peter Miller]

When side or down thrust is needed I put it on the plan. If I don't put it on you don't need it.

[Geoff Bradley]

Thanks for the compliment Keith - Peter answered your question !

[Quantumsquid]

Thanks Peter, I needed re-assurance because from previous builds (not your designs) and after the first few flights I have nearly always added some side or down, which my construction variations may have played some part!!

[Peter Miller]

Down thrust is only needed when the centre of drag is a long way above the centre of thrust. eg my Slingsby T-31 and the Big Ship. Sometimes one needs up thrust if the engine is very high and dthe wing low.

Side thrust prevents swing on take off. I just correct with a dab of rudder. Interestingly, I don't know of any full size aircraft that uses side thrust but there are several that use an off set fin. Thus I reason that if the model needs it rudder trim will act like an offset fin.

I expect there will be the expert aerodynamicists who will tell me that I am wrong. Lets just say it works for me.

[Quantumsquid]

Appreciate the explanation. My dab of rudder is not always a dab hence some rather interesting take offs...

[Geoff Bradley]

Finally managed to get to the field and fly her - in 17mph winds .........

No problem whatsoever - she flew beautifully

If you are new to building pick one of Mr Millers gems - the Harlequin would be a good plane for your first build - IC or Lecky !!!!!

[Peter Miller]

Great news. Glad that you liked her so much.

Well done for testing in that wind. I would not normally fly her in tah wind speed but I know she will do it..

I managed to get two new models test flown yesterday in very calm conditions, sunny too for the first one but it clouded over before I could get piuctures of the second one.

[IanR]

Seconded, Geoff. Great news. I don't want to gush too much but I must say its been an inspiration to watch your Harlequin come together. Thanks for taking the time to photograph your progress.

I shall keep my eyes open for the next Geoff Bradley build. How about Peter's Van's RV-3?

[Geoff Bradley]

I'm blushing Ian

I've got Mr Millers book ' Designing Model Aircraft' so i'm considering having a go at designing one myself. On the other hand I may find a model I like and draw up my own plans for it.

Untill then I could do with some serious flying time

[Peter Miller]

Geoff, Definitely go for designing your own models. IT is the most satisfying of all modelling.

Any questions on that will be answered.

[Geoff Bradley]

Thanks Peter - from a brief look through your book you make it seem straight forward - I'm sure it isn't !!

I could do with a small plane to take on holiday in my caravan so that may be my first attempt.

I'm sure there will be many questions so be prepared

[Peter Miller]

IT is pretty easy. Start off with a simple known layout. Don't try for complicated shapes on your first design. You will be learning to draw formers from a plan and side view so either square formers or ones with an angular top (like Harlequin) will be easier.

I have a very old and basic computer program that allows me to draw ellipses to do the rounded tops of formers. They can be done by estimation but it is not as reliable.

Take figures such as wing area and span for and engine size from known figures. You can vary them remarkkably but they give a starting point.

I use tailplane areas down to about 14% of the wing area with a forward CG and long moment arm. Just do what you think. What looks right will fly right.

[Geoff Bradley]

Thanks for the advice - fingers crossed !!

I'm happy with drawing the formers - I did lots of engineering drawing many years ago.

A couple of questions allready .....

From what I've read a long moment arm gives stability - typically 1.5 cord length ? How long is it adviseable to go up to ?

If you use a 14% tailplane area do you increase the elevator area percentage ?

I will put any further questions on your 'plan builders' area.

[Peter Miller]

Right, with your engineering drawing experience you won't have any problmes.

Yes, a long moment arm does give more stability. I have found that my models with the longer moment arms are much easier to land well.

The long moment arm gives more leverage so the elevators can be quite small. MY new model has a long moment arm, 15% tail with small elevators. More than enough authority. Havent got the figures to hand. IT was drawn on the TLAR method. I drew the tailplane and elevators. Looked and thought, "Those elevators look a bit small" and added 1/2" to the elevator chord.

Just got the plans out. Span 46, Chord 9.5" Area 437sq.i.n Moment arm wing TE to T/P LE 15" TOtal Tailplane area 68.25 sq.in. Elevator area 19.25 sq. in.

[Geoff Bradley]

Thanks Peter - time to have a good read and put some thought to what to design and build.

[Sean Murray-Smith]

Hi

I used the free plans which came with RCM&E and built the Hralequin. No photos yet as I didn't want to risk a pilot until after the trial flight so no cockpit.

Power is a Turnigy 32 flinging a 13/4 prop driven by a Zippy 2200 14.8V LiPo and a Turnigy 70Amp ESC with UBEC.

To say that she flew well is an understatement; take off run straight and true with up elevator to keep the tail down; eased off on the stick and she lifted beautifully. Two clicks of trim on the elevator and she was on rails. Climbed to a "two mistake" altitude; throttled right back and fed in up elevator until the stall, when suddenly... nothing happened. No wing drop, just a slight mush. Flying at half throttle was like a trainer, but when I opened the taps she leapt ahead. Even then she was well behaved; loops and Cuban 8s were crisp with no sign of roll out (so I built her straight). Even a stall turn, which looks like my dog shaking a rat when I try it with my Apprentice, was clean and crisp with alittle opposite rudder to tidy up. Then, the landing. As the man said "Takeoffs are voluntary, landings are compulsory". Throttled well back on base leg; turned onto finals bleeding off power; flared and landed like a butterfly with sore feet.

Mr Miller I salute you; you have designed a magnificent machine; a pussy cat at low speed, but a (well behaved) tiger when you give her her head. Thank you. Next week I shall be a little more confident and try her on flick rolls, bunts, inverted flight and knife edge. I am now confident enough to put a cockpit on.

Cheers

Sean Murray-Smith; Adelaide; South Australia

[Peter Miller]

Hi Sean.

I am so glad that you enjoyed Harlequin and found how nice she is.

I love her myself. As I say, when flyin the only time I fly straight and level is when she is inverted.

I had her out a couple of Sundays ago to give a relative novice some extra experience. He found her easy to fly.

Then I had a good old thrash. half way through I realised I had an audience about 100 yards away. I then pulled off the best landing that I have done for a long time.

Of course Harlequin should be "he"

Anyway, Have fun

[Dave W]

I have just hit the dihedral problem mentioned on page 2 of this thread.

I made the dihedral brace exactly as on the plan and then dry-fitted it to the first wing half to check the dihedral. With the exposed bit horizontal (as it would be when fitted in the other wing half flat on the board) the wing tip was raised by only about 3/4 inch.

I have done some quick calculations and estimate that the angle on the dihedral brace should be about 2.6 degrees instead of the 1.5 degrees of the one on the plan (which I agree was difficult to measure accurately).

I shall make another brace with the new angle and see what happens.