Harvard build help

[Djay]

Does anyone have any clear construction photos of the wing center section stepped leading edge area?

the photos on the web site do not match the plan constuction, and the plan does not show how it all goes together clearly. It only shows a top view, no clear side view. The rib L/E's are aprox 17mm and the LE1 and 2 are made of 12mm balsa. Also the ribs R2 and R3 have different profiles so how do you get the skin to form over the top of them without cutting the skin at R2. If you do that the skin will go down the side of R2 exposing the u/c bay cutout.

Any help appreciated.

Darryl

[Djay]

a couple of pics to help explain.

this one shows the height and curvature difference between ribs 3/4 and rib 2 in the background. If you sheet over the two ribs in the foreground the skin will butt up against the side of rib 2 and expose part of the u/c bay cutout instead of sitting flush across the top of all the ribs.

this pic shows the LE bridging piece which is to shallow going between ribs 2 and 3. you can see the curvature difference between rib 2 and rib 3, in all Tony's construction photos it shows the top skin sitting flush across the tops of these ribs, the skin will not sit flush on mine due to the height and curvature difference, it requires a compound curve to fit.

anyone out there built one of these?, did they encounter the same problem?

this is the first time on any of TN's models I have encountered a problem which has stopped me in my tracks.

Darryl

[jrman]

Have you looked at the photographs on the TN web site? They show this area very clearly.

[Djay]

As stated in the first and second posts.

The photos do not match the plan construction.

The photos show a bridging piece of flat wood between the ribs and no height difference between the ribs. The plan shows no bridging piece but 2 blocks of 12 mm wood which are to shallow, and the rib curvature causes a height difference which you will have to mold a compound curve out of the skin to fit across the ribs .

The photos show the wing top and bottom skins going straight across flush with all the ribs with no steps or height or curvature difference as shown in my pictures.

Darryl

[Pete B]

Looking at the build pics PDF on TN's website, look at the pic following the one entitled 'The Aileron servo mounting points'.

Comparing that with your pic above, you need to increase the height of the l/edge spar piece (which is pinned to the wing) to the same height as the rest of the l/edge spar. Trim off the l/edge spar just beyond where you have pinned it.

You will see that the front right corner of the sheeting in the PDF pic does indeed have a pronounced change of profile where it changes height. Shouldn't be a problem if you use some soft sheet, well-wetted....

My 2p worth...

Pete

Just to add that if yopu look closely at the outer rib in the area concerned, there's a defined crease in the skin above that rib

Edited By Pete B - Moderator on 17/07/2013 13:11:15

[Richard scarborough]

Hi Darryl, I have built one of these models so maybe I can help. From memory there is no bridging piece between W2 & W3, just the block, LE1. 12 mm is not wide enough, I glued 2 bits of balsa together to make the block the same width as the inner leading edge. I think I did the same with LE2. The front edge of LE1 should be flush with the outer face of inner leading edge, where it is glued to W2. As for the skin, yes it has a sort of compound curve. Insetad of trying to sheet this area in one piece, try planking it with strips about 15mm wide. It's one of those fiddly areas but it does work out ok. Hope this helps, let me know how you get on with it, cheers Richard.

[Djay]

Thanks Pete, but as I keep mentioning the photos are completly different to the plan.

The photo shows a flat bridging piece going between the inner and outer leading edges with a smooth transition and the skins flowing smoothly.

The plan has a 12 mm block in two pieces, the inner which is in the photo above,which bridges the gap between rib 2 and rib 3, wh the outer fitted after the outer leading edges are fitted.to get the skin to go over rib 2 and 3 distorts the whole structure to breaking point even when wet, believe me I have tried always to work this out as per the plan.

Thanks for the info Richard, the wood in my picture is not a bridging piece as per Tony's photos but is LE1 made exactly as per the plan.

Tony has replied to me saying I have to build up the bridging pieces(LE1 and 2) to match both leading edges and to stop the inner top skin at rib 2, and the outer skin a seperate piece goes up against the side of rib 2 and over ribs 3 and 4 outwards with some block to infill and sanded to shape.

Will give this a try but the Harvard is going on hold as I have jut received a kit of the Ilyushin Sturmovik IL2 which I will build.

Richard what engine did you use in your Harvard?

The only small motor I have spare is an OS 110 four stroke, which is physically the same size as a 90 but lighter, but I may use this in the IL2 instead.

Darryl

[Djay]

Decided to bin the plan and build the leading edge like Tony has in his build photos.

A flat bridging piece between ribs 2 and 3, so the inner leading edge is one continuos piece, then sheet over the area leaving the triangle at the step area to be covered by a seperate piece of wood, and the leading edge blocks fitted and sanded to shape.

This is the easiest way to build this area.

Darryl

[Richard scarborough]

Hi Darryl, Sounds like you have the stepped LE worked out. There's no need to stick rigidly to the plan in areas like this, as long as you get the desired result in the end. I used an electric set up in my model, Turnigy G60 -500Kv (supposed to be .60 2 stroke equivalent), with a 14x7 prop gives more than adequate performance. Flying weight is 4.4 Kg (includes 300g of lead in nose). Using the heaviest motor you can fit will probably save some lead. Tony used an ASP .91 and still needed 113g of weight in the cowl area. Cheers, Richard.

[Djay]

Hi Richard.

I used the Turnigy G60-480 kva in my Top Flite P39, running 6 cells and turning a 16x10 prop. Fantastic amount of power from these engines and almost unlimited vertical from a 9lb warbird.

I did think of using the same motor in my Harvard and my new Sturmovic, but can not be bothered with the charging and changing out of batteries.

Here in Dubai, we can fly all day long, all year round, so when we go flying for a day with multiple models it is easier to fuel up, then to re-charge batteries, especially if you have multiple electric planes. So fuel up and fly all day.

That and to lazy to keep changing batteries.

Going to try and buy an OS 90 size fourstroke after work today and that will go in the Harvard, with the OS 110 going in the Sturmovik, all going to plan.

I have also fitted mechanicaal retracts, as I have run out of pneumatic, and the hobby stores were out of electric systems. So the parts box was raided and a set of mechanicals from a World Models Tucano fitted exactly right, the servo was mounted as per the TN Hurricane, upside down outside the center section of the wing, with just the top of the servo poking inside the wing structure, works a treat.

Darryl

[Richard scarborough]

Hi Darryl, Mechanical retracts sound like the way to go, I used E-Flite 60 - 120 size electric units which do fit, but only just. Because the legs are quite short, bending them to fit inside the wheel meant they would hit the end of the retract body, no matter how tight I made the bends.So they fit on the outside. When it's in the air you can't tell. Cheers Richard.

[HughG]

Hi, Darryl,

I'm glad I'm not the only one who's been puzzling over the centre section. I, too, built up the linking pieces. I'm finding that a well wetted piece of the wing sheet balsa can be persuaded into a compound curve. At least, I hope it can!. I'll find out tomorrow when the clamps come off.

Richard, I hope mine turns out looking as good as yours! I bought the 60-120 e-Flite retracts. As you indicate, they are a really tight squeeze. Thanks for the tip on the legs.

Hugh