Designing my own plane

[Craig Spence]

Hi all,

 

the thread title isnt strictly true, but the end product will be my own.

I am redesigning the Frantic Fun fly to a mid wing 3D plane, I have some fuselage templates from the Frantic which I have modified to fit mid wing.

 

I have also built a card model from the templates to give me an idea of the size of formers I need etc..

 

Here's the pic's.

 

Minus the tail.

Removeable top hatch.

 

I would appreciate as much advise on these ideas before I start my project, many thanks all.

 

Cheers.

[Craig Spence]

Sorry all,

 

I have also added some height to the tail of the fuz for better knife edge ability, I will be increaseing the size of the rudder and also the elevator.

 

The nose has been made longer to accomodate the wing tubes and elastic bands (it will be plug in wings, two tubes and hooks front and rear for bands.

 

The fuselage has been made slightly wider to accomodate radio gear easier and I will have to put a rudder servo in here this time so its going to be tight for room inside.

 

I have thought about how these mods will affect the CofG and disscussed it with people in the know and I think it will be fine. The Frantic was always a little tail heavy so extending the nose should be fine.

 

The only thing thats bothering me about the build id getting the tail plane right.

 

Should I have the elevator slightly above the main wing line or would it be OK to have it in line with the main wing line?

 

Well advise appreciated,

 

Cheers all.

[Simon Chaddock]

Craig

The changes you are incorporating are quite significant so expect some trial and error flight testing before it all works as intended.

 

The trick is to understand what & why something is happening and then work out a likely solution. Tackle things a bit at a time, it is all to easy to correct one problem only to create another.

 

Nevertheless it is very satisfying when a specific feature you have designed works as you intended.

 

If you look at other designs a tailplane position can be above , below or in line with the wing. There are some aerodynamic variations between them but I doubt it will be a problem when compared say to variations in the CofG or angles of incidence.

 

Well done and do keep us all informed as you go along. 

[Craig Spence]

Hi Simon,

 

sorry for the very late reply im at work (oil rig in north sea) and the computers have been down.

 

Im trying to design it so im only changeing a few factors and im hopeing it all goes well. The Fuselage is quite similar in shape apart from a bit wider, longer nose, formers and a strung top and of course alot more gut's due to plug in wings (so not very similar at all lol).

 

Im happy to hear your thoughts on the tail plane though, I will have to remember to get the incidence just right, I know of someone who designed thier own plane and it took off nice slow and flyed slow but as soon as you opened up the throttle it plowed towards the ground.

 

Got any tips on how to fabricate tubes for my wing brace tubes?, I was thinking covering the tube in cling film then epoxy glass cloth to the cling film once dry, pull off and cut to size. Any thoughts.

 

Cheers Simon.

[Bob Cotsford]

speaking in very general terms, as long as the CofG, incidences and thrustlines are kept the same, and the tail surfaces don't get smaller, you have a good chance of emulating the original's performance.  You can change tip and tail outlines, fuselage profiles, taildragger to trike or vice verce, and you will keep the characteristics of the base model.  It's good to add a your own flavour to models so that you end up with something unique, and to your own taste.

[Craig Spence]

Hi Bob,

 

thanks for the feedback, I think what youve said  has boosted my confidence a little. When I decided to do the plane as a mid winger I have tried to stay as close to the original shape as possible and have changed things where they need to be changed to fit together (oh and asthetically as well).

 

The tail section is the biggest difference though, it will be around the same size but now the elevator will be split and the rudder longer to accomodate a tail wheel and better surface for knife edge manouvers.

 

Hope it goes well, cheers Bob.

[Craig Spence]

I thought id put this pic here so people can get an idea of what it will look like useing a bit of imagination of course and my card model.

[Simon Chaddock]

Bob

Take care the tail plane & fin mods you are doing do not extra weight. They are a long way back so even a few extra grams here has a significant effect on the CofG position. If you do add some weight at the tail be prepared to move something heavy (the engine?) forward to keep the original CofG.

Keep going!

[Bob Cotsford]

Que?

Simon, I assume you meant to address Craig?

You're right of course about adding weight to the tail, but as Craig has said he's extending the nose, he should be ok.

[Simon Chaddock]

Sorry Bob - its an age thing!

[Craig Spence]

Hi Simon and Bob,

 

thanks for the feedback fellas, I appreciate the reminder about the tail and to tell you the truth I didnt remember to consider that.

 

Thinking about it now though the nose will be extended quite a bit, the tail although bigger in size may still be lighter as I will be cutting alot more out of the tail of the fuz this time, also it will be a two part elevator which will probably be lighter, oh plus lightening holes like my high wing.

 

Cheers lads.

[Craig Spence]

Hi all,

 

im looking for help in the terms of materials. I am thinking about how I can build the fuselage as light but as strong and rigid as possible.

 

Mid wings ive bought in the past have been almost all ply fuselage and very little wood but this would be far to complicated for me so Im looking for advice.

 

I will be useing balsa sheet for the sides and bottom of the fuselage with lightening voids cut in the areas where less stress occurs. The top will be a stringer and sheet job.

 

I was thinking could I use ply for the fuselage sides and balsa for the underside, and top remains the same?. I want it light without sacrificeing strength.

 

I think the balsa sheets used last time were between 5 and 10 mm and its the same sheet on the tail so could you get a ply lighter than this but which is stronger without being brittle (for lightening voids)?.

 

Cheers all, feedback appreciated.

[Peter Miller]

Use balsa sheet for the sides and glue on thin ply doublers from the fireall back to behind the wing. I use 3/32" sides and 1/32" ply doublers. This is plenty for up to .35 engines, for larger engine use 1/8" sides and 1/16" ply doublers.

 

Do not end the doublers in a straigh line, make it a curved line to prevent a stress point.

[Bob Cotsford]

just to add to Peter's comment, I usually use a strip of 1/4" square or 3/8" triangle along the inside of the top and bottom of the fuselage sides.  It gives a little more stiffness to the sides, some more gluing area for attaching the top and bottom, and allows you to sand the corners to a nice radius.

[Craig Spence]

Hi fella's,

 

thanks for the feedback there, I built my last fuselage like you have both said and I intend to do the next similar. I was just wondering if there was a way to have ply fuselage sides, would it be heaver? would it be better or worse?.

 

Im trying to go as light as possible with it.

 

Cheers lads.

[Craig Spence]

Hi all,

 

well after talking to my LMS I will now be picking up some matterials for my project on Thursday. But due to work I probably wont get much done untill im back.

 

The project now is pretty much my own design as ive changed the fuselage completly, in fact there is nothing the same as the old one apart from the length. The wing will be the same minus the tips and of course it will now be plug in wings and the tailplane will be totally different as well.

 

The tailplane will be a split elevator and full rudder with tail wheel. So this is my own design (nearly) lol!.

 

I was hopeing for some advice as to matterials, what is the thinest thickness of fuz sheets I could get away with. Obviously taking into account the ply doublers and lightening voids.

 

What would be the best way to build in tubes in the wing to accommodate the wing spar tube?.

 

Is there another way to secure the wings other than elastic band's?, Im not totally keen on bands. 

 

Because they are going to be plug in wings should I reinforce the fuz side with ply where the wing attaches for extra strength or should the wing spar be strong enough to stop any movement?.

 

What benifit would I get (if any) from haveing a cambered elevator and rudder (stabiliser and fin).?.

 

Has anyone got any advice on making your own cowl&canopy, I was going to cut balsa blocks and glue them around the engine in two halfs then shape as required, same for the canopy. Once done get some filler and sand to desired shape, then vac form. Help on this one would be great.

 

Formers, I was planing on haveing two strong ply formers where the wing is (one in front of the LE and one behind the TE) and the two tail fuz formers would be balsa to achieve good shape for the tutle deck, any thoughts on this?.

 

Cheers all.