Slabby things often referred to as "Silhouettes"

Cribbs74 wrote:Not sure why someone gave you a negative rep point for your post, i'll fix that.
Ron

Yeah, whats that about?
Here's another greenie Ian.
Bob

I am using these to examine what I call the "fuselage potential".

I was surprised by how quick these things are to build but on closer examination the fuselage has many weak spots.

The fuselage has the grain at odds with the the leading and trailing edge of the wing. A recipe for splitting wood - rather like using an axe to make kindling.

These are built per plan and the area around the leading edge of the wing is reinforced but the rear is not. There will always be a difficult balance between strength and weight but there must be a better way.

I have done quite a bit of searching and can see that even a bit of a landing somersault (It happens to me with RC quite a lot) can wreck the fuselage.

This seems to be in two main areas - behind the trailing edge and the fin.

The fin on these is a seperate piece of balsa simply butt jointed - end grain against straight grain - nose over and this will pop off.

I will be experimenting and weighing. I intend to build some profile " sandwiches".

Ply profiles from balsa and ply. Rather than say 1/4 or 1/2 inch solid balsa - say use 1/64 or 1/32 ply as a central core, 1/8 balsa either side (lightened), 1/64 ply skin.

The core being used and appropiately sectioned to incorporate the fin.

All theory at the moment but the "Rocking Donkey" was made with a 3/16 balsa core and 1/64 ply sides. I had trouble snapping a test piece.

There are all sorts of permutations possible. Purely balsa ply structures or mixes with other materials.

These models will be my test bed.

I think the -ve was a touch of "finger trouble" - I don't take the adverse seriously, I have manged to hit the - instead of the + with my fat fingers. There is no way of withdrawing it other than finding more postings and plussing.

After a long time I resurrected these from my "part built" drawer and got on with the Gazelle. The Mamba will be next.



I am working on a wedge tank for it. Don't know whether to just do a normal stunt wedgy or a uniflo. It will be about 11/2" x 11/2" x 3/4". Advice please.

Finishing - I will paint the slabby bit but not sure whether to glass it first. The fin looks very vunerable.
More advice please.

So far as pictured, no tank no finishing it weighs 271g - about 9.6 ounces. the engine is a PAW 1.5cc. The plan recommended 1 to 1.5 cc diesel (without silencer).


A muffler is known as a silencer in the UK

That looks nice.

On your statements from 2014, reinforcement on the outside of the balsa brings more strength than putting a strong core in. I do admit I laminated fuselages with some fiberglass drywall tape in the middle since I was already adding a glue joint. In practice the results have not added much strength to the fuselages. A layer of very lightweight glass or carbonfiber set with dope or polycryllic might be a much better choice that adds very little weight.

On 1/2A this is a problem all around since weight is critical already.

Phil

1/64" ply really strengthens these. I make the fin and fuse all one piece. The rudder gets laminated from balsa with the grain ~30 off from each laminate then this gets attached to the fin with the grain running along the 'hinge' line. This strengthens the fin and the rudder won't easily break in case of a somersault. If the fuse is 1/4" balsa then the rudder might be 1/8" core with two 1/16" sides.

You can rip the entire fuselage in half lengthwise below the wing root, and glue it back together with a long strip of 1/16(1/2A) spruce sandwiched into it. 1/8" thick if it's bigger than 1/2A. That does give it significant strength to resist breaking the fuse aft of the wing and near the stab too.
Rusty

Thanks guys this is all food for thought for future builds.

I love that Gazelle Ian.  Everything works, the enclosed lead-out wires, the wing, and the profile especially the slope of the vertical stablizer.  It reminds me of my scratch built "flaps" plane.  But why is the stab made up of two pieces of balsa, why not just a single piece?  Wouldn't a single piece be stronger and avoid separation on a nose-over?  



It's going to be interesting how you "wedge" a fuel tank inbetween the muffler and the leading edge of the wing, seems like the nose moment is not long enough.  I'm a fan of building wedge tanks into the fuselage, but that procedure is not popular here due to strength issues.  But from my perspective properly done no strength is lost.  It makes for a much cleaner installation with no requirements for straps or screws.  



Bob

The fin is made from two pieces per the plan and the grain direction on the plan. It has two purposes, the first being by presenting the grain at the best angle through the curve, the leading edge is stronger. The second is that the glued joint adds strength and prevents warping.

I accept that this is debatable but the real weak point is the joint of the fin to the fuselage body.

With a degree in hindsight, I would construct the fuselage differently and follow advice from this topic. The central core of the fuselage would include the fin.

The tank will be a wedge but it will be homemade (and tailored to fit). I haven't decided whether standard stunt tank piping or uniflo but it will be adjustable up and down (slightly). There have been many postings on this forum that emphasise the benefit of having the tank adjustable. I always thought that lining up the outlet pipe with the NVA was all that was necessary.

I will probably show the tank construction - metal fuel tanks are not widely avaiable in the UK. Den's Models import a few Brodak ones but I have found a source of tinned metal sheet.

I think that embedding the tank like you have is fine as you get a larger tank and the outlet lined up in two planes. I am afraid that the Gazelle would not cope with that. There are no bearers for the tank to sit between - the engine is mounted in a ply balsa sandwich.


Fin - UK general term for Vertical Stabiliser. We prefer less complex words, abrupt and to the point. Tailplane - rather than Horizontal Stabiliser.

Ian, I agree with your statements on the vertical stab 100%. This plane is very Flite Streak like. Similar aspects in all areas. The vertical stab to fuse is a joint with little to no footprint. I typically epoxy these connections to the fuse after fitting them very close. I don't like to fillet in these areas due to if an accident occurs it usually takes a heck of a lot more other pieces with it. I guess I like to call it a sacrificial joint and if it does continuously break, I lay light weight glass cloth along the dorsal portion of the rudder and onto the fuse.

As far as a tank is concerned, I personally would make a uniflow tank due to the fact that if it doesn't work, standard vent is a alternative and you can just cap the uniflow to block it off. The diesel with it's rear muffler is taking up critical nose length. Why does the muffler need to be on there? I do know from my diesel experience that most of them are generally quieter than glow. That being said, my cheap Chinese Silver Swallow is damn near deafening when compared to a PAW.

Seeing that the diesels are more economical with fuel compared to a glow, how much fuel does that engine require? Generally we like to have the capability to run in the air for 6 minutes. That's also to fly the required maneuvers of the stunt pattern without exceeding 7 minutes. Is the diesel affected by tank shape and design? I wish I could accurately answer that question. Currently my flying buddy is using a PAW .19 on a Flite Streak using a 2.5 oz. tank. While I have watched him fly many patterns, what I do see is that he can never seem to get back to back results due to tweaking the Tommy bar and needle thus changing the flight time.

What I've seen done many times is the leading edge gets notched back into the sheeting allowing for a larger tank which now sits back into the wing. Shear webbing must be placed from center rib out beyond that bay where the leading edge was interrupted to offer strength back. Ken

Hi Ian, I really like your choice of slabby designs! It just looks racy! Definitely Flight Streakish! How thick is the fin? I have pinned my fins with toothpicks.. (birchwood) to give them some lateral strength. Yours is fairly low-profile as fins go.. but it's a safe-guard you can make. I used a pin-vise to bore the holes in the fin.. and stuck-in stubs with points-out, to mark the locations on the fuse. Just center it.. and press down. Drill two more holes and cement it in. A fillet might crack.. but it will take a total wipe-out to break the fin off. It's a lightweight mod. too.



I agree with Ken on the hard tank. You won't need a big tank. You probably don't "want" a big tank. There should be enough room between that muffler and the wing's L/E to get you started. I bought a coil of 3mm copper tubing for gauges at the auto-parts store to plumb the last tanks I built. I lightly sanded the tubing and it soldered up well against .2mm tin-sheet with a pencil iron using leaded solder. I'd like to see your wedge-tank example though. Mine were simple little 6-7cc boxes for 1/2A speed.

The silencer position can be changed but that is the only position that stops it protruding below the fuselage. The Gazelle was designed pre silencer requirements.

On these PAW engines the silencer can be placed in three distinct positions but these positions form a triangle. If I reverse it, the exit sticks out below the fuselage.

Any flying site in the UK permitting IC engines has a noise level restriction of 82db. A PAW 1.5cc, unsilenced pips the post. 1cc and below seems fine.

The space behind the engine will easily take a 1.5" x 1.5" wedge tank. Not too worried about flight time - I am more concerned about building, finishing and perfecting my techniques. I made loads of mistakes building this but I have lots more to build and learn from.

The first ones I am likely to fly will be electric - the Gazelle is not a suitable candidate for that.

A lot of variables with fuel consumption on a diesel engine. I never thought about time limited flights. Usually though, a diesel runs at about 2/3 the consumption of a glow. It sups less fuel but I do know that external temperature makes a noticeable difference as well.

Thanks for the comments.

Nice slab.
For a buildoff on another site I chose an old FF slab model, converting to RC. Should be working on it this weekend by instead goint to the WRAM show.

Back to the Gazelle - here is the tank fitted ( silencer turned so that the tank can be seen)



Slotting the mounts will allow for vertical adjustment of the tank.

The Gazelle went over to the "Dark Side" and is now almost finished.

Strange thing I notice when looking at the pictures. The wing looks rubbish and wrinkly and the fuselage looks quite good. I had to go back and have another look.

Trust me - the wing looks good but I managed to wrinkle up the fuselage.









I also added the undercarriage so that I can fly it solo.

Looks Good Ian ! Why did you decide to go to the Dark Side when you had the engine mounted ? I am thinking the timer delay for the elect. but you can always use a pin stooge with not that much trouble >

getback wrote:Looks Good Ian ! Why did you decide to go to the Dark Side when you had the engine mounted ? I am thinking the timer delay for the elect. but you can always use a pin stooge with not that much trouble >

We are not allowed to fly with IC engines locally and would be heavily fined if caught. Decided not to wait until I retire to the North of England where there is a control line club.

Honestly.. I like some of the advantages of electric flight. There's a learning-curve associated with it.. that many dedicated IC-engine fliers are resistant to. I understand that.. but a "kid" who's learned the ropes of EP-flight... would experience a "bigger" learning-curve, if switching to IC.. (IMHO). Let's isolate this conversation to C/L (tethered-flight).. A brushless-motor has a rating. It will meet the specs when it's powered-up with the recommended battery-voltage and prop. Run-duration is dictated by the battery's capacity and a timer. He needs to understand circuitry, the importance of reliable elec.-connections.. how to program the timer and match that power-system to an airplane within its range. Let's assume he understands how to balance/trim the model aerodynamically. His "motor" and prop-combo are going to work the same.. every time; regardless of the atmospheric-conditions. It's a repeatable function that he doesn't need to be concerned with. Field-equipment need only consist of extra prop(s) a field-charger.. and a couple extra battery-packs.

As for IC-powered flight.. "what's in your wallet"? ( field-box).. fuel.. alternate fuel.. power-panel/glow-starter.. clips/wires extra glow-plugs.. syringes.. fuel-bulbs.. engine-related tools.. rags.. spray-cleaner.. after-run oil..

just sayin'.. I love running a real "engine" as much as the next guy.. but anyone wishing to improve their "flight-skills" is better-off with repeatable power-system performance. It's also getting increasingly harder (as Ian has stated..) to operate noisy engines in urban areas.. without complaints.

Ian, I'm glad to hear there is a club in your new flying area. That will be a huge help for your interests, things you may have never thought to try, and new people make it much more exciting.

I was waking up this morning and re-perused the whole thread while having my coffee. Glad to see it back in the mix. And Ken said what I'd already thought too, it looks very much Flite Streakish, and if it flies like one of those, it may well be the best most fun plane you've flown on lines.
Good luck,
Rusty

I like the idea of the Cowel , It covers up that Thing LOL I just cant get in to it being a IC engines man all my life and luckily wee don't have that restrictions out here where I am . Bee good to see it in the air though and the fling is what its all about whether it ELC> or I/C but I know deep down Ian is a I/C Man .

Rusty,

I liked Ken's comments and his suggestion on tanks. It became clear to me when finishing that I wanted to fly it locally and so to the dark side it went.

I did note the comments about repeatability with settings, particularly compression, on the diesel resulting in varying flight times. I haven't really experienced this and neither have my pals flying team racers but we don't really have that much variation in air pressure or temperature on a daily basis and tend to stick to a start and running setting.

I did various tests on some of my diesel "running ins" and didn't see that much variation on a tank full but then again I am not using a hot competition diesel fuel.

Getback

I am an IC aficionado particularly diesels - lets face it, I have many IC engines. I love the sound and the smell but as Roddie points out - electrickery is far easier and acceptable in my local park. I spend quit a bit of time flying RC there. That said, I firmly believe that electrickery - although not as difficult a learning curve as IC is a lot more dangerous.

I am building some IC stunt model but they will be full fuselage - one for 1.5cc and another for 2.5cc. I have the plans and the parts cut out but I never have enough time!

Roddie,

You are almost right but one of the problems with electric flight is voltage for two reasons.

Batteries are expensive and stocking up on batteries for a lengthy session soon amounts to quite an expense. They also take a while to charge and will only be charged so many times before they start to fail. Fuel is cheap compared to that and quality batteries (and chargers) are expensive.

Cheap Speed controllers don't cut it for control line. I didn't really notice this with RC because then throttle is just stick waggling and constant adjustments become the norm. As the battery voltage drops so does the motor speed. Also keeping constant revs when the model comes under load requires some sophistication. The quality ESCs have governors and constantly read the revs and adjust current - some of the timers can do this - but you are looking at quite a jump in cost.

Catching up on my reading tonight and seeing your great progress. The colors came out really good. Simple and dramatic.