Profile vs Built up

I have tried analyzing why it is I seem to be worried about built up fuselages rather than sticking to profiles and it seems to me the reasons are:

1. So many fuselages use the dreaded 'hollowed block' construction which seems wasteful, complicated, messy and time consuming to achieve - it's no mistake that most of my favoured designs (APS Thunderbolt, Skiffler, Coy Lady etc) do not use 'hollowed block' fuselage construction. Do Brodak fuselage blocks come pre-shaped?

2. I'm concerned about achieving a neat cockpit canopy installation - cutting a canopy to match the multiple curves of the fuselage seems more like magic or art than model making to me at the moment! At least with Brodak I suppose you can always buy a replacement if you mess up!

3. Wing installation - and in general keeping everything straight - this seems much easier with a profile - allied to this is the method of wing/fuselage installation - it seems to me easiest to 'build the fuselage onto the wing' rather than build a separate wing and fuselage and join them either by sliding the whole fuselage onto the wing or chopping out the bottom of the fuselage to install the wing.

I know many of you out there are 'wizard' builders - but I'm not - I would welcome your feelings on the above and your comments may give me the confidence to splash out on a built up fuse ship rather than stick to the 'easy option' of sticking to profiles..

Hi Tony,
Brodak kit blocks need hollowing. The Oriental needs very little
hollowing.
Get a pair of Hobbico Canopy scissors. When I started using thses
my canopy fits improved alot.
I like to finish small pieces of the plane then put it all together. I find it easier then handeling the whole plane while sanding etc.
Profiles have some draw backs. They tend to have more engine vibration, leading edge to body glue joint problems & rear fuselage flex. The full fuselage fixes thses problems & gets the
engine & tank out of sight, plus the wider fuse. looks more like
a full size aircraft.
You still need profile planes for Profile Stunt events so keep
building them.

This is strange, as my first airplane (u/c) was a full fuselage type. In fact the first 4 were. I built my first profile in 1965 and found it lacking. In fact I have never liked them except for slow combat, ballon bust, profile carrier and Good Year racing. I have never seen nor flown a profile stunter any where as good as a full bodied stunter. Brodaks sells some easy to build full fuselage types and I think once you build one, you will see that they are better flyers and not all that hard to build. Actually, the wing sets straighter and so does the tail section and much smoother flights due to very little vibration. I would try the Fancy Pants first. The engine is upright and it harks back to the 50's and 60's and is basically a box for the wing. Ty M.

>I have tried analyzing why it is I seem to be
>worried about built up fuselages
>rather than sticking to profiles

>1. So many fuselages use the dreaded 'hollowed block'
>construction which seems wasteful, complicated,
>messy and time consuming to achieve -

Then mold the blocks. It is faster, easier, stronger, and usually lighter. Not a bad combination. Basically you carve a piece of blue (or white) foam the size and shape of the block on the outside. Attach this to a piece of plywood that is undersize at the bottoom, and then wrap two or three layers of moistened 1/32 balsa over the mold. Wrap it with rags or elastic bandages and let it dry. Pull the shells apart, apply a thin layer of yellow glue between the shells, and then put them back on the mold until dry. Then trim and fit to the plane. No carving on the outside. No hollowing on the inside. No carving through a block. Nice!

>2. I'm concerned about achieving a neat cockpit canopy
>installation - cutting a canopy to match the multiple
>curves of the fuselage seems more like magic
>or art than model making to me at the moment!

You can carve or paint a canopy. You can even paint a clear canopy. You don't need to keep it clear. Then you don't need to do cockpit detail and you can fix your "goofs". But it isn't hard to cut a canopy to fit. Just go a little at a time. And if you apply the canopy with Ambroid (or similar) with pin holes around the perimeter, it will stick quite well. Then mask slightly above the canopy and apply a thin layer of Epoxolite to simulate a frame. This will then fill any gaps and give you nice detail to boot. (I still like the carved canopy the best, however.)

>
>3. Wing installation - and in general keeping everything
>straight - this seems much easier with a profile -
>allied to this is the method of wing/fuselage installation -
>it seems to me easiest to 'build the fuselage onto the wing'
>rather than build a separate wing and fuselage and join
>them either by sliding the whole fuselage onto the wing
>or chopping out the bottom of the fuselage to install
>the wing.
>
>
>Tony

Then do it that way. If you build the wing first and then cut the opening for the wing slightly undersize, you can fit each fuselage side to the wing with no gap. Build the engine mount as a crutch. Make the engine mounts long enough to go all the way back to the wing and put 1/2 inch balsa cross grain between the engine bearers except where the engine itself fits. Draw the thrust line on the inside of the fuselage sides and a line parallel to this 1/2 inch above the thrust line (assuming an inverted engine). Then put a 1/8 inch square balsa strip above that line and use it to "jig" the crutch perfectly along the thrust line. Glue the crutch to one fuselage side first. Keep it square and let it dry. Then slide each side over the wing and glue the crutch to the other side. You now have a solid and square nose section up to the wing and you can complete the rest of the fuselage while it is attached to the wing. Just make sure you attach your pushrods to the horns and slide in the tail before pulling everything together.

That's one way. There are others and people who will prefer building the fuselage separate and assembling as you mentioned above. Both methods work and they are not difficult to do.

Leonard: I wish you had written the instructions for the kits and other planes I have built! I just printed them out. The fuselage instructions are worth the price of a kit to anybody who hasn't already learned these techniques. (And you could have counted me among that crowd until today.) Thanks. John

Tony,

There is little to worry about when doing a built up fuselage. I am not a millimetre perfect builder but never theless the wing fuselage gaps on my Toreador are quite minimal and there was very little play. Had those gaps been present on a profile fuselage there certainly would have been a lot of 'rock and roll' when fitting the two together. Have a look at the air frame/wing gap on the Toreador

[photo not recovered: toreador.jpg]

It's not that big, is it?

The gap can sometimes be cused the hole on the plan being bigger than the wing profile. It's always worth offering up a centre rib with capping attached to the drawing of the fuselage to see if the wing hole will be too big.

As far as carving turtle decks go, if you use a dremel for quick hollowing, do the hollowing outside in the open. Stand upwind and wear a dust mask. I covered everything in my shed with a thin layer of balsa dust and had to have several days of work with inflamed air passages. Despite taking care one or two holes appeared which I patched with the shavings produced when I razor planed the outside of the balsa block.

I am certainly going to try moulding a turtle deck using a blue foam mould. It also means that ou can quickly reproduce a deck if you want to build another identical model.

Any suggestions how I can carve the blue foam with minimal dust? It's nearly as bad as balsa dust for spreading around and I don't have a hot wire cutter.

Try carving a block Tony, it really isn't that bad. It's nearly as wasteful as prop carving for vintage rubber powered Wakefields but I find it very therapeutic after a day teaching recalcitrant pupils. Just don't let your attention wander.

On some airplanes, it works nicely to make the fuselage in separate front and rear sections, and install them independently on the wing. One trick I like is to make a small epoxy and microballon fillet on the inside of the fuselage-wing joint. It doesn't have to be as neat as an outside fillet and really increases the contact area.

I'll have to chew on all this a bit. I hate typing!
On the canopies, you trim to rough outline and then SAND to final fit, DON'T use scissors or knife, it will never work.
Fit and try, a little at a time, once you get it close, you can tape the sandpaper to the fuselage, and work the canopy against it slowly and carefully to get an exact fit. Polish out any scratches with progressively finer grits of paper, then use a GOOD plastic polish to finish.

Tony --

Built-ups will probably always be better performers, and certainly prettier. But for a good "working-man's" stunt trainer, I suspect you will in the future see some profiles that are superior to classic profiles.

The paradigm of a balsa profile, and a hole through fuse for a pre-built wing can be replaced by the the U-Key paradigm of a skinny hardwood fuse and two separate cantilevered wings built on stub spars stuck through the fuse. The U-Key fuse approach has not been applied to built-up wings to my knowledge, but I see no reason it would not work, and result in a superior profile. Ugly, but lighter and stiffer (I think)than traditional profiles.

This makes a stunt plane that looks and smells more like a big combat model than a "real" stunt plane, but the aesthetics are such that it would appeal to some.

I have started a winter project based on this approach, and some alternative construction materials.

Try looking at a Berkley Interceptor 35.

My Trixter AB profile has the wing spars, leading and trailing edge go through the fuselage. There is no sheeting. The main wing strength is from a large spar. I've put it in the ground five times, three from the top of the circle, and thrown two prop blades in flight. There were easily repariable tears in the plyspan with the thrown prop blades, other than that no damage.

There is a 1/8 rib on each side of the fuselage and I glued on a 1/2 wide strip of typing paper to have something to stick the plyspan to.

If I were to scratch build something like a Twister or a Magician, I think I would seriously consider redesigning the wing center section to build the wing through the body rather than cutting a hole and sticking the wing through.

This also works with full fuselage airplanes. A lot of the I-beamers are built that way, and a number of Larry Scarenzi's airplanes published in Flying Models have similar construction.

I think it is easier to accurately cut spar holes than a wing cutout, and the wing is built in alignment with the fuselage at the time rather than being aligned later.

>I think it is easier to
>accurately cut spar holes than
>a wing cutout, and the
>wing is built in alignment
>with the fuselage at the
>time rather than being aligned
>later.

Jim;

In my misspent youth, I experimented with a lot of design stuff - probably too much so. I built a smaller 15 size ship, I-Beam construction, with the solid fuse and only spar, LE, TE, and bellcrank mount going through the 3/8 balsa fuse. It held up fine.

I thought the same would be so for a large 35 ship, so I did one at about 480 sqi for an OS 35 Max-S. Fuse was 1/2 inch. Wing on the larger ship flexed like crazy. Airplane lasted the summer, but I was not happy with it.

This led me to a number of observations for wings in larger profiles:

1. A wing that has a sheeted LE and Sheeted Center section is far less likely to flex than one that isn't. This is especially important in a profile where you have a very small amount of fuse support, and that support runs directly through the center of the wing. Think of the stress running through the center of that wing as opposed to a full fuse ship. Take away the strength that the center sheeting and covering can add, and it gets scary.

2. Most of us who build a profile instead of a full fuse ship do so for a number of reasons: nostalgia, time, experimentation, or training. In a profile, the hardest thing to build is normally the wing. If I am going to sacrifice anything, I don't want it to be the component I spent the longest time on...

My personal experience with profiles without a wing cutout was that in the smaller models it was fine. Get up to something with a 45" span or so, and that wing wanted to start flapping... I could have beefed up the I-Beam and the LE/TE some more, but then it would have been heavier than a conventional wing.

I have built about a dozen built-up fuselage ships. Last winter, I built a Legacy and, for the first time, built the fuselage around the wing. It was actually easier to square everything doing this. The wing served as a helpful weight when the fuse glue was drying. I glued the ply reinforcements on the fuse sides first, then the motor mounts and the ply firewall to one side. Slipped the sides over the wing and joined the front half. Then, I pinched the back together and carefully inserted the rear formers, using a small plywood 45-degree triangle to square them. Putting the pushrod in was a bit of a chore, but no worse than building the fuse separately. I moved the windshield back and build a turtledeck using formers and 1/16 balsa covering. As far as hollowing goes, the amount of work depends on how perfect you want the hollow area to be. No one will see it and you might have another once or two if you don't hollow it until you can see light through it, but it doesn't have to be perfect to get a good flyer. I sometimes scrap the block and put in formers covered with thin balsa unless I have to file the heck out of the top, as the very, very front of the cowling.
I think this is easier than cutting the bottom away, inserting the wing and gluing the bottom pieces back. I got the tightest wing/fuse fit I've ever had. You can see a picture of my Legacy (that looks like a giant Nobler) at Yahoo Clubs control line flying forum pictures under Stunt Ships.
The main problem I have with built-up fuselages is the after-build modifications and adjustments involving the fuel tank set-up. Never built one I didn't have to go in with an x-acto for modifications to move/adjust/replace fuel tank and lines. Major crash repairs are also generally easier with profile ships. Good luck if you try one.

>The main problem I have with built-up fuselages is the after-build modifications and adjustments involving the
>fuel tank set-up. Never built one I didn't have to go
>in with an x-acto for modifications to move/adjust/replace
>fuel tank and lines.

In order to easily deal with tank problems, eliminate the forward firewall. Replace it with something sturdier yet, such as cross- grain half inch balsa for a tank compartment floor/top. Make up a motor mount crutch assembly before attaching the beams to the rest of the fuselage. Drill the mount holes before then, also.

For old Fox engines, I either used wood screws or dowels to make the crutch to web joints vibration-proof. Use small dabs of silicone seal near the front, where they can be cut later, to position the tank and still be able to take it out again to add new spacers to re-position it for equal speed both directions.

The idea of removable tanks and pre-assembled mount crutches can be used by either building style, be it the "cut the belly out to stick the wing in" crowd, or the "build the fuse around the wing" bunch. I do caution the latter group that they need to be much more cautious with alignment, since they will have more chances to end up mis-aligned than the former group normally will!

Kiwi