I was wondering what types of changes must be made if you take a R/C model and make a full scale plane out of it. What type of difficulties would be encountered. I have a set of L-39 pusher prop design that I was wondering if it could be blow up and successfully flown. (This is hypothical guys!) A group of us was talking about a venture of this kind. Coffee talk.

Ah, coffee talk.... my favourite kind (I gotta get off this board and go cut balsa... Darn all you folks for making this site so addictive )

First off the airfoil would probably have to change to something for suitable for "real life". Stall behaviour that we don't bat an eye over in model flight becomes much more important in full size. Airfoils or washout designs that offer lots of warning and a soft break are much more important.

Secondly the force setup in terms of decalage and CoG placement would change to a more conservative setup. Here again we tolerate setups much closer to neutral than they do in full size stuff. The only full size that come close to models for the overall force arrangement are probably the aerobatic planes. I talked with a full sized Pitts pilot a few years back and he told me the aircraft was very neutral but it was like riding a hungry lion. One moments inattention and you were a meal.

And finally the control surface sizes would probably need to be made a lot smaller. The full sized stuff I've had a chance to fly have all had control reactions that I classify as being very trainer like by model standards. And this includes a Murphy Rebel bipe that has a reputation for being quite the aerobatic mount among the ultralite types.

And finally, finally I suspect you'll have to special order the large sizes of balsa for building the big version......... :stupid: :bananahea and all the rest of the smilies.....

Wow, I had no idea things change that much. The plane that is the center of all this controversy is the L-39 Albatross. A pusher design by someone overseas. It is a darling to fly especially for a intro ducted fan model. The wing is built up and fully symmetrically as is the rudder and elevator which sits atop the engine.
What got us started on this slippery slope is the fact that the fuse is basically lock joined together by four longerons running the lenght of the fuse from the inlets back. The formers are secured to the longerons and are planked. (Would never plank for a full scale job! This was a job in itself!)
Group think was that the plans set up for the fuse would work for a full scale plane. As for the wings, you are right and I wouldn't even know where to start.

All I can say is pass another cup, but decaffe!!

LOL. That high test got to ya did it?

Hey, we didn't even get into the structural aspects.....

What about the structural aspects?

Just go try some searches on homebuilt aircraft structure and ultralite airframe structure and the like. I think you'll quickly learn that they don't build dem big birds like us littl'uns do....

And for heaven's sake get RID of that espresso will ya? ! ? !

LOL

Actually, I have a set of wooden ultralight plans. We looked them over but there is a major different between something going a maxium of 70mph and 200mph!

This is starting to make sense. Better up my medication! Damnit, where's my coffee!!

Is there a good website on homebuilt structure? I haven't found one yet.

you do realise there is already a 100% scale L-29.....
why try and build a full size one of tubes and a VW engine when you can have the propper toy...

But then you would have waisted a good COFFEE RUSH :sunsmiley Pete

i think sitting on a real turbine might replace that.
but if thats not enough theres a real Mig-29 on E-bay for sale

Hey Guys,

Haven't you ever had a model you thought would make a great full scale airplane? (Excuse me while I take another coffee sip.) Most full scale planes, let alone jets, are out of the reach of us working class stiff. But a prop pushing, jet wannabe looking, thousands of dollars cheaper, homebuilt plane may have merits.

(I don't know what's worst? The obsession with the topic or my 40th cup of coffee?)

Anywho, remember orville and wilber. People thought they were nuts. Two bike mechanics making an airplane. Today, they are herald as geniuses. If it is possible to build such a plane using the basic formers of the model plans with some modifications, how fieasable could it be from conception to take off.
(Damnit, got to go to the store! Out of coffee.)

Can you say "Triple Esspresso Rush"?..... I knew you could.......

And the passion of a smaller version of the "real thing" has been done many a time.

Look at the 5151 ultralite P-51, the numerous Spitfire mini clones and the place in Edmonton that has plans for homebuilt versions of 3/4 sized WW1 fighters.

Don't let them grind (oooo, there's that coffee reference again) you down Tamecat, you're walking a well respected road. Just get a big travel mug to take with you....

i was quite perplexed last year when i saw a Me-109 flying low over St Ives.. that was until i realized it didn't roar, but putter. A nice home built job that

You are basically describing in detail the Rutan Vari Viggen.

Sounds like your looking for a BD-5! Those things are a definate low-bucks alternative to a jet. I think they do around 280 mph on less than 100hp.
Cheers,
Grant

P.S. A bit off topic here guys but certainly there is no harm with this sort of thing.

It probably wouldn't be all that hard to build a "full size" telemaster or something of the sort, given you have some basic knowledge of aerodynamics an construction.
The problem would be convincing the aviation authoroties this thing will fly.
And talking about money...a homebuild is NOT cheap. You probably would spend less money just ordering a kit from some manufacturer...
And talking about early aviators...remember a lot of them did not live to tell the story...

Scaling up a model has very serious structural implications. If you make every thing X times as big, using the same materials, the strength of any structural element goes up as X squared which is the crossectional area increase of the structural element's crossection. The forces go up as the volume of the structural element, which is proportional to X cubed. Therefore the strength to weight ratio declines in proportion to 1/X.

For example, take a 1/4 by 1/2 spruce longeron 48 inches long. It has a crossectional area of 1/8 of a square inch and a strength in compression of 701 pounds. It has a volume of 6 cubic inches and weighs about 1.4 ounces.
If you scale up the structure by a factor of three, the new spruce longeron would be 3/4 by 1-1/2 by 12 feet long. Its strength in compression would be 6311 pounds but it would weigh 37.8 ounces and its strength to weight ratio would be only 1/3 that of the model's longeron. This means that the empty wing loading of the larger aircraft would be three times greater than the model and the relative strength only one third of the model.

If the original empty weight of the model was 30 pounds then the empty weight of the larger aircraft would be about 810 pounds. Add the weight of the pilot and the gross weight would be about 1000 pounds. To be able to generate the lift necessary, the larger plane would have to fly almost twice as fast as the model. The kenetic energy involved is proportional to the square of the speed and would be almost four times as great as with the model. So you would have a structure that is only 1/3 the strength to weight ratio trying to absorb four times the energy in say a hard landing. The larger plane would be much, much more fragile than the model. If you were scaling up the structure by a factor of four or more, the situation would be much, much worse.

The point is that you can't scale up a structure that much and get away with it. You would have to redesign the structure.

Most homebuilts are rated to around 6 G's or so. Easily less than 1/3 of what models can handle. If you want to see some model-type geodetic construction, check out www.fisherflying.com. Structural concerns aside, there are a number of homebuilts that are similar in mission to their R/C counterparts.

OH MY GOD!! COFFEE, MORE COFFEE!!

So the best way to build a plane as this or any other would be to go to EAA and have someone shadow you through the process of design and building of the plane. that way, any Authorties who would normally raise an eyebrow and shake their heads no, would let it go because of the help recieved.

Oh My God, I'm Losing My Caffeine high! MORE COFFEE!! I NEED MORE COFFEE!

My dream plane. A 3/4 scale P-51 kit plane that doesn't just putter around in the sky. It can outperform the original. When I become wealthy I'm getting one. In other words, probably never.

Check it out.

www.thundermustang.com

I had to clean up the drool after watching the videos.

AQ...... thanks. I had to clean off my keyboard before I could type this. DANG, that's a fine looking peice of work. I couldn't find the cost anywhere that I looked. But this sure looks like one of those "if you have to ask then...." sort of affairs.

It was amazing how many of the performance figures matched. That's what I call a properley scaled effort..... And the climb figure....

If you're into that, check out the Stewart S-51. All metal, none of this composite stuff to ruin the P-51 effect.

One hell of a plane...
However...of course the V-12 sound is awesome, but everytime I see these composite warbird replica's, I wonder how it would perform on a high power turbo prop...
But then again...what's the use in flying a P-51 if it don't sound like one...