Topgun2mo

My Feedback: (45)

Once I mount the wing I will start working on the rear turtledeck and redesigned tail surfaces. The tail surfaces will employ built up construction.

More to come.........

rcguy!

My Feedback: (69)

WOW!

Hardly able to call it a Reaction 54 anymore?

Will the increased area in front of the CG need to be compensated for with a larger fin?

Keep the pictures rolling.

Dave Rigotti

Topgun2mo

My Feedback: (45)

Yes, I am scaling it from a 3 view I have. I am one of those people who get as much pleasure from building as flying and I have a desire to make projects "unique".

Topgun2mo

My Feedback: (45)

Actually I am more concerned with the increase in the fuselage area in front of the wing (bottom area) and how it will affect CG at the wing. It will probably need to shift forward a bit.

Topgun2mo

My Feedback: (45)

Ok Dave, I'll go ahead and give it up.....this is what the vertical will look like

I was parusing 3 views one day when I realized that the wing planform of the Reaction is very close to the L-39 wing. I LOVE the look of the L-39. The planform is close and the spacing of the wing to the tail is also pretty close. The only thing needed was to lengthen the nose a bit and reshape the fuselage, and of course incorporate trailing link landing gear. Like I said I will be retaining the exposed engine and other features like a one piece elevator to simplify things. But the vertical and horizontal stabilizers will be scaled from this drawing. I will be using a 3/16" spruce spar, 3/16 balsa framework and sheeted with 3/32 balsa. The entire airframe will be glassed and painted and I was kind of leaning toward this color scheme.

BruceTharpe

My Feedback: (1)

Man, that was the shortest "Guess the Plane" contest ever

rcguy!

My Feedback: (69)

Mike,
"You da man!" WOW!

Having fun is what it is all about!

Keep us posted.

Dave Rigotti

Woketman

My Feedback: (6)

Yeah, Mike just could not help himself. He REALLY wanted to tell us bad!!!

Topgun2mo

My Feedback: (45)

I couldn't count to 3....if you have heard that expression before......

Molar mender

Mike
Coooool!!!! Keep the photo's and build comments coming. I like your color scheme.


Hey Bruce!
I'll bet you never thought that your kit would turn into a L-39 look alike. Looks like Mike has done his home work. Nice project.

Roy

bobparks2

My Feedback: (1)

j

A LITTLE bit, but not much. Due to the way the air flows around the wing, the fuselage area just in front of the wing has huge local angle of attack changes for a small change in airplane angle of attack. (like 3 or 4 x). This is due to the wing upwash. Extending the nose beyond the already long nose of of the R54 is going to have a lot less effect than you might otherwise expect. It has a lot of moment arm, but does not have the upwash.

The effect is also a function of the fuselage width squared, compared to the wing area. And the R54 is pretty skinny by that measure.

So, without actually going and calculating it, I would guess shifting the CG forwrd by a few percent of average chord would take care of it. If you are changing the tail area, then you need to allow for that effect also.

OTOH, I would be quite concerned about yaw stability. You are adding length and height up front, so expect to need quite a bit more vertical tail area. Chances are a scale looking tail will be just fine, but double the stock tail area would not be unreasonable.

Bob

rcguy!

My Feedback: (69)

OTOH, I would be quite concerned about yaw stability. You are adding length and height up front, so expect to need quite a bit more vertical tail area. Chances are a scale looking tail will be just fine, but double the stock tail area would not be unreasonable.

Yeah! That's what I meant!

Dave Rigotti

Wayne22

My Feedback: (2)

That is one of the beauties of kits...once it is in your hands you are free to be as creative as you want - if you want! I'm modifying the heck out of an AV8R right now, although by time I am finished no one will remember what the stock one looked like

Topgun2mo

My Feedback: (45)

Bob, the stock tail height is about 11". The scaled L-39 tail is 19" tall. So that is a considerable increase in area. Also the fuse width at the front of the wing is 5 1/2" on the stock Reaction. Mine is 7" Not as big as scale but enought to suggest the shape. It will have L-39 type inlets, not as big as scale but again to suggest the outline. They will be however, non functional and I will carve a small fairing to streamline the front of the inlets but still have the "look". Bob, can you explain what you mean by the "tail effect" in reference to how it affects the CG?

Thanks!

causeitflies

Ha! Yeah, some contest that was. L-39 would have been my 2nd guess.
My 1st guess was a B-52.

bobparks2

My Feedback: (1)

And just about as important is the increase in span (aspect ratio), which helps even more. Its likely going to be fine.

Well, since the fuselage destabilizing effect is a function of the width squared, and that has nearly doubled. So that is worth worrying about, since it combines with the extra length.

The bigger the tail, or the longer the moment arm, the farther aft the CG can be.

If you want to properly figure out where CG should be, lots of things matter. For most models people just figure out where the wing mean aerodynamic chord is, and put the CG at 25 or 30% and leave it at that. That works fine for most models, because they all look pretty much the same anyway... same tail size and moment, small fuselage etc.

To do it properly, lots of other things matter. The tail size and moment arm, wing and tail aspect ratio, fuselage size, wing downwash effect on the tail etc. are all significant. For example, the wide fuselage on a Sukhoi 26 type aerobatic plane is destabilizing enough that the CG needs to come forward about 5% of the wing mean chord to compensate for it. An extreme case is a general aviation light piston twin. A wide fuselage and 2 wide nacelles, and those need to bring the CG forward by 10 to 15% of the wing chord to compensate.

An extreme case of body effect is the Northrop Tacit Blue (school bus) stealth airplane. It needed the CG in front of the wing leading edge to be stable! I did the stability analysis for Ivan Munninghof's scale model of that beast.. it said the Cg had to be about an inch in front of the LE, but the model flew just fine (until the tails fluttered off!)

So, jets are often enough different from normal RX sport models, that all these effects can be significant.

For something like your plane, there is a commercial program (Excel spreadsheet actually) available to do that kind of analysis. Its called Plane Geometry, by Envision Design, about $20 Its a bit techie to use, but the manual is quite good. IT only works on "traditional" airplanes, i.e. tail in back, but its a LOT better than guessing.

Bob

Woketman

My Feedback: (6)

Mike, i have Plane Geometry.

Topgun2mo

My Feedback: (45)

Thanks Bob and I'll guess we'll run some numbers Mark.

Thanks!


As a side note I overted disaster today. My first mistake was trying to use a pneumatic grinder to drill that 1/4" hole. I had a 1/4" collet for it and I thought it would work....but the holes wallowed to about 5/16"...

My second mistake..... I put the balsa blocks against W-1 instead of W-2 ribs. I had missed the blocks altogether and that is one reason the holes wallowed so bad. A quick call to Bruce and he said move the holes inboard. So I plugged the holes in the wing and the matching bulkhead and drilled the other holes with a long 1/4" brass tube. I first drilled out the holes in the bulkhead to 1/4" and then chucked up the brass tube and it worked perfectly. Whewwwww

Topgun2mo

My Feedback: (45)

Well I guess I'll just keep the engine top secret then.......

Woketman

My Feedback: (6)

Anyone wanting to know about the "top secret" engine, just PayPal me $20 and I'll tell all!!!

gbjets

Mike

Don't feel bad Mike, I made the same mistake on my left wing and noticed it before I made the other one, I just removed a bit of the sheeting and relocated the block. I never thought of Bruce's idea, makes sense. Maybe you didn't notice but I posted an easy way to make the holes for the dowels, I'm just hoping somebody will try it and let me know what they think. I also admire your patience with your customizing, I wish I had your enthusiasm.

Good job

Gaston

Ontario
Canada

Topgun2mo

My Feedback: (45)

Gaston, I drilled a 1/4" drill bit into a 4x4 and then loosened the chuck. I then attempted to drill a hole in the end and I barely made a dent. That is when I made the other goof up.

gbjets

Mike

Maybe you have better quality bits, I found it very easy to drill mine, actually I used a 3/32 bit of the same quality as the 1/4in. I put the 1/4in. bit in a vise, punched and drilled it, I guess thera are different hardness of drill bits. I just drilled a hole in a 1/4in. HSS bit this time just for a test, a few minutes ago and I found that a lot of pressure was needed, having it in a vise probably helps a lot. I'm glad to hear that you have everything under control.
I don't that we are the only ones making mistakes, while putting a kit together, I've heard of a lot worse, I'm just glad others learn by ours.

Gaston

p.s. safety tip: please make sure to use a small variable speed drill for the wing dowel holes and set it slow, the material is easy to go through.

bobparks2

My Feedback: (1)

Yeah, if Mark has Plane Geo go set it up and see what it says. If you want me to look at the results just email me the file. Mark has my address.

BTW, the best way to interpret the results is to go put in a plane that you know flies well, and then tweak CG and elevator throw until you match the parameters. In this case, compare to a stock R54 would be good.

Bob

gbjets

Hi Mike

I found a different way to secure the piano wire to the 1/4in. bit if you can't drill it, maybe a lower quality bit would be been easier, here's another alternative. I did it tonight and drilled a hole in a 1/2in. piece of plyood, which is a lot harder than the R54 wing without any problem. All you need to do is solder the wire without drilling a hole, I wish I would have thought of it earlier, might have been easier for you.
I presume you don't need it anymore but I hope it can still be handy. The critical parts of the process are as follow, for silver soldering, the parts have to be super clean, just lightly sand the end of the bit and the wire, you have to use the proper flux, the pic shows two different makes and the silver solder has to be the right type, I think the one I used is called Easy-flow 45 and we use it in refrigeration for copper, brass and dissimlar metals, another alternative is to use bronze welding, which I'm sure everyone is familiar with but then you will need an oxy-acetylene torch.
The wire I used tonight was 5/64in. piano wire, I think it's the same size as 2-56 threaded rod but I prefer 3/32in. As you can see I couldn't show my other hand holding the bit steady because I was holding the camera but that's what you have to do for proper alignment. I just hope I'm not being a pest with this tip but I found it extremely helpful.

Gaston

Ontario
Canada