combatpigg

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I won't pretend to be "MR SPEED PLANE BUILDER" here, but I have had some success with a 1/2A project, and thought it would be interesting to do a speed plane build up here, and maybe we can all learn as we go. The engine will be a K&B 6.5 RIRE with a MACS header and pipe. I am hoping for 200 mph, but would be happy with 180! I took DER STEUERMANNs' advice and made the fuselage quite long, as long as the wing span [40 inches]. The target weight is 3 pounds. The wing will be sheeted foam and the fuselage will be fiberglass. I am hoping that my work situation here will allow me to attend next years' SPEED CONTEST in GERMANY! Right now is a tough time to be a commercial electrician with 1/4th of our UNION guys out of work for the last 3 years, so I can only cross my fingers that our economy will improve. Anyway, I will continue to post progress, and I will highly welcome any and all advice about how to proceed from all of you! The work you see so far represents about 2 hours of butchery with a table saw and the hand tools that are pictured.

HavinFun

My Feedback: (4)

Looks like this will be a very interesting thread, sorry I can't help with any building tips as I'm just getting into this speed thing. I will be following your project closely as I'm sure there's a lot I could learn here. Keep the posts coming.

combatpigg

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The next item to address will be the airfoil template. With a root chord of 10", the advice I have got so far indicates an airfoil thickness of 8%, or in other words about 13/16" is the way to go. I figure a full depth spar made out of 1/8" spruce to re-enforce the thickest part of the airfoil. There might be a case for using a couple of spars. 40" of span isn't that much wing to support, so there is no need for dead weight either. I figure on using a mostly flat bottomed airfoil, with the bottom right on the center line of thrust. I think this will use the least angle of attack to fly level, it has worked well already with the 1/2A speed plane. The biggest decision/assumption about building any plane from scratch is the fore and aft placement of the wing to get the correct CG. I can only go with scaling the photos in the GERMAN speed thread to get a rough idea, the fine tuning will have to come from gear placement. In my line of work, if you aren't sure of what you are doing, you still move on in a way that leaves you with an "out", which is what we will be doing here!

der_steuermann

My Feedback: (2)

Hi combatpigg,

great!

designing a scratch built speed sucker sure takes some time, but once finished you'll be proud of that unique creation!

Some additional notes:

- for .40 to .50 sized engines the fuse could be up to 45" long. However, you also might consider to equip that fuse with a .20 to .30 sized rear exhaust engine in future, then 40" fuse length would be fine

- the wing span can be reduced to 35" if powered by .20 to .30 speed engine

- spinner diameter should be 1.5" (several good speed pylon 'integral' aluminum spinners available)

- smooth transitions between fuse and the rest

- preferably fully symmetrical airfoil for horizontal stab and fin (sandwich construction for rigidity)

- wing: use only fully symmetrical airfoils such as NACA 0008 or 0006 (CNC cut foam cores highly recommended for ultimate precision)

- angle of incidence 0.3 degrees

- smoothed wing tips

- root chord 10" to 11", double taper wing geometry

- a wing spar + fiber glass is needed if covering the foam core with balsa. If covered by ply wood or by obeche only fiber glass is needed

- one aileron is enough (or no aileron at all, but taileron)

- sealed gap-less hinges, heavy duty hinges

- widest part of fuse equals to the engine's width

- bubbless tank (if enough space) or custom made brass tank (0.2 to 0.3 mm thick brass, soldered) incorporated into a silicone 'tub' copying the contour of the fuselage

- the engine should have no throttle (fuel shut-off device required)

- only non-muffled dual cone tuned pipe

- 0 degrees of motor right thrust and down thrust

- engine + pipe cooling: even if fully cowled the engine will be cooled effectively if keeping the inlet area of the opening(s) slightly smaller than the outlet area

- all linkages within the fuse, heavy duty linkages (3 mm wire dia, CF or glass pushrod)

- antenna routing within/parallel to the fuse.

- no metal to metal contacts for linkages

- for 40. sized engines use 50 N*cm torque BB servos, no MG required

- 700 mAh battery pack sufficient, since one speed run only last 1 to 3 minutes



The goal is to design a speed plane behaving fully neutral in every respect.

pdxpaul

My Feedback: (1)

What is the reasoning for an 8% wing, and not thinner? You should dowload the Compufoil demo program. It has a NACA generator, and you play with airfoils as thin as 5%. I agree with DS, go fully symmetrical, such as a NACA 65-xxx (65-005 or 65-006), and taper it. I would think you want close to 400 sq. in. of wing area. If you go with a 10 in. root chord, 6 inch tip, and 48 span, you will be around 400. Some of the local pylon guys may have Compufoil, and may help you out. The program generates the foam templates (accounts for sheeting thickness), and plan view.

Paul

combatpigg

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Thanks VERY MUCH for all the info! After reading D.S.s' entry, I think I'm ready to take the final exam for RC SPEED 101! And thanks to PDXPAUL for reminding me about COMPUFOIL, I will look into that. Yes the goal is to design a plane that flies straight from the work bench with out the need for any trim. My goal for today will be getting a wing cut.

jaka

Hi!
It is not my pourpose to be rude in any way...but the K&B engine is rather outdated powervise compared to a Nelson or Russian IR 6,5cc engine ....or the dominant engine today in pylonracing... the Dutch MB.
Why not get one of these instead?

Regards!
Jan K
Sweden

der_steuermann

My Feedback: (2)

The answer is simple, the 8% and 9% NACA 000 series airfoils have been proved to be super fast in the long history of the German Speed-Cup. Trial and error principle. For instance 4 of the first 6 winners of the last contest held in Achmer use these airfoils. Whereas for .20 sized and smaller speed planes I would select a reduced wing thickness...

48" wing span would be too large [sm=stupid.gif]

Razor-RCU

My Feedback: (50)

Wow- I just wanted to say thanks for starting this thread to Combatpig, and thanks for all your years of expertise to (Der, Jaka, and PDX so far..)

I will watch with much anticipation as I have been at this for 20 years and I would have no idea how to do something like this...

Is the Dutch MB, the same as the Profi I read about?

Cheers all and good luck!
James

P.S. der_steuermann: What does your name mean? (Just curious)

der_steuermann

My Feedback: (2)

Hi Razor,

direct translation would be "the steersman"...

yep

combatpigg

My Feedback: (3)

That's a fair question to ask, I'm using the K&B because that is all I have and I don't have the money to throw into anything hotter right now. Besides, this is my first .40 sized speed attempt, and I would rather learn about this stuff with a $65 [auction] engine, than dig up a row of corn with a $700 bullet. I bet the K&B will make the end result of this project fun to fly, and fast enough to learn something from.

Rudeboy

Way to go Combatpigg! This is what this forum is about... [sm=thumbup.gif]

Now about that K&B engine... look at it this way: if you manage to build a plane that moves on that engine, you can always save up for an MB afterwards. No need to get a 700$ engine just for testing....

Wing: I'd say go for symmetric... or maybe the slightest amount of camber to avoid having to trim the plane. But you don't really need much, almost nothing is more than enough at 200 mph.
IMO an airfoil with the highpoint placed further backwards as the NACA four digit series is more suited for speed. So a 0006 or 0008 is not the way to go I think.
I agree with PDXPAUL: the 65-xxx is a better place to start.

der_steuermann... a good translation for your name would be "a wheelman"... like a driver for bankrobbers...

combatpigg

My Feedback: (3)

HI RAZOR, Even I don't have much knowledge about the fine points of speed, I thought this would be the perfect place to learn how to do it, and since I have some experience with different building techniques, like foam and glass, the mechanical part of pulling this off is something that I can at least demonstrate to others who might be intimidated by the unknown. Today, I looked up the NACA 65-0008 and took a tracing of it off the screen onto tissue paper. After doing the freehand tracing, I cleaned the line up by using an arched piece of piano wire as a guide, and retraced the outline. With a symetric foil, all you need is a center line, and a good profile of one side, fold the traced pattern down the centerline, then cut the pattern out with an XACTO. Don't worry about absolute perfection. Contact cement the tissue pattern onto heavier paper, then contact this assembly to some formica. I scroll saw the formica almost to the pattern line, but finish up with a file[ to remove low spots], then sandpaper, down to 320 grit. Drill some pin holes on the center line. Now you have a template for hot wiring foam. I use a $6.50 light dimmer switch to control the 115 volt AC, and .020 stainless wire for cutting. Check out other threads and sources for the fine points and techniques for hot wiring. Don't expect instant success, it takes experience to get the set up just right, but foam is cheap and makes good fire starter material if you have a reject pile. Here are some photos that show some of todays' progress, about 2 hours worth of fun in the work shop.

der_steuermann

My Feedback: (2)

Vmax

@combatpigg
Looks good.
Do not sweep back the wing. It should have 0 degree in the 1/3 line. That means take 1/3 from the airfoil in the wingroot (measured from the front), take 1/3of the airfoil on the tip on both sides and connect these three points. It should have no angle. If you go for one third of the airfoil -> put your CG right there. And it flies. The stab area should be around 1/7 to 1/8 of the wing area.
Another idea is to use a NACA 65008 at the root and a NACA65006 at the tip. That gives you more stiffness for the wing insted of using 65006 for the whole wing.
Take one layer of approx. 80g/qm (don´t know how much this is for you guys)of glass between the wood and the foam. Direction is 45/45 degeers.NOT 0/90 degress.
one layer about an inch wide along the trailing edge (80g/qm; gives you very strong and very sharp trailing edges). One layer elliptical shaped from one outer end of a aileron to the other. All that at the upper and the lower side of the wing (symmetrical). For the K&B plane is a airfoil like a NACA at the stabilizer not necessary. If you go for a Nelso or whatever the stab should have a fast airfoil as well. As hinges for the ailerons you can use a thin aramid layer 45/45 degrees. It works great.


Niels


Please excuse my english. It´s not perfect.

der_steuermann

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...a recommended addition to the wing design: For good high speed stability you can incorporate a positive dihedral. Meaning that the top side along the entire wing span is planar...

pdxpaul

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Nice cores. This is going to be fast. A couple more thoughts. Have a rounded leading edge, rather than a knife edge. +/- 3/32 in. diameter or so. Do a knife edge on the trailing edge, with 1/64 ply strip between the sheets. Have you done the old Forumula 1 wing tips, where you extend the sheet beyond the core?

Paul

smchale

My Feedback: (67)

The is GREAT!! CombatPigg, I'm doing something very similar for kicks. Der-S has been most helpful with the thoughts and direction he has shared so far. I'm going with a 21 sized engine in all likelyhood.

This past weekend I experimented with my hotwire and cut a couple wing cores. That's about as far as I have progressed. Was thinking of also using foam for the fuse and using a 'lost wax' type method by removing the foam once the fiberglass has been applied.

My sport/speed plane design is called the HEATSEEKER....an AC/DC reference there... [8D]

Anyways, here's a sketch of my design...I can continue to post pics here, or on a new thread if you like....

smchale

My Feedback: (67)

Here's the sketch of the HEATSEEKER....

bob27s

My Feedback: (19)

fun thread.....
following along and lurking intently


btw....... I am about 90% sure the K&B 6.5 and F-1 engine has the same mounting holes as a ST X-40 engine. Which, in that case, means its the same bolt pattern and footprint as the Jett and Nelson F-1 and FAI engines.

I will have to check, but if this is the case, it would mean you could swap out the engine for a jett or nelson at any time in the future. Makes starting out with your current engine and upgrading the engine later a whole lot easier.

HighPlains

My Feedback: (1)

Interesting design Sean, but could I make a could of suggestions?

Wing - advancing tips are a lower drag design. What are advancing tips? As you move from the leading edge to the trailing edge, the span increases.

You can reduce the size of the ailerons. Inboard from the tips like you have them is good.

A straight leading edge with all the taper in the trailing edge gives a slight effect of a forward swept wing. Helps lower the spanwise flow of the air, helps to decrease the wingtip vortex.

Fuselage - looks pretty tight

Tail - since the prop size is pretty small, you don't need much vertical surface, especially with such a long fuselage. A higher aspect vertical would be more effective and lower the drag. Horizontal area only needs to be around 12% of wing area, though 15% is more stable. Again the long fuselage helps here.

General - anything that reduces surface area lowers drag.

proptop

My Feedback: (8)

Hey Helge, see what ya started with that speed event thread?! Looks like more than a few of us have the same ideas...
Question: If the horiz. stab area is 12-15% of the wing area, what % should the vertical fin/ rudder area be? You probably don't really need a rudder, but it might come in handy just in case...

combatpigg

My Feedback: (3)

WOW! It sure is great to come home from a typical day at work to be greeted with such great visitors to my workshop from BELGIUM, GERMANY, SWEDEN, and several points in the STATES. I am sure now that we are going to pull this one off! I like DER STEUERMANNs' idea to have the top of the wing flat, on just one plane. It sounds like less work to build and less work to fly. I like to know what the minimums are for tail surface area, because we all know why less is good there. I like the idea about letting the wing tips come to a zero thickness, but I don't want to exceed the recommended span[ 40"] by too much. We will seek a compromise there. I have a full scale drawing of the basic layout, but it is on butcher paper, and does not photograph well. The drawing that SMCHALE submitted of his .21 powered plane is a beauty, and you are welcome to tag along with this thread, but it will dilute the information that I get, and your project deserves it's own space. It will be fun to have several speed plane build threads to look at, and we will gather more interest and information this way, I think. Tonight I got a late start, so I will be happy to get the 1/16" balsa sheet contact cemented to the foam cores, and call it a night. Tommorow night will be dedicated to installing a repaired cylinder head on car #1, so no hobby work until WEDNESDAY[&o].

HighPlains

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Vertical area around 5-6 % should be fine.

smchale

My Feedback: (67)

Good idea...I'll start a new thread. This is great stuff! ... and a nice change of pace from the scale stuff I'm usually knee-deep in. [8D]