The Stabilizer Of A Plane
 

HEY does anyone know if it's possible to design a an aircraft that doesn't need a vertical stabilizer. if it is how stable would the aircraft be. what would the ratio of wing span to fuse length be. most importantly what are the equasions for such a plane.

The Stabilizer Of A Plane
 

Yes, look at the B2 bomber.

The vertical is used as a passive method of keeping the nose going where you want it to. Verticals are cheap, easy to install and work with no extra fuel, plumbing or electronics - a pretty good device.

On something like the B2 the use of drag flaps on the wings and an active autopilot keeps the airplane stable or at least it thinks it is stable. You can use jets of air, rockets, etc. to accomplish the same thing. All you have to do is have something that will create a force of the right magnitude and direction to keep the fuselage pointing in the direction that you want it to go.

The Stabilizer Of A Plane
 

hey cool thanks man

The Stabilizer Of A Plane
 

I built a pile of gliders about 10 years ago that had no vertical stabilizer. They looked a lot like today's zagi design.

Take 2 pieces of 1/16 balsa 3" x 6". Cut the ends at a 30 degree angle, and taper them to 1 1/2" at the tip. Score each wing with a sharp x-acto knife from the trailing edge at the root to the leading egde at the tip. Shim this scored area up 1/16", and lock it in place with thin CA. Remember to make a left and a right wing.
Stick the two wings together along the root line and shim one wingtip up 1" for dihedral. GLue.
glue 2 #10 washers at the leading edge of the root seam for balance.
Make a little hook from scrap balsa 3/8 x 3/16 x 1/8" thick (two layers of 1/16" scrap) triangular and glue it under the leading edge.

It helps to buff the wing smooth with a coupla' passes with a fine sanding block, and round the leading edge while you're sanding.

Put two #56 rubber bands strung together on a pencil, hook in the plane, and catapult launch. Bank it 45 degrees to launch and it will spiral climb. Otherwise it may just loop and hit you in the back of the head.

With the dihedral and the sweep of the wing, it will have stability.

I rubberbanded a pile of these on a trainer, took 'em up high, and released 'em all at once. GReat fun. SOmebody thought parts had fallen off my plane.

With the proper airfoil, I don't know why you could not make a successful r/c thermal glider this way.

The Stabilizer Of A Plane
 

Hi! I'm building an 8' span B-2 Bomber and in the process I learned a few things. #1 Mach tuck - on aircraft with swept wings the center of lift shifts back as speed increases. it goes so far behind the c/g that swept wing airplanes become unstable at high speed and dive gaining speed and are unable to pull out. Airliners use a Mach Tuck computer that trims the stabilizer or pumps fuel to a tank in the vertical stab to counteract Mach Tuck. Another answer is also handy on any aircraft - build the wing with enough washout especially toward the wing tip to counter act this problem. #2 Dutch Roll - another problem with swept wing A/C is if it gets going sideways one wing is getting more air over it than the other so it gets more lift and drag. The extra lift and drag pulls the original wing back so far that the opposite wing is facing to far forward so it has to much lift and drag. It goes back and forth and gets worse unless corrected. Airliners use a Dutch Roll computer I'm using a rudder Gyro to stabilize my B-2. I hope this info is helpful. It sounds like allot of info but if you get an understanding for these principals then flying wings make more sense.

The Stabilizer Of A Plane
 

Well the airplanes arn't unstable when the Mach tuck thing happens. It is the opposite I believe.

For example a design that has a conventional wing tail configuration will have a neutral point of about 35% subsonically that moved to 60% supersonically. The numbers are approximate but are the kind of trend that is seen. This makes the airplane much more stable.

If you have set the CG and sized the horizontal tail to handle the airplane at 30% (which you must in order to be able to land the airplane and maneuver in flight) then because the airplane supersonically at 60% is so stable the tail isn't adequate to trim the airplane. Coupled with a loss of tail effectiveness at supersonic conditions makes it all that much worse. So you would see the Mach tuck phenomena occurring. The cure is to size the tail for supersonic maneuvering and trim and adjust as necessary with a control system.

The transition area of going from subsonic to supersonic conditions is where the change from nicely stable to way too stable is occurring.

Washout on the wing wouldn't seem to be the best cure for the problem as the shift in Neutral Point is Mach number dependent. A wing at subsonic conditions has the Neutral Point at 25% and supersonically the Neutral Point is at 50%. The twist doesn't affect the Neutral Point, just the pitching moment of the wing. Could be something here that I am missing though.

Swept-wing aircraft.....
 

deltatech....your info on mach tuck and dutch roll are accurate but needs some refined explanations....Mach tuck is compensated by trimming the horizontal stab/elevator with the A/P engaged....on older Boeings its done by a Mach Trim actuator trimming the elevator slightly up with the NSS(Neutral shift sensor ) retrimming the stabilizer to keep the plane flying @ the same altitude(using Alt Hold)....on newer Boeings its done thru the FCC,s and a Mach Trim actuator or thru the FCC,s/IRU accelerometers and retrim of the horizontal stab thru the A/P (Alt Hold or VNAV with FMC flying the airplane)....Dutch Roll on the older Boeings is compensated for by a Yaw Damper coupler using inputs from the VG,s to drive yaw damper actuator.....newer Boeings use a Yaw Damper computer using inputs from IRU accelerometers to drive the yaw damper actuator ...these IRU accelerometers are so precise they can measure the rotation of the earth around its axis.....Some aircraft incorporate the use of fuel in the horzontal stab to help with Mach Trim...a dedicated microprocesssor moves fuel from the wing tanks to the Hor stab fuel tanks to accomplish this(A330-A340)....the Concorde moves fuel inside the fuselage thru several fuel tanks to compensate for mach trim also done by a dedicated computer.....Good Luck with your B2...let us know how it does....Bill....

The Stabilizer Of A Plane
 

To Ben Lanternman: In my reply both principals were in reference to Airliners not Supersonic A/C. Mach Tuck is just called that because the center of lift changes at different Mach Numbers. Not implying that most Airliners can go Supersonic it's just a measure of speed.

The Stabilizer Of A Plane
 

hey i appreciate all of the info that you have provided but would it bossible to build and fly a RC plane that doesn't have a vert stabilizer.

The Stabilizer Of A Plane
 

Yes it's possible but as you've seen the planform is pretty much restricted to a swept flying wing similar to the Northrop XB-35. Neither did the Horten wings require a fin as did that swept flying wing model from a few years back that was kitted. It's name started with an "H" also but I can't remember the name. It had a rep for being a little dicey for spiral stability but it DID fly without using any gyro or vertical fin as long as you respected it's limits.

For Zagi types and other flying wings using a prop as a power source adds some measure of fin effect. This means it had better be a pusher and not a nose (center leading edge?) mounted tractor design.Note that when the XB-35 prop plane was redone and came out as the YB-49 jet powered flying wing the reduction in fin effect caused by removing the props required the use of some small fins.

Add to this the possibility of using a heli gyro coupled to the split ruddervator controls and you have a fairly good possibility for success.

If you're talking about a conventional planform then I guess it would be possible but there would be so much more to look into. The F-36 tailless fighter uses a pretty fancy computer to control the flight mode. But I note that this pic seems to show split "rudderons" so perhaps something like this would be possible. I have NO idea where you'd start with equations though. It would be up to the side forces and drags and having the ability for the "rudderons" to overpower these forces to achieve a meaningful control effect.

http://www.dfrc.nasa.gov/gallery/pho...97-44294-2.jpg

The Stabilizer Of A Plane
 

The b-35 had the props mounted on shafts that exited the top surface of the airfoil. The shafts had fairings on them that acted as vertical fins. It wasn't the propellers that provided the stability. With the B-49 and its jet engines, it was found to need some vertical fins to restore the lost area of the fairings.

forgotenplane17: yes you can design an RC plane without a vert stab. Swept flying wing with dihedral. Use washout at tips for pitch stability. Use up-moving ailerons only, or spoilers for roll and tip-mounted elevators for pitch. I'd build it as a sailplane first, then maybe as electric. Balance would be pretty critical. Glo power migh not be so good: Having a fuel tank would make the CG shift around probably enough to make you unhappy. It would fly with a symmetrical airfoil. It would be more efficient with a reflexed airfoil.

The Stabilizer Of A Plane
 

Jim, I don't remember the source but it was mentioned in more than one place that I read that the props did provide some fin like stabilizing effect and that the major reason for the small fins was the lack of props on the jet model. Certainly the size of the jet version fins was much larger than the prop shaft fairings.

Either way props do have a vertical fin effect and where they go makes a difference on what size fin area is needed.

And the name of the flying wing model with no fin? The Klingberg wing.

The Stabilizer Of A Plane
 

Look at this site. Its pretty interesting.

http://pr.erau.edu/~allenm/wing.html

Jim it seems that you have it right except for the aileron deflections. To get a favorable yaw on aileron control input (right roll causes the nose to yaw right also) the aileron on the left side needs to go down and the aileron on the right goes up. The right aileron works as expected when going upward. When the left aileron goes down it causes an increase in lift on the left wing tip area which because of the large wing tip twist gives you a vector forward which stops the adverse yaw.

The center of drag of their flying wing is aft of the CG which gives the baseline directional stability. Zagi and others use the tip fins for directional stability.

I would think that CG placement shouldn't be any more critical on it than any other flying wing. As long as you are adequately stable it would work.

The Stabilizer Of A Plane
 

Bruce,
I remember reading that the Northrop flying wing suffered stability problems when they removed the props and put on/in jets. I also remember that the reason was the fairings over the driveshats acting as fins. These fairings were removed when the driveshafts were removed, then they found they needed fins on the jets. The props don't provide the stabilizing influence and the B-35 had counterrotating props so any stabilizing effect of nonaligned flow going thru the prop blades would have been cancelled out anyway.

The Stabilizer Of A Plane
 

I can't get two images to post at once, so here's the B-49 to compare.

(If it were MY choice, I'd have made it look like a Zagi)

Vertical-less
 

forgotenplane- there are two ways you could build an R/C aircraft without resorting to a flying wing: use two pusher engines or use airbrakes. Both would have to be mounted pretty far away from the airplane's centerline. An example might be an airplane that looks similar to that X-36, except with with two pusher engines mounted on the back of the wing, or one pusher engine with airbrakes way out on the wing. Either way, if you ditch the vertical stab altogether, the yaw control system will need a gyro to give it stability (without a passive stabilty system, an active is needed).

One caveat: do NOT use spoilers. Raising one spoiler at a time will give a yawing moment, but it will also give a banking moment also. This is great if you want to make a turn, but not if you want the plane to fly level in a crosswind.

Also, the fuselage itself contributes to yaw stability. If the tail area is flat vertically, and the nose is flat horizontally, that will help, and it might not look as if the plane has a real vertical.

Anyways, good luck, and post some pictures of the completed plane

The Stabilizer Of A Plane
 

Hey Jimcasey. I noticed that you mentioned that glo power could be a problem because of weight shift as fuel is burned. I'm building my B-2 with the fuel tank directly on the c/g and the center of the fuselage. Do you think this is enough to calm down fuel burn weight shift? Do you think having fuel sloshing around in a 10 oz tank could be a problem?

The Stabilizer Of A Plane
 

If it's a problem you'll notice it after you take off and burn off some fuel.
I assume with a 10 oz tank you are running a .60 size engine. 10 ounces of fuel in a 6-8 pound airplane is not really a lot of weight, so the CG of the plane won't be moving much. I was criticised earlier for saying that CG would be critical. More specifically, a flying wing has a small CG range compared to a conventional plane with a long fuselage and a large horizontal stab. My Sig Wonder was <nearly> a flying wing, and it had to be balanced juuust right. I could notice the balance/trim change as the 4-0z tank, well in front of the CG, burned off. You're doing the right thing putting the tank at the CG.

I assume you will use a pusher installation. One thing sometimes not realized with pushers is that you should still have the connections to the tank in front so the clunk is in the rear. You want the clunk deep in the fuel while you are climbing, not sticking forward into an air bubble.

The Stabilizer Of A Plane
 

Bruce.....It seems I recall reading that the engines/props also added stability because of their gyroscopic effects and that stability was lost when the turbine engines were installed and because of the lack of computers in those days they were hard pressed to find a form of compensation.....Bill......

The Stabilizer Of A Plane
 

Thanks for the info Jimcasy. I'm using an O.S. 70x4 stroke. I know odd choice for power but it will give me enough thrust untill I know that the thing fly's then I will buy an easyer to conceal engine. Unfortunately I designed my B-2 with the engine in the nose. Like some fighters with the engine in the nose. I thought that having thrust on the nose and drag at the split rudders there would be stability but I can see what you mean by saying it would be best to have the power on the tail. I couldn't get it to balance out any other way and I couldn't afford a $4,000 turbine.

The Stabilizer Of A Plane
 

With the engine in the nose and the tank at the CG, you might need a pump.