Flying in reverse (apparently
 

I am kicking around the idea (challange) of trying to build an RC plane that flies backwards. My simple vision is to have a plane that on the ground, looks exactly like a basic trainer but when powered up heads down the runway in reverse, flies a basic pattern and lands safely. This trick should have a pretty nice WOW factor.

Has this been done before?

It seems to me that the real challanges are:
1) getting the main air foil to generate adequate lift when operating backwards relative to air flow.
2) building in sufficient stability to keep the plane in the air and get it down at some reasonable speed.

Obviously this design challange is not about efficiency it about getting it to work. My first thoughts are to focus on fiding the right angle of incidence of both the main wing and the stablizer. While I don't want the planes profile on the ground to be abnormal modest amounts of positive incidence would likely not be noticeable.

I'm just a dumb old RC model fan with no particular training in aerodynacs (obviuosly) who likes a challange.

Any ideas on how to make this happen? Can't be done is not an option.

Thanks for your thoughts in advance!!!

Larry

RE: Flying in reverse (apparently
 

sounds like a cannard

RE: Flying in reverse (apparently
 

One of the big differences with a canard design, I believe, is that I want the wing to fly backwards not just move the tail to the front.

Larry

RE: Flying in reverse (apparently
 

Premium:

Your biggest stumbling block is the vertical fin. If you make it look JUST LIKE a trainer in reverse, you'll have it way out on the front ahead of the center of drag and center of mass. That is about as unstable a setup as you could make, and not really possible without computer stability control.

Now, if you made just a fin-shaped hollow frame... and put big clear plexi "Winglets" on the ends of the wings to counteract that fin you might just have enough lateral stability to work.

By a "Frame" I mean the outline of the fin with nothing inside the outline. Like an empty picture frame. Nake the plexi winglets full sheets though, because that's where your stability will come from now. It will still likely be mushy around the yaw axis, but it might fly. Remember, though, your control surfaces must still be on the rear of the fixed surface with respect to flight direction. Having your stab with the elevator on the leading edge (w/r/t flight direction) is unstable, will deflect unpredictably, and may part from the airframe due to flutter.

N

RE: Flying in reverse (apparently
 

Flying the wing backwards is not really practical because the thick part of the airfoil is toward the back of the chord. This will cause detatchment of airflow and ailerons will not really work. It will also shed vortecies off the top surface and be REALLY CRUDDY to unflyable at low speeds.

You gotta turn the airfoil around.

N

RE: Flying in reverse (apparently
 

With regard to the control surfaces. I have a couple of ideas. What if I made the horizontal and vertical stablizers one piece (each) control surfaces. I think you call it "flying stablizers". I have these on my thermal glider and they work very well in that traditional application.

The other approach that I was thinking about was to make the two stablizers LOOK normal but I would have the rudder and elevator surfaces slightly oversized and fixed realtive to the fuselage and make the fin and horizontal stab move. On the ground it would normal but it would put the control surfaces downstream of the coresponding fixed surfaces.

Larry

RE: Flying in reverse (apparently
 

i would love to see a vid and pics, keep us posted:D

RE: Flying in reverse (apparently
 

Bruce McCall designed a plane like that way back when... showed up in "Car & Driver" in the middle '60s.
It resembled a Macchi Saetta, cut in twain at the cockpit, with the front end and back looking the same, but pointing opposite each other.
Push-pull.. one wing, with tip rudders if memory serves.. :(
It could fly either forwards or backwards, depending on which side the Italian air force was aligned with at the moment.

RE: Flying in reverse (apparently
 

To fix your problem of have in the control surfaces on the leading edge of the stabilizer, make normal (to the untrained eye) stabilizers but have the part that normally is the elevatoror/rudder be stationary and the vertical and horizontal stabilizers actually move. It would look very normal.

RE: Flying in reverse (apparently
 

Rangerstl,

I have been thinking about your advice regarding the fin and the problem with stabilty when if it where to be located forward of the CG and CD. What if the fin/rudder were made solid/one piece which pivots around a vertical axis (rod), like a weather vain? Since it would offer little or no resistance then it should not affect yaw nor adversely affect stability. It is merely going along for the ride.

So where does rudder control come from? How about adding a set of wheel skirts? The trainer I have in mind would use tricycle landing gear. With skirts, the front wheel (normally) could perform double duty. On the ground, it would steer the plane as ussual (all be it in reverse). In the air, the skirt on the (what is now in the rear position) would act as the rudder. Perhaps the skirts on the main gear would also add to the overall stability of the plane, as well.

Regarding the orientaton of the main wing. Right now I'm not inclind to take the easy way out and just turn the wing around so that it operates in the way that it was designed. Assuming that ailerons on the effective leading edge won't work what about this? Make the main wing solid with a fair amount of dihedral (for roll stability) but use the last few inches of the wing tips for roll control. My idea is to make the wing tips so that they rotate (under control and in apposing directions) effectively turning them into the ailerons. Given the lever arm involved, small movements should have a big effect on roll. Obviously picking the right point of rotation is critical.

Finally, I expect that the main wing will need a significant amount of positive incidence in order to generate sufficient lift when flying backwards. What about the forward wing? How will the angle of the main wing affect the nominal angle of incidence of the forward wing?

Thanks for your thoughts!!!

Larry

RE: Flying in reverse (apparently
 

P:

Hmmm....... After some more thought.

Incidence of a flat-bottom wing with a "canard" stab way out front should probably be zero/zero. Can't explain why, but that's my instinct. The weather-vaning vertical fin out front is an innovative solution, I like it! That will help, but not eliminate the problem because there is a lot of fuselage side area up front there. I wouldn't worry too much about rudder control right now.

With the long moment arm of the canard you may also be pitch-sensitive because the plane is going to be flying that "canard" rather than dragging it around as a stab... Now you have to count that canard lift in the center of lift equation, and I think this is going to make you want to shift the center of gravity forward w/r/t direction of flight... like a bunch. Maybe even as far FWD as the LE (w/r/t flight direction) of the main wing.

If I were doing this... and I just now might try it... I would take some sheet foam and some of the electric stuff I have laying around and mock this thing up about 1/2 to 3/4 your desired final size and try it out.

Another thing to remember is that with the canard out front, your elevator throw direction is REVERSED from what you are used to. to make plane go up, the "elevator" needs to go DOWN!

Another thing to consider is that if you use tricycle gear set up backwards the ground handling will be ultra-ultra bad. Bring it in nose high will cause you to contact the central "nosegear" first and you'll be all over the place if you can even hold onto it.

If I ever get my house in order and get the workshop usable I might just try this myself.... I have an old RCM with a push/pull canard plan, and it has a long nose moment and flat canard. Let me check the CG and incidence on that plane and get back to you.

N

RE: Flying in reverse (apparently
 

And what would the Italian Airforce of that era want with an airplane that flew forward?

RE: Flying in reverse (apparently
 

Premium2000,
What you actually want is entirely possible.

You want an airplane that looks like it should fly in one direction, but flies in the other.

Screw all the theoretical argument about airflow over backward airfoils etc etc etc. They mean well, but have missed the overall purpose. To fake the public out. Ain't hard at all.

Right off the bat, you're locked in to using a pusher prop. And that'll be obvious to some of the intelligent and experienced flyers in your audience. So you're stuck with some risk. OK, let's go with "some risk".

A cambered airfoil or almost all conventional ones are going to be very obvious to a lot of people. A flat plate one will not.
Almost everyone is familiar with ailerons being on the back of the wing. So be a bit deceptive. Use some striping tape and outline some fake ones. And use your covering "paint scheme" to hide the real, out of place, on the "leading edge" ailerons. Cover the ailerons like the almost standard color shemes that have say red leading edge trim on a white wing. Red ailerons, white wing. Only this time the leading edge trim happens to be the ailerons. Add another color "sun ray" on the wing and the mix of many colors will almost hide the fact that the leading edge trim is actually an aileron.

Building the empennage reversed ain't much of a problem. The vertical stab becomes the rudder. The rudder becomes the stab. The horizontal stab becomes the elevator. The elevator the stab. Also add some rear sweeping color trim and the mix of lines will also camoflage which surfaces are now connected to the fuselage that aren't usually connected etc etc etc

And when you crank the sucker up and start to taxi it out "backwards" all the details of that color scheme that seem now to be going backwards will add to the impact. Only then will the most observant and experienced flyers notice that the stab is moving up and down while the elevator seems to be rigidly attached to the fuse, and the LE of the wing seems to be working like ailerons.

Heck, I think it'd be a hoot.

And might just fly ok.
The side area of the fuselage might have to be adjusted to insure you have enough "rudder" area up there.... uh..... back there. And you might need to have a smaller rudder/stab back.... uhh.... forward. And working your nose wheel..... uh, tail wheel will require two pushrods going in opposite directions from the rudder servo.....

I KNOW it'll be a hoot!

Hell, it'll be fun just building the sucker. You want a test pilot?

RE: Flying in reverse (apparently
 

Larry (Premium), if you would like to continue this, I would love it. I think I just might be qualified to give advice and would like very much if others would chime in with truely helpful and relevant comments. I would like to mock this up myself with light electric gear and foam, but like I said, my model time is limited right now.

Keep the questions coming!

N

RE: Flying in reverse (apparently
 

Somebody had this same idea a little while back. Try a search for reversable or reversing airplane or flying backwards.

Basically it can't be done without altering the CG and vertical fin area and somehow altering the control surfaces so the hinge lines move or you use fully movable surfaces. Otherwise it would be like trying to fly a dart backwards.

RE: Flying in reverse (apparently
 

Oh, yeah almost forgot. Hello, Rock? ------> :eek:

N

RE: Flying in reverse (apparently
 

Ah-HAH!!! Another voice of reason! Thanks BMatthews!

N

RE: Flying in reverse (apparently
 

I've seen one or two of the reversing pitch prop 3d electric funflies.. neither of them can actually fly backwards in a controlled manner.
The feathers are at the wrong end of the arrow in backwards flight.

RE: Flying in reverse (apparently
 

This is all a non starter. Yes I suppose it's possible that your "fin" could be rigged to weathervane and thus not have much effect. But for the model to achieve the directional stability it would need you would need a WAAAAAYYYYY bigger vertical area than just the wheel skirt idea. The amount of effect of the stabilizers and fins are sort of like levers. You can use a small amount at the end of a long lever or a big amount at the end of a short lever. So if the trainer fin works OK with the lever it normally has to make it work with your backward plane it would need to be roughly twice as big (based on the canardly more middle CG location) than the regular fin. The model will look pretty darn silly with a huge fin on the "nose" but trust me, it will be needed.

There's a perfectly good reason why canard models don't look like backwards normal planes other than the areas of the lifting surfaces. You're running into this issue and you can't ignore it.

RE: Flying in reverse (apparently
 

If a hefty amount of dihedral is used it can substitute for fin area (when flying BACKWARDS)

Control can be effected by the use of Control Wing principle as used by Bill Wolf on full size aircraft. Have a word with dicknadine on Vintage thread for how to control the incidence of individual wings.

A flat plate wing would work as inefficiently in either direction.



old git - - - - - - aka John L.

RE: Flying in reverse (apparently
 

This scan is from the back of Andy Leonard's most excellent book, "Basics of R/C Model Aircraft Design"

Notice the yellow airplane that is pictured in the 3rd from the top on the right side of the page?

It's a canard. If you were to scratch build a slightly different looking fuselage (lose that "rear looking" window layout for example) and place a necessarily small rudder on the sucker, would it look backward enough then to fake out the public?

RE: Flying in reverse (apparently
 

BTW, the plans for that canard are in that book. As is a fairly good explanation of what design considerations were important to it's success.

Also, the book's cover prominently displays a canard on it's cover and it is positioned such that your first impression is that it's a slightly odd looking model with a somewhat strange look to it. In other words, the picture illustrates how canards look very much like the majority of models only backward, and when viewed from the rear are easily misunderstood.

I'd say you've got a little study to do concerning the yaw stability problem, but that your idea is certainly possible. After all, it's more slight of hand that you're needing than any aerodynamic breakthroughs.

RE: Flying in reverse (apparently
 

As for the yaw problem.

The fuselage side area is going to need to be larger toward the back and smaller toward the front. It'll need to be smaller especially since you'll need a vertical stab/rudder up front. That stab/rudder needs to be as small as you can get away with.

If you look at Andy Leonard's canard, you'll notice two things that relate to all that. His fuselage projecting forward to the canard has reduced side area. And the fuselage area toward the back has a subfin to increase it's side area and he also has tip fin/rudders that also increase the side area aft. You might need even more side area aft as well, depending on how large your forward fuselage is and how large you need to build your pseudo stab/rudder.

I would suggest that if Andy had painted his Canada Goose canard with a backwards paint scheme and always parked the sucker backwards in the pits, a lot of people would have thought it was a conventional layout. Would it fake out anyone with any aeronautical experience? Nah..... Not if they saw it from 10-20 feet or less. But is that your goal?

What you want is something about as convincing as the flying lawnmower, right?

RE: Flying in reverse (apparently
 

Thanks for all the great ideas, for me this question is as much about the intellectual challange as it is about modeling. Both aspects get the juices flowing. From the various responses, so far, we have a fairly broad range of opinions of whether or not it can be done and if so, how. I think that's great, if it were that simple or obvious we would all likely have moved on to other more interesting threads.

That said, my interpetation of what I've read so far is that there are three major issues to be delt with, all related to flight stability.

1) How to create more "fin effect" (area x lever arm) behind the center of lift than exists in front.
2) How to incorporate rudder, airlerone, and elevator control surfaces which are effective but not obvious
3) How to keep the centers of lift and gravity at a reasonable location on the main wing.

Is there anything other critical problems to deal with?

With regard to issue #1, would it help if a series of veritical vains are added to the bottom of the flat bottom wing and fuselage behind the center of lift. Vains that are 1" or so tall could add up to a significant amount of area depending on the number added and how far forward the new center of lift has moved. Of course the available lever arm is far less with the plane turned around. Maybe by creating enough downstream fin area, and reducing the side profile of the fuselage upstream this problem could be delt with. By placing the vains under the plane and by using dark covering materials they should stay relatively hidden.

I would really like to come up with a design that keeps the plane looking conventional to the causual observer. I don't expect to fool any model enthusiast other than getting a good second look. I just think this would be a cool fun fly plane and frankly I hope that it would challange others in my club to do an even better job.

Thanks again for any and all comments, each one has made me think and ultimately will save me time money and frustration!!!

Larry

RE: Flying in reverse (apparently
 

Your mind is active enough to do this!
You might even get it to work.
Chuck gliders or EPP foamies for the "never do it this way again" stuff to get a handle on what might work.