# Can a push-prop model plane use control surfaces forward of the propeller, but which do not extend beyond the perimeter of the propeller's swept area?

While reading about various drone airframe configurations, in particular the trade-offs between various wing designs, I thought of a propulsion and control pairing which I have yet to find in the literature: a push-prop plane with stubby, forward mounted control surfaces.

To illustrate, consider the following model aircraft:

In this video, Tom Stanton builds a tractor configuration "rocket": https://www.youtube.com/watch?v=vWgwYBDSHGo

The propeller is mounted on the nose, and the stabilizer fins at the tail. Extending a cylinder down from the edge of the swept area of the propeller, the tips of the fins do not seem to extend beyond this perimeter. However, neither do they have any control surfaces.

The "Ikarus" is another tractor configuration drone, with thrust vectoring control: https://hackaday.com/2018/08/31/single-rotor-drone-a-thrust-vectoring-monocopter/

In this case, the control surfaces are mounted rear of the propeller, and within the same cylindrical "perimeter" extended down from the swept area of the propeller.

I am curious about inverting this arrangement, with a pusher propeller mounted to the rear of the control surfaces, which themselves do not project outside of the swept area cylinder.

This diagram shows the configuration:

       _      _
/ |____| |
<[[|c ____ p|
\_|    |_|


C is the wing+control surfaces, P is propeller. Note that the tips of the propeller and wing are level.

I would consider a lifting body push-prop to also satisfy this inquiry.

Any links to examples of this kind of design would be greatly appreciated. The nearest instances that I have been able to find thus far are stub wing planes or narrow blended wing-bodies. Grid fins also come close, but I have only seen those on rocket propelled models (e.g. https://www.youtube.com/watch?v=QM6tvAVNLnk), and they still extend outside the perimeter of a the body of the airframe.

Thank you.

I'm not sure what you're trying to achieve with this design, or how you plan to use it.

It is entirely possible to fly a plane with control surfaces that are not in the prop-wash. Jets and gliders are obvious examples, and most planes have ailerons that are not in line with the prop. Canard planes like the LongEZ have control surfaces at the front.

However there are a few issues. You'll notice that the above plane has swept wings in order to place the vertical surfaces as far aft as possible. Yaw stability is hard to achieve without a long tail, especially if you put a heavy motor at the back. Although you can steer with a front rudder, it would have a long lever arm, and your vertical stabilisers would have to be correspondingly larger or further aft.

The other one is that you would be relying on forward speed to provide airflow over the controls. If you look at the airflow into a static propeller in photo (a), you'll see that there isn't a column of air in front (like diagram (b)), instead air comes from all sides and the airspeed rapidly drops to zero as you move forwards. I don't think you could building a hovering drone like this.

You could put controls very close to the prop and in front of it, but they still would have slower airflow than behind it (as the prop accelerates the air) - and it would also be very noisy. The low pressure areas on the front of the prop aerofoil extend further than the high pressure area behind it, and they would be interrupted every time they pass a control surface. This regular pressure change is a sound wave.

• Thank you for your response. I am interested in this configuration in the spirit of experimentation, and possibly to build a demonstration model, since to my knowledge an example of this control system does not exist. > I don't think you could building a hovering drone like this. I suspect that as well, and that maintaining forward air speed will be critical to effective control. The canards in the LongEZ, while fore of the propeller, are wider than the cylinder of the airstream directly in front of the swept area of the propeller. This is the key geometric constraint.
– jpt4
Commented Apr 26, 2022 at 16:39
• I think that what matters is the area of the control surface, as that (and the speed) limits the force it can generate. Higher aspect ratio is more efficient, and the LongEZ is designed for cruise efficiency. Various people have made radio control models of missiles with little stubby controls. I've not seen one in the configuration you describe but I see no reason it couldn't be done. Commented Apr 28, 2022 at 8:01