A workmate of mine has decided to build an aircraft with the following description:-

28" wingspan
36" chord
6" camber.
The airfoil is flat bottomed.
Weight is expected to be 2.2 lbs.
It has a semicircular cutout at the trailing edge effectively making it twin boom, with 2 vertical fins and a high tailplane and elevator on top, the main lifting surface at the tips is angled about 45 degrees downward and inward.
Construction will be completely of polystyrene ( except for engine bearers etc )
It will be powered by an OS LA 25. Covering will most likely be coloured parcel tape or similar.
He intends to use rudder/elevator only, and expects that it will be able to fly slowly, and be able to hover at low throttle settings with an extremely high angle of attack.

I'm not so sure about all this, so I would appreciate any comments (or advice) regarding this project.

sounds like its going to be an underpowered feather!

i doubt it will hover with just rudder/elevator control and im not sure i understand the 'the main lifting surface at the tips is angled about 45 degrees downward and inward.' bit.

it sounds like it might work, is it just a rectangle? does he have expperience in radio control or is it an experiment?

It's basically a flying fuselage and could be described as a rectangle.
The sides/ends/wingtips are angled as they would be on any basic trainer wingtips. if you can understand what I mean.
He is a reasonably experiencied RC flier, also he is an avid experimenter and does work outside the square a lot. (generally with success and the odd failure, I might add )
I've told him that he's really done it this time, but he's convinced I'm wrong!

It looks like this?
Might be a handful...

Tall Paul,
Four possible scenarios :-

1. My description isn't very good.
2. Your comprehension isn't great
3. You like to play with the new software you bought yesterday.
4. You've got a good sense of humour.
Cheers Will.

I'm not sure I follow your description either, but it sounds somewhat like a vaiant on a PBF-type plane with a high-mounted horizontal stab and elevator. My first thought is that you'll want some roll control, rudder only won't do it, as I don't think you'll have enough dihedral effect. I'm not sure though, since I'm not sure I follow the description.

I'll choose 1, 3 and 4.

tell him that it will be uncontrollable with rudder control and no dihedral.


a picture or drawing or even a scribble on a fag packet would help us muchly!

I'm with Paul. The description would have led me to sketch out something alot weirder.

Have you seen a pizza-box flyer (PBX)? It's a flat square with a vertical fin, elevons, and a motor. Go ahead, search on the term and take a look. Anyway, the rudder is a more powerfull directional control than the ailerons - but the ailerons are there because pilots are more used to steering with them. A PBX could easily be flown without dihedral or ailerons. It's dihedral EFFECT that's important, not just the actual angle.

Hi everybody,
Please understand that I'm only the messenger but I'll do my best to explain!.

The guy who is building it believes only in the simple ways of doing things, and leaves out anything which he considers unnecessary, hence his 3 channel radio, and his dislike of computers! ( also computer radios ). However, he does seem to be very good with hunches and has built quite a few weird contraptions which flew successfully.
I think that you are probably on to it JOHNG, I'll look up the machine you mentioned.
Actually it doesn't look completely unlike TALL PAUL'S light hearted depiction, but it won't have wheels ( he considers them totally unnecessary) nor the broken looking tailplane.
He will hand launch it, and land it on a polystyrene pod under the engine bay, which will be ahead of the leading edge, the pod being there to make hand launching easier, and to prevent the prop hitting the ground on landing if the engine is still running. ( This is standard practice for him - He thinks that all the hassle of takeoff is unnecessary.)
He also believes that it will be possible to land it vertically, (tail first of course, and controlled! ).
I will post a sketch of this aircraft, (as I envision it to be ) as soon as I find out how to send it.

Have you seen a pizza-box flyer (PBX)?
---------------------------------------------

yeah, ive got 2 !!!!


point taken, however, using the rudder in normal flight for turning etc does cause problems like the terminal flat spin to the ground. i tend to just use the rudder in the prophang, maybe a bit mixed in with the ailerons for turning.

my big pbf gets a lot of dihedral in normal flight anyways, it just bends!

Please note!
The guy who is building it says that it does NOT hang on the prop, he says that it is a lifting body and can hover at low revs with a normal size prop.

PS. how do I get my sketch posted? I haven't found anywhere it tells you how.

Look at the lower left on the reply page...

Well hope it works, ( the picture that is ), I do believe the plane will work. despite it's looks.


UPDATE NOTE:- There is a more accurate drawing on page 2 ( post 39)
Also a report on its flying characteristics further on.

The control surfaces must be in the prop blast.
A .25 will be using a 8x5 or 9x4 prop.
Not much airflow possible.

That's not that far off what Tall Paul did after all.

First off I think the tips being angled like that will function much like dihedral. But for the airplane to have any roll control it MUST be moving forward so that the yaw can act on the angled tips and roll the model In a hover it won't work that way. In fact the rudders being on the upside of the model will tend to roll the model in an adverse manner instead of pro. But in truth they won't even do that because as Paul said you MUST have the controls in the prop blast during any super slow harrier type flight and especially for hovering.

As for the airfoil there's so much cut away that it won't operate as an airfoil at all. It may fly just based on light weight and body area but it won't be pretty if the engine quites. And the flat bottomed airfoil rements are going to have all sorts of pitch to speed coupling problems. He would be way better if he used a symetrical shape.

Bottom line? I truly think he's not thinking the factors out very well. It may fly but not in the manner intended as you described it.

Hi folks,

I'll pass on all the comments so far, but I won't see him again until Tuesday.
Turns out that he was going to use a 9x4 prop.
Remember that my sketch is not a scale drawing, done purely from memory in just a few minutes, so please don't take it too literally.
Possibly you are right that the rudders will work in an adverse manner, if they do he will accept that, but not before trying it. The same goes for airfoil shape, but this is his starting point. Remember it's made of polystyrene and will cost virtually nothing!
In fact he will accept any shortcomings it may have, and if he fails to rectify them after a few attempts he will scrap it, and move on to something else.
Believe me, he is very much a thinker.

Hi, just like Tall Paul mentioned, it needs the control surfaces directly behind the prop-blast for any kind of hovering performance unless you consider a strong headwind. Basically its a variation of the flying STOP SIGN with an airfoil. That will help creat more lift and hence the slow flight at normal AOA. I do agree that to have better control at slow speeds ailerons should be used. Rudder alone can help so much on tip stalls. If the airfoil is thick enough that will also help fly it because high reynolds number. Consider lowering the "sorta T-tail" configuration to avoid high center of gravity and the possibility for tip stall sooner.

forget the cutout, go with elevons. use the handle at the back for carrying and grabing from the air.
the cut out the way it is now is gonna cause a LOT of drag with it's flat rear face.

Phillybaby,
Remember, three channel radio,and no mixer! and yes, he's tried a mechanical mixer before, in case you ask.
You've said more or less what I said, (except for that brilliant handle idea of course, that's ground breaking stuff), - but this guy won't be told, so live with it.

ok, forget the cut out, make them ailerons, and go with the handle as elevator,, only as you get nose high the wing will blank it, it'll need to be high enough so you see it when the wing is at 30 degrees AOA

i skipped most of the text coz it got boring lol

Phil,
Most of what you say is probably correct, but as I said before I am only the messenger and I won't have any input in the design or construction.
The guy who is doing it seems to be like you with a head full of ideas - most of which he puts into practice! He ( like you ) would rather be building than talking about building, and judging by your website you also do a lot ( of building ).

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I'll pass everyone's ideas on when I see him on Tuesday, but my guess is that he will have the machine flying by then, although the weather here is terrible at the moment


Thanks again everyone.

hey, i've seen some real weird things fly, some of my designs flew well inculding the DD fast delta, but once i made the fins bigger, they popped out of the turbulent air and BINGO! walking pace stall speed. totaly changed the plane. let us know how it flys, or... how the clean up went, little snowy beads of foam floating across the field lol

question.. why are you asking for input when none is going to be taken? or is it just so you can say "told ya so" when it all goes boom?

Sorry Phil,
Looking at my last post, my message could easily have been misconstrued, just an unfortunate arrangement of words, no malice intended. So I've edited it with brackets to make things a little clearer.
The builder does not have a computer ( doesn't like them ) and I just want to let him know what other people think, whether he will take any advice or not, who knows.
No, I don't want to say "I told you so", I'm a little too old and wise for that! also I am just a little bit sceptical about this project too! However I've seen a lot of his weird things work, so I don't argue!
We'll let you know what happens ( warts and all ), even about the little snowy beads!