Originally Posted by
Malcolm H
Firstly Brian it's great to see Ireland still at the forefront of European aerobatic flying. Hopefully your home brewed bipe will add to a long list including composite construction, 4 strokes, electric power, contradrives to name a few.
Like Doug I would be wary of sweepback. It moves the aerodynamic centre of the wing back and with it the neutral point of the aeroplane and so you are negating the increase in yaw stability you will be gaining by moving the wings forward. Yaw/roll couple is always a problem with bipes which is why you see the latest designs moving the wings closer together and introducing anhedral to the top wing. Anything that promotes yaw/roll couple, even if it is with angle of attack is to be avoided.
Moving away from the aerodynamics for a minute, remember I commented to you at the Triple Crown that your Mid Rex only looks like a bipe some of the time flying through the schedule? To me its important that it looks like a bipe the whole time and its something your Venture did very well. You might think about this when you position the wings with respect to one another and the fuz. The yaw/roll couple with wing separation needs to be addressed and one area where small improvements might be made is in the vertical centre of gravity of the model. I suspect that getting the weight i.e. the batteries as low as possible may help a little.
Structurally the flying surfaces need to be as stiff as possible. To this end I'm not keen on film covering and I'm certainly put off the Biside by the instructions on how to remove the warps due to the very light balsa used in the construction to make weight. I think you need to consider imaginative solutions such as fully geodetic construction which with laser cutting is not difficult. An all flying tail is a great idea, has been proved aerodynamically on the Biside and does away with control surfaces to warp so perfect for geodetics. Actually the same argument applies to the wings. Ailerons are just something to warp so why not do away with them and go for all flying wings also geodetically built? This isn't as daft as it sounds with the wing panels pivoting on thin section ball raced tubes and driven by S-bus high voltage servos. There is one now which gives 38kg.cm of torque and 0.082s/60deg! As an aside HV S-bus is looking to be a great way to go weight wise, with two servos in the tail and four in the wings and one 3 core cable feeding them. I know that camber is more effective than angle of attack at changing lift but years ago there were a few successful aerobatic soarers which used wing twist and they flew very well.
I hope this might give you a few ideas to play with and you know the address to send the plans to!
Malcolm
Hi Malcolm,
The glider guys ,who I try to stay in touch with, are very innovative.
There are some great systems for all moving wings developed at this stage - complicated to do on a bipe with skinny and light wings.
They also are way out there with wing construction.
I just can't justify the effort required to create plugs,moulds and then mouldings for a one off - for wings or fuz,, .
( There is too much nice stuff out there ,available and little work to do
. )
As you know I've been there before, but back then there was little or nothing ,of any quality, available.
i was tempted and I have developed some thoughts on fuz,, design to control flows , inside and out.
Also ,for these difficult knife edge based manoeuvres, a fuz,, that develops lift effectively, a stable wing and stab platform coupled with a contra is clearly the way to go.
If the entire platform is stable enough then the contra will really shine as it will not disturb it nearly as much as a single prop set up will while transitioning through the AOA's required for the KE based forms.
However flying at that level is not something that I have to worry about
.
I just really enjoy the biplanes and they give me that little extra time as they still fly well at the somewhat slower speeds.
Weight is my real motivation here.
I'm fed up with having to use a small battery to be comp,, legal.
My aim is to get a bipe comp,, legal with a 5800 to 6000mAh on board.
I have to use 4400's at present and practising with these in our weather is not working all that great as it's too easy to 'hurt' them.
So I've decided that while I'm at it I will try a few little things just to do something that's new/fresh so as to keep the interest up.
I want a little more stability, particularly in yaw, so as to get my P schedule as good as I can.
I'm hoping to do this and have glassed skins - I'm not sure that there is even tissue on my current ones.
With glassed skins and good struts it will easily be stiff enough.
My current set up is not bad now but it did require attention. I have carbon packing shims on the heels and toes of the strut bases to tighten and set the fits.
The model is much better that it was at the Triple Crown.
Re the look; I don't altogether agree with you on that. These are F3A planes first and foremost.
The monos don't really look like anything other than what they are so why should the bipes.
So for me it's function first - then we'll see re the form.
Brian