BFoote

Reality check:
1) You better not be basing your numbers off of a 30mph Take off or landing.
2) At low Re, the ol' axiom that thicker camber = lower AoAcr is just wrong in a LOT of cases. Take for instance standard ol' Clark Y or RG15 airfoils. They invert.
3) Cl "needed" on canard is useless to know unless you know how much moment you have to overcome first. This also ties back into the hopelessly unrealistic 30mph you claimed in 1) as at 30mph said model should already be flying. Where is the extra lift for rotation at lower speeds ... Hmm? This is VERY problematic on canards without the prop wash to help rotate. This means the cl/area needed are vastly higher as rotation needs to happen around 15mph.

If he really wants to know, he can go to University of Urban Champagne of Illinois like everyone else and download the low speed Airfoil data and do his own research. Quite an informative perusal. Yea, I have the data, so does everyone else it is free after all. Though I did spend $$$ for it in book form.

The only one who can do this is the guy doing the scaled design. Filling in the blanks 2nd hand is an epic failure, especially in canard land.

Bottom line its an RC plane you can pretty much do anything and get away with it. The only one you really really want to watch out for in canard land is making sure your vertical fins are extra large.

rmh

and or far enough aft
The model mags -over the years have published plans for absolutely wretched canard designs
center of lateral area is always way too far forward

BFoote

I should have been a bit more emphatic about the bolded above. For this reason, part bolded, it is hopelessly optimistic to believe you can get away with using the same airfoil for the canard as the main wing. The Cl of the canard generally must be Pretty high in comparison to the main wing. Now if you only take off from 1000' paved runways... Sure optimize your plane for in flight speed and ignore rotation needs.

Giving a guy "data" for his design of which I do not have the numbers, is absurd. I would have to give him my Performance Stability program and let him fill in the blanks(A LOT OF BLANKS) and then I could make recommendations on how to modify or I would have to do all the work for him( I won't).

Per dutch roll canard problems and why RC planes have much harder time than those actually flown. When flying, your senses see the yaw in much sooner time. Likewise you will note that on the LONG-EZ there is significant wing sweep giving at least a bit of moment arm to counter the yaw naturally. On RC, creating a swept wing is a bit more problematic, though not really once one quits *****ing and groaning about all this "extra work" and since you are not "in" the plane you do not sense the yaw in time. Therefore when your reactions catch up to the plane one needs a larger, quicker throw. TO compensate for the LAG inherent to the ground observer compared to first person and the fact it is not NATURALLY in a stable position, larger fins are a near must. In the Shinden case, I would sweep those suckers back, higher, and longer. Its moment arm is abysmally short.

As per washout on main wing, sure go for it. Speaking from experience: thickening the camber is easier to implement while building, but requires more engineering book work and becomes very problematic at lower Re. Generally, I would cheat and add dihedral before doing either of the above. Yea, adding dihedral isn't true "scale", but vastly easier to implement and 99% will not notice. Not OK for scale competitions though.

alasdair

BMathews,
I wasn't being harsh, rude or derogatory. I was just trying to get him off hid soapbox and say something relevant to the original post, and the aircraft in question.

I take note of your point
It's known that prop discs have an equivalent side area effect
Do you have a reference online for this? Presumably, due to rotational symmetry, they should have a H-stab equivalent area as well????

BMatthews

Nothing in terms of math or statements of theory. Just references to some examples.

One being the situation with the XB-35 when it changed to the jet powered XB-49. The loss of the rear pusher props required the addition of the small fins located along the rear of the wing of the XB-49 to maintain the same level of yaw stability.

Some of the final versions of the Spitfire got a yet again bigger fin and rudder when they went over to the big contra rotating prop from the single disc version. Even the early marks went to a bigger vertical when they went over to the three and four blade props. The reasoning I read being due to first off the prop change then later the nose area increase and prop change when the 4 bladed props and longer Griffon engines were fitted. The case with the Spitfire being that the original fin was sized "just right" for the shorter Merlin and two bladed prop to the point where the tail had to grow larger with every little change up front to maintain the yaw stability.

Also some free flight pusher prop rubber powered models do fine with the prop on the rear running under power or when freewheeling but become unstable if tested as gliders with the prop removed. Then there's the old twin pusher A frame old timer models. Another example of where the prop discs have enough of a fin effect that the models didn't require addtional vertical area.

I'd have to guess and say that it would have some of the same effect on the horizontal stab as well. But it would appear that it's not as significant when compared to the bigger effects of the CG being located at some point forward of the overall aircraft neutral point. In effect to the pitching stability the effect of the prop is small by comparison to the pitching stabilty loads where for vertical stability the forces ARE significanty large enough to be noticable.

Going back to the Spitfire situation it's perhaps notable that the later Griffon/contra rotating prop models DID have a larger size stabilizer as well. Now whether this was due to the prop disc area effect or simply to get back the control authourity related to the heavier mass/moments of the heavy engine models I can't say. It's likely that it was to ensure adequite pitch response with the heavier engine and perhaps more pitch damping due to the higher mass/ moment factors of the heavier engine. Certainly I've seen it remarked in quite a few books on the Spitfire that the later Marks did not have the delightful harmoney and ballet dancer like qualities of the early Marks. They were certainly more capable machines of war despite this and certainly the upgrades were needed. But the much appreciated harmony between the controls and flyability did take a nose dive.

rmh

In a fight to the death-which one would YOU want ? the lovely ballet dancer or a mean SOB that would out climb and out shoot the other guy
It's all about compromise -

BFoote

You were blasting away spouting cl's without even knowing the lift needed to compensate for the moment created from the main wing, let alone what would be needed EXTRA for rotation! You call yourself knowledgeable in aeronautics? [:'(]

I originally was going to rip your post to shreds for being utterly ill informed and horrid advice. Instead I didn't because it wouldn't have been positive. Instead I gave the designer major things to contemplate and if he does then he will draw the correct conclusions.

You design a plane back asswards and have the gall to call someone else out for a reality check? Of course you are going to take flak on your backside. It would appear I need to type more "bombastic" posts than my rate of 10 a year.

BMatthews

A couple of posts have been edited or deleted. If the participants want to "take it outside" via PM's that's fine. But no more attacks in public.

BMatthews

Oh, I very much agree. For the weapon of war that it was designed to be it HAD to change. Mind you by the time the design had run its course the last few Marks would have likely been better off with a all new replacement. But there again it was all about the time and materials and the need to keep producing that made modifying something well know easier than trying to develop a whole new fighter. Especially with the late war and early post war jets already in development.

It doesn't prevent the pilots of the time being a little sad that with each gain in performance something of the joy of flying went away.

donnyman

Tdstaf

Permit me to offer some assistance, nuttin fancy, just a set of plans by COL. Bob Thacker for a 62in. version of the SHINDEN

It is from Model builder magazine ...plan # 8841-B

All the rhetoric in this thread has my head spinning, everyone has a theory I intend to build one also, it's number 7000 in my build cue but I will follow the plans then, maybe, modify it.

Good luck to ya...................DONNY

donnyman

Tim

There is another set of plans from Mike Bealieu scale r/c models it's 73" and another I have on file (if it uploaded)

My intent was to build a copy then try to improve on it, no need to get involved in a totally new design these flew!