donnyman

I have been stumped by the use of square leading edges, no matter where they are used it is my thought it is not the thing to put on a flying machine.

If you know otherwise now is the time to say so or forever hold your peace!

Yes I have used them with success, but don't know WHY???

speedracerntrixie

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Can you provide an example? I’ve never built a model with square leading edges but many with square trailing edges.

donnyman

The model I flew with square Horizontal and vertical leading edges was the Goldberg eaglet, I saw a stunt plane (full scale) with square horizontal stab also don't remember what it was. Squared trailing edges did not seem to make any difference.

I offer the flying stop sign sign, my friend rounded the edges and it didn't fly well at all.

Lownverted

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Flat foamys are this way. At that low of a Rn, it can actually be beneficial. It promotes clean separation for snaps and high Alpha. If the Eaglet had square LE's on the tail, someone didn't use the sanding block lol.

donnyman

That flat foamy is one thing,Granted the sanding block was ignored but the eaglet was a total success. now the ones I built with rounded edges were failures as far as I am concerned

speedracerntrixie

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I’ve not built anything but flat foamies with square leading edges. I’ve built plenty with squared off trailing edges including wings. In fact my latest design has very thick trailing edges on all surfaces. It tends to soften the controls around center and introduces drag where you want it. In these two photos, you can clearly see the thick/square trailing edges.

donnyman

Trailing edges do not cause turbulent airflow over control surfaces but leading edges ..................... ?

speedracerntrixie

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Are you certain the square leading edges create turbulence?

donnyman

my post does end with a question mark!

speedracerntrixie

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I was curious so I did a Google search of cars with a blunt front end being tested in a wind tunnel. Although the noses are blunt, it appears to not affect the airflow much.

donnyman

Not only cars... Boats use rounded bulbous noses. the idea is to induce a smooth transitional laminar flow over the surface at the speed for which the vehicle will travel.
The car isn't as blunt as it could be it has a downward slope to the front inducing air to flow over as apposed to bunching up.

Consider the ww1 se5 biplane it had a huge flat nose but was a mean flying machine. (inquiring minds wanna no)

speedracerntrixie

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Reminds me of the first time saw an F-16 in the flesh. The wing LE was about 1/4” squared off. The wing tip if an F-15 not only has about 6 degrees washout but is undercambered. Point is, sometimes aerodynamics don’t make sense to us layman.

donnyman

trying to down load pics........ wont work. how does this file look to you?

speedracerntrixie

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I remember getting that issue back in the day. My hypothesis is that it works better with square leading edge due to the relatively high AOA in which it flies.

allanflowers

The air forms its own pocket in front of a blunt face so the free stream air doesn't follow the square shape anyway. This is true of a car front and no doubt a wing section. Generally cars are "bluff" bodies and not very relevant to airplanes anyway. This is especially true since they run along a surface (the ground).
Of course any crisp edge on the front of a form may trigger the boundary layer to go from laminar to turbulent which, due to its higher energy, will not separate as soon. This can reduce the overall drag due to the smaller wake area produced.

donnyman

maybe I missed it but I have seen many of these stop signs fly and not one appeared to have a high angle of attack and were highly maneuverable

Allanflowers I appreciate your response but ............ To me what you said sounds like pure nonsense. (I intend no offensiveness) It is likely what you say is far over my head.

speedracerntrixie

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IMO, with models anything over 4 or 5 degrees is considered a high angle.