Another speculative thread - adding forward sweep to solve CG problems

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TFF

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True issue or best practices? The DH folding wing mounts are still used yet you can’t fold the wings on the Tiggie. Charming it got away with it all. Not death to design but better is always better.
 

Chilton

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I think it would be a stroke of luck if any rib on a fabric covered wing was truly parallel with the local airflow once you consider inflow over the wing, outflow beneath it, interference around struts and the fuselage, propeller slipstream, etc. In any case, the Tiger Moth has all its ribs at 90° to the (swept) spars and it doesn’t seem to be an issue.
There has been a Tiger Moth built with the ribs parallel to the aircraft centre line, it showed a slight improvement in performance compared to the standard wing. The builder was initially puzled by the performance of the Tiger compared to the Moth Major and so set out to investigate. Apparently the angled ribs do increase drag. It was written up in the Moth Club magazine many years ago, so if I find the article I will post it but that may take some time!
 

Tiger Tim

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There has been a Tiger Moth built with the ribs parallel to the aircraft centre line, it showed a slight improvement in performance compared to the standard wing.
I’m not really surprised that it showed some improvement, I guess my point was that the plane will still fly Andy probably not be weird to handle. I haven’t flown a Stampe or a Jungmann (yet) but I’d like to give them a go for comparison’s sake against the Tiger Moth. I hear they’re better flying but to be fair they weren’t the end result of twenty years of compromises either.
 

Sraight'nlevel

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How much aerodynamic efficiency comes with forward sweep ?


Is there a rule of thumb...like 10% ?
 

cluttonfred

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Since the primary aero effects of sweep are a function of the leading edge sweep angle, I define a swept wing as one whose leading edge is at an angle other than 90 degrees to the fuselage axis.

BJC

That's true for spanwise flow effects, but does it apply to other effects as well? For example, does a Mooney wing get any anhedral effect from it's forward-swept trailing edge? I don't know.
 

cluttonfred

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On a related note, what are the aerodynamic impacts of a rearward swept trailing edge, such as Ed Fisher's Raceair Skylite with its reverse-tapered full-span ailerons? Imagine (figuratively) bolting the tip of the Mooney's left wing on the right side of the fuselage, and the tip of the right wing on the left side of the fuselage. Something like this drawing but with a straight leading edge.

1653059518782.png 1653059445004.png
 

Riggerrob

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On a related note, what are the aerodynamic impacts of a rearward swept trailing edge, such as Ed Fisher's Raceair Skylite with its reverse-tapered full-span ailerons? Imagine (figuratively) bolting the tip of the Mooney's left wing on the right side of the fuselage, and the tip of the right wing on the left side of the fuselage. Something like this drawing but with a straight leading edge.

View attachment 125698 View attachment 125697

On the Skylite, I suspect that they tapered ailerons to move the aileron center-of-lift farther outboard to improve roll control.
Otherwise, aileron taper might just be an aesthetic trick (ala. Thatcher CX-5).

OTOH, large fixed wing tip chords improve roll stability.

Slightly swept trailing edges are used on Schumann planforms (see competition sailplanes and Formula 1 racers) to equalize spanwise airflow on both top an bottom surfaces in an effort to minimize wing-tip vortices. Schumann wings try to introduce a bit of spanwise flow along the top skin to equal spanwise flow (outboard) along the bottom skin. However, I doubt if Skylite wings are anywhere near smooth/precise enough to benefit from refining spanwise airflow.

Back in 1949, Republic built a pair of XF-91 Thunderceptor prototypes with reverse tapered wings. They were basically F-84 fuselages fitted with swept, reverse-taper wings. One goal was to solve a problem with pitch-up during stall. This problem was caused by span-wise airflow and was later solved by wing fences, vortilons, dogs teeth, etc. One advantage (?) was that dual wheel (tandem) main wheels had plenty of room to retract into wing tips.
A side effect is that shorter wing root chords supposedly produce less drag. See the wing root cut-outs on Luscombe 8 high wing.
 

bhooper360

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Honeyview_csm_Duo-Discus-XLT-Christoph-Schwarz-eingefahren_823e767a2f.jpg

Since the primary aero effects of sweep are a function of the leading edge sweep angle, I define a swept wing as one whose leading edge is at an angle other than 90 degrees to the fuselage axis.

Technically you have to specify which chord percentage when you use the term. I assume max chord line, so 30% for NACA 0012. That's what determines whether the ideal wing spar is angled or straight.
 
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WonderousMountain

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Since the primary aero effects of sweep are a function of the leading edge sweep angle, I define a swept wing as one whose leading edge is at an angle other than 90 degrees to the fuselage axis.

BJC
I take great pleasure in contradicting BJC, However, not today, this measure is cannon. Calculation of any intermediate wing chord would be more difficult to measure. My take is trailing edge effect is equal, but there is no good reason to switch. On sailplanes, the angle is so minimal as to not matter, a clipped wing racer might very well need to use chord-line. Remember this since one draft had a straight leading edge & I was using spar sweep in lue of forward.
 

trimtab

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On a related note, what are the aerodynamic impacts of a rearward swept trailing edge, such as Ed Fisher's Raceair Skylite with its reverse-tapered full-span ailerons? Imagine (figuratively) bolting the tip of the Mooney's left wing on the right side of the fuselage, and the tip of the right wing on the left side of the fuselage. Something like this drawing but with a straight leading edge.

View attachment 125698 View attachment 125697
I've never seen that before!

Going to make a cheesy CFD model to see what happens. I can't find papers on a reverse taper planform.

Intriguing!
 

Lucky Dog

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Structure is one issue, yaw stability is another. Also if it's a fabric covered wing, the ribs won't be parallel to the airflow any more which could make for some funny (i.e. undesirable) effects.
Fabric wing Ercoupes all had V-shaped ribs, so the drag penalty is probably not an issue if the ribs don't exactly align with the airstream. 1653260155145.png
 

Tiger Tim

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Also if it's a fabric covered wing, the ribs won't be parallel to the airflow any more which could make for some funny (i.e. undesirable) effects.
The Tiger Moth has its ribs perpendicular to the swept leading edge and it seems to fly okay. Its contemporaries the Stampe SV.4 and Bucker Jungmann much more elegantly have their ribs parallel to the centreline of the airplane.
 

TFF

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I would put the Tiggie wing ribs down to British conservative nature. The were just modified Gypsy wings. Why retool? Its just a trainer. Last of the line. It’s what happened to British motorcycles. In the early 60s Honda was buying some of the first automated machine tools, while the British bike companies were still manning manual drill presses that were old in WW2. Ercoupe it’s part of a structure exercise. Moth, just wing ribs. The only Ercoupe I have been in had fabric wings. I know one thing, you appreciate rib stitching when you can see the tops of the wings.
 

Sraight'nlevel

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8° forward sweep is not so much that It should cause major problems. The real innovation of the P.1076 was a 2,750 hp liquid-cooled engine with evaporative cooling so no radiators!
Wing tip vortices might have a different point to this conversation ?

 
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