Moving the rear spar in?

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ToddK

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Another thought would be to sweep the wing to keep the trailing edge from interfering with the engine. The fringe benefits would be the directional and roll stability from the sweep coupled with any washout giving a bit of pitch stability would allow you to size the tail feathers on the smaller side and save weight, drag, etc.
That's a dang good idea too. Keeping the tail weight down is a major chore with a pusher. A lot of times they end up being rather short coupled for that reason. You know of any swept tube spar wings (other then a weedhopper)?
 

Riggerrob

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Another thought would be to sweep the wing to keep the trailing edge from interfering with the engine. The fringe benefits would be the directional and roll stability from the sweep coupled with any washout giving a bit of pitch stability would allow you to size the tail feathers on the smaller side and save weight, drag, etc.
Yes!

Sea Rey is a good example of a slightly swept wing. It has a straight trailing edge and a swept leading edge to move the center-of-lift farther aft and closer to the weight of the engine.

Republic Sea Bee had similar balance problems that were only solved by an extended propeller shaft that allowed the engine mass (originally Franklin air-cooled, flat 6) to be installed near the main spar, but keep the propeller aft of the trailing edge. When the supply of original Franklin engines got scarce, several after-market STCs were developed, but without extension shafts, they suffered balance problems. The other alternative was installing a heavy bus battery in the nose - for balance - but the battery was so heavy that it reduced the useful load to only two humans and some fuel. The most successful after-market engine - for Sea Bees is an LS Corvette, V8, automobile engine with an extension shaft.

Spencer's later Air Car amphibian had similar balance problems. The last version had a slightly swept wing (with constant chord) to solve balance problems with a heavier engine.
 

ToddK

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Here are the current changes:
1.) No swept back tail (Thanks for the info guys)
2.) No swept wing. I need the wing to be largely homogenous for the sake of simplicity.
3.) No additional bits (motor mount or other wise) to mount a rear spar that is at the back of the wing (ultralight style). The rear spar must mount forward of the engine.
4.) 6061 Aluminum tube/square/angle rather then welded construction (or tube with a few a welded fittings) is now on the table.

A kitfox style wing really makes the most since given my goal: A totally uncluttered open and flexible motor mount area. Every single pusher requires the engine sit on top of the wing like a giant carbuncle, or be tucked up underneath requiring an inverted 2 stroke, or a giant belt redrive.

Now the question comes back to the wing configuration.

Aluminum Tube spars with:
A.) Glued plywood ribs
B.) Bent aluminum tube ribs
C.) Bent aluminum angle ribs
D.) Fiberglass ribs like what Rotax 618 used on his bird
E.) Formed/Flanged Aluminum Sheet ribs.

Next and probably most pressing question on my mind is what to do with the rear wing/ aileron
A.) I could do false rear spar made of tube or aluminum channel to attach the rear ailerons/flaps (along with gap seal tape). No need for this to be heavy. A small tube should do.
B.) I could do strait kitfox ripoff and go for Junkers flap.
C.) I could hang large(ish) brackets off the Rear spar.

Simplicity and ease of construction are a top priority.

Either option will include a differential system. I am on the fence about including flaps.

Thoughts?
 

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ToddK

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Good grief aluminum pricing has gotten insane. After working up some new drawings, I talked to a supplier on the phone about 5" body tube stock today... Didn't even ask about the spar stock. Think this little exercise is coming to an abrupt stop till things get back to normal. She said 18-24 months.
 

Lendo

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Sweep is a big deal with lifting bodies such as Wing, HT and VT. Some designers like the aircraft to look sleek and sporty by introducing sweep into everything, but it introduces efficiency cost into everything in terms of Extra Area and Weight.

A very helpful friend and adviser (here on HBA) provided me with the tools to calculate the lost efficiency of sweep. It is actually exponential and Minimal at 20° sweep at 25% chord, but rises quickly after that.

A straight leading edge is THE most efficient and a straight Trailing Edge is also the most efficient, but getting the balance in Taper so as to reduce the Induced Tip Drag is the secret. The RV is a good example of these design characteristics especially in the VT. Although the Elliptical Lift Distribution (ELD) of a Tapered Wing, has less Tip Drag than a Hershey Bar (rectangle) wing.

The secret with the ELD is to keep the trailing edges (TE) Vortices rolling smoothly toward the Tip, which if small, keeps the whole Tip Vortex small. The rolling TE is kept smooth by keeping their transition small in line with the ELD, as they move toward the Tip.

That's why Gliders have long , High AR efficiency wings ending in a small Wing Tip. How small you may ask, some texts suggest 50% of the Root to be safe in light aircraft, I've seen some provided information on 45% and 40%. I would think too small a Tip might be too flexible.

Hope that helps.
George
 

Riggerrob

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Sweep is a big deal with lifting bodies such as Wing, HT and VT. Some designers like the aircraft to look sleek and sporty by introducing sweep into everything, but it introduces efficiency cost into everything in terms of Extra Area and Weight.

A very helpful friend and adviser (here on HBA) provided me with the tools to calculate the lost efficiency of sweep. It is actually exponential and Minimal at 20° sweep at 25% chord, but rises quickly after that.

A straight leading edge is THE most efficient and a straight Trailing Edge is also the most efficient, but getting the balance in Taper so as to reduce the Induced Tip Drag is the secret. The RV is a good example of these design characteristics especially in the VT. Although the Elliptical Lift Distribution (ELD) of a Tapered Wing, has less Tip Drag than a Hershey Bar (rectangle) wing.

The secret with the ELD is to keep the trailing edges (TE) Vortices rolling smoothly toward the Tip, which if small, keeps the whole Tip Vortex small. The rolling TE is kept smooth by keeping their transition small in line with the ELD, as they move toward the Tip.

That's why Gliders have long , High AR efficiency wings ending in a small Wing Tip. How small you may ask, some texts suggest 50% of the Root to be safe in light aircraft, I've seen some provided information on 45% and 40%. I would think too small a Tip might be too flexible.

Hope that helps.
George
Yes, and small wing tips are more likely to stall before the center section, depriving you of airflow over the ailerons near the stall.
Thanks for explaining why Schumann planforms have slightly swept railing edges.
 

Lendo

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There has been a lot of discussion on the size of Wing Tips, but from my research the issue of Stalling Wing Tips can be because some designers that want the look of a nice thin Wing Tip and reduce the Airfoil height from say 15% Root to 12% Tip, do cause the greatest problem. Keeping the thickness % throughout the Span goes a long way to solve this issue as Wings naturally stall first at the area of Largest CL which is at the Root (of exposed Wing naturally).
But too small a Wing Tip can Flex and induce Aileron Reversal. So Strength, Thickness and Size are all part of the overall assessment to best performance.
These are my opinions drawn from 25 years research, however there are always differing opinions, for one reason or another. We are all learning every day and in Aviation nothing is set in cement.
George
 
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