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J.L. Frusha

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I still dont think you grasp thrust line vs center of mass .
I am talking about horizontal thrust line and horizontal CofM
Vertical CofG is something else

Let me greatly exaggerate ....
--- Place your engine on a mount 25 feet above your machine
--- give it full throttle
--- will your aircraft move forward or fall on its nose ???

.

I understand EXACTLY what you mean. Perhaps I can state this more succinctly...

For a straight 1/2 VW Engine directly driving a propellor, the thrust line will be higher than preferred, without redesigning the fuselage.

I DO NOT WANT the added weight, expense, or maintenance of a REDUCTION DRIVE, if I can possibly avoid it, especially over a few inches difference.

Just because I've been busy doing other stuff doesn't mean I won't be reworking the pic to move the engine and prop lower. It ain't much, but I DO have a life and a family outside of this forum.
 

Victor Bravo

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Trust me on one thing here - do NOT take offense or feel "attacked" when some or all of us start poking at your idea, or pointing out why X will not work but Y will work, etc. Trust me, I'm giving you good advice. There are plenty of people here who are smart, stupid, and everywhere in between. Spaceship engineers and cow-turd shovelers, nice people and nasty people.

Constrain your thoughts to figuring out whether the prodding and poking and challenging is technically valid, and forget completely about the personality of the guy or girl challenging you. Even if the person poking at you is doing it like a total moron, or looking down their nose at you.

If you are able to accomplish this, you are getting very valuable free data, very valuable outside "eyes and ears" put on your idea, etc. I'm not saying it is easy, because the way some people come across on a forum can be totally different than they would come across if you were standing together in a hangar or workshop.

But if you let a hundred critics and naysayers take pot shots at your idea, and the idea technically/mechanically survives the challenges... you will have gained tremendous confidence in whatever the idea is. If the peanut gallery here manages to show the idea to not be technically sound, then you got incredibly valuable information at zero cost, and saved some amount of time/money/engineering that would have been wasted.

All you have to do is just not get personally bothered or insulted by people who think, or write, differently than you.
 

J.L. Frusha

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YES ... your thrust line is is up on the wing ... (draw a straight line through prop and engine) ... (sideways view)

... your center of mass would be about your chest height (sideways view) ... draw a straight line through it (parallel to thrust line)

... your thrust line would be at least 36 inches above center of mass .... very high .... full thrust wants to push you both forward and nose down .... the exact opposite of what you want on takeoff and for stable flight .

.

Research early gyrocopters ... many had high thrust lines (8-12 inches) ... no tail feathers .... they tumbled out of the sky on a regular basis .... lowered thrust lines combined with horizontal stabilizers now make them very safe.

In your case the engine mounted behind the seat might work OK (similar to gyrocopters)

.

.

It won't move significantly without cutting through necessary wing structure. It stays more-or-less where it is.

It can be angled, but that cuts efficiency and efficacy significantly.
 
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Victor Bravo

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Here is my take on what would fix some of the larger issues with JLF's wing:

Two smaller engines mounted on a spanwise tube that mounts to the main upright fuselage member. Smaller engines turning smaller diameter propellers, but two of them. Puts the thrust line much further down, and also keeps the mass of the engines further out from the CL, so the structure can be a tiny little bit lighter.

Fruscha STOL Wing.jpg
 

J.L. Frusha

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Here is my take on what would fix some of the larger issues with JLF's wing:

Two smaller engines mounted on a spanwise tube that mounts to the main upright fuselage member. Smaller engines turning smaller diameter propellers, but two of them. Puts the thrust line much further down, and also keeps the mass of the engines further out from the CL, so the structure can be a tiny little bit lighter.

View attachment 120902
That could work. I'll see if I can find a Cri-Cri/Cricket, scale it and put it together.

It would also get the props clear of the draggiest part of the plane... Namely, the pilot.
 

Victor Bravo

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No need for finding a CriCri, this is a totally different configuration on a much lower speed / higher drag airplane. CriCri is 95% irrelevant IMHO.

Pick two small, cheap 18-20HP "paramotor" engines, Simonini, Zanzottera, Polini, etc. There's probably Chinese clones for cheap if you need it.

Mount them on maybe a 2 or 3 inch square 6061-T6 aluminum tube, .063 wall or something like that. We got guys here who can fine tune that with numbers.

Make the tube long enough that the inboard propeller tips are at least 6-9 inches apart so the irflows don't screw with each other.

Make a (free) scrap foam and tape fairing over the square tube so the turbulence doesn't mess with the propeller inflow too badly.
 

Aesquire

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I love it!

Naturally I have suggestions. ;)

A.
First, I get the budget constraints on models. Guys that already own the expensive and need to learn how to use RC gear automatically go to that "better solution". Plus they have years of experience controlling a model that is at off angles. There's a great low budget cheat.

Build glider ( duct tape a rock where the engine goes ) free flight models and get the general shapes and relationships figured out. Don't bother with complex slats on the first ones, a fixed slot is easy to carve in foam & you can tape over it. Take it to a local RC glider hill once you've got it flying really good in your back yard, and be friendly and receptive to the special modeling ideas they have.

Here's the CHEAT! At some point, when your cheap free flight model actually impresses a local you've met. Offer to build the next one with places for the RC servos, and maybe motors, and give it to him to finish and test fly while you observe and learn more. He's going to be much better at skills ( than any inexperienced RC idiot, like me ) and the time before he wrecks it much longer. ( may be weeks, instead of first try )

If your ideas are good you might have multiple models in multiple hands, be a published model designer, and have guys begging you to make them one, please! And dropping off minivans full of foam boards and supplies.

Meanwhile you will have refined your design so the full sized almost final version actually works well.

B.
Don't get too married to a particular feature. Function over pride, every time.

For example, if you already OWN a half-VW engine set up with a prop hub, then sure, your budget limits you. Use it. If you don't already own one, then the best budget solution might be getting used paramotor packs on Craigslist. That's a Terrible idea if you want to paramotor cheap and aren't already an expert on fixing high power tiny 2 strokes and inspecting welds! But may be the cheap and smart way to get a working engine, mount, PRSU, and the hands on experience of rebuilding them. Cheap.

Or if it turns out those lovely leading edge slats inspired by a Superstol are unnecessary, then don't waste money and mass on vanity. ( I like them! They have been great performance enhancers on many designs for a century )

C.
Detail thoughts? Configuration opinions.

I don't know diddle about free wings, Spratts, etc. The guys who love them think they're Awesome, but I don't know how well they actually work. I'm skeptical and ignorant. So... No informed opinion.

I like Junkers type ailerons because they make wing construction easier at the cost of some drag. They Work. See Kitfox.

The bad news is on a forward swept wing they may suck as elevons. The good news is your design has a tail in the perfect place ( as far back as possible ) for a decent horizontal stabilizer and elevator. Not, perhaps, as sexy, but that is proven to work.

The biggest advantage of a wretchedly conventional tail, ;) is it gives you the best leverage to overcome pitching moments from airfoil and engine placement. The rest of your design ideas are easily groovy enough to compensate for the one conservative feature that will make it work much better. ( not sarcasm, open ego manipulation! )

Carry on! Neat!
 

Jay Kempf

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There are numerous flying wings with little, or even no vertical stab, from the Hortons and before, through the B1 Bomber.
Did not imply or try to say there weren't successful flying wings. Working on a flying wing program right now. What I said was there aren't any with LE slats, or traditional flaps for that matter or the combination of the two which you find on almost all heavy airliners.

Your reference to the Hortons is interesting. Have you looked into their systems for yaw control and the PIREPS from all that testing? And your reference to the B2 bomber I assume not B1 is interesting because the only reason that program is successful is because of active fly by wire controls that are constantly adjusting making it flyable. It is too much pilot load to fly by hand.

So careful casually referencing solutions to your problem when your references are actually going against your claims not supporting them. S&C is a tough science but well established. Very math intensive but fascinating. Just looped back to the main difference between you and those you reference: forward sweep vs. aft sweep. Forward sweep is actually less stable in yaw.
 
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Map

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Make sure you understand how to balance the various pitching moments at all angles of attack. Flying wings have the disadvantage of having very short elevator arms that can only balance very small changes in pitching moments. I have participated in building a flying wing glider (SB-13) and have also flown it, so I have some first hand experience.
 

J.L. Frusha

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No need for finding a CriCri, this is a totally different configuration on a much lower speed / higher drag airplane. CriCri is 95% irrelevant IMHO.

Pick two small, cheap 18-20HP "paramotor" engines, Simonini, Zanzottera, Polini, etc. There's probably Chinese clones for cheap if you need it.

Mount them on maybe a 2 or 3 inch square 6061-T6 aluminum tube, .063 wall or something like that. We got guys here who can fine tune that with numbers.

Make the tube long enough that the inboard propeller tips are at least 6-9 inches apart so the irflows don't screw with each other.

Make a (free) scrap foam and tape fairing over the square tube so the turbulence doesn't mess with the propeller inflow too badly.
I meant to get the image for the Engines and props, not the plane itself... IF I have to, I can add a Horizontal Stab/Elevator. Don't think I'll need to.

Used the Spinner to make the pod... Mount it on a strut, instead... (positioned correctly for the FSW)

1642895308688.png
 
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TFF

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The wing drawing looks like a Comet Sparky wing swept forward with the ailerons added. My first flying model was a Sparky.
 

Martin W

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Here is my take on what would fix some of the larger issues with JLF's wing:

Two smaller engines mounted on a spanwise tube that mounts to the main upright fuselage member. Smaller engines turning smaller diameter propellers, but two of them. Puts the thrust line much further down, and also keeps the mass of the engines further out from the CL, so the structure can be a tiny little bit lighter.

View attachment 120902
.

THANK YOU ....... that is exactly what I was trying to explain to J.L.F.

.
 
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Don't forget, the wing is forward swept.

I did. 😖
Was just looking at the center line view. Sweep could significantly change the longitudinal CG of the air-frame.

Probably more work to reconfigure than cutting from scratch.
Maybe not? Take a look at the old Ken Brock Avion. Making all of the little 'trivial' parts takes more time than we generally think they will.

It can be angled, but that cuts efficiency and efficacy significantly.

This bothered me too - until I did the trig. The loss of thrust and added download on the wing is actually very minimal for small angles.
Sin(10deg) = 0.173 Cos(10) = 0.984
200 pounds of prop thrust = 196 forward and 35 down at 10 deg.
 

Aesquire

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I'll point out we have an entire thread with spin offs dedicated to one member's actually flying aircraft dealing with the unwanted effects of a high thrust line. Worth looking through even if you disagree with various folk's posts and opinions.

But there are several actually successful flying machines that have high thrust lines and can be flown with proper tail design and pilot technique. It's a Very Real Thing you deal with when applying power and having to compensate.

there have also been spectacular Failures.

I will point out 2 "bad failure examples" from recent history . ( one I have witnessed personally )

1. In gyroplanes, a thrust line above the vertical CG applies a variable nose down force. Normally the balance of forces works out ok. But in turbulence, or by sudden nose down control application, the lift & stability of the rotors may drop below a critical level, and thrust may push the nose down in an unrecoverable almost always fatal crash called "bunting". Think tumbling end over end shedding parts and flailing rotors hitting the airframe until total destruction Impact.

The "cure" in designs that have the thust offset issue, is often a fixed horizontal stabilizer to damp the pitching movement. See multiple threads here on subject.

Also "special piloting techniques" MUST BE LEARNED to safely fly gyros. My own learned response to sudden lack of wind noise, prompt nose down pilot input , learned on low powered, & unpowered, draggy, slow craft often flown low & close to stall speed, is Exactly The WRONG reaction on a gyroplane.

2. One early idea for putting an engine on a hang glider, so we could fly when there wasn't good wind speed and direction on the limited sites available, was to bolt the engine to the kingpost.

That had a LOT of advantages. The balance on take off, flight, landing was minimally affected. The spinning prop was away from the fragile squishy pilot. It was really easy to engineer the mounts. The kingpost was easy to remove and store separately from a wing you didn't want to spill gasoline and oil on.

Unfortunately... When you stalled under power, or hit turbulence that caused momentary low Gs, the aerodynamic balances... Kinda vanished. Leaving a screaming engine rotating the craft into a forward tumble ( some times recoverable as the terms Plummet and Ballistic applied but not necessarily ) resulting in pilot falling into wing, structural failure, and Bad Results. This before full airframe hand deployed parachutes were commercially available. And with a very very low probability of escape from the tumbling mess of wadded high strength sailcloth, nigh unbreakable cables, and jagged aluminum tubing, with a gyrating screaming engine flailing the plummeting tangle with shattering prop blades.

Although there was seldom a decent Hollywood fireball. Just a smoky melting plastic shroud.

So we don't do that anymore.
 

Tiger Tim

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I couldn’t help myself, I made one at about 1:24 scale to play with.
D6356BB3-11BD-4D37-829F-DCA44E181559.jpeg
8A09867A-1407-4B00-99D9-FF21C4EB0B76.jpeg

It’s crude but it only took twenty minutes to make out of stuff I had lying around for a total cost of zero dollars. It still needs elevons and for the glue to fully dry, then I’ll toss it around and see how it goes.

Of course a little chuck glider really shouldn’t be a final go/no-go on a design but I think it’s a fun way to mess around with a configuration and it’s a decent first step to seeing if the thing can even be stable.
 

J.L. Frusha

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I couldn’t help myself, I made one at about 1:24 scale to play with.
View attachment 120913
View attachment 120914

It’s crude but it only took twenty minutes to make out of stuff I had lying around for a total cost of zero dollars. It still needs elevons and for the glue to fully dry, then I’ll toss it around and see how it goes.

Of course a little chuck glider really shouldn’t be a final go/no-go on a design but I think it’s a fun way to mess around with a configuration and it’s a decent first step to seeing if the thing can even be stable.


Love it!

Busy building a Coal Forge for knife making. Of course, I couldn't copy the ones from the internet, so mine is more of a PITA to make, and somewhat messy, too. Hopping online while stuff dries atop our radiant heater, then making more pieces as the first batch dries.
Swiping some of the design from traditional Japanese forges and smelters, but using my variant of the cookie-dough intumescent insulation. Once it's proven, we'll be releasing stuff on YouTube.
 
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