# Rear Bear Vs. The Russian Bear

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#### JimCovington

##### Well-Known Member
Question? Did the 140lbs include instruments and gear?
Yes, if you call it that. It's a foot-launched glider. The carbon dragon lands on a wheel, the magic dragon (I think - it's been a while) lands on a skid. The magic dragon is lighter. You'll have to add more weight for a wheel (maybe) and more weight for engine instruments.

Think about it for a second - you're talking about removing HALF the weight from one of the lightest rigid airframes in the world. It's a VERY light airframe. This plane was planned by people who weighed each part to the TENTH of an ounce - and you're going to remove 70 lbs - ONE THOUSAND+ ounces.

The weight's just not there to remove.

You say you'll get the weight from the wing. The wing is designed to weigh 68.6 lbs. That means you can THROW AWAY THE WING from a plane that is SEVENTEEN INCHES WIDE at the seat and you STILL are over your limit. Of course, with no wing, your aerodynamic profile will suffer somewhat. :gig:

BTW, you can't just ad an engine without an engine mount. That energy has to be transmitted to the airframe somehow. Ooops, more unplanned weight!

Are you beginning to grasp just how impossible your 100lb high-AR high-performance plane is?

Put the BD-5 on a really serious diet.
Again - WHAT are you removing? It's already one of the lightest airplanes in the world! You keep saying you'll "remove weight" but haven't offered anything concrete - just your opinion that skilled designers & builders in front of you have been ignoring one of the MOST important factors when building for years. I don't buy it.

#### Starman

Tony

##### Moderator
Autoreply has said and I believe him that about ½ of the weight factor in a glider is for flutter. At 1/3 the speed the airplane should need a lot less mass to combat flutter.
It's a bit more complicated than that, but the counter-torsion structure is much heavier than the whole spar is.
No PRSU. Probably 16lbs installed. 15Hp on a self launch hang glider needs a re-drive. At the slow speeds that the hang glider flies at it needs the extra mass flow for good thrust. At a faster speed you don't need as much prop diameter to do the trick.
I've been reading about airplanes my hole life, and I've got reasonably good recall, I know it will work. Showing you why is a different story.
Let's look at those remarks for a while.
If you're making a claim you have to prove it, not me to disprove it. I and many others are polite enough to tell you friendly that your ideas (not all of them, but most and most combinations of ideas) are not realistic.
I tell you, it's impossible to have a 16 lbs, 16 HP installed aircraft engine including prop.
Glider pilots are willing to trade or compromise everything, including steep maintenance, reliability and their wives to loose weight. A turbo (30HP-ish foldable engine) is in many environments almost a requirement. Again, lower weight to whatever price and that price is very steep.
So, we have a two-stroke engine plus prop, driven by a belt for a total weight of 37 kg (80lbs). That's the minimum weight, no electric starter (windmilling), no engine mounts (that's not included in the weight), no battery, just an engine, prop (fixed pitch, LIGHT) and a reduction drive. You won't get rid of it since that'll ruin your prop properties, but just assume we can ditch that weight too, that might get us to 35 kg (75 lbs).
How in heavens sake are you going to scale that down to 16 lbs?

I've been discussing with Autists/Aspergers a couple of times and had the pleasure (without sarcasm) to meet (some of) them in real life afterwards as well. Some are capable of more or less understanding the excellent points Topaz wrote, most don't. That majority usually ends up pretty sad "because no-one understands them" and that's a self-reinforcing attitude you don't get away with in real life.

There's a good reason I've told you several times before: "go out and prove us wrong" since reality is the ultimate judge, not the way you communicate, perceive or think, or the way you type some words over the internet

#### Starman

##### Well-Known Member
Very good! I was thinking of a shape like this for my low aspect ratio ultralight because it's the lightest possible shape for the wing area. With this you could meet FAR103 with a 100 pound plane, not counting engine and fuel and maybe landing gear. Are we counting those things yet?

The problem with that design is that there's no view of the scenery from the cockpit, the cockpit should be at the leading edge for good visibility, with the engine at the back for balance.

Here's one with better visibility:

#### JimCovington

##### Well-Known Member
Here's one with better visibility:
There are many who think that's a highly underrated design that had the misfortune to appear at the beginning of the jet age when just about everything with a prop was considered old-fashioned. Since it required big props to neutralize the large wingtip vortices and could't be converted to a pure jet, it got left behind.

Charles Zimmerman and his "Skimmer" | Flight Journal | Find Articles at BNET

It was designed for a 425mph top speed and a 20!mph landing speed. That 20:1 ratio beats the snot out of the 4:1 that's the goal of many designers today.

#### pie_row

##### Well-Known Member
Nothing taken out of context. .
You changed what you wrote and what you quoted of me after the fact. And so this statement of yours is a lie. And in doing this you abused you moderator privileges.

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#### JimCovington

##### Well-Known Member
I think that I've found a way to get what I see in my head about airplanes out past the blender. Autocad. I watched someone use a 3D graphics program and I can use that to get the stuff in my head out.
Excellent! I'm really looking forward to it. There are also some basic aeroengineering programs that allow you to draw planes *and* test them.

http://www.homebuiltairplanes.com/forums/design-structures-cutting-edge-technology/5025-what-software-do-you-use.html

#### Mac790

##### Well-Known Member
8 lbs engine... well, prop, PSRU and respective fairing are all made of Helium?
Theoretically it could be possible, check out this little turboprop

Power 5.62KW (7.5hp)
Diameter 86mm (core engine)
Length 326mm (12.8in)
Engine Weight 1750g (3lbs 13oz)
Ancillaries Weight 200g (7oz)
Propeller RPM range 1200 - 9000 RPM
Wren Turbines Ltd | 44 Turboprop

Seb

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#### JimCovington

##### Well-Known Member
Theoretically it could be possible, check out this little turboprop

Power 5.62KW (7.5hp)
Diameter 86mm (core engine)
Length 326mm (12.8in)
Engine Weight 1750g (3lbs 13oz)
Ancillaries Weight 200g (7oz)
Propeller RPM range 1200 - 9000 RPM
Wren Turbines Ltd | 44 Turboprop

Seb
So cute! You measure its weight in grams, its fuel flow in ounces, and its lifespan in minutes.

#### pie_row

##### Well-Known Member
As for engines, most European engines are about 1/3rd the size of an American, use about 1/3rd of the fuel and have more torque and power at much lower weight and size. A V8 is nice in a dragster, but otherwise completely the wrong way to go for a normal car. It's unwise at least to have a 3, 4 or 5 liter V8 when a 1.5 liter L4 with turbo does the same with all the aforementioned benefits..
I love it when someone argues and actual believes both sides of the same argument. I really do.

What a lot of people really want is a 454 chev V-8 from before emission conrtols went in. (7.5L)

#### Mac790

##### Well-Known Member
... and its lifespan in minutes.
Rather in hours, it seems that the maintenance is required after 50 hours or 500 million revolutions. Model Jet Club - Turbines.
The Wren Company has more than 20 years of experience with those engines, so I think that they can build an engine which last more than few minutes, plus I really doubt that someone would pay 3000-6000$for so unreliable engine. Also I have more belief in those engines than in 50lbs titanium structure. This idea isn't new. [video=youtube;sEMFhEGgCUM]http://www.youtube.com/watch?v=sEMFhEGgCUM&feature=fvw[/video] Seb Last edited by a moderator: #### JimCovington ##### Well-Known Member Rather in hours, it seems that the maintenance is required after 50 hours or 500 million revolutions. Model Jet Club - Turbines. The Wren Company has more than 20 years of experience with those engines, so I think that they can build an engine which last more than few minutes, plus I really doubt that someone would pay 3000-6000$ for so unreliable engine.
Seb
1) Sure people would pay that for an unreliable engine - it's going on a model airplane, after all. Crashes are a part of the hobby.

2) Their website says they've been doing it for 10 years, not 20. How many engines have they made?

3) The Wren factory site (not the distributor) says that "maintenance" may be required after 25 hours, not 50. Hmmm...your numbers aren't looking so good.

4) It's not maintenance, it's a bearing change - which is an overhaul. Changing oil is maintenance. Changing bearings is an overhaul.

So let's sum up - We have a engine that offers less time between OVERHAULS than most engines do between OIL CHANGES. It's got a TBO of 25 hours, which is 1500 minutes - less than the number of HOURS that most aircraft engine manufacturers allow.

So yes, its lifespan is measured in minutes.

And I know it's not a new idea - at least TWO!!! human-carrying aircraft have been powered by these engines. But that doesn't mean it's a practical - or even good - idea.

I am sure more airplanes will be built with these engines. But I'm also sure they'll be just novelty* acts for the foreseeable future.

*The two flying (that I know of) are novelties.

1) The jet wing requires launching from a mothership and cannot climb from sea level due to fuel/payload constraints.

2) The jet cri-cri uses almost 5lb of fuel PER MINUTE at full throttle. It's fuel load is barely FAA-legal.

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