BD-5 - Why is it so engrained in our psyches?

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Tom DM

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We can discuss flying wing stability in a different thread...they can be extremely stable without FBW or other computer-aided augmentation...if designed correctly. I can testify to this; I have flown a few and am currently developing one!

Anyways, back to the BD-5!

Do not testify: show it

Flying wings are inherently efficient, so big interest here. Get a new thread :)
 
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Allen is a master fabricator, very knowledgeable on the art and an all around good guy. He showed me around his Wingco shop many a year ago and got to see the plug he used for the Atlantica. The thing looked like a curved mirror- not a flaw on it. It was just not a good design, and thankfully, nobody got killed.

We can discuss flying wing stability in a different thread...they can be extremely stable without FBW or other computer-aided augmentation...if designed correctly. I can testify to this; I have flown a few and am currently developing one!

Anyways, back to the BD-5!
I agree entirely that a flying wing can be designed to be positively stable. However, it will not have the big L/Ds, etc without relaxing the stability. Allen was trying to duplicate NASA and Boeing efforts on BWB not realizing the experimental vehicles had relaxed stability.
 

AndyCapp

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Are you absolutely sure about that? A 2-stroke Rotax 582 is not exactly a high torque output motor. Also, a prop of that size running at that kind of speed would be a tad 'loud'...because the blade tips would be well beyond supersonic. The Tu-95 Bear is loud because the tips are transonic, and the XF-84H program was cut short because its supersonic prop created a plethora of noise and handling problems (among other issues). Without knowing the exact diameter (I'd guess about 48 inches based on pictures), hear me out:

The circumference of a 4-foot prop would be 12.5664 feet. Multiply that by the aforementioned 7200 rpm, then dividing by 60, you're talking about a tip speed of 1507.96 feet per second. The approximate speed of sound in 20C conditions is around 1125 feet/second, giving those blade tips an approximate Mach speed of 1.34. Pretty doubtful that a direct drive Rotax 582 can pull that off.

I've never seen a 582 without a PSRU outside of overhaul...much less one being run without it. I'd say the prop speed is significantly less than the 7200 RPM you are referring to.

Not trying to break nuts, but if you are willing to show a photo otherwise, I'll be happy to eat crow!
Hi 007,
Sorry my bad. What I meant was that the Rotax does not have the gearbox attached, but is connected via a flex coupling then through the standard belt drive with the necessary reduction pulleys.
 

AndyCapp

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...And probably using one of the available cog belt reduction systems to move power from the crankshaft up to the broomstick shaft. By "direct drive" he probably means that the engine doesn't have a Rotax gearbox on the provision end.
Exactly
 

pylon500

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Turning the 582 at 7200rpm must be giving you close to 70hp, although the Rotax manuals suggest your power is starting to drop off even before the rated 6800rpm redline. Your inlet and exhaust system look pretty standard, so I'm surprised it's breathing so well.
So, many other BD-5's in SA?
 
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Gotta love the ads that say “complete
"Complete" when it comes to BD-5 kits only means that everything the original purchaser got is still there. Lots of critical little things never got shipped. Not just the drive system but for the landing gear as well.
Common things missing are the forgings to attach the main spar to the fuselage skins, the machined and hardened gear pivot pins, and the castings to attach the axle to the glass gear spring. The only way to know is to buy the kit, go through the plans and inventory the parts piece by piece.

$650 is probably worth it if it has B wings and a good canopy ........ and you really want a BD-5.
 

TFF

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It is a steal at that price, but don’t expect miracles like the original dreamers. Think of every part as one you just started yesterday. It’s there, it has shape, but still needs 3-4 more days until it’s useable to be fitted. Then of course there is fitting time.
 

daveklingler

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There seem to be two different airplanes under discussion here:

1. An early airplane kit introduced in 1971 that failed mostly for lack of availability of the powerplant around which the design was based. By today's standards, the kit was crude and incomplete, but some of the designer's ideas turned out to be good ones. The airplane was very pretty, took a long time to build but potentially less time than other scratch-builts of its era, and tried to be economical with its snowmobile powerplant.

2. A cluster of memes popular among pilots and builders with very little basis in fact. The "cluster of memes" airplane seems to inspire very strong emotions, including one poster here who even expressed his opposition to BD-5 flight simulators.

Here are three quotes from pilot reports:

Les Berven:
"Both the looks and the performance of the BD-5 are excellent, but the thing that really makes this little airplane great is the flying qualities. Almost invariably the first question everyone asks is "Isn't that fast little short-coupled airplane going to be awful sensitive and hard to fly?" The answer is absolutely not! "

Bud Davisson:
"Now, almost nobody reading this is going to believe my next statement, yet it's absolutely true: the BD-5 is one of the most stable little airplanes flying. When I'd set it up hands-off and then pulse the stick–just bash it forward or back–the nose would come up and then–bam–come back to level and not move again. There was almost no sign of oscillations of any kind. The same if true of yaw: punch rudder, and the nose snaps back as soon as you let go. In roll it seems just a little more neutral. The wings stay pretty much where you put them. I tested all this stability out by grooving around for a while while I used both hands to adjust my headset and boom mike to eliminate some communications problems (which turned out to be my inability to read "volume" one the radio face)."

Bob Grimstead, Pilot Magazine, from the article posted earlier about the crash of a BD-5 that was at least 200 pounds overweight:
"I can only say that, despite initial misgivings, I was mightily impressed with this little aeroplane, which is better sorted, with superior control and stabilities than most production machines, peerless visibility, and matchless performance and economy."

From HBA's Tinbuzzard, who actually has one:
"Absolutely perfect thought controlled handling with its side stick, not twitchy at all! Excellent stability in all three axis, with proper damping of induced upsets. Any halfway competent pilot wouldn't have problems with mine once they got used to the low seated position over the ground and the different speed cues that causes. Once airborne, it handles like a much bigger aircraft stability-wise, although it is quick, with a 360 deg. roll rate of little more than a couple of seconds!"

And HBA's AndyCapp, who also has one:
"She is a blast to fly. Landing speed is a little on the high side @ 80 MPH. Takes some getting used to when on the ground due to the low riding position. Mostly flying is done via the trim once aircraft is setup. When flying attention needs to be given to air speed and throttle management as the plane has a very low inertia due to its low weight and loses speed rapidly."

So as far as the airframe goes, it's not twitchy or difficult to fly or any of the other criticisms that have been leveled here at the "cluster-of-memes" airplane. The BD-5 is a real airplane, stable and fun to fly, much like Bede's other designs. Bede knew how to design an airplane, and he wanted to innovate.
 

daveklingler

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Regarding the safety of the BD-5, it seems to relate to two major issues:

1. Despite the number of kits sold and shipped, the design powerplant didn't appear until after Bede's bankruptcy. The design never achieved a "best practices" experience base or an ecosystem like other designs have. One example would be the KR-2 scratchbuilt that came along in 1972 and has developed into a great little aircraft, despite its initial shortcomings (see this month's Kitplane article).

2. As a pusher with a low CG, it has the same issue as many amphibs, in that the engine is mounted up high and there's a consequent moment arm that requires experience to get around for someone flying the aircraft for the first time. That moment arm causes a quick stall in the event of an engine failure. In Bob Grimstead's words:

“Its one significant failing is that it pitches up after engine failure. If you don’t catch the pitch-up within two seconds (the FAA’s assumed fit, professional pilot’s reaction time) you can’t prevent it stalling. Depending on span and aerofoil, stall recovery takes around 500 feet. After that it’s fine, if you’re still above ground."

The lack of a developed powerplant meant that a lot of builders chose engines that were wildly overweight. Combining a grossly overweight airplane with the second problem, a quick pitch-down pitch-up in the event of an engine failure, seems to kill most BD-5 pilots sooner or later. Compounding that problem, some of the builders chose to go with the shorter "A" wings for extra speed.

Blame for those fatalities should be placed squarely on the shoulders of the builders, not the design or the designer. Frankly, it would be safer to put an O-540 in a KR-2. The Hirth engine that the BD-5 was originally designed for finally arrived and is currently available, as are lots of engines of comparable weight and power. Honda and Mazda engines are just crazy.
 
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daveklingler

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Why is it still engrained in our psyches? It's a very elegant and efficient design that promised to be something an ordinary builder could build in his garage and fly. The ensuing delivery problems, engine problems and bankruptcy left a lot of people angry and frustrated. Those that try to finish one run into the difficulty of designing their own airplanes.

It also turned out that building an aluminum aircraft was no easy thing. It wasn't until much later that Van worked out how to make aluminum aircraft fast and easy to build, with the help of CNC machinery. (BD-Micro, incidentally, will pre-drill your BD-5 parts for you, 50 years later.)

There are many people that would still love to have a flying BD-5 or something like it. The result is that many of us still sigh when we think about them.

And some of us have settled for Rutan's not-quite-as-fast consolation prize, the Quickie.
 
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Dan Thomas

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“Its one significant failing is that it pitches up after engine failure. If you don’t catch the pitch-up within two seconds (the FAA’s assumed fit, professional pilot’s reaction time) you can’t prevent it stalling. Depending on span and aerofoil, stall recovery takes around 500 feet. After that it’s fine, if you’re still above ground."
Because it's light and it's short, bad stuff happens quickly, and a lot of pilots that learned to fly in Cherokees and 172s weren't prepared for that, and Bede didn't warn them.
The lack of a developed powerplant meant that a lot of builders chose engines that were wildly overweight. Combining a grossly overweight airplane with the second problem, a quick pitch-down in the event of an engine failure, seems to kill most BD-5 pilots sooner or later. Compounding that problem, some of the builders chose to go with the shorter "A" wings for extra speed.

Blame for those fatalities should be placed squarely on the shoulders of the builders, not the design or the designer.
Oh, but this is experimental aviation, doncha know? Anything goes. We get that all the time here when we try to point out the shortcomings of some "new" idea. There is no lack of people who want to add safety by adding weight in the form of more structure and beefups. They're not thinking about the rise in stall speeds, the altitude required for recovery, the increased risk of spin if that extra weight moves the CG aft, and the loss of glide range.

Bede's promotion of the thing before it was complete was unethical. Too many lost their shirts on it, had their dreams shattered, or killed themselves in it because they ended up with some dangerous homebrew systems, or had inadequate piloting skills.

The KR-1, on the other hand, was easily within the reach of anyone that had some money to buy some spruce and some plywood, some foam, some hardware and wheels, and could convert a VW engine or could afford to have someone convert it for them. Aircraft-quality spruce was widely available and not nearly as expensive, adjusted for inflation, as it is now. VW engines were everywhere, though they could sometimes be pretty worn out. An engine from a newer wreck was a good bet.

But the KR-1 didn't look like a little rocket like the BD-5. Emotions often figure heavily in selecting a design. I remember Budd Davidson warning us about that way back in 1975 or so.
 

BJC

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Almost invariably the first question everyone asks is "Isn't that fast little short-coupled airplane going to be awful sensitive and hard to fly?" The answer is absolutely not! "
Lots depends on the pilot’s experience. My friend, a Navy test pilot, had never flown anything as sensitive as the BD-5. His first, and only, takeoff led to a crash due to PIO. That would not have been an issue for a pilot with time in many homebuilts.

Another friend / coworker / father of a classmate was a navy jet pilot with combat experience in Korea. I convinced him not to build a BD-5. He built a Lancair 320, but was not really experienced with the big airbrake (constant speed propeller) out front. He got slow on his first final approach, got into a high sink rate, hit the ground and burned to death. For flying time to be an asset, it needs to be relevant to the aircraft.

What I may deem to be easy to fly, others may have a problem with. What they find easy may be an impossible challenge for me.


BJC
 

Dana

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And some of us have settled for Rutan's not-quite-as-fast consolation prize, the Quickie.
The Quickie is in an entirely different class.
Another friend / coworker / father of a classmate was a navy jet pilot with combat experience in Korea. I convinced him not to build a BD-5. He built a Lancair 320, but was not really experienced with the big airbrake (constant speed propeller) out front. He got slow on his first final approach, got into a high sink rate, hit the ground and burned to death. For flying time to be an asset, it needs to be relevant to the aircraft.
Both are airplanes that are unforgiving when things go wrong, and the high speed means the energy to do serious damage to the aircraft and occupants, and little time to deal with it. The Titan T-51 is another example.
 

TFF

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With my old employment, the pilots who were hardest to train were the ones that were military trained. The military did a great job of job specific training. That’s why they get to fly a T-38 at 500 hours or some such low number. It’s their job. 500 hrs GA, buying fuel, might be Bonanza grade for the regular pilot. Out in the wild, one has to push yourself past the trainers. No one will do it for you. The issue with many military pilots is they think they got it because they are “ downgrading “ with GA. The pilot part is fine, they forgot they were made to transition new planes through training at work, where in GA you have to ask. Smart ones ask. They are quick studies because they are pros, but anyone can be out of their element and need acclimation.

BD5 is kind of the last single seater of the original homebuilts. When it came out, the two seat Pitts was only a couple of years old. Pitts were mostly singles, RV3, the tamer stuff like Flybaby and Baby Ace. The 70s was the two seat revolution. There was still much to the cowboy test pilot thing of the BD. The 70s was the first step of buy and fly. Before it was a very small group that was successful. In some ways it’s the end of the old ways and start of the new ways.
 
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