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

[BBerson]

I cruise at [email protected] 6200RPM.

Cool. What is the prop rpm?

 

[PMD]

Hi Gents,
I own and fly a BD5-B for the past two years as well as a Mooney M20j. See photographs. It is powered by a Rotax 582, 65hp silver top engine driving a 42x42 prop. I have more than 10 hours on her since I managed to get her Re-certified after 40 years standing in a Hanger. I cruise at [email protected] 6200RPM.

Are you using the damping within a Rotax gearbox to drive the prop shaft? What can you tell us about the driveshaft length, diameter, materials, couplings? Just getting one of these airplanes in the air at all is quite an accomplishment. Racking up some hours is even more impressive.

 

[Phenomdriver]

I sold one in January 2020 to a builder in Northern Idaho. Never got to the engine and drivetrain stage. I bought numerous parts from Skeeter and Richard Karnes at BD Micro and also from the guy at SD Gillespie Field during my last days with it. The neighbor kids thought I was building a rocket to go to the moon.

 

[SpruceForest]

Good discussion on sims. My suggestion that kicked it off was actually focused on part-task training to get the right response the first time out in the aircraft. We did this in military and contractor sim training for all the stuff that stood a pretty good chance of bending the aircraft if crew response was not as desired. Example would be fam with T-tail over-rotation or practicing engine loss in certain corners of the flight envelope. Pretty much useless for some stuff, even where fidelity in the flight model and motion base was capable.

Re: kids... I think they do so well because the sims are NOT that immersive, which reduces the effects of that cognitive over-load that instructors see so often where new aircraft/new tasks are involved. Once in a real aircraft, the net load is reduced (they can at least manipulate the flight controls and have some idea of power/pitch, etc.), so more stuff can be covered before saturation.

 

[PMD]

IMHO sims are a great thing to help you fly an airplane better, but a HORRIBLE way to LEARN to fly.

 

[djfawcett]

Case 1 in point:

Many years ago, Wingco (the group that fabricates the fast-build options for the Velocity line) developed the Atlantica blended wing-body aircraft. On their website, they openly talked about how they used X-Plane to 'test & refine their design'. Only one problem with that. Yes, you can create and simulate aircraft on X-Plane. We have done it with our all-wing design we are currently developing. However, like any analysis model, the "BS in, BS out" rule is in full effect. Wingco had a bad model in the software...and it manifested itself into an accident (inadvertent takeoff) during high speed taxi tests that severely damaged the aircraft and injured the pilot.

The Atlantica accident was more about the pilot's lack of knowledge when dealing with flying wings. He actually did attempt to fly. But during takeoff he attempted to rotate against advise.......big mistake. With a positively stable flying wing, the aircraft has to fly off the runway. When rotating, the pilot will induce a forward drift of the neutral point resulting is reduced stability and possibly negative stability. What the pilot attributed to hit a runway bump and gust of wind was actually a pitch up induce by his actions. Result, BOOM, a bunch of money lost, and an injured pilot.

 

[Pops]

Hi Gents,
I own and fly a BD5-B for the past two years as well as a Mooney M20j. See photographs. It is powered by a Rotax 582, 65hp silver top engine driving a 42x42 prop. I have more than 10 hours on her since I managed to get her Re-certified after 40 years standing in a Hanger. I cruise at [email protected] 6200RPM.
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. Attention must also be given when cycling undercarriage and flaps as the pitch attitude changes instantly when any of the two changes are made.
I had a serious incident 3 weeks ago when the canopy opened straight after take off. Opening would not have been an issue if the canopy moved straight back, but in my case it twisted sideways causing a lot of drag.I managed to do the circuit with one hand holding onto the canopy and the other flying the BD. I have since fitted the same latches as the Jet pilots use. Just for interest I am a low time pilot with only 290 hours.

One time when taking off flying my Falconar F12 I didn't latch the rear latch on the gull wing door on my side. I had to fly the pattern with one hand trying to hold the door down and not ripping off and fly the airplane with the other hand. Center stick on the 2 place side by side and also center flap handle and elevator trim and throttle on the left side. Had to build a new door.

 

[AndyCapp]

Cool. What is the prop rpm?

Unfortunately I do not know the reduction ration from the engine to the prop. Th engine is direct drive

 

[AndyCapp]

Are you using the damping within a Rotax gearbox to drive the prop shaft? What can you tell us about the driveshaft length, diameter, materials, couplings? Just getting one of these airplanes in the air at all is quite an accomplishment. Racking up some hours is even more impressive.

The couplings and drive shaft is as per OEM (original plans). The Rotax is direct coupled with no G/box. Take off RPM max is @ 7200. Static RPM IS @ 6200. Weight and Balance is very important to get correct as you only have 3'' margin. I think the BD would have been an astounding success if the Rotax engine was available earlier.

 

[BoKu]

Hi Gents,
I own and fly a BD5-B for the past two years as well as a Mooney M20j. See photographs. It is powered by a Rotax 582, 65hp silver top engine driving a 42x42 prop...

Just curious, do you have a special warmup regimen you use to bring the engine up to temperature?

 

[AndyCapp]

Just curious, do you have a special warmup regimen you use to bring the engine up to temperature?

Yes I actually do pay strict attention to the warmup. I will start the engine and by using a fuel pump to inject a quick quirt of fuel into the intake as I do not have a mechanical choke on the carb's. I would let the engine run at low 1500-2000 rpm to warm up till operating temperature. I have a radiator in the belly with a scoop to channel air as well as a electric fan. No overheating issues.

 

[cblink.007]

With a positively stable flying wing, the aircraft has to fly off the runway. When rotating, the pilot will induce a forward drift of the neutral point resulting is reduced stability and possibly negative stability.

During my case study, all the literature I got my hands on made no mention of an actual flight attempt when this accident occurred, only a high speed taxi test with a runway hop.

In either case, I am very familiar with flying wings!

 

[cblink.007]

The couplings and drive shaft is as per OEM (original plans). The Rotax is direct coupled with no G/box. Take off RPM max is @ 7200. Static RPM IS @ 6200. Weight and Balance is very important to get correct as you only have 3'' margin. I think the BD would have been an astounding success if the Rotax engine was available earlier.

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!

 

[TFF]

He is probably running a sled engine not an airplane engine.

 

[BoKu]

He is probably running a sled engine not an airplane engine.

...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.

 

[cblink.007]

...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.

This is what I am thinking he is running- a sled engine belted from the crank to the prop driveshaft, maybe a 2.4:1-ish reduction ratio?

There is a local guy with a prop-driven BD-5 collecting dust in a hangar corner....I am actually curious to see it now, but its owner hasn't been seen at his hangar for months. I know the airport manager wants him out- that hangar is a storage unit for this guy (but that is another topic of discussion).

 

[Hot Wings]

Here is the de-facto standard BD-5 drive system.

 

[Hephaestus]

The couplings and drive shaft is as per OEM (original plans). The Rotax is direct coupled with no G/box. Take off RPM max is @ 7200. Static RPM IS @ 6200. Weight and Balance is very important to get correct as you only have 3'' margin. I think the BD would have been an astounding success if the Rotax engine was available earlier.

Any chance you'd share some pictures? I'd love to see/understand configuration and how cooling was handled.

 

[djfawcett]

During my case study, all the literature I got my hands on made no mention of an actual flight attempt when this accident occurred, only a high speed taxi test with a runway hop.

In either case, I am very familiar with flying wings!

Hi, the investors on the program had hired me to look over Shaw's shoulder. Allan is a nice guy, but was he ever strong headed. Anyway, it came close to costing him his life. What makes a BWB work as advertised is relaxed stability, which means a fly by wire system.

 

[cblink.007]

Hi, the investors on the program had hired me to look over Shaw's shoulder. Allan is a nice guy, but was he ever strong headed. Anyway, it came close to costing him his life. What makes a BWB work as advertised is relaxed stability, which means a fly by wire system.

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!