# Bd-5B

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by stikmunkey, Jul 23, 2010.

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1. Mar 26, 2019

### Scheny

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I don't think they actually did modify it a lot at all... If you look at the plans, they just put it in where it would fit. That's why the exhaust is where the propshaft would be and also why they put it at an angle.

As for the safety: I am not aware either of any plane this size having safety (JSX pretends to be safe as they offer an optional BRS...). This is why our Beast One is designed as a BD-5J alternative with good stall characteristics, low landing speed, good longitudinal stability, a safety cell and a BRS.

The safety cell is designed for 30G, while the nose incorporates a 2 feet crash attenuator design followed by a one feet severity reduction element (damper+antisnag) all derived from formula one by our chassis experts (final layout will start in September).

As for the "good flight behaviour" of the BD-5: Longitudinal stability is below any standard while landing speed is rather high. If the engine fails it will nose up, which is fatal right after start. Some BD-5 pilots say "it is absolutely no problem, you got a full sencond to react", but decide on your own...

You can see it with the Boeing 737 Max. There are only professional pilots flying them and they had apprximately 40 seconds to react to MCAS and still 2 out of 2 crashed... So, of course if you specifically train for the bad behaviour of the BD-5, it can be a nice plane with cool performance (until it kills you).

With a safety record of almost half of the built planes already crashed (some statistics say only a third), it reminds me of the Starfighter where they interviewed a former pilot who said "you just get in and tell yourself you are better than the others, this will not happen to you".

2. Mar 26, 2019

### kent Ashton

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Do you have $50K for the jet engine and$30K to build the airplane around it? I just sold my BD-5 prop kit but a fellow who knows about the jets told me the folks who know how to build and install the jets want to build the whole thing and don't want to take a half-finished, poorly-build project and try to convert it to a jet. I asked a jet owner for advice or plans and he said "get it done professionally". This is probably good advice because many people who build a BD-5 do not even have the skill, experience, or machine shop required to build a nice, straight, clean airplane. I certainly went through that with mine back in the day. When it was finally on-the-gear, I said, "this is not nice enough to justify a $60K jet engine installation". If you can provide one of the professional builders with a mostly complete kit and$75K+ (a very rough estimate), I believe it is very doable--not much more complicated than increasing the fuel capacity and installing the intakes, engine, and tailpipe. The pros know how to do it but they are not interested in sharing their hard-won knowledge. There is reason why we don't see 4000 jet BD-5s.

3. Mar 26, 2019

### kent Ashton

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This one of the most complete photo documentations of a BD-5 build I've seen. It will give you a good idea what's involved.
http://s1192.photobucket.com/user/amnpilot/library/?sort=3&page=1
It all looks pretty doable but remember that what get in the kit are skins, preformed wing ribs, spars and lots of raw materials. Yes, I am oversimplifying but it ain't like a modern Van's RV kit. A scratch-built Long-ez is easier to build.

4. Jul 27, 2019

### David Moxley

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Anything is possible, if you want to spend the time & most of all the money on it. I had 5 BD-5 kits from on the gear to unstarted that I sold after the first of this year. Oddly enough they went to Finland. Kind of hated to see them go, but was glad after they were gone.
As Kent pointed out , the kits supplied from BD were not in anyway complete. I have built 2 different BD-5 to the point they were sitting on the gear, there are a lot of parts to make or buy to get it to that point. There is a little support out there for the BD, by nothing like Van’s. I have a very nice RV-4 I built ,and it was a lot of work, if you run into a problem, or a not sure about something, you can get on the phone and get help very quickly. You will not be able to do this building a BD-5 . That my 2 cents on the matter.

Last edited: Jul 27, 2019
5. Jul 27, 2019

### Phenomdriver

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The jet install is possibly easier than the piston/prop version. A huge issue is torsional resonance, which played a role in causing structure cracks during the prototype stage. Some expert help will be needed to build a soft drive with a sprag clutch.

Jet Cat just came up with a P-1000 engine that puts out 244 pounds. The cost is in the $22k range, much less than the PBS TJ 100 at$55K. See attached file.

I have a BD-5 on gear and in the decision stage on which direction to go.

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6. Jul 29, 2019

### BJC

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Is there a difference in the jet wing verses the two prop wings, other than the span?

BJC

7. Jul 29, 2019

### Billrsv4

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Yes, stall speed and controllability at stall. The jet was a totally different animal. I worked on an alternate engine project for a BD-5. It was the way to go. Air cooled 900 Kawasaki engine. Bailed when that wouldn't pay me for my work or listen to the cautions I gave them.
T.O. Bill

8. Jul 29, 2019

### Scheny

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Can you state the values for both wings for comparison?

9. Jul 29, 2019

### Hot Wings

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My memory, which is getting less comprehensive over the years, is that the jets used the "G" wing. The "G" wing was/is 17 foot span and uses the GAW airfoil - thus the name.

10. Jul 29, 2019

### Derswede

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Back in '76 or '75 at Oshkosh, there was a BD-5J that crashed on landing. Thrust diverter plate stuck in fully engaged position, according to the pilot. I was just at the point of impact on the sidelines, one of the event guys got a couple of us together to help drag the plane off the field. He had a golf cart and trailer which we loaded the pieces onto to get them clear. Somewhere there is a photo of me holding one of the wings on the cart. I was surprised on how much damage the airframe suffered. Lost both wings and the fuselage had a major failure right at a bulkhead in front of the engine.

Derswede

11. Jul 30, 2019

### jedi

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and the pilot was a well known aircraft designer with many credits to his name. So pleased that he is still building and flying his designs.

12. Jul 30, 2019

### Scheny

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This is why I started the Beast project as a successor for the BD-5. It has a double wing spar to shield the fuel tank, a crash attenuating nose and a crash-proof cockpit section (+a BRS as standard equipment). It is designed to incorporate an airbrake instead of the thrust diverter.

litespeed and Derswede like this.
13. Jul 30, 2019

### Shane D Johnson

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some one please tell me where there is 0% assembled kit, so I can look away from the computer and blink;it has been five days!

14. Jul 31, 2019

### Scheny

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I have found a source with comprehensive information about the different wings:
• BD-5A: 14'4" 32.2ft²
• BD-5B: 21'6" 47.4ft²
• BD-5J: 17'0" 37.8ft²
• BD-5D/G: 17'0" 38.0ft² GA(W)-2 profile instead of NACA 64-21x
• BD-5S: 27'10" 60.0ft²
All wings except for the D/G have NACA 64-212 at the root and 64-218 at the tip, so thickness would be constant. The original A-wing had a sweet spot at 150kt, enormous induced drag and really high landing speed. With the B-wing, induced drag was drastically improved and my simulations show 8kt improved landing speed.

The jet got a compromise, which is slightly better than the A-wing at low speeds, but the same at high speeds. For all "newer" versions, they took the jet wing and changed the profile to the LS-413 (GA(W)-2) profile and went away from constant thickness at only slightly decreased maximum G's.

My simulations show, that the D/G wing has the same speed envelope as the B-wing, but with slightly higher drag at the benefit of a much improved stall behaviour. The wing stalls at the rear instead of the front, so it will stall more gently and it will be easier to get out of a stall (less hysteresis).

In case you wonder why the NACA stalls at the front already: this is due to Reynolds effects at low speed and the small chord. This is exactly why I used a new profile for the Beast, which has the benefits of the NACA 64xxx and the GA(W) combined.

BJC likes this.
15. Jul 31, 2019

### BJC

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Thanks.

Is the internal structure of the jet wing the same? Is the skin thicker?

Also, I‘ve read that no customer built aircraft flew with the short wing. IIRC, someone here reported that some had flown with the short wing.

BJC

16. Jul 31, 2019

### REVAN

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I was about four when the BD-5 saga was unfolding, but I remember hearing later from my dad that the original BD-5 V-tail design had problems with lateral stability and with the engine catching the fuselage on fire. I can imagine that the later of those problems would have pushed the design to evolve into a metal structure.

17. Jul 31, 2019

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