BD4 Performance specs

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SamP

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I've started looking for the next kit, and came across the BD4C. It seems to have really good numbers, even if it wasn't a 60 year old design

I'm trying to understand what the reasoning is. It's got a higher wing loading than an RV-10, yet still lands and takeoff in comporable distances. Aerodynamically, a rivetless wing might be the reason for some of the gain, but a very boxy fuselage. An all moving tail means there is no trim losses there, so might help with the cruise speed.

Any other reasons for its high performance?
 

Tiger Tim

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Lying on the brochure could also be a possibility. Maybe not outright lying but stacking the deck for testing then rounding the results judiciously.

Or it could be something else. Maybe that broad, flat fuselage factors in a little.
 

TFF

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My opinion is to get the BD4C numbers, the pilot has to be on the game more. Vans tend to be close to publicize numbers for an average plane average pilot. The RV10 will be less hot to fly. A fan of the simple BD4 design since I was a kid because there was an assembly manual at the library and I could check it out. I had an erector set, and it is built just like one. I think it’s brilliant in its own way. The RV10 is a better airplane. Depends on what you want out of the project. For me, I would like to build a BD4; I would like to own a RV10.
 

Vigilant1

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I am suspicious of the BD supplied numbers. Unfortunately, the CAFE Foundation didn't do a full report on the BD-4, but when BD-4s turned in fast times in the CAFE 400 races, it was accomplished by burning a lot of fuel.
The most obvious drag reduction feature is the plane's small wing (for it's MTOW). That is a tradeoff.
 

llemon

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Apr 29, 2021
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Given the 72mph clean stall speed, the wing would have to be around a CL of 1.8. That seems pretty unbelievable for the airfoil used. Flaps down would be around 2 which is believable.

Now, if they measured stall at well under gross then its doable.
 

Kyle Boatright

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I got interested, then not-so interested in the BD-4 a couple of times over the years. The stock airplane is kind of a 2+2 airplane, and none of the owners seem to report the same performance as claimed in the marketing info.

I think it is a neat airplane, but the performance numbers are overstated.
 

Apsco17

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Jun 6, 2020
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Hello Sam,

I'm currently building a BD-4C kit. Before buying the kit, I went to Florida in 2019 and flew the factory plane. Two of us, 50 % fuel on an 85 deg day, we cruised at 165 Knots TAS at 5500'. That is with an IO-360, CS prop and wheel pants. There are you tube videos with similar performance that you can easily find.

The fuselage , following the contour of the wing, generates about 20% of the total lift. The wing is extremely smooth due to the rivets only being on the trailing edges, the skin is bonded to the ribs and results in a very clean wing. Stalls seem to be in the 55 - 60 kias range for most recent planes, though how you build it will have an effect on any aircraft's performance.

The current BD-4C has been lengthened by 18" with a higher back seating area roofline, bringing it closer to a 4 pers plane. Unlike some 4 place planes, with 45 gallons (270 lbs) of fuel, a 1300# ZFW you have 830 lbs of usable capacity left for people and baggage.

Though the RV-10 is a very nice plane, I'm happy with my choice and the BD-4C seems to be a much simpler plane to build. Tim Becker at Bede in Florida would be able to answer any questions you might have and arrange a demo flight, which I highly recommend for any kit you are considering building. I'm also happy to answer any other questions you might have, good luck with your search!

Todd
 
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