Bede BD-5, BD-5J, BD-10 etc..

[Weaver]

Given the amount of whiff interest these things generate, I was surprised to see there wasn't a research/ideas thread for them, so now there is.

BD-5 info:
https://en.wikipedia.org/wiki/Bede_BD-5
http://bd5.com/
https://www.eaa.org/en/eaa/aviation-communities-and-interests/homebuilt-aircraft-and-homebuilt-aircraft-kits/kits-and-plans/00---c/bede-bd-5


Original V-tailed prototype:



BD-5 and -5J cutaways:




Yes, it really is that small!



They DO have a military use! These SMART aircraft are/were BD-5Js used to simulate cruise missiles for training:


Some oddball variations:







Possibly the safest BD-5s ever!


(Yes, that was Bede's real 'simulator' setup... )


Why do I say that? Well reading the articles, they are quite 'crashy'...

[Weaver]

BD-10 info (not a happy story!):
https://en.wikipedia.org/wiki/Bede_BD-10

[Weaver]

Okay, so reading the articles, a few things strike me:

1. The aircraft is SO small that it's impractical: you need at least space for an overnight bag and a few tools!

2. The original V-tailed prototype suffered longitudinal stability issues, causing Bede to go over to a conventional tail. However, when you look at how much bigger that conventional tail was, you've got to wonder if the V-tail's problem wasn't it's V-ness, just the fact that it was too small.

3. Pilots of early versions reported longitudinal trim issues, and the solution developed by support companies was simply to lengthen the airframe a little.

4. The high thrust line is a contributory factor in crashes due to the pitch-up moment induced by an engine failure, leading to an avoidable stall. The prop version obviously needs that high thrust line to avoid a prop/ground interface, but the jet version really doesn't...


So, put all this together, and I can see a product-improved BD-5J with a longer fuselage (two or three feet), a baggage compartment behind the seat, the jet engine lowered so that it's thrust line goes through the centre of mass parallel to the fuselage datum, and a reversion to the V-tails, but with much more surface area. If you can find (or make) a suitable small turbofan (for better fuel efficiency), then the V-tail arrangement also makes room for enlarged conventional air intakes to feed the greater mass flow.

[PR19_Kit]

So, put all this together, and I can see a product-improved BD-5J with a longer fuselage (two or three feet), a baggage compartment behind the seat, the jet engine lowered so that it's thrust line goes through the centre of mass parallel to the fuselage datum, and a reversion to the V-tails, but with much more surface area. If you can find (or make) a suitable small turbofan (for better fuel efficiency), then the V-tail arrangement also makes room for enlarged conventional air intakes to feed the greater mass flow.

....and longer wings. 

[MiB]

The James Bond's jet!!!

[Weaver]

So, put all this together, and I can see a product-improved BD-5J with a longer fuselage (two or three feet), a baggage compartment behind the seat, the jet engine lowered so that it's thrust line goes through the centre of mass parallel to the fuselage datum, and a reversion to the V-tails, but with much more surface area. If you can find (or make) a suitable small turbofan (for better fuel efficiency), then the V-tail arrangement also makes room for enlarged conventional air intakes to feed the greater mass flow.

....and longer wings. 

Maybe so actually: the prop-job's wings are longer, so if you've pushed the weight up enough, they could be justified.

[Weaver]

Hah! The BD-5 page has this photoshopped concept of a stretched one: great minds (and me) think alike!




From here: http://www.bd5.com/bd01001.htm I disagree with the website author: this definitely SHOULD be attempted!

[JayBee]

So, put all this together, and I can see a product-improved BD-5J with a longer fuselage (two or three feet), a baggage compartment behind the seat, the jet engine lowered so that it's thrust line goes through the centre of mass parallel to the fuselage datum, and a reversion to the V-tails, but with much more surface area. If you can find (or make) a suitable small turbofan (for better fuel efficiency), then the V-tail arrangement also makes room for enlarged conventional air intakes to feed the greater mass flow.

....and longer wings. 

The BD-5B had longer wings for cross country use,
and the BD-5S had even longer wings of 27'10" (8.48M) span.
Only one of this sailplane version of the BD-5 was built and it had considerable control problems, so it was not progressed with.
The longer fuselage might well have worked.

As far as the BD-5 goes, the Nov/Dec 2013 issue of Jets magazine has an artcle on the FLS Microjet which is a 40years down the line re-vamp of the BD-5.
It looks the same from the outside but has a lot of changes internally including a full electronic cockpit display.

The LS, and later Otaki re-pop, give the BD-5J and the BD-5B, with appropriate wings. It is easy enogh to cut down the wing for the original BD-5 span.

Jim

[Weaver]

Other interesting Bedery:

Bede XBD-2. That rear fuselage keel and high prop line look familiar, don't they? Only one built.
Laminar flow design with suction from 1600 holes generated by a compressor in the (twin) engine compartment.




Bede BD-7. BD-5ish four-seater. Prototype never flew.





Bede BD-8. That rear fuselage keel etc, etc....  Only one built.



Bede BD-12. Two-seat side-by-side BD-5, basically. Only one built.





Bede BD-14. Stretched four-seat BD-12. Only one allegedly built, but there seem to be no pics of it...

[Weaver]

Aaaand thanks to them being mentioned on a totally unrelated thread, I'm please to point out that Draw Decal do decal sheets for the BD-5J in Bud Light and Coors Light schemes:





http://www.shopdrawdecal.com/searchresults.asp?cat=2207

[PR19_Kit]

It is easy enough to cut down the wing for the original BD-5 span.

Heresy, HERESY I say! 

[Weaver]

Actually, there were FOUR different wing sizes on various BD-5 versions:

BD-5A : This had the original small wing for highest performance and agility, with a span of 14'3". It was supposed to have been dropped during development because it only showed an advantage near Vmax and had a very high stall speed (for a light aircraft) but due to the chaotic state of manufacture and delivery, some of the earliest kits were only shipped with an A-wing. ALL four aircraft completed with this wing crashed on their first flight, three on take-off and one on landing, with three fatalities.

BD-5B : This has the original 'touring' wing, with a span of 21'6". It's the standard wing for prop-driven BD-5s.

BD-5J : This has an 'intermediate' wing with a span of 17'.

BD-5G : This is a third party kit by Alturair Inc. which has a modern piston engine and the 17' wing.

BD-5S : This is the unsuccessful sailplane version of which only one was made. I've seen a figure of 38' for the wingspan, but I'm not sure that it's right.

[rickshaw]

I think the high thrust line of the propeller powered BD-5 could be fixed with longer landing gear legs.  That would allow the prop-shaft to be lowered and there wouldn't be any risk of a ground strike.   

[Weaver]

I think the high thrust line of the propeller powered BD-5 could be fixed with longer landing gear legs.  That would allow the prop-shaft to be lowered and there wouldn't be any risk of a ground strike.   

Shouldn't be a problem with the main gear, but making the nosewheel leg longer could be problematic: it pivots about six inches behind the nose and the tire's already at risk of getting pregnant by the pilot...

Another solution that occurs to me is to move the prop shaft down, then replace the prop with a multi-blade ducted fan of about the same diameter as the height of the fuselage. As a bonus, the increased side area might let you reduce the size of the fin a bit.

[rickshaw]

I think the high thrust line of the propeller powered BD-5 could be fixed with longer landing gear legs.  That would allow the prop-shaft to be lowered and there wouldn't be any risk of a ground strike.   

Shouldn't be a problem with the main gear, but making the nosewheel leg longer could be problematic: it pivots about six inches behind the nose and the tire's already at risk of getting pregnant by the pilot...

Just increase the length of the nose.  Might need a taller fin as well.