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Modifying Vision plans for retractable gear...



 
 
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  #1  
Old February 27th 04, 01:12 PM
Chris
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Default Modifying Vision plans for retractable gear...

Dear All:

I am researching various options for a homebuilt aircraft. I am
located in Thailand, and over here labor is significantly more
obtainable than money, so cost is definitely a primary concern. Build
time can always be compensated for by enlisting help. Based on what I
want, it appears that the plans built Vision is the best option, but I
wanted to get some feedback on the plane itself and also the
difficulty involved in modifying it to fit my requirements.

I have the following requirements:

Seats: minimum of 2
Cruise speed = 200 kts.
Landing speed: 50 kts.
Construction: composite
Aesthetics: conventional low wing tractor preferred/don't like high
wings
Engine: Diesel

I really want retractable gear. I have heard all the arguments both
for and against. I've heard the fixed evangelists say that the extra
lbs. outweigh the 5% speed gain, and I've heard the opposite extreme
with the retract guys saying it's more like 10%, and extra weight of
fuel is more than the weight of the gear. I don't know who is correct,
and the real story is probably somewhere in the middle.

Bottom line: I like the look of retractables. I'm willing to accept
the risk of a gear up. Since this is my dream, I want an RG plane.

This is my dilemma. I really want an RG, and I think I've found the
perfect combination minus this problem.

I'm looking at building a plans built Vision
(http://www.visionaircraft.com). It fits within my budget. The engine
I'm considering for it is the 160HP inverted turbo diesel from
deltahawk. While this isn't shipping in quantity yet, I don't need it
for about 2 years. Besides, if this engine falls through there are
several other diesels to choose from, but the deltahawk seems to be
the best choice for now. (This is actually 327 lbs, and the Vision
specifies a maximum of 300, but I'll do what I have to in order to
make it work.)

Based on numbers from people flying a 160 HP vision w/ an O-320, I
should easily be able to pull 210 KTAS from a turbo diesel version at
16,000 ft.

I would appreciate any comments anyone has on this plane (or the
engine if you have them) and issues which I might not be aware of.
Does anyone have something better that I haven't seen? (Remember the
price issue. I can't afford the Glasair/Lancair kits)

A more pressing concern I have is the gear. As I said above, I really
want RG, but the Vision plans only come for a fixed tricycle or
taildragger. Can anyone comment on how difficult (or hopefully, not
difficult) it might be to modify the Vision plans to accomodate an RG
config?

I like the plane, it's in my budget, I think I can do it. I haven't
seen anything else that comes close. I have concerns about my ability
to safely modify the plans for an RG given my lack of experience.

I am an electrical engineer by trade. Never done any mechanical
design. If anyone has done this before, how difficult is it, and where
should I begin?

Thanks for any help or comments.

Chris
  #2  
Old February 27th 04, 10:23 PM
Craig
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Default

(Chris) wrote in message . com...
Dear All:

I am researching various options for a homebuilt aircraft. I am
located in Thailand, and over here labor is significantly more
obtainable than money, so cost is definitely a primary concern. Build
time can always be compensated for by enlisting help. Based on what I
want, it appears that the plans built Vision is the best option, but I
wanted to get some feedback on the plane itself and also the
difficulty involved in modifying it to fit my requirements.


Chris: You've already got two strikes against you for making the
Vision into what you want. First is that you are planning to use an
engine that is already at least 27 pounds over the maximum weight the
structure was designed for. Not being familiar with this particular
engine, if that weight is just the dry weight of the engine, then you
have to account for the additional weight for cooling and accesories.
Now couple that with a complete redesign of the landing gear and
adding all the necessary items to make it fold and do so reliably and
without causing a big drag penalty. Between the two, you are looking
at adding at least 50 to 100 pounds minimum to the basic aircraft
weight. Now take that increase and drop your useful load by the same
amount and see if the Vision is still within all of your wants. You
will probably find out that you will end up doing an almost complete
redesign of a significant amount of the structure, so much to the
point that you would be better off creating your own design from
scratch.

No matter which route you take, take the time and make the effort to
have all of your design information and calculations checked by
someone that is qualified and knows composite design. It isn't a
pretty picture to find out when it's too late that you misplaced a
decimal point or forgot to account for structural change.

Food for thought.....

Craig C.

 




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