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Old Dec 19, 2006, 05:57 PM
Boring holes in sky & runway
Waterbug's Avatar
Michigan
Joined Jun 2004
268 Posts
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Fuji BT-86 EI or....

I am doing my first 1/4 scale in a Bob Dively Super Stearman Kit. Beautiful Spun Aluminum cowl 11.25"Ø.
I'm estimating All up Weight at 35# on two 8' wings.
I'd like some aggressive climb out & a "tad more vertical", maybe even approach hover.
Ever since my first airshow, I think bipes look great in a smoky tailslide.

The cute little Fuji BT-86 is my first choice for four reasons:
Power good.
Weight OK on the EI version.
Fits in 11.25" cowl without cutouts or bumps for plugs.
All up with mufflers only $700.

Next choice would be a DA-100, but $1300-1400 w/ mufflers.
QUESTIONS: Is this Fuji a reasonable choice?
Is the Fuji BT-86 prone to the casting cracks of their 32?
Is the extra $100 for their EI version a good or bad idea?
I was going EI for 8oz. weight reduction and ease of starting.
I see 26 x 10 recommended prop- would a 28 x 8 be better for hover?
(I often put 12.25 x 3.75 props on .46's for climbout and hover)
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Old Dec 21, 2006, 02:21 AM
there is no spoon...
Cap232ac's Avatar
Pueblo, Colorado
Joined Jul 2005
598 Posts
Quote:
Originally Posted by Waterbug
Next choice would be a DA-100, but $1300-1400 w/ mufflers.
QUESTIONS: Is this Fuji a reasonable choice?
Is the Fuji BT-86 prone to the casting cracks of their 32?
Is the extra $100 for their EI version a good or bad idea?
I was going EI for 8oz. weight reduction and ease of starting.
I see 26 x 10 recommended prop- would a 28 x 8 be better for hover?
(I often put 12.25 x 3.75 props on .46's for climbout and hover)

I personaly havn't seen any great performing Fuji engines. Sure they run ok, just not high performance. The few I've seen don't have the greatest power, and the long shaft extension can get off center easily resulting in a really bad vibrasion. Your plane is to weigh 35 pounds? A DA-100 isn't going to give you the high power climbs your after. Forget about hovering. My buddy flys a 42% Extra on a DA-150 that hovers like a dream and has great verticle performance. The plane weighs in at 38 pounds. The prop size is corect. Your turning around 6800 to 7000 RPM (6200 on the 150). A little diferent from smaller engines.

E.I. is the way to go. Just remember to keep your electronics away from the ignition box. This also includes your radio batteries. Modern stuff is better insulated against R.F. interferance, but I've lost a plane due to it.
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Old Jan 01, 2007, 01:05 PM
Boring holes in sky & runway
Waterbug's Avatar
Michigan
Joined Jun 2004
268 Posts
Problem Solved- ZDZ80

After talking to some others and searching the forums, I saw that the Zenoah GT80 may be a better choice. The tradeoff there is Fuji BT86Ei for $700 vs Zenoah's great reputation and widely available parts- but Magneto based ignition. Besides, I couldn't find a good drawing of the GT80 anywhere to see if it would fit in the cowl.

Long story short, the Bob Dively Stearman didn't seem to have enough cowl ventilation (~1/4" around cowl perimeter only ~7 sqin and not flow efficient)
so I went for a slightly used "just broken in" ZDZ80 for $600 w/Pitts muffler included. As I have come to understand it, the mfrs generally grossly exaggerate the available HP so you need to base decisions on flying/hover performance EXPERIENCE and the ZDZ80 actually delivers near the performance of a DA 100 due to its light weight. That of course is dependent on the plane and its weight.

Thanks for the feedback- first one is always a tough one and the more non-commercial input the better.

HNY
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Old Jan 01, 2007, 01:15 PM
Boring holes in sky & runway
Waterbug's Avatar
Michigan
Joined Jun 2004
268 Posts
Clarification

Umm- the point I failed to make is that I'd probably have to punch holes in the (now cylindrical) spun aluminum cowl anyway for adequate ventilation. So I figured what the hey- mount a big single can "popper" inverted and who cares if the plug sticks out of the cowl 1/2" on the bottom. My guess from Troy Built Models 55# THRUST estimate is that the ZDZ80 may actually climb out of a hover on a 35# plane. I used to fly with Gene P and I don't think he's big on blowing smoke. If he says it delivers 55lb thrust then he probably measured it (statically). Dinking around with static thrust a few years ago in 40ish engines, we found that prop selection based on our measured static thrust is a good indicator of hover performance- which makes sense.
My only question now is how the ZDZ80 VR I just got differs from the ZDZ80 VR-J currently on the market.

Thanks again cap232ac for helping put my ideas in order.
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Old Jan 01, 2007, 02:02 PM
Boring holes in sky & runway
Waterbug's Avatar
Michigan
Joined Jun 2004
268 Posts
Redirect to Giant Scale forum?!

I think I may have asked these questions in the wrong forum. Apologies.

For anyone that happens to stumble into this thread, here's a lifeline- be sure to see the Giant scale forum for more info- for example the following thread is a good overall intro to the gas engine choices out there:
http://www.rcgroups.com/forums/showt...&highlight=ZDZ

You need to decide between the cheaper heavier engines and the performance ones early in your shopping!
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