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Mar 04, 2020, 09:35 PM
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dhal22's Avatar
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Discussion

K&B 7.5 ducted fan


Sam Ehab got me thinking about K&B ducted fans recently. I collected a few (all nib) but sold them as interest seemed high. A couple of weeks later I see this......

https://www.rcgroups.com/forums/show...e#post43957627

Used so I won't be so afraid to run it. Should I make some noise and wake up the neighborhood?
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Mar 04, 2020, 11:45 PM
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SeismicCWave's Avatar
Quote:
Originally Posted by dhal22
Sam Ehab got me thinking about K&B ducted fans recently. I collected a few (all nib) but sold them as interest seemed high. A couple of weeks later I see this......

https://www.rcgroups.com/forums/show...e#post43957627

Used so I won't be so afraid to run it. Should I make some noise and wake up the neighborhood?
Put a 8.5 X 8.5 pylon prop on it and let it scream.
Mar 05, 2020, 12:27 AM
Registered User
Yep, I used APC 8.75x8.25 and that thing just ran like a bat out of hell with needles in its Ar$e...LOL..

I am thinking of a delta ARF, if they make one, to put it on it!
Last edited by Sam Ehab; Mar 05, 2020 at 12:44 AM.
Mar 08, 2020, 03:16 PM
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dhal22's Avatar
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Interesting 7.5.......... Is that a mount added to the engine?
Mar 08, 2020, 03:18 PM
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More
Mar 08, 2020, 03:19 PM
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Clean on the inside at first look.
Mar 08, 2020, 04:57 PM
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Quote:
Originally Posted by dhal22
Interesting 7.5.......... Is that a mount added to the engine?
Yes, I believe this is a custom firewall mount...

You also have the "short" prop/fan thrust plate...Hmm...
Mar 08, 2020, 05:01 PM
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Quote:
Originally Posted by Sam Ehab
Yes, I believe this is a custom firewall mount...

You also have the "short" prop/fan thrust plate...Hmm...
Short thrust plate?
Mar 08, 2020, 05:04 PM
Registered User
The whatshamcallit thingy that the prop bolts to, thrust prop washer... My brain is not coming up with the right name....need some Coffee...LOL
Last edited by Sam Ehab; Mar 08, 2020 at 07:26 PM. Reason: funny stuff
Mar 08, 2020, 05:08 PM
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This is my 6.5CC DF front end...you see the difference?
Mar 08, 2020, 09:56 PM
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dhal22's Avatar
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I see. Don't know, I've had 7.5's before but never used them as they were all nib. This one needs to run though.
Mar 08, 2020, 10:12 PM
And You're Not
I ran an OS 46VRDF on a Diamond Dust, nice combo. I liked the CF APC Q40 props, I think 7.4 x 8.25 is what they were. Don't think they make em anymore. Should be pretty comparable to the K&B 7.5

I've still got a DD kit, there's not much to them as far as scratch building, and CF tubes are probably easier to come by now than back then.
Mar 08, 2020, 10:47 PM
Scott
Pylonracr's Avatar
That is surely a custom backplate mount. I have never seen one like that, and there is no way it would have fit in a fan unit. The carbon Q40 props are 7.4 x 7.5 and 7.4 x 7.6. The nylon Q500 props are 8.8 x 8 through 8.8 x 9.25 in .25 increments. The Q500 props are good to 20K and we run the carbon Q40 props to 28k regularly. The K&B 7.5 never really made that much power, so I would start off with an 8.8 x 8.5, set the pipe for 19K, fun 20/20 fuel on the test stand and see how happy it is. Adjust prop load and pipe length as needed.


Any questions PM me and I will be glad to help.

Scott
Mar 09, 2020, 12:06 AM
Registered User
Hey Scott, does the K&B 6.5 DF I have need a head shim for 20% nitro? I have YS 20/20 and some 30% Heli fuel.
Mar 09, 2020, 01:13 AM
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Thx Scott.


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