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Old Mar 30, 2006, 02:15 AM
Registered User
Netherlands, Groningen
Joined Jan 2004
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Discussion
48" BAe hawk conversion ?

pjp-jets

Would it be possible to convert this kit to electric ducted fan ?
What kind of fan/motor/battery could get it in he air ?

The biggest EDF i have is a minifan, this is quite a bit bigger.

Hope you can help me out here..

Thanks,

Aldert
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Old Mar 30, 2006, 08:41 AM
EDF all the way!
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Gilbert, Az
Joined Jun 1999
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Whose kit?
Bob
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Old Mar 30, 2006, 09:03 AM
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Netherlands, Groningen
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Edited the first post and there's a link now....
Thanks Bob.
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Old Mar 30, 2006, 09:26 AM
EDF all the way!
bruff's Avatar
Gilbert, Az
Joined Jun 1999
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I would use a DS-94 fan or Turbo 4000 fan. See ejf.com or warbirds-rc.com for fan details.
Bob
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Old Mar 30, 2006, 01:49 PM
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Braintree, Essex
Joined Mar 2006
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I just did an AMD hawk with a turbo fan 4000 see "AMD Hawk thread with 120mm fan" Also Chris true did a century jets version with the same fan. You wont get the batteries in with a bigger fan and a 90mm will be to small.
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Old Mar 30, 2006, 02:31 PM
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Irvine, Calif USA
Joined Feb 1999
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Quote:
Originally Posted by aldert
pjp-jets
Would it be possible to convert this kit to electric ducted fan ? What kind of fan/motor/battery could get it in he air ? ...
I looked into converting this particular PJP Hawk to electric a few months ago, it seemed like a very nice model, and a good value.

The weight quoted (8lbs rtf for gas DF) seemed ok for such a large model. Not having seen it in person, the danger with any of these large conversions is that the model - not being designed for electric setup from the start - ends up way too heavy and flies like an overweight dog.

Again, based mostly on speculation, I would say that the quoted weight rtf of around 8lbs would suggest looking for a power setup of 8 x 200W = 1600W which would be in the Midifan (stretching it a bit) or better in the DS-51 fan range. Both are 90mm fans. That would of course assume that the model cannot be lightened for electric setup (lighter ply, lighter retracts, no seven layers of primers etc).

The motor would then be in Hacker B50L-XL range and the batts in the 1600W/50A = 30V/3.3V = 10S Lipo range, with a capacity of ca. 50A/15C = 3000mAh (or possibly more). These as I said are very rough estimates.

If a 120mm fan fits, eg Aeronaut TF-4000 or DS-94, (with batteries and retracts etc - after all the batts would go in the nose, so I don't see much problem there) then the power can be as much as 2500+ Watts. In wich case you would be looking at the Tango/Kora, large Lehner, large Hacker B50XL or large Plettenberg setups... and 12S LiPo setups.

I hope one of our British friends, who maybe had a chance to see this model close up, will comment on the fiberglass weight and setup issue.

Last but not least, occasionally the vendor is willing to do an ultralight fiberglass layup, specifically for edf.
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Old Mar 30, 2006, 02:49 PM
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Netherlands, Groningen
Joined Jan 2004
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Thanks everyone for your answers.
This is a picture of the second-hand kit that was offered to me.
I would prefer (read: my wallet would be pleased with) a 90 mm fan.

So, i will give it a try and will be back with a lot of questions.

Aldert
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Old Mar 30, 2006, 03:59 PM
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Irvine, Calif USA
Joined Feb 1999
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Aah ... No canopy ? More comments: What does the empty kit weigh? Also, the intakes could be too small for a 120mm fan! What is the intake area, can you measure it? A 90mm fan would need a total intake area of around 50 cm^2, the 120mm fan around 90 cm^2.
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Old Apr 01, 2006, 02:23 PM
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Netherlands, Groningen
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Aah ... No canopy !!!!

I don't know what the weight is... or how big the intake is...
But i do know that i bought it today.
The guy i bought it from lives in Belgium, i live in the Netherlands so it's
gonna take a few weeks before i can pick it up.

If a conversion is not possible i can always turn it in to a pusher prop
(But my guess is that a 90 mm fan will fit and can get enough air.)
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Old Apr 13, 2006, 03:52 PM
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Netherlands, Groningen
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Arrived today, so i'm quite happy.

The fuselage-weight is 600 gram, thats 21.2 ounce.
Wingcores including balsa : 310 grams, 10.9 ounce.
Fin an horizontal stabilizers : 80 grams, 2.82 ounce.

Have to calculate inlet area, don't know how to be honnest, but i will
find out...
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Old Apr 13, 2006, 05:14 PM
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Hi Aldert

I inserted your pic into AutoCAD and scaled it to the horizontal measurement. Guesstimating the intake's area boundary to be 0.15in inside the outer periphery of the intake moulding as seen on the pic, the area for one inlet = 3.45sq in, so the total area is 6.9sq in, which is Schuebeler DS51 territory (DS 51 has 51sq cm swept area = 7.9sq in). Your tailpipe outlet area should be no bigger than the inlet area, say 3in diameter.

I'd go with a 9s lipo setup at about 60A on that fan for about 3.4 x 9 x 60 = 1836W, implying a Hacker B50-XL series motor or a Lehner.

This thread will help you to choose the motor: http://www.rcgroups.com/forums/showthread.php?t=463710

Another solution is to cut off the front 4in of the intake mouldings, and make new ones with a bigger area suitable for a bigger fan.

Gordon
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Old Apr 13, 2006, 05:24 PM
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Braintree, Essex
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Dont get too paranoid about the weight the lighter the better of course, but it will still work if you can get good airflow. My hawk is 53in span has flaps and retract and a TOW of 12.5 lbs, bare airframe weight without engine and batteries is 8.5lbs. Goes pretty well. Having seen the picture I am also coming to the conclusion that that your intakes and model size are a little to small for a 120mm. Making the intakes bigger with a nicely rounded lip will help enormously I think, I have found that the only drawback with larger intakes is the drag when you back off on the throttle, the larger the intakes in relation to the fan size the greater pronounced the affect. You may be able to fit the bigger fan, but you may also have trouble getting the batteries around the unit. With the hawk the best place for the batteries is over the wing just forward of the CG, my pack(s) only just fit and my hawk is larger than yours. An alternative I am considering for the Lipos is two 5s packs in the forward position over the wing and two in the position between the intakes. I will then have to move the ESC from behind the motor to below the top hatch to keep the leads short. Nice and conviniant the way it is for charging etc. The CG is only just right now I have move the reciever pack right up into the nose.
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Old Apr 13, 2006, 05:28 PM
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United States, MO, St Charles
Joined Nov 2002
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Hi Aldert,
Gordon beat me to it but the results are some what the same. I show 2.2574 sq. inches for the area enclosed but the green line.

Dan Eaton
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Old Apr 15, 2006, 04:00 PM
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Netherlands, Groningen
Joined Jan 2004
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@ Gordan and Dan,

Thanks guys, it would have took me a lot of time to calculate the inlet-area.
I'm going for a 90 mm fan.

First i'm going to restore the wing, the man i bought it from started some work on it but did'nt do a very good job...
I will make some pictures so you can guide me through the process of building this plane, and hope that you can prevent me from making major
errors....
First jet... scarry...

@ Mr. Watts,

You have a 120 mm fan ?
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Old Apr 16, 2006, 04:09 PM
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Braintree, Essex
Joined Mar 2006
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Quote:
Originally Posted by aldert
@ Gordan and Dan,

Thanks guys, it would have took me a lot of time to calculate the inlet-area.
I'm going for a 90 mm fan.

First i'm going to restore the wing, the man i bought it from started some work on it but did'nt do a very good job...
I will make some pictures so you can guide me through the process of building this plane, and hope that you can prevent me from making major
errors....
First jet... scarry...

@ Mr. Watts,

You have a 120 mm fan ?
Mine is the AMD Hawk which is 53 inch span and was designed for a 5inch IC Fan. Inlets are plenty big enough for that reason and as the 120mm fan is smaller diameter so I have the space to get the 4 5s packs down the side as shown. I will see if I can get a look at your Hawk in the UK somewhere.
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