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Author Topic: Mp jet 040 Tomboy combo  (Read 345 times)
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Fourfingers
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« on: June 04, 2019, 08:05:24 AM »

Any help welcome on this one:
MP jet 040 not quite up to swinging an 8x4 (for me, anyway). 8x3 seems to lack thrust .... 7x4 revs OK but also little thrust.  Get a nice sinking flight path with these, but not really the objective!
What next?  Cut down 8x4 a shade?  7x5?
Someone mentioned 3mm under wing LE might work.
Or 049 motor ... ?
Thanks
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cvasecuk
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« Reply #1 on: June 04, 2019, 09:24:24 AM »

A few years ago my club ran our own "Tomboy 3" style comps. We all had MP Jet 040 engines and I'm pretty sure we all had 7x4 props. We all had to hold in a lot of down elevator to stop the very steep climb from going over the top! Glides were quite good, so if your Tomboy glides OK from a hand launch then I suspect your engine is not up to scratch.
Ron
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Fourfingers
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« Reply #2 on: June 04, 2019, 02:40:19 PM »

Ron
Many thanks for that.  Will try 7x4 again when wind drops ....
fYI weight is under average (first time for me) and CG is well back, but seems OK on glide.
Will,let you know!
Ff
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Olli-Matti
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« Reply #3 on: June 08, 2019, 01:25:17 PM »

I've liked MasterAirscrew 7x4 3-blade a lot recently. Works great on the MP Jet 040 (and on an Enya09 glow engine aswell). Loadwise it is something between MA 8x3 and 8x4. Pulls my 200g Poppet with ease: https://www.youtube.com/watch?v=xLFBgaAXJ58
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Fourfingers
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« Reply #4 on: June 08, 2019, 02:14:43 PM »

Well, thanks for that too. 
I envy the calm Baltic conditions ... here (SW England) we have constant wind, just now.
Must say you have that poppet going really well.
I will give the MA 3- blade a try, thanks for the tip.
john
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Fourfingers
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« Reply #5 on: June 09, 2019, 04:49:25 AM »

Olli
Just noticed a couple ot things on your post ...
Poppet 200g!  That is seriously light.  Reckon a rubber band would lift that ship skyward...
My Tomboy is 327 g flight ready - and thats lighter than many Ive seen.
Also my Enya 09 would destroy a 2- blade 7x4 .... even with the venturi restrictor in place.  Without it the engine scares me.
Will try it just the same.
Thanks again
john
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OZPAF
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« Reply #6 on: June 10, 2019, 06:13:42 AM »

Beautiful flight Olli and what a great site!

John
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martina
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« Reply #7 on: June 16, 2019, 07:36:47 AM »

I have used the MP jet 040 with a 7x4 in a Tomboy and it needed the power backed off to stop it climbing vertically! - first step in my opinion is to carefully check the cg and wing and tail incidence and try again. Any idea what the model weighs?

I have several of these motors and haven't come across one that is down on power, from new they are sometimes a bit tight and benefit from having 20 or so tanks of fuel put through them. They feel more powerful than a good English Mills .75 and I use one of these (again with a 7x4) in a 44" Tomboy which has a very respectable climb.

Kind regards, Martin
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Fourfingers
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« Reply #8 on: June 19, 2019, 05:00:25 AM »

Finally got my 7x4 3-blader ......now wind has subsided I am on crutches for a few weeks!!
Will report later.
john
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cvasecuk
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« Reply #9 on: June 19, 2019, 08:28:44 AM »

John, The review in Feb '98 Aeromodeller gave 7710rpm on an APC 7x4. I have just checked mine and I got 7840 on a Master 7x4. That gives a static thrust of about 200g. More than enough for even a very heavy Tomboy. I suggest you use an ordinary 7x4 and measure your revs. Even 6000 to 6500 would be enough to get your Tomboy flying. Mine weighs the same as yours and as I pointed out needs full down elevator to control the climb!!!
Ron
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Olli-Matti
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« Reply #10 on: June 19, 2019, 11:11:07 AM »

I get 7500rpm on a MA 7x4x3 and about 6600~6800 with compression backed down. Poppet on the video flew with this under compressed setting.
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Fourfingers
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« Reply #11 on: June 19, 2019, 01:50:04 PM »

Thanks All for comments , advice etc.
Martin, mine weighs 327 which surprises me as I used laminated longerons, extra thick cross pieces, double length bearers and two extra formers .... No u/ c however.
Wing is from another craft, 42 in span, 5 in chord, but area comparable.  CG is well back but glides very nicely.
Good flying weather, bad legs.  Rats.
john
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