learn2turn

Just starting to layout the build for my Monolog 70. It will be powered by a Hacker A50 (which looks to be the motor in the instructions so it should be an exact fit.)

The instructions don't call for cutting the cowl except for the 2 1/4" opening for the motor. I was thinking of getting a TruTurn Turbo-Cool Spinner. That has openings in the front and a build in fan in the back plate to direct air back.

Do you think that will be enough cooling?

The bottom of the fuse behind the cool has a large open around about 6" (15cm) long and 3" wide (7cm) and 2" (5cm) deep where the ESC goes on electric (and I suspect the muffler would go on glow). That should let a lot of air out from the bottom of the motor. I think I'm more concerned with air in.

-Ken aka l2t.

learn2turn

I'm also wondering if I should really go with a 2 1/4" spinner. Below is an image of a old Dubro 2 1/4" from my junk box. It is maybe 1/32" wider the front of the cowl. If I go with a 2", it'd have a wisker under an 1/8" on each side narrower than the front of the cowl.

I'm not sure why but that spinner just looks goofy. Maybe it's the blue. Maybe it's because it's longer than what you'd expect to see. I believe TruTurn makes Standard and an "FAI" spinnner and the only difference that I could see is the FAI one is 1/4" shorter. Maybe that's the one to do with. Still have to decide 2" or 2 1/4".

Anthony-RCU

My Feedback: (2)

The Dubro spinner does have a bit of a goofy shape and have a large offset backplate. I have been using the great planes ones with the aluminum backplate. They look better and a cheap alternative to the Tru Turn.

learn2turn

I'm thinking if I don't got with a vented spinner, I'll have virtually no cooling. I've seen people take spinners with open AL backs and just cut the nose off. The other option would be to use a 2" spinner and cut the cowl hole 2 1/4" so there's an 1/8" open ring around the spinner. I think one of the stock pictures on the BJ Craft site has it that way.

But, the vented spinner is kinda cool so if I can get it for about $50, I might go for it.

woodie

To be candid, in the testing we have done, the most effective way to provide cooling via the spinner is to cut the nose off the spinner so there is about a 3/4" - 1" opening. It ain't pretty, but it works, is cheap and easy to do. It cooled better than any of the slotted, fan backplate spinners we tested. Out here, the spinner of choice to make this mod are the GP spinners with the aluminum back plate.

Woodie

learn2turn

I've seen that done and don't think it looks that bad.

The other easy option would be to use a 2" spinner with the cowl having a 2 1/4" hole yielding and open ring 1/8" around the spinner, superficially like the inlets on an SR71 in appearance.

A 3/4" spinner hole would have an area of 0.44in^2.
A 1" spinner hole would have an area of 0.79in^2.
The 1/8" ring would have an area of 0.83in^2.

So the ring provide more area. Don't know if the flow would be such that it would change the amount of air going in either one.

I could actually try both those solutions for well less than the cost of a custom spinner. Each would be just the cost of a plastic-coned spinner.

Will think about it more.
-l2t

Jetdesign

My Feedback: (8)

Well, another option is to cut the chin cowl. It might not be in the instructions but that doesn't mean you can't do it. There is heat from the motor and from the batteries. It is best to keep your batteries from getting too warm.

I'm not saying the spinner won't be enough - I don't know with that plane and setup, I'm just saying it's an option, and it doesn't have to look bad. I personally would cut openings in the cowl, and exits in the bottom of the fuse. But you can always try it and cut later if necessary.

FAI spinner would look better in my opinion. The other one mentioned above is a decent spinner too, just longer.

I don't know how I feel about the vented spinners. I got the Falcon vented spinner because it's light, and at least I don't think it will reduce cooling. From the little bit I know about fans and aerodynamics (which is specifically what we do at work), I see a lot missing from the design of these things. If I were to present one of them at a design review I would likely get coffee thrown at me.

Jetdesign

My Feedback: (8)

If you cut a 1/8" ring would there be anything holding the center portion, or vice versa? More area is best.

The SR71 uses that specially designed inlet to direct shock waves at sonic speeds (and possibly for stealth profile), so the compressors don't stall. It is not about accelerating air or trying to increase volume through the engine/airplane.

learn2turn

One of the build threads on the Monolog 70 has some vents in the chin cowl. But looking at the layout, it doesn't look like that woud bring air up around the motor.

On the 1/8" ring. There's no center section. The cowl just has a 2 1/4" in hole. If you use a 2" spinner, the spinner is 1/4" too small yielding a 1/8" open ring. (in the style of an SR71 air inlet; obviously not absolutely analogous in a pure aero dynamic sense to super sonic air ram. It just that you have a cone with an opening around it.)

Jetdesign

My Feedback: (8)

Aahhh, gotcha. Yeah that spinner style looks good on some planes. There are a few pics sprinkled around.

It looks like your plane has a little air scoop just above the spinner that could be cut out. That would look cool and would work. I was thinking of putting a NACA duct on the front of my plane to do something similar.

The scoop and a cut in the chin cowl would bring air in above and below the motor. That would be enough to get things flowing and remove heat from that area.

Some people make a light weight dam or duct to direct air past the motor. You can use a little balsa for the frame and cover it with monokote/ultracoat. The batteries are important to cool, too. I think you are on the right track. You can always cut more holes if you're not getting enough cooling.

Jetdesign

My Feedback: (8)

learn2turn

Joe,

I think I will do the cutout above the spinner as in your mocked-up image. Not sure about the chin;the cowl is open in the bottom back drawing air down so I don't think any cutout below the motor is going to draw as much air around the motor as a cut out above or in front of the motor.. I might go with a 2" spinner using the 1/8" open ring or I might go with the cut-off spinner nose thing.

In some ways I actually like the look of those cut-nose spinners. I've I had to coin a name it would be "Hollow Point". Reminds, me of the .22 ammo we used to use to hunt varmints on my buddy's grandma's farm back in high school.

-Ken aka l2t.

learn2turn

Found this pic on a thread somewhere.


That's the too small spinner ala SR71 idea. Certainly cheap and easy. It also gets the air exactly where needed around the edge of the motor.

I might just go for that for the first rendition.

-l2t

Jetdesign

My Feedback: (8)

You could even cut the center of that one! Tons of cooling!!

Jetdesign

My Feedback: (8)

Here's another, don't remember who's it is though.

karlwatt

My Feedback: (14)

I just received my Monolog 70. What servos are you using?

learn2turn

I went with Hitec HS-7975HB. Seemed a decent point, digital, carbon gears, but not too pricey at about $45. A three pack from Tower knocked a few bucks off and I got one of their $20 email coupons which knocked a bit more off when I ordered a total of $200 in part. They are standard size. I figured that would make it easier as I wouldn't have to modify the mounts. I know some plans the same size, like the 3DHS Osiris use mini servos for A and E so I considered buying three smaller servos but then decided it would just be easier with standard.

I really am not rushing with the build as I don't expect to finish until April as winter is coming. I work on it maybe 1/2 or an hour every few days.


-Ken aka l2t

karlwatt

My Feedback: (14)

Thanks for the quick reply. I think I will get these also. Hope to have mine done this winter so I can put some time in practice for the upcoming pattern season.

learn2turn

Well do post updates and report on how your build goes.


I work a second job in winter at as a ski instructor and pretty much forget about flying until late April. I usually don't even build in winter. But I figure if I bought and airframe in the fall, it would give me enough motivation to do something during the winter. I read about those contests in FL and CA in all winter. It's been cold here and my home mountain is opening this weekend. No flying in New England unless we luck out and get a warm Sunday, the only day I don't work in winter.

-Ken

PatternFlyer

My Feedback: (182)

http://www3.towerhobbies.com/cgi-bin...&I=LXRBB5&P=ML

I used spinner shown in the link above

Cut the spinner front of the line. It will be a little smaller than an inch hole. Sand smooth.
Enlarge the backplate hole to fit the motor/prop adapter.

I don't know what size prop you are using, but I used 16x10 on my A50-12S on 5S 5000mah packs for over 2 years without any heat problem.

learn2turn

I was thinking with a spinner like that, if you were really motivated you could use a dremel to shape the spokes into vanes and make it a fan. Of course you'd hae to be hugely careful to rebalance the back plate.

Dave Harmon

Hi Joe.....yep...that's my Nuance.
This spinner and prop worked fine...no cooling problems whatsoever....but...because the APC prop weighs a ton I waited until Falcon mfgd the correct size carbon spinner to fit the Nuance.
I put the Falcon prop on and it cools just as well as the cool looking 'too small' spinner.
It was important to me to have the cooling and prop blade slots cut at the factory......
I resisted buying the Marquet spinner that I would have had to cut the slots.
The Falcon is just as good or better at half the price and I dont have to do anything other than install it.

Dave