Velco

The rule of a thumb is that the intake:exhaust area ratio should be at least 1:3. With this ratio some kind of a sub pressure is created at the intake and the air is sucked in rather than pushed into the fuse, which is much better.

So you can easily calculate what ever is the area of the ring created between the spinner and the cowl, multiply that by 3 and that should be the opening of the exhaust.

Just to warn you, every time I do this I get shocked how big the exhaust area should be, but that is how it works. If the exhaust turns out to be too big it is much better to reduce the area of the intake rather than not have the exhaust big enough!

Velco

Doug Andre

Velco,

Thanks for the info! I will keep your ratio in mind when I cut my exhaust.

Regards,

Doug

Corsair 29

Velco,

I was wondering if you can plug some numbers in ecalc and give me the best optimum performance propeller for a 65cc 160kv using 12s lipos?
I too have recently bought this bird an I'm in the process of gathering the materials.

Velco

I guess it is Rimfire 65cc right?

Well it shows that 22x14 would be ideal but such prop doesn't exist. So it is either 21x14 or 22x12. You should try both and see which one suits you. My choice would be 21x14 because it gives more reserve thrust at cruising speed with less, but enough static. Or, make the first flights on 22x12 and move on to 21x14.

I can explain some other time in more detail some theory and practice how prop choice differs from gas to electric.

Velco

Corsair 29

Velco,

Yes, it is a Rimfire 65cc. Thanks for the reply, I will try the 22x12 on the first flight.

kahloq

Ummmm....a 22x14 doesnt exist??? Might want to check around again....just as the M&M's commercial goes...."THEY DO EXIST".

http://www.hobbyking.com/hobbyking/s...propeller.html

Those cherry wood props are some of the BEST Ive ever used for electric motors...hands down beats Xoar props. really nice fat paddle blades produce massive thrust relative to other brands. They are light weight and cost $9 a prop. You cant beat that. There are other sizes too.

http://www.hobbyking.com/hobbyking/s...idCategory=306

Corsair 29

Good find Kahlog. Thanks!

Velco

I searched the net before posting and yes the only 22x14 available was from HK, but some of my friends have tried those props some 2 years ago and they were really crap, thats why I did not take them into consideration. But now what kehlog is saying sounds very interesting, probably some new version. kahlog, can you please post some of your results, I am really curios about Turnigy Cherry wood props now and will definitively give them a try.

I did a lot of experimenting with props including APC-E, TGS from HK and Turnigy Light Elelctric. I ended up using practically Turnigy LE on all of my planes. I have only recently purchased XOAR 20x13 and 19x15 as well as PT carbon 20x13 for my F3A bird to test this year.

At Scorpion site there are motor tables where APC-E and XOAR are compared and XOAR results compare almost identical to my findings about Turnigy LE. I even believed that they are the same thing, but they are not. One things is almost certain, they are produced at the same place.

Velco


Edit: Iwent to XOARwebsite to check once again and XOAR PJN Beecwood series do look identical to Turnigy Light Electric. These props can also be found under various brands all around Europe. The XOAR props I have are F3A props and they are shaped differently, slightly more curvy for less noise.

kahloq

The turnigy type E cherry wood props are not the same as the light electric stuff. The cherry wood props are thicklyLAMINATED unlike some of the other stuff.

Ive used several different sizes of the cherry wood turnigy props and they are the only turnigy props I will use now. The largest current turnigy cherry prop Im running right now is a 20x10 on a few different models(esm me-109e, esm p-51b). Also have a few 18x12's .... 1 on CMP me-109F on 10s and one on a DVII. Ive tried running same sized xoar/ top flite etc and they just didnt perform as well.
These are far and away better then trying to use APC E props as well, but then again...im at 5000ft so for me, the APC cuts thru air more then it actually pushes it resulting in less thrust since air density is kind low.

Direct comparison using 18x12 APC-e and 18x12 turnigy cherrywood on the esm 109e...e-flite power 110 on 8s 5000
Took about 3/4 runway(800ft runway) to get the plane off the tarmac safely using the apc...once in the air.....required at least 3/4 throttle to maintain safe airspeed to keep from stalling on mild bank turns. max flight time 5 mins

Used only about 1/3 to 1/2 runway using the turnigy cherry and in flight...same motor/batteries, only 1/2 throttle is required for exact same flight performance as the APC prop. max flight time 8 mins.

ive used the other types of turnigy wood props and they arent as good performance wise. I think it comes down to how large the blade paddles are and the nice and very thick lamination layers.

Brad330l

My Feedback: (1)

I too have used the Cheery wood props on my ESM 109 and have had no problems. I have to reduce the thickness of the hub a bit to get the spinner, prop and lock nuts to fit so the laminations help ensure it all stays together.
I like and use them and they are a great price as well. At least give them a go.

Cheers,

Brad

Velco

Thanks for the info, I will definitively give them a try now. Unfortunately there is no 15x10 available that I am using on Sebart MissWind50 but there is 17x10 that I am using on Wind110E. I have E-logger so it will be easy to compare.

After talking a bit to Mirce I figured out that 50% more static from flying weight is really not necessary so I have come up with one more interesting solution for Rim 65cc on 12S (or any other motor with kV around 170 like AXI 5345/18) which is also more scale especially on Dora and it is Biela 3 blade 20x14. Would really look nice painted in black .

Velco

mirce

I never fly models with electric set up, but maybe you can something compare...

On my CMP zero with 2,1 meter wingspan and 11,5 kilograms, I have Zenoah G 45 which swing Xoar 20x10 propeller. It fly very good, with a lot of power reserve. G 45 is 3,2 HP...
Top Flight Thunderbolt with 2,17 meter wing span and 12,5 kilogram, I was flying first with G 45, but later I change it with G 62. Bigger engine give better flying performance, shorter take off, and more power reserve. Propeller was 22x10 Xoar.

In my yard I measure thrust on P 47, and with G 62 it was same as weight 12,5 kg.

On Ziroli Hellcat I have Zenoah GT 80. OK, Hellcat is bigger 2,4 meter wingspan, heavier 19,5 kilograms on take off, and have thrust 15,5 - 16 kilograms. Propeller is 23x10, and it fly great also...

So, my opinion is not to exaggerate with set up. For warbirds 80% thrust from the weight is more than enough, same thrust and weight is great, and more thrust than weight is no necessary. Warbirds are not 3D models...

Regards

Mirce

Corsair 29

This is also quite interesting as well. Does ecalc show you what the current draw is on the 3 bladed prop at 100% throttle verses a 2 bladed prop? Obviously there will be more current draw for more load, which may require a larger battery pack(mah).

kahloq

Pretty big fuse. Larger battery packs wouldnt be an issue IMO.

Velco

OK here are the numbers from ecalc for Rimfire 65cc on 12S, beased on APC-E props with +/-10% tollerance

21x14: 88A, 15,5kg, 147kmh
22x14: 102A, 17,3kg, 145kmh
20x14 3 blade: 98A, 16,7kg, 146kmh

I have to say that all the values on all the props fall withing the Rimfire 65cc specification and that 20x14 3 blade can be considered as an "ideal" prop for this combo because in that case the motor is achieving its theoretical max efficiency of 93,5%! I have to admit that this motor looks to be a real winner on any 50CC WW2 plane also because of its weigth which can deffinitively help balancing the modell corectly without any lead.

As there is no good Do 335 thread (at least I could not find it) I have some interesting options for that modell too as I consider the suggested 2 Eflite160 on 10S and 20x10 completely unnecessary and the plane sounds very bad with those props spinning at such high revs.

A question from my side, which way to go, Benedini or Model Sound Inc way? Some pro and contra from the filed would be nice.

Velco

kahloq

Ummm.... there is definitely a good esm do 335 thread headed up by Fockewulf37. In it there are a few examples on electric versions and there has been one done with two power 160's. But..yea its quite overpowered and could be flown with power 60s or power 90s with smaller props. A bendini sound system would definitely make it sound nice, but ive no experience with Model Sound Inc.

Thread here:
http://www.rcuniverse.com/forum/m_10..._1/key_/tm.htm

Corsair 29

Thanks for the numbers Velco. This will lead me to decide on a battery pack of around 8000mah.

Velco

kahlog thanks for the link, I could not find that one, will look into it as it is another very interesting plane.

Velco

Doug Andre

Friends,

I am finally ready to adjust the CG on my Dora.    What was the best CG measurement determined by flight testing so far?  I have 12 LiPo cells up against the firewall and hope to avoid the usual chunk of lead!

Regards,

Doug Andre

ticketec

My Feedback: (2)

As per the manual worked out just fine for me.

Thanks

dave

Doug Andre

Thanks Ticketec.

I will assume leading edge of wing at the root.

Doug

jhutchey

The Xoar PJH-E F3A series electric prop is available in the 22x14 size. You can find them at Esprit Model here: http://www.espritmodel.com/xoar-prop...-f3a-pjhe.aspx.

Doug Andre

Friends,

I have balanced my EP Dora project and was pleased to discover that I was slightly nose heavy at 155mm with no added lead.  The setup is a Rimfire 50cc motor.  Two six-cell 5000mah LiPos as far forward as possible and a 4200 mah  4cell  NiMH receiver pack attached to the front of the firewall.

Ready to fly weight is 25lbs. 8oz.

I should have a flight report soon.

Regards,

Doug Andre

WarbirdMadMan

Hi all,

Has been a long read of this thread but interesting stuff and lots of good links.

Was out at Gratton Field on Sunday and watched Dave (Ticketec) put the Dora through its paces. I must say it is a superb flyer. Can't believe how slow Dave could get it doing low slow passes.[X(]
You would swear it was not possible yet it looked soooo stable.

And that sweet little XYZ 53.....I absolutely love the sound it makes, such a sweet sounding engine. It definately wasn't short in the power department either. Down the track if I can
find an 80" Hellcat then I would definately be giving one of these a go for sure

Nice flying on the weekend Dave. Catchya at the next Gratton Field fly in.

Cheers Tim
(T8 Race Engineering)

Duplicator41

My Feedback: (1)

http://www.lasercutkits.com.au/

Laser Cut Kits are waiting to take your money for the 80" Hellcat by Jerry Bates.

Cheers,