Balance point for a MPM 105 hydro

Hello,

I will start building a 1:8 scale (or so) hydro from MPM : the MPM 105.

Here are some photos : clickable thumbnails
http://i169.photobucket.com/albums/u...h__DSC0033.jpg http://i169.photobucket.com/albums/u...h__DSC0040.jpg http://i169.photobucket.com/albums/u...h__DSC0039.jpg
http://i169.photobucket.com/albums/u...h__DSC0037.jpg http://i169.photobucket.com/albums/u...h__DSC0036.jpg

I would like to know where should be placed the center of balance for this kind of hull.

Any help would be greatly appreciated.

Best regards.

Mathieu

Hello Mathieu

centre of balance should be between 5 and 10 cm behind the end of the sponsons, at the end edge of the turnfin. from there you can try how the boat runs best...

regards, Joern

Thank you for your replies Joern and Endlesspain.

Now I have a starting point to try to place everything in the hull, just have to choose a motor.

Best regards,

Mathieu

what kind of LIPO Pack do you want to use ? what kind of ESC ?

regards,Joern

Joern,

The ESC is a 40.160WK and the cells are 8S2P 5000 40C Flightmax.
I don't have the money for a Hi-end motor so (from what I read on US board) a scorpion 4035-800 might be a good choice.
I wonder if a Leopard 5682/3Y 910 can do the job... Almost twice the weight but easier to cool.

Any advice ?

Best regards,

Mathieu

Hello Mathieu,

first of all, the "Balance point" you´re looking for, is translated as "CG", or "Center of Gravity". This just if you want to exceed you search via Google or such.
Concerning the LBP56mm ... please read the PN i wrote you.

Kind regards,
Jan-Nicolas

You're right Jan-Nicolas,

I misnamed the "balance point". I tried to search for "rule of thumbs" to get a proper CG but no luck till now.

Checking your PN right now ;)

Best regards,

Mathieu

Later this year i will try the Leopard in my CT06 Hydroplane, currently i`m running a Plettenberg 370/50A1S at 10S2P LiPo. i have a total rpm of around 26000 , that is ok for a 1:8 Hydroplane. i use a prop with a diameter of 58 mm and 1,5 pitch factor.

Endlesspain currently sells a Pletti 370.

if you want to use the Leo 5682/3Y on 8S you would a total RPM of around
23000 , in my opinion a little bit less.

you would have to use a prop like the Octura X462 or something like this.

Got your point Joern.

I guess it's a matter of the top speed you (and/or I) want to get from the package.

Want kind of speed are you getting with your setup ? What about runtime ?

I have seen the Endlesspain's sale, very tempting.
But Jan-Nicolas have made me an offer I can't refuse. I'll try the 5682 and see what I can achieve with it.

Best regards,

Mathieu

i have a total running weight ( with LiPo ) around 10 kg, so very heavy, but runs very stable. have a look.. :
http://www.youtube.com/watch?v=MHEOkHnXZZU

If you are building light weight it will run with the Leo, as i wrote, i will try the Leo too this year.
If you need a prop thats fits, let me know, i can finish one and sent it to JN, would save shipping money.

Joern

Nice video Joern ! This 3 views video is really nice.

Regarding the prop, thanks a lot ! But at this time I don't know what size is best suited for my hull.

I'll get back to you when I'll know more about the weight of my hull, and we"ll see if we can get a selection of props.

Best regards,

Mathieu

Hi all,

Just wanted to let you know I tried for the first time the MPM105 last week-end.
Unfortunately the weather was not very nice so I was not able to perform real tests...

Here the video of the first (and only run) made last w-e.
http://www.megaupload.com/?d=3ESBD1IS

Really hope to be able to make real tests soon (maybe next week-end) to see what the power package worth. From what I've seen last w-e it will do it :D

CU

Mathieu

Hello Mathieu,

well, choppy water conditions - no chance to "give it a go" for a longer distance.
But it seems as if the CG is a bit far in the back, huh ? Is that possible ?

What motor did you use for this maiden-run ? The LBP5682 ?
How many cells are you running ... and can you give us a short "first impression" on the temperatures the motor reached in this 2-minute run ?

Best regards,
JN

Hello Jan-Nicolas,

Yes, the motor is the 5682 and I was using 8S2P 5000 40C Flightmax cells.
The prop is a K60 for the moment.

I agree with you the CG was too far back for this water & wind conditions. Next runs will be made with better conditions.

Regarding the motor temp, the can & the motor coupler were barely warm.

Greets,

Mathieu

Hello Mathieu,

so you have approximately 27000KV (without load).
I guess this is a fairly good start.

Keep us informed here, i am really keen on your conclusion about the motor ... :cool:

JN

the total rpm is ok for a 1:8 Scale.. the first run looks good, will be interesting when you have better conditions and drive full throttle.

do you plan to add front or rear wing later ? in this class, the rearwing and even the front wing have a lot of effect ,how the boat runs. could be total different as with the current trim.

please keep us informed...

Hi guys,

I can't wait to perform next tests ! Really existed by this short first test run.

Regarding the rear wing, I would like to add it but :
- I don't really know at this time how to mount it on the hull.
- It will add a lot of weight on the back, and I'm not sure to be able to have the right CoG with the rear wing...

Next test will be made without the rear wing.

I let you know the result of the next tests for sure, thanks for your help so far.

Mathieu

Hi,
when you do your tests remove the turn fin the first runs.
Even the fin is thin and perfectly mounted they have an effect.

you can setup the boat perfectly in the straights without fin(less spray, flying on the edge etc.) and look for a proper cg and wing-setup.
after that you know whta fu**ing behaviour a fin is adding and you can work with different shapes, angles etc. to get it nearly back to the perfect conditions.

needles to say, you need calm water for that :)


Regards
Ralf

Hello,

Thank you for the advice Ralf. I'll give a try without the turn fin to see how she run.

:thx:

Mathieu

EDIT : just a little shot of the hull during the maiden run

http://i169.photobucket.com/albums/u...SC_8055_cr.jpg