The Ohmen

[Didier]

Hello guys. 
Really appreciated all the help. In the meantime I did get a copy of the article send by PM. 
I have night shift tonight. Guess what I am gonna read tonight 😉

[Didier]

1 hour ago, Martin McIntosh said:

The Ohmen is a  very simple build. I changed mine from electric to an OS 26FS and it transformed the model.

Nice!

This definitely helps my motivation. 😃

What prop do you use and did you put the servos in the tail to counter act the heavier motor? Any other mods?

[Martin Harris - Moderator]

I scaled down the design to 40" span and used an OS20FS - cracking little engine by the way.  To help balance it, I fitted the receiver battery as far back as it would go in the rear fuselage which worked well.

[EarlyBird]

13 hours ago, Didier said:

What prop do you use and did you put the servos in the tail

Your IC looks ideal and it's interesting that balance is a common issue.

 

Mine flies on a 3535 ~1000kv 4S 10x5 prop with both servos in the tail. Shortening the nose by 15mm was my big mistake as I needed 60 grams of lead in the nose for balance. I should have added say 2 degrees of side thrust as I fly straight and level for most of my flight. Not to worry as my next Ohmen will rectify these short comings.

 

Steve

[Didier]

You are gonna build another one?

Nice. 
Did you find 2 degrees side thrust required especially during take-off or in general as well?

[Didier]

11 hours ago, Martin Harris - Moderator said:

I scaled down the design to 40" span and used an OS20FS - cracking little engine by the way.  To help balance it, I fitted the receiver battery as far back as it would go in the rear fuselage which worked well.

I have been quickly through this thread and I saw 2 Ohmen’s with FS20/26. 
Both models the engines are upside down. No problems with starting or cooling of the engines?

I was thinking about installing the engine with the cilinder pointing to the right from pilots view (flight direction). 
To prevent flooding the engine and better cooling. But the looks are better with the cilinder down of course. 

[Martin McIntosh]

10x6 APC. The servos are at the rear of the fus in front of the wing bolts. No cg issues.

[EarlyBird]

19 minutes ago, Didier said:

Did you find 2 degrees side thrust required especially during take-off or in general as well?

I have one waiting in the queue along with Peggy Sue 2, Destiny, T31M and Basic 3D (not Peter's 😲). Building the Ohmen at the same time would add interest for me so it could be next, Rhapsody and xRES to finish though.

 

Taking advice on here I added right trim to the rudder which in effect is the same as right thrust. For me this solved an issue of the left wing dropping as I increased the throttle to enter a loop. Similarly with a stall turn it enable vertical flight without a spin. So yes all the time. I was surprised at how big the effect was without side thrust so the next will have the standard 2 degrees side thrust. Zero vertical thrust is fine so for once I will leave that as designed by Peter.

 

Steve

[Didier]

30 minutes ago, Martin McIntosh said:

10x6 APC. The servos are at the rear of the fus in front of the wing bolts. No cg issues.

Cool thanks

[Peter Miller]

I NEVER use side thrust.  I just use rudder to correct any swing on take off. 

[Didier]

7 minutes ago, EarlyBird said:

I have one waiting in the queue along with Peggy Sue 2, Destiny, T31M and Basic 3D (not Peter's 😲). Building the Ohmen at the same time would add interest for me so it could be next, Rhapsody and xRES to finish though.

 

Taking advice on here I added right trim to the rudder which in effect is the same as right thrust. For me this solved an issue of the left wing dropping as I increased the throttle to enter a loop. Similarly with a stall turn it enable vertical flight without a spin. So yes all the time. I was surprised at how big the effect was without side thrust so the next will have the standard 2 degrees side thrust. Zero vertical thrust is fine so for once I will leave that as designed by Peter.

 

Steve

You mean with the queue the delivery from Sarik? What is the normal turnaround time from Sarik?

[EarlyBird]

Just now, Peter Miller said:

I NEVER use side thrust.  I just use rudder to correct any swing on take off. 

I wish I was as good as you but as I am not I have to cheat a little bit.

 

Steve

[Martin McIntosh]

One thing I did notice was that when a fair bit of rudder was applied on take off it would push the nose down ( think it is this model). Just had a peek at it and it has 30g of weight at the tail - I do keep tail end construction as light as possible.

[EarlyBird]

1 minute ago, Didier said:

You mean with the queue the delivery from Sarik? What is the normal turnaround time from Sarik?

I have them all waiting patiently to find out who will be the next victim. The delivery from Sarik is normally about two weeks but with Christmas and you being in the Netherlands obviously it could be longer. Sorry.

 

 Steve 

[Peter Miller]

10 minutes ago, EarlyBird said:

I wish I was as good as you but as I am not I have to cheat a little bit.

 

Steve

Any tendency to swing on Take off is cured with a dab of opposite rudder.It is now so automatic I don't even have to think about it

 

I was interested a while ago to see WW2 fighters taking off from a US Navy carrier.  They were using great big bootfulls of right rudder.

[Didier]

36 minutes ago, Martin McIntosh said:

One thing I did notice was that when a fair bit of rudder was applied on take off it would push the nose down ( think it is this model). Just had a peek at it and it has 30g of weight at the tail - I do keep tail end construction as light as possible.

I saw in one of your post you modified the rake of the vertical stabilizer. I could not exactly see the difference in the picture. So you mean you cut the leading edge of the vertical stab to have more rake?

[Didier]

29 minutes ago, Peter Miller said:

Any tendency to swing on Take off is cured with a dab of opposite rudder.It is now so automatic I don't even have to think about it

 

I was interested a while ago to see WW2 fighters taking off from a US Navy carrier.  They were using great big bootfulls of right rudder.

All taildraggers, especially warbirds, requires right rudder during take-off. The trick is to slowly build up speed during take-off.

 

 

[Denis Watkins]

3 hours ago, Didier said:

I have been quickly through this thread and I saw 2 Ohmen’s with FS20/26. 
Both models the engines are upside down. No problems with starting or cooling of the engines?

I was thinking about installing the engine with the cylinder pointing to the right from pilots view (flight direction). 
To prevent flooding the engine and better cooling. But the looks are better with the cylinder down of course. 

 

Hi Didier, I see you chose a more suitable model.

If you want to fit and run your motor without flooding, and inverted

Build a floor of your own design low down on the front bottom of this picture, 

For your fuel tank to be correctly feeding more inline with your carb

As the original is designed for electric propulsion.

 

 

Edited December 10, 2022 by Denis Watkins

[Martin McIntosh]

Yes, I did alter the rudder angle and lower area a little but I am a former F3A flyer and things like that and the dihedral can have a huge effect on performance but then I am probably over fussy. Just build as is and you will have a good model.

Dropping a wing in a loop would suggest a serious wing imbalance. The way to check this is to fly downwind directly away from you at height, close the throttle and push down into a half outside loop. Note which wing drops and add weight (nails) to the other side until the model exits level.

[Didier]

1 hour ago, Denis Watkins said:

 

Hi Didier, I see you chose a more suitable model.

If you want to fit and run your motor without flooding, and inverted

Build a floor of your own design low down on the front bottom of this picture, 

For your fuel tank to be correctly feeding more inline with your carb

As the original is designed for electric propulsion.

 

 

Thanks for your suggestions! 👍

[Didier]

Peter or anyone else. 
What size are those clips?

I try to collect as much as possible before the kit comes. 

Edited December 10, 2022 by Didier

[Peter Miller]

2 inches wide but that is not critical

[Didier]

56 minutes ago, Peter Miller said:

2 inches wide but that is not critical

Thanks peter

[kc]

Those clips are called 'Fold Back Clips' although most of us think of them as 'Bulldog' clips which are slightly different.  Available on Amazon or Ebay but are quite a normal thing in stationers shops in England.

[Didier]

I found them! 50mm (+/- 2 inch)