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Old May 27, 2012, 04:13 PM
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Originally Posted by flyrod View Post
PeterF, have you been flying much? I was wondering if anyone puts different pitch propellers on twins. With both engines turning the same direction the airplane is asymmetric anyway, so with one low pitch prop and one high pitch prop there might be an advantage? This might also help with engines that are possibly undersized because the low pitch prop would help with takeoff and the high pitch prop would help with good airspeed. It seems like you would want the low pitch prop on the left engine so that the higher thrust at low airspeed would be more inline with the C.G.
Flew it yesterday again to appreciative comments from the other members at the field. April and May weather in the UK has been dire so had not flown it for a while. It is a nice idea the worry in my mind would be in deciding how much you needed to balance the small assymetry from the left and right engines. I know that on my DC3 400-500rpm difference in 10,000rpm seems to make little difference. On the RCV60SPs in my Mossie I would worry that 16x12 on one side and 15x14 on the other would be too great to handle as that is a 15% difference on pitch speed but that is just gut feel rather than any underlying technical knowledge.

I was reading a magazine article recently on flying twins and the issue of the assymetric behavious even if the engines are balanced. The theory proposed for twins veering the one way on take of mainly occurs with taildraggers when the tail is down so the wing is presenting an angle of attack and that this diminishes once the tail is up. Until I read this I had been trying to keep the tailwheel down for as long as possible for better steering but after reading this I am letting the tail rise sooner and it does seem to track straighter with less rudder input. Sometime with my DC3 I got nice straight tracking on take offs and others I was fighting the plabe for longer and never understood why. Live and learn.

Peter.
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Old May 27, 2012, 05:51 PM
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Baltimore MD USA
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Alright it's unmoulded and I learned a few things.
1)you can't use to much wax
2) use more plaster to make it thicker
3) use more catalyst on the first layer
4) make first layer thicker be for adding glass
5) let it cure for 24 hrs at least

And with that said the next one should be better
there are a couple of spots that I will have to do cosmetic surgery on where there was a few trapped bubbles.
but all and all for the first time this came out alright I don't have a scale but it's not very heavy. I had thought about doing a gel coat on the first layer but didn't because it was another $30 or so but when I touch up and prime the cowl I think it will do.
Now comes the real hard part making a right hand copy That will be in a few days but any way check it out and let's hear about it good or bad.
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Old May 27, 2012, 06:54 PM
No Hangar Queens!
Maryland
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Looks GREAT for your first time! Use some automotive spot putty like J does. Work well and is not too hard to make booboos better.
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Old May 27, 2012, 07:05 PM
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Originally Posted by PeterF View Post
I was reading a magazine article recently on flying twins and the issue of the assymetric behavious even if the engines are balanced.
I think this is caused mainly by p-factor, which is asymmetrical when both engines turn the same direction. This would be another argument for using different pitch propellers on a twin...

http://en.wikipedia.org/wiki/P-factor
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Old May 27, 2012, 08:46 PM
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Well I put a quick skim coat of Bondo on the whole cowl and ground off the aft edge then gave the whole cowl a rough sanding 80-120 grit just got rid of all of the bumps. And the bondo dust got rid off the stickyness of the resin then wiped the whole thing down w/ alcohol and shot it w/ high fill primer now let it dry until tomorrow and I'll see everything that needs filling.
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Old May 27, 2012, 11:00 PM
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New Zealand, Manawatu-Wanganui, Palmerston North
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Quote:
Originally Posted by flyrod View Post
I think this is caused mainly by p-factor, which is asymmetrical when both engines turn the same direction. This would be another argument for using different pitch propellers on a twin...

http://en.wikipedia.org/wiki/P-factor
Saw this video a while back, and shows what happens with different pitch rpops on a model
Mosquito RC plane crash (1 min 40 sec)
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Old May 27, 2012, 11:16 PM
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OUCH ....Thanks grahamj4 ...WE don't need any of that kind A ACTION!!!

I think the best solution to this whole problem is to change the timing of one of the engines so it runs the opposite of the other and they cancel each other out and there for a plane that doesn't pull to one side.

of course this requires quite a bit of work and knowledge of your engine,skill,time and patience.

I guess that's why not very many people go this rout!
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Old May 28, 2012, 12:45 AM
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Originally Posted by splinterz25 View Post
OUCH ....Thanks grahamj4 ...WE don't need any of that kind A ACTION!!!

I think the best solution to this whole problem is to change the timing of one of the engines so it runs the opposite of the other and they cancel each other out and there for a plane that doesn't pull to one side.

of course this requires quite a bit of work and knowledge of your engine,skill,time and patience.

I guess that's why not very many people go this rout!
It's easy if you go electric
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Old May 28, 2012, 01:59 AM
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United Kingdom, England, North York
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Quote:
Originally Posted by flyrod View Post
I think this is caused mainly by p-factor, which is asymmetrical when both engines turn the same direction. This would be another argument for using different pitch propellers on a twin...
Just looked at the Wikipedia article and yes P factor was what it was called in the magazine article. The Wiki article also states that it will be worse for taildraggers if the tail is kept down. Very interesting and finding this nugget and has helped my twin engined take off runs stay much straighter. I am the only person flying twins at my club so no one there knows these sorts of nuggets.

Quote:
Originally Posted by grahamj4 View Post
Saw this video a while back, and shows what happens with different pitch rpops on a model
Well I am glad I did not try it out on my Mossie, said my gut feel would be too much difference.
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Old May 28, 2012, 04:19 AM
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Here is a photo of Traplet's MK XVI cowls and mine MKVI mine does not have the scoop just under the spinner and I've added the lower intake scoop in fiberglass instead of balsa. this will let me use the scoop for cooling, I will add small bumps,scoops and panel lines later the other thing I did was maker it a bit deeper so (hopefully) I don't have to cut my cowl.
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Old May 28, 2012, 06:52 AM
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Okay now that the primer has dried I sand off about 80-90 percent this shows you where to spot puddy I use Claw Glaze. But you can use any glazing puddy you can get at a auto store mine is very old one tube of this stuff last a very long time, and you don't want it to thick so I use thinner and spread it out thin (dries faster) and sands easer if you still have any big holes use bondo again there.
You can see what the heavy coat of the black primer has filled once dry I'll sand again and shoot another coat of black primer.
This will again show what I've missed and repeat w/ the puddy.
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Old May 28, 2012, 03:39 PM
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I've been trying to find photos with the color scheme the 143 Sq. used at Banff and the the call letters for one of the planes that carried rockets so far I have found one color photo and from what I have read the under side of the planes were light grey/sky blue and the topside was dark sea grey and they had yellow spinners and the call letters were RS625-NED on one of the birds. Max Aitken's plane had drop tanks and red spinners and I can't find what his call letters were, I'm not sure who flew the RS625-NED but I'm trying to get a few books to see if I can find this out.
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Old May 28, 2012, 07:45 PM
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Well I didn't do so much today just sanded the spot puddy once dry and shot another coat of high build black primer and letting that dry over night,
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Old May 29, 2012, 09:25 AM
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Alright made a test fit of the cowl this morning and it looks to be real close with a few adjustments it should work out fine.
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Old May 29, 2012, 01:58 PM
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Jersey, St Peter
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I'm getting to hate this man.Every time I look on this blog he does something original.But still hooked though.Keep up the good work Bruce.Inspiring me!
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