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HomeAircraftFixed-WingFixed-Wing Main Discussion › Sorry, another plank question.
02-05-2010 01:48 AM  8 years agoPost 1
Spitfire1

rrElite Veteran

Perth Australia

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I have know where else to get info.

When I got my Foamie cessna the motor was not bolted on straight to the fuse, I thought it was a design flaw and fixed it to make it straight, now Im hearing there meant to be at an offset, does any one know which direction there meant to be pointing??.

Im trying to work out if it was a design flaw and if its why Im haveing so much problems landing the damn thing, my ducted fan jets seem way easier to get down but there all belly landers.

Jason,.

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02-05-2010 01:54 AM  8 years agoPost 2
Spitfire1

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Perth Australia

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If I dont use any washers, the prop will be slightly angled to the right if looking from the tail.

So the prop will try and turn/yaw the aircraft to the right, is this the way its meant to be?, if so Il remove the washers I put in to make it straight.

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02-05-2010 02:03 AM  8 years agoPost 3
thtoyman

rrKey Veteran

Gone ,Flying.

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All you done was to put washers in? If so just take them out. Yes some planes need to have off set motor/engine.

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02-05-2010 02:11 AM  8 years agoPost 4
Spitfire1

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Perth Australia

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Thankyou, Ive removed the washers now the prop should pull to the right next time I fly.

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02-05-2010 04:37 AM  8 years agoPost 5
500Driver

rrApprentice

Burlington, IA

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In case you are the curious type...the reason for the "offset" is due to "P-Factor" and "Spiraling Propwash":

P-Factor is an aerodynamic effect that causes prop-driven planes to yaw when they are flown at high power and low speed (takeoff and climb out, for example.)

At low speeds, the plane flies at a substantial angle of attack, and so the airflow is not parallel to the plane's axis. Relative to the plane, the airflow is directed several degrees upwards. Now the prop axis is normally parallel to the plane's axis. As the prop rotates, on one side the blades are travelling upwards and on the other side they are travelling downwards. (On most planes, the prop turns clockwise, as seen from behind, so the left side goes up and the right side goes down.)

The upwards angle of the airflow causes the downward (right) side of the prop to have a greater airspeed and angle of attack than the upward (left) side. So the downward (right) side of the prop generates more thrust. Pull harder on the right side of the plane than on the left and the plane will yaw to the left.

This is one of the reasons why most real prop planes need a certain amount of right rudder to keep them straight during takeoff and climb out.

The other factor that requires right rudder on takeoff (in planes with clockwise props) is spiral propwash. The sideways component of the spiral propwash strikes the vertical stabilizer from the left (in conventional single engine configurations), also causing a yaw to the left. In general, the spiral propwash effect is a lot stronger than P-factor.

You also need right aileron to keep the plane straight to counteract the rotational torque from the engine(s).

When in doubt...auto out

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02-05-2010 05:07 AM  8 years agoPost 6
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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What he said, and he left out nothing. In a nutshell it's for better control at low speed / high thrust moments.
Sorry, another plank question.
How 'bout you get over this 'apologetic about planks' rot right now! This may be a heli forum, but planks have been around a lot longer than they have.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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02-05-2010 01:32 PM  8 years agoPost 7
fla heli boy

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cape coral, florida

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I built a highly modified Goldberg Xtra 300 with a YS four stroke and I had to build in a ton of offset due to torque. If it came with an offset, it was done so on purpose. Usually offset is down and to the left if looking from the rear.

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02-05-2010 07:07 PM  8 years agoPost 8
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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Usually offset is down and to the left if looking from the rear.
Down and to the right, actually.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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02-05-2010 08:17 PM  8 years agoPost 9
fla heli boy

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cape coral, florida

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yep, you're right.....it's been so long since I built that 300 (my last build).

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02-05-2010 09:11 PM  8 years agoPost 10
nitrojunkie

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N.C

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Thanks 500Driver I have recently wondered about this my self.I am working on a Depron Fokker DR1 that has an offset and was curious as to why myself.You gave a very good explanation.Nice to know plane guys have some similar issues that we do to deal with.

I love the smell of nitro in the morning..

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02-05-2010 10:57 PM  8 years agoPost 11
AirWolfRC

rrProfessor

42½ N, 83½ W

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Usually offset is down and to the left if looking from the rear.
I thought it was down and to the right.

. . . . yep . . . to the right.

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02-06-2010 08:43 AM  8 years agoPost 12
Spitfire1

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Perth Australia

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Sorry about no reply, not doing to well right now, not even well enough to read everyones reply`s, hurt my back real bad.
Hopefuly read responses tommorow. Thanx.

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02-06-2010 04:00 PM  8 years agoPost 13
500Driver

rrApprentice

Burlington, IA

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Don't tell anyone but I went to Daniel Webster College and learned how to fly planks before helicopters.

I know...we all have dirty secrets and skeletons in our closets

When in doubt...auto out

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02-06-2010 04:06 PM  8 years agoPost 14
fla heli boy

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cape coral, florida

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I think quite a few of us are guilty of that. Though, shhhhh..., I do miss my planks. I love building, so when I get the appropriate space again, I'll probably get another one. I bailed 60% of the way thru on a 33% xtra 260, no way I've got room for something that big.

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02-07-2010 05:20 AM  8 years agoPost 15
Spitfire1

rrElite Veteran

Perth Australia

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I just want to get to the point I can have a nice looking composite 70mm jet and be able to land it without breaking the retracts, at the moment Ive had to spend money Ide rather not on a couple of planes I dont realy like to try and learn landings, which is not working out to well for me at the moment.

I really only like flying the fast jets, but at the moment its only belly landings I can do with them, trying to bring one of them down with fragile retracts is out of the question at this point of time.

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02-07-2010 05:30 AM  8 years agoPost 16
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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I just want to get to the point I can have a nice looking composite 70mm jet and be able to land it without breaking the retracts
Do you use a flight sim?

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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02-08-2010 03:47 AM  8 years agoPost 17
Spitfire1

rrElite Veteran

Perth Australia

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Im useing Phoenix, but not sure its much use, Ive only flown foamies so far and I think I need a wood or composite plane thats more responsive.

Feeling heaps better now though, managed last night to land the Cessna over and over again without issue, did not think the plane would last long enough to get to this point, up til now every 1 out of 2 landings was a crash.

Finding the trick with the big 1.4 foamie cessna is the wings are so unresponsive on landing that big jabs of full aileron are required due to keep it level when the wind makes the wings dip.

Just about have my rc lander f16 ready to maiden, will stick to belly landings with it though, Ive used a freewing f35 to get ready for the RC Lander.

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02-08-2010 03:57 AM  8 years agoPost 18
GimbalFan (RIP)

rrProfessor

Big Coppitt Key, FL

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A repeat from another plank thread:

Best advice I got on landings was while getting my full-size ticket: You don't really land a plank. After setting up on final and throttling back, you glide 'em to about a foot off the runway, then hold them there until they land themselves.

op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t

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