Gemma Jane

I'm pretty sure Eric that P-Factor doesn't come into rotor theory, heli blades are flappy to avoid it, not fixed like the props on most models and small planes. Could be wrong though, never studied rotor theory much but I think for a heli you would actually be looking at  dis-symmetry of lift...    P-Factor is 'real' it is experienced by fixed wing  prop aircraft whenever the prop(s) is(are) inclined to the free stream velocity. However it isn't why motors are offset....... as you say that is because of the the helical flow.   We also should be careful about saying 'theory', to me this stuff is like trying to convince people the earth is round.... aerodynamic theory is a lot more involved, P-Factor and helical flow are just basic physics and known to any pilot and hardly rocket science, I gave up talking about aerodynamics theory on the internet a long time ago!

It really depends on the type exactly what the prop wash does Richard, but it's real. One of the other ways to counteract apart from offsetting the motor is to offset the fin, if it wasn't there why would that be done!   There is an old saying that states if we could see the airflow we wouldn't fly... I tend to believe it.  Oil stains are little to go on, the boundary layer has a totally different flow pattern to air just  millimetres or more away from the aircrafts skin.   They say a picture says a thousand words:   But at least this one does show how prop wash can bypass the wing and when it strikes the fin cause yaw, fluid dynamics... who needs it eh!   PS I filched this picture from a forum thread where the poster was happily describing the above as depicting 'P-Factor'.... the blind leading the blind!Edited By Gemma Jane on 25/07/2010 19:17:02

Gonna have to get me one of these Stephen, thanks for sharing. Ditto the bench, I always spend half a day tidying up before starting a model... it doesn't last long into the build though!   I had exactly the same problem will belly landing at first, it's how I lost my PZ Mustang after being use to a U/C on the HZ Cub. It comes though with practice as you have found.  I think the mind is saying it's gonna hurt so we slow it down too much and then it stalls and does hurt! I'm now wondering if I could land a model with a U/C as my preference for the last couple of years has been belly landings once I got the hang of it.

Truth is sparks59 practically anyone in the real world would just consider all the effects as 'torque' and get on with it!   When I fly full size or models I'm no more worried about the 'net circulation' around the wing than I am P-factor. Most of these things are either of purely academic interest or worth having some grasp of when designing models or full size. When it comes to flying either, well that's an art not a science and the theory is best left where it belongs in the books!! So I would just keep to thinking what you did, I'm sure it's not done your flying any harm at all.

Another vote for the actual reason for building in side thrust being the helical airflow hitting the fin and rudder.   P-Factor is transient as Martin has said. As is gyroscopic procession. We wouldn't build in side thrust to combat them as they are not effects that are constantly experienced. They are effects which we compensate for with the controls, if with a model they are even noticeable.   Reaction torque.. well I bet we have all seen it, open the throttle too fast and the model flips on it's back as it takes off the ground (DP take note... it's not caused by using the ailerons!) The cure is then of course... don't open the throttle too fast as P-51D pilots knew very well, so lets leave that out of the discussion.   One of the interesting things is that by building in some side or down thrust there is a P-Factor being introduced. I'm not about to sit and do the vector analysis for a typical model (too lazy) but I bet it's pretty much negligible in straight and level flight and we would just trim it out on the transmitter without a second thought. When P-Factor becomes an issue  as Martin has said is when a taildragger lifts it's tail... oops the P-Factor disappears as the prop is no longer asymmetrically loaded so one suddenly finds they are overcompensating.... or perhaps not because right at the same time gyroscopic procession will start to have an effect... how much and how long for? Well it depends how fast the tail is lifted.   So Simon, those more qualified than yourself are in my opinion leading you down the wrong path. If you can pick up a copy of Harvey S. Ploude's 'The Compleat Taildragger Pilot' he not only explains all the effects in clear detail, he also carries out a mathematical analysis of P-Factor - you'll soon see it is only transient and that the side thrust is there to counteract helical flow... also in reality adding side thrust or down thrust is going to introduce a P-Factor in level flight - so clearly the reason for adding it is not to counteract P-Factor... as if we didn't add the offsets there would be no P-Factor when the model was in level flight....   Time for bed me thinks....   

I didn't find this message until 2400... but then again that might be because I was watching telly all day and not on the forum much.     Sure was a great days telly on Discovery!  

You could glass straight over it Craig, then with a razor blade cut away the material you don't want to free up the ailerons. You would actually stick it to the trailing edge as such, just work to the edge of each surface leaving strips of glass cloth in between to trim later.   Perfectly valid though to cover each part separately if one wanted to.     Whichever seems logical and easiest to you will be best, I tend to do tail surface separately, wings and ailerons together, can't even tell you why, it just works for me.

Also the plan is for a bomber, which is fine but I would have loved to have had the night gunner/ fighter, there are no plans for this though. I suppose the plane in it self is more or less the same, I would make the guns on the nose myself however im finding it hard to get good photos of the night fighter, this would be helpfull so I can construct the guns for the nose and also thier seats if that makes sense.   There were a lot of mossie variants though a Google image search will bring many photos another way is to buy a plastic kit of the variant you want as a guide. Even a 1/72 scale kit helps. I used one as a guide when putting guns in the nose of my GWS P-38.    Here's a search  I did for 'mosquito night fighter'   http://www.google.co.uk/images?rlz=1C1GGGE_enGB360&q=mosquito%20night%20fighter&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi    And one of the sites it turned up:    http://www.vectorsite.net/avmoss_1.html   And a piccy of the guns and ports on a night fighter:      http://www.flickr.com/photos/flufzilla22/2553403178/lightbox/   Your build would be a good excuse to go see this plane at the Yorkshire Air Museum and take lots of photos!   Glassing with either resin or PolyC is one of those things that seems more difficult than it is. I use to think wow that must be hard but it's actually much easier to do than I expected. 

Good point John! I should clarify what I meant Paul was you will not need to worry about rudder inputs once in the air, just use the ailerons to bank and turn with a little up elevator, just the same as you used the rudder and a little up elevator with the HZ Cub. It should feel very natural to you, you won't even be thinking is it aileron or rudder doing the work the model will handle in much the same way as before.   But as John says you will need to use left stick (Mode 2) to steer on the ground. Just get use to it with a little slow taxi around first, but be prepared once airborne to turn with the ailerons.

Hi Paul,   I went HZ Cub to PZ Trojan, no problem at all.   With the HZ Cub transmitter rudder is on the right stick along with the elevator (well the only stick) so it just becomes natural to use the aileron instead of rudder to turn when you have 4 axis in Mode 2. Effectively you will find you will replace your rudder inputs you learnt with aileron, then have to remember to use a little rudder sometimes to keep it all nice and in balance.    So in effect what you will be able to do with your 4 channel model is not use the rudder, as opposed to sticking with the rudder and not use aileron.

Thanks for the heads up on A Plane is Born Ad's. I've been recording the series on Quest and got some time this afternoon to watch four episodes, well worth watching.  

Dauntless link for Romeo Whiskey   http://www.windrider.com.hk/product.asp?id=164      Windrider ship direct btw $20 worldwide    Edited By Gemma Jane on 19/07/2010 20:35:38

Windrider to a foam Dauntless, it's a lovely kit too, must get around to doing it!   Agreed Romeo Whisky, I would go for a very scale Skyraider too.

Agreed Mike, a spreadsheet is the way to go. Best way I've found is to make it do all the calculations automatically so one can play with things that might be a problem and figure it all out to a target wing loading. Otherwise it's just guessing and my guessing can be miles out. I've also done a spreadsheet so I can do weight and balance, no point trying to cut weight out of a design and then adding 400g of lead in the nose so it will fly!   I really hope Leslie hasn't been put off, I'm looking forward to seeing what the trainer will look like with what I hope has been some helpful guidance and perhaps the Bullet as a 3rd/4th project build??

PS regarding the wind, best learn when there isn't much or it's right down your selected runway. How do foam models fly in the wind? Depends a lot on who has the sticks! Generally though when learning, go early mornings and late evenings when it is very calm.

Chris better not start with a foamy fighter, it will last you about 30 seconds if you have no previous experience.   If you want to go the teach yourself route, look at the HZ Cub as a first model, not a fighter. The cub will forgive far more mistakes.   My progression was HZ Cub, PZ Trojan then PZ Corsair, then it's pretty much which ever you like the look of and go enjoy. All three of these are Z foam and survive crashing pretty well. (Not that I ever crash them!)   Also if going self taught, buy a descent sim like Phoenix and make sure you can fly in different winds and with different models before trying it for real. The main thing is the coordination which is best learnt well in advance of your first real RC flight.   Edited By Gemma Jane on 15/07/2010 14:38:21

I've just realised Spackle was already done... doh!