kevinbell

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Has anyone ever had to correct the geometry on a badly built Wellington Bomber???
I bought a second hand Aerotech Wellington Bomber and measured the plane but found some very unusual readings.
I'm in the need of some geometry specs.
This is what I found. [:@]

-Right wing wash out -1 degree
-Left wing wash out +2 degrees
-Engines down thrust 6 degrees
-Wing at 0 degree incidence with the horizontal stabiliser leading edge down 2 degrees and a twist of 2 degrees.
The C of G is unknown ( 4 1/2" ) ??

I did fly the plane knowing this but there was not a lot I could do about the wing, it flew for about 10 minutes with great difficulty then ended in tears..... It stalled the right wing and crashed.
I'm in the process of repairing it and want to correct these problems.
If anyone has ideas or can help, please let me know.... I will appreciate it.
Cheers
Kevin

Ram-bro

My Feedback: (101)

sorry to hear about your misfortune. I have the Wellington by Aerotech. I did nt build it so I cant pass those #s on to you. It flies great, pretty fast on the 2 os 46s, a little heavy on the ailerons but a great 1st twin airplane. If there is anyother way I can help....let me know

Sledge-RCU

----- Original Message -----
From: Marv & Shirl Reese
To: Tom Hammer
Sent: Thursday, April 07, 2005 7:25 PM
Subject: Re: Wellington Bomber set up geometry


The Wellington was a twin engine WW11 bomber with a geodetic wooden fuselage and a strongly tapered wing. For all practical purposes I would call the horizontal stab zero degree's and 2 degrees positive incidence in the wing. As a result I would put in 3 degrees of wash out in both wings and flatten the horizontal so that it has no twist. A right wing stall would be no surprise if it actually had wash-in, as he reports.
I doubt the need for 6 degrees of downthrust as 2 or 3 degree's is usually enough. As for the balance point I would refer him to http://users.mo-net.com/shirl/Design.html#balance

kevinbell

My Feedback: (2)

Thanks for the reply.
I do appreciate it, I've found it difficult to get some real feedback on this issue...
I have repaired the one wing to match the other, so now with the centre of the wing reading zero both tips have 2 degrees wash out, not 3, too much work to change the other just to get another degree.[:'(]

I had a look at the link to the website, it seems that the wing does have 2 degrees incidence if you take it that the horizontal stab as zero.

I don't know why it climbed so much, I had a ridiculous amount of down elevator trim, maybe c of g. I think it was 5" from the leading edge.... I thought 4 1/2" wasn't enough.[&o]
I fly aerobatic planes mostly and have the c of g as far back as recommended.

Cheers


Kevin

Baldeagle

My Feedback: (7)

Is the bomber an all wood kit? Does Aerotech have a Web site? Thanks Rich

Ram-bro

My Feedback: (101)

kEVIN, AS i NOW REMEMBER, MY wELLINGTON HAS A LOT OF DOWNTRIM IN IT ALSO JUST TO FLY LEVEL.

kevinbell

My Feedback: (2)

The plane is a foam/veneered balsa/ply construction.
They don't seem to manufacture the Wellington anymore, well... not that I can see on the only web site for Aerotech.
I think 12mm of down elevator trim is far too excessive....

Kevin

Idigbo

Kevin, the Aerotek kits are all copies from somewhere or other. The Wellington is a copy of Eric Evans plan, 86" span for two 30 motors. I've had a couple, they fly well although the tailplane is set with the leading edge very high, which would explain your need for a stickful of down trim. The plan is still available, along with cowls canopies nacelles etc. I have the plan if you want to know anything, like movements and the Cg. You really dont want one of these with a rearward Cg, you will never see a twin flick in quicker! Pleasant thing to fly, although does become a real *****cat to land if you fit flaps. Flaps are not on the plan, but they are a simple mod to make. Here's a pic of my second, shame to cover it up!

Ian.

MANFRED

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Looks like the field of unbuilt dreams

Idigbo

Manfred, you can never have too many projects on the go!!!!

Ian.

kevinbell

My Feedback: (2)

Thanks for the info.
My tail plane leading edge in down 2 degrees with the wing centre reading 0. Would it make sense to have the wing and tailplane 0? If not, how do you know if the tail or wing has the the incidence?
I fly and set up my aerobatic planes with 0 incidence on both wing and tail. I thought the tail naturally will fly at 0, hence it being the datum then put positive incidence on the wing. If that's how I measure the plane then it has 0 on the tail and +2 on the wing.

Kevin

dicknadine

A real beauty. and I thought that I had a hanger full--WOW they all look super. dick

Idigbo

Kevin, I wouldn't put the tail at 0, as the plan shows a lot of positive incidence, which is why your plane pitched up. The motors would be better with a couple of degrees down thrust at the most. The port engine needs to have little or no sidethrust, with the starboard motor at about 2 degrees right thrust. I could root out the plan and look for the incidence set up if you like, or, if you are good, I could send you the plan so you can sort it completely.

Dick, cheers for the nice comments, most of the planes in that pic are now fliable, one or two of them have found new homes, but there is more to fill the space! (isn't there always?)

Ian.

kevinbell

My Feedback: (2)

Thanks Ian,
I would appreciate anything you could give me, I don't understand how you decide which is zero or positive. I suppose you have a line down the fuz as zero and try to set up from that.

Cheers

Kevin

Idigbo

Kevin, I'll be at Old Warden at the weekend for the ************* fly in, if that is close enough for you you could pick them up if you say you are going, or you can give me your address, but I won't be able to send them till next week.

Ian.

Blue Sky

My Feedback: (1)

Hi Ian,
Would you happen to know where I can get the Eric Evans plans from that you mention? Are they the ones that RCM&E/Nexus offer (I have no details on that particular design as their website is u/s)?

Cheers!
Blue

alanc

IAN IS BANG ON ON THIS a mutual friend of ours had this the eric evans welly, and the aerotech is a pooooor copy, our friends had the tendency to want loads of down, so, off i went to his place, with my robart incidence meters, we put the plan on a wall, and i positioned the 2 meters, settting the wing level, the tail had 6degrees positive, the engine also had a rake of down in them, we re-set the tail, with the doubting owner looking on-----it flew SUPERB! the sit in the air was bang on, we both havnt seen him for a while, wonder if he still has it?

and, if you want to se what that indigbo is up too, ask him to show yu the piccys pf his tiger moth, and his new;y restored lanzo record breaker!!!!!

Idigbo

Blue, the plan is the same one you mention, 86" span, for two 30's, built as per the plan, they do fly well, but recommend the fitting of flaps to slow the landings up very nicely. The plan shows all of the structure, the fitting of the retracts etc. There was cowls, nacelles and a full set of transparencies available too, The plastics and the cowls are simple enough to scratch build, but the nacelles are worth finding as they are one piece mouldings that are built into the wingat the rear, with the mainspar going through at the front end, forming part of the retract mounting, a well thought out design.

Ian.

Purple Pilot

Blue,
Looks like an interesting project - don't forget to do a build thread

JohnMac

Hi Kevin
The advice that Sledge has given you is correct. The tailplane is ALWAYS 0 degrees incidence because the cordline of the tailplane is the datum line from which we measure. Forget the fuselage, it is irrelevant to this discussion. The wing root then has an incidence angle of 2 degrees, which is reasonable. The wingtips should be washed out about 2.5 degrees. (to be honest this depends on the section but this figure is a good guide).
Lets turn our attention to the CG position. This is not an aerobatice model, it is a heavily loaded complex scale model. Therefore the CG position should be safe and conservative. I would recomend a starting point of about 27 % of the root cord, and hopefully the model should prove a little nose heavy, but safe. Then move the cg back a little at a time until you are happy with the flight.
Good luck and good flying.
regards,

John

alanc

SORRY JOHN, respect you as i do, the evans plan, which this aerotech kit is ripped from, show a positive tail incidence, the welly was a plane that sat with its ass high up, and the mates welly i talked about, had the loads of down syndrome--until i had a good look at the evans plan, set it up on the wall, and measuerd its accuratly, with 2 robart incidence meters, when transposed to the model, it gave a sweet flying machine, how this would do with the aerotceh one, in the stae it is in, i dont know, the evidence on here, of repeated loads of down, to fly level, would bear me out

best thing, is to get a copy of the superb evans plan, and see for yourself

JohnMac

Hi Alan,
I am sorry but you are wrong. The Wellington cannot have had a positve tail incidence 'cos there aint no such thing. If it's written down on the plan, the plan is wrong! Let me say this again, the cordline of tailplane is the datum line for the aircraft. There are no maybe's, caveats, or exceptions to this rule, it is a law of physics!
However what matters is that there is a difference between the cordline of the tailplane and the cordline of the wing, and that we can measure and fix this angle. For the Wellington to fly correctly, the advice I gave previously is good advice and will get Kevins model in the ball park, so that he has the chance to perform the final trim.
You quite correctly mentioned that the Wellington flew with a nose down sit. This is a secondary consideration, but let us deal with it.
Most modellers believe that the datum line is a line drawn on the fuselage. From an aerodynamic standpoint it is not as I have already stated. The fuselage is irrelevant to trim and can be totally removed and replaced with any damn thing you like that will hold the wing at the correct to the tailplane. But since this is a Wellington, it would be awfully nice if we "hung" a Wellington fuselage on the wing and tail, and this is exactly the way to think about it. Get the realtionship between the tailplane and wing correct first and then add the fuselage at the correct angle to provide a scale "sit".
So to design our model the first four steps are:
1) Draw a horizontal line.
2) Draw the section of the tailplane on this line.
3) Measure the incidence angle that has been decided on and draw the wing root section in the correct position and at the correct angle.
4) Draw in the fuselage in place at the angle that provides the correct sit.
To work the other way will end in confusion rather like knitting fog.
Whether the correct sit will result will depend upon the Angle of the wing first and foremost.
I hope this better explains what I am trying to say.
Regards,

John

Idigbo

John, to say that your way is the only way is stetching things a little, no question. I have designed a few models in the past and always draw a datum line along the fuselage and work from that for everything. If you used the tail incidence of the Wellington as the datum, it would nearly come out of the top decking as it works its way forward. Do you use the same method for T Tails and the like? And what about biplane tailed aeroplanes, do yo have two datums?

The sit of a plane has to rely on the relationship of the mainplane to tailplane, also to a lesser degree the thrustlines too. If you set the tail at 0 and have +ve on the wing, then you CAN end up with the plane needing lots of down trim which is what has happened with this Wellington.

It makes no difference where or what is used for the datum, as long as this datum is used for all aspects of the airframe.

Ian.

JohnMac

Ian,
I never claimed that this is my way as you put it. Far cleverer people than I decided that this is just the way it works from the point of view of aerodynamics, that is all.
So Ian tell me, exactly what standard line on the any fuselage can you ALWAYS use as a datum? Yes, I understand that any line will do in principle, but what is the point in A) making it harder, and B) going against a standard aerodynamic convention which provides a unified point of reference for every occasion? One may ask a fellow passenger on a train !QUOT!what time does Kings Cross arrive at this train?!QUOT!. Not inaccurate from a Physics point of view, but rather unconventional. Conventions can be defined as a set of standard terms of reference that everyone can understand. So we ask !QUOT!when will this train arrive at Kings Cross?!QUOT! and we define incidence as an angle measured from the cordline of the tailplane. Two things matter to longitudinal stability, the incidence of the wing and the CG position ( I am assuming here that we are not going to play with the tail volume coefficient, but even if we did, the statement remains true). We ignore the fuselage since it is not relevant to longitudinal stability at all.
The trim of any aircraft and the sit of an aircraft are two quite different things, and the later follows from the former. If Kevin ends up with a Wellington that sits right in the air, but is unstable and crashes, will he be a happy bunny? Conversely, if he has a Wellington that flies great but sits a bit wrong will he care? Both would be nice but since this is a kit, to some degree the die is cast.
As for your biplane tailplane, well only one such comes to mind that I have examined. In this case the tailplanes !QUOT!appears!QUOT! to be parallel. This factor is important since if the angles were different then we would need to engage in some fairly complex math to find a line of aggregate influence (but why would anyone use different angles anyway?).
So based on the above assumption, the two line are parallel and therefore either line can be used as you datum.
Next, you mention the thrustlines. Thrust lines do not affect aerodynamic trim as such but of course the the power coupling does. For this reason my advice for trimming is to make the model climb to height, Throttle back to tick over, and trim the model for longitudinal stability. This way removes the thrust couple influence and ensures that we have a model that will glide in a stable manner. Once this step is done, apply power and note the result. Any severe pitching or rolling moment should then be countered by adjusting the engine(s) thrust line.
Finally. let us return to Kevin's problem Wellington. The most pertinent piece of advice I provided was to use a safe CG position,which will have an immediate effect on the flying characteristics.
Regards,

John

Blue Sky

My Feedback: (1)

Ian,
Thanks for the info. Do you happen to know how scale the outline of Mr. Evans' plan is? Looking at the construction (in your photo) I should imagine it is one of the better designs .
I have ordered a copy from Nexus/Highbury so I just hope it turns up.
Cheers!