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Old Jan 15, 2014, 10:30 PM
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Johannesburg SA
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Build Log
RCG Build Off Handley Page Hampden

Good progress with the drawings so far although this is a nice complicated design and my first twin.

Will be going with a 12% scale giving a span of 1,768mm or just under 70 inches. Getting the CG in the right place has been a real challenge in terms of placing all the bits and pieces but with some careful design and building should be able to achieve it without having to revert to too much ballast.

I will be going "full house" with this one, ailerons, flaps, elevator, rudders, electric retracts, and gear doors. Scary number of servos, 14 in all, so will have to come up with a very safe electrics system. Suggestions would be most welcome.

Planning to use 2 x Turnigy TR3548/6 790 Kv motors each running on 4S 2650 maH batteries running through 40A ESC's. Each motor will draw a maximum of 31 amps swinging 10 x 7 three bladed props. This gives about 880 watts which will be more than sufficient and will provide reasonable flight times at about 75 - 85% throttle.

Can hopefully complete the drawings in the next couple of days, get the parts cut and maybe get started building by the end of this month.
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Old Jan 15, 2014, 10:43 PM
Übung macht den Meister..
Deuce's Avatar
United States, OR, Fairview
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James
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Old Jan 17, 2014, 12:27 AM
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Have completed the elevator and rudder drawings now and made a start on the nacelles.

Was going to try a complex system of levers to drive the rudders but space is a limitation so will opt for two micro servos for the rudders. The individual rudders are quite small in area so these servos should be able to handle the loads. Will use a separate mini servo to drive the tail wheel steering. The elevator and steering servo will be mounted forward in the fuselage to try and keep weight out of the tail.

The nacelles are going to be quite crowded with all the components that need to go into them.

Next task is the wings plus the joining of them to enable transport. My thinking is to split them just outboard of the nacelles and them permanently fix the middle section as part of the fuselage. This will make for a sound structure and ensure that there will just be the aileron servo leads to plus in when assembling at the field. Will also make transport easy.

Some progress but I find that a little time spent thinking through the design at the drafting stage, saves heaps when building.
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Old Jan 17, 2014, 08:37 AM
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Nice drawings of "The Suitcase". Have often considered it.

With the fixed centre section, why did you decide on two battery packs rather than a single 4S 5000 pack in the C/S? It would alleviate the crowding in the nacelles. Could a large pack fit in the bomb bay withe radio above it?

Martin
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Old Jan 17, 2014, 09:42 AM
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Hi Martin,

Thanks for the suggestion.

Yes it could just fit into the fus but the problem becomes cooling for both the battery and the ESC's. It would also involve a 420mm cable run from ESC to motor not that that is such a great problem if sized correctly.

We have fairly high ambient temperatures here particularly in the summer where daytime can see +30 degrees C or +88 F. This makes cooling air essential for all the power train components.

Having all these components in the nacelles with the big radials allows lots of cooling air through which will exhaust through the gap around the main gear even with the gear doors closed. I have made a rough calculation and it should give enough throughput.
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Old Jan 17, 2014, 09:59 AM
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Hi All,

I know I am still a veeeery long way away from finishing work but came across this really interesting variant of the Hampden as it appeared in the Coastal Command colours in the latter stages of WW2 when they were equiped with torpedoes. These were painted with a white underside and a dark sea grey topside.

There was one minor modification to the airframe where the aft rear gunner turret was made smaller to accommodate the tail fins of the torpedoes.

Have attached two images of plastic models showing the conventional camo scheme and one showing the Coastal Command scheme.

At the moment I am tending towards the Coastal Command scheme just because it looks different.
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Old Jan 17, 2014, 10:35 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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Soarbird have you tried a Google Images search on, Handley Page Hampden plans

It shows some plans, and certainly plenty of pictures of the 'Flying Suitcase'.

A nice project
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Old Jan 18, 2014, 03:14 AM
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Hi All,

Thanks eflightray. Have done a lot of looking around the internet to find the necessary information and collected a lot of the photo's an so on.

Here is an interesting link to a renovation/rebuild being undertaken at RAF Cosford museum. Many of these photographs have been utilised to scale the correct proportions particularly for the fuselage shape.

http://flickrhivemind.net/Tags/p1344/Interesting

Searching the internet, came across a great cutaway drawing.

In the meanwhile the wing plans are almost complete with just a few more ribs to be drawn. I think another week should see me ready to send of the component drawings to have them laser cut. I normally do all the cutting by hand but in this case there are so many parts that I may as well take advantage of technology. Besides, it will save many hours of time.

More news as and when it happens.
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Old Jan 18, 2014, 11:30 AM
The "pro" in procrastination
Steve85's Avatar
Canada, ON, Kingston
Joined Mar 2004
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You sure work fast, Malcolm! That link to the restoration project is fascinating. When it was shot down in 1942, the Hampden was so evidently outclassed by contemporary fighters that it must have taken nerves of steel to climb aboard for a mission. As an interesting factoid, Guy Gibson of Dambuster fame flew the Hampden on many ops earlier in the war.

Steve
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Old Jan 18, 2014, 02:55 PM
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I certainly understand the cooling consideration. Just one other thought - if the bomb aimers glazing was left out, it would let lots of air through.

I like the Coastal Command scheme very much. Easy to see when you are flying.

Martin
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Old Jan 19, 2014, 05:56 AM
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Thanks for the info Steve. In my reading up on the plane I saw that pilots loved flying this aircraft as it handled really well but as you say, it was a sitting duck when it came to defensive measures against fighters. Knowing that Guy Gibson also flew them adds just a bit more glamour to this project.

Martin, your suggestions re placing the battery in the fuselage and the cooling idea got me thinking and playing around with my design. I have tried to standardise on 4S 2650 maH batteries as many of my other planes use this set up. By paralleling a pair of them they will fit into the fuselage with easy access through the bomb bay doors which in this case will be a simple hatch. It also solves another problem in that when working on the mass and balance calculations, I would have needed about 110 gms of nose ballast to get the CG right. As the batteries can now be moved further forward, that problem is solved. In terms of the air exit, both the aft top and bottom gun positions had canopies that hinged backwards so will fit the "open" version to the bottom rear gun position, giving a very good through flow of cooling air.

Found some photographs showing the arrangement.

Otherwise progressing well but off to the field now to get some flying in.
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Old Jan 19, 2014, 08:19 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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If your batteries get hot, even quite warm, then the model may be grossly over powered for a bomber.

My B-25 93" span, B-17 100" span, and Sunderland 90" span, all have the batteries in the fuselage along with the ESC's. Plus they fly on 3s per motor, (3s per 2 motors on the 4 motors).
Once off the ground the throttle need to come right back, and they will fly on surprisingly little power. I currently use 4000mAh or 4500mAh packs and could probably have halved that Lipo capacity, and still had long flights for less weight.

Weight, generally = higher speed, the lighter the model the more 'scale like' a flight is possible.
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Old Jan 20, 2014, 10:35 AM
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Now things start to get interesting!

Looking at all the "bits" that need to be housed in the fuselage;

Elevator servo
Tail wheel servo
UBEC
Gear door sequencer
Rx
UBEC switch
Possible separate backup Rx battery??

it becomes a little crowded inside where there is just 65mm between the main stringers.

Whilst I liked the idea of mounting the batteries within the fuselage, with all the other bits in there we run out of space for a pair of batteries and ESC's so have had to revert back to crowded nacelles. The important thing is that all the kit fits in there.

But here's a question on which I would really appreciate some advice. Altogether, this plane will have the following servos;

Elevator x 1
Rudders x 2
Tail wheel steering x 1
Ailerons x 2
Flaps x 2
Gear doors x 4
Elec retracts x 2

This a lot of servo's (more than twice as many as I have used in one plane before) and consequently, a lot of current draw. Ideally, at least in my thinking as limited as it may be, these loads need to be split somehow so any suggestions, ideas, past experience, etc, would be very well received.
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Old Jan 20, 2014, 10:48 AM
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Thanks for the comment eflightray.

The reason I will use the 4S 2650 batteries is that I have tried to standardise across as many of my planes as possible, 5 for this particular size.

I agree this will be a case of overpowering for this model but careful use of the throttle not only gives a more realistic flight speed but also extends flight time considerably. In this case, 15 minutes should be more than possible at around 50% throttle which translates into roughly 77 watts per pound. When used in another of my models with similar characteristics, the batteries are not even warm after a flight.

I notice you have built many successful multi engined aircraft so would be most interested for your comment on my post above.
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Old Jan 20, 2014, 02:58 PM
An itch?. Scratch build.
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South Wales U.K.
Joined Mar 2003
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I have never run that many servos, (will anyone actually see the gear doors ?, I rarely even notice the wheels retract ), but I do usually power the retracts, (mechanical with a standard servo to slow them down), separate from the flight controls.

As for the servo count and current drawn, I generally rely on not all the servos will be working at the same time, (unless I am in deep deep trouble but then I usually shut my eyes ).

But as with the retracts, separating anything that could possible jam and stall a servo could be worth having their own power supply.

Actually a wattmeter is pretty good at showing what the servos are drawing, (no motor running), especially if you load them slightly, finger pressure.

It's beginning to sound like you need a much bigger plane .
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