BE2e Centre of Gravity Position.

[David Davis]

Today, 29th March 2017, turned out to be something of a red letter day. There was virtually no wind and it was tee shirt weather in La Creuse. I took the BE2e to the strip for the first time since adding nearly 500 grammes of lead under the OS 70 FL.

Long story short, we replaced the propeller with a 14x6 and took off with my friend Roger Aubard on the buddy box, but he wasn't on the buddy box, I gave him control from the outset! He's a Mode 1 pilot and I'm Mode 2. I'm not a bad pilot but Roger once finished tenth in the French national championships and I'm not that standard! The model took off and just required a small amount of down trim. Then I took control and proceeded to do a series of eights before handing back control to Roger for the landing. The engine cut on the landing approach and the model nosed over in the grass but there was no damage.

We need to make a few adjustments to improve the low speed running of the engine but the extra weight has made all the difference.

The c/g as shown on the plan is simply wrong!

I'm looking forward to flying it again soon!

 

Happy Landings!

 

 

[Denis Watkins]

My neck on the chopping block again David,

Try a 13 x 6 prop if you have one,

The motor should then tickover and even run better

[David Davis]

Denis, part of the long story short involved me looking through my prop collection. I had 12 inch props in various pitch sizes and a 14x6 but no 13s at all, that's why we went with the 14x6.

[Denis Watkins]

Due to this lovely aeroplane being such an handful from the beginning, I wondered if the prop could be adding to your woes, and am glad you are aware of it.

In the olden days, all manner of props were available and I ran a .70 on a 12.5 x 6, but am certain more modern motors are more powerful.

For speed every 2 stroke was a .60, but nowadays a 2 stroke .46 would leave the older lump in the shade.

[David Davis]

I will try a 13" prop Denis, I may even try a 14x5 but the problems I had in flying the model were caused by the centre of gravity being too far to the rear. Thank you Matty B for putting me right on this. Putting nearly 500 grammes, 18ozs, of lead under the engine made all the difference and as I said above, the c/g position on the plan is incorrect.

[Jon H]

I still have my doubts that the plan was that wrong, 500g is a massive amount and it just seems crazy that a plan that old would be wrong for so long and no one notice/update the c/g. As a curiosity, what angle dose the model balance at now when suspended from the plan c/g position?

I also agree about the props. 14x5 would be a nice way to go

[Cuban8]

Posted by David Davis on 16/12/2016 19:15:03:

JD8, another thing to bear in mind was that that generation was generally physically fitter than we were even when we were young.

But not forgetting the scourge of disease that could easily pick you off if you were unlucky and for most people very limited access to a doctor. Polio, measles, rheumatic fever etc etc. And if you were working class, poor nutrition and poor housing, which just exacerbated all of the above.

I think I'll stick with what we've got in the here and now, rather than what my parents and grandparents endured.

[David Davis]

I agree that we live in much better times Cuban 8 and I'm pleased that I have never been called upon to oppose German militarism. They were tough men in both world wars and we have much to be grateful to them for.

I've got a busy day ahead so I won't have the time before this evening to check the model at the plan c/g position. Maybe I'll be able to remove a little of the additional lead but at the moment I'm very happy with the way the aeroplane flies.

FWIW the kit instructions state,"See that the model balances at the C.G. position shown on the plan, for safety just slightly nose down at the rearmost C.G. point." That can mean anything.

Finally, my model weighs in at 4.65kg or 10lbs 4oz. There is one on RC Scale Builder powered by a Laser 80 which weighs 5.3kg or 11lbs 11oz. **LINK**

The prototype weighed 8lbs 8oz powered by an OS 60 two-stroke.

[Jon H]

that is pretty vague it must be said.

As i think i said before there was much discussion on the precedent stampe thread about the c/g and tail incidence. I balanced mine exactly as the plan slightly nose down and its perfect.

I do wonder though if the extra weight and power of our models vs their prototypes days plays a part. with the extra weight we have to fly faster, extra power can require a change in thrust line etc. I found this recently when i test flew an old flair se5 for someone and got it all set up and flying well. i gave it to him and he was convinced it was tail heavy as it kept climbing when in fact he was just flying too fast as he had a massive engine for the size of the model. Having not flown your Be2 or even seen it i cant say that was he case here and im not opposed to the idea of the cg being wrong, it just seems to be so far out that i cant help wondering if something else is contributory.

[David Davis]

With all that lead under the nose the model appears to balance about level at 12.5 centimetres from the leading edge of the upper wing, and well nose -down at the plan position. It's a bit difficult to be accurate because you have to stick your hands in between all of that rigging, balance a seven-foot, 10lb biplane on your finger tips,and lift the lot above your head!

If you have a look at Ken McDonough's free- flight BE2e on the Outerzone or at David Hurrell's BE2c plan sold by Traplet you will see that the balance point is above the centre of the observer's cockpit in both cases, not close to the rear cabane struts as shown on Roy Scott's plans. The model on the RC Scale Builder site referred to above, also balances at 12.5 centimetres from the leading edge of the top wing, so that's good enough for me.

Why no-one has ever spotted this before, I have no idea. Perhaps for every ten plans bought, only one model is ever produced. Suffice it only to say that I am very happy with the flight characteristics of the model as it now is. When I last flew the model, in the summer of 2016, it was at one point so unstable that it was actually upside down!! I got it down in one piece; I must be a better pilot than I give myself credit for! Once the slow-speed running of the engine has been improved, it should be a delightful model to fly on calm days.

As for having more powerful engines than in the old days, I don't know whether my OS 70 FL four-stroke is more powerful than Roy Scott's OS 60 GP as marked on the plan but I doubt it. It certainly has more than enough power to fly the model. I found myself closing the throttle to reduce the model's speed to what seemed like a more scale-like velocity on Wednesday. Furthermore with all of that wing area it climbs like the proverbial homesick angel at WOT.

Before buying this model I was in the process of building another one. I plan to finish it in the markings of an aircraft flown by a namesake who was killed by Baron Manfred von Richtofen in April 1917. I had hoped that his aircraft was brand new when it was shot down so that I would be spared the task of painting squadron markings but no, Davies's aircraft had been with the squadron since December 1916 which was when he was first posted to the squadron.

I'm fortunate that my new home has a very large cellar and that I own a Volkswagen LT28. This means that I can leave the model fully rigged all the time!

Finally, the only other Englishman in my club is building the same model. We could have a flight of BE2es next year!

[Jon H]

I now have a curious picture in my mind of a man walking into A&E somehow stuck between the wings of a Be2 and his arms tied up in the rigging...

Can it not be balanced by picking it up at the centre section? Thats how i did the stampe as it was the only way i could see to do it.

In any event, i assume that significantly nose down at the plan c/g means about 20 degrees, if so then i would take the plan c/g as correct on the basis that i always balance biplanes nose down. Not that it really matters at this point, if its flying well then its not really important

[MattyB]

I have never understood this concept of "balancing nose down" - what constitutes "nose down", 1 degree, 15, 30? It just adds in an unnecessary potential failure point which could contribute to a maiden flight crash if the builder balances for level at the plan marked CG point rather than nose down. It is too late now to standardise now, but it would have been much better if all plans/ARFs had the marked CG position set for a "level flight" balance - that can be judged plenty accurately enough by eye, and thee is no room for misinterpretation.

[Jon H]

a fair comment for sure. Im not exactly sure where it came from and i couldnt honestly tell you in degrees how far nose down i balance my biplanes but its probably 20 or so a least. I have never checked and just eyeball it. Where it was that i learned that the angle i was seeing was right i couldnt tell you.

Also, to make life really exciting i wouldnt balance an ultimate or a pitts nose down by as much as a tiger moth or WWI model. I would probably balance one of those just about level and go from there.

Where you balance the model also has an impact as picking up the top wing centre section is more stable than sitting the model on the lower wing. Its like balancing low wing models inverted, the mass of the model below the c/g position changes the whole thing.

[J D 8]

Nice to hear model is now flying well and you can now enjoy flying it. All the best John.

[David Davis]

A few pictures of last Wednesday's events taken by our club's treasurer Fabrice Caron, on his tablet.