Huge B25 Mitchell

[LMA Dave]

The video of this B25 Mitchell started a bit of a debate on the LMA Forum as it seem to be lacking power and took the pilot a long time to rotate, still a beautiful model and a credit to the owner, so what do you think?

 

Edited By LMA David Parry on 30/01/2013 14:21:15

[Biggles' Elder Brother - Moderator]

Beautiful model, with excellent detail and patina. But yes its underpowered. Even with a "brakes on" (via two mates hanging on" roll the acceleration was anything but brisk. The climb out was scary! Only just having flying speed and that first turn must have had the pilot's heart in his mouth!

TBH, in the interests of safety, I think he should have aborted when it was obvious the aircraft wasn't reaching rotation speed nearly quickly enough.

But fly it did. I assume that was off grass? (We can't quite see the runway surface). If so it well go better off tarmac - but could still do with significantly more power. If that was off a solid runway - then I wouldn't even think about flying it again until it acquires some additional umph from somewhere. It might be worth his while thinking about a change of prop as well?

BEB

[Ernie]

Seemed pretty realistic to me. Maybe it was an intentionally long take off run.

What about these WW1 biplanes that take off in about 6 inches, and go vertical

ernie

[Mowerman]

I wonder how long the take off run was for the fullsize B25 and how that would scale down to the model size. Also bearing in mind the model was not a 3D flyer.

As Ernie says we are used to seeing scale models take off in very un-scale short runs.

[Biggles' Elder Brother - Moderator]

Chaps - I too am a devotee of the scale take-off, nothing better. And I too have been know to bemoan the dragging off the deck after 6 feet of scale models into a 45 degree climb - just because they can! But I don't think that is the case here - two reasons;

1. Watch the climb out. He's at a high AoA, but is getting a very low climb rate. This aircraft had very little speed margin at that point. Slow climb rate OK, but with a high AoA - not OK!

2. I think we can safely assume this was a very experienced and responsible pilot. His doing a maiden flight - not a flying display. He knows nothing about the stall characteritics of this model at this point. His focus 100% would surely have been on achieving a safe, incident free, flight. The first step to that would be a no-nonsense full power take-off, becoming airborne later in the model's flight envelope rather than earlier and ensuring he had a more than adequete speed margin over the stall point. Fancy scale take offs come later, when all the model's little "features" have been adequetely explored and are fully understood surely.

I can see why this provoke discussion on the LMA forum!

BEB

[Concorde Speedbird]

I agree with BEB. I think it is always good to have a safe power margin. Imagine if an engine (or motor) cut out? You need some powerrr!

CS

[LMA Dave]

You are right there BEB if you watch Dave Johnson when we where witness to its maiden flight with the Vulcan, the plane rotated very quickly Dave knew as soon as he lifted the nose it was going to fly and had enough power for a safe take off, he never attempted to do it scale. In fact he had 13 flight with it testing everything that could go wrong like stalls, engine to idle to represent total engine failure, emergence landing, all this before he stated to fly it scale the videos I posted on YouTube only represent a fraction of the testing this plane has gone though. The B25 is defiantly under powered in my view and the pilot must have been struggling to see it when it took off it was that far away from him, however he did make a safe flight and he did land it. But if I had been there it would have gave me course for concern.

Edited By LMA David Parry on 30/01/2013 17:27:52

[Codename-John]

Posted by Mowerman on 30/01/2013 16:21:27:

I wonder how long the take off run was for the fullsize B25 and how that would scale down to the model size. Also bearing in mind the model was not a 3D flyer.

As Ernie says we are used to seeing scale models take off in very un-scale short runs.

according to Wikipedia - Jimmy doolittle`s raid of 16 B25`s had 467 feet (142 m) of takeoff distance on the USS Hornet aircraft carrier, though they were modified a bit to make them lighter obviously

[nasa_steve]

it certainly looked blissfully underpowered unless the props were particularly low in pitch. i would certainly have aborted.......that said it looked superb

[Turbycat]

Great looking model. Almost as big as my full size Turbulent! Definately looked underpowered to me. I would guess at it needing a good 50% increase in power, maybe even more. I also wonder what wing section was used and would a higher lift section have helped. If you have lots of power you use the throttle to keep it more scale like. Nothing looks/sounds less scale than a beautiful airframe flying by being maxed out on the throttle just keep in the air.

Still I wouldn't mind having a go with something that big. Must write letter to Chairman of our club " Please sir can we have a runway extension!!"

Andy

[Bob Cotsford]

I've got no large model experience so this is just my impression. The model acheived what looked to be a fair turn of speed for the size of it and rotated ok, but seemed to be suffering a lack of lift.

That could be down to either lack of speed or excessive wing loading depending on how you look at it. To my mind the speed looked ok so it's overweight. I doubt much weight could be shed at this stage so it would have to be more power and to my mind too high a resultant airspeed to look right.

[Adrian Smith 1]

Hmmm... not sure about whether the ROG was stretching the boundaries I would love to have heard the pilot's opinion on that so we can't make any certain judgement really. To my untrained eye it just looked scale-like, however I do agree that the visibility from the pilots view at ROG was a bit dodgy. That's what I like about this forum with seeing things like this. Given that the largest aircraft I am ever going to fly is my 2.3 metre 50 cc Sbach I can only stare in awe at what these guys aspire to.

[Tim Mackey]

I didnt think it looked too bad TBH.

Lovely long scale like take off run, and the climb out seemed about the right angle too. Flying speed was Ok, although to my eye, she was sitting a tad tail down, so perhaps the balance point needs a bit of adjustment?

Sure, more power would be good, but that could encourage some rather non-scale like behaviour

Lovely model BTW

[John Muir]

Marginal, to say the least. The nose was up about ten degrees for the whole flight and the flying speed looked too low for comfort. Not remotely safe. Models that size scare me to death anyway.

I know scale fidelity is everything to these chaps, but maybe next time they should reduce the bomb load a little.

John.

[Biggles' Elder Brother - Moderator]

Posted by John Muir on 31/01/2013 10:36:58:

I know scale fidelity is everything to these chaps, but maybe next time they should reduce the bomb load a little.

LOL

BEB

[Delta Whiskey]

Perphaps he was overloaded with ordanance !

For safety, more power would have been better IMO, but it's hard to judge from a video once it was up and after the first turn it did seem ok and large birds always look like they fly slow and it sounded lovely sucking in air. Nice model too !

Edited By Delta Whiskey on 31/01/2013 12:35:01

[Lindsay Todd]

Very difficult to make any real judgement, the sit in the air being tail down slightly suggested some trim change be that CG or incidence was required. Size and speed may have been influenced by the appearance, that being said though you can always throttle back if you have some excess.

Linds

[Stefan Hafner]

To me it looked underpowered, i think if i had been flying I would only have felt it had enough power in the slight dives. It may be important to achieve a scale appearance in the air an all, but we do have throttles , and while i don't have anything that big I prefer to have enough extra power available to get out of trouble if i need it, even if it not scale flying

Change of props perhaps? but even that is expensive at that size

[Martyn K]

I wonder if it would maintain altitude with one engine dead, I suspect not, therefore from a safety point of view it is underpowered, but not massively so.

Still an awesome sight though.

I congratulate the pilot/builder on that model - do you know if it is an ARTF from Hobbyking?

Martyn

[John Muir]

I just read that it weighs 180kg/400lbs! It can't be flown in its home country Germany because it would be illegal. Here too I think. France must have more relaxed rules. Explains why it was maidened at La Ferte.

It's a beautiful model and the engines sound absolutely stunning, but too big for me. Wouldn't fit in my car even if HobbyKing has it on a special.

John.

[Greybeard]

Posted by Codename-John on 30/01/2013 18:00:35:

Posted by Mowerman on 30/01/2013 16:21:27:

I wonder how long the take off run was for the fullsize B25 and how that would scale down to the model size. Also bearing in mind the model was not a 3D flyer.

As Ernie says we are used to seeing scale models take off in very un-scale short runs.

according to Wikipedia - Jimmy doolittle`s raid of 16 B25`s had 467 feet (142 m) of takeoff distance on the USS Hornet aircraft carrier, though they were modified a bit to make them lighter obviously

Also the carrier was steaming flat out into what ever hear wind ther was so they could have been traveling at 40mph before they turned a wheel.

[Biggles' Elder Brother - Moderator]

True - but even so, 467 feet is not much - putting it mildly!

BEB

[Chris Channon]

What a beautiful model and doesn't it sound superb ?

Brill

Regards

Chris.

[Greybeard]

Posted by Biggles' Elder Brother - Moderator on 31/01/2013 16:58:05:

True - but even so, 467 feet is not much - putting it mildly!

BEB

Maybe the crew pulled up on the arm rests as well. If you watch the film of the take off they wern't travelling very fast, maybe another 40mph. I'm not sure what the normal rake off speed is but I'm sure it's slow by modern standards. I agree that the model looked overweight but that can be the penalty of scale detail.