EA 81 - Douglas Redrive

[NiqueNaque]

One reason I don't want to raise the seat any further is that the controls would have to be moved, it was a pain setting them up as is was, but, it may end up having to happen eventually, see how it works out to move the keel and the battery / radiator first.One day I'll be back in the air again..Cheers,Nick.

[asra]

NickWhat is the thrust line offset, it's a bit hard to tell from the pic. It looks easier to move the seat and play with the controls than to step the keel.So your going to use 2mm 5005 road sign material, excellent choice. Paint stripper is the stuff to get of the self adhesive reflective coatings off the sign.I noticed on Sunday some of my old street sign tail has been used to reinforce the new hangar steel frame.When will you be back flying again, I have all these great trips planned.RossB

[NiqueNaque]

Ross,It is in the order of about 4 inches, serious damage unfortunately.I don't think the tail will be too hard because it would consist of leaving the front keel section and mains cross member in situ. New side plates would be required though to splice the rear keel section in under the mains cross member, the rudder cables would need a rework as well, but none of these is viewed as being difficult, at least not until I try doing it...With offsetting the keel in this fashion the tail can be dropped about 3 ", which is ok because the tail wheel is down at least that far as it is, to boot I could rake the keel up toward the rear and give the rudder a little authority in a vertical descent.As to the old street sign I hope they took electrolysis into account on that one, I guess I'll see when I get back to the club.Cheers,Nick.

[asra]

Er, Nick, why don't you complete it and fly it as is? - with a decent Hz Stab that is. I will probably be labelled a heretic, but I don't believe CLT is anything more than a passing obsession, admittedly it is a good idea, but with the raised prop shaft it's probably going to be difficult to achieve, and hardly worth all the trouble. Thrust offset is only one of the factors involved in Pitch stability.I await the onslaught[xx(]PS I posted this as Llewella by accident, on second thoughts maybe that was a good idea[]JohnLlewellaYou shouldn't push your luck. Play it safe and move the ladder..

[mrford61]

Nick,I,m with John. That thrustline looks lower than most machines I have seen. Put a nice big stab on and go fly the sucker.Mark

[NiqueNaque]

Gentlemen,Thank you, your words are akin to those of Bob Jumaeu, ie, it will fly.. And Jack Allen says I'm going a little overboard, eg, look at the two seater with its thrust line up near your head. I can't disagree with any of you, but I will try to get it as right as I can.A large stab will help, but as you know it is more weight below the COG, true, it moves the COG a little lower and may help by virtue of its weight alone to mitigate the issue. [editorial note by nick - this is wrong, moving the COG higher is the objective - the things I say when I'm half asleep - more coffee!]There is some sage advice in your post John, ie, what Llewella says - "Don't push your luck. Play it safe and move the ladder." Wise words indeed.I may as well do this before I get back in the air so the machine is as friendly as it can be to the 'novice' and 'test pilot' rank I'm demoting myself to when I get back in the saddle again. I will just have to be vigilant in my ground handling procedures to avoid ground roll over due to the raised COG with respect to the ground.Cheers,Nick.

[asra]

NickWhat about a pre-rotator? That may be all the change in COG you require.(Ground handling is not an issue if you spend all your time flying.)Ross B

[NiqueNaque]

What Ross, one of those hub bar wreckers? I'll mark that I did order a 1" thick hub bar off Jack, so maybe it will be ok from that perspective.It is worthy of some serious consideration, as to pre rotate I will have to stand on the seat to do it, the mast grew that much, doing it off the ground is certainly out of the question.That would mean another $1k blown on the thing, I tell you the costs on this job are certainly running out of control.. however, my life is definitely worth more than $1k to get it right (Some might say this is over valued to buggery).I've got a stab in the fab shop, will pick it up tomorrow and post pics when in receipt..Cheers,Nick.

[asra]

You've got me comfused Nick! How will you spend $1k on a pre-rotator? Unless of course you buy one of those flexible cable things.Ross is right, put a starter up there, mount the battery above the engine, [remember where I had it on the old VW? ] soft start it and stop worying about CLT, you'll probably then be pretty close to it anyway. This CLT thing is turning into something like the search for the Holy Grail.John EvansThink logically and do things well, think laterally and do things better.

[asra]

I agree with you and others John, it is out of control it is about the only thing that people seem to talk about and i for one am just about sick of it..If people spent half the time flying their machine instead of trying to get it within 1/2" of clt, abit of offset isnt a problem.boy i hope i'm not going to regret this..Remember -- A good friend will come and bail you out of jail...BUT a true friend will be sitting next to you saying, "Damn...that was fun!"Mark

[asra]

quote:Originally posted by NiqueNaqueHere's a quiz for all those mettalurgists out there..Is there any reason why copper tubing could not be used to make up the intake manifold?Does anyone have any experience with same?Cheers,Nick.I think you would have severe electrolytic corrosion problems. ie Bits of alloy would become a white powder and blow away. I agree with the others that the vibration would quickly work harden the copper, too, resulting in cracks. This would more likely happen before any other form of failure. You could always rubber-mount it.....[]R.J.W.S.

[NiqueNaque]

Ron,Welcome, and thank you for your commentary, I have fabricated the manifold from steel tubing - the copper ended up in the connectors between the radiator and the engine - rubber mounted of course by virtue of the radiator hoses. I've used copper because I am a plumber some of the time, it is easy to work and for me inexpensive as scraps cover any small incidentals such as this one.John and Mark,A small offset is tolerable, I agree, but mine is in the order of 4", with 320 lbs of thrust behind it, it is in the order of 100 ft lbs of torque on the air frame that has to be resisted by other control surfaces on the aircraft, that is if the rotor unloads itself unexpectedly. I guess it is a lot less than, say, an unmodified RAF 2000 which might have up to 400 ft lbs of torque with 400 lbs of thrust at 1' offset (guesstimated). 100 ft lbs is a significant torque, it is about the same as I would use on an M20 bolt when torquing up a 200 NB pipe flange, when you've got to pull that much load repetitively you can feel it, especially after 12 bolts on 20 flanges...I will mark that the Holy Grail is an elusive thing, hard to get because nobody knows where it is or what it looks like, on the other hand CLT is easy to find, just a little more difficult to achieve, expecially with a high thrust line belt drive.Gentlemen,I thank you.Cheers,Nick.

[Tim]

Nick, 320 lbs of thrust @ 4" offset is not all that bad (certainly not as bad as some would like to have us believe). If you measure from the C of P of the H/S to the gyro C of G you will see that it would not require a very large down force to compensate completely for the thrustline offset. (measure in a straight line, not horizontally). A point worth considering is that effective thrust falls off as airspeed increases, and will finally reach zero at V-max plus approx 20%. Thus at your cruise speed your full throttle thrust may only be something like 200lbs. Consider also that at cruise you may only be using 75% power and this brings your actual thrust down further again - possibly to something like 175 lbs. These figures are obviously only hypothetical but I am sure you get my meaning. This is something that the full on CLT supporters forget to tell you.Tim McClure

[asra]

Yes Tim thrust falls as speed increases but fuselage drag,the other part of the power pushover equation increases significantly?M Barker

[Tim]

As does the power of the H/S. You are correct Murray though this is something that most CLT supporters also forget to tell you.Tim McClure