iron eagel

Cp,
Yea, the cg range with a flying wing is very critical, I have noticed that even a small shift can make all the difference in the world, I been down that path myself with one. My first one was far to heavy, as well as underpowered, and it's flight time was measured in seconds. Once you get them right they are fun to fly, and they do seem to be a lot faster that standard tube and wing type, flying on the same power at roughly the same weight. One of these days I am going to do a YB-35 with today's electric motors it wouldn't be all that hard.
I think the sweep on your wing should allow for a bit more leeway as far as cg, granted not all that much but a bit; and like you said it really helps as far as pitch.

Did you cut some new cores or is this one on the back burner for awhile?

MJD

My Feedback: (1)

I would say the sensitivity or appearance of sensitivity to the CG on a flying wing has a lot to do with the fact that stability margins are functions of the mean aerodynamic chord - the average chord. So with a flying wing, you might only have a 8" average chord as opposed to a delta (delta flying wing that is) whose average chord may be 16". That means for a change from 10% to 5% static margin, you would move the CG rearward 0.4" on the wing and 0.8" on the delta. Accidentally moving the flying wing CG rearward 0.8"like on the delta would render it neutrally stable and impossible to fly I would think, versus the delta that would gain responsiveness but retain positive pitch stability. The other issue is inertia - short coupling means the mass is closer to the CG about which everything rotates. So a small linear change in CG can have compound effect on your thumbs if you don't watch the numbers.

MJD

combatpigg

My Feedback: (3)

Right now I'm rescuing some old engines that got soaked because of a roof leak in my barn. They were laying in a tupperware container with no lid, so they were submerged. Fox .35s, .36s,.40s ... ST .35s, old junk I should sell some of and let someone else have fun with and take care of.

I'll have to cut some more wings and build one to be able to develope an accurate fuselage mold...I want the fillets to be right on the first go around. The next plane will have no lakes or cakes of Bondo.....[>:]!

MJD

My Feedback: (1)

CP, I think you're thinking like an electrician - these are DC motors, they don't behave the same as AC synchronous motors. Give them more voltage and the rpm goes up. RPM goes up, load goes up. AC motors try to maintain rpm, and draw more current in response to a voltage drop under load, or heat up bad when they can't get what they want. Is this where your thoughts wre coming from?

MJD

iron eagel

Oh yes roofs are such fun, and out there I bet it is a ongoing battle.
I have been dealing with projects around the house of late myself, so I know how you feel.
Well hope your rescue efforts are successful, if you unload them all you might have enough for a down payment on an engine you may really want...

I hear you about the "accurate mold" for the fuselage given what you are doing Bondo is not an option. If I have to use filler sometimes I will use microballoons and epoxy, or some other binder, given the application but try to avoid filler if possible. My problem is when I work with fiberglass I usually have to use filler or it looks really nasty! At some point I do want to try doing some layups using molds from a plug, I know I could never do the free form work that you do without it looking like a wad of steel wool without using Bondo by the quart.
That is why I have stuck with building with balsa, and using silk, tissue or carbon fiber veil for strength and finish.

combatpigg

My Feedback: (3)

MJD, yeah that's part of it. I automatically look at a 120 volt 10 amp motor and know that the optional 240 volt hookup will pull only 5 amps. But the internal resistance of the motor must still be raised [by selecting the 240 volt tap] or else you will smell burnt cookies.

Speedy-Gonzales

My Feedback: (202)

CBP,
You mentioned that I should consider a "big block" engine for my larger sized "Rapier" delta. Were you talkiing about the Jett 60 LX FIRE? What is the report for this engine? I see it has a throttle type RC carb. Where could I get a good prop for this set up? I don't like running "sport" props at 19K and above. I have never thrown a blade before but I'm sure it wouldn't be much fun. Something we must all consider when operating and tuning these type of engines. A 3" blade segment at 600 mph will kill you or it would require a surgeon at the least to remove it! What prop diameter/pitch would you recommend?

Speedy

combatpigg

My Feedback: (3)

Speedy, I don't know about the Jett.60, but ILJ seems to know quite a lot about this engine. He talked about it some in his lengthy speed plane "where to buy them" thread.
There are so many OS .90 DF engines for sale out there for sacrifice prices.........
Same goes for the other monster motors like OPS and Picco.
RocketRob makes a pretty universal big block speed prop......I'm just too heavily invested in .40 sized stuff to jump ship and switch, plus I just like those screamin' 40s.

iron eagel

I know what you mean about the big blocks I Picked up a NIB OS 91df with pipe and RCMV for less than the cost of the pipe.
I have yet to find a home for it but have been thinking about a scaled up SD equipped with retracts would be fun.
Somehow the thought of trying to had launch a delta with a .91 isn't all that appealing, and I just happen to have a set of century jet retracts that would fit the bill nicely.

Edit to add:
Do they sell glow in 5 gal. cans?

Speedy-Gonzales

My Feedback: (202)

CBP,
You and I think alike. The .90's are a real chunk of metal hanging out there on the nose. I just sold a PICCO 60 FIRE for that reason. A real brick! I LOVE the Nelson engines for raw power to weight and user friendly. Nelson engines are music to my ears. I may just run a Nelson Q500 in this plane turning the larger Q500 prop and just settle for some good old 150 mph "slow" fun.

From what I have been reading the Jett 60 LX is hot but the Nelson 40's are hotter. I think staying below 3.5 lbs is the ticket to a good flying delta. Too much weight up front only means adding more weight to the back. That is what I term as a "Double Dork". My deltas have all come out nose heavy so I end up with a AA pack way to the back.


I'm happy with my "Henry"![sm=thumbup.gif]

Speedy

combatpigg

My Feedback: (3)

I bought a 55 gallon drum of methanol from the local Chevron dealer for $163 and a couple gallons of castor from Sig for something like $50 [IIRC]
I'm not sure what nitro is going for right now, but I have been buying that from a local VP dealer.

iron eagel

The OS .91 and a 1.08 are the only big blocks I have, real good deals I could not pass up.
I was going to use the .91 in a df setup, but have since decided to use a pair of EDF's in that plane instead.
Most of my planes are in .40-60 range much easier to deal with in all aspects. I have one plane powered by Zenoah 38cc that spends most of it's life at home these days, just too much work involved, although it is easy to see, so I am keeping it around for awhile yet.