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  1. #1
    MJD's Avatar
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    Screamin Demon .65, flights 3&4

    Snuck out today to crack off a couple of flights, this time with the cowl on.. I finally figured out how to use the fueling valve with the bladder tank set-up and get it all to fit. Notice the precise Dremel work on the air inlet and fuel line access, no NACA ducting either. The engine stayed cool enough, but a I could probably reduce drag with more care. Whatever. Also note I forgot my hemostat, but a pair of needle-nose and a #64 rubber band did the job.

    This time I set up a camera on a tripod, on the hope that I could get comfortable enough to get some low and close passes in.

    Flight 1, using a CF 8.2x11 wide blade cuffed prop (known as a Newton-McGee D prop) hand launch went well, lots of trimming and a couple of "okay" passes. I must have captured some air because I ran out of fuel early.

    Flight 2 on the Demon was faster than flight 1. While there are a few variables and too early to make firm conclusions, it is quite possible that the wide cuffed blades of the 8.2x11 probably suffer because of the dirty aerodynamics close to the prop hub, including the LE intersecting the nose. The second flight was a Tornado D 8.5x11, more like a typical "toothpick" style prop with more blade area out in clean air. (That's the one in the pics here)

    Flight 2 Wav-O-Scope readings:

    Pass 1: 177
    Pass 2: 170
    Pass 3: 172
    Pass 4: 183
    Pass 5: 191-192
    Pass 6: 194-196
    Pass 7: 178
    Pass 8: 177

    I tried to be honest and objective picking the start and end points on Wave-O-Scope. As the flight progressed I got more comfortable and started diving and throttling up earlier, as you can see in passes 5&6. On the earlier passes the run up was shorter, I did not give enough time to accelerate to top speed. The last two passes were much more lackadaisical efforts since I was concerned about fuel remaining, in fact after pass 8 it ran out. The numbers seem to agree.

    Although the prop was set correctly relative to TDC, it was hanging a prop blade on flight 2 and the pics show the results. That was a $16.00 flight [:'(] , but it comes with the territory.

    Results look promising. I bet I can crack 200 as is with a better flight profile and some more prop experimentation, and no doubt about it if I convert the engine to a 7-port .67. I really need to get radar out to validate the Doppler numbers. But visual impressions don't argue with the numbers, it was cooking along. Funny thing is, in close, i.e. within 2 seconds of front and center, it doesn't feel that fast. Make no mistake, you have to be on your toes, but it's not such a big deal. But trust me, once you get out any farther, the inherent visual issues with skinny wing deltas rear their ugly head big time. This thing is a bee-atch to see during the turnarounds! And cooking off speed during the long final, once levelled out and lined up it nearly disappears. On flight 2 at speed but luckily at altitude I made the mistake of glancing down at the Tx to find the mixture control knob. Bad, bad idea, I lost visual for a couple of seconds before reacquiring it [X(]. I know better..



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    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  2. #2
    combatpigg's Avatar
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    RE: Screamin Demon .65, flights 3&4

    Good job MJD..!
    You are on the hunt now with lots of firepower and ammo. It's just a matter of weeding out things that don't seem to work.
    Props can be confusing...sometimes it takes a few runs on a prop to be able to see what it's got.
    Yesss....never look down. This time of year with a low Sun angle might not be the best visibility either.
    What does your elevon trim look like with the plane sitting on the bench..?
    WHO GUNNA FEED MAW KEEEIDS..???

  3. #3
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    You can barely see any trim at all, a couple of very thin short and curlies above neutral is all.

    One thing I am coming to grips with is the balance between aileron and elevator deflections.. I think some of the uncertainty I have felt in flight has to do with having too much roll sensitivity relative to pitch. As I see it so far, in terms of physical deflection I need a heck of a lot less in roll than pitch compared to setups I am used to. I think this may have to do with the substantially higher wing loading. In actual terms I have a about 1/8" travel in elevator, and almost half that in roll.

    Hand launches went much better today. Mostly because I kept my grubby paws off the sticks for as long as possible, and then just gently pitched up. This is what I tell other people to do, but fighting the instinct to control it is tough when the time comes. At 4.2lb plus fuel and a tiny prop, it needs to be left the heck alone to pick up speed before it will tolerate any inputs.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  4. #4
    combatpigg's Avatar
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    RE: Screamin Demon .65, flights 3&4

    Keep dialing down the roll control then. It sounds like you've got a very straight plane with a spot on CG.
    I'm not sure why you are moving the throttle in flight [if I read you right]. If you ARE able to throttle that thing then I suspect that the throttle is too small.
    WHO GUNNA FEED MAW KEEEIDS..???

  5. #5
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    It's a Jett .90 carb, pretty big hole. Having the throttle reduces the stress level a lot. I couldn't see myself venturing into .65 powered RC speed models without being able to rein it in when needed. I am sure the time will come that I run a venturi and pressure. I want to work up to it. Besides, I don't think it is suffering too badly for top end, and if I can make the magic 200 mark with a carbureted engine that's alright. The engine is stupid easy to handle, I guess there's a reason Jett's sport engines throttle the way they do and still run like a bear which is why I had Dubb Jett machine a carb to fit.

    I wonder how much top end I am losing with the carb?
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  6. #6
    combatpigg's Avatar
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    RE: Screamin Demon .65, flights 3&4

    It would be pretty easy to either make a venturi or possibly find one on ebay if it comes to that. In the mean time , if you've got an easy to run carbureted engine already doing 190s I'd do like you say and see what more you can get out of it with prop work and engine tuning.
    As for how much rpm you might be losing, the guys who run the Speed Cup might know.
    For reference [IIRC] the hot .40s run 13mm venturis..but they are supporting 30,000 rpm.
    WHO GUNNA FEED MAW KEEEIDS..???

  7. #7
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    These .65's are timed for peak power about where I'm running them or a little higher. This one turned the bench prop at about 21.5k. I think they should be kept to 23k or a bit lower in the air for the best part of the power band.

    I quickly learned to richen off more with the IMC in the air as it unloads, and lo and behold the plug is still good after flight #2. When I pull back in some situations it sounds like a donkey as it chunters* at part throttle on that little prop. It throttles remarkably reliably so far, and idles smooth as silk. Probably means the carb isn't big enough..

    [I've actually seen this word in print more than once referring to that unique wobbly sound 2-strokes make when you back off on the throttle.]

    I really, really want a genuine F3S type 10cc airframe..

    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  8. #8
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4


    ORIGINAL: combatpigg

    It would be pretty easy to either make a venturi or possibly find one on ebay if it comes to that. In the mean time , if you've got an easy to run carbureted engine already doing 190s I'd do like you say and see what more you can get out of it with prop work and engine tuning.
    As for how much rpm you might be losing, the guys who run the Speed Cup might know.
    For reference [IIRC] the hot .40s run 13mm venturis..but they are supporting 30,000 rpm.
    The F3S guys as far as I know run their VAE .60's up in the 25-26k range, at least the fastest ones. Someone correct me if I am off but I believe that's where the higher timed engines are being run. I was told to keep the disc valve on the OPS below 24k for longetivity. I also don't have the needle bearing rod which I think is preferred for running it that hard.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  9. #9
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    Wav-O-Scope of 6th pass on flight 2. Am I picking the start and end points correctly?
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    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  10. #10
    combatpigg's Avatar
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    RE: Screamin Demon .65, flights 3&4

    That looks like a very fair placement of the lines on the graph.
    If you are pushing an rpm where failure is predictable, then look at where material could be removed from the piston and rod. Micrograms of dead weight add up to extra stress at high rpms. A lighter piston/rod will place less stress on the crankpin and help it to run true as it drives the intake valve.
    Some engines come with overly thick skirts and pin bosses.
    I found so much dead weight inside a few engines that weight needed to be removed from the crankshaft counterweight. OTOH, most engines simply run as smooth if not smoother afterwards with no material taken from the counterweight.
    details like these individually don't usually make much difference, but it's the sum total of doing a bunch of little things that can add up to the difference between getting to your goal or not.
    As for the disk valve, you're running a generous amount of oil and not letting the engine get too hot, so I suppose the best you can do is keep an eye on it and round up some spares.
    WHO GUNNA FEED MAW KEEEIDS..???

  11. #11

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    RE: Screamin Demon .65, flights 3&4

    Mike,

    I ordered one of these from your website December 8, 2011 and paid via pay pal.  My card was charged but I never received the kit.  Since I did not have a paypal account I was unable to get my money back.  I don't suppose you would be willing to fulfill the order?

    Dave

  12. #12
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    PM sent. I'll look after you.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  13. #13

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    RE: Screamin Demon .65, flights 3&4

    Congratulations on your .65 Demon. I would like to hear an audio file of that engine on a scorching hot pass. You flying the "split-S" pattern? That is a gut wrenching feeling when you lose visual and you know you only have less than a second to find it. Very important to have a spotter at these speeds. I totally agree with you on having a throttle too. I would also like some contact info on those props you are using.

    Great job!

    Speedy-Gonzales
    Revver Bro #182

  14. #14
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4


    ORIGINAL: Speedy-Gonzales

    Congratulations on your .65 Demon. I would like to hear an audio file of that engine on a scorching hot pass. You flying the ''split-S'' pattern? That is a gut wrenching feeling when you lose visual and you know you only have less than a second to find it. Very important to have a spotter at these speeds. I totally agree with you on having a throttle too. I would also like some contact info on those props you are using.

    Great job!

    Speedy-Gonzales
    Revver Bro #182
    I uploaded the video to YouTube: SD .65 flight 4 audio

    It isn't running at the rpm of the F3S guys overseas, but sounds okay. The camera is fixed staring across the field, so this is audio only BORING. Skip to 2:30 or so for the later passes. Early in the video you can hear me commenting on looking down at the transmitter and losing it.

    Hey, you can actually see it for a sec at 2:18. Lucky, notice how far I am from the camera.

    At 1:25 it's throttled back and sounds like Chewbacca.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  15. #15

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    RE: Screamin Demon .65, flights 3&4

    You are right...it does sound like "Chewie"! I also watched your video of the OPS .65 bench run. Music to my ears! I could actually smell and feel all the greasy lube and fuel coming from the pipe while watching the video. I love going home with my body and clothes covered in oil and the golden sweet smell of spent fuel.

    Are you mixing your own "brew"? Just straight methanol and castor?

    I don't know about you guys but do you also encounter "shrinkage" after a flight like that?

    Mine dissappears like a "frightened turtle"

    Speedy-Gonzales
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  16. #16
    combatpigg's Avatar
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    RE: Screamin Demon .65, flights 3&4


    ORIGINAL: Speedy-Gonzales

    I don't know about you guys but do you also encounter ''shrinkage'' after a flight like that?

    Mine dissappears like a ''frightened turtle''

    Speedy-Gonzales
    Shrinkage after a crash, yes...but nothing but New Hampshire Rock Maple during a good run.....
    WHO GUNNA FEED MAW KEEEIDS..???

  17. #17
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    I run Omega 15% and bring the total oil up to about 23% with additional castor. I also added two .002 head shims. Yeah, I am pretty puckered after flying this thing, but I'm starting to get used to it. I still tend to land a bit hot and go lonnnnng, but that's what grass runways are for. The hand launch is the moment of truth, if that goes well the rest seems that much easier.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  18. #18
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    RE: Screamin Demon .65, flights 3&4

    Depending upon temperature it looks as if you were flirting with 200...

  19. #19
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    I won't be flying it much more without a radar gun at the field. I don't consider this to be an aircraft with a long life potential, so I better get some solid data while I can!

    When I can write a number >=200 on the wing with a Sharpie marker and be confident it's for real, I'll be pretty happy.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  20. #20
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    RE: Screamin Demon .65, flights 3&4

    Shrinkage after a crash, yes...but nothing but New Hampshire Rock Maple during a good run.....
    Ditto!
    A guy who used to live on this site and now is rarely here due to the "upgrade".
    Most likely fading away till the My Forums is fixed. Too bad.

  21. #21
    combatpigg's Avatar
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    RE: Screamin Demon .65, flights 3&4

    I remember hitting 199 on my very last prop late in the season and having to wait for Steve Wilk to make me another batch of potential "winning" props.
    All this time, Wavoscope and the onboard telemetry were giving exact results..without question. 199 means 199 when you activate the "HowFast" onboard readout.
    So, during the 10-14 day wait for turn around service from Steve Wilk, I got about 20 hours worth of sleep.
    Wonderful hobby....huh?
    WHO GUNNA FEED MAW KEEEIDS..???

  22. #22
    MJD's Avatar
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    RE: Screamin Demon .65, flights 3&4

    199.. wow, that's like pulling out at the last moment.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  23. #23
    combatpigg's Avatar
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    RE: Screamin Demon .65, flights 3&4

    What really haunts you is the mathematics that predicts the amount of extra power that is required to take one of these little planes from 199 to 200.
    Thankfully, this is DEVELOPED power that considers the stored energy from gravity assist and not just the power that is created from burning fuel.
    Figure how much potential power is wasted from aerodynamic imperfections, incorrect CG, lousy flight technique, etc. These Demons can be flown with just the trim levers at top speed and that really helps eliminate the human error aspect when going for the smoothest high speed passes.
    The old wive's tales about how ALL deltas need lots of reflex or AOA to maintain level flight only apply to those old school, overweight and overly thick monstrosities that ARE disappointing to see in action.
    WHO GUNNA FEED MAW KEEEIDS..???

  24. #24

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    RE: Screamin Demon .65, flights 3&4

    MJD,
    Do you now have kits available ( in stock ) for sale and are you offering the formed cowl and rear hatch as shown in your pics? I am in the mood for another DEMON but have heard that none are available.

    CBP,
    You are absolutely right on the changes you must make to gain 1 MPH as you near 200. My quest for the elusive 200 mark on my last flight with my DEMON was aborted when I realized I was close to, or had meet my limitations with an exposed carb and side exhaust. You get a rhythm going between you and your plane at these speeds and if you lose that composure you have to grab some sky in a hurry and then work on getting it back in the groove.

    We now know that a reflexed wing causes drag and is unwanted in the speed arena.

    Time is not on your side at 200 MPH and 50-100 feet off the ground. Just a blink is all it takes. Been there and done that.

    3-4 flights on a sunny day can also be very expensive even if you do not have any incidents.

    "P" times 3...................Plugs, Props, Persistance.

  25. #25
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    RE: Screamin Demon .65, flights 3&4

    Hi Speedy,

    I went off-line with the kits for a long time. I do not have any stock at the moment, but I plan to make a run in the near future. I'll announce it when they are ready.

    That cowl is made on a crappy little mold I made for myself - to offer them in production is an idea but I think the design should be improved, and a better mold has to be made. I would have this work done by someone else, I don't want to be in the fiberglass production game.

    In four flights I've eaten two plugs and one prop, that works out to about $26.00, or $6.50 per flight plus fuel.

    Sorry I'm late dear, I had to help my uncle Jack off his horse.


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