RE: Bifurcated pipe thrust loss
Harry, of course it's a simplification, but the percentages used take many variables into consideration. So, just knowing the temp difference from a Standard Day and the altitude above sea level, makes it an easy calculation and a very good approximation of overall thrust reduction. Certainly for our purposes. Ray
Posted on: 2/2/2012 5:05 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10940953

RE: Bifurcated pipe thrust loss
George, I did quite a bit of work w/ Tam back in the 90s determining bi-furcated pipe losses. I used several of his pipes w/ AMT engines (Pegasus and Merc ). The average loss was approximately 4-5%, i.e., about a pound for a 22-pound thrust engine, Standard Day. Of course, these were Tam pipes...the best designed and crafted, IMO. And i knew what the AMT engines were actually putting out. Yours is rated at 22.....(STD, sea level)....wonder if it is. Re temp and altitude losses: figure 2% for every 10F above a Standard Day and same for every 1000' above sea level. At your 60F, no losses; at 5400', perhaps 12%. So, your total loss w/ a good pipe, your engine, and that altitude, is more like 16%, or 3.5-pounds. My first jet was an Avonds DF converted to turbine....using he almost 5-pound Pegasus w/ the original 22-pounds thrust (plane weighed 31-pounds at TO). I flew it in and out of 410' good grass, sea level...well barely, as sometimes w/o a headwind I was bending the stick on TO. Over the years, engine was updated to 30-pounds....a real performer in that model. Try full brakes until thrust is full, then release; look for a headwind; also some positive AOA of the wing while rolling makes things easier (i.e. the model sits nose high by a few degrees). Ray
Posted on: 2/2/2012 5:39 AM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10939924

RE: Reno crash
Still wondering: why not design in robust horizontal stab down deflection at re-build time to better compensate for the increasing load needed at speed? I.e the elevator trim would have/become less load(ed) rather than be maximally loaded at critical speeds. Higher trim deflections at lower/approach/landing speeds would be required but w/ much less component strain. Tx Ray
Posted on: 9/27/2011 7:57 AM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10736426

RE: Reno crash
I'm not an aero guy at all, though the above explanations sound quite plausible. And if so, then why not a hor stab/wing incidence angle set up at a better compromise for high speeds when building up a Reno Mustang? As speeds increase, elevator/tabs deflections would tend to decrease and unload rather than as posited w/ the GG. Would require more highly deflected surfaces at low speeds, but w/ aft CGs, I'd think enough up elevator would still be available at landing. Ray
Posted on: 9/23/2011 2:39 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10730882

RE: Global JetClub Mig 15 arrives
Wow! Mike's MiG looks the ultimate. I've already GJC's F4D Skyray....everything you could ask for. Incidentally, extremely rugged...ask me how I know...... Mike: what other color schemes are/are eventually going to be available? Tx! Ray
Posted on: 9/7/2011 2:59 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10706133

BiGBri and NEJR
BigBri, e-mail me redavis2010@comcast.net re how yer making out w/ your 160. NEJR was best I've ever been to, great flying again w/ everyone, wonderful venue. Thank you Jeff and Karen! Ray
Posted on: 8/24/2011 6:40 AM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10684864

RE: Plum Island Jet Rally
BB....I could come outa 'retirement' to see that! Great idea/execution.......great year for the Bruins! Linda and I were at game four.....a historic year for Boston hockey and esp TT. Nearing the end of a three-year house/small farm restoration; chronic back problems have curtailed travel but not jet flying, so doing much of that locally (went to all little Wrens to make things easier). Did just have some good medical news/consensus Weds, re a surgery, that should greatly help. Likely be this fall and hopefully off the DL and back on the event circuit next season. Say hello, safe flying, and my best to all at PI. Jeffie....I will be at the NEJR! Ray
Posted on: 6/16/2011 7:34 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10577929

RE: Skymaster F4 pipe and wet start
Best I can tell from the pictures, I notice the outer pipe is gold colored, indicating the inner pipe must have gotten pretty pretty hot. Gold color OK, extensive areas of 'blued' metal, however, indicates tempering (softening), i.e., the pipe has lost its stiffness. If that's the case re the inner pipe, it becomes subject to collapse at full thrust (Bernoulli effect). If the blued portions can be permanently deformed easily (dented), then that pipe should be replaced. Just curious Jetflash: you mention you live in the Boston area....'Cape Code'. You mean Cape Cod? That's where I'm from and the only turbine guy around, to my knowledge. Where do you fly? And absolutely nothing wrong (and much to be gained!) in using properly installed (tubing ends square, pushed fully in) Festo products on the suction side. I prefer a ball valve there, to on the pressure side, where mine are straight runs from pump to turbine. Festo products are actually manufactured for pneumatic uses, pressure and suction, but it's certainly been proven worldwide over the past fifteen years that they are fully reliable in our installations! Ray
Posted on: 5/20/2011 6:05 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10531835

Wicked Extreme motor...astounding!
Flew my Alfa MiG today (3-blade, 4S, 2100) with Don's RC 5400Kv EDF motor and his Pentium 40-amp ESC. Was truly a quantum jump over the previous Little Screamer in it....punch it from a stall and you get vertical...true vertical(!) out of sight. It screams, seems reliable after three flights, ESC remains cool enough (it's inside w/ no special cooling). About $75 for both....nice stuff, great service. My fourth Alfa MiG now, and I've seen a lot of them at jet (turbine) events....this combo will blow all of them out of the sky. And mine's 'heavy', as I foam the interior nose and tail, CF band some weak spots, etc. I forget who, but thanks for putting me on to Don. Ray
Posted on: 4/25/2011 3:15 PM by Author "67Jag" in the forum "Electric RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10484464

Little Screamer motors...
...anyone know where to find them? LS doesn't communicate; HL hasn't gotten back. I'm looking for a 5100Kv replacement (w/ mount extension), for the Alfa MiG three-blade fan, 4S. Or...anyone have a better suggestion than the LS? Tx! Ray
Posted on: 4/12/2011 10:00 AM by Author "67Jag" in the forum "Electric RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10458384

RE: '70's Pattern Planes
Guys, I'm desperately trying to replace a Tetra 90mm aluminum hub wheel I've lost. Love to find a set but happy w/ a good used one; pay top dollar. Anyone have one you don't need? Tx! Ray Davis 508-444-6350 redavis2010@comcast.net
Posted on: 2/11/2011 2:19 PM by Author "67Jag" in the forum "RC Pattern Flying"
http://www.rcuniverse.com/forum/fb.asp?m=10329024

RE: Needed badly!
Tx, but Central was my first try....apparently they are no longer manufactured w/ those hubs. Needed to replace/match a lost one on my A-6/Intruderized 44-Gold Facet. Ray
Posted on: 2/8/2011 8:49 AM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10320857

Needed badly!
One or a set of Tetra 90mm wheels w/ the aluminum hubs. Desperate, name your price, any payment form. Tx! Ray redavis2010@comcast.net 508-444-6350
Posted on: 2/7/2011 4:52 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10319619

Needed badly!
One or a set of Tetra 90mm diameter wheels w/ aluminum hubs. Or a source. Name your price, any form of payment fine. Tx! Ray redavis2010@comcast.net 508-444-6350
Posted on: 2/7/2011 4:48 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10319618

RE: Repair crushed foam fuselage ...?
Incidentally.....I now use a max-expanding aerosol foam (PU) to fill those forward cavities. Adds only grams, and once cured (overnight) easily carved out again if you've applied too much (and you will ). Messy...follow directions(!)... but amazing how much it strengthens everything! Ray
Posted on: 1/19/2011 5:05 PM by Author "67Jag" in the forum "Electric RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10274884

RE: Repair crushed foam fuselage ...?
Many minutes over a teakettle will just about restore the crushed portions to original shape. No worries....you can't apply too much steam/heat, rather you need plenty of patience and a glove to pull/squeeze/prod things back into shape while in the steam stream. Try and direct the steam to every side/surface of the deformed part. It works. Ray
Posted on: 1/19/2011 5:00 PM by Author "67Jag" in the forum "Electric RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10274876

RE: 2.4 antenna inside a metal finish?
Thanks guys! Ray
Posted on: 12/8/2010 2:30 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10184808

2.4 antenna inside a metal finish?
Can't recall the earlier discussions.....is there any consensus that 2.4 (Futaba FASST in my case) antennas can remain fully inside a metallic-painted fuselage, w/o link loss? Or even aluminum skinned models (such as Flite-Metal)? Tx! Ray
Posted on: 12/6/2010 2:44 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10180787

RE: Downwind turn Myth
brenthampton79....physics is w/ you. Forget the winds, your flying at 100mph AS in that sea of air, plane feels/acts as if it's in still air. Grant that. Now instantly turn/pivot it 180 and you are flying some speed backwards relative to the wind, due to inertia alone, no matter the thrust, etc. Negative airspeed, loss of lift, etc. Of course, we cannot get a plane to anywhere approach that 180 turn instantly, but the closer one approaches a very fast turn, and w/ a higher inertia a/c, then the greater lag in going fully forward into the air again, and back up to that 100mph AS. The case above is the extreme and illustrates the effect quite graphically..... at the other end of things, w/ very slow/wide turns, or w/ less inertial effects, then yes, we are back up to our AS relatively quickly, perhaps undetected. But there is a gradient, hence an effect, however small. The above alone would make no distinction for UW/DW, yet I believe we see a ballooning turning UW, and a loss of altitude turning DW, even though we 'can't' according to HH, etc. Where's the flaw in my thinking above (perhaps it's in the definition of a 'turn' [has to be 'coordinated/constant speed/altitude?], or perhaps both camps are 'theoretically' correct?) but show me, and I'm in the HH camp. But I don't think so, not yet, whether by observation or analysis. Ray
Posted on: 11/25/2010 12:36 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10159082

RE: Downwind turn Myth
EddieC: OK, so don't do it 'quickly' and the effect will be less 'significant', that's all. Just more illustrative when the extremes are approached.....but the case holds, nonetheless. And, as I said, by observing AFTER the turn, all effects of turning/drag, etc. are eliminated. I just don't understand why so many here think a model can accelerate at an infinite rate and immediately match the wind. It would HAVE TO to have no DW turn effect....but it can't, it doesn't. And that real world lag results in a loss of AS, lift, and altitude. I.e., the 'Dreaded DW Turn' effect. However small it may be. And from any POV, too: your aboard, the ground gets closer....your at the Tx, you'll see less clearance. Ray
Posted on: 11/23/2010 3:41 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10154667

RE: Downwind turn Myth
Forget the loops...go back to original simple question: does turning DW cause any effect re altitude? Trim/power for straight and level flying into a significant wind. Hands off. Quickly initiate a 180 turn/let the model turn itself. Then make no control inputs, no compensations. What happens? After the 180 is complete and leveled, the model keeps losing altitude until it has fully caught up and exceeded that steady sea of air to return to the original AS. The amount of time that takes obviously proportional to the height loss....and, yeah, going pretty damn fast, now, relative to the Tx....and definitely lower in the sky. Greater the WL/wind/the closer the AS is to the wind speed, the greater the effect. A powered feather be less noticeable; only a model w/ no mass would truly show no DW altitude loss. Myth of the myth exploded. Period. But I know it won't be for some. Ray
Posted on: 11/23/2010 12:56 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10154380

RE: Downwind turn Myth
p51Dpony, rjbob, Tim (parachute example) make my point better than I did.....and true, perhaps folks in the a/c do not detect minor accelerations (maneuvers), though they would if abrupt enough (my 100-200mph, for example, and much less extreme ones). All posited frames of reference 'making a difference' are moot...they cancel out, so long as there is constant speed or such minor accelerations as to be unnecessary to consider (earth/sun/universe). Comes down to the simplest frame of ref that has meaning and where there are actual/significant speed changes: a mass in the air that changes direction. Our model. And if that mass changes direction or speed, then there is an effect on it.....whether being observed form the ground or aboard. And so it will slow, or speed up, drop or rise, as conditions change (going from UW to DW, etc.), unless actively compensated for. Recall: the original issue here is the effect on the mass (a/c) of a maneuver...not necessarily what folks observe...though it's certainly observable. You (the wind or prop/turbine thrust) simply cannot bring that mass back up to the same AS instantly, there is a lag, and that lag can produce (for one) the effects of 'the dreaded DW turn'. Sorry, but again (in our classical conditions, anyway), F does equal Ma. Mike, I meant to answer earlier: I'm a retired mechanical engineer, though that's hardly a credential here. Commonsense and an open mind suffices. The aero phds/books are not wrong...but most often they are speaking of specific cases/conditions, eliminating variables/difficult quantities in order to clarify/solve an aero problem, etc. Really.....just go out and observe it. Turn fast from UW to DW, esp w/ a heavy highly WLed model. Do nothing but get it to turn...and watch it drop. POV does not matter (someone said correctly inertia is a property of the object/the a/c). It will drop because it has to, as it has lost AS. Ray
Posted on: 11/23/2010 9:05 AM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10153983

RE: Downwind turn Myth
C'mon guys....I'm the one who has been saying we CAN'T instantly accelerate (rotating Earth examples, etc.). And so we see the effects of that impossibility on our models as they turn DW. One more try, then bedtime: Your model is capable of 100mph AS and headed right-to-left in a left-to-right, 100mph, steady wind. IOWs, it's hovering from your POV on the ground. Now you quickly turn it DW. In order to not lose lift, it somehow would have to turn and accelerate instantly to 200mph, now going from your left to right, so as to have an AS of 100mph. Instantly....and if it couldn't do that, then it would drop as it went from a 100mph tailwind, struggled through an AS of zero for a moment, until finally catching up and exceeding the 100mph 'sea of air' by 100mph in order to regain its 100 AS. Where is the above reasoning flawed? Great fun(!)....tomorrow, then. Ray
Posted on: 11/22/2010 10:19 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10153352

RE: Downwind turn Myth
psuguru......exactly correct, I believe. On both counts...and so, can a UW to DW change in direction be likened to a longer period, steadier gust.? I think so, and with just the effects you describe. I'm just a lowly retired ME, minored in aero. Hardly recall a specific thing, except that F does equal Ma and therefore compensating forces are required to maintain equilibrium w/ the accelerations described....or there will be the observable effects only a few of us seem to see. Ray
Posted on: 11/22/2010 8:33 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10153032

RE: Downwind turn Myth
Confusing several things here. To get back to the original position of HH: 'A plane turning downwind will not be affected (as closely observed by the pilot), as it is in a sea of air that is moving evenly.....so the plane exactly follows that 'sea' during the maneuver. I.e. a turn within the air will be an exact circle...no slowing or increase of speed, no increase/decrease of lift.' Close enough? Think about it, folks. Your asking that aircraft's mass to undergo no acceleration (change in speed), for if it does, then there must be forces changed (or effects realized) to compensate, since F=Ma. If at HH's 'steady state' (which is NOT same as steady wind), then true....I guess....if SS means no acceleration. But a turn/maneuver is by definition an acceleration and therefore some force is required for equilibrium (more power/more lift/whatever). And, since the mass cannot be accelerated at an infinite rate, there is a time lag...and therefore observable effects (e.g., some temporary loss of lift turning DW...until the aircraft catches back up to the wind). The more inertia or the greater the acceleration, then the greater this effect. Common sense if nothing else...supported by physics. Physics is hardly junk science, HH, simply because you don't observe it. Ray
Posted on: 11/22/2010 8:04 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10152954

RE: Downwind turn Myth
Highhorse.......I'll let David comment on your 'real world' observations (though you immediately contradict and state there were observable speed differences), knowing at low accelerations, effects may not be so observable. Doesn't mean they don't exist.....further, your experiences are anecdotal, the senses easily fooled while flying, and if were true, do indeed, defy the laws of physics. (Again, you'd need to be in an inertialess aircraft, one that could instantly match [infinite acceleration] changing conditions in order NOT to have an effect. Impossible). F=MA, i.e., there MUST be effects, whether observed, or not. And, in fact, those effects are demonstrable/repeatable and significant (as I wrote earlier), as observed from a steady platform (earth).....and while also anecdotal, most importantly, they do have physics on their side. Your observations are either flawed or taking place at such gentle accelerations (as opposed to speeds) as to be (humanly) undetectable. This is a topic that surfaces every few years here. Certainly an aircraft properly instrumented and recorded has dispelled the myth of 'The Myth' by now! Anyone? Ray
Posted on: 11/22/2010 6:15 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10152706

RE: Downwind turn Myth
Highhorse....you say 'steady state' and by that if you also mean inertial effects are not to be considered, then, of course, your arguments are correct. But that's kinda disingenuous. Because, in the real world, planes/models have mass, and therefore are subject to the laws of physics ...i.e., they cannot accelerate at an infinite rate to immediately match changing conditions....whether gusts or a turn from (say) downwind to upwind. There will be an effect, however small, as the plane/model does, indeed, require some time to 'catch up' to that sea of air around it. That effect may be undetectable during slow turns/maneuvers....perhaps your 'steady state'. But a fast transition (e.g., from upwind to downwind) will produce a loss in altitude (all else being same), as the model must lose lift in not being capable of accelerating instantly to maintain a same relative AS. I.e., maneuvers (accelerations) even in steady wind conditions do produce an effect. Simple physics, and demonstrable all the time at the field, esp w/ high inertia (heavy) models. And nothing to do w/ AS vs GS, etc. Ray
Posted on: 11/22/2010 4:23 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10152410

RE: Which afterburner light ring is best???
No one w/ direct experience installing/using Hyperdyne Labs AB? Tx! Ray
Posted on: 11/1/2010 12:13 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10108517

RE: Global Jet Club / JHI F4D Skyray Product Release
I dunno...I am just uncomfortable and unfamiliar re putting any gyro on the elevons....and be certain I'm correcting roll only and not anything else...then having to go through a trial and error process during flight as Andy describes. Duke, you mentioned your yaw gyro installation (on rudder only) damped the roll oscillation considerably......how did you set it up? Roll right, slight right rudder to counter....but wouldn't that be the beginning of a coordinated turn (however slightly)? Or, was it roll right, left rudder to induce a slight undetected slip. Which way....and was it just so self-correcting that it was unnoticed? How much rudder deflection? Love to eliminate that roll oscillation w/ a simple yaw gyro alone. Or are we blowing this thing out of proportion....and most guys 'just fly it fine' w/o gyro aids? Thanks! Ray
Posted on: 9/23/2010 8:07 AM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10021575

RE: New England Jet Rally 2010
Yeah, just great, Chris........ Take yer pick: I hadda hit the head; "That Grip ever gonna get out there?"; "Oh, oh...here comes Nunza, knife edge, at ten feet!" Davis
Posted on: 8/25/2010 5:54 PM by Author "67Jag" in the forum "RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=9959482