speedbrake

I changed the radio..... no improvement. I changed the propane valve......no improvement. I changed the battery pack (flat 4 cell).....no improvement. I even changed the TEMS. I'm stuck....can't think of any other thing I can do without some expert help.

I will change turbines. This won't help the current condition but I'll be able to move ahead with the project.

Help PST!! What needs to be done? This turbine should be running.

Keith

pdubree

Hey Keith. Good idea. Change engine get your money back and get a kero start kingtech and eliminate the propane bomb.

Your Bud
Pete

PS: Got in 10 flights this week on the shockjet.

speedbrake

I replaced the turbine with another PST600R. It fired up with no problem (same radio and receiver as before). I let it idle for several minutes and then increased the throttle. It shut down due to low ECM battery. I'll try again tomorrow. There are several things I want to check...first to make sure both wing tanks provide good fuel flow and second to insure the exhaust doesn't melt the monokote behind the engine. So far all is good. For the first start I laid a piece of plywood behind the turbine to protect the monokote.....then removed it after engine start. I'll replace the plywood with a metal plate in the future.

I will attempt the first flight this weekend.

Obviously there is a problem with the other engine. Will need to have the factory look it over...unless somebody has an idea about the cause.

Keith

Ed

Good luck with it Keith, and don't forget to video the flight.

ed

speedbrake

The second PST600 turbine initially ran but bubbles formed in the fuel line and it quit running. I tried a couple of things but no joy. I have since re-installed the turbine in another plane. I will try again some day...right now I'm working on other projects. The main tanks are located inside the wing, just hope I don't need to tear into the wing to find/fix the problem.

The first turbine still sits on the bench. Not sure what to do with it. It just returned from the factory and I'm not excited about returning it for a fix. The downside of having a PST turbine

Speedbrake

speedbrake

Wow! I can't believe it has been so long since the last attempt to fly this thing. I dusted it off and put some fuel in it and it ran. I took it to the field and attempted to fly it. The nose gear wire isn't strong enough to support the weight, it folded back during takeoff roll. The elevons didn't have enough authority to over come the nose low attitude. I installed a Fults (sp) nose gear last night. I hope this gear will be stiff enough to support the weight. The CG has me concerned because of the way it rolled down the runway....nose low. It could be nose heavy right now. I'm rechecking CG with the canard CG program I have. I'll try again when the weather is favorable.

It occurred to me that the nose gear is too far back and needs to move forward so it doesn't support as much weight. It is now located in the stock location. Might have to relocate it if the next flight attempt shows the same problem.

BruceTharpe

My Feedback: (1)

A voice from the past! Glad you found time to play with this again. Yeah, Fults is the way to go on the nose gear. Moving it forward would reduce the stress on it, I suppose, but I do like that long, over-hanging nose.

Another thing pushing the nose down is your high thrust line. It will be most noticeable during low speed + high thrust situations, like takeoffs and go-arounds.

Woketman

My Feedback: (6)

"Use a pulsejet". PulseJet Harry circa 2002.

speedbrake

Hi Bruce,
Yep the bug hit me again. I know it will fly....just need to spend more time on those nagging little things that are preventing a successful first flight. I too like the long over-hanging nose. I didn't consider the thrust line. If a similiar nose-low situation occurs again I'll try changing the thrust line. The Fults gear seems very stiff and hopefully will remedy the problem. The CG is about 25 inches from the trailing edge.


Woketman: Oh yeah, what a sound that would make!! I used to attend the IMAA events in Las Vegas years ago. A guy from Germany brought a scale V-1. Wow! That thing was so loud and deafening your ears would still be ringging thirty minutes after the flight.

Woketman

My Feedback: (6)

Yes, the pulsejets are quite amazing. I have almost forgotten how loud they were since it has been a decade since PJH even got one to run, let alone fly. That's OK, it's kept me from starving thanks to my free winnings at Outback Steakhouse!!!!!

speedbrake

Bruce: I recalculated the CG using a program available on line. The CG is 22.3 inches behind the canard LE, which is about 24.75 inches from the wing TE (that includes rounding up from a 3rd to a half). The difference between the two calculations is including the wing area inside the fuselage. Just read I should have included that area in the calculations, the difference between the two is1/2 inch. I will be able to disgard some ballast...thus decrease weight on the nose gear. The CG was just behind the main spar on the first take-off attempt....much too far forward. I will balance the model dry and then again with the tanks full just to ensure fuel won't cause it to be tail heavy.

flyinfool1

My Feedback: (2)

Glad to see you back on this. I have been following it since the beginning.

A couple of times now you mentioned an on line CG calculator, can you share a link to the one you are using?

speedbrake

Flyinfool1: From a search program, type in "canard center of balance calculator", that should provide several available programs to choose from. I've used several different ones and gotten pretty much the same output.

I've always thought the nose feels heavy when lifted up.....with the main wheels still on the ground. I have a Reaction and a Sprint and both feel lighter than the Delta. I think the reason is I didn't move the main wheels forward with the CG shift. The total weight from the nose back five inches behind the CG is being lifted. I wonder if that has something to do with the stress on the nose gear and the difficulty for the model to rotate on takeoff. Just a thought.......

I balanced the model again tonight. I was able to use a lot less ballast than before. The CG is located 2.75 inches ahead of the stock forward CG location. The weatherman says 70 degrees for us on Sunday......I'll be ready.

BruceTharpe

My Feedback: (1)

Another simple test for CG is to build a simple chuck glider from sheet balsa. Get all the areas and incidence angles correct. Hand toss and balance with clay until you get a smooth, fast glide (not floaty). Hopefully, the final balance point will be close to what you have found with the calculators. Will also tell you if your model has enough vertical fin area. It most likely does, but that long nose is destabilizing in yaw. If your chuck glider won't fly straight, you might need more fin area.

speedbrake

Too windy to fly today but was able to start/run the turbine. Had too many air bubbles coming from the UAT...the engine was surging at full throttle. Will take the UAT apart and find the source of the bubbles.

While fueling today I discovered the tanks were already full, the tanks are imbedded inside the wings so it is very hard to determine the fuel level. The delta is relatively light compared with most other jets so the extra weight wasn't noticed. Will have to balance it again.......the extra weight I felt when lifting the nose was obviously the full tanks.

speedbrake

Replaced the UAT. The bladder inside the original one was completely flat. Will relocate the nose wheel steering servo to provide better access to the steering linkage. Rebalanced the plane, only needed 4 oz. of lead for a slight nose down attitude. Balanced again with fuel to ensure the tanks didn't cause it to be tail heavy. Increased the canard elevator travel to 3/8 inch up and down. Will be ready to fly when the weather improves.

speedbrake

It Flew! Got one flight today...about four minutes. Takeoff roll was about four hundred feet! Just didn't want to rotate. Once in the air it proved to be very responsive, overly responsive in roll but pretty much normal pitch control. There wasn't any yaw problems. It flies extremely fast, that was the big surprise. I always thought it would be relatively slow. The PST600 is more than enough power. I think a smaller turbine would be better. The aileron travel proved to be way too much....I started out with stock control throws. The fults nose gear folded back on takeoff. I think Bruce is correct about the high thrust line pushing the nose down. Not sure how/what to do to fix it. I think moving the nose gear forward will remedy some of the stress on the nose gear and allow the nose to rotate. I also think a Robart type strut will be stiff enough to handle the stress. I was pretty busy most of the flight trying to keep it flying straight and level. Obviously less control throws will help and some expo as well. Half throttle was the best throttle setting.

I didn't notice any problems with the canard. Control throw is 3/8 inch up and down....I'll probably leave it there for now. The fuel bubble problem turned out to be crossed fuel lines on the left fuel tank. By isolating each tank it became evident what I had done when the tanks were installed. Because of the sensitive roll I allowed the engine to run out of fuel and glided the Delta in for a landing. The glide rate was fantastic. That gave me more confidence in the CG location.
I welcome ideas about the thrust line problem. Because of its location on the airframe, moving the thrust line down (thrust downward) is limited because of the aft structure. Moving it upward has no restrictions. As for the nose gear, I see no alternative but to move it forward and to lengthen it so the plane has a positive attitude on the ground. Something like the F-5 has....the front strut is lengthened on takeoff roll to enhance rotation.

A friend took pictures of the Delta in flight. I include those to the thread very soon.

speedbrake

[IMG]G:/delta on ground.chr[/IMG] It seems I can no longer insert photos. Not sure what has changed with RC Universe, but all photos I try in insert are labeled incorrect file type. What's up?

Rocketman612

My Feedback: (85)

Congratulations. Nice to see a project of this scope go the distance. Followed a lot of threads that died when getting delayed like yours. Well done sir.

Pete

BruceTharpe

My Feedback: (1)

Yeah, congrats my friend! That must have been a real thrill to finally see it in the air.

Not sure on the pics, haven't uploaded one for some time. Don't use the Quick Reply box, be sure click "reply" at the bottom of the last post for the full editor. Would love to see that flight pic...

BruceTharpe

My Feedback: (1)

About the thrustline... The thrustline is a straight line that passes through the center of the turbine. Right now, that line is a certain distance, vertically, above the balance point. I'm talking about the true balance point, or center of mass, located somewhere in the fuselage ahead of the turbine. It is that vertical distance that creates a moment, in this case a negative moment pushing the nose down. If you can reduce that vertical distance (arm), that should result in a reduced pitching moment. You could eliminate the arm (and the moment) by moving the turbine downward, in line with the balance point. But there is a wing in the way. You could move it aft of the wing, but that creates balance problems. So at this point, I think your best alternative is to try altering the angle of the thrustline. If you angle the turbine nose down, the vertical distance between the thrustline and balance point (arm) should be reduced, resulting in a reduced pitching moment. I would try creeping up on it, maybe two or three degrees at a time between flights. Ideally, you would like to have the model exhibit zero pitch changes when moving the throttle up or down.

speedbrake

Thanks Pete

Good input Bruce. Here is what I know at this point. Sitting on the ground without the engine running the plane will sit normally, no obvious stress on the nose gear. At the start of take off roll the nose is beginning to lower because the nose gear is bending. And at full throttle the plane is at a nose down attitude and the nose gear is bent backward. During take off roll the elevator has little effect until a very fast speed is reached. After rotation and lift off the plane climbed at a very flat angle. Once in the air it took a lot of up trim to maintain level flight. As I decreased throttle pitch control became more sensitive. Because of the exaggerated roll rate I didn't experiment much during the flight. Once the engine shut down the plane flew well. The glide angle was fairly flat.

I'll follow your suggestion and tilt the turbine nose low 3 degrees and see what happens...... And of course the aileron throws will be adjusted. Hopefully the poor nose gear will survive long enough to get the plane trimmed for normal flight!

speedbrake

As you can see, the nose gear is already bent backward at the beginning of the take off roll. I'll include more pictures once I figure out how I got this one inserted

speedbrake

speedbrake