bweight

Hi, I visit these forums quite often, but don't post much (as you can probably tell by my post count )... But I have a dilemma...

Anyways, I've got a Bob Parkinson DF Avro Arrow.. I've been building it since last August and up until today, I've tried 6 attempts at a maiden flight. On my 2nd attempt today, i veered off course while in my take-off and clipped out safety barrier causing some pretty extensive damage to the right wing L.E.. Our field is 800' x 80' and it's grass.. Now, all accounts from B.P. say that his planes can, and do, take off from a grass surface. I believe it as I've watched the video for the Regal Eagle F-15 that he manufactures.

So here's my issue.. I'm new to DF jets and I'm getting quite frustrated with the inability to get this plane off the ground, however, I understand after today's crash that patience is a virtue. I have a Rossi .81 installed in the Arrow, and it weighs 11lbs dry. I have 2 11oz Sullivan saddle tanks installed and after balancing correctly, I can't see a reason that this plane doesn't take off. I don't know the thrust of this particular engine, but it's tuned and really screams at full power.

I am running 3" main wheels and a 2.5" nose wheel.

This model requires the Byron pusher system and so that's sort of restrictive in what I can either upgrade or switch too.. Now, would a Rossi 105 be too powerful? Would an OS. 91 w/large head be not powerful enough? Or *should* this Rossi .81 actually work on this model in the conditions that I've described in my post?

I don't want to rush the plane, but we have an event coming up on July 2nd and I *was* hoping to fly at it.

Is there anyone who has an OS .91 w/ Byron setup (pipe and large head) that is looking to sell? If so what price?

Thanks in advance for any and all assistance. I hope I can find out how to get this plane in the air.

Brian.

Miniflyer

Brian, are you running steering AND rudder? With both of those, veering off should not be an issue......and a jet needs those in my opinion (lost a plane mainly because it had no rudder......)

Apart from that, i see no reason why it should not take off on 800ft (well cut) grass. Could you describe how it accellerates? Does it just accellerate to a point and then keep going at that speed, or does it keep getting faster? If it maintains a certain speed, the drag from the grass is too great.....mow it shorter then .
If it does keep accellerating and should be around flying speed: Do you have a cheater hole below the fuse? If you do, chances are it will suck itself to the ground...had that on my sabre before conversion....only fix there was to pull the power on rotation/liftoff....not a wise thing, but worked (most of the time even without damage to the plane *g*).
CG and throws are all set up correctly?
Regards
Hank

Countryboy

My Feedback: (25)

Brian,

Before you go making drastic changes, put the aircraft on a level surface and check the wing incidence. You want a least a couple degree's of positive or a prominent nose high attitude. The grass may be pushing the nose down on acceleration causing a negative incidence...... hence the failure to rotate.

MMallory

My Feedback: (1)

Countryboy has the number one reason.

Another "Byron" thing to consider. Sometimes the plane gets sucked to the ground due to the cheater hole. You may need to pull back on the throttle a bit, after rolling at full speed, to get off of the ground. The problem with this is you need to get right back to full as soon as you break ground.

Also, keeping up in during your roll will help with your steering.

Mark M.

grbaker

My Feedback: (29)

I agree. Also you have to make sure that the nose gear wire is not too weak (bending bacK) causing the nose to drop.

gmeister

My Feedback: (8)

The incidence thing is a good thing to check. Also have lots of up elevator available as in high rates. I don't know about the Arrow but most jets need lots of up to rotate.

grbaker

My Feedback: (29)

Another good point. I always had more up elevator in my Regal Eagles that flew off of grass.

bweight

Thanks for the input guys.. I'll answer all the questions I can....

Miniflyer - Unfortunately, the plans say Rudder is optional, and well, I opted not to install them. The resident "mechanic" in our club is likely going to get that squared away for me as he repairs the damage. The rudder is actually cut and installed with hinges as well, except that we pinned it stationary.. So I guess it's a good thing we can fix it...
As for the acceleration, well, no.. it doesn't seem to pick up a heck of a lot more speed once the engine's full open. It does, but not like any of the other planes we fly at the club... Could be the grass, but I'm still not certain. There isn't a cheater-hole per-se, however the bottom hatch has been left off while testing and it's a fairly large area that's open so it could be keeping it down on the ground.

Countryboy - Yes, the nose is pointed up a certain degree. This was done on purpose by using a slightly longer nose gear than the mains.. The real Arrow had that type of stance, so I went with it too... IT's a fultz (sp?) dual strut wire gear on the nose which is plenty rigid as well..


This afternoon after work, I stopped by to check out the damage and verdict with it... the "mechanic" said that the Rossi .81 isn't powerful enough for grass, and that the .91 should work.. I've thought about scrapping the DF altogether and putting in a turbine, but I don't have the experience needed by M.A.A.C. yet to run a turbine in an RC aircraft.. so that's out of the question at least for now.. One other thing that he mentioned that could be causing some lackluster performance is the ducting at the back.. it didn't fit all the way to the tail cones and they're rounded in a little bit at the very back. So it's causing some turbulence I guess you could say, instead of pushing the air straight out...

Does anyone have an OS .91 for sale that's setup for the byron style system?

I was also looking at a Rossi 1.05 on Ebay which is tempting.. but I don't think it'll mount on the Byron mount that I have....

Thanks again for the help..

vasek

My Feedback: (4)

Brian, if I were you, I would go to the nearest club with a tarmac runway... make the first few flights there and tune the engine/plane combo to the max. Only then I would try it on the grass.

donniercjet

My Feedback: (10)

your byron fan and rossi 81 is a good poiwerplant for your app. do you have a thrust tube?? you must have a thrust tube on a fan to get your 10-12 pounds of thrust i've seen a byron f-15 weighing 32 pounds fly beautifully off a pair of rossi 81's my byron mig-15 weighs 14 pounds with all the bells and whistles and i fly with a rossi 81 its slow on the ground but it flys good onces its in the air as to the rossi 105 i've seen a lot of the 105's and heard all the pilots cursing at them also. unless rossi changed the carb set-up the carbs are not reliable from what i've heard from other 105 owners good luck donniercjet

MMallory

My Feedback: (1)

A couple of things. Byron systems need air. unless the inlets are huge, you need the cheater hole. The rear ducting must be complete. If you are not getting speed on the ground, either the grass is too thick (use larger wheels) or your gear is set up wrong (make sure your main wheels are rubbing on the strut and you have a degree or two of toe in. The rudder is a good idea but not necessary.

I agree the first flights should be on a jet friendly field. Remember once this plane breaks ground to keep your climb shallow and don't make your first turn until you have built up some speed.

Mark