SkyKnight

My Feedback: (67)

I need a DV8R pro. There must be something wrong with mine. I tried to fly yesterday. I must have burned 2 gals. after several unsuccessful takeoff attempts. Makes a strange looking race car! I tried no flaps, 20 degrees of flaps, switching runways (no wind yesterday - slight crown in runway) Anyway, construction was straight forward, Robart gear (really nice too) JetCat P80 (plenty o thrust 8D ) balanced at the revised location of 10 5/8". It zooms down the runway at what seems like 100mph but will not rotate. Runway is 700' of well groomed short grass. I rechecked the manual but there are no reference lines to check by. Ya know, like thrust line or some other reference marks. Any ideas will be great.

thanx

Gordon Mc

My Feedback: (11)

Pat is here on RCU ; in case he doesn't immediately see your question, you can send him a PM or an email via the contact info on http://www.rcuniverse.com/community/...=1&memid=24080

Good luck,
Gordon

Wren Turbines USA

My Feedback: (39)

Not trying to be funny.....but........by any chance ....could you have elevator reversed???

fly109

My Feedback: (1)

SkyKnight,

Something sounds wrong for sure. Balance would be my first guess. Second guess is that you don't have enough elevator throw or possibly have less incedence in the stab than required.

SkyKnight

My Feedback: (67)

Hi Pat,
My balance is at 10 5/8ths from the LE at the root with the UAT full and main tanks empty and the canopy in place. I did see an RCU thread where the the owner said you told him to balance such that when the nose is lifted it will fall slowly if balanced correctly. I didn't try that. All throws are per the manual measured at the root. A couple of attempts I even maxed out the ATV on the Ele too. As for the stab incidence, it is set according to the dowel holes in the balsa plate. Is there a way to make measurements?

BlackCloud

My Feedback: (12)

Make sure you are using the high rate elevator setting for takeoff to start. One time I forgot after flying a different plane previously and it was kinda scary as it rolled off the end of the runway with full back stick disappeared as the runway slopes down and then just in time it started climbing. Really pretty funny now but not then. Start with that. Also of the ones I have seen they need up elevator to fly level. I would say about 1/8" up elevator as your neutral trim point. CG at 10 5/8. I had more success when it was measured from the back end of the fuse wing saddle rather than the beginning of the wing at the fuselage side. Your CG should be okay but not preventing liftoff. Double check and put some up elevator in for your neutral and probably more throw or at least go to your high setting for takeoff. Mine sat pretty much level when on the gear. Make sure your nose strut is not short causing the nose to be down. From the bottom of the fuse it should be pretty much level with the ground.
Good luck. Those are just my personal experiences. Pat will probably chime in with more appropriate help.
BC

Roger_Martin

What kind or wheels/tires are you using? I had a Hot Spot that did the same thing because the tires were too soft. They came with the kit, too. The 27 pounds of thrust times the length of the main gear struts causes a significant nose down pitch moment if there is any rolling resistance from the tires. It can easily be greater than the nose up pitching moment generated by the up elevator. Changing to hard tires solved the problem on my Hot Spot.
Roger

SkyKnight

My Feedback: (67)

3" Sullivan on the nose and 4" Sullivans in the mains. The RoboStrut on the nose will only allow for a 3 -3 1/2" tire max. When retracted, the nose wheel tire just touches the servo mount which is against the steering servo.

Woketman

My Feedback: (6)

Make sure that the wing has a slightly positive angle of attack when sitting on the gear.

grbaker

My Feedback: (29)

This is more critical on grass than on pavement. I have seen jets that fly great off pavement that would not get off of the grass.

Woketman

My Feedback: (6)

For the wing to lift it off of the runway, you will NEED lift and therefore and effective positive AOA. This is normally easier on pavement because there is less drag from the wheels and therefore you can use the elevator to overcome a nose-down pitching moment easier due to greater speed and therefore more stabilizer down force. But either way, the wing needs to LIFT you OFF of the runway. Make it easy on the DV8R and see if a slightly positive wing AOA on the gear solves your issues. Does it currently have a positive AOA on the gear? Or is it negative?

SkyKnight

My Feedback: (67)

I understand. I asked for ways to take measurements hoping to verify correct assembly. I want to be certain that any adjustments on the ground don't hide a more serious problem like wing and/or stab incidence. I didn't checked the wing incidence or AOA while on the gear though. The shape of the fuse makes it difficult to tell if the plane is level or not. The nose gear is 6" long and the mains are 7" measured from the base of the retract unit in the extended, gear down position.

Adil Nasim

My Feedback: (61)

If you feel that all the rest is fine (CG, incidence, etc.):

Easiest test would be to try to eyeball the airframe sitting level on the ground. If that is not possible, put a bigger wheel on the nose or lengthen the nose strut about an inch. If you fly off pavement, you can also put 3" wheels on the mains (vs the current 4". )

The plane flies just fine with the gear not retracted so don't retract the gear with this setup. Once you know that the airplane rotates this way, you can go from there.

Adil

DelGatoGrande

My Feedback: (23)

.......thrust angle....maybe u have build "down" move???....just try to help

Woketman

My Feedback: (6)

Just place it on a flat surface, take a ruler and measure the height of the center of the leading wing edge near the root and the center of the wing's trailing edge at about the same spot distance-wise from the airframe's center line. If the leading edge number is higher, you should be OK.

SkyKnight

My Feedback: (67)

I discussed the project with Pat of PCM this afternoon. It appears I have a problem with the height if the struts causing a negative AOA. He suggested some mods which I am in the process of making right now. Looks like bad weather will be holding up progress for the next few days. The changes will be complete this evening and the DV8R will be on Ready 5 in case we get a break in the weather.

Thanx for all the help guys. I'll let ya know how I make out. Stay tuned..............

tylers600rr

My Feedback: (10)

[sm=spinnyeyes.gif] tapping fingers.....waiting to go try this again....Shady always on hot standby!!