Flap extension speeds for the Rocket.

Gt-401 · #1 11-08-2018, 08:49 PM

I?ve got about 150 hrs on my new to me rocket since I got it a little over a year ago. I have been flying it with the same flap extension speed as the RV-4. Now that I am flying it IFR more and more, I am wondering if anyone has beefed up the flaps to allow for a higher extension speed. It sure would be nice if I could get approach flaps in at 100 or even 120 KTAS

Mel · #2 11-09-2018, 06:28 AM

Flaps are the only control surfaces that get extended into the airstream and stay there. All other control surfaces extend into the airstream only momentarily. Flaps carry some pretty extreme loads. I wouldn't try expanding on the designer's limits without doing some extensive engineering.

F1Boss · #3 11-09-2018, 09:11 AM

You can drop the flaps about an inch at 120KIAS - just look at flap speeds on a C210 or similar - certain speeds are OK for various angles. Same applies here.

If you have the Rube Goldberg setup under the floor, you might need to change to the F1/RV8 style system to keep things from bending...that short length of 1/4" threaded rod might not survive, along with the actuator rods.

vetterman · #4 11-09-2018, 09:16 AM

I assure you. It isn?t a Rube Goldberg setup under the floor.

Toobuilder · #5 11-09-2018, 11:03 AM

I removed the Rube Goldberg mess under the floor and went with an RV-8 style primarily to address the poor geometry. In the process I reduced complexity and weight and as a bonus the existing linear actuator is now capable of exerting more force at the flap attachment points without bending or stalling. The Rocket flaps are smaller and have closer rib pitch than RV-4, so should be stiffer in torsion. All that said I have no idea where the LIMFAC is on this system but I've busted published limits from time to time without damage.

Gt-401 · #6 11-09-2018, 05:46 PM

Is there an intensional weak spot in the flap mechanism that is meant to bend or shear to keep from damaging more important parts, like for example a clutch on the motor, or maybe a breaker that would pop if to high a load was applied to the flaps? Leading to my next question, is the flap motor powerful enough to bend stuff if it is active at too high a speed?

rocketbob · #7 11-09-2018, 06:46 PM

My opinion is the weak point in the flap system is the torsional load on the main tube in the flap weldment. I believe the main tube would bend before anything breaks.

That said, I redesigned and implemented a "rube goldberg" flap drive completely hidden under the floor. "out of sight, out of mind."

The goal was to have no holes open in the floorboards which allow smoke and cold air to come in, and be easily accessible for maintenance.

I'd venture to guess its at least 3x more rigid than the stock RV-4/rocket setup. There are four spherical bushings supporting the main tube. The mechanical advantage of the linear actuator is also improved.

Titanium components were fabricated to keep the weight down.

If interested I can post a video of it in operation.

Toobuilder · #8 11-09-2018, 07:33 PM

Quote:

Originally Posted by rocketbob

...If interested I can post a video of it in operation.

Post a link, please!

The "Rube Goldberg" aspect of the original design include (IMHO): transmitting a high load through 90 degrees of change using high friction nylon pillow blocks; a walking beam that has such poor bearing support that the linear actuator needs a nylon sliding support to keep the whole mess from carving an arc through the aluminum on the bottom of the fuselage; poor mechanical advantage on the too small torque tube; heavy, solid rod linkage in several places; and using stud mounted heim joints at the flaps instead of spacers and through bolts.

Other than that, its a great system!

rocketbob · #9 11-09-2018, 08:15 PM

https://photos.app.goo.gl/AF5hgkqcfEKZebk7A

smokyray · #10 11-10-2018, 07:14 AM

Quote:

Originally Posted by Gt-401

I’ve got about 150 hrs on my new to me rocket since I got it a little over a year ago. I have been flying it with the same flap extension speed as the RV-4. Now that I am flying it IFR more and more, I am wondering if anyone has beefed up the flaps to allow for a higher extension speed. It sure would be nice if I could get approach flaps in at 100 or even 120 KTAS

First answer: WHY? My manual flaps on my HR2 were extended at either half or full or "pilot's choice" by pressing the button and pulling slightly.
You might try your prop in a flatter pitch, different power setting and be happy with it.
As mentioned by Mel, Flaps get enough abuse as it is...adhere to the RV4 max extension speeds and they will last a long time...
V/R
Smokey