Robertson STOL = Slow Me Down

by **SLIMDREDGER** » Tue Mar 16, 2010 9:58 pm

Hi Scott: From my experience, I wonder if your instrumentation is incorrect. ie You are not getting the power that the settings would indicate.

When I added the Robertson to my airplane, (It was number 2 or 3 done by Robertson) I felt I lost 2 to 3 mph in 65% cruise power settings. Later, after I added various Lopresti, Knots 2 U mods, and Han's hubcaps, I feel the airplane is slightly faster than the original. I get just under 160 knots burning 15 to 15 1/2 gallons per hour when I fly in normal temp air at 6 to 8 K altitude.

I once took off just behind a turbo 260 Comanche near San Francisco and we were both flying to near Portland, Oregon. We were at the same altitude. (around 8000 feet as I remember) We ended up making the same time enroute and both airplanes burned almost identical fuel for the trip. With this experience, I would be interested to know how your speed and fuel burn compared with the other airplane. If either of your instruments were off, I can see how the speeds could be distorted for a comparison.

One other thing that I would consider: When I was buying my airplane, I had no twin experience and asked the Piper dealer to demonstrate VMC and single engine performance. He slowed down with one feathered and the next thing I knew we made a quick 1/2 to 1 turn spin. He recovered and didn't seem bothered and I assumed that's the way it is and should be. I bought the airplane and then for the next few years I read about all the VMC training accidents, changing of VMC speeds, stall strips, counter rotated engine, and rudder dam by Piper. When Robertson advertised their mod, they emphasized single engine safety. I went for a demo ride with their check pilot. When I feathered one and slowed down below VMC, the airplane started over the top. I shoved the nose down and stood on the rudder and the airplane recovered nicely without upset or the spin.

The demonstration ended then and there. I told the demo pilot I wanted the mod. They wanted to get some of the kits out in the field and I believe the special price I got was $3500 installed.

With the speed mods I have added, I am now slightly better than Piper book speeds, but I would even accept losing a little speed to acquire what I feel is a great modification to the PA30. I have landed on 1000 foot strips and have for many years operated off of a 2500 foot grass strip.
The 3800# gross is nice when headed of OSH with a load of camping gear.

Warm regards, Al Powers ICS 2978

by **Kristin Winter** » Wed Mar 17, 2010 2:12 am

When looking for a twinkie, I ruled out all aircraft with the Robertson mod. I didn't care to pay the price in speed and I don't operate out of a tiny strip. I really think that Piper/Swearingen got it right the first time. The Vmc characteristics don't bug me as I learned to respect Vmc and don't find the Twinkie scary in that regard, unless you feel compelled to practice single engine stalls. I can resist any urge to do that.

by **MULEFLY** » Wed Mar 17, 2010 4:39 am

Scott you may have flown a 260C with incorrect instrumentation too. I owned a B for 12 years... had it tuned like a concert piano... my 39 Robertson is tuned pretty darn good too... the 39 would leave the B in the dust.

It is itsy stuff on both airplanes... baffles, gear ... Matt has my gear going back up in the wells further than a turtle's head retracts... I have/had many mods on both airplanes.

My 39 (with Robertsons) is about 5 kts faster than the B... and man do I love that 200#s. My wife and I can fly to FL with everything that she possibly needs for two weeks (5 suitcases) and I just pack my toothbrush... no problems.

I filed my B at 160 kts.. I file my 39 at 165.... it just works out that way.

Your and my airplane mostly differ in that I have the Miller nose... but I don't think that is a "speed mod".

Let's compare notes... The C is a fast airplane. Zach claims that the turbo C is the fastest Comanche ever made... but a properly trimmed C shouldn't be "big time" faster than a properly trimmed twin even with a Robertson

by **MULEFLY** » Wed Mar 17, 2010 1:22 pm

Scott you may have flown a 260C with incorrect instrumentation too. I owned a B for 12 years... had it tuned like a concert piano... my 39 Robertson is tuned pretty darn good too... the 39 would leave the B in the dust.

It is itsy stuff on both airplanes... baffles, gear ... Matt has my gear going back up in the wells further than a turtle's head retracts... I have/had many mods on both airplanes.

My 39 (with Robertsons) is about 5 kts faster than the B... and man do I love that 200#s. My wife and I can fly to FL with everything that she possibly needs for two weeks (5 suitcases) and I just pack my toothbrush... no problems.

I filed my B at 160 kts.. I file my 39 at 165.... it just works out that way.

Your and my airplane mostly differ in that I have the Miller nose... but I don't think that is a "speed mod".

Let's compare notes... The C is a fast airplane. Zach claims that the turbo C is the fastest Comanche ever made... but a properly trimmed C shouldn't be "big time" faster than a properly trimmed twin even with a Robertson

by **Jay** » Wed Mar 17, 2010 7:18 pm

I wouldn't trust anything based on indicated airspeed. There is an awful lot of instrument variation out there.

But I do think the Robertson slows a Twinkie down by 3 to 5 kts down low. I also think that this comes back at around 12K, and that at higher altitudes the Robertson may be faster.

To your question about removing the mod, the thing I'd worry about is the cuff and removing it without damaging the integrity of the wing. You may need to talk to a DER about that.

Jay

by **N8632Y** » Wed Mar 17, 2010 10:52 pm

Scott,
You LOVE your plane, u'd be unhappy without the STOL mod, especially when you're on final for central jersey and u see that tree in the way,,,,,
To test against another twinco for speed, think u gotta run side by side, full power,,,cause if i set at 24 square and you do,,,we're both NOT going to be identical power settings...
ps..i'm out of the shop...
steve

by **SLIMDREDGER** » Wed Mar 17, 2010 11:02 pm

Jay: One more thing on the Robertson mod. I believe it accomodates ice better than the sharp nosed standard wing. Don't ask why I have that opinion.

AHP

by **Jay** » Thu Mar 18, 2010 3:03 pm

Al, I agree on the ice carrying, but "further deponent sayeth not."

We do have to remember that we still have the stock stab, and I worry about ice on that as much as on the wing.

Jay

by **SLIMDREDGER** » Thu Mar 18, 2010 7:37 pm

Jay: I agree fully with your stabilator icing comment. I have also noted that my approach to flying around icing conditions is much more conservative than it used to be. A tail stall due to ice is something that I would not care to experience.

Warm regards, Al Powers ICS 2978

by **Jay** » Thu Mar 18, 2010 7:50 pm

Yep, same here. Brings to mind something about old pilots and bold pilots...

All the best,

by **Kristin Winter** » Fri Mar 19, 2010 5:58 am

I wonder if a stabilator will stall in icing. I never ran into it in the Aztec, and never heard of anyone doing that. Not so some airplanes with a horizontal stabilizer/elevator combination.

That being said, I do worry more about the tail in any aircraft than the wing. A very useful addition to an icing protection system would be a little camera mounted to look under the wing and one to look at the tail. Hook it up to a page on the MFD, and you would get a much better idea of what things looked liked. There were times when I really would like to have been able to see more of my lifting surfaces on my "Jo" while running around the Great Lakes.

by **Jay** » Fri Mar 19, 2010 9:14 pm

I've never heard of a stab stalling on a Comanche, but then, you probably wouldn't, if you know what I mean.

Ditto on the camera. Wouldn't be bad to show the main gear, either.

Jay

by **Kristin Winter** » Fri Mar 19, 2010 9:43 pm

Jay,

The NTSB managed to figure out that a few Baron's have stalled their tails in ice.

It would be very comforting to be able to see the landing gear.

by **Jay** » Fri Mar 19, 2010 9:45 pm

Yep, I talked to a guy who had a horizontal stabilizer stall in a P-Baron over Arizona or all places. I seem to recall he lost something like 6,000 feet recovering.

Jay