Hi,
Is any one flying/ has flown the Morris Hobbies penknife ? I built one recently and mounted a MVVS 40 on it, thinking that more is better,even though they recommend a .25/.30 engine. The throws on all surfaces is 30 degrees.
The first flight was a nightmare. the model did quite a few unexpected things. Thinking that I had radio interference I changed the set but that did not make a difference. Are the throws to much or do i have too much power ?
Any suggestions would be helpful.

I would first double check the balance point. I bet the MVVS .40 is SEVERAL ounces heavier than the recommended .25 - .30 engine ,and that could easily screw up the flight characteristics. Excess power is OK as long as you practice judicious use of the left stick. What specifically is the plane doing? Is this your first aircraft of this type? They typically are VERY maneuverable and if you have the throws cranked up, the plane may be flying as intended, but your thumbs just aren't up to the task yet. And I don't mean that in a condescending or insulting way......just throwing it out for consideration.

Erik

Is it too twitchy for you? Are you using expo? If not, then you may want to try it. If you are, then you may want to add some. As for your balance, roll your plane inverted while flying. You are going to want it to either fly neutral or with slight down. If it climbs inverted, then you're too tail heavy.

Have built and flown the Morris Hobbies Sudokoi, and Gee whiz bee without any problems. The penknife I built, behaves nothing like the other two. Soon after take off,before I realized, the plane was inverted and after several hair raising corrections/over corrections, I managed to land the aircraft in one piece. I do have 50 % expo dialed in.

I did exactly the same thing, Penknife/MVVS 40. It is not a good combination as the engine is to much for the little plane. An MVVS 28 would be great as the older 21 does not quite get it on this plane.
A good 32 2 stroke would also work out or similar sized 4 stroke.
I ran out of fuel and badley damaged the plane as it had the glide ratio of a 747 when 15 feet off the ground and it was properly balanced.

Have an old OS 25 FSR lying around. Do you think that it would have adequate power ?

Nothing like giving it a try, it may well work out let me know.

The FSR no doubt fly it but not 3D...the MVVS 21 would not 3D the plane and it's quite strong. If it were me I would look for a 32-36 small case bb engine for this plane.

There still is the question of why it was unflyable. Was it controllable at partial throttle settings? Was it speed caused or too much throw on surfaces or balance. A too powerfull motor itself doesn't cause problems. Weight could have been an issue but then it goes back to a balance problem. The only way too much power causes a problem could be too much torque or too much speed. Too much torque would be mostly an effect on take off rolling to the left and throttling down would reduce that, too much speed would be causing flutter, flex in contol pushrods and failure of flight surfaces....

You still need to find out why you had problems.

The .25SF was a great motor, it's what the .32SX was made out of. It'll fly it well, unlimited vertical, probably yes with the right prop.

Any thick airfoil air plane needs to keep it's speed up when dead stick to land or you'll have a "dead" stick.... The thicker the wing, the more drag, the faster it slows down.

RHK,
Keep it light ,use your 25 FSR with the right prop,save weight on battery, small tank etc.
The idea is to keep a light wing loading to have slower flying speed.
The 40 engine work fine on 44".
A good investment is to get a digital scale to select the lightest gear.
If any questions let us know.

Phil

Basically the engine and servos, etc. weighed more than the scratch build plane. MVVS 40 and pipe are not light when trying to make this work. Balanced, yes. To much torque, yes. fun to fly, no. You can never relax for one second.
This plane previously had a MVVS 21/with pipe and would not go verticle unlimited, that little 21 puts out more than an FSR OS 25 I would bet, I do have an FX 25 so know how that works.
So you don't misunderstand, I have a scratch built Morris Knife with MVVS 45 on it, a great combo that does it all and never lacks for power, plus it actually glides on deadstick, unlike the penknife w/Mvvs 40, that starting to settle when power is lacking.
I like lots of power but I did not enjoy this setup at all.

I am amazed to read that the PENKNIFE does not perform with the MVVS .21. I have been hanging onto a Morris promotional video of this combo for many years and have always meant to get this combo someday. The video makes it look like a awesome package. BTW, the .21 is piped if I remember correctly. I have heard mixed reviews over the years about MVVS engines in general, I hate to think that Morris was trying to pull a fast one with this PENKNIFE video. I bought the SU-DO-KHOI / ROSSI .45 package from him several years ago and it was [is] one of the best all around values I ever ran across, at the same time introducing me to 3D. What gives?

Were I to build the Penknife now, I would use the MVVS 28 or a good bb32, just the little more needed to do it right. Great little plane ......

Thanks, Gizmo. If you could see this video, the MVVS .21 can blast the plane out of a hover and go right into a tight KE loop [pinwheel], plus do everything else with ease. This video dates way back, I wonder if the model in this video is a smaller version of the one you guys are talking about? The plane in this video I believe was marketed for .15s and the impression I got was that they stuffed a .21 into the demo plane so they could shoot a hot video.

I really can't speak to the vidio but the 21 is just a little light for the application. I seriously doubt Morris would delibertly deceive anyone about this, all I know is the plane was extremely light and still didn't like the 21......?
I no longer have the plane as I gave it to a young guy who was planning a Mag. 32 for it, he just discovered girls so it may be years before it happens.

I doubt Walt Morris would deceive anyone too, he actually talked me out of getting the MVVS for the .40 sized SuDoKoi and steered me into getting the Rossi. 4 or 5 years later I called him to get replacement parts for the Rossi, and after BSing about planes for awhile he wouldn't take my money for a new P/L set, said the engine was still under "waranty" . What a guy! Anyway, I hear that he sold the business, hopefully to good people.

The plane is clearly trying to commit suicide. Next time try not to intervene.

What's it weigh?

Paul,
Think you directed the weight question to me? If so I really couldnt say, but the plane was scratch built of selected wood. The builder is very good about such. I have a Taco which most likley is a little lighter?

I'm just asking because it will have a huge affect on the performance of the plane... Performance on these little planes is all about wing loading... I agree with many that have said the MVVS .40 is waaaay to much for this plane... Will send the wing load to the moon and make it a squirely little bird for sure!

Post the weight and wing span and cord so we can do a wing load calc.

I can tell you that with the 40 it was a total handful. A buddy asked me if I was having fun after the first flight, then he started laughing.........I was really lucky to land it that time.