jb6290

Hi
I am new to RC airplanes and never built one before. My father was on a B-25 bomber during the war so I'm interested in building a big working plane for him. I just bought off Ebay the Royal B-25 Bomber kit and found someone willing to build it for me.
The problem is that the directions say to use a .40 to .65 size engines but it also says you can use the Wankel Rotary engines which are only .30. I would like to use the Wankel motors but we are very concerned that it will be underpowered.
Has anyone used the Wankel in the Royal kit? How did it work out? How well does it run? Is it underpowered?
If not, then what other engine would you recommend for that kit?
Thank you so much!
Bob McDonald

JohnBuckner

My Feedback: (1)

Bob its commendable that you want to do something like this for your father. I know nothing of the Royal B-25 but do have some experiance with the .30 Wankel. They were everbodys dream engine for that radial engine warbird single and multi, Except I don, t beleve it worked out quite that way. I have two and have used them on some competiive fun fly airplanes in years past. They like to run at a reasonably high rpm however I never had much luck getting them to idle much below about 30% power. The engine is not equipped with a mid range mixture adjustment, either a second needle or an airbleeder.. This is not the kind of tractibility you need for a multiengine aircraft. The second problem The engine need to use relatively small props and this is not good when you have an airplane with a radial cowl.

So I beleve that it is an inappropriate engine for that airplane for reasons beyond just its a little short on power for an airplane that is likely to come out heavy.

You never stated who is going be flying the airplane. Its important to remember this is not going to be the kind of airplane that just anyone can go out and fly on their own. Learning to fly this airplane will take a concerted plan of steps in the learning process and training aircraft.

John

jb6290

Hi John,
Thank you so much for the kind words and advice. It's appreciated. I guess I should look elsewhere for an engine. I had the Mazda RX 7 many years ago and loved the rotary engine in that car so I was fascinated with the possibility of putting it into this plane. I'm surprised it doesn't actually run that well at idle but not surprised to hear that it likes to run opened up. So did the RX 7.

I know you don't know anything about the Royal B 25 so I'm hoping someone will tell me what engines they recommend for it.

I have no intentions of actually flying it myself, since I have no experience doing it, but would still like for it to be ready to fly in case I find someone who is capable of doing it. If I'm going to go through the expense of putting it together I would like to know that it works.

Thank you!
Bob

clscale-RCU

My Feedback: (7)

Hi there,

I have run an Wankel on the test stand, it ran just like any other glow engine for the most part but the carb and especially the muffler sticks out so if the goal is hide the entire engine in the cowl you might be forced to make a custom muffler even with this engine.

I have built lots of models over the years and the Royal B-25 is a builders kit and requires some prior buiding experience. Also Twins are another challenge. Keep the B-25 idea alive, but consider a newer B-25 kit that is easier to build. The old royal kits tended to have alot of "block" balsa that required carving and sanding.

Find a flat sided fuselage single engine kit that you like and make the B-25 a project for later. There is alot to think about when putting a twin together of that size and complexity. Also join a model airplane club and ask for help in getting started. There is nothing like building and flying your own model, every model I have built I learned something new. Even after 15 years of building airplanes from kits, ARF's and my own plans I still am learning on how to build model airplanes. The Royal B-25 is complex project.



Good luck,
Fred Cronenwett

jb6290

Hi Fred,
Thank you for the advice. I'm afraid that I can't put it off. It would be a gift for my Dad who is now 79 years old and in failing health. I really need to do it now or never. I have an experienced builder who is going to build it for me so I'm not worried about that. I just have to figure out the engines for it.
Thank you!
Bob

TAZ

Hi there I was reading up on the OS wankel engine a couple of weeks ago and what people had to say about it was that it revs very high and gets very hot, the only way to cool it down while running is to have the fuel mix quite rich but this causes the engine to use fuel a lot more quickly that normal engines.

If you use the search engine in the top left of the forum page and type in "wankel" i'm very sure you will find a lot of remarks on this engine.... It's a pitty i would buy a 4 of these engines only if some one would better them and vary the sizes

Taz

lrb75

My Feedback: (12)

I have a royal B-25 and fly it with two saito 45s. Flies nicely but it could use more power. Inverted saito 56s would be perfect. However, the royal kits are not easy builds. KMP is coming out with an 85" ARF soon. Maybe you can wait for that.

jb6290

Hi Taz and IRB,
Thank you both very much for all of your help and information! It's really appreciated.
It seems that the Royal kit is much more complicated than I thought.
Why do you think the KMP kit will be better than the Royal? Is it easier to build?
Thank you!
Bob

Bob Paris

My Feedback: (13)

Dear Bob,

In the early 80"s I built the Royal B-25, and it is a builders kit. My kit requierd a bit of wood working, sanding and carving...but it came out beautiful. I did not put retracts in my bird, and I did my best to build it light. I flew great...but marginal on one engine. Take the time and build it light. Carve, widdle down and hollow out all your wood blocks...for that is all you get...is a lot of real rough cut wood blocks. Take your time...and have a ball...and it will bring a excellent rendition to a fine airplane. Go get a plastic model kit...build the plastic kit...and use it as a guide to help you out some. This is what I did...and it worked for me.

I used two O.S Wankle engines...and I was dully impressed with the powerplants. Break them in on a bench...your mufflers will exit the cowels...no big deal...just place them inboard between the cowels and the fuse. The engines are rated as .30's...but will pull like a strong 40...real strong .40. They are thersty beasts, and have a high fuel burn for the displacement. From slow idle to full rev's is lightening fast...the quickest of any model engine I ever had. They sound different...and awesome too. Keep your fuel clean. The Wankle engine uses carbon brushes to seal the chambers...so dirt will kill the seal and you will damage your engine. Put the largest fuel tanks you can in the model...and build a hatch to get access to your fuel tanks...take the time, it will be well worth it latter down the line.

Your in for a real treat...and so is your Dad.

Soft and gentle landings always,
Bobby of Maui

jimcork1

My Feedback: (4)

I would consider the Saito .52 , .70 or .80 size for this bird. I have seen one and I have build a C130 model of the one I flew.

I understand the reason for your schedule. Saito's are very reliable and I used 4 on the C130. I hope you have a skilled flyer to fly this bird. The more engines the more complex the plane. Best of luck,, Jim

TAZ

www.kmp.ca/new.htm this is where the KMP B-25 is, it is an ARTF plane from what i have heard and the picture of it are excellent this lloks like one of those must have's

jb6290

Hi
I want to thank you all for your wonderful imput! It's really appreciated. I just hope I can get it built before something happens to my father.
Thank you again!
Bob

ELTIGRE

Ive owned a partial built Royal B-25 & the OS wankel. The Mitchell makes a nice twin & is not overly difficult to fly for the experienced modeler . The kit is a builders kit , that is to come out right requires some background building. two good .45's fly it ok as I've seen.remember two props you have a lot of disc area working for you -provided they both stay running.
The Wankel is a strange engine . you can't hand crank it , electric starter is a must. heavy for its size. acceleration is INSTANT. I know a lot of engines seem that way but in this case its true &very weird the first time you see it. it will not lug large props either. wankels would be great for something a bit smaller. those who have flown them claim they're great-its also something of a fuel hog.